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{{About|the astronomical structure|other uses}}
{{Use mdy dates|date=February 2015}}
{{Multiple image |direction=vertical |align=right |width=310|image1=NGC 4414 (NASA-med).jpg|caption1=[[NGC 4414]], a typical spiral galaxy in the [[constellation]] [[Coma Berenices]], is about 55,000 [[light-year]]s in diameter and approximately 60 million light-years away from Earth|image2=M104_ngc4594_sombrero_galaxy_hi-res.jpg|caption2=The [[Sombrero galaxy]] (M104), a bright nearby spiral galaxy.|image3=Irregular_galaxy_NGC_1427A_(captured_by_the_Hubble_Space_Telescope).jpg|caption3=[[NGC 1427A]], an example of an irregular galaxy, 52 million [[light-year]]s away}}

A '''galaxy''' is a [[gravitation]]ally bound system of [[star]]s, [[stellar remnant]]s, [[interstellar medium|interstellar gas]] and [[cosmic dust|dust]], and [[dark matter]].<ref name="sparkegallagher2000"/><ref name=nasa060812/> The word galaxy is derived from the [[Ancient Greek|Greek]] ''{{transl|grc|galaxias}}'' ({{lang|grc|γαλαξίας}}), literally "milky", a reference to the [[Milky Way]]. Galaxies range in size from [[dwarf galaxy|dwarfs]] with just a few thousand (103) stars to giants with one hundred [[Trillion (short scale)|trillion]] (1014) stars,<ref name=science250_4980_539/> each orbiting their galaxy's own [[center of mass]]. Galaxies are categorized according to their visual morphology, including [[elliptical galaxy|elliptical]],<ref name=uf030616/> [[Spiral galaxy|spiral]], and [[irregular galaxy|irregular]].<ref name="IRatlas"/> Many galaxies are thought to have [[black hole]]s at their [[active galactic nucleus|active center]]s. The Milky Way's central black hole, known as [[Sagittarius A*]], has a mass four million times greater than the Sun.<ref name="smbh"/> As of July 2015, [[EGSY8p7]] is the oldest and most distant galaxy with a [[light travel distance]] of 13.2 billion [[light-years]] from Earth, and observed as it existed 570 million years after the Big Bang. Previously, as of May 2015, [[EGS-zs8-1]] was the most distant known galaxy, estimated to have a [[light travel distance]] of 13.1 billion [[light-year]]s away and to have 15% of the mass of the Milky Way.<ref name="ARX-20150503">{{cite journal |authors=Oesch, P.A. et al. |title=A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE |url=http://arxiv.org/abs/1502.05399 |date=May 3, 2015 |journal=[[ArXiv]] |arxiv=1502.05399 |accessdate=May 6, 2015 |bibcode = 2015arXiv150205399O }}
</ref><ref name=p15>{{cite web |author=Staff |title=Astronomers unveil the farthest galaxy |url=http://phys.org/news/2015-05-astronomers-unveil-farthest-galaxy.html |publisher=[[Phys.org]] |accessdate=May 6, 2015|date=May 5, 2015}}</ref><ref name="NYT-20150505">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Astronomers Measure Distance to Farthest Galaxy Yet |url=http://www.nytimes.com/2015/05/06/science/astronomers-measure-distance-to-farthest-galaxy-yet.html |date=May 5, 2015 |work=[[New York Times]] |accessdate=May 6, 2015 }}</ref><ref name="AP-20150505">{{cite news |last=Borenstein |first=Seth |title=Astronomers find farthest galaxy: 13.1 billion light-years |url=http://apnews.excite.com/article/20150505/us-sci--farthest_galaxy-46c792535a.html |date= May 5, 2015 |work=[[AP News]] |accessdate=May 6, 2015 }}</ref>

Approximately 170 billion ({{nowrap|1.7 × 1011}}) galaxies exist in the [[observable universe]].<ref name="apj624_2"/> Most of the galaxies are 1,000 to 100,000 [[parsec]]s in diameter and usually separated by distances on the order of millions of parsecs (or megaparsecs). The [[intergalactic space|space]] between galaxies is filled with a tenuous gas with an average density less than one [[atom]] per cubic meter. The majority of galaxies are gravitationally organized into associations known as [[galaxy group]]s, [[galaxy cluster|clusters]], and [[supercluster]]s. At the [[Large-scale structure of the Cosmos|largest scale]], these associations are generally arranged into [[galaxy filament|sheets and filaments]] that are surrounded by immense [[void (astronomy)|voids]].<ref name=camb_lss/>

==Etymology==
The word ''galaxy'' derives from the [[Greek language|Greek]] term for our own galaxy, ''{{transl|grc|galaxias}}'' (''{{lang|grc|{{linktext|γαλαξίας}}}}'', "milky one"), or ''{{transl|grc|[[kyklos]] galaktikos}}'' ("milky circle")<ref name=oed/> due to its appearance as a "milky" band of light in the sky. In [[Greek mythology]], [[Zeus]] places his son born by a mortal woman, the infant [[Heracles]], on [[Hera]]'s breast while she is asleep so that the baby will drink her divine milk and will thus become immortal. Hera wakes up while breastfeeding and then realizes she is nursing an unknown baby: she pushes the baby away and a jet of her milk sprays the night sky, producing the faint band of light known as the Milky Way.<ref name=waller_hodge2003/><ref name=konean2006/>

In the astronomical literature, the capitalized word "Galaxy" is often used to refer to our galaxy, the [[Milky Way]], to distinguish it from the other galaxies in our [[universe]]. The English term ''Milky Way'' can be traced back to a story by [[Chaucer]] {{circa|1380}}:
{{Quote|"See yonder, lo, the Galaxyë  Which men {{linktext|clepe}}th ''the Milky Wey'',  For hit is whyt."|Geoffrey Chaucer|[[The House of Fame]]''<ref name=oed/>}}

When [[William Herschel]] assembled [[Catalogue of Nebulae|his catalog]] of deep sky objects in 1786, he used the term ''[[spiral nebula]]'' for certain objects such as [[Andromeda Galaxy|M31]]. These would later be recognized as conglomerations of stars when the true distance to these objects began to be appreciated, and they would later be termed ''island universes.'' However, the word ''Universe'' was understood to mean the entirety of existence, so this expression fell into disuse and the objects instead became known as galaxies.<ref name=rao2005/>

==Nomenclature==
Tens of thousands of galaxies have been catalogued, but only a few have well-established names, such as the [[Andromeda Galaxy]], the [[Magellanic clouds]], the [[Whirlpool Galaxy]] and the [[Sombrero Galaxy]]. Astronomers work with numbers from certain catalogues, such as the [[Messier catalogue]], the NGC ([[New General Catalogue]]), the IC ([[Index Catalogue]]), the CGCG ([[Catalogue of Galaxies and of Clusters of Galaxies]]), the MCG ([[Morphological Catalogue of Galaxies]]) and UGC ([[Uppsala General Catalogue|Uppsala General Catalogue of Galaxies]]). All of the well-known galaxies appear in one or more of these catalogues but each time under a different number.
For example, [[Messier 109]] is a spiral galaxy having the number 109 in the catalogue of Messier, but also codes NGC3992, UGC6937, CGCG 269-023, MCG +09-20-044, and PGC 37617.

Because it is customary in science to assign names to most of the studied objects, even to the smallest ones, the Belgian astrophysicist [[Gerard Bodifee]] and the classicist Michel Berger started a new catalogue ([[Gerard Bodifee#Works|CNG-Catalogue of Named Galaxies]])<ref>{{Cite web|url=http://www.bodifee.be/acms/acmsdata/document/9/184_CNG%20catalogue.pdf|title=CNG-Catalogue of Named Galaxies |author=Bodifée G. & Berger M.|date=2010|accessdate=January 17, 2014}}</ref> in which a thousand well-known galaxies are given meaningful, descriptive names in Latin (or Latinized Greek)<ref>{{cite web |title=Contemporary Latin |url=http://www.isnare.com/encyclopedia/Contemporary_Latin#In_science |accessdate= January 22, 2014}}</ref> in accordance with the binomial nomenclature that one uses in other sciences such as biology, anatomy, [[paleontology]] and in other fields of astronomy such as the geography of Mars.
One of the arguments to do so is that these impressive objects deserve better than uninspired codes. For instance, Bodifee and Berger propose the informal, descriptive name ''{{lang|la|Callimorphus Ursae Majoris}}'' for the well-formed barred galaxy Messier 109 in Ursa Major.

==Observation history==
The realization that we live in a galaxy, and that ours is one among many, parallels major discoveries that were made about the Milky Way and other [[nebula]]e in the night sky.

===Milky Way===
{{Main|Milky Way}}
The [[Greek philosophy|Greek]] philosopher [[Democritus]] (450–370 BC) proposed that the bright band on the night sky known as the Milky Way might consist of distant stars.<ref name="Plutarch">{{cite book | title=The Complete Works Volume 3: Essays and Miscellanies | publisher=Echo Library | author=Plutarch | authorlink=Plutarch | date=2006 | location=Chapter 3 | pages=66 | isbn=978-1-4068-3224-2}}</ref>
[[Aristotle]] (384–322 BC), however, believed the Milky Way to be caused by "the ignition of the fiery exhalation of some stars that were large, numerous and close together" and that the "ignition takes place in the upper part of the [[atmosphere]], in the [[Sublunary sphere|region of the World that is continuous with the heavenly motions]]."<ref name=Montada>
{{cite web
| last1=Montada |first1=J. P.
| date=September 28, 2007
| title=Ibn Bajja
| work=[[Stanford Encyclopedia of Philosophy]]
| url=http://plato.stanford.edu/entries/ibn-bajja
| accessdate=July 11, 2008
}}</ref> The [[Neoplatonism|Neoplatonist]] philosopher [[Olympiodorus the Younger]] ({{circa|495}}–570 AD) was critical of this view, arguing that if the Milky Way is [[sublunary]] (situated between Earth and the Moon) it should appear different at different times and places on Earth, and that it should have [[parallax]], which it does not. In his view, the Milky Way is celestial.<ref name=heidarzadeh23/>

According to Mohani Mohamed, the [[Islamic astronomy|Arabian]] astronomer [[Alhazen]] (965–1037) made the first attempt at observing and measuring the Milky Way's parallax,<ref name=mohamed/> and he thus "determined that because the Milky Way had no parallax, it must be remote from the Earth, not belonging to the atmosphere."<ref>
{{cite web
| last1=Bouali |first1=H.-E.
| last2=Zghal |first2=M.
| last3=Lakhdar |first3=Z. B.
| date=2005
| title=Popularisation of Optical Phenomena: Establishing the First Ibn Al-Haytham Workshop on Photography
| publisher=The Education and Training in Optics and Photonics Conference
| url=http://spie.org/etop/ETOP2005_080.pdf
| accessdate=July 8, 2008
}}</ref> The [[Persian people|Persian]] astronomer [[al-Bīrūnī]] (973–1048) proposed the Milky Way galaxy to be "a collection of countless fragments of the nature of nebulous stars."<ref>{{MacTutor Biography|id=Al-Biruni|title=Abu Rayhan Muhammad ibn Ahmad al-Biruni}}</ref><ref name=al_biruni/> The [[Al-Andalus|Andalusian]] astronomer [[Ibn Bajjah]] ("Avempace", {{abbr|d.|died}} 1138) proposed that the Milky Way is made up of many stars that almost touch one another and appear to be a continuous image due to the effect of [[refraction]] from sublunary material,<ref name=Montada/><ref name="heidarzadeh25"/> citing his observation of the [[Conjunction (astronomy and astrology)|conjunction]] of Jupiter and Mars as evidence of this occurring when two objects are near.<ref name=Montada/> In the 14th century, the Syrian-born [[Ibn Qayyim]] proposed the Milky Way galaxy to be "a myriad of tiny stars packed together in the sphere of the fixed stars."<ref name=Livingston>
{{cite journal
|last1=Livingston |first1=J. W.
|date=1971
|title=Ibn Qayyim al-Jawziyyah: A Fourteenth Century Defense against Astrological Divination and Alchemical Transmutation
|journal=[[Journal of the American Oriental Society]]
|volume=91 |issue=1 |pages=96–103 [99]
|doi=10.2307/600445
|jstor=600445
}}</ref>
[[File:Herschel-Galaxy.png|thumb|The shape of the Milky Way as estimated from star counts by [[William Herschel]] in 1785; the solar system was assumed to be near the center.]]
Actual proof of the Milky Way consisting of many stars came in 1610 when the Italian astronomer [[Galileo Galilei]] used a [[optical telescope|telescope]] to study the Milky Way and discovered that it is composed of a huge number of faint stars.<ref>Galileo Galilei, ''Sidereus Nuncius'' (Venice, (Italy): Thomas Baglioni, 1610), [https://archive.org/stream/Sidereusnuncius00Gali#page/n37/mode/2up pages 15 and 16.] 
English translation: Galileo Galilei with Edward Stafford Carlos, trans., ''The Sidereal Messenger'' (London, England: Rivingtons, 1880), [https://archive.org/stream/siderealmessenge80gali#page/42/mode/2up/ pages 42 and 43.]</ref><ref>
{{cite web
|last1=O'Connor |first1=J. J.
|last2=Robertson |first2=E. F.
|date=November 2002
|title=Galileo Galilei
|url=http://www-gap.dcs.st-and.ac.uk/~history/Biographies/Galileo.html
|publisher=[[University of St. Andrews]]
|accessdate=January 8, 2007
}}</ref> In 1750 the English astronomer [[Thomas Wright (astronomer)|Thomas Wright]], in his ''An original theory or new hypothesis of the Universe'', speculated (correctly) that the galaxy might be a rotating body of a huge number of stars held together by [[gravitation|gravitational forces]], akin to the solar system but on a much larger scale. The resulting disk of stars can be seen as a band on the sky from our perspective inside the disk.<ref>Thomas Wright, ''An Original Theory or New Hypothesis of the Universe'' … (London, England: H. Chapelle, 1750). [http://books.google.com/books?id=80VZAAAAcAAJ&pg=PA48#v=onepage&q&f=false From p.48:] " … the stars are not infinitely dispersed and distributed in a promiscuous manner throughout all the mundane space, without order or design, … this phænomenon [is] no other than a certain effect arising from the observer's situation, … To a spectator placed in an indefinite space, … it [i.e., the Milky Way (''Via Lactea'')] [is] a vast ring of stars … " 
[http://books.google.com/books?id=80VZAAAAcAAJ&pg=PA73#v=onepage&q&f=false On page 73], Wright called the Milky Way the ''Vortex Magnus'' (the great whirlpool) and estimated its diameter at 8.64×1012 miles (13.9×1012 km).</ref><ref name="our_galaxy"/> In a treatise in 1755, [[Immanuel Kant]] elaborated on Wright's idea about the structure of the Milky Way.<ref>Immanuel Kant, [http://books.google.com/books?id=nCcaAQAAMAAJ&pg=PP9#v=onepage&q&f=false ''Allgemeine Naturgeschichte und Theorie des Himmels'' …] [Universal Natural History and Theory of the Heavens … ], (Koenigsberg and Leipzig, (Germany): Johann Friederich Petersen, 1755). Available in English translation by Ian Johnston at: [http://records.viu.ca/~johnstoi/kant/kant2e.htm Vancouver Island University, British Columbia, Canada]</ref>

The first project to describe the shape of the Milky Way and the position of the [[Sun]] was undertaken by [[William Herschel]] in 1785 by counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with [[Galactocentrism|the solar system close to the center]].<ref>William Herschel (1785) "On the Construction of the Heavens," ''Philosophical Transactions of the Royal Society of London'', '''75''' : 213-266. Herschel's diagram of the galaxy appears immediately after the article's last page. See:
* [http://books.google.com/books?id=IU9FAAAAcAAJ&pg=PA213#v=onepage&q&f=false Google Books]
* [http://rstl.royalsocietypublishing.org/content/75/213.full.pdf+html The Royal Society of London]</ref><ref name=paul1993/> Using a refined approach, [[Jacobus Kapteyn|Kapteyn]] in 1920 arrived at the picture of a small (diameter about 15 kiloparsecs) ellipsoid galaxy with the Sun close to the center. A different method by [[Harlow Shapley]] based on the cataloguing of [[globular cluster]]s led to a radically different picture: a flat disk with diameter approximately 70 kiloparsecs and the Sun far from the center.<ref name="our_galaxy" /> Both analyses failed to take into account the [[extinction (astronomy)|absorption of light]] by [[cosmic dust|interstellar dust]] present in the [[galactic plane]], but after [[Robert Julius Trumpler]] quantified this effect in 1930 by studying [[open cluster]]s, the present picture of our host galaxy, the Milky Way, emerged.<ref>
{{cite journal
|last1=Trimble |first1=V.
|date=1999
|title=Robert Trumpler and the (Non)transparency of Space
|journal=[[Bulletin of the American Astronomical Society]]
|volume=31 |issue=31 |pages=1479
|bibcode=1999AAS...195.7409T
}}</ref>

[[File:Milky Way Arch.jpg|thumb|center|600px|A [[Fisheye lens|fish-eye]] mosaic of the Milky Way arching at a high inclination across the night sky, shot from a dark-sky location in Chile]]

===Distinction from other nebulae===

A few galaxies outside the Milky Way are visible in the night sky to the unaided eye. In the 10th century, the Persian astronomer [[Al-Sufi]] made the earliest recorded identification of the [[Andromeda Galaxy]], describing it as a "small cloud".<ref name="NSOG"/> In 964, Al-Sufi identified the [[Large Magellanic Cloud]] in his ''[[Book of Fixed Stars]]''; it was not seen by Europeans until [[Ferdinand Magellan|Magellan]]'s voyage in the 16th century.<ref name="obspm">
{{cite web
|title=Abd-al-Rahman Al Sufi (December 7, 903 – May 25, 986 A.D.)
|url=http://messier.obspm.fr/xtra/Bios/alsufi.html
|publisher=[[Observatoire de Paris]]
|accessdate=April 19, 2007
}}</ref><ref name="obspm2">
{{cite web
|title=The Large Magellanic Cloud, LMC
|url=http://messier.obspm.fr/xtra/ngc/lmc.html
|publisher=[[Observatoire de Paris]]
|accessdate=April 19, 2007
}}</ref> The Andromeda Galaxy was independently noted by [[Simon Marius]] in 1612.<ref name="NSOG"/>

In 1750, [[Thomas Wright (astronomer)|Thomas Wright]] speculated (correctly) that the Milky Way is a flattened disk of stars, and that some of the [[nebula]]e visible in the night sky might be separate Milky Ways.<ref name="our_galaxy">
{{cite web
|last1=Evans |first1=J. C.
|date=November 24, 1998
|title=Our Galaxy
|url=http://physics.gmu.edu/~jevans/astr103/CourseNotes/ECText/ch20_txt.htm
|publisher=[[George Mason University]]
|accessdate=January 4, 2007
}}</ref><ref>See text quoted from Wright's ''An original theory or new hypothesis of the Universe'' in {{Cite book
|last1=Dyson |first1=F.
|date=1979
|title=Disturbing the Universe
|page=245
|publisher=[[Pan Books]]
|isbn=0-330-26324-2
}}</ref> In 1755, [[Immanuel Kant]] used the term "island Universe" to describe these distant nebulae.
[[File:Pic iroberts1.jpg|thumb|right|Photograph of the "Great Andromeda Nebula" from 1899, later identified as the [[Andromeda Galaxy]]]]
Toward the end of the 18th century, [[Charles Messier]] compiled a [[Messier object|catalog]] containing the 109 brightest celestial objects having nebulous appearance. Subsequently, William Herschel assembled a catalog of 5,000 nebulae.<ref name="our_galaxy" /> In 1845, [[William Parsons, 3rd Earl of Rosse|Lord Rosse]] constructed a new telescope and was able to distinguish between elliptical and spiral nebulae. He also managed to make out individual point sources in some of these nebulae, lending credence to Kant's earlier conjecture.<ref>[http://parsonstown.info/people/william-rosse "Parsonstown | The genius of the Parsons family | William Rosse"]. ''parsonstown.info''.</ref>

In 1912, [[Vesto Slipher]] made spectrographic studies of the brightest spiral nebulae to determine their composition. Slipher discovered that the spiral nebulae have high [[Doppler shift]]s, indicating that they are moving at a rate exceeding the velocity of the stars he had measured. He found that the majority of these nebulae are moving away from us.<ref>
{{cite journal
|last1=Slipher |first1=V. M.
|date=1913
|title=The radial velocity of the Andromeda Nebula
|journal=Lowell Observatory Bulletin
|volume=1 |pages=56–57
|bibcode=1913LowOB...2...56S
}}</ref><ref>
{{cite journal
|last1=Slipher |first1=V. M.
|date=1915
|title=Spectrographic Observations of Nebulae
|journal=[[Popular Astronomy (US magazine)|Popular Astronomy]]
|volume=23 |pages=21–24
|bibcode=1915PA.....23...21S
}}</ref>

In 1917, [[Heber Curtis]] observed nova [[S Andromedae]] within the "Great [[Andromeda (constellation)|Andromeda]] Nebula" (as the Andromeda Galaxy, [[Messier object]] [[Andromeda Galaxy|M31]], was then known). Searching the photographic record, he found 11 more [[nova]]e. Curtis noticed that these novae were, on average, 10 [[magnitude (astronomy)|magnitudes]] fainter than those that occurred within our galaxy. As a result, he was able to come up with a distance estimate of 150,000 [[parsec]]s. He became a proponent of the so-called "island universes" hypothesis, which holds that spiral nebulae are actually independent galaxies.<ref>
{{cite journal
|last=Curtis |first1=H. D.
|date=1988
|title=Novae in Spiral Nebulae and the Island Universe Theory
|journal=[[Publications of the Astronomical Society of the Pacific]]
|volume=100 |pages=6
|bibcode=1988PASP..100....6C
|doi=10.1086/132128
}}</ref>

In 1920 the so-called [[Great Debate (astronomy)|Great Debate]] took place between [[Harlow Shapley]] and [[Heber Curtis]], concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the Universe. To support his claim that the Great Andromeda Nebula is an external galaxy, Curtis noted the appearance of dark lanes resembling the dust clouds in the Milky Way, as well as the significant Doppler shift.<ref>
{{cite web
|last1=Weaver |first1=H. F.
|title=Robert Julius Trumpler
|url=http://www.nap.edu/readingroom/books/biomems/rtrumpler.html
|publisher=[[United States National Academy of Sciences|US National Academy of Sciences]]
|accessdate=January 5, 2007
}}</ref>

In 1922, the [[Estonia]]n astronomer [[Ernst Öpik]] gave a distance determination that supported the theory that the Andromeda Nebula is indeed a distant extra-galactic object.<ref>
{{cite journal
|last1=Öpik |first1=E.
|date=1922
|title=An estimate of the distance of the Andromeda Nebula
|journal=[[Astrophysical Journal]]
|volume=55 |pages=406
|bibcode=1922ApJ....55..406O
|doi=10.1086/142680
}}</ref> Using the new 100 inch [[Mount Wilson Observatory|Mt. Wilson]] telescope, [[Edwin Hubble]] was able to resolve the outer parts of some spiral nebulae as collections of individual stars and identified some [[Cepheid variable]]s, thus allowing him to estimate the distance to the nebulae: they were far too distant to be part of the Milky Way.<ref>
{{cite journal
|last1=Hubble |first1=E. P.
|date=1929
|title=A spiral nebula as a stellar system, Messier 31
|journal=[[Astrophysical Journal]]
|volume=69 |pages=103–158
|bibcode=1929ApJ....69..103H
|doi=10.1086/143167
}}</ref> In 1936 Hubble produced a classification of [[Galaxy morphological classification|galactic morphology]] that is used to this day.<ref>
{{cite journal
|last1=Sandage |first1=A.
|date=1989
|title=Edwin Hubble, 1889–1953
|journal=[[Journal of the Royal Astronomical Society of Canada]]
|volume=83 |issue=6 |pages=351–362
|url=http://antwrp.gsfc.nasa.gov/diamond_jubilee/1996/sandage_hubble.html
|accessdate=January 8, 2007
|bibcode = 1989JRASC..83..351S }}</ref>

===Modern research===
[[File:GalacticRotation2.svg|thumb|right|200px|[[Galaxy rotation curve|Rotation curve]] of a typical spiral galaxy: predicted based on the visible matter (A) and observed (B). The distance is from the [[Bulge (astronomy)|galactic core]].]]
In 1944, [[Hendrik C. van de Hulst|Hendrik van de Hulst]] predicted that [[microwave]] radiation with [[hydrogen line|wavelength of 21 cm]] would be detectable from interstellar atomic [[hydrogen]] gas;<ref>
{{cite web
|last1=Tenn |first1=J.
|title=Hendrik Christoffel van de Hulst
|url=http://www.phys-astro.sonoma.edu/BruceMedalists/vandeHulst/
|publisher=[[Sonoma State University]]
|accessdate=January 5, 2007
}}</ref> and in 1951 it was observed. This radiation is not affected by dust absorption, and so its Doppler shift can be used to map the motion of the gas in our galaxy. These observations led to the hypothesis of a rotating [[barred spiral galaxy|bar structure]] in the center of our galaxy.<ref>
{{cite journal
|last1=López-Corredoira |first1=M.
|display-authors=etal
|date=2001
|title=Searching for the in-plane Galactic bar and ring in DENIS
|journal=[[Astronomy and Astrophysics]]
|volume=373
|issue=1 |pages=139–152
|bibcode=2001A&A...373..139L
|doi=10.1051/0004-6361:20010560
|arxiv = astro-ph/0104307 }}</ref> With improved [[radio telescope]]s, hydrogen gas could also be traced in other galaxies.
In the 1970s, [[Vera Rubin]] uncovered a discrepancy between observed galactic [[galaxy rotation curve|rotation speed]] and that predicted by the visible mass of stars and gas. Today, the galaxy rotation problem is thought to be explained by the presence of large quantities of unseen [[dark matter]].<ref>
{{cite journal
|last1=Rubin |first1=V. C.
|date=1983
|title=Dark matter in spiral galaxies
|journal=[[Scientific American]]
|volume=248
|issue=6 |pages=96–106
|bibcode=1983SciAm.248...96R
|doi=10.1038/scientificamerican0683-96
}}</ref><ref>
{{cite journal
|last1=Rubin |first1=V. C.
|date=2000
|title=One Hundred Years of Rotating Galaxies
|journal=[[Publications of the Astronomical Society of the Pacific]]
|volume=112 |issue=772 |pages=747–750
|bibcode=2000PASP..112..747R
|doi=10.1086/316573
}}</ref> A concept known as the [[universal rotation curve]] of spirals, moreover, shows that the problem is ubiquitous in these objects.

Beginning in the 1990s, the [[Hubble Space Telescope]] yielded improved observations. Among other things, Hubble data helped establish that the missing dark matter in our galaxy cannot solely consist of inherently faint and small stars.<ref>
{{cite news
|title=Hubble Rules Out a Leading Explanation for Dark Matter
|publisher=Hubble News Desk
|date=October 17, 1994
|url=http://hubblesite.org/newscenter/archive/releases/1994/41/text/
|accessdate=January 8, 2007
}}</ref> The [[Hubble Deep Field]], an extremely long exposure of a relatively empty part of the sky, provided evidence that there are about 125 billion ({{val|1.25|e=11}}) galaxies in the Universe.<ref>
{{cite web
|date=November 27, 2002
|title=How many galaxies are there?
|url=http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/021127a.html
|publisher=[[NASA]]
|accessdate=January 8, 2007
}}</ref> Improved technology in detecting the [[electromagnetic spectrum|spectra]] invisible to humans (radio telescopes, infrared cameras, and [[x-ray astronomy|x-ray telescopes]]) allow detection of other galaxies that are not detected by Hubble. Particularly, galaxy surveys in the [[Zone of Avoidance]] (the region of the sky blocked by the Milky Way) have revealed a number of new galaxies.<ref>
{{cite journal
|last1=Kraan-Korteweg |first1=R. C.
|last2=Juraszek |first2=S.
|date=2000
|title=Mapping the hidden Universe: The galaxy distribution in the Zone of Avoidance
|journal=[[Publications of the Astronomical Society of Australia]]
|volume=17 |issue=1 |pages=6–12
|bibcode=1999astro.ph.10572K
|arxiv = astro-ph/9910572
|doi=10.1071/AS00006 }}</ref>

==Types and morphology==
{{Main|Galaxy morphological classification}}
[[File:Hubble sequence photo.png|thumb|360px|Types of galaxies according to the Hubble classification scheme: an ''E'' indicates a type of elliptical galaxy; an ''S'' is a spiral; and ''SB'' is a barred-spiral galaxy.<ref group=note>Galaxies to the left side of the Hubble classification scheme are sometimes referred to as "early-type", while those to the right are "late-type".</ref>]]
Galaxies come in three main types: ellipticals, spirals, and irregulars. A slightly more extensive description of galaxy types based on their appearance is given by the [[Galaxy morphological classification|Hubble sequence]]. Since the Hubble sequence is entirely based upon visual morphological type, it may miss certain important characteristics of galaxies such as [[star formation]] rate in [[Starburst galaxy|starburst galaxies]] and activity in the cores of [[active galaxy|active galaxies]].<ref name="IRatlas" />

===Ellipticals===
{{Main|Elliptical galaxy}}
The Hubble classification system rates elliptical galaxies on the basis of their ellipticity, ranging from E0, being nearly spherical, up to E7, which is highly elongated. These galaxies have an [[ellipsoid]]al profile, giving them an elliptical appearance regardless of the viewing angle. Their appearance shows little structure and they typically have relatively little [[interstellar medium|interstellar matter]]. Consequently, these galaxies also have a low portion of [[open cluster]]s and a reduced rate of new star formation. Instead they are dominated by generally older, more [[stellar evolution|evolved stars]] that are orbiting the common center of gravity in random directions. The stars contain low abundances of heavy elements because star formation ceases after the initial burst. In this sense they have some similarity to the much smaller [[globular cluster]]s.<ref name="elliptical">
{{cite web
|last1=Barstow |first1=M. A.
|date=2005
|title=Elliptical Galaxies
|url=http://web.archive.org/web/20120729081504/http://www.star.le.ac.uk/edu/Elliptical.shtml
|publisher=[[Leicester University]] Physics Department
|accessdate=June 8, 2006
}}</ref>

The largest galaxies are giant ellipticals. Many elliptical galaxies are believed to form due to the [[interacting galaxy|interaction of galaxies]], resulting in a collision and merger. They can grow to enormous sizes (compared to spiral galaxies, for example), and giant elliptical galaxies are often found near the core of large galaxy clusters.<ref>
{{cite web
|date=October 20, 2005
|title=Galaxies
|url=http://web.archive.org/web/20140629115612/http://curious.astro.cornell.edu/galaxies.php
|publisher=[[Cornell University]]
|accessdate=August 10, 2006
}}</ref> Starburst galaxies are the result of such a galactic collision that can result in the formation of an elliptical galaxy.<ref name="elliptical" />

====Shell galaxy====
[[File:NGC 3923 Elliptical Shell Galaxy.jpg|thumb|NGC 3923 Elliptical Shell Galaxy-Hubble Space Telescope photograph]]
A shell galaxy is a type of elliptical galaxy where the stars in the galaxy's halo are arranged in concentric shells. About 1/10 tenth of elliptical galaxies have a shell-like structure, which has never been observed in spiral galaxies. The shell-like structures are thought to develop when a larger galaxy absorbs a smaller companion galaxy. As the two galaxy centers approach, the centers start to oscillate around a center point, the oscillation creates gravitational ripples forming the shells of stars, similar to ripples spreading on water. For example, galaxy [[NGC 3923]] has over twenty shells.<ref>{{Cite web|title = Galactic onion|url = http://www.spacetelescope.org/images/potw1519a/|website = www.spacetelescope.org|accessdate = 2015-05-11}}</ref>

===Spirals===
{{Main|Spiral galaxy|Barred spiral galaxy}}

[[File:M101 hires STScI-PRC2006-10a.jpg|thumb|right|The [[Pinwheel Galaxy]], NGC 5457.]]

Spiral galaxies resemble spiraling pinwheels. Though the stars and other visible material contained in such a galaxy lie mostly on a plane, the majority of mass in spiral galaxies exists in a roughly spherical halo of [[dark matter]] that extends beyond the visible component, as demonstrated by the universal rotation curve concept.<ref name="Williams2009">{{cite doi|10.1111/j.1365-2966.2009.15582.x}}</ref>

Spiral galaxies consist of a rotating disk of stars and interstellar medium, along with a central bulge of generally older stars. Extending outward from the [[bulge (astronomy)|bulge]] are relatively bright arms. In the Hubble classification scheme, spiral galaxies are listed as type ''S'', followed by a letter (''a'', ''b'', or ''c'') that indicates the degree of tightness of the spiral arms and the size of the central bulge. An ''Sa'' galaxy has tightly wound, poorly defined arms and possesses a relatively large core region. At the other extreme, an ''Sc'' galaxy has open, well-defined arms and a small core region.<ref>
{{cite web
|last1=Smith |first1=G.
|date=March 6, 2000
|url=http://casswww.ucsd.edu/public/tutorial/Galaxies.html
|title=Galaxies — The Spiral Nebulae
|publisher=[[University of California]], San Diego Center for Astrophysics & Space Sciences
|accessdate=November 30, 2006
}}</ref> A galaxy with poorly defined arms is sometimes referred to as a [[flocculent spiral galaxy]]; in contrast to the [[grand design spiral galaxy]] that has prominent and well-defined spiral arms.<ref name=bergh1998/>

It appears the reason that some spiral galaxies are fat and bulging while some are flat discs is because of how fast they rotate.<ref>[http://phys.org/news/2014-02-fat-flat-galaxies.html "Fat or flat: Getting galaxies into shape"]. ''phys.org''. February 2014</ref>
[[File:Hubble2005-01-barred-spiral-galaxy-NGC1300.jpg|right|thumb|300px|[[NGC 1300]], an example of a [[barred spiral galaxy]].]]
In spiral galaxies, the spiral arms do have the shape of approximate [[logarithmic spiral]]s, a pattern that can be theoretically shown to result from a disturbance in a uniformly rotating mass of stars. Like the stars, the spiral arms rotate around the center, but they do so with constant [[angular velocity]]. The spiral arms are thought to be areas of high-density matter, or "[[Density wave theory|density waves]]".<ref name=bertin_lin1996/> As stars move through an arm, the space velocity of each stellar system is modified by the gravitational force of the higher density. (The velocity returns to normal after the stars depart on the other side of the arm.) This effect is akin to a "wave" of slowdowns moving along a highway full of moving cars. The arms are visible because the high density facilitates star formation, and therefore they harbor many bright and young stars.<ref name=belkora355/>
{{multiple image
| align = right
| direction = vertical
| width = 230
| image1 = Hoag's object.jpg
| caption1 = [[Hoag's Object]], an example of a [[ring galaxy]]
| image2 = File-Ngc5866 hst big.png
| caption2 = [[NGC 5866]], an example of a [[lenticular galaxy]]
}}

====Barred Spiral Galaxy====
A majority of spiral galaxies, including our own [[Milky Way]] galaxy, have a linear, bar-shaped band of stars that extends outward to either side of the core, then merges into the spiral arm structure.<ref>
{{cite journal
|last1=Eskridge |first1=P. B.
|last2=Frogel |first2=J. A.
|date=1999
|title=What is the True Fraction of Barred Spiral Galaxies?
|journal=[[Astrophysics and Space Science]]
|volume=269/270 |pages=427–430
|bibcode=1999Ap&SS.269..427E
|doi=10.1023/A:1017025820201
}}</ref> In the Hubble classification scheme, these are designated by an ''SB'', followed by a lower-case letter (''a'', ''b'' or ''c'') that indicates the form of the spiral arms (in the same manner as the categorization of normal spiral galaxies). Bars are thought to be temporary structures that can occur as a result of a density wave radiating outward from the core, or else due to a [[Galactic tide|tidal interaction]] with another galaxy.<ref>
{{cite journal
|last1=Bournaud |first1=F.
|last2=Combes |first2=F.
|date=2002
|title=Gas accretion on spiral galaxies: Bar formation and renewal
|journal=[[Astronomy and Astrophysics]]
|volume=392
|issue=1 |pages=83–102
|bibcode=2002A&A...392...83B
|doi=10.1051/0004-6361:20020920
|arxiv = astro-ph/0206273 }}</ref> Many barred spiral galaxies are active, possibly as a result of gas being channeled into the core along the arms.<ref>
{{cite journal
|last1=Knapen |first1=J. H.
|last2=Perez-Ramirez |first2=D.
|last3=Laine |first3=S.
|date=2002
|title=Circumnuclear regions in barred spiral galaxies — II. Relations to host galaxies
|journal=[[Monthly Notices of the Royal Astronomical Society]]
|volume=337 |issue=3 |pages=808–828
|bibcode=2002MNRAS.337..808K
|doi=10.1046/j.1365-8711.2002.05840.x
|arxiv = astro-ph/0207258 }}</ref>

Our own galaxy, the [[Milky Way]], is a large disk-shaped barred-spiral galaxy<ref>
{{cite journal
|last1=Alard |first1=C.
|date=2001
|title=Another bar in the Bulge
|journal=[[Astronomy and Astrophysics Letters]]
|volume=379 |issue=2 |pages=L44–L47
|bibcode=2001A&A...379L..44A
|doi=10.1051/0004-6361:20011487
|arxiv = astro-ph/0110491 }}</ref> about 30 kiloparsecs in diameter and a kiloparsec thick. It contains about two hundred billion (2×1011)<ref>
{{cite news
|last1=Sanders |first1=R.
|date=January 9, 2006
|title=Milky Way galaxy is warped and vibrating like a drum
|publisher=[[UC Berkeley|UCBerkeley News]]
|url=http://www.berkeley.edu/news/media/releases/2006/01/09_warp.shtml
|accessdate=May 24, 2006
}}</ref> stars and has a total mass of about six hundred billion (6×1011) times the mass of the Sun.<ref>
{{cite journal
|last1=Bell |first1=G. R.
|last2=Levine |first2=S. E.
|date=1997
|title=Mass of the Milky Way and Dwarf Spheroidal Stream Membership
|journal=[[Bulletin of the American Astronomical Society]]
|volume=29 |issue=2 |pages=1384
|bibcode=1997AAS...19110806B
}}</ref>

===Other morphologies===
* [[Peculiar galaxy|Peculiar galaxies]] are galactic formations that develop unusual properties due to tidal interactions with other galaxies. An example of this is the [[ring galaxy]], which possesses a ring-like structure of stars and interstellar medium surrounding a bare core. A ring galaxy is thought to occur when a smaller galaxy passes through the core of a spiral galaxy.<ref>{{cite journal
|last1=Gerber |first1=R. A.
|last2=Lamb |first2=S. A.
|last3=Balsara |first3=D. S.
|date=1994
|title=Ring Galaxy Evolution as a Function of "Intruder" Mass
|journal=[[Bulletin of the American Astronomical Society]]
|volume=26 |pages=911
|bibcode=1994AAS...184.3204G
}}</ref> Such an event may have affected the [[Andromeda Galaxy]], as it displays a multi-ring-like structure when viewed in [[infrared]] radiation.<ref>{{cite press release
|publisher=[[European Space Agency]]
|date=October 14, 1998
|title=ISO unveils the hidden rings of Andromeda
|url=http://www.iso.vilspa.esa.es/outreach/esa_pr/andromed.htm
|accessdate=May 24, 2006
}}</ref>

* A [[lenticular galaxy]] is an intermediate form that has properties of both elliptical and spiral galaxies. These are categorized as Hubble type S0, and they possess ill-defined spiral arms with an elliptical halo of stars<ref>{{cite web
|date=May 31, 2004
|title=Spitzer Reveals What Edwin Hubble Missed
|url=http://web.archive.org/web/20060907042809/http://www.cfa.harvard.edu/press/pr0419.html
|publisher=[[Harvard-Smithsonian Center for Astrophysics]]
|accessdate=December 6, 2006
}}</ref> ([[Barred lenticular galaxy|barred lenticular galaxies]] receive Hubble classification SB0.)

* [[Irregular galaxy|Irregular galaxies]] are galaxies that can not be readily classified into an elliptical or spiral morphology. An Irr-I galaxy has some structure but does not align cleanly with the Hubble classification scheme. Irr-II galaxies do not possess any structure that resembles a Hubble classification, and may have been disrupted.<ref>{{cite web
|last1=Barstow |first1=M. A.
|date=2005
|title=Irregular Galaxies
|url=http://web.archive.org/web/20120227172628/http://www.star.le.ac.uk/edu/Irregular.shtml
|publisher=[[University of Leicester]]
|accessdate=December 5, 2006
}}</ref> Nearby examples of (dwarf) irregular galaxies include the [[Magellanic Clouds]].

* An [[ultra diffuse galaxy]] (UDG) is an extremely-low-density galaxy. The galaxy may be the same size as the Milky Way but has a visible star count of only 1% of the Milky Way. The lack of luminosity is because there is a lack of star-forming gas in the galaxy which results in old stellar populations.

===Dwarfs===
{{Main|Dwarf galaxy}}
Despite the prominence of large elliptical and spiral galaxies, most galaxies in the Universe are dwarf galaxies. These galaxies are relatively small when compared with other galactic formations, being about one hundredth the size of the Milky Way, containing only a few billion stars. Ultra-compact dwarf galaxies have recently been discovered that are only 100 parsecs across.<ref>
{{cite journal
|last1=Phillipps |first1=S.
|last2=Drinkwater |first2=M. J.
|last3=Gregg |first3=M. D.
|last4=Jones |first4=J. B.
|date=2001
|title=Ultracompact Dwarf Galaxies in the Fornax Cluster
|journal=[[Astrophysical Journal]]
|volume=560 |issue=1 |pages=201–206
|bibcode=2001ApJ...560..201P
|doi=10.1086/322517
|arxiv = astro-ph/0106377 }}</ref>

Many dwarf galaxies may orbit a single larger galaxy; the Milky Way has at least a dozen such satellites, with an estimated 300–500 yet to be discovered.<ref>
{{cite news
|last1=Groshong |first1=K.
|date=April 24, 2006
|title=Strange satellite galaxies revealed around Milky Way
|publisher=[[New Scientist]]
|url=http://www.newscientist.com/article/dn9043-strange-satellite-galaxies-revealed-around-milky-way.html
|accessdate=January 10, 2007
}}</ref> Dwarf galaxies may also be classified as [[dwarf elliptical galaxy|elliptical]], [[dwarf spiral galaxy|spiral]], or [[irregular galaxy|irregular]]. Since small dwarf ellipticals bear little resemblance to large ellipticals, they are often called [[dwarf spheroidal galaxy|dwarf spheroidal galaxies]] instead.

A study of 27 Milky Way neighbors found that in all dwarf galaxies, the central mass is approximately 10 million [[solar mass]]es, regardless of whether the galaxy has thousands or millions of stars. This has led to the suggestion that galaxies are largely formed by [[dark matter]], and that the minimum size may indicate a form of [[warm dark matter]] incapable of gravitational coalescence on a smaller scale.<ref>
{{cite web
|last1=Schirber |first1=M.
|date=August 27, 2008
|url=http://news.sciencemag.org/physics/2008/08/no-slimming-down-dwarf-galaxies
|title=No Slimming Down for Dwarf Galaxies
|publisher=[[ScienceNOW]]
|accessdate=August 27, 2008
}}</ref>

==Unusual dynamics and activities==

===Interacting===
{{Main|Interacting galaxy}}
[[File:Antennae galaxies xl.jpg|thumb|right|200px|The [[Antennae Galaxies]] are undergoing a collision that will result in their eventual merger.]]
Interactions between galaxies are relatively frequent, and they can play an important role in [[galaxy formation and evolution|galactic evolution]]. Near misses between galaxies result in warping distortions due to [[galactic tide|tidal interactions]], and may cause some exchange of gas and dust.<ref name="umda">
{{cite web
|url=http://www.astro.umd.edu/education/astro/gal/interact.html
|title=Galaxy Interactions
|publisher=[[University of Maryland]] Department of Astronomy
|accessdate=December 19, 2006
|archiveurl=http://web.archive.org/web/20060509074300/http://www.astro.umd.edu/education/astro/gal/interact.html
|archivedate=May 9, 2006
}}</ref><ref name="suia">
{{cite web
|title=Interacting Galaxies
|url=http://Cosmos.swin.edu.au/entries/interactinggalaxies/interactinggalaxies.html?e=1
|publisher=[[Swinburne University]]
|accessdate=December 19, 2006
}}</ref>
Collisions occur when two galaxies pass directly through each other and have sufficient relative momentum not to merge. The stars of interacting galaxies will usually not collide, but the gas and dust within the two forms will interact, sometimes triggering star formation. A collision can severely distort the shape of the galaxies, forming bars, rings or tail-like structures.<ref name="umda" /><ref name="suia" />

At the extreme of interactions are galactic mergers. In this case the relative momentum of the two galaxies is insufficient to allow the galaxies to pass through each other. Instead, they gradually merge to form a single, larger galaxy. Mergers can result in significant changes to morphology, as compared to the original galaxies. In the case where one of the galaxies is much more massive, however, the result is known as [[Interacting galaxy#Galactic cannibalism|cannibalism]]. In this case the larger galaxy will remain relatively undisturbed by the merger, while the smaller galaxy is torn apart. The Milky Way galaxy is currently in the process of cannibalizing the [[Sagittarius Dwarf Elliptical Galaxy]] and the [[Canis Major Dwarf Galaxy]].<ref name="umda" /><ref name="suia" />

===Starburst===
{{Main|Starburst galaxy}}
[[File:M82 HST ACS 2006-14-a-large web.jpg|thumb|right|200px|[[Messier 82|M82]], a starburst galaxy that has ten times the star formation of a "normal" galaxy.<ref>
{{cite web
|date=April 24, 2006
|url=http://hubblesite.org/newscenter/archive/releases/2006/14/image/a
|title=Happy Sweet Sixteen, Hubble Telescope!
|publisher=[[NASA]]
|accessdate=August 10, 2006
}}</ref>]]

Stars are created within galaxies from a reserve of cold gas that forms into giant [[molecular cloud]]s. Some galaxies have been observed to form stars at an exceptional rate, known as a starburst. Should they continue to do so, however, they would consume their reserve of gas in a time frame lower than the lifespan of the galaxy. Hence starburst activity usually lasts for only about ten million years, a relatively brief period in the history of a galaxy. Starburst galaxies were more common during the early history of the Universe,<ref name="chandra">
{{cite web
|date=August 29, 2006
|url=http://chandra.harvard.edu/xray_sources/starburst.html
|title=Starburst Galaxies
|publisher=[[Harvard-Smithsonian Center for Astrophysics]]
|accessdate=August 10, 2006
}}</ref> and, at present, still contribute an estimated 15% to the total star production rate.<ref>
{{cite conference
|last1=Kennicutt Jr. |first1=R. C.
|display-authors=etal
|date=2005
|title=Demographics and Host Galaxies of Starbursts
|work=Starbursts: From 30 Doradus to Lyman Break Galaxies
|page=187
|publisher=[[Springer (publisher)|Springer]]
|bibcode=2005sdlb.proc..187K
}}</ref>

Starburst galaxies are characterized by dusty concentrations of gas and the appearance of newly formed stars, including massive stars that ionize the surrounding clouds to create [[H II region]]s.<ref>
{{cite web
|last1=Smith |first1=G.
|date=July 13, 2006
|title=Starbursts & Colliding Galaxies
|url=http://casswww.ucsd.edu/public/tutorial/Starbursts.html
|publisher=[[University of California]], San Diego Center for Astrophysics & Space Sciences
|accessdate=August 10, 2006
}}</ref> These massive stars produce [[supernova]] explosions, resulting in expanding [[supernova remnant|remnants]] that interact powerfully with the surrounding gas. These outbursts trigger a chain reaction of star building that spreads throughout the gaseous region. Only when the available gas is nearly consumed or dispersed does the starburst activity come to an end.<ref name="chandra" />

Starbursts are often associated with merging or interacting galaxies. The prototype example of such a starburst-forming interaction is [[Messier 82|M82]], which experienced a close encounter with the larger [[Messier 81|M81]]. Irregular galaxies often exhibit spaced knots of starburst activity.<ref>
{{cite web
|last1=Keel |first1=B.
|date=September 2006
|title=Starburst Galaxies
|url=http://www.astr.ua.edu/keel/galaxies/starburst.html
|publisher=[[University of Alabama]]
|accessdate=December 11, 2006
}}</ref>

===Active nucleus===
{{Main|Active galactic nucleus}}
[[File:M87 jet.jpg|thumb|right|200px|A jet of particles is being emitted from the core of the elliptical radio galaxy [[Messier 87|M87]].]]
A portion of the observable galaxies are classified as active. That is, a significant portion of the total energy output from the galaxy is emitted by a source other than the stars, dust and [[interstellar medium]].

The standard model for an [[active galactic nucleus]] is based upon an [[accretion disc]] that forms around a [[supermassive black hole]] (SMBH) at the core region. The radiation from an active galactic nucleus results from the [[gravitational energy]] of matter as it falls toward the black hole from the disc.<ref name="keel">
{{cite web
|last1=Keel |first1=W. C.
|date=2000
|url=http://www.astr.ua.edu/keel/galaxies/agnintro.html
|title=Introducing Active Galactic Nuclei
|publisher=[[University of Alabama]]
|accessdate=December 6, 2006
}}</ref> In about 10% of these objects, a diametrically opposed pair of energetic jets ejects particles from the core at velocities close to the [[speed of light]]. The mechanism for producing these jets is still not well understood.<ref name="monster">
{{cite web
|last1=Lochner |first1=J.
|last2=Gibb |first2=M.
|title=A Monster in the Middle
|url=http://imagine.gsfc.nasa.gov/docs/science/know_l2/active_galaxies.html
|publisher=[[NASA]]
|accessdate=December 20, 2006
}}</ref>

Active galaxies that emit high-energy radiation in the form of [[x-ray]]s are classified as [[Seyfert galaxy|Seyfert galaxies]] or [[quasar]]s, depending on the luminosity.

====Blazars====
{{Main|Blazars}}
[[Blazar]]s are believed to be an active galaxy with a [[relativistic jet]] that is pointed in the direction of Earth. A [[radio galaxy]] emits radio frequencies from relativistic jets. A unified model of these types of active galaxies explains their differences based on the viewing angle of the observer.<ref name="monster" />

====LINERS====
Possibly related to active galactic nuclei (as well as [[starburst (astronomy)|starburst]] regions) are [[low-ionization nuclear emission-line region]]s (LINERs). The emission from LINER-type galaxies is dominated by weakly [[ion]]ized elements.<ref name="heckman1980">
{{cite journal
|last1=Heckman |first1=T. M.
|date=1980
|title=An optical and radio survey of the nuclei of bright galaxies — Activity in normal galactic nuclei
|journal=[[Astronomy and Astrophysics]]
|volume=87 |pages=152–164
|bibcode=1980A&A....87..152H
}}</ref> Approximately one-third of nearby galaxies are classified as containing LINER nuclei.<ref name="keel" /><ref name="heckman1980" /><ref name="hoetal1997b">
{{cite journal
|last1=Ho |first1=L. C.
|last2=Filippenko |first2=A. V.
|last3=Sargent |first3=W. L. W.
|date=1997
|title=A Search for "Dwarf" Seyfert Nuclei. V. Demographics of Nuclear Activity in Nearby Galaxies
|journal=[[Astrophysical Journal]]
|volume=487
|issue=2 |pages=568–578
|bibcode=1997ApJ...487..568H
|doi=10.1086/304638
|arxiv = astro-ph/9704108 }}</ref>

====Seyfert Galaxy====
{{Main|Seyfert Galaxy}}
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei (very luminous, distant and bright sources of electromagnetic radiation) with very high surface brightnesses but unlike quasars, their host galaxies are clearly detectable. Seyfert galaxies account for about 10% of all galaxies. Seen in visible light, most Seyfert galaxies look like normal spiral galaxies, but when studied under other wavelengths, the luminosity of their cores is equivalent to the luminosity of whole galaxies the size of the Milky Way.

====Quasar====
{{Main|Quasar}}
Quasars (/ˈkweɪzɑr/) or quasi-stellar radio sources are the most energetic and distant members of a class of objects called active galactic nuclei (AGN). Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that appeared to be similar to stars, rather than extended sources similar to galaxies. Their luminosity can be 100 times greater than that of the Milky Way.

===Luminous infrared galaxy===
{{Main|Luminous infrared galaxy}}
Luminous Infrared Galaxies or (LIRG's) are galaxies with luminosities, the measurement of brightness, above 1011 L☉. LIRG's are more abundant than starburst galaxies, Seyfert galaxies and quasi-stellar objects at comparable luminosity. Infrared galaxies emit more energy in the infrared than at all other wavelengths combined. An LIRG's luminosity is 100 billion times that of our sun.

==Formation and evolution==
{{Main|Galaxy formation and evolution}}
Galactic formation and evolution is an active area of research in [[astrophysics]].

===Formation===
[[File:Artist's impression of a protocluster forming in the early Universe.jpg|align=right|thumb|Artist's impression of a protocluster forming in the early Universe.<ref>{{cite web|title=Construction Secrets of a Galactic Metropolis|url=http://www.eso.org/public/news/eso1431/|website=www.eso.org|publisher=ESO Press Release|accessdate=October 15, 2014}}</ref>]]
Current cosmological models of the early Universe are based on the [[Big Bang]] theory. About 300,000 years after this event, atoms of [[hydrogen]] and [[helium]] began to form, in an event called [[Recombination (cosmology)|recombination]]. Nearly all the hydrogen was neutral (non-ionized) and readily absorbed light, and no stars had yet formed. As a result, this period has been called the "[[Timeline of the Big Bang#Dark Ages|dark ages]]". It was from density fluctuations (or [[anisotropy|anisotropic]] irregularities) in this primordial matter that [[structure formation|larger structures]] began to appear. As a result, masses of [[baryon]]ic matter started to condense within [[cold dark matter]] halos.<ref name="hqrdvj">
{{cite web
|date=November 18, 1999
|title=Search for Submillimeter Protogalaxies
|url=http://web.archive.org/web/20080325183740/http://cfa-www.harvard.edu/~aas/tenmeter/proto.htm
|publisher=[[Harvard-Smithsonian Center for Astrophysics]]
|accessdate=January 10, 2007
}}</ref><ref name=rmaa17_107/> These primordial structures would eventually become the galaxies we see today.
[[File:Young Galaxy Accreting Material.jpg|thumb|right|200px|Artist's impression of a young galaxy accreting material.]]

====Early galaxies====
Evidence for the early appearance of galaxies was found in 2006, when it was discovered that the galaxy [[IOK-1]] has an unusually high [[redshift]] of 6.96, corresponding to just 750 million years after the Big Bang and making it the most distant and primordial galaxy yet seen.<ref>
{{cite journal
|last1=McMahon |first1=R.
|date=2006
|title=Journey to the birth of the Universe
|journal=[[Nature (journal)|Nature]]
|volume=443 |issue=7108 |pages=151–2
|doi=10.1038/443151a
|pmid=16971933
|bibcode = 2006Natur.443..151M }}</ref>
While some scientists have claimed other objects (such as [[Galaxy Abell 1835 IR1916|Abell 1835 IR1916]]) have higher redshifts (and therefore are seen in an earlier stage of the Universe's evolution), IOK-1's age and composition have been more reliably established. In December 2012, astronomers reported that the [[UDFj-39546284]] is the most distant object known and has a redshift value of 11.9. The object, is estimated to have existed around "380 million years"<ref name="Space-20121212">{{cite web |last=Wall |first=Mike |title=Ancient Galaxy May Be Most Distant Ever Seen |url=http://www.space.com/18879-hubble-most-distant-galaxy.html |date=December 12, 2012 |publisher=[[Space.com]] |accessdate=December 12, 2012 }}</ref> after the [[Big Bang]] (which was about 13.8 billion years ago),<ref name="Cosmic Detectives">{{cite web
|last =
|first =
|title = Cosmic Detectives
|url=http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives
|authorlink =
|work =
|publisher = The European Space Agency (ESA)
|date = April 2, 2013
|doi =
|accessdate = April 15, 2013}}</ref> is about 13.42 billion light years away. The existence of such early [[protogalaxy|protogalaxies]] suggests that they must have grown in the so-called "dark ages".<ref name="hqrdvj"/> As of May 5, 2015, the galaxy [[EGS-zs8-1]] is the most distant and earliest galaxy measured, forming 670 million years after the [[Big Bang]]. The light from EGS-zs8-1 has taken 13 billion years to reach Earth, and is now 30 billion light-years away, because of the [[expansion of the universe]] during 13 billion years.<ref>{{Cite web|title = HubbleSite - NewsCenter - Astronomers Set a New Galaxy Distance Record (05/05/2015) - Introduction|url = http://hubblesite.org/newscenter/archive/releases/2015/22/|website = hubblesite.org|accessdate = 2015-05-07}}</ref><ref>{{Cite web|title = This Galaxy Far, Far Away Is the Farthest One Yet Found|url = http://www.space.com/29319-farthest-galaxy-ever-found.html?cmpid=NL_SP_weekly_2015-05-06|accessdate = 2015-05-07}}</ref><ref name="phys.org">{{Cite web|title = Astronomers unveil the farthest galaxy|url = http://phys.org/news/2015-05-astronomers-unveil-farthest-galaxy.html|accessdate = 2015-05-07}}</ref><ref name="phys.org"/><ref>{{Cite news|title = Astronomers Measure Distance to Farthest Galaxy Yet|url = http://www.nytimes.com/2015/05/06/science/astronomers-measure-distance-to-farthest-galaxy-yet.html|newspaper = The New York Times|date = 2015-05-05|access-date = 2015-05-07|issn = 0362-4331|first = Dennis|last = Overbye}}</ref><ref>{{Cite journal|title = A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE|url = http://arxiv.org/abs/1502.05399|journal = arXiv:1502.05399 [astro-ph]|date = 2015-02-18|access-date = 2015-05-07|first = P. A.|last = Oesch|first2 = P. G.|last2 = van Dokkum|first3 = G. D.|last3 = Illingworth|first4 = R. J.|last4 = Bouwens|first5 = I.|last5 = Momcheva|first6 = B.|last6 = Holden|first7 = G. W.|last7 = Roberts-Borsani|first8 = R.|last8 = Smit|first9 = M.|last9 = Franx}}</ref>

====Early galaxy formation====
The detailed process by which early galaxies formed is an open question in astrophysics. Theories can be divided into two categories: top-down and bottom-up. In top-down theories (such as the Eggen–Lynden-Bell–Sandage [ELS] model), protogalaxies form in a large-scale simultaneous collapse lasting about one hundred million years.<ref>
{{cite journal
|last1=Eggen |first1=O. J.
|last2=Lynden-Bell |first2=D.
|last3=Sandage |first3=A. R.
|date=1962
|title=Evidence from the motions of old stars that the Galaxy collapsed
|journal=[[Reports on Progress in Physics]]
|volume=136 |pages=748
|bibcode=1962ApJ...136..748E
|doi=10.1086/147433
}}</ref> In bottom-up theories (such as the Searle-Zinn [SZ] model), small structures such as [[globular cluster]]s form first, and then a number of such bodies accrete to form a larger galaxy.<ref>
{{cite journal
|last1=Searle |first1=L.
|last2=Zinn |first2=R.
|date=1978
|title=Compositions of halo clusters and the formation of the galactic halo
|journal=[[Astrophysical Journal]]
|volume=225 |issue=1 |pages=357–379
|bibcode=1978ApJ...225..357S
|doi=10.1086/156499
}}</ref>

Once protogalaxies began to form and contract, the first [[halo star]]s (called [[Metallicity#Population III stars|Population III stars]]) appeared within them. These were composed almost entirely of hydrogen and helium, and may have been massive. If so, these huge stars would have quickly consumed their supply of fuel and became [[supernova]]e, releasing heavy elements into the [[interstellar medium]].<ref>
{{cite journal
|last1=Heger |first1=A.
|last2=Woosley |first2=S. E.
|date=2002
|title=The Nucleosynthetic Signature of Population III
|journal=[[Astrophysical Journal]]
|volume=567 |issue=1 |pages=532–543
|bibcode=2002ApJ...567..532H
|doi=10.1086/338487
|arxiv = astro-ph/0107037 }}</ref> This first generation of stars re-ionized the surrounding neutral hydrogen, creating expanding bubbles of space through which light could readily travel.<ref>
{{cite journal
|last1=Barkana |first1=R.
|last2=Loeb |first2=A.
|date=1999
|title=In the beginning: the first sources of light and the reionization of the Universe
|journal=[[Physics Reports]]
|volume=349 |issue=2 |pages=125–238
|bibcode=2001PhR...349..125B
| arxiv = astro-ph/0010468
|doi=10.1016/S0370-1573(01)00019-9
}}</ref>

In June 2015, astronomers reported evidence for [[Metallicity#Population III stars|Population III stars]] in the [[Cosmos Redshift 7]] galaxy at {{math|''z'' {{=}} 6.60}}. Such stars are likely to have existed in the very early universe (i.e., at high redshift), and may have started the production of [[chemical element]]s heavier than [[hydrogen]] that are needed for the later formation of [[planet]]s and [[life]] as we know it.<ref name="AJ-20150604">{{cite journal |last1=Sobral |first1=David |last2=Matthee |first2=Jorryt |last3=Darvish |first3=Behnam |last4=Schaerer |first4=Daniel |last5=Mobasher |first5=Bahram |last6=Röttgering |first6=Huub J. A. |last7=Santos |first7=Sérgio |last8=Hemmati |first8=Shoubaneh |title=Evidence For POPIII-Like Stellar Populations In The Most Luminous LYMAN-α Emitters At The Epoch Of Re-Ionisation: Spectroscopic Confirmation |url=http://arxiv.org/pdf/1504.01734.pdf |format=[[PDF]] |date=4 June 2015 |journal=[[The Astrophysical Journal]] |accessdate=17 June 2015 }}</ref><ref name="NYT-20150617">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Astronomers Report Finding Earliest Stars That Enriched Cosmos |url=http://www.nytimes.com/2015/06/18/science/space/astronomers-report-finding-earliest-stars-that-enriched-cosmos.html |date=17 June 2015 |work=[[New York Times]] |accessdate=17 June 2015 }}</ref>

===Evolution===
Within a billion years of a galaxy's formation, key structures begin to appear. [[Globular cluster]]s, the central supermassive black hole, and a [[bulge (astronomy)|galactic bulge]] of metal-poor [[metallicity|Population II stars]] form. The creation of a supermassive black hole appears to play a key role in actively regulating the growth of galaxies by limiting the total amount of additional matter added.<ref>
{{cite news
|date=February 9, 2005
|title=Simulations Show How Growing Black Holes Regulate Galaxy Formation
|url=http://www.cmu.edu/PR/releases05/050209_blackhole.html
|publisher=[[Carnegie Mellon University]]
|accessdate=January 7, 2007
}}</ref> During this early epoch, galaxies undergo a major burst of star formation.<ref>
{{cite news
|last1=Massey |first1=R.
|date=April 21, 2007
|title=Caught in the act; forming galaxies captured in the young Universe
|url=http://web.archive.org/web/20131115031412/http://www.ras.org.uk/index.php?option=com_content&task=view&id=1190&Itemid=2
|publisher=[[Royal Astronomical Society]]
|accessdate=April 20, 2007
}}</ref>

During the following two billion years, the accumulated matter settles into a [[disc (galaxy)|galactic disc]].<ref>
{{cite journal
|last=Noguchi |first=M.
|date=1999
|title=Early Evolution of Disk Galaxies: Formation of Bulges in Clumpy Young Galactic Disks
|journal=[[Astrophysical Journal]]
|volume=514 |issue=1 |pages=77–95
|bibcode=1999ApJ...514...77N
|doi=10.1086/306932
|arxiv = astro-ph/9806355 }}</ref> A galaxy will continue to absorb infalling material from [[high-velocity cloud]]s and [[dwarf galaxy|dwarf galaxies]] throughout its life.<ref>
{{cite web
|last1=Baugh |first1=C.
|last2=Frenk |first2=C.
|date=May 1999
|url=http://web.archive.org/web/20070426043157/http://physicsweb.org/articles/world/12/5/9
|title=How are galaxies made?
|publisher=[[PhysicsWeb]]
|accessdate=January 16, 2007
}}</ref> This matter is mostly hydrogen and helium. The cycle of stellar birth and death slowly increases the abundance of heavy elements, eventually allowing the [[planetary formation|formation]] of [[planet]]s.<ref>
{{cite conference
|last1=Gonzalez |first1=G.
|date=1998
|title=The Stellar Metallicity — Planet Connection
|work=Proceedings of a workshop on brown dwarfs and extrasolar planets
|pages=431
|bibcode=1998bdep.conf..431G
}}</ref>
{{Multiple image |direction=vertical |align=right |width=200 |image1=XDF-scale.jpg|image2=Constellation Fornax, EXtreme Deep Field.jpg |image3=XDF-separated.jpg |caption1=''[[Hubble Extreme Deep Field|XDF]]'' view field compared to the [[angular diameter|angular size]] of the [[Moon]]. Several thousand galaxies, each consisting of billions of [[star]]s, are in this small view. |caption2=''[[Hubble Extreme Deep Field|XDF]]'' (2012) view: Each light speck is a galaxy, some of which are as old as 13.2 billion years<ref name="Space-20120925">{{cite web |last=Moskowitz |first=Clara |title=Hubble Telescope Reveals Farthest View Into Universe Ever|url=http://www.space.com/17755-farthest-universe-view-hubble-space-telescope.html|date=September 25, 2012 |publisher=[[Space.com]] |accessdate=September 26, 2012}}</ref> – the [[observable universe]] is estimated to contain 200 billion galaxies. |caption3=''[[Hubble Extreme Deep Field|XDF]]'' image shows (from left) fully mature galaxies, nearly mature galaxies (from 5 to 9 billion years ago), [[Protogalaxy|protogalaxies]], blazing with [[young star]]s (beyond 9 billion years). |header=''[[Hubble Extreme Deep Field|Hubble eXtreme Deep Field (XDF)]]'' }}

The evolution of galaxies can be significantly affected by interactions and collisions. Mergers of galaxies were common during the early epoch, and the majority of galaxies were peculiar in morphology.<ref name="sa296">
{{cite journal
|last1=Conselice |first1=C. J.
|date=February 2007
|title=The Universe's Invisible Hand
|journal=[[Scientific American]]
|volume=296 |issue=2 |pages=35–41
|doi=10.1038/scientificamerican0207-34
}}</ref> Given the distances between the stars, the great majority of stellar systems in colliding galaxies will be unaffected. However, gravitational stripping of the interstellar gas and dust that makes up the spiral arms produces a long train of stars known as tidal tails. Examples of these formations can be seen in [[NGC 4676]]<ref>
{{cite news
|last1=Ford |first1=H.
|display-authors=etal
|date=April 30, 2002
|title=Hubble's New Camera Delivers Breathtaking Views of the Universe
|url=http://hubblesite.org/newscenter/archive/releases/2002/11/image/d
|publisher=Hubble News Desk
|accessdate=May 8, 2007
}}</ref> or the [[Antennae Galaxies]].<ref>
{{cite journal
|last1=Struck |first1=C.
|date=1999
|title=Galaxy Collisions
|doi=10.1016/S0370-1573(99)00030-7
|journal=Physics Reports
|volume=321
|pages=1
|arxiv=astro-ph/9908269
|bibcode = 1999PhR...321....1S }}</ref>

The Milky Way galaxy and the nearby Andromeda Galaxy are moving toward each other at about 130 [[metre per second|km/s]], and—depending upon the lateral movements—the two might collide in about five to six billion years. Although the Milky Way has never collided with a galaxy as large as Andromeda before, evidence of past collisions of the Milky Way with smaller dwarf galaxies is increasing.<ref>
{{cite news
|last1=Wong |first1=J.
|date=April 14, 2000
|title=Astrophysicist maps out our own galaxy's end
|url=http://www.news.utoronto.ca/bin/000414b.asp
|publisher=[[University of Toronto]]
|accessdate=January 11, 2007
|archiveurl=http://web.archive.org/web/20070108183824/http://www.news.utoronto.ca/bin/000414b.asp
|archivedate=January 8, 2007
}}</ref>

Such large-scale interactions are rare. As time passes, mergers of two systems of equal size become less common. Most bright galaxies have remained fundamentally unchanged for the last few billion years, and the net rate of star formation probably also peaked approximately ten billion years ago.<ref>
{{cite journal
|last1=Panter |first1=B.
|last2=Jimenez |first2=R.
|last3=Heavens |first3=A. F.
|last4=Charlot |first4=S.
|date=2007
|title=The star formation histories of galaxies in the Sloan Digital Sky Survey
|journal=[[Monthly Notices of the Royal Astronomical Society]]
|volume=378 |issue=4 |pages=1550–1564
|arxiv=astro-ph/0608531
|doi=10.1111/j.1365-2966.2007.11909.x |bibcode=2007MNRAS.378.1550P
}}</ref>

===Future trends===
Spiral galaxies, like the Milky Way, produce new generations of stars as long as they have dense [[molecular cloud]]s of interstellar hydrogen in their spiral arms.<ref>
{{cite journal
|last1=Kennicutt Jr. |first1=R. C.
|last2=Tamblyn |first2=P.
|last3=Congdon |first3=C. E.
|date=1994
|title=Past and future star formation in disk galaxies
|journal=[[Astrophysical Journal]]
|volume=435 |issue=1 |pages=22–36
|bibcode=1994ApJ...435...22K
|doi=10.1086/174790
}}</ref> Elliptical galaxies are largely devoid of this gas, and so form few new stars.<ref>
{{cite book
|last1=Knapp |first1=G. R.
|date=1999
|title=Star Formation in Early Type Galaxies
|publisher=[[Astronomical Society of the Pacific]]
|bibcode=1998astro.ph..8266K
|oclc=41302839
|isbn=1-886733-84-8
}}</ref> The supply of star-forming material is finite; once stars have converted the available supply of hydrogen into heavier elements, new star formation will come to an end.<ref name="cosmic_battle">
{{cite web
|last1=Adams |first1=Fred
|last2=Laughlin |first2=Greg
|date=July 13, 2006
|title=The Great Cosmic Battle
|url=http://www.astrosociety.org/pubs/mercury/0001/cosmic.html
|publisher=[[Astronomical Society of the Pacific]]
|accessdate=January 16, 2007
}}</ref><ref>{{Cite web|title = Cosmic 'Murder Mystery' Solved: Galaxies Are 'Strangled to Death'|url = http://www.space.com/29398-galaxy-strangulation-death-mystery.html?cmpid=NL_SP_weekly_2015-05-13|accessdate = 2015-05-14}}</ref>

The current era of star formation is expected to continue for up to one hundred billion years, and then the "stellar age" will wind down after about ten trillion to one hundred trillion years (1013–1014 years), as the smallest, longest-lived stars in our universe, tiny [[red dwarf]]s, begin to fade. At the end of the stellar age, galaxies will be composed of [[compact star|compact objects]]: [[brown dwarf]]s, [[white dwarf]]s that are cooling or cold ("[[black dwarf]]s"), [[neutron star]]s, and [[black hole]]s. Eventually, as a result of [[relaxation time|gravitational relaxation]], all stars will either fall into central supermassive black holes or be flung into intergalactic space as a result of collisions.<ref name="cosmic_battle" /><ref>
{{cite web
|last1=Pobojewski |first1=S.
|date=January 21, 1997
|title=Physics offers glimpse into the dark side of the Universe
|url=http://www.umich.edu/~urecord/9697/Jan21_97/artcl17.htm
|publisher=[[University of Michigan]]
|accessdate=January 13, 2007
}}</ref>

==Larger-scale structures==
{{Main|Observable universe#Large-scale structure|Galaxy filament|Galaxy groups and clusters}}
Deep sky surveys show that galaxies are often found in groups and [[Clusters of galaxies|clusters]]. Solitary galaxies that have not significantly interacted with another galaxy of comparable mass during the past billion years are relatively scarce. Only about 5% of the galaxies surveyed have been found to be truly isolated; however, these isolated formations may have interacted and even merged with other galaxies in the past, and may still be orbited by smaller, satellite galaxies. Isolated galaxies<ref group=note>The term "field galaxy" is sometimes used to mean an isolated galaxy, although the same term is also used to describe galaxies that do not belong to a cluster but may be a member of a group of galaxies.</ref> can produce stars at a higher rate than normal, as their gas is not being stripped by other nearby galaxies.<ref>
{{cite web
|last1=McKee |first1=M.
|date=June 7, 2005
|title=Galactic loners produce more stars
|url=http://www.newscientist.com/article.ns?id=dn7478
|publisher=[[New Scientist]]
|accessdate=January 15, 2007
}}</ref>

On the largest scale, the Universe is continually expanding, resulting in an average increase in the separation between individual galaxies (see [[Hubble's law]]). Associations of galaxies can overcome this expansion on a local scale through their mutual gravitational attraction. These associations formed early in the Universe, as clumps of dark matter pulled their respective galaxies together. Nearby groups later merged to form larger-scale clusters. This on-going merger process (as well as an influx of infalling gas) heats the inter-galactic gas within a cluster to very high temperatures, reaching 30–100 [[megakelvin]]s.<ref>
{{cite web
|url=http://chandra.harvard.edu/xray_sources/galaxy_clusters.html
|title=Groups & Clusters of Galaxies
|publisher=[[NASA]]/[[Chandra]]
|accessdate=January 15, 2007
}}</ref> About 70–80% of the mass in a cluster is in the form of dark matter, with 10–30% consisting of this heated gas and the remaining few percent of the matter in the form of galaxies.<ref>
{{cite web
|last1=Ricker |first1=P.
|title=When Galaxy Clusters Collide
|url=http://www.sdsc.edu/pub/envision/v15.2/ricker.html
|publisher=[[San Diego Supercomputer Center]]
|accessdate=August 27, 2008
}}</ref>
{{multiple image
| align = right
| direction = vertical
| width = 230
| image1 = Seyfert Sextet full.jpg
| width1 =
| alt1 =
| caption1 = [[Seyfert's Sextet]] is an example of a compact galaxy group.
| image2 =
| width2 =
| alt2 =
| caption2 = [[Millennium Simulation]] showing large-scale structure of the Cosmos. The image spans about 400 million light years across.
}}
Most galaxies in the Universe are gravitationally bound to a number of other galaxies. These form a [[fractal]]-like hierarchical distribution of clustered structures, with the smallest such associations being termed groups. A group of galaxies is the most common type of galactic cluster, and these formations contain a majority of the galaxies (as well as most of the [[baryon]]ic mass) in the Universe.<ref>
{{cite web
|last1=Dahlem |first1=M.
|date=November 24, 2006
|title=Optical and radio survey of Southern Compact Groups of galaxies
|url=http://www.atnf.csiro.au/people/mdahlem/sci/SCGs.html
|publisher=[[University of Birmingham]] Astrophysics and Space Research Group
|accessdate=January 15, 2007
|archiveurl=http://web.archive.org/web/20070613151936/http://www.atnf.csiro.au/people/mdahlem/sci/SCGs.html
|archivedate=June 13, 2007
}}</ref><ref>
{{cite web
|last1=Ponman |first1=T.
|date=February 25, 2005
|title=Galaxy Systems: Groups
|url=http://web.archive.org/web/20090215023446/http://www.sr.bham.ac.uk/research/groups.html
|publisher=[[University of Birmingham]] Astrophysics and Space Research Group
|accessdate=January 15, 2007
}}</ref> To remain gravitationally bound to such a group, each member galaxy must have a sufficiently low velocity to prevent it from escaping (see [[Virial theorem]]). If there is insufficient [[kinetic energy]], however, the group may evolve into a smaller number of galaxies through mergers.<ref>
{{cite journal
|last1=Girardi |first1=M.
|last2=Giuricin |first2=G.
|date=2000
|title=The Observational Mass Function of Loose Galaxy Groups
|journal=[[The Astrophysical Journal]]
|volume=540 |issue=1 |pages=45–56
|bibcode=2000ApJ...540...45G
|doi=10.1086/309314
|arxiv = astro-ph/0004149 }}</ref>

Clusters of galaxies consist of hundreds to thousands of galaxies bound together by gravity.<ref name="Hubble protocluster">{{cite news|title=Hubble Pinpoints Furthest Protocluster of Galaxies Ever Seen|url=http://www.spacetelescope.org/news/heic1201/|accessdate=January 22, 2015|newspaper=ESA/Hubble Press Release}}</ref> Clusters of galaxies are often dominated by a single giant elliptical galaxy, known as the [[brightest cluster galaxy]], which, over time, [[tidal force|tidally]] destroys its satellite galaxies and adds their mass to its own.<ref>
{{cite journal
|last=Dubinski |first=J.
|date=1998
|title=The Origin of the Brightest Cluster Galaxies
|url=http://www.cita.utoronto.ca/~dubinski/bcg/
|journal=[[Astrophysical Journal]]
|volume=502 |issue=2 |pages=141–149
|doi=10.1086/305901
|bibcode=1998ApJ...502..141D
|arxiv = astro-ph/9709102 }}</ref>

[[Supercluster]]s contain tens of thousands of galaxies, which are found in clusters, groups and sometimes individually. At the [[large-scale structure of the Cosmos|supercluster scale]], galaxies are arranged into sheets and filaments surrounding vast empty voids.<ref>
{{cite journal
|last1=Bahcall |first1=N. A.
|date=1988
|title=Large-scale structure in the Universe indicated by galaxy clusters
|journal=[[Annual Review of Astronomy and Astrophysics]]
|volume=26
|issue=1 |pages=631–686
|bibcode=1988ARA&A..26..631B
|doi=10.1146/annurev.aa.26.090188.003215
}}</ref> Above this scale, the Universe appears to be the same in all directions ([[isotropy|isotropic]] and [[wikt:Homogeneity|homogeneous]]).<ref>
{{cite journal
|last1=Mandolesi |first1=N.
|display-authors=etal
|date=1986
|title=Large-scale homogeneity of the Universe measured by the microwave background
|journal=[[Letters to Nature]]
|volume=319
|issue=6056 |pages=751–753
|doi=10.1038/319751a0
|bibcode = 1986Natur.319..751M }}</ref>

The Milky Way galaxy is a member of an association named the [[Local Group]], a relatively small group of galaxies that has a diameter of approximately one megaparsec. The Milky Way and the Andromeda Galaxy are the two brightest galaxies within the group; many of the other member galaxies are dwarf companions of these two galaxies.<ref>
{{cite journal
|last1=van den Bergh |first1=S.
|date=2000
|title=Updated Information on the Local Group
|journal=Publications of the Astronomical Society of the Pacific
|volume=112 |issue=770 |pages=529–536
|bibcode=2000PASP..112..529V
|doi=10.1086/316548
|arxiv = astro-ph/0001040 }}</ref> The Local Group itself is a part of a cloud-like structure within the [[Virgo Supercluster]], a large, extended structure of groups and clusters of galaxies centered on the [[Virgo Cluster]].<ref name="tully1982">
{{cite journal
|last1=Tully |first1=R. B.
|date=1982
|title=The Local Supercluster
|journal=[[Astrophysical Journal]]
|volume=257 |pages=389–422
|bibcode=1982ApJ...257..389T
|doi=10.1086/159999
}}</ref> And the Virgo Supercluster itself is a part of the [[Pisces-Cetus Supercluster Complex]], a giant [[galaxy filament]].

==Multi-wavelength observation==
{{See also|Observational astronomy}}
{{multiple image
| align = right
| direction = vertical
| width = 220
| image1 =
| caption1 = A visual light image of [[Andromeda Galaxy]] shows the emission of ordinary stars and the light reflected by dust.
| image2 = Andromeda galaxy.jpg
| caption2 = This ultraviolet image of [[Andromeda Galaxy|Andromeda]] shows blue regions containing young, massive stars.
}}
The peak radiation of most stars lies in the [[visible spectrum]], so the observation of the stars that form galaxies has been a major component of [[optical astronomy]]. It is also a favorable portion of the spectrum for observing ionized [[H II region]]s, and for examining the distribution of dusty arms.

The [[cosmic dust|dust]] present in the interstellar medium is opaque to visual light. It is more transparent to [[far infrared astronomy|far-infrared]], which can be used to observe the interior regions of giant molecular clouds and [[Bulge (astronomy)|galactic cores]] in great detail.<ref>
{{cite web
|title=Near, Mid & Far Infrared
|url=http://www.ipac.caltech.edu/Outreach/Edu/Regions/irregions.html
|publisher=[[Infrared Processing and Analysis Center|IPAC]]/[[NASA]]
|accessdate=January 2, 2007
}}</ref> Infrared is also used to observe distant, [[redshift|red-shifted]] galaxies that were formed much earlier in the history of the Universe. Water vapor and [[carbon dioxide]] absorb a number of useful portions of the infrared spectrum, so high-altitude or space-based telescopes are used for [[infrared astronomy]].

The first non-visual study of galaxies, particularly active galaxies, was made using [[radio astronomy|radio frequencies]]. The atmosphere is nearly transparent to radio between 5 [[Hertz|MHz]] and 30 GHz. (The [[ionosphere]] blocks signals below this range.)<ref>
{{cite web
|title=The Effects of Earth's Upper Atmosphere on Radio Signals
|url=http://radiojove.gsfc.nasa.gov/education/educ/radio/tran-rec/exerc/iono.htm
|publisher=[[NASA]]
|accessdate=August 10, 2006
}}</ref> Large radio [[interferometry|interferometers]] have been used to map the active jets emitted from active nuclei. [[Radio telescope]]s can also be used to observe neutral hydrogen (''via'' [[hydrogen line|21 cm radiation]]), including, potentially, the non-ionized matter in the early Universe that later collapsed to form galaxies.<ref>
{{cite news
|title=Giant Radio Telescope Imaging Could Make Dark Matter Visible
|url=http://www.sciencedaily.com/releases/2006/12/061214135537.htm
|publisher=[[ScienceDaily]]
|date=December 14, 2006
|accessdate=January 2, 2007
}}</ref>

[[UV astronomy|Ultraviolet]] and [[X-ray astronomy|X-ray telescopes]] can observe highly energetic galactic phenomena. An ultraviolet flare was observed when a star in a distant galaxy was torn apart from the tidal forces of a black hole.<ref>
{{cite news
|title=NASA Telescope Sees Black Hole Munch on a Star
|url=http://www.nasa.gov/mission_pages/galex/galex-20061205.html
|publisher=[[NASA]]
|date=December 5, 2006
|accessdate=January 2, 2007
}}</ref> The distribution of hot gas in galactic clusters can be mapped by X-rays. The existence of supermassive black holes at the cores of galaxies was confirmed through X-ray astronomy.<ref>
{{cite web
|last1=Dunn |first1=R.
|title=An Introduction to X-ray Astronomy
|url=http://www-xray.ast.cam.ac.uk/xray_introduction/
|publisher=[[Institute of Astronomy, Cambridge|Institute of Astronomy]] X-Ray Group
|accessdate=January 2, 2007
}}</ref>

==See also==
{{Wikipedia books|Galaxies}}
{{colbegin|2}}
* [[Dark galaxy]]
* [[Galactic orientation]]
* [[Galaxy formation and evolution]]
* [[Illustris project]]
* [[List of galaxies]]
* [[List of nearest galaxies]]
* [[Luminous infrared galaxy]]
* [[Supermassive black hole]]
* [[Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure]]
{{colend}}
{{Portal bar|Astronomy|Space|Cosmology}}

==Notes==
{{reflist|group=note}}

==References==
{{Reflist|colwidth=30em|refs=
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<ref name="heidarzadeh23">{{harvnb|Heidarzadeh|2008|pp=23–25}}</ref>

<ref name="heidarzadeh25">{{harvnb|Heidarzadeh|2008|p=25, Table 2.1}}</ref>

<ref name=paul1993>{{harvnb|Paul|1993|pp=16–18}}</ref>

<ref name=al_biruni>{{harvnb|Al-Biruni|2004|p=87}}</ref>

<ref name=mohamed>{{harvnb|Mohamed|2000|pp=49–50}}</ref>

<ref name="NSOG">{{harvnb|Kepple|Sanner|1998|p=18}}</ref>

<ref name=bergh1998>{{harvnb|Van den Bergh|1998|p=17}}</ref>

<ref name=waller_hodge2003>{{harvnb|Waller|Hodge|2003|p=91}}</ref>

<ref name=bertin_lin1996>{{harvnb|Bertin|Lin|1996|pp=65–85}}</ref>

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<ref name=konean2006>
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}} 

=== Other references ===
* {{cite web
|date=May 3, 2000
|title=Unveiling the Secret of a Virgo Dwarf Galaxy
|url=http://web.archive.org/web/20090109032310/http://www.eso.org/outreach/press-rel/pr-2000/pr-12-00.html
|publisher=[[ESO]]
|accessdate=January 3, 2007
}}

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|title=The Book of Instruction in the Elements of the Art of Astrology
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|isbn=0-7661-9307-1
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|title=Minding the Heavens: the Story of our Discovery of the Milky Way
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*{{Cite book |ref=harv
|last1=Bertin |first1=G.
|last2=Lin |first2=C.-C.
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|title=Spiral Structure in Galaxies: a Density Wave Theory
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|last2=Merrifield |first2=M.
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|last1=Dickinson |first1=T.
|date=2004
|title=The Universe and Beyond
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}}
*{{Cite book |ref=harv
|last1=Heidarzadeh |first1=T.
|date=2008
|title=A History of Physical Theories of Comets, from Aristotle to Whipple
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}}
* {{Cite book |ref=harv
|last=Ho |first= Houjun
|last2=van den Bosch|first2=Frank
|last3=White|first3=Simon
|author3-link=Simon White
|date=2010
|title=Galaxy Formation and Evolution
|publisher= [[Cambridge University Press]]
|edition=1
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|last1=Kepple |first1=G. R.
|last2=Sanner |first2=G. W.
|date=1998
|title=The Night Sky Observer's Guide, Volume 1
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|last=Merritt |first=D.
|author-link=David Merritt
|date=2013
|title=Dynamics and Evolution of Galactic Nuclei
|publisher=[[Princeton University Press]]
|isbn=9781400846122
}}
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|last1=Mohamed |first1=M.
|date=2000
|title=Great Muslim Mathematicians
|publisher=[[Penerbit UTM]]
|isbn=983-52-0157-9
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}}
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|last1=Paul |first1=E. R.
|date=1993
|title=The Milky Way Galaxy and Statistical Cosmology, 1890–1924
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|last1=Sparke |first1=L. S.
|last2=Gallagher III |first2=J. S.
|date=2000
|title=Galaxies in the Universe: An Introduction
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|isbn=0-521-59740-4
}}
*{{cite book |ref=harv
|last1=Van den Bergh |first1=S.
|date=1998
|title=Galaxy Morphology and Classification
|publisher=[[Cambridge University Press]]
|isbn=0-521-62335-9
}}
*{{cite book |ref=harv
|last1=Waller |first1=W. H.
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|date=2003
|title=Galaxies and the Cosmic Frontier
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}}
{{refend}}

==External links==
{{Sister project links|wikt=galaxy|common=Category:Galaxies|q=no|v=no|s=no|b=High School Earth Science/Galaxies}}
* {{In Our Time|Galaxies|p003c1cn|Galaxies}}
* [http://messier.seds.org/galaxy.html Galaxies, SEDS Messier pages]
* [http://www.atlasoftheuniverse.com/ An Atlas of The Universe]
* [http://www.nightskyinfo.com/galaxies Galaxies — Information and amateur observations]
* [http://science.nasa.gov/headlines/y2002/08feb_gravlens.htm The Oldest Galaxy Yet Found]
* [http://www.galaxyzoo.org Galaxy classification project, harnessing the power of the internet and the human brain]
* [http://www.physics.org/facts/sand-galaxies.asp How many galaxies are in our Universe?]
* [http://www.astronoo.com/en/galaxies.html The most beautiful galaxies on Astronoo]
* [http://www.youtube.com/watch?v=08LBltePDZw 3-D Video (01:46) – Over a Million Galaxies of Billions of Stars each – BerkeleyLab/animated.]

{{Galaxy}}

{{Featured article}}

{{Authority control}}

[[Category:Galaxies| ]]

User:WikipediaTutorials/sandbox

2015-08-25T02:22:22Z

WikipediaTutorials: added citation

{{redirect|ISS}}
{{Use British English|date=December 2013}}
{{Use dmy dates|date=February 2015}}
{{Infobox space station
| station = International Space Station
| station_image =International Space Station after undocking of STS-132.jpg
| station_image_alt = A rearward view of the International Space Station backdropped by the limb of the Earth. In view are the station's four large, gold-coloured solar array wings, two on either side of the station, mounted to a central truss structure. Further along the truss are six large, white radiators, three next to each pair of arrays. In between the solar arrays and radiators is a cluster of pressurised modules arranged in an elongated T shape, also attached to the truss. A set of blue solar arrays are mounted to the module at the aft end of the cluster.
| station_image_size = 300px
| extra_image_size = 300px
| extra_image_caption = The International Space Station on 23 May 2010 as seen from the departing {{OV|104}} during [[STS-132]].
| sign = ''Alpha'', ''Station''
| crew = Fully crewed: 6 Currently aboard: 6 ([[Expedition 44]])
| launch = 20 November 1998
| launch_pad = {{nowrap|[[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|1/5]] and [[Baikonur Cosmodrome Site 81|81/23]] [[Kennedy Space Center|Kennedy]] [[Kennedy Space Center Launch Complex 39|LC-39]]}}
| mass = Approximately {{convert|450000|kg|lbs|abbr=on}}
| length = {{convert|72.8|m|ft|abbr=on}}
| width = {{convert|108.5|m|ft|abbr=on}}
| height = c. 20 m (c. 66 ft) nadir–zenith, arrays forward–aft (27 November 2009){{Update after|2010|05|23|reason=MRM-1 & MRM-2}}
| volume = {{convert|916|m3|abbr=on}} (3 November 2014)
| pressure = 101.3 [[pascal (unit)|kPa]] (29.91 [[inch of mercury|inHg]], 1 [[Atmosphere (unit)|atm]])
| apogee = {{convert|{{Orbit|apogee|416}}|km|abbr=on}} [[Above mean sea level|AMSL]]{{Orbit|ref|<ref name="heavens-above">{{cite web|url=http://www.heavens-above.com/orbit.aspx?satid=25544|title=ISS - Orbit|last=Peat|first=Chris|publisher=Heavens-Above|date=25 January 2015|accessdate=25 January 2015}}</ref>}}
| perigee = {{convert|{{Orbit|perigee|409}}|km|abbr=on}} [[Above mean sea level|AMSL]]{{Orbit|ref|<ref name="heavens-above"/>}}
| inclination = {{Orbit|inclination|51.65}} [[degree (angle)|degrees]]{{Orbit|ref|<ref name="heavens-above"/>}}
| speed = {{convert|{{Orbit|speed at epoch|7.66}}|km/s|km/h mph}}{{Orbit|ref|<ref name="heavens-above"/>}}
| period = {{Orbit|period|92.69}} minutes{{Orbit|ref|<ref name="heavens-above"/>}}
| in_orbit = {{age in days|1998|11|20}} ({{date||dmy}})
| occupied = {{age in days|2000|11|02}} ({{date||dmy}})
| orbits = {{Orbit|orbits|92579}}{{Orbit|ref|<ref name="heavens-above"/>}}
| orbit_epoch = {{Orbit|epoch|25 January 2015}}{{Orbit|ref|<ref name="heavens-above"/>}}
| decay = 2 km/month
| NSSDC_ID = 1998-067A
| as_of = 9 March 2011 (unless noted otherwise)
| stats_ref =<ref name="heavens-above" /><ref name="ISStD" /><ref name="OnOrbit" /><ref>{{cite web|format=PDF|url=http://www.nasa.gov/pdf/451029main_sts132_press_kit.pdf|publisher=NASA|accessdate=19 June 2010|title=STS-132 Press Kit|date=7 May 2010}}</ref><ref>{{cite web|url=http://www.nasa.gov/pdf/521138main_fd04_ep.pdf|publisher=NASA|date=27 February 2011|accessdate=27 February 2011|title=STS-133 FD 04 Execute Package}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html|publisher=NASA|date=3 November 2014|accessdate=5 December 2014|title=NASA — Facts and Figures — International Space Station}}</ref>
| configuration_image = ISS configuration 2011-05 en.svg
| configuration_alt = The components of the ISS in an exploded diagram, with modules on-orbit highlighted in orange, and those still awaiting launch in blue or pink
| configuration_caption = Station elements {{As of|2011|12|lc=on}}, but missing ''Pirs'' ([[exploded view]])
| configuration_size = 300px
}}

The '''International Space Station''' ('''ISS''') is a [[space station]], or a habitable [[satellite|artificial satellite]], in [[low Earth orbit]]. Its first component launched into orbit in 1998, and the ISS is now the largest artificial body in orbit and can often be seen with the [[naked eye]] from Earth.<ref>{{cite web|title= Central Research Institute for Machine Building (FGUP TSNIIMASH) Control of manned and unmanned space vehicles from Mission Control Centre Moscow |publisher= Russian Federal Space Agency |url=ftp://130.206.92.88/Espacio/Mesa%20Redonda%205%20-%20R3%20-%20TSNIIMASH%20-%20V%20M%20IVANOV.pdf| accessdate=26 September 2011}}</ref><ref>{{cite web|url=http://spaceflight.nasa.gov/realdata/sightings/help.html |title=NASA Sightings Help Page |publisher=Spaceflight.nasa.gov |date=30 November 2011 |accessdate=1 May 2012}}</ref> The ISS consists of pressurised modules, external trusses, [[solar arrays]] and other components. ISS components have been launched by Russian [[Proton (rocket)|Proton]] and [[Soyuz (rocket family)|Soyuz]] rockets as well as American [[Space Shuttle]]s.<ref name="ISSBook">{{cite book|isbn=978-0-387-78144-0|date=17 June 2008|publisher=Springer-Praxis|author=John E. Catchpole|title=The International Space Station: Building for the Future}}</ref>

The ISS serves as a [[microgravity]] and [[space environment]] research laboratory in which crew members conduct experiments in [[biology]], [[human biology]], [[physics]], [[astronomy]], [[meteorology]] and [[Scientific research on the ISS|other fields]].<ref name="ISS overview">{{cite web|url=http://www.shuttlepresskit.com/ISS_OVR/index.htm|title=International Space Station Overview|publisher=ShuttlePressKit.com|date=3 June 1999|accessdate=17 February 2009}}</ref><ref name="NASA Fields of Research">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/A-fieldsresearch/index.html|archiveurl=https://web.archive.org/web/20080123150641/http://pdlprod3.hosc.msfc.nasa.gov/A-fieldsresearch/index.html|archivedate=25 March 2008|title=Fields of Research|date=26 June 2007|publisher = NASA}}</ref><ref name="NASA ISS Goals">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/B-gettingonboard/index.html|archiveurl=https://web.archive.org/web/20071208091537/http://pdlprod3.hosc.msfc.nasa.gov/B-gettingonboard/index.html|archivedate=8 December 2007| title = Getting on Board|date = 26 June 2007| publisher=NASA}}</ref> The station is suited for the testing of spacecraft systems and equipment required for missions to the [[Moon]] and Mars.<ref name="ResProg">{{cite web|url=http://spaceflightsystems.grc.nasa.gov/Advanced/ISSResearch/|title=ISS Research Program|publisher=NASA|accessdate=27 February 2009}}{{dead link|date=August 2011}}</ref> The ISS [[Orbital station-keeping|maintains an orbit with an altitude]] of between {{convert|330|and|435|km|mi|0|abbr=on}} by means of reboost manoeuvres using the engines of the [[Zvezda (ISS module)|Zvezda module]] or visiting spacecraft. It completes {{Orbit|daily orbits|15.54}} orbits per day.<ref name="tracking" />asdfasdfsdf

ISS is the ninth space station to be inhabited by crews, following the Soviet and later Russian [[Salyut]], [[Almaz]], and [[Mir]] stations as well as [[Skylab]] from the US. The station has been continuously occupied for {{age in years and days|2 Nov 2000|sep=and}} since the arrival of [[Expedition 1]] on 2 November 2000. This is the longest continuous human presence in space, having surpassed the previous record of {{age in years and days|5 Sep 1989|28 Aug 1999|sep=and}} held by Mir. The station is serviced by a variety of visiting spacecraft: [[Soyuz (spacecraft)|Soyuz]], [[Progress (spacecraft)|Progress]], the [[Automated Transfer Vehicle]], the [[H-II Transfer Vehicle]],<ref name="ISSRG" /> [[Dragon (spacecraft)|Dragon]], and [[Cygnus (spacecraft)|Cygnus]]. It has been visited by astronauts, cosmonauts and space tourists from [[List of International Space Station visitors|15 different nations]].<ref name="10th">{{cite web|url=http://www.nasa.gov/mission_pages/station/main/10th_anniversary.html|title=Nations Around the World Mark 10th Anniversary of International Space Station|publisher=NASA|date=17 November 2008|accessdate=6 March 2009}}</ref>

After the US Space Shuttle program ended in 2011, Soyuz rockets became the only provider of transport for astronauts at the International Space Station, and Dragon became the only provider of bulk [[downmass|cargo-return-to-Earth]] services (downmass capability of Soyuz capsules is very limited).

The [[International Space Station program|ISS programme]] is a joint project among five participating space agencies: [[NASA]], [[Russian Federal Space Agency|Roscosmos]], [[Japan Aerospace Exploration Agency|JAXA]], [[European Space Agency|ESA]], and [[Canadian Space Agency|CSA]].<ref name="ISSRG" /><ref name="PartStates">{{cite web|url=http://www.esa.int/esaHS/partstates.html|title=Human Spaceflight and Exploration—European Participating States|accessdate=17 January 2009|publisher=European Space Agency (ESA)|year=2009}}</ref> The ownership and use of the space station is established by intergovernmental treaties and agreements.<ref name="ESA-IGA">{{cite web|url=http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station/International_Space_Station_legal_framework|title=International Space Station legal framework|publisher=European Space Agency (ESA)|accessdate=21 February 2015|date=19 November 2013}}</ref> The station is divided into two sections, the [[Russian Orbital Segment]] (ROS) and the [[US Orbital Segment|United States Orbital Segment]] (USOS), which is shared by many nations. {{asof|2014|January}}, the American portion of ISS was funded until 2024.<ref>{{cite web|url=http://www.washingtonpost.com/national/health-science/nasa-space-station-operation-extended-by-obama-until-2024-at-least/2014/01/08/9819d5c8-788e-11e3-8963-b4b654bcc9b2_story.html|title=NASA: International space station operation extended by Obama until at least 2024|last=Achenbach|first=Joel|publisher=washingtonpost.com|date=8 January 2014|accessdate=8 January 2014}}</ref><ref>{{cite web|url=http://spaceflightnow.com/news/n1003/11station/|title=Space station partners set 2028 as certification goal|last=Clark|first=Stephen|date=11 March 2010|publisher=Spaceflight Now|accessdate=1 June 2011}}</ref><ref>{{cite news| url=http://www.cbc.ca/news/technology/story/2012/02/29/science-international-space-station.html | work=CBC News | title=Canada's space station commitment renewed | date=29 February 2012}}</ref> Roscosmos has endorsed the continued operation of ISS through 2024,<ref name="sn20150225"/> but have proposed using elements of the Russian Orbital Segment to construct a new Russian space station called [[Orbital Piloted Assembly and Experiment Complex|OPSEK]].<ref name="moscow20141117">{{cite news |url=http://www.themoscowtimes.com/business/article/russia-may-be-planning-national-space-station-to-replace-iss/511299.html |title=Russia May Be Planning National Space Station to Replace ISS |work=The Moscow Times |first=Matthew |last=Bodner |date=17 November 2014 |accessdate=3 March 2015}}</ref>

On March 28, 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS.<ref name=":0">{{cite web|url= http://www.independent.co.uk/news/science/russia-and-the-us-will-build-a-new-space-station-together-10140890.html|title=Russia and the US will build a new space station together |publisher=The Independent|date=28 March 2015}}</ref><ref name=":1">{{Cite news|url = http://rt.com/news/244797-russia-us-new-space-station/|title = Russia & US agree to build new space station after ISS, work on joint Mars project|last = |first = |date = March 28, 2015|work = RT|access-date = March 28, 2015}}</ref> NASA later issued a guarded statement expressing thanks for Russia's interest in future cooperation in space exploration, but fell short of confirming the Russian announcement.<ref>{{Cite news|url = http://www.engadget.com/2015/03/28/nasa-is-working-with-russia-on-a-new-space-station/|title = NASA is working with Russia on a new space station (update: not quite) |last = Moon|first = Mariella|date = 28 March 2015|work = Engadget|access-date = 29 March 2015}}</ref><ref name="no plans">{{cite web|url=http://spacenews.com/nasa-says-no-plans-for-iss-replacement-with-russia/|title=NASA Says No Plans for ISS Replacement with Russia|date=March 28, 2015|author=Jeff Foust|publisher=SpaceNews}}</ref>

{{TOC limit|limit=3}}

==Purpose==
[[File:STS-129 Zvezda sunrise.jpg|thumb|Sunrise at ''Zvezda'']]
[[File:STS-134 EVA4 view to the Space Shuttle Endeavour.jpg|thumb|right|Fisheye view of several labs]]
According to the original Memorandum of Understanding between NASA and Rosaviakosmos, the International Space Station was intended to be a laboratory, observatory and factory in [[low Earth orbit]]. It was also planned to provide transportation, maintenance, and act as a staging base for possible future missions to the Moon, Mars and asteroids.<ref name="RSA-MOU">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/nasa_rsa.html|title=Memorandum of Understanding Between the National Aeronautics and Space Administration of the United States of America and the Russian Space Agency Concerning Cooperation on the Civil International Space Station|publisher=NASA|accessdate=19 April 2009|date=29 January 1998}}</ref> In the 2010 United States National Space Policy, the ISS was given additional roles of serving commercial, diplomatic<ref>{{cite journal|last=Payette|first=Julie|title=Research and Diplomacy 350 Kilometers above the Earth: Lessons from the International Space Station|journal=Science & Diplomacy|date=10 December 2012|volume=1|issue=4|url=http://www.sciencediplomacy.org/article/2012/research-and-diplomacy-350-kilometers-above-earth}}</ref> and educational purposes.<ref name=USNSP>{{cite web|title=National Space Policy of the United States of America|url=http://www.whitehouse.gov/sites/default/files/national_space_policy_6-28-10.pdf|publisher=White House; USA Federal government|accessdate=20 July 2011}}</ref>

===Scientific research===
{{Main|Scientific research on the ISS|l1=Scientific research on the ISS}}
The ISS provides a platform to conduct scientific research. Small unmanned spacecraft can provide platforms for zero gravity and exposure to space, but space stations offer a long term environment where studies can be performed potentially for decades, combined with ready access by human researchers over periods that exceed the capabilities of manned spacecraft.<ref name="10th" /><ref name="Worldbook at NASA" />

The Station simplifies individual experiments by eliminating the need for separate rocket launches and research staff. The wide variety of research fields include [[astrobiology]], [[astronomy]], [[Zero g#Health effects of weightlessness|human research]] including [[space medicine]] and [[life science]]s, [[physical science]]s, [[materials science]], [[space weather]], and weather on Earth ([[meteorology]]).<ref name="ISS overview" /><ref name="NASA Fields of Research" /><ref name="NASA ISS Goals" /><ref>{{cite web|url=http://www.isas.jaxa.jp/e/forefront/2009/ueno/index.shtml|title=Monitor of All-sky X-ray Image (MAXI)|year=2008|publisher=JAXA|accessdate=12 March 2011}}</ref><ref>[http://www.spaceref.com/news/viewpr.html?pid=33007 ESA via SPACEREF] "SOLAR: three years observing and ready for solar maximum", 14 March 2011</ref> Scientists on Earth have access to the crew's data and can modify experiments or launch new ones, which are benefits generally unavailable on unmanned spacecraft.<ref name="Worldbook at NASA" /> Crews fly [[List of International Space Station expeditions|expeditions]] of several months duration, providing approximately 160-man-hours per week of labour with a crew of 6.<ref name="ISS overview"/><ref name="Science in School">{{cite web|url=http://www.scienceinschool.org/2008/issue10/iss|title=The International Space Station: life in space|publisher=Science in School|date=10 December 2008|accessdate=17 February 2009}}</ref>

To detect dark matter and answer other fundamental questions about our universe, engineers and scientists from all over the world built the [[Alpha Magnetic Spectrometer]] (AMS), which NASA compares to the [[Hubble space telescope]], and says could not be accommodated on a free flying satellite platform due in part to its power requirements and data bandwidth needs.<ref>[http://www.nasa.gov/mission_pages/shuttle/main/amsprocessing.html NASA – AMS to Focus on Invisible Universe]. Nasa.gov (18 March 2011). Retrieved 8 October 2011.</ref><ref>[http://science.nasa.gov/science-news/science-at-nasa/2009/14aug_ams/ In Search of Antimatter Galaxies – NASA Science]. ''Science''.nasa.gov (16 May 2011). Retrieved 8 October 2011.</ref> On 3 April 2013, [[NASA]] scientists reported that hints of [[dark matter]] may have been detected by the Alpha Magnetic Spectrometer.<ref name="APS-20130403">{{cite journal |authors=Aguilar, M. et al. (AMS Collaboration) |title=First Result from the Alpha Magnetic Spectrometer on the International Space Station: Precision Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–350 GeV|url=http://prl.aps.org/abstract/PRL/v110/i14/e141102 |date=3 April 2013 |journal=[[Physical Review Letters]]|accessdate=3 April 2013 |doi=10.1103/PhysRevLett.110.141102 }}</ref><ref name="AMS-20130403">{{cite web |author=Staff |title=First Result from the Alpha Magnetic Spectrometer Experiment|url=http://www.ams02.org/2013/04/first-results-from-the-alpha-magnetic-spectrometer-ams-experiment/ |date=3 April 2013 |work=AMS Collaboration |accessdate=3 April 2013 }}</ref><ref name="AP-20130403">{{cite news |last1=Heilprin|first1=John |last2=Borenstein |first2=Seth |title=Scientists find hint of dark matter from cosmos|url=http://apnews.excite.com/article/20130403/DA5E6JAG3.html |date=3 April 2013 |agency=Associated Press |accessdate=3 April 2013 }}</ref><ref name="BBC-20130403">{{cite news |last=Amos |first=Jonathan |title=Alpha Magnetic Spectrometer zeroes in on dark matter |url=http://www.bbc.co.uk/news/science-environment-22016504 |date=3 April 2013 |work=[[BBC News]] |accessdate=3 April 2013 }}</ref><ref name="NASA-20130403">{{cite web |last1=Perrotto|first1=Trent J. |last2=Byerly |first2=Josh |title=NASA TV Briefing Discusses Alpha Magnetic Spectrometer Results|url=http://www.nasa.gov/home/hqnews/2013/apr/HQ_M13-054_AMS_Findings_Briefing.html |date=2 April 2013|work=[[NASA]] |accessdate=3 April 2013 }}</ref><ref name="NYT-20130403">{{cite news |last=Overbye |first=Dennis |title=New Clues to the Mystery of Dark Matter |url=http://www.nytimes.com/2013/04/04/science/space/new-clues-to-the-mystery-of-dark-matter.html |date=3 April 2013 |work=[[The New York Times]] |accessdate=3 April 2013 }}</ref> According to the scientists, "[[Alpha Magnetic Spectrometer#First results|The first results]] from the space-borne Alpha Magnetic Spectrometer confirm an unexplained excess of high-energy positrons in Earth-bound cosmic rays."

{{Double image|right|Iss030e015472 Edit.jpg|117|ISS-08 Michael Foale conducts an inspection of the Microgravity Science Glovebox.jpg|241|[[C/2011 W3 (Lovejoy)|Comet Lovejoy]] photographed by [[Expedition 30]] commander [[Dan Burbank]]|[[Expedition 8]] Commander and Science Officer [[Michael Foale]] conducts an inspection of the [[Microgravity Science Glovebox]]}}
The space environment is hostile to life. Unprotected presence in space is characterised by an intense radiation field (consisting primarily of protons and other subatomic charged particles from the [[solar wind]], in addition to [[cosmic ray]]s), high vacuum, extreme temperatures, and microgravity.<ref name="Space Microbiology">{{cite web|url=http://syntheticbiology.arc.nasa.gov/files/SpaceMicrobiology%20MMBR%201.pdf|title=Space Microbiology, section Space Environment (p. 122)|publisher=Microbiology and Molecular Biology Reviews|date=March 2010|accessdate=4 June 2011|author=G Horneck, DM Klaus & RL Mancinelli}}</ref> Some simple forms of life called [[extremophile]]s,<ref name="Beer microbes">{{cite news|url=http://www.bbc.co.uk/news/science-environment-11039206|title=Beer microbes live 553 days outside ISS|work=[[BBC News]]|date=23 August 2010|accessdate=4 June 2011|author=Jonathan Amos}}</ref> including small invertebrates called [[tardigrade]]s<ref name="Waterbears">{{cite web|url=http://www.nature.com/news/2008/080908/full/news.2008.1087.html|title=Spacesuits optional for 'water bears'|work=Nature|date=8 September 2008|accessdate=4 June 2011}}</ref> can survive in this environment in an extremely dry state called [[Desiccation#Biology and ecology|desiccation]].

Medical research improves knowledge about the effects of long-term space exposure on the human body, including [[muscle atrophy]], [[Osteoporosis|bone loss]], and fluid shift. This data will be used to determine whether lengthy [[human spaceflight]] and [[space colonisation]] are feasible. As of 2006, data on bone loss and muscular atrophy suggest that there would be a significant risk of fractures and movement problems if astronauts landed on a planet after a lengthy interplanetary cruise, such as the six-month interval required to [[Manned mission to Mars|travel to Mars]].<ref name="JCB">{{cite book|author=Jay Buckey|title=Space Physiology|publisher=Oxford University Press USA|date=23 February 2006|isbn=978-0-19-513725-5}}</ref><ref>{{cite web|url=http://www.newscientist.com/article/dn17476-ion-engine-could-one-day-power-39day-trips-to-mars.html?full=true|work=New Scientist|accessdate=8 January 2010|date=24 July 2009|author=List Grossman|title=Ion engine could one day power 39-day trips to Mars}}</ref>
Medical studies are conducted aboard the ISS on behalf of the [[National Space Biomedical Research Institute]] (NSBRI). Prominent among these is the [[Advanced Diagnostic Ultrasound in Microgravity]] study in which astronauts perform ultrasound scans under the guidance of remote experts. The study considers the diagnosis and treatment of medical conditions in space. Usually, there is no physician on board the ISS and diagnosis of medical conditions is a challenge. It is anticipated that remotely guided ultrasound scans will have application on Earth in emergency and rural care situations where access to a trained physician is difficult.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/science/experiments/ADUM.html|date=1 May 2009|accessdate=1 October 2009|author=Brooke Boen|publisher=NASA|title=Advanced Diagnostic Ultrasound in Microgravity (ADUM)}}</ref><ref>{{cite journal|author=Sishir Rao|display-authors=etal|year=2008|title=A Pilot Study of Comprehensive Ultrasound Education at the Wayne State University School of Medicine|journal=Journal of Ultrasound in Medicine|volume=27|pages=745–749|pmid=18424650|issue=5}}</ref><ref>{{cite journal|author=Michael Fincke|display-authors=etal|year=2004|title=Evaluation of Shoulder Integrity in Space: First Report of Musculoskeletal US on the International Space Station|journal=Radiology|issue= 2|pages=319–322|pmid=15533948|doi=10.1148/radiol.2342041680|volume=234}}</ref>

====Microgravity====
[[File:Space Fire.jpg|thumb|A comparison between the combustion of a candle on [[Earth]] (left) and in a microgravity environment, such as that found on the ISS (right)]]
The Earth's gravity is only slightly weaker at the altitude of the ISS than at the surface, but objects in orbit are in a continuous state of [[Free fall|freefall]], resulting in an apparent state of weightlessness. This perceived weightlessness is disturbed by five separate effects:<ref name="gravity">{{cite web|url=http://www.esa.int/Our_Activities/Human_Spaceflight/Human_Spaceflight_Research/European_User_Guide_to_Low-Gravity_Platforms
|title=European Users Guide to Low Gravity Platforms|accessdate=22 March 2013|date=6 December 2005|publisher=European Space Agency}}</ref>
* Drag from the residual atmosphere; when the ISS enters the Earth's shadow, the main solar panels are rotated to minimise this aerodynamic drag, helping reduce [[orbital decay]].
* Vibration from movements of mechanical systems and the crew.
* Actuation of the on-board attitude [[control moment gyroscope]]s.
* [[Rocket engine|Thruster]] firings for attitude or orbital changes.
* [[Gravity-gradient stabilization|Gravity-gradient effects]], also known as [[tidal force|tidal]] effects. Items at different locations within the ISS would, if not attached to the station, follow slightly different orbits. Being mechanically interconnected these items experience small forces that keep the station moving as a [[rigid body]].

[[File:ISS-20 Robert Thirsk at the Minus Eighty Degree Laboratory Freezer.jpg|thumb|left|ISS crew member storing samples]]

Researchers are investigating the effect of the station's near-weightless environment on the evolution, development, growth and internal processes of plants and animals. In response to some of this data, NASA wants to investigate [[microgravity]]'s effects on the growth of three-dimensional, human-like tissues, and the unusual [[protein crystal]]s that can be formed in space.<ref name="NASA Fields of Research" />

The investigation of the physics of fluids in microgravity will allow researchers to model the behaviour of fluids better. Because fluids can be almost completely combined in microgravity, physicists investigate fluids that do not mix well on Earth. In addition, an examination of reactions that are slowed by low gravity and temperatures will give scientists a deeper understanding of [[superconductivity]].<ref name="NASA Fields of Research" />

The study of [[materials science]] is an important ISS research activity, with the objective of reaping economic benefits through the improvement of techniques used on the ground.<ref>{{cite web|url=http://science.nasa.gov/newhome/headlines/msad15sep99_1.htm|title=Materials Science 101|publisher=Science@NASA|accessdate=18 June 2009|date=15 September 1999}}</ref> Other areas of interest include the effect of the low gravity environment on combustion, through the study of the efficiency of burning and control of emissions and pollutants. These findings may improve current knowledge about energy production, and lead to economic and environmental benefits. Future plans are for the researchers aboard the ISS to examine [[aerosol]]s, [[ozone]], [[water vapour]], and [[oxide]]s in Earth's atmosphere, as well as [[cosmic ray]]s, [[cosmic dust]], [[antimatter]], and [[dark matter]] in the universe.<ref name="NASA Fields of Research" />

===Exploration===
[[File:Mars500.jpg|thumb|right|A 3D plan of the Russia-based [[MARS-500]] complex, used for ground-based experiments which complement ISS-based preparations for a [[manned mission to Mars]]]]
The ISS provides a location in the relative safety of Low Earth Orbit to test spacecraft systems that will be required for long-duration missions to [[the Moon]] and [[Mars]]. This provides experience in operations, maintenance as well as repair and replacement activities on-orbit, which will be essential skills in operating spacecraft farther from Earth, mission risks can be reduced and the capabilities of interplanetary spacecraft advanced.<ref name="ResProg">{{cite web|url=http://spaceflightsystems.grc.nasa.gov/Advanced/ISSResearch/|title=ISS Research Program|publisher=NASA|accessdate=27 February 2009}}{{dead link|date=August 2011}}</ref> Referring to the [[MARS-500]] experiment, ESA states that "Whereas the ISS is essential for answering questions concerning the possible impact of weightlessness, radiation and other space-specific factors, aspects such as the effect of long-term isolation and confinement can be more appropriately addressed via ground-based simulations".<ref name="esa mars500 ">{{cite web|title=Mars500 study overview | publisher = ESA |date= 4 June 2011| url = http://www.esa.int/esaMI/Mars500/SEM7W9XX3RF_0.html }}</ref> Sergey Krasnov, the head of human space flight programmes for Russia's space agency, Roscosmos, in 2011 suggested a "shorter version" of MARS-500 may be carried out on the ISS. <ref name="Mars thing on ISS">{{cite web| title=Space station may be site for next mock Mars mission| url = http://www.newscientist.com/blogs/shortsharpscience/2011/11/space-station-may-be-site-for.html|date=4 November 2011|work=New Scientist}}</ref>

In 2009, noting the value of the partnership framework itself, Sergey Krasnov wrote, "When compared with partners acting separately, partners developing complementary abilities and resources could give us much more assurance of the success and safety of space exploration. The ISS is helping further advance near-Earth space exploration and realisation of prospective programmes of research and exploration of the Solar system, including the Moon and Mars."<ref name=IAF2009>{{cite web|title=The Sustainable Utilisation of the ISS Beyond 2015|url=http://www.iafastro.org/docs/2009/ISS2015.pdf|publisher=International Astronautical Congress|accessdate=15 December 2011}}</ref> [[Manned mission to Mars|A manned mission to Mars]] may be a multinational effort involving space agencies and countries outside the current ISS partnership. In 2010, ESA Director-General Jean-Jacques Dordain stated his agency was ready to propose to the other four partners that China, India and South Korea be invited to join the ISS partnership.<ref name="ESAproposesInvite">{{cite web|title=ESA Chief Lauds Renewed U.S. Commitment to Space Station, Earth Science | publisher =Peter B. de Selding, Space News. |date=2 March 2010 | url =http://www.spacenews.com/civil/100203-esa-chief-lauds-renewed-commitment-space-station-earth-science.html}}</ref> NASA chief [[Charlie Bolden]] stated in February 2011, "Any mission to Mars is likely to be a global effort".<ref name="Mars a global effort">{{cite web|title= Charlie Bolden | publisher = space.com |date=4 June 2011 | url = http://www.space.com/11335-nasa-mars-exploration-space-station.html }}</ref> Currently, American legislation prevents NASA co-operation with China on space projects.<ref name="justice1">{{citation|first=Virginia|last=Seitz|title=Memorandum Opinion for the General Counsel, Office of Science and Technology Policy|url=http://www.justice.gov/olc/2011/conduct-diplomacy.pdf|journal=Office of Legal Counsel|volume=35|date=11 September 2011|accessdate=23 May 2012|archiveurl=https://web.archive.org/web/20120713080223/http://www.justice.gov/olc/2011/conduct-diplomacy.pdf|archivedate=13 July 2012}}</ref>

===Education and cultural outreach===
[[File:ISS-36 HTV-4 berthing 2.jpg|thumb|Japan's Kounotori 4 docking]]
The ISS crew provides opportunities for students on Earth by running student-developed experiments, making educational demonstrations, allowing for student participation in classroom versions of ISS experiments, and directly engaging students using radio, videolink and email.<ref name="ISSRG" /><ref>{{cite journal|author1=Gro Mjeldheim Sandal |author2=Dietrich Manzey|title=Cross-cultural issues in space operations: A survey study among ground personnel of the European Space Agency|journal=Acta Astronautica|volume=65|date=December 2009|pages=1520–1529|doi=10.1016/j.actaastro.2009.03.074|issue=11–12}}</ref> ESA offers a wide range of free teaching materials that can be downloaded for use in classrooms.<ref>[http://www.esa.int/SPECIALS/Education/SEM0LW4KXMF_0.html ESA – Education – Online material]. Esa.int (7 September 2011). Retrieved 8 October 2011.</ref> In one lesson, students can navigate a 3-D model of the interior and exterior of the ISS, and face spontaneous challenges to solve in real time.<ref>[http://www.esa.int/SPECIALS/Education/SEM1LL3Z2OF_0.html ESA – Education – ISS 3-D Teaching Tool: Spaceflight Challenge I]. Esa.int (24 May 2011). Retrieved 8 October 2011.</ref>

JAXA aims both to "Stimulate the curiosity of children, cultivating their spirits, and encouraging their passion to pursue craftsmanship", and to "Heighten the child's awareness of the importance of life and their responsibilities in society."<ref>[http://www.oosa.unvienna.org/pdf/pres/copuos2010/tech-17E.pdf Building Peace in Young Minds through Space Education]. Committee on the Peaceful Uses of Outer Space, 53rd Session. June 2010, Vienna, Austria; Space Education Center, Japan Aerospace Exploration Agency (JAXA)</ref> Through a series of education guides, a deeper understanding of the past and near-term future of manned space flight, as well as that of Earth and life, will be learned.<ref>[http://www.edu.jaxa.jp/education/international/ISS/SSK/en/ JAXA Space Education Center : JAXA Spaceflight Seeds Kids I : Spaceflight Sunflower seeds – Let's make them flower! and learn freshly the Earth environment just by contrast with the Space one]. Edu.jaxa.jp. Retrieved 8 October 2011.</ref><ref>[http://www.edu.jaxa.jp/education/international/ISS/SIS/en/ JAXA Space Education Center : JAXA Seeds in Space I : Let's Cultivate Spaceflight Asagao, Miyako-gusa Seeds and Identify the Mutants!]. Edu.jaxa.jp. Retrieved 8 October 2011.</ref> In the JAXA Seeds in Space experiments, the mutation effects of spaceflight on plant seeds aboard the ISS is explored. Students grow sunflower seeds which flew on the ISS for about nine months as a start to 'touch the Universe'. In the first phase of Kibō utilisation from 2008 to mid-2010, researchers from more than a dozen Japanese universities conducted experiments in diverse fields.<ref>{{cite web |author=Keiji Murakami |url=http://www.spacepolicyonline.com/pages/images/stories/Micro%20Oct%2009%20JEM.pdf |title=JEM Utilization Overview |publisher=JAXA. Steering Committee for the Decadal Survey on Biological and Physical Sciences in Space |date=14 October 2009}}</ref>

[[Image:Crew in ATV with Jules Verne manuscript.jpg|thumb|left|Original Jules Verne manuscripts displayed by crew inside Jules Verne ATV]]
Cultural activities are another major objective. Tetsuo Tanaka, director of JAXA's Space Environment and Utilization Center, says "There is something about space that touches even people who are not interested in science."<ref name="jaxa2">{{cite web |author=Tetsuo Tanaka |url=http://www.jaxa.jp/article/special/kibo/tanaka01_e.html |title=Kibo: Japan's First Human Space Facility |publisher=JAXA |accessdate=8 October 2011}}</ref>

[[ARISS|Amateur Radio on the ISS]] (ARISS) is a volunteer programme which encourages students worldwide to pursue careers in science, technology, engineering and mathematics through [[amateur radio]] communications opportunities with the ISS crew. ARISS is an international working group, consisting of delegations from 9 countries including several countries in Europe as well as Japan, Russia, Canada, and the United States. In areas where radio equipment cannot be used, speakerphones connect students to ground stations which then connect the calls to the station. <ref>{{cite web|url=http://www.rac.ca/ariss/oindex.htm|title=Amateur Radio on the International Space Station|date=6 June 2011|accessdate=10 June 2011}}</ref>

''[[First Orbit]]'' is a feature-length documentary film about [[Vostok 1]], the first manned space flight around the Earth. By matching the orbit of the International Space Station to that of Vostok 1 as closely as possible, in terms of ground path and time of day, documentary filmmaker Christopher Riley and ESA astronaut [[Paolo Nespoli]] were able to film the view that Yuri Gagarin saw on his pioneering orbital space flight. This new footage was cut together with the original Vostok 1 mission audio recordings sourced from the Russian State Archive. Nespoli, during Expedition 26/27, filmed the majority of the footage for this documentary film, and as a result is credited as its [[Cinematographer|director of photography]].<ref>{{cite news|last=Riley|first=Christopher|title=What Yuri Gagarin saw: First Orbit film to reveal the view from Vostok 1|url=http://www.guardian.co.uk/science/blog/2011/apr/11/yuri-gagarin-first-orbit-vostok|newspaper=The Guardian|date=11 April 2011|location=London}}</ref> The film was streamed through the website firstorbit.org in a global YouTube premiere in 2011, under a free license.<ref>{{cite web|url=http://www.firstorbit.org/first-orbit-faqs |title=Yuri Gagarin's First Orbit – FAQs |publisher=Firstorbit.org |accessdate=1 May 2012}}</ref>

In May 2013, commander [[Chris Hadfield]] shot a music video of [[David Bowie]]'s ''[[Space Oddity (song)|Space Oddity]]'' on board the station; the film was released freely on YouTube.<ref>{{cite web|last=Warr |first=Philippa |url=http://www.wired.co.uk/news/archive/2013-05/13/commander-hadfield-space-oddity |title=Commander Hadfield bids farewell to ISS with Reddit-inspired Bowie cover |publisher=Wired.co.uk |date=13 May 2013 |accessdate=22 October 2013}}</ref> It was the first music video ever to be filmed in space.<ref>{{Cite web|title = Chris Hadfield sings "Space Oddity" in the first music video in space|url = http://io9.com/chris-hadfield-sings-space-oddity-in-the-first-music-503764317|accessdate = 2015-08-25|first = Lauren|last = Davis}}</ref>

==Assembly==
{{Main|Assembly of the International Space Station|List of ISS spacewalks}}
[[File:ISS-with-S0-S1-P1.jpg|thumb|right|alt=S0, S1 and P1 truss structures installed|Partially constructed ISS in December 2002]]
[[File:S3-S4 Truss Installed 2.jpg|thumb|S3-S4 Truss Installed in 2007]]
[[File:Soyuz TMA-19 spacecraft departs the ISS.jpg|thumb|[[Soyuz TMA-19]] departs in 2010]]
[[File:ISS after STS-117 in June 2007.jpg|thumb|ISS in 2007, with fewer solar arrays]]
The assembly of the International Space Station, a major endeavour in [[space architecture]], began in November 1998.<ref name="ISStD" /> Russian modules launched and docked robotically, with the exception of ''[[Rassvet (ISS module)|Rassvet]]''. All other modules were delivered by the Space Shuttle, which required installation by ISS and shuttle crewmembers using the [[Mobile Servicing System#Canadarm2|Canadarm2]] (SSRMS) and [[List of ISS spacewalks|EVAs]]; {{as of|2011|06|05|lc=y}}, they had added 159 components during more than 1,000 hours of EVA. 127 of these spacewalks originated from the station, and the remaining 32 were launched from the airlocks of docked Space Shuttles.<ref name="ISStD" /> The [[beta angle]] of the station had to be considered at all times during construction, as the station's beta angle is directly related to the percentage of its orbit that the station (as well as any docked or docking spacecraft) is exposed to the sun; the Space Shuttle would not perform optimally above a limit called the "beta cutoff".<ref name="mcc">{{cite web|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-113/11_23_20_01_179.html|title=MCC Answers|author=Derek Hassman, NASA Flight Director|date=1 December 2002|publisher=NASA|accessdate=14 June 2009}}</ref>

The first module of the ISS, ''[[Zarya]]'', was launched on 20 November 1998 on an autonomous Russian [[Proton (rocket)|Proton rocket]]. It provided propulsion, attitude control, communications, electrical power, but lacked long-term life support functions. Two weeks later a passive NASA module ''[[Unity (ISS module)|Unity]]'' was launched aboard Space Shuttle flight [[STS-88]] and attached to Zarya by astronauts during EVAs. This module has two [[Pressurized Mating Adapter]]s (PMAs), one connects permanently to Zarya, the other allows the Space Shuttle to dock to the space station. At this time, the Russian station Mir was still inhabited. The ISS remained unmanned for two years, during which time Mir was de-orbited. On 12 July 2000 [[Zvezda (ISS module)|Zvezda]] was launched into orbit. Preprogrammed commands on board deployed its solar arrays and communications antenna. It then became the passive vehicle for a rendezvous with the Zarya and Unity. As a passive "target" vehicle, the Zvezda maintained a stationkeeping orbit as the Zarya-Unity vehicle performed the rendezvous and docking via ground control and the Russian automated rendezvous and docking system. Zarya's computer transferred control of the station to Zvezda's computer soon after docking. Zvezda added sleeping quarters, a toilet, kitchen, CO2 scrubbers, dehumidifier, oxygen generators, exercise equipment, plus data, voice and television communications with mission control. This enabled permanent habitation of the station.<ref>[http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/servmod.pdf NASA Facts. The Service Module: A Cornerstone of Russian International Space Station Modules]. NASA. January 1999</ref><ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/missions/sts-88/mission-sts-88.html |title=STS-88 |publisher=Science.ksc.nasa.gov |accessdate=19 April 2011}}</ref>

The first resident crew, [[Expedition 1]], arrived in November 2000 on [[Soyuz TM-31]]. At the end of the first day on the station, astronaut Bill Shepherd requested the use of the radio call sign "''Alpha''", which he and cosmonaut Krikalev preferred to the more cumbersome "''International Space Station''".<ref name=TIME-Nov2>{{cite news|url=http://www.time.com/time/arts/article/0,8599,59500,00.html|title=Upward Bound: Tales of Space Station Alpha|author=Brad Liston|date=2 November 2000|work=Time|accessdate=5 August 2010}}</ref> The name "''Alpha''" had previously been used for the station in the early 1990s,<ref name=GAO>{{cite web|url=http://archive.gao.gov/t2pbat3/151975.pdf|title=Space Station – Impact on the expanded Russian role of funding and research|date=21 June 1994|publisher=[[Government Accountability Office|United State General Accounting Office]]|accessdate=9 August 2010}}</ref> and following the request, its use was authorised for the whole of Expedition 1.<ref name=SPACE-Nov3>{{cite web|url=http://www.space.com/missionlaunches/missions/alpha_male_001103.html|title=Call Bill Shepherd the Alpha Male of the International Space Station|author=Alan Ladwig|date=3 November 2000|publisher=Space.com|accessdate=9 August 2010}}</ref> Shepherd had been advocating the use of a new name to project managers for some time. Referencing a [[Ship naming and launching|naval tradition]] in a pre-launch news conference he had said: "For thousands of years, humans have been going to sea in ships. People have designed and built these vessels, launched them with a good feeling that a name will bring good fortune to the crew and success to their voyage."<ref name=SPACE-Nov2>{{cite web|url=http://www.space.com/missionlaunches/missions/exp1_alpha_001102.html|title=Expedition One Crew Wins Bid To Name Space Station Alpha|date=2 November 2000|author=Todd Halvorson|publisher=Space.com|accessdate=9 August 2010}}</ref> [[Yuri Semenov]], the President of [[S.P. Korolev Rocket and Space Corporation Energia|Russian Space Corporation Energia]] at the time, disapproved of the name "''Alpha''"; he felt that ''Mir'' was the first space station, and so he would have preferred the names "''Beta''" or "''Mir 2''" for the ISS.<ref name=SPACE-Nov3 /><ref>{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=5913|title=Interview with RSC Energia's Yuri Semenov|publisher=Space.com|date=3 September 2001|accessdate=22 August 2010}}</ref><ref>{{cite web|url=http://english.ruvr.ru/2001/03/29/100146.html|title=Interview with Yuri Semenov, general designer of Space Rocket corporation Energy|date=21 March 2001|publisher=[[Voice of Russia]]|accessdate=5 October 2010}}</ref>

[[Expedition 1]] arrived midway between the flights of [[STS-92]] and [[STS-97]]. These two Space Shuttle flights each added segments of the station's [[Integrated Truss Structure]], which provided the station with Ku-band communication for US television, additional attitude support needed for the additional mass of the USOS, and substantial [[solar array]]s supplementing the station's existing 4 solar arrays.<ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/missions/sts-92/mission-sts-92.html |title=STS-92 |publisher=Science.ksc.nasa.gov |accessdate=19 April 2011}}</ref>

Over the next two years the station continued to expand. A [[Soyuz-U]] rocket delivered the [[Pirs (ISS module)|''Pirs'' docking compartment]]. The Space Shuttles ''Discovery'', ''[[Space Shuttle Atlantis|Atlantis]]'', and ''Endeavour'' delivered the [[Destiny (ISS module)|''Destiny'' laboratory]] and [[Quest Joint Airlock|''Quest'' airlock]], in addition to the station's main robot arm, the ''[[Canadarm2]]'', and several more segments of the Integrated Truss Structure.
[[File:Zvezda rear.jpg|thumb|left|Aft view showing a Progress spacecraft docked to Zvezda]]
The expansion schedule was interrupted by the {{OV|102}} [[Space Shuttle Columbia disaster|disaster]] in 2003, with the resulting two year hiatus in the [[Space Shuttle program]]me halting station assembly. The space shuttle was grounded until 2005 with [[STS-114]] flown by ''Discovery''.<ref>{{cite web|url=http://www.nasaspaceflight.com/2005/07/discovery-launches-the-shuttle-is-back/|title=Discovery launches—The Shuttle is back|author=Chris Bergin|publisher=NASASpaceflight.com|accessdate=6 March 2009|date=26 July 2005}}</ref>

Assembly resumed in 2006 with the arrival of [[STS-115]] with ''Atlantis'', which delivered the station's second set of solar arrays. Several more truss segments and a third set of arrays were delivered on [[STS-116]], [[STS-117]], and [[STS-118]]. As a result of the major expansion of the station's power-generating capabilities, more pressurised modules could be accommodated, and the ''[[Harmony (ISS module)|Harmony]]'' node and ''Columbus'' European laboratory were added. These were followed shortly after by the first two components of ''Kibō''. In March 2009, [[STS-119]] completed the Integrated Truss Structure with the installation of the fourth and final set of solar arrays. The final section of ''Kibō'' was delivered in July 2009 on [[STS-127]], followed by the Russian ''[[Poisk (ISS module)|Poisk]]'' module. The third node, ''[[Tranquility (ISS module)|Tranquility]]'', was delivered in February 2010 during [[STS-130]] by the Space Shuttle ''Endeavour'', alongside the [[Cupola (ISS module)|Cupola]], closely followed in May 2010 by the penultimate Russian module, ''[[Rassvet (ISS module)|Rassvet]]''. Rassvet was delivered by Space Shuttle ''Atlantis'' on [[STS-132]] in exchange for the Russian Proton delivery of the Zarya Module in 1998 which had been funded by the United States.<ref>{{cite web|url=http://www.russianspaceweb.com/iss_mim1.html |title=Mini-Research Module 1 (MIM1) Rassvet (MRM-1) |publisher=Russianspaceweb.com |accessdate=12 July 2011}}</ref> The last pressurised module of the USOS, ''Leonardo'', was brought to the station by ''Discovery'' on her final flight, [[STS-133]],<ref name="STS-133">{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/main/index.html |title=STS-133 |publisher=NASA |accessdate=1 September 2014}}</ref> followed by the [[Alpha Magnetic Spectrometer]] on [[STS-134]], delivered by ''Endeavour''.<ref name="STS-134">{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/main/index.html |title=STS-134 |publisher=NASA |accessdate=1 September 2014}}</ref>
[[File:Exterior of Cupola - Exp28.jpg|thumb|The Cupola arrived in 2010]]
{{As of|2011|06}}, the station consisted of fifteen pressurised modules and the [[Integrated Truss Structure]]. Still to be launched are the Russian [[Nauka (ISS module)|Multipurpose Laboratory Module]] ''Nauka'' and a number of external components, including the [[European Robotic Arm]]. Assembly is expected to be completed by April 2014,{{update inline|date=October 2014}} by which point the station will have a mass in excess of 400 [[metric ton|tonnes]] (440 [[short ton]]s).<ref name="OnOrbit">{{cite web|url = http://www.nasa.gov/externalflash/ISSRG/pdfs/on_orbit.pdf|title = On-Orbit Elements|publisher = NASA|author = NASA|date = 18 February 2010|accessdate = 19 June 2010|format = PDF}}</ref><ref name="Manifest">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/iss_manifest.html|title=Consolidated Launch Manifest|accessdate=8 July 2008|publisher=NASA|author=NASA|year=2008}}</ref>

The gross mass of the station changes over time. The total launch mass of the modules on orbit is about {{convert|417289|kg|lbs|abbr=on}} (as of 3 September 2011).<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/isstodate.html |title=NASA – The ISS to Date (03/09/2011) |publisher=Nasa.gov |accessdate=12 July 2011}}</ref> The mass of experiments, spare parts, personal effects, crew, foodstuff, clothing, propellants, water supplies, gas supplies, docked spacecraft, and other items add to the total mass of the station. Hydrogen gas is constantly vented overboard by the oxygen generators.

==Station structure==
{{Double image|right|ROS Windows 0114 complete.jpg|130|USOS window identification.png|160|Russian Orbital Segment Windows|USOS International Space Station window locations}}

The ISS is a third generation<ref>{{cite web|url=http://www.dlr.de/iss/en/desktopdefault.aspx/tabid-1945/2746_read-4182/gallery-1/gallery_read-Image.19.2296/ |title=DLR – International Space Station ISS – From Cold War to international cooperation – the story of the ISS |publisher=Dlr.de |accessdate=1 May 2012}}</ref> modular space station.<ref>{{cite web|url=http://www.astronautix.com/articles/thistems.htm |title=Third Generation Soviet Space Systems |publisher=Astronautix.com |accessdate=1 May 2012}}</ref> Modular stations can allow the mission to be changed over time and new modules can be added or removed from the existing structure, allowing greater flexibility.

Below is a diagram of major station components. The blue areas are pressurised sections accessible by the crew without using spacesuits. The station's unpressurised superstructure is indicated in red. Other unpressurised components are yellow. Note that the Unity node joins directly to the Destiny laboratory. For clarity, they are shown apart.

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PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | |AMS|~|ZVEZDA|~|AMS|
AMS = [[Zvezda (ISS module)|Solar array]]
|ZVEZDA = [[Zvezda (ISS module)|'''Zvezda DOS-8''' Service Module]]
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PIRS = [[Pirs (ISS module)|'''Pirs''' Airlock]]
|SGM2 = [[Poisk (ISS module)|'''Poisk''' (MRM-2) Airlock]]
|PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | | | | | | |!|!|}}
{{familytree| | | | | | | | | | | | |!|`|-|MLM|~|ERA| | |
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| ERA = '''[[European Robotic Arm|European Robotic Arm]]'''
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{{familytree| | | | | | | | | | | | |!| | | | | | | | |}}
{{familytree| | | | | | | |SA|~|ZARYA|~|SA| | | |
SA = [[Zarya (ISS module)|Solar array]]
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{{familytree| | | | | | | | | | | | |!|!|}}
{{familytree| | | | | | | | | | | | |!|`|-|SGM1|PORT1|
SGM1 = [[Rassvet (ISS module)|'''Rassvet''' (MRM-1)]]
|PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | | | | | | |!| | | | | | | | |}}
{{familytree| | | | | | | | | | | | |!| | |PMM| | |
PMM = [[Leonardo (ISS module)|'''Leonardo''' cargo bay]]
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{{familytree| | | | | | | |QUEST|-|UNITY|-|NOD3|PORT2| |
UNITY = [[Unity (ISS module)|'''Unity''' Node 1]]
|QUEST = [[Quest Joint Airlock|'''Quest''' Airlock]]
|NOD3 = [[Tranquility (ISS module)|'''Tranquility''' Node 3]]
|PORT2 = [[Pressurized Mating Adapter#PMA-3|'''PMA 3''' docking port]]
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{{familytree| | | | | | | |ESP2| | |!| | |CUPOLA|
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{{familytree| |FE0|F|FE| |RADIATOR|!|RADIATOR| |FE|7|FE| | | |
RADIATOR = [[External Active Thermal Control System|Heat Radiator]]
|FE = [[ISS Solar Arrays#Solar arrays|Solar array]]
|FE0 = [[ISS Solar Arrays#Solar arrays|Solar array]]
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{{familytree| |:| | |:| | | | | |:| |!| |:| | | | | |:| | |:|}}
{{familytree| |:| | |:|ELC| | |:|FZ1|:| | |ELC3|:| | |:|
ELC = [[ExPRESS Logistics Carrier#ELC-2|ELC 2]], '''[[Alpha Magnetic Spectrometer|AMS]]'''
|FZ1 = '''[[Z1 truss]]'''
|ELC3 = [[ExPRESS Logistics Carrier#ELC-3|ELC 3]]
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FS56 = '''[[P5 Truss Segment|S5/6 Truss]]'''
|FS34 = '''[[Integrated Truss Structure#P3/P4, S3/S4 truss assemblies|S3/S4 Truss]]'''
|FS1 = '''[[S1 Truss]]'''
|FS0 = '''[[S0 Truss]]'''
|FP1 = '''[[S1 Truss|P1 Truss]]'''
|FP34 = '''[[Integrated Truss Structure#P3/P4, S3/S4 truss assemblies|P3/P4 Truss]]'''
|FP56 = '''[[P5 Truss Segment|P5/6 Truss]]'''
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{{familytree| |:| | |:|ELC4| | | |:|!|:| | | |ELC1|:| | |:|
ELC4 = [[ExPRESS Logistics Carrier#ELC-4|ELC 4]], [[External Stowage Platform#ESP-3|ESP 3]]
|ELC1 = [[ExPRESS Logistics Carrier#ELC-1|ELC 1]]
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{{familytree| |:| | |:| | | | |DEXTR|!|CANADARM| | | | |:| | |:|
CANADARM = '''[[Canadarm2]]'''
|DEXTR = '''[[Dextre]]'''
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|boxstyle_DEXTR = border: 2px solid #fee067; background:#fff4cc;}}
{{familytree| |FE0|L|FE| | | | |!| | | | |FE|J|FE| | | |
FE0 = [[ISS Solar Arrays#Solar arrays|Solar array]]
|FE = [[ISS Solar Arrays#Solar arrays|Solar array]]
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{{familytree| | | | | | | | | | | | |!| | | | |}}
{{familytree| | | | | | | | |ESP1|DESTYNY| | |
DESTYNY = [[Destiny (ISS module)|'''Destiny''' Laboratory]]
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KIBOPS = [[Japanese Experiment Module#Experiment Logistics Module|'''Kibō logistics''' Cargo Bay]]
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{{familytree| | | | | | | | | |HTV|!|HTV| |!|
HTV = '''[[H-II Transfer Vehicle|HTV]]'''/'''[[Dragon (spacecraft)|Dragon]]'''/'''[[Cygnus (spacecraft)|Cygnus]]''' berth ([[Common berthing mechanism|docking port]])
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{{familytree| | | | | | | | | | | |!|!|!| | | |!|KiboRobo|
KiboRobo = [[Japanese Experiment Module|'''Kibō''' Robotic Arm]]
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{{familytree| | | | |COLEXT|COLUMBUS|-|HARMONY|-|KIBO|KiboPlat|
HARMONY = [[Harmony (ISS module)|'''Harmony''' (Node 2)]]
|KiboPlat = [[Japanese Experiment Module|'''Kibō''' External Platform]]
|COLUMBUS = [[Columbus (ISS module)|'''Columbus''' Laboratory]]
|KIBO = [[JEM-PM|'''Kibō''' Laboratory]]
|COLEXT = External Payloads
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{{familytree| | | | | | | | | | | |PORT2| |
PORT2 = [[Pressurized Mating Adapter#PMA-2|'''PMA 2''' docking port]]
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==Pressurised modules==

===Zarya===
[[File:Zarya from STS-88.jpg|thumb|upright|Zarya as seen by [[Space Shuttle Endeavour]] during [[STS-88]]]]
'''''[[Zarya]]''''' (Russian: Заря́; lit. dawn), also known as the [[Functional Cargo Block]] or FGB (from the Russian "Функционально-грузовой блок", Funktsionalno-gruzovoy blok or ФГБ), was the first module of the International Space Station to be launched. The FGB provided electrical power, storage, propulsion, and guidance to the ISS during the initial stage of assembly. With the launch and assembly in orbit of other modules with more specialized functionality, Zarya is now primarily used for storage, both inside the pressurized section and in the externally mounted fuel tanks. The Zarya is a descendant of the [[TKS spacecraft]] designed for the Soviet [[Salyut program]]. The name Zarya was given to the FGB because it signified the dawn of a new era of international cooperation in space. Although it was built by a Russian company, it is owned by the [[United States]]. Zarya weighs {{convert|19300|kg|lb|abbr=on}}, is {{convert|12.55|m|ft|abbr=on}} long and {{convert|4.1|m|ft|abbr=on}} wide, discounting solar arrays.

Built from December 1994 to January 1998 in Russia at the [[Khrunichev State Research and Production Space Center]] (KhSC) in [[Moscow]], Zarya's control system was developed by the Khartron Corp. ([[Kharkiv, Ukraine]]).

Zarya was launched on 20 November 1998, on a Russian [[Proton-K|Proton rocket]] from [[Baikonur Cosmodrome Site 81]] in [[Kazakhstan]] to a {{convert|400|km|mi|abbr=on}} high orbit with a designed lifetime of at least 15 years. After Zarya reached orbit, STS-88 launched on 4 December 1998, to attach the Unity Module.

Although only designed to fly autonomously for six to eight months, Zarya did so for almost two years due to delays with the Russian Service Module, Zvezda, which finally launched on 12 July 2000, and docked with Zarya on 26 July using the Russian [[Kurs (docking system)|Kurs docking system]].

===Unity===
[[File:ISS Unity module.jpg|thumb|Unity as pictured by Space Shuttle Endeavour]]
'''''[[Unity (ISS module)|Unity]]''''', or Node 1, is one of three nodes, or passive connecting modules, in the [[US Orbital Segment]] of the station. It was the first US-built component of the Station to be launched. Cylindrical in shape, with six berthing locations facilitating connections to other modules, Unity was carried into orbit by {{OV|105}} as the primary cargo of [[STS-88]] in 1998. Essential space station resources such as fluids, environmental control and life support systems, electrical and data systems are routed through Unity to supply work and living areas of the station. More than 50,000 mechanical items, 216 lines to carry fluids and gases, and 121 internal and external electrical cables using six miles of wire were installed in the Unity node. Unity is made of aluminum. Prior to its launch aboard Endeavour, conical Pressurized Mating Adapters (PMAs) were attached to the aft and forward berthing mechanisms of Unity. Unity and the two mating adapters together weighed about {{convert|25600|lb|kg|disp=flip|abbr=on}}. The adapters allow the docking systems used by the Space Shuttle and by Russian modules to attach to the node's hatches and berthing mechanisms.

Unity was carried into orbit as the primary cargo of the Space Shuttle Endeavour on STS-88, the first Space Shuttle mission dedicated to assembly of the station. On 6 December 1998, the STS-88 crew mated the aft berthing port of Unity with the forward hatch of the already orbiting Zarya module.

===Zvezda===
'''''[[Zvezda (ISS module)|Zvezda]]''''' ({{lang-ru|link=no|Звезда́}}, meaning "star"), also known as DOS-8, Service Module or SM ({{lang-ru|link=no|СМ}}). It provides all of the station's critical systems,{{clarify|date=August 2013}} its addition rendered the station permanently habitable for the first time, adding life support for up to six crew and living quarters for two. Zvezda's DMS-R computer handles guidance, navigation and control for the entire space station.<ref name="Navigation" /> A second computer which performs the same functions will be installed in the [[Nauka (ISS module)|Nauka]] module, FGB-2.

The hull of Zvezda was completed in February 1985, with major internal equipment installed by October 1986. The module was launched by a Proton-K rocket from Site 81/23 at Baikonur, on 12 July 2000. Zvezda is at the rear of the station according to its normal direction of travel and orientation, its engines are used to boost the station's orbit. Alternatively Russian and European spacecraft can dock to Zvezda's aft port and use their engines to boost the station.

===Destiny===
[[File:Destiny as just installed.jpg|thumb|''Destiny'' interior in 2001]]
'''''[[Destiny (ISS module)|Destiny]]''''' is the primary research facility for United States payloads aboard the ISS. In 2011, NASA solicited proposals for a not-for-profit group to manage all American science on the station which does not relate to manned exploration. The module houses 24 [[International Standard Payload Rack]]s, some of which are used for environmental systems and crew daily living equipment. ''Destiny'' also serves as the mounting point for the station's Truss Structure.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/destiny.html|title=NASA—US Destiny Laboratory|date=26 March 2007|accessdate=26 June 2007|publisher = NASA}}</ref>

===Quest===
'''''[[Quest Joint Airlock|Quest]]''''' is the only USOS airlock, and hosts spacewalks with both United States [[Extravehicular Mobility Unit|EMU]] and Russian [[Orlan space suit|Orlan]] [[Space suit|spacesuits]]. It consists of two segments: the equipment lock, which stores spacesuits and equipment, and the crew lock, from which astronauts can exit into space. This module has a separately controlled atmosphere. Crew sleep in this module, breathing a low nitrogen mixture the night before scheduled EVAs, to avoid [[decompression sickness]] (known as "the bends") in the low-pressure suits.<ref>{{cite web|url=http://spaceflight.nasa.gov/station/eva/outside.html|title=Space Station Extravehicular Activity|accessdate=11 March 2009|publisher=[[NASA]]|date=4 April 2004}}</ref>

===Pirs and Poisk===
'''''[[Pirs (ISS module)|Pirs]]''''' ({{lang-ru|link=no|Пирс}}, meaning "[[pier]]"), ({{lang-ru|link=no|Стыковочный отсек}}), "docking module", SO-1 or DC-1 (docking compartment), and '''''[[Poisk (ISS module)|Poisk]]''''' ({{lang-ru|link=no|По́иск}}; lit. ''Search''), also known as the [[Mini-Research Module]] 2 (MRM 2), {{lang|ru|''Малый исследовательский модуль 2''}}, or МИМ 2. Pirs and Poisk are Russian airlock modules. Each of these modules have 2 identical hatches. An outward opening hatch on the MIR space station failed after it swung open too fast after unlatching, due to a small amount of air pressure remaining in the airlock.<ref>{{cite web|url=http://www.russianspaceweb.com/mir_close_calls.html |title=Mir close calls |publisher=Russianspaceweb.com |accessdate=1 May 2012}}</ref> A different entry was used, and the hatch repaired. All EVA hatches on the ISS open inwards and are pressure sealing. Pirs was used to store, service, and refurbish Russian [[Orlan suits]] and provided contingency entry for crew using the slightly bulkier American suits. The outermost docking ports on both airlocks allow docking of Soyuz and Progress spacecraft, and the automatic transfer of propellants to and from storage on the ROS.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/pirs.html|title=Pirs Docking Compartment|publisher=NASA|accessdate=28 March 2009|date=10 May 2006}}</ref>

{{multiple image |align=right |image1=Node 2 - STS-134.jpg |width1=171 |image2=Node 3 - Isolated view.jpg |width2=190 |caption1=''Harmony'' node in 2011 |caption2=''Tranquility'' node in 2011}}

===Harmony===
'''''[[Harmony (ISS module)|Harmony]]''''' is the second of the station's node modules and the utility hub of the USOS. The module contains four racks that provide electrical power, bus electronic data, and acts as a central connecting point for several other components via its six Common Berthing Mechanisms (CBMs). The European Columbus and Japanese Kibō laboratories are permanently berthed to the starboard and port radial ports respectively. The nadir and zenith ports can be used for docking visiting spacecraft including HTV, Dragon, and Cygnus, with the nadir port serving as the primary docking port. American Shuttle Orbiters docked with the ISS via PMA-2, attached to the forward port.

===Tranquility===
'''''[[Tranquility (ISS module)|Tranquility]]''''' is the third and last of the station's US nodes, it contains an additional life support system to recycle waste water for crew use and supplements oxygen generation. Two of the four berthing locations are not used. One location has the ''[[Cupola (ISS module)|Cupola]]'' installed, one has the docking port adapter, and the third one is occupied by the [[Leonardo (ISS module)|''Leonardo'' PMM]].

[[File:S122e008264.jpg|thumb|left|Columbus module in 2008]]

===Columbus===
'''''[[Columbus (ISS module)|Columbus]]''''', the primary research facility for European payloads aboard the ISS, provides a [[European Drawer Rack|generic laboratory]] as well as facilities specifically designed for [[Biolab|biology]], [[European Physiology Modules|biomedical research]] and [[Fluid Science Laboratory|fluid physics]]. Several mounting locations are affixed to the exterior of the module, which provide power and data to external experiments such as the [[European Technology Exposure Facility]] (EuTEF), [[Solar Monitoring Observatory]], [[Materials International Space Station Experiment]], and [[Atomic Clock Ensemble in Space]]. A number of expansions are planned for the module to study [[quantum physics]] and [[cosmology]].<ref>{{cite news|url=http://www.nasaspaceflight.com/2008/01/prcb-plan-sts-122-for-net-feb-7-three-launches-in-10-11-weeks/|title=PRCB plan STS-122 for NET Feb 7—three launches in 10–11 weeks|accessdate=12 January 2008|author=Chris Bergin|date=10 January 2008|publisher=[[NASASpaceflight.com]]}}</ref><ref>{{cite web|url=http://www.esa.int/esaHS/ESAAYI0VMOC_iss_0.html|title=Columbus laboratory|publisher=[[European Space Agency]] (ESA)|accessdate=6 March 2009|date=10 January 2009}}</ref> ESA's development of technologies on all the main areas of life support has been ongoing for more than 20 years and are/have been used in modules such as Columbus and the ATV. The German Aerospace Center [[German Aerospace Center|DLR]] manages ground control operations for Columbus and the ATV is controlled from the French [[CNES]] [[Toulouse Space Center]].

===Kibō===
[[File:きぼうエアロック Kibo airlock.jpg|thumb|Not large enough for crew using spacesuits, the airlock on Kibō has a sliding drawer for external experiments.]]
'''''[[Kibo (ISS module)|Kibō]]''''' ({{lang-ja|きぼう}}, "[[hope]]") is the largest single ISS module. This laboratory is used to carry out research in space medicine, biology, Earth observations, materials production, biotechnology, communications research, and has facilities for growing plants and fish. During August 2011, an observatory mounted on Kibō, which utilises the ISS's orbital motion to image the whole sky in the X-ray spectrum, detected for the first time the moment a star was swallowed by a black hole.<ref>{{cite web|author=[[JAXA]] |url=http://kibo.jaxa.jp/en/experiment/ef/maxi/ |title=Monitor of All-sky X-ray Image (MAXI):Experiment – Kibo Japanese Experimental Module – JAXA |publisher=Kibo.jaxa.jp |date=30 March 2007 |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://www.jaxa.jp/press/2011/08/20110825_maxi_e.html |title=JAXA | Scientific paper in Nature using the Monitor of All-sky X-ray Image (MAXI) on Kibo and the Swift satellite (USA) observations – First observation of a massive black hole swallowing a star |publisher=Jaxa.jp |accessdate=1 May 2012}}</ref> The laboratory contains a total of 23 racks, including 10 experiment racks and has a dedicated airlock for experiments. In a 'shirt sleeves' environment, crew attach an experiment to the sliding drawer within the airlock, close the inner, and then open the outer hatch. By extending the drawer and removing the experiment using the dedicated robotic arm, payloads are placed on the external platform. The process can be reversed and repeated quickly, allowing access to maintain external experiments without the delays caused by EVAs.

<gallery widths="115px" mode="nolines">
File:Kibo - Pressurized Module.jpg|Pressurized Module
File:Kibo - Experiment Logistics Module (Pressurized Section).jpg|Experiment Logistics Module
File:Kibo - Exposed Facility.jpg|Exposed Facility
File:Kibo - Experiment Logistics Module (Exposed Section).jpg|Experiment Logistics Module
File:Kibo - Remote Manipulator System.jpg|Remote Manipulator System
</gallery>

A smaller pressurised module is attached to the top of Kibō, serving as a cargo bay. The dedicated Interorbital communications system allows large amounts of data to be beamed from Kibō's ICS, first to the Japanese KODAMA satellite in geostationary orbit, then to Japanese ground stations. When a direct communication link is used, contact time between the ISS and a ground station is limited to approximately 10 minutes per visible pass. When KODAMA relays data between a LEO spacecraft and a ground station, real-time communications are possible in 60% of the flight path of the spacecraft. Ground staff use [[telepresence robotics]] to conduct on-orbit research without crew intervention.

===Cupola===
{{multiple image |align=right |image1=STS130 cupola view1.jpg |width1=190 |image2=ISS-27 Dmitri Kondratyev and Paolo Nespoli photograph the Earth through the Cupola.jpg |width2=190 |caption1=The [[Cupola (ISS module)|Cupola]]'s design has been compared to the ''[[Millennium Falcon]]'' from ''[[Star Wars (film)|Star Wars]]''. |caption2=[[Dmitri Kondratyev]] and [[Paolo A. Nespoli|Paolo Nespoli]] in the Cupola. Background left to right, [[Progress M-09M]], [[Soyuz TMA-20]], the [[Leonardo (ISS module)|Leonardo]] module and [[Kounotori 2|HTV-2]].}}
'''[[Cupola (ISS module)|Cupola]]''' is a seven window observatory, used to view Earth and docking spacecraft. Its name derives from the Italian word cupola, which means "dome". The Cupola project was started by NASA and Boeing, but cancelled due to budget cuts. A barter agreement between NASA and the ESA resulted in the Cupola's development being resumed in 1998 by the ESA. It was built by Thales Alenia Space in Torino, Italy. The module comes equipped with robotic workstations for operating the station's main robotic arm and shutters to protect its windows from damage caused by micrometeorites. It features 7 windows, with an {{convert|80|cm|in|adj=on}} round window, the largest window on the station (and the largest flown in space to date). The distinctive design has been compared to the 'turret' of the fictitious ''[[Millennium Falcon]]'' from the motion picture ''[[Star Wars (film)|Star Wars]]'';<ref>{{cite web|url=http://www.space.com/7932-astronauts-bask-spectacular-views-space-windows.html |title=Astronauts Bask in Spectacular Views From New Space Windows |publisher=Space.com |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://news.nationalgeographic.com/news/2010/02/photogalleries/100218-international-space-station-cupola-iss-obama-nasa-pictures/ |title=First Photos: Space Station's Observation Deck Unveiled |work=National Geographic |accessdate=1 May 2012}}</ref> the original prop [[lightsaber]] used by actor [[Mark Hamill]] as [[Luke Skywalker]] in the 1977 film was flown to the station in 2007.<ref>{{cite web|url=http://www.space.com/4283-nasa-shuttle-launch-luke-skywalker-lightsaber.html |title=NASA Shuttle to Launch Luke Skywalker's Lightsaber |publisher=Space.com |date=28 August 2007 |accessdate=1 May 2012}}</ref>

===Rassvet===
'''''[[Rassvet (ISS module)|Rassvet]]''''' ({{lang-ru|link=no|Рассве́т}}; lit. "dawn"), also known as the Mini-Research Module 1 (MRM-1) ({{lang-ru|link=no|Ма́лый иссле́довательский модуль}}, {{lang|ru|МИМ 1}}) and formerly known as the Docking Cargo Module (DCM), is similar in design to the [[Mir Docking Module]] launched on [[STS-74]] in 1995. ''Rassvet'' is primarily used for cargo storage and as a docking port for visiting spacecraft. It was flown to the ISS aboard NASA's {{OV|104}} on the [[STS-132]] mission and connected in May 2010,<ref>{{cite web|url=http://www.nasaspaceflight.com/2009/04/sts-132-prcb-baselines-mission-to-deliver-russias-mrm-1/|title=STS-132: PRCB baselines Atlantis' mission to deliver Russia's MRM-1|author=Chris Gebhardt|publisher=NASAspaceflight.com|date=9 April 2009|accessdate=12 November 2009}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts132/news/STS-132-09.html|author=NASA|date=18 May 2010|accessdate=7 July 2010|title=STS-132 MCC Status Report #09}}</ref> Rassvet is the only Russian owned module launched by NASA, to repay for the launch of Zarya, which is Russian designed and built, but partially paid for by NASA.<ref>[http://www.russianspaceweb.com/iss_mim1.html MIM1]. russianspaceweb.com</ref>  Rassvet was launched with the Russian Nauka Laboratory's Experiments airlock temporarily attached to it, and spare parts for the European Robotic Arm.

===Leonardo===
[[File:STS-133 Installation PMM 3.jpg|thumb|''Leonardo'' installed]]
'''''[[Leonardo (ISS module)|Leonardo]]'' Permanent Multipurpose Module''' (PMM) is a storage module attached to the ''[[Tranquility (ISS module)|Tranquility]]'' node.<ref name="leo-esa20110301">{{cite news |url=http://www.esa.int/Our_Activities/Human_Spaceflight/MagISStra/Leonardo_attached_to_Space_Station |title=Leonardo Attached to Space Station |work=ESA.int |date=1 March 2011 |accessdate=11 June 2013}}</ref><ref>{{cite web |url=http://blogs.nasa.gov/spacestation/2015/05/27/module-relocated-prepping-station-for-commercial-crew/ |title=Module Relocated Prepping Station for Commercial Crew |publisher=NASA |first=Mark |last=Garcia |date=27 May 2015 |accessdate=27 May 2015}}</ref> The three NASA Space Shuttle [[Multi-Purpose Logistics Module|MPLM]] cargo containers—Leonardo, Raffaello and Donatello—were built for NASA in [[Turin]], Italy by Alcatel Alenia Space, now [[Thales Alenia Space]].<ref>[http://www.thalesaleniaspace-issmodules.com/ Thales Alenia Space and ISS modules – Thales Alenia Space and ISS modules]. Thalesaleniaspace-issmodules.com. Retrieved 8 October 2011.</ref> The MPLMs were provided to NASA's ISS programme by Italy (independent of their role as a member state of ESA) and are considered to be US elements. In a bartered exchange for providing these containers, the US gave Italy research time aboard the ISS out of the US allotment in addition to that which Italy receives as a member of ESA.<ref>[http://www.spaceref.com/iss/elements/mplm.html Space Station User's Guide]. SpaceRef (3 April 2001). Retrieved 8 October 2011.</ref> The Permanent Multipurpose Module was created by converting Leonardo into a module that could be permanently attached to the station.<ref name="PLM1">{{cite news|url=http://www.nasaspaceflight.com/2009/08/sts-133-five-crew-one-eva-mission-leave-mpm-on-iss|title=STS-133 refined to a five crew, one EVA mission—will leave MPLM on ISS|publisher=NASASpaceflight.com|author=Chris Gebhardt|date=5 August 2009}}</ref><ref name="PLM2">{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8226309.stm|title=Europe looks to buy Soyuz craft|work=BBC News|last=Amos|first=Jonathan|date=29 August 2009}}</ref><ref>{{cite web|url=http://forum.nasaspaceflight.com/index.php?topic=17437.msg483604#msg483604|publisher=NASASpaceflight.com|accessdate=12 October 2009|title=Shuttle Q&A Part 5|date=27 September 2009}}</ref>

===Scheduled additional modules===

====Nauka====
'''''[[Nauka (ISS module)|Nauka]]''''' ({{lang-ru|link=no|Нау́ка}}; lit. "science"), also known as the Multipurpose Laboratory Module (MLM) or FGB-2 ({{lang-ru|link=no|Многофункциональный лабораторный модуль}}, {{lang|ru|МЛМ}}), is the major Russian laboratory module. It was scheduled to arrive at the station in 2014, docking to the port that was occupied by the Pirs module.<ref>{{cite web|url=http://www.aviationweek.com/Article.aspx?id=/article-xml/asd_05_23_2012_p05-01-460939.xml|title=Russia Sees Moon Base As Logical Next Step| last=Morring| first=Frank| date=23 May 2012| publisher=Aviation Week|accessdate=29 May 2012}}</ref> The date has been postponed to February 2017.<ref>{{cite web|url=http://www.russianspaceweb.com/iss_fgb2.html|title=MLM (FGB-2)|author=Anatoly Zak|publisher=Russian Space Web|date=29 April 2014|accessdate=14 May 2014}}</ref> Prior to the arrival of the Nauka module, a Progress spacecraft was used to remove Pirs from the station, deorbiting it to reenter over the Pacific Ocean. Nauka contains an additional set of life support systems and attitude control. Originally it would have routed power from the single Science-and-Power Platform, but that single module design changed over the first ten years of the ISS mission, and the two science modules, which attach to Nauka via the [[Uzlovoy Module]], or Russian node, each incorporate their own large solar arrays to power Russian science experiments in the ROS.

Nauka's mission has changed over time. During the mid-1990s, it was intended as a backup for the FGB, and later as a universal docking module (UDM); its docking ports will be able to support automatic docking of both spacecraft, additional modules and fuel transfer. Nauka has its own engines. Smaller Russian modules such as Pirs and Poisk were delivered by modified [[Progress (spacecraft)|Progress]] spacecraft, and the larger modules; Zvezda, Zarya, and Nauka, were launched by Proton rockets. Russia plans to separate Nauka, along with the rest of the Russian Orbital Segment, before the ISS is deorbited, to form the [[OPSEK]] space station.

====Uzlovoy Module====
The '''[[Uzlovoy Module]]''' (UM), or Node Module is a 4 metric ton<ref name=Zak>{{cite web|last1=Zak|first1=Anatoly|title=Node Module|url=http://www.russianspaceweb.com/iss_node.html|website=RussianSpaceWeb.com|accessdate=7 January 2015}}</ref> ball shaped module that will support the docking of two scientific and power modules during the final stage of the station assembly and provide the Russian segment additional docking ports to receive Soyuz TMA and Progress M spacecraft. UM is to be incorporated into the ISS in 2016. It will be integrated with a special version of the Progress cargo ship and launched by a standard Soyuz rocket. The Progress would use its own propulsion and flight control system to deliver and dock the Node Module to the nadir (Earth-facing) docking port of the Nauka MLM/FGB-2 module. One port is equipped with an active hybrid docking port, which enables docking with the MLM module. The remaining five ports are passive hybrids, enabling docking of Soyuz and Progress vehicles, as well as heavier modules and future spacecraft with modified docking systems. The node module was conceived to serve as the only permanent element of the future Russian successor to the ISS, [[Orbital Piloted Assembly and Experiment Complex|OPSEK]]. Equipped with six docking ports, the Node Module would serve as a single permanent core of the future station with all other modules coming and going as their life span and mission required.<ref>[http://www.energia.ru/en/news/news-2011/news_01-13.html S.P. Korolev RSC Energia – News]. Energia.ru (13 January 2011). Retrieved 8 October 2011.</ref><ref>[http://www.russianspaceweb.com/iss_node.html Node Module]. Russianspaceweb.com. Retrieved 8 October 2011.</ref> This would be a progression beyond the ISS and Russia's modular MIR space station, which are in turn more advanced than early monolithic first generation stations such as Skylab, and early Salyut and Almaz stations.

'''Science Power Modules 1 & 2''' (NEM-1, NEM-2) ({{lang-ru|link=no|Нау́чно-Энергетический Модуль-1 и -2}})

====Bigelow Expandable Activity Module====
On 16 January 2013, [[Bigelow Aerospace]] was contracted by NASA to provide a [[Bigelow Expandable Activity Module]] (BEAM), scheduled to arrive at the space station in 2015 for a two-year technology demonstration.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/station/news/beam_feature.html |title=NASA to Test Bigelow Expandable Module on Space Station |publisher=NASA |date=16 January 2013 |accessdate=17 January 2013}}</ref> BEAM is an inflatable module that will be attached to the aft hatch of the port-side Tranquility module of the International Space Station. During its two-year test run, instruments will measure its structural integrity and leak rate, along with temperature and radiation levels. The hatch leading into the module will remain mostly closed except for periodic visits by space station crew members for inspections and data collection. Following the test run, the module will be detached and jettisoned from the station.<ref>{{cite web | url=http://www.spaceflightnow.com/news/n1301/16bigelow/ | title=Bigelow inflatable module bound for space station | last=Harwood | first=William | date=16 January 2013 | publisher=Spaceflightnow | accessdate=17 January 2013}}</ref>

[[image:ISS Habitation module.jpg|thumb|left|The cancelled Habitation module under construction in 1997]]

===Cancelled components===
Several modules planned for the station have been cancelled over the course of the ISS programme, whether for budgetary reasons, because the modules became unnecessary, or following a redesign of the station after the 2003 [[Space Shuttle Columbia disaster|''Columbia'' disaster]]. The US [[Centrifuge Accommodations Module]] was intended to host science experiments in varying levels of [[artificial gravity]].<ref>{{cite web|url=http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=12560&mid=269666|title=Where is the Centrifuge Accommodation Module (CAM)?|publisher=NASASpaceflight.com|accessdate=12 October 2009}}</ref> The US [[Habitation Module]] would have served as the station's living quarters. Instead, the sleep stations are now spread throughout the station.<ref>{{cite web|url=http://www.space.com/missionlaunches/060214_iss_module.html|title=NASA Recycles Former ISS Module for Life Support Research|author=Tariq Malik|accessdate=11 March 2009|publisher=Space.com|date=14 February 2006}}</ref> The US [[Interim Control Module]] and [[ISS Propulsion Module]] were intended to replace functions of ''Zvezda'' in case of a launch failure.<ref>{{cite web|title=ICM Interim Control Module|publisher=U.S. Naval Center for Space Technology|url=http://code8200.nrl.navy.mil/icm.html|archiveurl=https://web.archive.org/web/20070208164211/http://code8200.nrl.navy.mil/icm.html|archivedate=8 February 2007}}</ref> The Russian [[Universal Docking Module]], to which the cancelled Russian Research modules and spacecraft would have docked.<ref name="Zak">{{cite web|url=http://www.russianspaceweb.com/iss_russia.html|accessdate=3 October 2009|publisher=russianspaceweb.com|author=Anatoly Zak|title=Russian segment of the ISS}}</ref> The Russian [[Science Power Platform]] would have provided the [[Russian Orbital Segment]] with a power supply independent of the ITS solar arrays,<ref name="Zak" /> and two [[Russian Research Module]]s that were planned to be used for scientific research.<ref>{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/components/russian_laboratory.html|title=Russian Research Modules|publisher=Boeing|accessdate=21 June 2009}}</ref>

==Unpressurised elements==
[[File:Truss breakdown.png|thumb|right|ISS Truss Components breakdown showing Trusses and all ORUs in situ]]
The ISS features a large number of external components that do not require pressurisation. The largest such component is the [[Integrated Truss Structure]] (ITS), to which the station's main solar arrays and thermal radiators are mounted.<ref name="Arrays" /> The ITS consists of ten separate segments forming a structure 108.5 m (356 ft) long.<ref name="OnOrbit" />

The station in its complete form has several smaller external components, such as the six robotic arms, the three [[External Stowage Platform]]s (ESPs) and four [[ExPRESS Logistics Carrier]]s (ELCs).<ref name="Manifest" /><ref>{{cite web|url=http://www.nasa.gov/centers/marshall/news/background/facts/expressrack.html|title=EXPRESS Racks 1 and 2 fact sheet|accessdate=4 October 2009|date=12 April 2008|publisher=NASA}}</ref> Whilst these platforms allow experiments (including [[MISSE]], the STP-H3 and the [[Robotic Refueling Mission]]) to be deployed and conducted in the vacuum of space by providing electricity and processing experimental data locally, the platforms' primary function is to store [[Orbital Replacement Unit]]s (ORUs). ORUs are spare parts that can be replaced when the item either passes its design life or fails. Examples of ORUs include pumps, storage tanks, antennas and battery units. Such units are replaced either by astronauts during EVA or by robotic arms. Spare parts were routinely transported to and from the station via Space Shuttle resupply missions, with a heavy emphasis on ORU transport once the NASA Shuttle approached retirement.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/12/soyuz-tma-03m-docks-iss-returns-station-six-crewmembers-future-ops/ |title=Soyuz TMA-03M docks to ISS, returns station to six crewmembers for future ops |publisher=NASASpaceFlight.com |date=23 December 2011 |accessdate=1 May 2012}}</ref> Several shuttle missions were dedicated to the delivery of ORUs, including [[STS-129]],<ref name="EVA129">{{cite web|url=http://www.nasa.gov/centers/johnson/pdf/404493main_EVA_129_F_E1.pdf|title=EVA Checklist: STS-129 Flight Supplement|author=L. D. Welsch|publisher=NASA|date=30 October 2009}}</ref> [[STS-133]]<ref name="STS-133">{{cite web|url=http://www.nasa.gov/pdf/491387main_STS-133%20Press%20Kit.pdf|title=Space Shuttle Mission: STS-131|date=February 2011|publisher=NASA}}</ref> and [[STS-134]].<ref name="STS-134">{{cite web|url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf|title=Space Shuttle Mission: STS-134|publisher=NASA|date=April 2011}}</ref> {{asof|2011|01}}, only one other mode of transportation of ORUs had been utilised – the Japanese cargo vessel [[H-II Transfer Vehicle|HTV-2]] – which delivered an FHRC and CTC-2 via its Exposed Pallet (EP).<ref name="HTV2">{{cite web|url=http://iss.jaxa.jp/en/htv/mission/htv-2/library/presskit/htv2_presskit_en.pdf|title=HTV2: Mission Press Kit|publisher=Japan Aerospace Exploration Agency|date=20 January 2011}}</ref>{{update after|2013|1|28}}

[[File:STS-116 spacewalk 1.jpg|left|thumb|Construction of the [[Integrated Truss Structure]] over New Zealand.]]
There are also smaller exposure facilities mounted directly to laboratory modules; the JEM [[Japanese Experiment Module#Exposed Facility|Exposed Facility]] serves as an external '[[porch]]' for the Japanese Experiment Module complex,<ref>{{cite web|url=http://kibo.jaxa.jp/en/about/kibo/jef/|title=Exposed Facility:About Kibo|publisher=JAXA|date=29 August 2008|accessdate=9 October 2009}}</ref> and a facility on the European ''Columbus'' laboratory provides power and data connections for experiments such as the [[European Technology Exposure Facility]]<ref name="NASA">{{cite web|url=http://www.nasa.gov/mission_pages/station/science/experiments/EuTEF.html|title=NASA—European Technology Exposure Facility (EuTEF)|publisher=NASA|date=6 October 2008|accessdate=28 February 2009}}</ref><ref name="ESA">{{cite web|url=http://www.esa.int/esaMI/Columbus/SEM7ZTEMKBF_0.html|title=ESA—Columbus—European Technology Exposure Facility (EuTEF)|publisher=ESA|date=13 January 2009|accessdate=28 February 2009}}</ref> and the [[Atomic Clock Ensemble in Space]].<ref>{{cite web|url=http://www.esa.int/SPECIALS/HSF_Research/SEMJSK0YDUF_0.html|publisher=ESA|accessdate=9 October 2009|title=Atomic Clock Ensemble in Space (ACES)}}</ref> A [[remote sensing]] instrument, [[Stratospheric Aerosol and Gas Experiment|SAGE III-ISS]], is due to be delivered to the station in 2014 aboard a [[Dragon (spacecraft)|Dragon capsule]], and the [[Neutron star Interior Composition ExploreR|NICER]] experiment in 2016.<ref>{{cite web |url=http://heasarc.gsfc.nasa.gov/docs/nicer/papers/NICER-SPIE-July2012-v4.pdf | publisher=Goddard Space Flight Center |title=The Neutron star Interior Composition ExploreR (NICER): an Explorer mission of opportunity for soft x-ray timing spectroscopy |accessdate=8 April 2013 |author=NICER Team }}</ref><ref>{{cite web|url=http://www.nasa.gov/topics/earth/features/sage3.html|date=1 March 2011|accessdate=12 March 2011|publisher=NASA|title=Time to Fly: SAGE III — ISS Prepped for Space Station|author=Michael Finneran}}</ref> The largest such scientific payload externally mounted to the ISS is the [[Alpha Magnetic Spectrometer]] (AMS), a particle physics experiment launched on [[STS-134]] in May 2011, and mounted externally on the ITS. The AMS measures [[cosmic ray]]s to look for evidence of [[dark matter]] and [[antimatter]].<ref>{{cite web|url=http://ams.cern.ch/|title=The Alpha Magnetic Spectrometer Experiment|publisher=[[CERN]]|date=21 January 2009|accessdate=6 March 2009}}</ref>

===Robotic arms and cargo cranes===
{{Double image|right|Iss017e011097.jpg|250|Dextrereallyhasnohead.jpg|250|Commander [[Sergey Alexandrovich Volkov|Volkov]] stands on Pirs with his back to the [[Soyuz spacecraft|Soyuz]] whilst operating the manual [[Strela (crane)|Strela crane]] holding photographer [[Oleg Kononenko|Kononenko]]. [[Zarya]] is seen to the left and [[Zvezda (ISS module)|Zvezda]] across the bottom of the image.|[[Dextre]], like many of the station's experiments and robotic arms, can be operated from Earth and perform tasks while the crew sleeps.||}}

The [[Integrated Truss Structure]] serves as a base for the station's primary remote manipulator system, called the [[Mobile Servicing System]] (MSS), which is composed of three main components. [[Canadarm2]], the largest robotic arm on the ISS, has a mass of {{convert|1800|kg|lb}} and is used to dock and manipulate spacecraft and modules on the USOS, hold crew members and equipment in place during EVAs and move Dextre around to perform tasks.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/station/structure/elements/mss.html |title=Canadarm2 and the Mobile Servicing System |publisher=NASA |date=8 January 2013 |accessdate=22 June 2015}}</ref> [[Dextre]] is a {{convert|1560|kg|lb|abbr=on}} robotic manipulator with two arms, a rotating torso and has power tools, lights and video for replacing [[orbital replacement unit]]s (ORUs) and performing other tasks requiring fine control.<ref>{{cite web |url=http://www.asc-csa.gc.ca/eng/iss/dextre/default.asp |title=Dextre, the International Space Station's Robotic Handyman |publisher=Canadian Space Agency |accessdate=22 June 2015}}</ref> The [[Mobile Base System]] (MBS) is 2 platforms which rides on rails along the length of the station's main truss. It serves as a mobile base for Canadarm2 and Dextre, allowing the robotic arms to reach all parts of the USOS.<ref>{{cite web |url=http://www.asc-csa.gc.ca/eng/iss/mobile-base/default.asp |title=Mobile Base System |publisher=Canadian Space Agency |accessdate=22 June 2015}}</ref> To gain access to the Russian Segment a [[Grapple Fixture|grapple fixture]] was added to Zarya on [[STS-134]], so that Canadarm2 can inchworm itself onto the ROS.<ref name="presskit134">{{cite web |url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf |title=Space Shuttle Mission STS-134: Final Flight of ''Endeavour'' - Press Kit |format=PDF |publisher=NASA |pages=51-53 |date=April 2011 |accessdate=22 June 2015}}</ref> Also installed during STS-134 was the {{convert|50|ft|m|abbr=on|order=flip}} [[Orbiter Boom Sensor System]] (OBSS), which had been used to inspect head shield tiles on Space Shuttle missions and can be used on station to increase the reach of the MSS.<ref name="presskit134"/> Staff on Earth or the station can operate the MSS components via remote control, performing work outside the station without space walks.

Japan's [[Kibo (ISS module)#Remote Manipulator System|Remote Manipulator System]], which services the JEM Exposed Facility,<ref>{{cite web |url=http://kibo.jaxa.jp/en/about/kibo/rms/ |title=Remote Manipulator System: About Kibo |publisher=JAXA |date=29 August 2008 |accessdate=4 October 2009}}</ref> was launched on [[STS-124]] and is attached to the JEM Pressurised Module.<ref>{{cite web |url=http://www.nasa.gov/centers/johnson/news/station/2002/iss02-03.txt |title=International Space Station Status Report #02-03 |publisher=NASA |date=14 January 2002 |accessdate=4 October 2009}}</ref> The arm is similar to the Space Shuttle arm as it is permanently attached at one end and has a latching end effector for standard grapple fixtures at the other.

The [[European Robotic Arm]], which will service the Russian Orbital Segment, will be launched alongside the [[Multipurpose Laboratory Module]] in 2017.<ref>{{cite web |url=http://www.russianspaceweb.com/iss_fgb2.html |title=MLM (FGB-2) module of the ISS |publisher=RussianSpaceWeb |accessdate=16 June 2014}}</ref> The ROS does not require spacecraft or modules to be manipulated, as all spacecraft and modules dock automatically and may be discarded the same way. Crew use the two ''[[Strela (crane)|Strela]]'' ({{lang-ru|link=no|Стрела́}}; lit. Arrow) cargo cranes during EVAs for moving crew and equipment around the ROS. Each Strela crane has a mass of {{convert|45|kg|lb|abbr=on}}.

===Comparison===
The ISS follows [[Salyut]] and [[Almaz]] series, [[Cosmos 557]], [[Skylab]], and [[Mir]] as the 11th space station launched, as the [[Genesis II|Genesis]] prototypes were never intended to be manned. Other examples of modular station projects include the Soviet/Russian Mir and the planned Russian OPSEK and [[Chinese space station]]. The first space station, [[Salyut 1]], and other one-piece or 'monolithic' first generation space stations, such as Salyut 2,3,4,5, DOS 2, Kosmos 557, Almaz and NASA's [[Skylab]] stations were not designed for re-supply.<ref>http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/history.pdf</ref> Generally, each crew had to depart the station to free the only docking port for the next crew to arrive, Skylab had more than one docking port but was not designed for resupply. Salyut 6 and 7 had more than one docking port and were designed to be resupplied routinely during crewed operation.<ref>{{cite web|url=http://www.pbs.org/spacestation/station/russian.htm |title=Space Station | Russian Space History |publisher=Pbs.org |accessdate=1 May 2012}}</ref>

==Station systems==

===Life support===
{{Main|ISS ECLSS|Chemical oxygen generator}}
The critical systems are the atmosphere control system, the water supply system, the food supply facilities, the sanitation and hygiene equipment, and fire detection and suppression equipment. The Russian Orbital Segment's life support systems are contained in the Service Module Zvezda. Some of these systems are supplemented by equipment in the USOS. The MLM Nauka laboratory has a complete set of life support systems.

====Atmospheric control systems====
[[Image:SpaceStationCycle.svg|thumb|The interactions between the components of the ISS Environmental Control and Life Support System (ECLSS)|alt=A flowchart diagram showing the components of the ISS life support system.]]
The atmosphere on board the ISS is similar to the [[Atmosphere of Earth|Earth's]].<ref>{{cite web|url=http://science.howstuffworks.com/space-station2.htm |title=How Space Stations Work|first=Craig|last=Freudenrich|publisher=Howstuffworks|date=20 November 2000|accessdate=23 November 2008}}</ref> Normal air pressure on the ISS is 101.3 [[kilopascal|kPa]] (14.7 [[Pounds per square inch|psi]]);<ref>{{cite web |url=http://nasaexplores.com/show2_5_8a.php?id=04-032&gl=58|archiveurl=https://web.archive.org/web/20061114010931/http://www.nasaexplores.com/show2_5_8a.php?id=04-032&gl=58|archivedate=14 November 2006|work=NASAexplores|title=5–8: The Air Up There|publisher=NASA|accessdate=31 October 2008}}</ref> the same as at sea level on Earth. An Earth-like atmosphere offers benefits for crew comfort, and is much safer than the alternative, a pure oxygen atmosphere, because of the increased risk of a fire such as that responsible for the deaths of the [[Apollo 1]] crew.<ref>{{cite book|author=Clinton Anderson|display-authors=etal|publisher=US Government Printing Office|title=Report of the Committee on Aeronautical and Space Sciences, United States Senate—Apollo 204 Accident|date=30 January 1968|location=Washington, DC|page=8|url=http://klabs.org/richcontent/Reports/Failure_Reports/as-204/senate_956/as204_senate_956.pdf}}</ref> Earth-like atmospheric conditions have been maintained on all Russian and Soviet spacecraft.<ref name=spacemed>{{Citation | last1=Davis | first1=Jeffrey R. | last2=Johnson | first2=Robert | last3=Stepanek | first3=Jan | lastauthoramp=yes | title=Fundamentals of Aerospace Medicine | publisher=Lippincott Williams & Wilkins | place=Philadelphia PA, USA | volume=XII | pages=261–264 | year=2008}}</ref>

The ''[[Elektron (ISS)|Elektron]]'' system aboard ''Zvezda'' and a similar system in ''Destiny'' generate oxygen aboard the station.<ref name="OGS">{{cite web|url=http://www.space.com/businesstechnology/060215_techwed_iss_oxygen.html|title=Air Apparent: New Oxygen Systems for the ISS|author=Tariq Malik|publisher=Space.com|date=15 February 2006|accessdate=21 November 2008}}</ref> The crew has a backup option in the form of bottled oxygen and [[Vika oxygen generator|Solid Fuel Oxygen Generation]] (SFOG) canisters, a [[chemical oxygen generator]] system.<ref name="breath easy">{{cite web|url=http://science.nasa.gov/headlines/y2000/ast13nov_1.htm|title=Breathing Easy on the Space Station|author=Patrick L. Barry|publisher=NASA|date=13 November 2000|accessdate=21 November 2008}}</ref> Carbon dioxide is removed from the air by the [[Vozdukh]] system in ''Zvezda''. Other by-products of human metabolism, such as methane from the intestines and ammonia from sweat, are removed by [[Activated carbon|activated charcoal]] filters.<ref name="breath easy" />

Part of the ROS atmosphere control system is the oxygen supply, triple-redundancy is provided by the Elektron unit, solid fuel generators, and stored oxygen. The Elektron unit is the primary oxygen supply, {{chem|O|2}} and {{chem|H|2}} are produced by [[electrolysis]], with the {{chem|H|2}} being vented overboard. The 1 kW system uses approximately 1 litre of water per crew member per day from stored water from Earth, or water recycled from other systems. MIR was the first spacecraft to use recycled water for oxygen production. The secondary oxygen supply is provided by burning {{chem|O|2}}-producing [[Vika oxygen generator|Vika]] cartridges (see also [[ISS ECLSS]]). Each 'candle' takes 5–20 minutes to decompose at 450–500 °C, producing 600 litres of {{chem|O|2}}. This unit is manually operated.<ref>[http://suzymchale.com/ruspace/issrslss.html RuSpace | ISS Russian Segment Life Support System]. Suzymchale.com. Retrieved 8 October 2011.</ref>

The US Orbital Segment has redundant supplies of oxygen, from a pressurised storage tank on the Quest airlock module delivered in 2001, supplemented ten years later by ESA built Advanced Closed-Loop System (ACLS) in the Tranquility module (Node 3), which produces {{chem|O|2}} by electrolysis.<ref>[http://science.nasa.gov/science-news/science-at-nasa/2000/ast13nov_1/ Breathing Easy on the Space Station – NASA Science]. ''Science''.nasa.gov (13 November 2000). Retrieved 8 October 2011.</ref> Hydrogen produced is combined with carbon dioxide from the cabin atmosphere and converted to water and methane.

===Power and thermal control===
{{Main|Electrical system of the International Space Station|External Active Thermal Control System}}

{{Double image|left|ROSSA.jpg|200|P4 deployed.jpg|200|Russian solar arrays, backlit by sunset.|One of the eight truss mounted pairs of USOS solar arrays}}
Double-sided solar, or [[Photovoltaic]] arrays, provide [[Electric power|electrical power]] for the ISS. These bifacial cells are more efficient and operate at a lower temperature than single-sided cells commonly used on Earth, by collecting sunlight on one side and light [[Albedo|reflected off]] the Earth on the other.<ref>{{cite web |url=http://wenku.baidu.com/view/a815121ffc4ffe473368ab7a.html |title=The early history of bifacial solar cell_百度文库 |publisher=Wenku.baidu.com |date=25 October 2010 |accessdate=14 August 2012}}</ref> 

The Russian segment of the station, like the Space Shuttle and most spacecraft, uses 28 [[volt]] [[direct current|DC]] from four rotating solar arrays mounted on ''Zarya'' and ''Zvezda''. The USOS uses 130–180 V DC from the USOS PV array, power is stabilised and distributed at 160 V DC and converted to the user-required 124 V DC. The [[High voltage|higher distribution voltage]] allows smaller, lighter conductors, at the expense of crew safety. The ROS uses [[Extra-low voltage|low voltage]]. The two station segments share power with converters.<ref name="Arrays" />

The USOS solar arrays are arranged as four wing pairs, with each wing producing nearly 32.8 kW.<ref name="Arrays">{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/truss_segment.html|title=Spread Your Wings, It's Time to Fly|publisher=NASA|date=26 July 2006|accessdate=21 September 2006}}</ref> These arrays normally track the sun to maximise power generation. Each array is about 375 m2 (450 yd2) in area and {{convert|58|m|yd|0}} long. In the complete configuration, the solar arrays track the sun by rotating the ''alpha [[gimbal]]'' once per orbit; the ''beta gimbal'' follows slower changes in the angle of the sun to the orbital plane. The [[Night Glider mode]] aligns the solar arrays parallel to the ground at night to reduce the significant aerodynamic drag at the station's relatively low orbital altitude.<ref>{{cite journal|author=G. Landis and C-Y. Lu|year=1991|title=Solar Array Orientation Options for a Space Station in Low Earth Orbit|journal=Journal of Propulsion and Power|volume=7|issue=1|pages=123–125|doi=10.2514/3.23302}}</ref>

The station uses rechargeable [[Nickel hydrogen battery|nickel-hydrogen batteries]] (NiH2) for continuous power during the 35 minutes of every 90-minute orbit that it is eclipsed by the Earth. The batteries are recharged on the day side of the Earth. They have a 6.5-year lifetime (over 37,000 charge/discharge cycles) and will be regularly replaced over the anticipated 20-year life of the station.<ref>{{cite web|url=http://www.grc.nasa.gov/WWW/RT/RT1999/5000/5420miller.html|title=Nickel-Hydrogen Battery Cell Life Test Program Update for the International Space Station|accessdate=27 November 2009|publisher=NASA|author=Thomas B. Miller|date=24 April 2000}}</ref>

The station's large solar panels generate a high potential voltage difference between the station and the ionosphere. This could cause arcing through insulating surfaces and sputtering of conductive surfaces as ions are accelerated by the spacecraft plasma sheath. To mitigate this, plasma contactor units (PCU)s create current paths between the station and the ambient plasma field.<ref>[http://www.grc.nasa.gov/WWW/RT/RT1998/5000/5430patterson.html Cathodes Delivered for Space Station Plasma Contactor System]. Grc.nasa.gov (18 June 1999). Retrieved 8 October 2011.</ref>

[[File:EATCS.png|thumb|ISS External Active Thermal Control System (EATCS) diagram]]
The large amount of electrical power consumed by the station's systems and experiments is turned almost entirely into heat. The heat which can be dissipated through the walls of the stations modules is insufficient to keep the internal ambient temperature within comfortable, workable limits. [[Ammonia]] is continuously pumped through pipework throughout the station to collect heat, then into external radiators exposed to the cold of space, and back into the station.

The International Space Station (ISS) External Active Thermal Control System (EATCS) maintains an equilibrium when the ISS environment or heat loads exceed the capabilities of the Passive Thermal Control System (PTCS). Note Elements of the PTCS are external surface materials, insulation such as MLI, or Heat Pipes. The EATCS provides heat rejection capabilities for all the US pressurised modules, including the JEM and COF as well as the main power distribution electronics of the S0, S1 and P1 Trusses. The EATCS consists an internal, non-toxic, water coolant loop used to cool and dehumidify the atmosphere, which transfers collected heat into an external liquid ammonia loop capable of withstanding the much lower temperature of space, which is then circulated through radiators to remove the heat. The EATCS is capable of rejecting up to 70 kW, and provides a substantial upgrade in heat rejection capacity from the 14 kW capability of the Early External Active Thermal Control System (EEATCS) via the Early Ammonia Servicer (EAS), which was launched on [[STS-105]] and installed onto the P6 Truss.<ref>[http://www.nasa.gov/pdf/473486main_iss_atcs_overview.pdf ATCS Team Overview]. (PDF). Retrieved 8 October 2011.</ref>

===Communications and computers===
{{Main|Tracking and Data Relay Satellite|Luch (satellite)}}
{{See also2|[[ThinkPad#Use in space|ThinkPad use in space]]}}
[[File:ISS Communication Systems.png|thumb|The communications systems used by the ISS * Luch satellite not currently in use|alt=Diagram showing communications links between the ISS and other elements.]]
Radio communications provide [[telemetry]] and scientific data links between the station and [[Mission Control Center|Mission Control Centres]]. Radio links are also used during [[Space rendezvous|rendezvous and docking procedures]] and for audio and video communication between crewmembers, flight controllers and family members. As a result, the ISS is equipped with internal and external communication systems used for different purposes.<ref name="BoeingComm" />


The Russian Orbital Segment communicates directly with the ground via the ''[[Lira (ISS)|Lira]]'' [[Antenna (radio)|antenna]] mounted to ''Zvezda''.<ref name="ISSRG" /><ref>{{cite web|url=http://www.nasa.gov/home/hqnews/2005/mar/HQ_ss05015_ISS_status_report.html|title=International Space Station Status Report: SS05-015|last=Mathews|first=Melissa|author2=James Hartsfield|date=25 March 2005|work=NASA News|publisher=NASA|accessdate=11 January 2010}}</ref> The ''Lira'' antenna also has the capability to use the ''[[Luch (satellite)|Luch]]'' data relay satellite system.<ref name="ISSRG" /> This system, used for communications with ''Mir'', fell into disrepair during the 1990s, and as a result is no longer in use,<ref name="ISSRG" /><ref name="SSSM">{{cite book|first=David|last=Harland|title=The Story of Space Station Mir|publisher=Springer-Verlag New York Inc|date=30 November 2004|location=New York|isbn=978-0-387-23011-5}}</ref><ref name="Harvey">{{cite book|last=Harvey|first=Brian|title=The rebirth of the Russian space program: 50 years after Sputnik, new frontiers|publisher=Springer Praxis Books|year=2007|page=263|isbn=0-387-71354-9}}</ref> although two new ''Luch'' satellites—''Luch''-5A and ''Luch''-5B—were launched in 2011 and 2012 respectively to restore the operational capability of the system.<ref>{{cite web|publisher=RussianSpaceWeb|url=http://www.russianspaceweb.com/2011.html|accessdate=12 January 2010|title=Space exploration in 2011|date=4 January 2010|author=Anatoly Zak}}</ref> Another Russian communications system is the [[Voskhod-M]], which enables internal telephone communications between ''Zvezda'', ''Zarya'', ''Pirs'', ''Poisk'' and the USOS, and also provides a VHF radio link to ground control centres via antennas on ''Zvezda''{{'s}} exterior.<ref>{{cite web|url=http://www.nasa.gov/directorates/somd/reports/iss_reports/2010/05022010.html|date=2 May 2010|accessdate=7 July 2010|publisher=NASA|title=ISS On-Orbit Status 05/02/10}}</ref>

The [[US Orbital Segment]] (USOS) makes use of two separate radio links mounted in the [[Z1 truss]] structure: the [[S band]] (used for audio) and [[Ku band|Ku band]] (used for audio, video and data) systems. These transmissions are routed via the United States [[Tracking and Data Relay Satellite]] System (TDRSS) in [[geostationary orbit]], which allows for almost continuous real-time communications with [[Christopher C. Kraft Jr. Mission Control Center|NASA's Mission Control Center]] (MCC-H) in [[Houston]].<ref name="ISSBook" /><ref name="ISSRG" /><ref name="BoeingComm">{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/systems/communications_tracking.html|publisher=Boeing|accessdate=30 November 2009|title=Communications and Tracking|archiveurl = https://web.archive.org/web/20080611115319/http://www.boeing.com/defense-space/space/spacestation/systems/communications_tracking.html |archivedate = 11 June 2008}}</ref> Data channels for the Canadarm2, European ''Columbus'' laboratory and Japanese ''Kibō'' modules are routed via the S band and Ku band systems, although the [[European Data Relay System]] and a similar Japanese system will eventually complement the TDRSS in this role.<ref name="ISSBook" /><ref name="JAXA-MOU">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/nasa_japan.html|title=Memorandum of Understanding Between the National Aeronautics and Space Administration of the United States of America and the Government of Japan Concerning Cooperation on the Civil International Space Station|publisher=NASA|accessdate=19 April 2009|date=24 February 1998}}</ref> Communications between modules are carried on an internal digital [[wireless network]].<ref>{{cite web|title=Operations Local Area Network (OPS LAN) Interface Control Document|format=PDF|publisher=NASA|url=http://www.spaceref.com/iss/computer/iss.ops.lan.icd.pdf|accessdate=30 November 2009|date=February 2000}}</ref>

[[File:STS-128 ISS-20 Destiny Canadarm2.jpg|thumb|left|Laptop computers surround the Canadarm2 console.]]
[[Ultra high frequency|UHF radio]] is used by astronauts and cosmonauts conducting [[Extra-vehicular activity|EVAs]]. UHF is employed by other spacecraft that dock to or undock from the station, such as Soyuz, Progress, HTV, ATV and the Space Shuttle (except the shuttle also makes use of the S band and Ku band systems via TDRSS), to receive commands from Mission Control and ISS crewmembers.<ref name="ISSRG" /> Automated spacecraft are fitted with their own communications equipment; the ATV uses a [[laser]] attached to the spacecraft and equipment attached to ''Zvezda'', known as the Proximity Communications Equipment, to accurately dock to the station.<ref>{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=16247|title=ISS/ATV communication system flight on Soyuz|accessdate=30 November 2009|publisher=[[EADS Astrium]]|date=28 February 2005}}</ref><ref>{{cite web|publisher=NASASpaceflight.com|author=Chris Bergin|url=http://www.nasaspaceflight.com/2009/11/sts-129-support-dragon-communication-demo-iss/|date=10 November 2009|accessdate=30 November 2009|title=STS-129 ready to support Dragon communication demo with ISS}}</ref>

The ISS is equipped with approximately 100 [[IBM]] and [[Lenovo]] [[ThinkPad#Use in space|ThinkPad]] model A31 and T61P laptop computers. Each computer is a [[commercial off-the-shelf]] purchase which is then modified for safety and operation including updates to connectors, cooling and power to accommodate the station's 28V DC power system and weightless environment. Heat generated by the laptops does not rise, but stagnates surrounding the laptop, so additional forced ventilation is required. Laptops aboard the ISS are connected to the station's [[wireless LAN]] via [[Wi-Fi]] and to the ground via Ku band. This provides speeds of 10 [[Megabit per second|Mbit/s]] to and 3 Mbit/s from the station, comparable to home [[digital subscriber line|DSL]] connection speeds.<ref name="issit">{{cite news |url=http://bits.blogs.nytimes.com/2010/01/22/first-tweet-from-space/ |title=First Tweet From Space |work=[[The New York Times]] |first=Nick |last=Bilton |date=22 January 2010 |accessdate=29 April 2014}}</ref><ref name="tested20121019">{{cite news |url=http://www.tested.com/science/space/449539-how-fast-isss-internet-and-other-space-questions-answered/ |title=How Fast is the ISS's Internet? (and Other Space Questions Answered) |work=Tested.com |first=Will |last=Smith |date=19 October 2012 |accessdate=29 April 2014}}</ref>

The operating system used for key station functions is the [[Debian]] [[GNU/Linux distribution]].<ref>{{cite news|last=Thomson|first=Iain|title=Penguins in spa-a-a-ce! ISS dumps Windows for Linux on laptops|url=http://www.theregister.co.uk/2013/05/10/iss_linux_debian_deployment/|accessdate=15 May 2013|newspaper=The Register|date=10 May 2013}}</ref> The migration from [[Microsoft Windows]] was made in May 2013 for reasons of reliability, stability and flexibility.<ref>{{cite news|last=Gunter|first=Joel|title=International Space Station to boldly go with Linux over Windows|url=http://www.telegraph.co.uk/technology/news/10049444/International-Space-Station-to-boldly-go-with-Linux-over-Windows.html|accessdate=15 May 2013|newspaper=The Daily Telegraph|date=10 May 2013}}</ref>

==Station operations==

===Expeditions and private flights===
[[File:Sts088-703-019e.jpg|thumb|Zarya and Unity were entered for the first time on 10 December 1998.]]
[[File:Soyuz tm-31 transported to launch pad.jpg|right|thumb|Soyuz TM-31 being prepared to bring the first resident crew to the station in October 2000]]
[[File:STS-115 ISS after undocking.jpg|thumb|right|ISS was slowly assembled over a decade of spaceflights and crews]]
[[File:Tracy Caldwell Dyson in Cupola ISS.jpg|thumb|Expeditions have included male and female crew-members from many nations]]
''See also the [[list of International Space Station expeditions]] (professional crew), [[space tourism]] (private travellers), and the [[list of human spaceflights to the ISS]] (both).''

Each permanent crew is given an expedition number. Expeditions run up to six months, from launch until undocking, an 'increment' covers the same time period, but includes cargo ships and all activities. Expeditions 1 to 6 consisted of 3 person crews, Expeditions 7 to 12 were reduced to the safe minimum of two following the destruction of the NASA Shuttle Columbia. From Expedition 13 the crew gradually increased to 6 around 2010.<ref name="ISSEx">{{cite web|title=International Space Station Expeditions|publisher=NASA|url=http://www.nasa.gov/mission_pages/station/expeditions/index.html|date=10 April 2009|accessdate=13 April 2009}}</ref><ref name="current">{{cite web|url=http://www.nasa.gov/mission_pages/station/main/index.html|title=International Space Station|accessdate=22 October 2008|publisher=NASA|year=2008|author=NASA}}</ref> With the arrival of the American [[Commercial Crew Development|Commercial Crew]] vehicles in the middle of the 2010s, expedition size may be increased to seven crew members, the number ISS is designed for.<ref>{{cite web|url=http://www.aviationweek.com/article.aspx?id=/article-xml/asd_07_26_2012_p01-02-480253.xml|title=ISS Research Hampered By Crew Availability|last=Morring|first=Frank|date=27 July 2012|quote=A commercial capability would allow the station's crew to grow from six to seven by providing a four-seat vehicle for emergency departures in addition to the three-seat Russian Soyuz capsules in use today.|publisher=Aviation Week|accessdate=30 July 2012}}</ref><ref>{{cite web|url=http://www.airspacemag.com/space-exploration/AS-Interview-Mike-Suffredini.html|title=Assembly (Nearly) Complete |last=Hoversten|first=Paul|date=1 May 2011|publisher=Air & Space Magazine|quote=In fact, we're designed on the U.S. side to take four crew. The ISS design is actually for seven. We operate with six because first, we can get all our work done with six, and second, we don't have a vehicle that allows us to fly a seventh crew member. Our requirement for the new vehicles being designed is for four seats. So I don't expect us to go down in crew size. I would expect us to increase it.|accessdate=8 May 2011}}</ref>

[[Sergei Krikalev]], member of [[Expedition 1]] and Commander of [[Expedition 11]] has spent more time in space than anyone else, a total of 803 days and 9 hours and 39 minutes. His awards include the [[Order of Lenin]], [[Hero of the Soviet Union]], [[Hero of the Russian Federation]], and 4 NASA medals. On 16 August 2005 at 1:44 am EDT he passed the record of 748 days held by [[Sergei Avdeyev]], who had 'time travelled' 1/50th of a second into the future on board MIR.<ref>{{cite web|url=http://www.popsci.com/scitech/article/2002-02/lets-do-time-warp-again?page=2 |archiveurl=https://web.archive.org/web/20100628190931/http://www.popsci.com/scitech/article/2002-02/lets-do-time-warp-again?page=2 |archivedate=28 June 2010 |title=Let's Do the Time Warp Again |publisher=Web.archive.org |date=28 June 2010 |accessdate=1 May 2012}}</ref> He participated in psychosocial experiment SFINCSS-99 (Simulation of Flight of International Crew on Space Station), which examined inter-cultural and other stress factors affecting integration of crew in preparation for the ISS spaceflights. Commander [[Michael Fincke]] has spent a total of 382 days in space – more than any other American astronaut.

Travellers who pay for their own passage into space are termed spaceflight participants by Roscosmos and NASA, and are sometimes informally referred to as space tourists, a term they generally dislike.{{refn|Privately funded travellers who have objected to the term include Dennis Tito, the first such traveller (''Associated Press'', 8 May 2001), [[Mark Shuttleworth]], founder of [[Ubuntu (operating system)|Ubuntu]] (''Associated Press, The Spokesman Review, 6 January 2002, p. A4''), Gregory Olsen and Richard Garriott.<ref>{{cite news|last=Schwartz|first=John|title=Russia Leads Way in Space Tourism With Paid Trips into Orbit|url=http://www.nytimes.com/2008/10/11/science/space/11space.html|newspaper=The New York Times|date=10 October 2008}}</ref><ref>{{cite web|last=Boyle|first=Alan|title=Space passenger Olsen to pull his own weight|url=http://msnbc.msn.com/id/9323509/#.Tz5lcFE-qr4|publisher=MSNBC}}</ref> Canadian astronaut Bob Thirsk said the term does not seem appropriate, referring to his crewmate, [[Guy Laliberté]], founder of [[Cirque du Soleil]].<ref>{{cite web|url=http://www.stcatharinesstandard.ca/ArticleDisplay.aspx?e=1975186&archive=true |title=Flight to space ignited dreams | St. Catharines Standard |publisher=Stcatharinesstandard.ca |accessdate=1 May 2012}}</ref> Anousheh Ansari denied being a tourist<ref>{{cite web|url=http://www.esa.int/esaHS/SEMD58BE8YE_business_0.html |title=ESA – Human Spaceflight and Exploration – Business – "I am NOT a tourist" |publisher=Esa.int |date=18 September 2006 |accessdate=1 May 2012}}</ref> and took offence at the term.<ref>{{cite web|url=http://www.space.com/2889-interview-anousheh-ansari-female-space-tourist.html |title=Interview with Anousheh Ansari, the First Female Space Tourist |publisher=Space.com |date=15 September 2006 |accessdate=1 May 2012}}</ref>|group=note|name}} All seven were transported to the ISS on Russian Soyuz spacecraft. When professional crews change over in numbers not divisible by the three seats in a Soyuz, and a short-stay crewmember is not sent, the spare seat is sold by MirCorp through Space Adventures. When the space shuttle retired in 2011, and the station's crew size was reduced to 6, space tourism was halted, as the partners relied on Russian transport seats for access to the station. Soyuz flight schedules increase after 2013, allowing 5 Soyuz flights (15 seats) with only two expeditions (12 seats) required.<ref>{{cite web|url=http://www.spaceflightnow.com/news/n1101/12soyuz/ |title=Breaking News | Resumption of Soyuz tourist flights announced |publisher=Spaceflight Now |accessdate=1 May 2012}}</ref> The remaining seats are sold for around {{US$|40 million}} to members of the public who can pass a medical. ESA and NASA criticised private spaceflight at the beginning of the ISS, and NASA initially resisted training [[Dennis Tito]], the first man to pay for his own passage to the ISS.{{refn|ESA director Jörg Feustel-Büechl said in 2001 that Russia had no right to send 'amateurs' to the ISS. A 'stand-off' occurred at the Johnson Space Centre between Commander Talgat Musabayev and NASA manager Robert Cabana. Cabana refused to train Dennis Tito, a member of Musabayev's crew along with Yuri Baturin. The commander argued that Tito had trained 700 hours in the last year and was as qualified as any NASA astronaut, and refused to allow his crew to be trained on the American portions of the station without Tito. Cabana stated training could not begin, and the commander returned with his crew to their hotel.|group=note|name}}  [[Toyohiro Akiyama]] was flown to Mir for a week, he was classed as a business traveller, as his employer, [[Tokyo Broadcasting System]], paid for his ticket, and he gave a daily TV broadcast from orbit.

[[Anousheh Ansari]] ({{lang-fa|انوشه انصاری}}) became the first Iranian in space and the first self-funded woman to fly to the station. Officials reported that her education and experience make her much more than a tourist, and her performance in training had been "excellent."<ref>{{cite web|last=Maher |first=Heather |url=http://www.rferl.org/content/article/1071358.html |title=U.S.: Iranian-American To Be First Female Civilian in Space |publisher=Radio Free Europe/Radio Liberty |date=15 September 2006 |accessdate=1 May 2012}}</ref> Ansari herself dismisses the idea that she is a tourist. She did Russian and European studies involving medicine and microbiology during her 10-day stay. The documentary ''[[Space Tourists]]'' follows her journey to the station, where she fulfilled "an age-old dream of man: to leave our planet as a «normal person» and travel into outer space."<ref>{{cite web|url=http://www.space-tourists-film.com/en/film_synopsis.php |title=Space Tourists | A Film By Christian Frei |publisher=Space-tourists-film.com |accessdate=1 May 2012}}</ref> In the film, some Kazakhs are shown waiting in the middle of the steppes for four rocket stages to literally fall from the sky. Film-maker Christian Frei states "Filming the work of the Kazakh scrap metal collectors was anything but easy. The Russian authorities finally gave us a film permit in principle, but they imposed crippling preconditions on our activities. The real daily routine of the scrap metal collectors could definitely not be shown. Secret service agents and military personnel dressed in overalls and helmets were willing to ''re-enact'' their work for the cameras – in an idealised way that officials in Moscow deemed to be presentable, but not at all how it takes place in reality."

Spaceflight participant [[Richard Garriott]] placed a [[Geocaching|geocache]] aboard the ISS during his flight.<ref>{{cite web|url=http://www.geocaching.com/seek/cache_details.aspx?wp=GC1BE91|title=International Space Station Traditional Geocache}}</ref> This is currently the only non-terrestrial geocache in existence.<ref>{{cite web |url=http://www.geekwire.com/2011/outer-space-ocean-floor-15m-geocaches-counting/|accessdate=27 February 2013|last=Cook|first=John|title=From outer space to the ocean floor, Geocaching.com now boasts more than 1.5 million hidden treasures|date=29 August 2011}}</ref>

===Orbit===
{{Double image|right|Internationale Raumstation Bahnhöhe (dumb version).png|300|Iss.ogg|235|Graph showing the changing altitude of the ISS from November 1998 until January 2009|Animation of ISS orbit from a North American geostationary point of view (sped up 1800 times)}}
The ISS is maintained in a nearly circular orbit with a minimum mean altitude of 330 km (205 mi) and a maximum of 410 km (255 mi), in the centre of the [[thermosphere]], at an [[inclination]] of 51.6 degrees to Earth's equator, necessary to ensure that Russian [[Soyuz (spacecraft)|Soyuz]] and [[Progress (spacecraft)|Progress]] spacecraft launched from the [[Baikonur Cosmodrome]] may be safely launched to reach the station. Spent rocket stages must be dropped into uninhabited areas and this limits the directions rockets can be launched from the spaceport.<ref name="MCC Answer">{{cite web|last=Cooney|first=Jim|title=Mission Control Answers Your Questions|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-112/09_04_12_54_17.html|location=Houston, TX|quote=Jim Cooney ISS Trajectory Operations Officer}}</ref><ref>{{cite book|last=Pelt|first=Michel van|title=Into the Solar System on a String : Space Tethers and Space Elevators|year=2009|publisher=Springer New York|location=New York, NY|isbn=0-387-76555-7|page=133|edition=1.}}</ref> The orbital inclination chosen was also low enough to allow American space shuttles launched from Florida to reach the ISS.

It travels at an average speed of 27,724 kilometres (17,227 mi) per hour, and completes {{Orbit|daily orbits|15.54}} orbits per day (93 minutes per orbit).{{Orbit|ref|<ref name="heavens-above"/>}}<ref name="tracking">{{cite web|url=http://spaceflight.nasa.gov/realdata/tracking/index.html|title=Current ISS Tracking data|accessdate=28 January 2009|publisher=NASA|date=15 December 2008|author=NASA}}</ref> The station's altitude was allowed to fall around the time of each NASA shuttle mission. Orbital boost burns would generally be delayed until after the shuttle's departure. This allowed shuttle payloads to be lifted with the station's engines during the routine firings, rather than have the shuttle lift itself and the payload together to a higher orbit. This trade-off allowed heavier loads to be transferred to the station. After the retirement of the NASA shuttle, the nominal orbit of the space station was raised in altitude.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/06/europes-atv-2-depart-iss-make-way-russias-progress-m-11m/ |title=Europe's ATV-2 departs ISS to make way for Russia's Progress M-11M |publisher=NASASpaceFlight.com |date=20 June 2011 |accessdate=1 May 2012}}</ref><ref name="Popular Mechanics">{{cite web|url=http://www.popularmechanics.com/science/air_space/4275571.html|title=The Uncertain Future of the International Space Station: Analysis|author=Rand Simberg|date=29 July 2008|accessdate=6 March 2009|publisher=[[Popular Mechanics]]}}</ref> Other, more frequent supply ships do not require this adjustment as they are substantially lighter vehicles.<ref name="Worldbook at NASA">{{cite web|url=http://www.nasa.gov/worldbook/intspacestation_worldbook.html|title = International Space Station|year=2005|accessdate=14 June 2008|publisher=World Book, Inc|author=James Oberg|work=World Book Online Reference Center}}{{dead link|date=May 2012}}</ref><ref name="nasa.gov-iss-environment">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archiveurl=https://web.archive.org/web/20080213164432/http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archivedate=13 February 2008|title=ISS Environment|accessdate=15 October 2007|publisher=[[Johnson Space Center]]}}</ref>
[[File:ISS orbits 04132013.jpg|thumbnail|Orbits of the ISS, shown in April 2013]]
Orbital boosting can be performed by the station's two main engines on the ''[[Zvezda (ISS module)|Zvezda]]'' service module, or Russian or European spacecraft docked to Zvezda's aft port. The ATV has been designed with the possibility of adding a [[Automated Transfer Vehicle#ATV evolution proposals|second docking port]] to its other end, allowing it to remain at the ISS and still allow other craft to dock and boost the station. It takes approximately two orbits (three hours) for the boost to a higher altitude to be completed.<ref name="nasa.gov-iss-environment" /> In December 2008 NASA signed an agreement with the [[Ad Astra Rocket Company]] which may result in the testing on the ISS of a [[VASIMR]] plasma propulsion engine.<ref name="vasimr">{{cite web|url=http://www.adastrarocket.com/AdAstra-NASA_PR12Dec08.pdf|publisher=AdAstra Rocket Company|title=Press Release 121208|accessdate=7 December 2009|date=12 December 2008|format=PDF}}</ref> This technology could allow [[Orbital station-keeping|station-keeping]] to be done more economically than at present.<ref name="future-prop">{{cite web|url=http://www.nasa.gov/vision/space/travelinginspace/future_propulsion.html|title=Propulsion Systems of the Future|accessdate=29 May 2009|publisher=NASA}}</ref><ref>{{cite web|work=New Scientist|accessdate=7 October 2009|url=http://www.newscientist.com/article/dn17918-rocket-company-tests-worlds-most-powerful-ion-engine.html|title=Rocket company tests world's most powerful ion engine|author=David Shiga|date=5 October 2009}}</ref>

The Russian Orbital Segment contains the station's engines and control [[Bridge (nautical)|bridge]], which handles Guidance, Navigation and Control (ROS GNC) for the entire station.<ref name="Navigation">{{cite web|url=http://www.esa.int/export/esaHS/ESAOXX0VMOC_iss_0.html|title=DMS-R: ESA's Data Management System for the Russian Segment of the ISS}}</ref> Initially, Zarya, the first module of the station, controlled the station until a short time after the Russian service module Zvezda docked and was transferred control. Zvezda contains the ESA built DMS-R Data Management System.<ref name="EsaComputer">{{cite web|url=http://www.esa.int/esapub/onstation/onstation17/os17_chapter6.pdf|title=Exercising Control 49 months of DMS-R Operations}}</ref> Using two fault-tolerant computers (FTC), Zvezda computes the station's position and orbital trajectory using redundant Earth horizon sensors, Solar horizon sensors as well as Sun and star trackers. The FTCs each contain three identical processing units working in parallel and provide advanced fault-masking by majority voting. Zvezda uses gyroscopes and thrusters to turn itself around. Gyroscopes do not require propellant, rather they use electricity to 'store' momentum in flywheels by turning in the opposite direction to the station's movement. The USOS has its own computer controlled gyroscopes to handle the extra mass of that section. When gyroscopes 'saturate', reaching their maximum speed, thrusters are used to cancel out the stored momentum. During [[Expedition 10]], an incorrect command was sent to the station's computer, using about 14 kilograms of propellant before the fault was noticed and fixed. When attitude control computers in the ROS and USOS fail to communicate properly, it can result in a rare 'force fight' where the ROS GNC computer must ignore the USOS counterpart, which has no thrusters.<ref>{{cite web|url=http://pims.grc.nasa.gov/pimsdocs/public/ISS%20Handbook/hb_qs_vehicle_RussianUSGNCForceFight.pdf |title=Microsoft Word – hb_qs_vehicle_RussianUSGNCForceFight_pg1.doc |format=PDF |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://spaceflight.nasa.gov/spacenews/reports/issreports/2005/iss05-7.html|title = International Space Station Status Report #05-7|date=11 February 2005|publisher=NASA|accessdate=23 November 2008}}</ref><ref>{{cite book|title=Dynamics and Control of Attitude, Power, and Momentum for a Spacecraft Using Flywheels and Control Moment Gyroscopes|author=Carlos Roithmayr|format=PDF|year=2003|publisher=NASA|location=Langley Research Center|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030038806_2003038772.pdf|accessdate=12 July 2011}}</ref> When an ATV, NASA Shuttle, or Soyuz is docked to the station, it can also be used to maintain station attitude such as for troubleshooting. Shuttle control was used exclusively during [[STS-117|installation]] of the S3/S4 truss, which provides electrical power and data interfaces for the station's electronics.<ref>{{cite web|url=http://www.nasaspaceflight.com/2007/06/atlantis-ready-to-support-iss-troubleshooting/|title=Atlantis ready to support ISS troubleshooting|publisher=NASASPaceflight.com|author=Chris Bergin|accessdate=6 March 2009|date=14 June 2007}}</ref>

==Mission controls==
The components of the ISS are operated and monitored by their respective space agencies at [[Mission Control Center|mission control centres]] across the globe, including:
* Roscosmos's [[Mission Control Center#RKA Mission Control Center|Mission Control Center]] at [[Korolyov (city)|Korolyov]], Moscow Oblast, controls the [[Russian Orbital Segment]] which handles Guidance, Navigation & Control for the entire Station.,<ref name="Navigation" /><ref name="EsaComputer" /> in addition to individual Soyuz and Progress missions.<ref name="ISSRG" />
* ESA's [[ATV Control Centre]], at the [[Toulouse Space Centre]] (CST) in [[Toulouse]], France, controls flights of the unmanned European [[Automated Transfer Vehicle]].<ref name="ISSRG" />
* JAXA's [[JEM Control Center]] and [[HTV Control Center]] at [[Tsukuba Space Center]] (TKSC) in [[Tsukuba]], Japan, are responsible for operating the Japanese Experiment Module complex and all flights of the 'White Stork' HTV Cargo spacecraft, respectively.<ref name="ISSRG" />
* NASA's [[Christopher C. Kraft Jr. Mission Control Center|Mission Control Center]] at [[Lyndon B. Johnson Space Center]] in Houston, Texas, serves as the primary control facility for the United States segment of the ISS and also controlled the Space Shuttle missions that visited the station.<ref name="ISSRG">{{cite book|author=Gary Kitmacher|title=Reference Guide to the International Space Station| publisher =[[Apogee Books]]|location=Canada|year=2006|isbn=978-1-894959-34-6|issn=1496-6921|pages=71–80}}</ref>
* NASA's [[Payload Operations and Integration Center]] at [[Marshall Space Flight Center]] in [[Huntsville, Alabama]], coordinates payload operations in the USOS.<ref name="ISSRG" />
* ESA's [[Columbus Control Center|Columbus Control Centre]] at the [[German Aerospace Center|German Aerospace Centre]] (DLR) in [[Oberpfaffenhofen]], Germany, manages the European ''Columbus'' research laboratory.<ref name="ISSRG" />
* CSA's [[MSS Control]] at [[Saint-Hubert, Quebec]], Canada, controls and monitors the [[Mobile Servicing System]], or Canadarm2.<ref name="ISSRG" />
{{wide image|ISS Centers.svg|880px|Space centres involved with the ISS programme|alt=A world map highlighting the locations of space centres. See adjacent text for details.}}

===Repairs===
{{Main|Orbital Replacement Units|International Space Station maintenance}}
'''[[Orbital Replacement Units]]''' ('''ORUs''') are spare parts that can be readily replaced when a unit either passes its design life or fails. Examples of ORUs are pumps, storage tanks, controller boxes, antennas, and battery units. Some units can be replaced using robotic arms. Many are stored outside the station, either on small pallets called [[ExPRESS Logistics Carrier]]s (ELCs) or share larger platforms called [[External Stowage Platform]]s which also hold science experiments. Both kinds of pallets have electricity as many parts which could be damaged by the cold of space require heating. The larger logistics carriers also have computer local area network connections (LAN) and telemetry to connect experiments. A heavy emphasis on stocking the USOS with ORU's occurred around 2011, before the end of the NASA shuttle programme, as its commercial replacements, [[Cygnus (spacecraft)|Cygnus]] and [[Dragon (spacecraft)|Dragon]], carry one tenth to one quarter the payload.

[[File:ISS Unpressurized Platforms.png|thumb|Spare parts are called [[Orbit Replaceable Unit|ORU]]s; some are externally stored on pallets called [[ExPRESS Logistics Carrier|ELC]]s and [[External stowage platform|ESP]]s.]]

Unexpected problems and failures have impacted the station's assembly time-line and work schedules leading to periods of reduced capabilities and, in some cases, could have forced abandonment of the station for safety reasons, had these problems not been resolved. During [[STS-120]] in 2007, following the relocation of the P6 truss and solar arrays, it was noted during the redeployment of the array that it had become torn and was not deploying properly.<ref name="Astronauts notice tear in solar panel">{{cite news|url=http://www.redorbit.com/news/space/1123767/astronauts_notice_tear_in_solar_panel/index.html |title=Astronauts notice tear in solar panel|accessdate=30 October 2007|agency=Associated Press|date=30 October 2007|author=Liz Austin Peterson}}</ref> An EVA was carried out by [[Scott E. Parazynski|Scott Parazynski]], assisted by [[Douglas H. Wheelock|Douglas Wheelock]]. The men took extra precautions to reduce the risk of electric shock, as the repairs were carried out with the solar array exposed to sunlight.<ref name="Space Station's Damaged Panel Is Fixed">{{cite news|url=http://www.washingtonpost.com/wp-dyn/content/article/2007/11/03/AR2007110300227.html|title=Space Station's Damaged Panel Is Fixed|accessdate=4 November 2007|work=The Washington Post|date=4 November 2007|first=Rob|last=Stein}}</ref> The issues with the array were followed in the same year by problems with the starboard Solar Alpha Rotary Joint (SARJ), which rotates the arrays on the starboard side of the station. Excessive vibration and high-current spikes in the array drive motor were noted, resulting in a decision to substantially curtail motion of the starboard SARJ until the cause was understood. Inspections during EVAs on STS-120 and [[STS-123]] showed extensive contamination from metallic shavings and debris in the large drive gear and confirmed damage to the large metallic race ring at the heart of the joint, and so the joint was locked to prevent further damage.<ref name="joint-update">{{cite news|url=http://spaceflightnow.com/shuttle/sts123/080325sarj/index.html|title=Station chief gives detailed update on joint problem|accessdate=5 November 2008|author=William Harwood|publisher=CBS News & SpaceflightNow.com|date=25 March 2008}}</ref> Repairs to the joint were carried out during [[STS-126]] with lubrication of both joints and the replacement of 11 out of 12 trundle bearings on the joint.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts126/126_overview.html|title=Crew Expansion Prep, SARJ Repair Focus of STS-126|accessdate=5 November 2008|publisher=NASA|date=30 October 2008}}</ref><ref>{{cite news|url=http://www.spaceflightnow.com/shuttle/sts126/081118fd5/index.html|title=Astronauts prepare for first spacewalk of shuttle flight|date=18 November 2008|author=William Harwood|publisher=CBS News & SpaceflightNow.com|accessdate=22 November 2008}}</ref>

[[File:STS-120 EVA Scott Parazynski.jpg|thumb|While anchored on the end of the [[Orbiter Boom Sensor System|OBSS]], astronaut [[Scott Parazynski]] performs makeshift repairs to a US Solar array which damaged itself when unfolding, during [[STS-120]].|alt=Two black and orange solar arrays, shown uneven and with a large tear visible. A crew member in a spacesuit, attached to the end of a robotic arm, holds a latticework between two solar sails.]]
2009 saw damage to the S1 radiator, one of the components of the station's cooling system. The problem was first noticed in [[Soyuz spacecraft|Soyuz]] imagery in September 2008, but was not thought to be serious.<ref name="Radiator">{{cite web|url=http://www.nasaspaceflight.com/2009/04/iss-concern-s1-radiator-may-require-replacement-shuttle-mission/|author=Chris Bergin|date=1 April 2009|publisher=NASASpaceflight.com|title=ISS concern over S1 Radiator – may require replacement via shuttle mission|accessdate=3 April 2009}}</ref> The imagery showed that the surface of one sub-panel has peeled back from the underlying central structure, possibly due to micro-meteoroid or debris impact. It is also known that a Service Module thruster cover, jettisoned during an EVA in 2008, had struck the S1 radiator, but its effect, if any, has not been determined. On 15 May 2009 the damaged radiator panel's ammonia tubing was mechanically shut off from the rest of the cooling system by the computer-controlled closure of a valve. The same valve was used immediately afterwards to vent the ammonia from the damaged panel, eliminating the possibility of an ammonia leak from the cooling system via the damaged panel.<ref name="Radiator" />

Early on 1 August 2010, a failure in cooling Loop A (starboard side), one of two external cooling loops, left the station with only half of its normal cooling capacity and zero redundancy in some systems.<ref>{{cite web|url=http://spaceflightnow.com/news/n1007/31station/ |title=Problem forces partial powerdown aboard station |publisher=Spaceflightnow.com |date=31 July 2010 |accessdate=16 November 2010}}</ref><ref>{{cite web|url=http://www.spaceref.com/news/viewsr.html?pid=34622 |title=NASA ISS On-Orbit Status 1 August 2010 (early edition) |publisher=Spaceref.com |date=31 July 2010 |accessdate=16 November 2010}}</ref><ref>{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/systems/atcs.html |title=ISS Active Control System |publisher=Boeing |date=21 November 2006 |accessdate=16 November 2010}}</ref> The problem appeared to be in the ammonia pump module that circulates the ammonia cooling fluid. Several subsystems, including two of the four CMGs, were shut down.

Planned operations on the ISS were interrupted through a series of EVAs to address the cooling system issue. A first EVA on 7 August 2010, to replace the failed pump module, was not fully completed due to an ammonia leak in one of four quick-disconnects. A second EVA on 11 August successfully removed the failed pump module.<ref>[http://spaceflightnow.com/station/exp24/100810evapre/index.html Spaceflight Now] "Wednesday spacewalk to remove failed coolant pump"</ref><ref>[http://www.nasaspaceflight.com/2010/08/live-second-eva-with-pump-module-changeout/ NASA spaceflight 11 August] "Large success for second EVA as failed Pump Module is removed"</ref> A third EVA was required to restore Loop A to normal functionality.<ref>[http://spaceflightnow.com/station/exp24/100811eva2/index5.html Spaceflight Now 12 August] "Station's bad pump removed; more spacewalking ahead"</ref><ref>[http://www.nasaspaceflight.com/2010/08/iss-cooling-returning-normal-confirming-etcs-pm-success/ Spaceflight Now, 18 August] ISS cooling configuration returning to normal confirming ETCS PM success</ref>

The USOS's cooling system is largely built by the American company [[Boeing]],<ref>{{cite web|url=http://www.space.com/businesstechnology/international-space-station-complexities-100802.html|title=Cooling System Malfunction Highlights Space Station's Complexity|publisher=Space.com|date=2 August 2010}}</ref> which is also the manufacturer of the failed pump.<ref>{{cite web|url=http://spaceflightnow.com/news/n1007/31station/|title=Spacewalks needed to fix station cooling problem|publisher=Spaceflightnow|date=31 July 2010}}</ref>

An air leak from the USOS in 2004,<ref>{{cite news|url=http://www.msnbc.msn.com/id/3882962/|title=Crew finds 'culprit' in space station leak|publisher=MSNBC|date=11 January 2004|author=James Oberg|accessdate=22 August 2010}}</ref> the venting of fumes from an ''[[Elektron (ISS)|Elektron]]'' oxygen generator in 2006,<ref>{{cite news|url=http://spaceflightnow.com/station/exp13/060918elektron.html|title=Oxygen Generator Problem Triggers Station Alarm|publisher = CBS News through Spaceflight Now|date=18 September 2006|author=William Harwood|accessdate=24 November 2008}}</ref> and the failure of the computers in the ROS in 2007 during [[STS-117]] left the station without thruster, ''Elektron'', ''[[Vozdukh]]'' and other environmental control system operations, the root cause of which was found to be condensation inside the electrical connectors leading to a short-circuit.{{Citation needed|date=June 2011}}
[[File:STS-134 EVA4 view to the Russian Orbital Segment.jpg|thumb|right|In the foreground, a set of heat radiators]]
The four Main Bus Switching Units (MBSUs, located in the S0 truss), control the routing of power from the four solar array wings to the rest of the ISS. In late 2011 MBSU-1, while still routing power correctly, ceased responding to commands or sending data confirming its health, and was scheduled to be swapped out at the next available EVA. In each MBSU, two power channels feed 160V DC from the arrays to two DC-to-DC power converters (DDCUs) that supply the 124V power used in the station. A spare MBSU was already on board, but 30 August 2012 EVA failed to be completed when a bolt being tightened to finish installation of the spare unit jammed before electrical connection was secured.<ref>{{cite web|author=30 August 2012 by Pete Harding |url=http://www.nasaspaceflight.com/2012/08/astronaut-perform-first-post-shuttle-spacewalk-iss |title=Astronaut duo complete challenging first post-Shuttle US spacewalk on ISS |publisher=Nasaspaceflight.com |date=30 August 2012 |accessdate=22 October 2013}}</ref> The loss of MBSU-1 limits the station to 75% of its normal power capacity, requiring minor limitations in normal operations until the problem can be addressed.

On 5 September 2012, in a second, 6 hr, EVA to replace MBSU-1, astronauts Sunita Williams and Akihiko Hoshide successfully restored the ISS to 100% power.<ref>[http://spaceref.com/international-space-station/critical-space-station-spacewalk-a-success.html Spaceref.com Sept 5, 2012] Marc Boucher "Critical Space Station spacewalk a Success".</ref>
[[File:Astronaut Mike Hopkins on Dec. 24 Spacewalk.jpg|thumb|Mike Hopkins on his Christmas Eve spacewalk]]
On 24 December 2013, astronauts made a rare Christmas Eve space walk, installing a new ammonia pump for the station's cooling system. The faulty cooling system had failed earlier in the month, halting many of the station's science experiments. Astronauts had to brave a "mini blizzard" of ammonia while installing the new pump. It was only the second Christmas Eve spacewalk in NASA history.<ref>{{cite web|last=AP|title=Astronauts Complete Rare Christmas Eve Spacewalk|url=http://www.leaker.com/astronauts-complete-rare-christmas-eve-spacewalk/|publisher=Leaker|accessdate=24 December 2013|date=24 December 2013}}</ref>

[[File:Iss orbit and expeditions.png|thumb|Iss orbit with calendar of expeditions and modules]]

==Fleet operations==
:{{See also|List of human spaceflights to the International Space Station|List of unmanned spaceflights to the International Space Station}}
A wide variety of manned and unmanned spacecraft have supported the station's activities. 
[[Progress M-28M]] (ISS-60P) was the 62nd Progress spacecraft planned to arrive at the ISS, including [[Progress M-MIM2|M-MIM2]] and [[Progress M-SO1|M-SO1]] which installed modules. 35 flights of the retired NASA Space Shuttle were made to the station.<ref name="ISStD">{{cite web|url=http://spaceflight.nasa.gov/station/isstodate.html|title=The ISS to Date|accessdate=21 March 2011|publisher=NASA|date=9 March 2011|author=NASA}}</ref> [[Soyuz TMA-16M|TMA-16M]] is the 42nd Soyuz flight, and there have been 5 [[Automated Transfer Vehicle|European ATV]], 4 Japanese [[H-II Transfer Vehicle|Kounotori]] 'White Stork', 8 [[SpaceX]] [[Dragon (spacecraft)|Dragon]] and 4 OSC [[Cygnus (spacecraft)|Cygnus]] planned arrivals.

===Currently docked/berthed===
''See also the list of [[List of International Space Station expeditions|professional]] crew, [[Space tourism|private]] travellers, [[List of human spaceflights to the ISS|both]] or just [[List of unmanned spaceflights to the ISS|unmanned spaceflights]].''

;Key
{{legend|lightblue|Uncrewed cargoships are in light blue}}
{{legend|#cfc|Crewed spacecraft are in light green}}

{| class="wikitable" style="margin: 1em auto 1em auto;text-align: left; font-size: 95%;"
|-Currently Docked
|style="text-align:center; background:#BBB" colspan="3" | '''Spacecraft and mission'''
|style="text-align:center; background:#BBB"|'''Location'''
|style="text-align:center; background:#BBB"|'''Arrived''' ([[UTC]])
|style="text-align:center; background:#BBB"|'''Departure date'''
|- style="background:#cfc;"
| {{flagicon|RUS}}
| [[Soyuz TMA-16M]]
| [[Expedition 43]]/[[Expedition 44|44]]
| [[Poisk (ISS module)|Poisk]] zenith
| 28 March 2015
| 11 September 2015
|- style="background:lightblue;"
| {{flagicon|RUS}}
| [[Progress M-28M]]
| Progress 60 Cargo
| [[Pirs (ISS module)|Pirs]] nadir
| 5 July 2015
| 19 November 2015
|- style="background:#cfc;"
| {{flagicon|RUS}}
| [[Soyuz TMA-17M]]
| [[Expedition 44]]/[[Expedition 45|45]]
| [[Rassvet (ISS module)|Rassvet]] nadir
| 23 July 2015
| 22 December 2015
|}

===Scheduled launches and dockings/berthings===
* All dates are [[UTC]]. Dates are the earliest possible dates and may change.
* Forward ports are at the front of the station according to its normal direction of travel and orientation ([[Yaw, pitch and roll#Aircraft attitudes|attitude]]). Aft is at the rear of the station, used by spacecraft boosting the station's orbit. [[Nadir]] is closest the Earth, [[Zenith]] is on top.
* Spacecraft operated by government agencies are indicated with 'Gov' and under commercial arrangements are indicated with 'Com'.

;Key
{{legend|lightblue|Uncrewed cargoships are in light blue colour}}
{{legend|#cfc|Crewed spacecraft are in light green colour}}
{{legend|wheat|Modules are in wheat colour}}

{| class="wikitable" style="margin: 1em auto 1em auto;text-align: left; font-size: 95%;"
|+Planned Missions
|style="text-align:center; background:#BBB"|'''Launch''' ({{abbr|NET|Not Earlier Than}})
|style="text-align:center; background:#BBB"|'''Launch Vehicle'''
|style="text-align:center; background:#BBB"|'''Launch Site'''
|style="text-align:center; background:#BBB" colspan="3"| '''Launch Service Provider'''
|style="text-align:center; background:#BBB"|'''Payload'''
|style="text-align:center; background:#BBB"|'''Spacecraft'''
|style="text-align:center; background:#BBB"|'''Mission'''
|style="text-align:center; background:#BBB"|'''Docking / Berthing Port'''
|style="text-align:center; background:#BBB"|'''Ref.'''
|-
| nowrap| 19 August 2015
| nowrap| [[H-IIB]]
| nowrap| {{flagicon|JPN}} [[Tanegashima Space Center|Tanegashima]] [[Yoshinobu Launch Complex|LA-Y2]]
| nowrap| {{flagicon|JPN}}
| nowrap| Gov
| nowrap| [[JAXA]]
| style="background:lightblue;" nowrap| [[Kounotori 5|HTV-5]]
| nowrap| [[H-II Transfer Vehicle|HTV]]
| ISS Resupply
| nowrap| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule">{{cite web |url=http://spaceflightnow.com/launch-schedule/ |title=Launch Calendar |work=Spaceflight Now |date=28 March 2015 |accessdate=28 March 2015}}</ref><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 2 September 2015
| nowrap| [[Soyuz-FG]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:#cfc;" nowrap| [[Soyuz TMA-18M]]
| nowrap| [[Soyuz (spacecraft)|Soyuz]]
| [[Expedition 45]]/[[Expedition 46|46]] including [[European Space Agency|ESA]] [[Denmark|Danish]] Astronaut [[Andreas Mogensen]] and [[Kazakhstan]] cosmonaut [[Aydyn Aimbetov]].
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 1 October 2015
| nowrap| [[Soyuz-U]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:lightblue;" nowrap| [[Progress M-29M]]
| nowrap| [[Progress (spacecraft)|Progress]]
| ISS Resupply
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| NET September 2015 (TBD)
| nowrap|[[Falcon 9 v1.1]]
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 40|SLC-40]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[SpaceX]]
| style="background:lightblue;" nowrap| [[SpaceX CRS-8]]
| nowrap| [[Dragon (spacecraft)|Dragon]]
| ISS resupply. Will deliver [[Bigelow Expandable Activity Module|Bigelow Expandable Activity Module (BEAM)]] to the ISS.
| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| 21 November 2015
| nowrap| [[Soyuz-2 (rocket)|Soyuz-2.1a]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:lightblue;" nowrap| [[Progress MS-1]]
| nowrap| [[Progress (spacecraft)|Progress]]
| ISS Resupply. First launch of the new [[Progress (spacecraft)#Progress MS|Progress-MS]] variant.
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 3 December 2015
| nowrap| [[Atlas V]] 401
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 41|SLC-41]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[United Launch Alliance|ULA]]
| style="background:lightblue;" nowrap| [[Cygnus CRS Orb-4]]
| nowrap| [[Cygnus (spacecraft)|Cygnus]]
| ISS Resupply
| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/><ref>{{cite web|url=http://www.space.com/27962-cygnus-cargo-spacecraft-new-rocket.html |title=Private Cargo Spacecraft Gets New Rocket Ride After Accident |publisher=Space.com |date= |accessdate=2015-04-04}}</ref>
|-
| nowrap| 15 December 2015
| nowrap| [[Soyuz-FG]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:#cfc;" nowrap| [[Soyuz TMA-19M]]
| nowrap| [[Soyuz (spacecraft)|Soyuz]]
| [[Expedition 46]]/[[Expedition 47|47]]
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| NET December 2015 (TBD)
| nowrap|[[Falcon 9 v1.1]]
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[SpaceX]]
| style="background:lightblue;" nowrap| [[SpaceX CRS-9]]
| nowrap| [[Dragon (spacecraft)|Dragon]]
| ISS resupply. Will deliver the IDA-2 segment of the [[NASA Docking System]] to the ISS.
| nowrap| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |
url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|}

===Docking===
{{See also|Docking and berthing of spacecraft}}
[[File:Progress M-14M.jpg|thumb|The [[Progress M-14M]] resupply vehicle as it approaches the ISS in 2012. Over 50 unpiloted [[Progress (spacecraft)|Progress]] spacecraft have been sent with supplies during the lifetime of the station.]]
All Russian spacecraft and self-propelled modules are able to rendezvous and dock to the space station without human intervention using the [[Kurs (docking system)|Kurs]] docking system. Radar allows these vehicles to detect and intercept ISS from over 200 kilometres away. The European ATV uses star sensors and GPS to determine its intercept course. When it catches up it then uses laser equipment to [[Computer vision|optically]] recognise Zvezda, along with the Kurs system for redundancy.  Crew supervise these craft, but do not intervene except to send abort commands in emergencies. The Japanese [[H-II Transfer Vehicle]] parks itself in progressively closer orbits to the station, and then awaits 'approach' commands from the crew, until it is close enough for a robotic arm to grapple and berth the vehicle to the USOS. The American Space Shuttle was manually docked, and on missions with a [[Multi-Purpose Logistics Module|cargo container]], the container would be berthed to the Station with the use of manual robotic arms. Berthed craft can transfer [[International Standard Payload Rack]]s. Japanese spacecraft berth for one to two months. Russian and European Supply craft can remain at the ISS for six months,<ref>{{cite web|url=http://www.esa.int/esaMI/ATV/SEMBW0PR4CF_0.html |title=ESA — ATV — Crew role in mission control |publisher=Esa.int |date=2 March 2011 |accessdate=23 May 2011}}</ref><ref>{{cite web|url=http://www.esa.int/esaHS/ESA4ZJ0VMOC_iss_0.html |title=ESA — Human Spaceflight and Exploration — International Space Station — Automated Transfer Vehicle (ATV) |publisher=Esa.int |date=16 January 2009 |accessdate=23 May 2011}}</ref> allowing great flexibility in crew time for loading and unloading of supplies and trash. NASA Shuttles could remain docked for 11–12 days.<ref>{{cite web|url=http://www.boeing.com/news/frontiers/archive/2005/july/i_ids4.html|title=Space Shuttle upgrade lets astronauts at ISS stay in space longer|last=Memi|first=Ed|publisher=Boeing|accessdate=17 September 2011}}</ref>

The American manual approach to docking allows greater initial flexibility and less complexity. The downside to this mode of operation is that each mission becomes unique and requires specialised training and planning, making the process more labour-intensive and expensive. The Russians pursued an automated methodology that used the crew in override or monitoring roles. Although the initial development costs were high, the system has become very reliable with standardisations that provide significant cost benefits in repetitive routine operations.<ref>David C. Wo±nden and David K. Geller [http://www.usu.edu/mae/aerospace/publications/JDSC_RoadToAutonomy.pdf The Road to Autonomous Orbital Rendezvous]. Utah State University, Logan, Utah</ref> An automated approach could allow assembly of modules orbiting other worlds prior to crew arrival.

[[File:ISS and Endeavour seen from the Soyuz TMA-20 spacecraft 27.jpg|thumb|left|{{OV|105}}, [[ATV-2]], [[Soyuz TMA-21]] and [[Progress M-10M]] docked to the ISS during [[STS-134]], as seen from the departing [[Soyuz TMA-20]]|alt=A side-on view of the ISS showing a Space Shuttle docked to the forward end, an ATV to the aft end and Soyuz & Progress spacecraft projecting from the Russian segment.]]
Soyuz spacecraft used for crew rotation also serve as lifeboats for emergency evacuation; they are replaced every six months and have been used once to remove excess crew after the [[Space Shuttle Columbia disaster|Columbia disaster]].<ref>{{cite web|url=http://www.astronautix.com/flights/isseo6.htm |title=ISS EO-6 |publisher=Astronautix.com |accessdate=1 May 2012}}</ref> Expeditions require, on average, {{nowrap|2 722 kg}} of supplies, and {{As of|2011|03|09|lc=yes}}, crews had consumed a total of around {{nowrap|22 000 meals}}.<ref name="ISStD" /> Soyuz crew rotation flights and Progress resupply flights visit the station on average two and three times respectively each year,<ref name="Livelist">{{cite web|url=http://www.nasa.gov/mission_pages/station/resupply/index.html|archiveurl=https://web.archive.org/web/20080803015945/http://www.nasa.gov/mission_pages/station/resupply/index.html|archivedate=3 August 2008|title=Live listing of spacecraft operations|publisher=NASA|date=1 December 2009|accessdate=8 December 2009}}</ref> with the ATV and HTV planned to visit annually from 2010 onwards.{{Citation needed|date=January 2012}} Following retirement of the NASA Shuttle [[Cygnus spacecraft|Cygnus]] and [[SpaceX Dragon|Dragon]] were contracted to fly cargo to the station.<ref>{{cite web|author=Space Operations Mission Directorate|title=Human Space Flight Transition Plan|publisher=NASA|date=30 August 2006|url=http://www.nasa.gov/pdf/315546main_space_flight_transition_plan.pdf}}</ref><ref>{{cite press release|publisher=NASA|date=18 January 2006|title=NASA Seeks Proposals for Crew and Cargo Transportation to Orbit|url=http://www.spaceref.com/news/viewpr.html?pid=18791|accessdate=21 November 2006}}</ref>

From 26 February 2011 to 7 March 2011 four of the governmental partners (United States, ESA, Japan and Russia) had their spacecraft (NASA Shuttle, ATV, HTV, Progress and Soyuz) docked at the ISS, the only time this has happened to date.<ref>{{cite news|title=NASA proposes Soyuz photo op; shuttle launch readiness reviewed (UPDATED)|url=http://www.cbsnews.com/network/news/space/home/spacenews/files/b0e194a8338c336e823c03601f046707-157.html|publisher=CBS|accessdate=11 February 2011}}</ref> On 25 May 2012, [[SpaceX]] became the world's first privately held company to send cargo, via the [[Dragon (spacecraft)|Dragon spacecraft]], to the International Space Station.<ref name="NYT-20120525">{{cite news |last=Chang |first=Kenneth |title=Space X Capsule Docks at Space Station |url=http://www.nytimes.com/2012/05/26/science/space/space-x-capsule-docks-at-space-station.html |date=25 May 2012 |work=[[The New York Times]] |accessdate=25 May 2012 }}</ref>

===Launch and docking windows===
Prior to a ship's docking to the ISS, navigation and attitude control (GNC) is handed over to the ground control of the ships' country of origin. GNC is set to allow the station to drift in space, rather than fire its thrusters or turn using gyroscopes. The solar panels of the station are turned edge-on to the incoming ships, so residue from its thrusters does not damage the cells. When a NASA shuttle docked to the station, other ships were grounded, as the carbon wingtips, cameras, windows, and instruments aboard the shuttle were at too much risk from damage from thruster residue from other ships movements.

Approximately 30% of NASA shuttle launch delays were caused by poor weather. Occasional priority was given to the Soyuz arrivals at the station where the Soyuz carried crew with time-critical cargoes such as biological experiment materials, also causing shuttle delays. Departure of the NASA shuttle was often delayed or prioritised according to weather over its two landing sites.<ref>{{cite web |url=http://www.nasa.gov/home/hqnews/2009/may/HQ_09-118_Shuttle_Landing_Delayed.html |title=NASA's Space Shuttle Landing Delayed by Weather |publisher=NASA |first1=Katherine |last1=Trinidad |first2=Candrea |last2=Thomas |date=22 May 2009 |accessdate=26 June 2015}}</ref> Whilst the Soyuz is capable of landing anywhere, anytime, its planned landing time and place is chosen to give consideration to helicopter pilots and ground recovery crew, to give acceptable flying weather and lighting conditions. Soyuz launches occur in adverse weather conditions, but the cosmodrome has been shut down on occasions when buried by snow drifts up to 6 metres in depth, hampering ground operations.

==Life aboard==

===Crew activities===
[[File:Exp18home nasa big.jpg|thumb|Crewmember peers out of a window]]

A typical day for the crew begins with a wake-up at 06:00, followed by post-sleep activities and a morning inspection of the station. The crew then eats breakfast and takes part in a daily planning conference with Mission Control before starting work at around 08:10. The first scheduled exercise of the day follows, after which the crew continues work until 13:05. Following a one-hour lunch break, the afternoon consists of more exercise and work before the crew carries out its pre-sleep activities beginning at 19:30, including dinner and a crew conference. The scheduled sleep period begins at 21:30. In general, the crew works ten hours per day on a weekday, and five hours on Saturdays, with the rest of the time their own for relaxation or work catch-up.<ref>{{cite web|url=http://www.nasa.gov/pdf/287386main_110508_tl.pdf|title=ISS Crew Timeline|date=5 November 2008|accessdate=5 November 2008|publisher=NASA|format=PDF}}</ref>

The time zone used on board the ISS is [[Coordinated Universal Time]] (UTC). The windows are covered at night hours to give the impression of darkness because the station experiences 16 sunrises and sunsets a day. During visiting space shuttle missions, the ISS crew will mostly follow the shuttle's [[Mission Elapsed Time]] (MET), which is a flexible time zone based on the launch time of the shuttle mission.<ref>{{Cite web|title = NASA - Time in Space, A Space in Time|url = https://www.nasa.gov/mission_pages/station/research/news/time_in_space.html|website = www.nasa.gov|accessdate = 2015-05-05}}</ref><ref>{{Cite web|title = A Slice of Time Pie|url = https://web.archive.org/web/20130317075600/http://blogs.nasa.gov/cm/blog/ISS%20Science%20Blog/posts/post_1340820317951.html|date = 2013-03-17|accessdate = 2015-05-05}}</ref><ref>{{Cite web|title = Human Space Flight (HSF) - Crew Answers|url = http://spaceflight.nasa.gov/feedback/expert/answer/crew/sts-113/index_2.html|website = spaceflight.nasa.gov|accessdate = 2015-05-05}}</ref>

The station provides crew quarters for each member of the expedition's crew, with two 'sleep stations' in the ''Zvezda'' and four more installed in ''Harmony''.<ref>{{cite web|url=https://www.youtube.com/watch?v=Q4dG9vSyUFQ|title=At Home with Commander Scott Kelly (Video)|date=6 December 2010|publisher=NASA|accessdate=8 May 2011|location=International Space Station}}</ref><ref>{{cite web|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080013462_2008012884.pdf|title=International Space Station USOS Crew Quarters Development|first1=James Lee |last1=Broyan |first2=Melissa Ann |last2=Borrego |first3=Juergen F. |last3=Bahr|year=2008|publisher=SAE International|accessdate=8 May 2011}}</ref> The American quarters are private, approximately person-sized soundproof booths. The Russian crew quarters include a small window, but do not provide the same amount of ventilation or block the same amount of noise as their American counterparts. A crewmember can sleep in a crew quarter in a tethered sleeping bag, listen to music, use a laptop, and store personal items in a large drawer or in nets attached to the module's walls. The module also provides a reading lamp, a shelf and a desktop.<ref name="ESALife">{{cite web|url=http://www.esa.int/esaHS/ESAH1V0VMOC_astronauts_0.html|publisher=ESA|accessdate=28 October 2009|date=19 July 2004|title=Daily life}}</ref><ref name="NASACrewEquip">{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/126_payload.html|title=Station Prepares for Expanding Crew|publisher=NASA|first=Cheryl L. |last=Mansfield|date=7 November 2008|accessdate=17 September 2009}}</ref><ref name="CSALife">{{cite web|url=http://www.asc-csa.gc.ca/pdf/educator-liv_wor_iss.pdf|title=Living and Working on the International Space Station|accessdate=28 October 2009|publisher=CSA}}</ref> Visiting crews have no allocated sleep module, and attach a sleeping bag to an available space on a wall—it is possible to sleep floating freely through the station, but this is generally avoided because of the possibility of bumping into sensitive equipment.<ref name="SRLife">{{cite web|url=http://www.space.com/missionlaunches/090827-sts127-space-sleeping.html|title=Sleeping in Space is Easy, But There's No Shower|first=Tariq|last=Malik|accessdate=29 October 2009|date=27 July 2009|publisher=Space.com}}</ref> It is important that crew accommodations be well ventilated; otherwise, astronauts can wake up oxygen-deprived and gasping for air, because a bubble of their own exhaled carbon dioxide has formed around their heads.<ref name="ESALife" />
{{See also|Christmas on the International Space Station}}

===Food===
[[File:Meal STS127.jpg|thumb|alt=Nine astronauts seated around a table covered in open cans of food strapped down to the table. In the background a selection of equipment is visible, as well as the salmon-coloured walls of the Unity node.|The crews of [[STS-127]] and [[Expedition 20]] enjoy a meal inside ''Unity''.]]
{{See also|Space food}}

Most of the food on board is vacuum sealed in plastic bags. Cans are heavy and expensive to transport, so there are not as many. The preserved food is generally not held in high regard by the crew, and when combined with the reduced sense of taste in a microgravity environment,<ref name="ESALife" /> a great deal of effort is made to make the food more palatable. More spices are used than in regular cooking, and the crew looks forward to the arrival of any ships from Earth, as they bring fresh fruit and vegetables with them. Care is taken that foods do not create crumbs. Sauces are often used to ensure station equipment is not contaminated. Each crew member has individual food packages and cooks them using the on-board galley. The galley features two food warmers, a refrigerator added in November 2008, and a water dispenser that provides both heated and unheated water.<ref name="NASACrewEquip" /> Drinks are provided in dehydrated powder form and are mixed with water before consumption.<ref name="NASACrewEquip" /><ref name="CSALife" /> Drinks and soups are sipped from plastic bags with straws; solid food is eaten with a knife and fork, which are attached to a tray with magnets to prevent them from floating away. Any food that floats away, including crumbs, must be collected to prevent it from clogging up the station's air filters and other equipment.<ref name="CSALife" />

===Hygiene===
[[File:Zvezda toilet.jpg|thumb|right|upright|Space toilet in the [[Zvezda (ISS module)|Zvezda Service Module]]]]

Showers on space stations were introduced in the early 1970s on Skylab and Salyut 3.<ref name="livingandworking">Benson, Charles Dunlap and William David Compton. ''[http://history.nasa.gov/SP-4208/contents.htm Living and Working in Space: A History of Skylab]''. NASA publication SP-4208.</ref>{{rp|139}} By Salyut 6, in the early 1980s, the crew complained of the complexity of showering in space, which was a monthly activity.<ref name="Portree1995-86">{{cite book |url=http://history.nasa.gov/SP-4225/documentation/mhh/mirheritage.pdf |title=Mir Hardware Heritage |publisher=NASA |first=David S. F. |last=Portree |page=86 |date=March 1995 |id=Reference Publication 1357 |oclc=755272548}}</ref> The ISS does not feature a shower; instead, crewmembers wash using a water jet and wet wipes, with soap dispensed from a toothpaste tube-like container. Crews are also provided with rinseless shampoo and edible toothpaste to save water.<ref name="SRLife" /><ref>{{cite AV media |url=https://www.youtube.com/watch?v=uIjNfZbUYu8 |title=Karen Nyberg Shows How You Wash Hair in Space |publisher=NASA |work=YouTube.com |first=Karen |last=Nyberg |date=12 July 2013 |accessdate=6 June 2015}}</ref>

There are two [[space toilet]]s on the ISS, both of Russian design, located in ''[[Zvezda (ISS module)|Zvezda]]'' and ''[[Tranquility (ISS module)|Tranquility]]''.<ref name="NASACrewEquip" /> These Waste and Hygiene Compartments use a fan-driven suction system similar to the Space Shuttle Waste Collection System. Astronauts first fasten themselves to the toilet seat, which is equipped with spring-loaded restraining bars to ensure a good seal.<ref name="ESALife" /> A lever operates a powerful fan and a suction hole slides open: the air stream carries the waste away. Solid waste is collected in individual bags which are stored in an aluminium container. Full containers are transferred to Progress spacecraft for disposal.<ref name="NASACrewEquip" /><ref>{{cite web |first=Ed |last=Lu |title=Greetings Earthling |url=http://spaceflight.nasa.gov/station/crew/exp7/luletters/lu_letter9.html |date=8 September 2003 |accessdate=1 November 2009 |publisher=NASA}}</ref> Liquid waste is evacuated by a hose connected to the front of the toilet, with anatomically correct "urine funnel adapters" attached to the tube so both men and women can use the same toilet. Waste is collected and transferred to the Water Recovery System, where it is recycled back into drinking water.<ref name="CSALife" />

==Crew health and safety==
{{Main|Effect of spaceflight on the human body}}

===Radiation===
The ISS is partially protected from the space environment by the Earth's magnetic field. From an average distance of about {{convert|70,000|km|abbr=on}}, depending on Solar activity, the [[magnetosphere]] begins to deflect solar wind around the Earth and ISS. [[coronal mass ejection|Solar flares]] are still a hazard to the crew, who may receive only a few minutes warning. The crew of [[Expedition 10]] took shelter as a precaution in 2005 in a more heavily shielded part of the ROS designed for this purpose during the initial 'proton storm' of an X-3 class solar flare,<ref>{{cite web|title=Solar Flare Hits Earth and Mars|author=Ker Than|publisher=Space.com|date=23 February 2006|url=http://www.space.com/2080-solar-flare-hits-earth-mars.html}}</ref><ref>{{cite web|title=A new kind of solar storm|publisher=NASA|date=10 June 2005|url=http://science.nasa.gov/science-news/science-at-nasa/2005/10jun_newstorm/}}</ref> but without the limited protection of the Earth's [[magnetosphere]], interplanetary manned missions are especially vulnerable.

[[File:Aurora Australis.ogv|thumb|left|Video of the [[Aurora Australis]] taken by the crew of [[Expedition 28]] on an ascending pass from south of [[Madagascar]] to just north of Australia over the Indian Ocean.]]

Subatomic charged particles, primarily protons from [[cosmic ray]]s and [[solar wind]], are normally absorbed by the Earth's atmosphere. When they interact in sufficient quantity, their effect becomes visible to the naked eye in a phenomenon called an aurora. Without the protection of the Earth's atmosphere, which absorbs this radiation, crews are exposed to about 1 [[millisievert]] each day, which is about the same as someone would get in a year on Earth from natural sources. This results in a higher risk of astronauts developing cancer. Radiation can penetrate living tissue, damage DNA, and cause damage to the [[chromosome]]s of [[lymphocytes]]. These cells are central to the [[immune system]], and so any damage to them could contribute to the lowered [[immunity (medical)|immunity]] experienced by astronauts. Radiation has also been linked to a higher incidence of [[cataracts]] in astronauts. Protective shielding and protective drugs may lower the risks to an acceptable level.<ref name="JCB"/>

The radiation levels experienced on the ISS are about five times greater than those experienced by airline passengers and crew. The Earth's electromagnetic field provides almost the same level of protection against solar and other radiation in low Earth orbit as in the stratosphere. Airline passengers experience this level of radiation for no more than 15 hours for the longest intercontinental flights. For example, on a 12-hour flight an airline passenger would experience 0.1 millisieverts of radiation, or a rate of 0.2 millisieverts per day; only 1/5 the rate experienced by an astronaut in LEO.<ref>{{cite web|url=http://jag.cami.jccbi.gov./cariprofile.asp|title=Galactic Radiation Received in Flight|accessdate=20 May 2010|publisher=FAA Civil Aeromedical Institute}}</ref>
{{See also|Coronal mass ejection|Aurora (astronomy)}}

===Stress===
[[File:Nikolai Budarin in a sleep station in Zvezda.jpg|thumb|Cosmonaut [[Nikolai Budarin]] at work inside [[Zvezda (ISS module)|Zvezda]] service module crew quarters]]
There has been considerable evidence that psychosocial stressors are among the most important impediments to optimal crew morale and performance.<ref>{{cite book| author1 =Peter Suedfeld1| author2 = Kasia E. Wilk| author3 = Lindi Cassel| title = Flying with Strangers: Postmission Reflections of Multinational Space Crews}}</ref> Cosmonaut [[Valery Ryumin]], wrote in his journal during a particularly difficult period on board the [[Salyut 6]] space station: "All the conditions necessary for murder are met if you shut two men in a cabin measuring 18 feet by 20 and leave them together for two months."

NASA's interest in psychological stress caused by space travel, initially studied when their manned missions began, was rekindled when astronauts joined cosmonauts on the Russian space station Mir. Common sources of stress in early American missions included maintaining high performance under public scrutiny, as well as isolation from peers and family. The latter is still often a cause of stress on the ISS, such as when the mother of NASA Astronaut [[Daniel M. Tani|Daniel Tani]] died in a car accident, and when Michael Fincke was forced to miss the birth of his second child.


A study of the longest spaceflight concluded that the first three weeks represent a critical period where attention is adversely affected because of the demand to adjust to the extreme change of environment.<ref>{{cite doi|10.1080/001401398186991}}</ref> Skylab's 3 crews remained one, two, and three months respectively, long term crews on Salyut 6, [[Salyut 7]], and the ISS last about five to six months and Mir's expeditions often lasted longer. The ISS working environment includes further stress caused by living and working in cramped conditions with people from very different cultures who speak a different language. First generation space stations had crews who spoke a single language; second and third-generation stations have crew from many cultures who speak many languages. The ISS is unique because visitors are not classed automatically into 'host' or 'guest' categories as with previous stations and spacecraft, and may not suffer from feelings of isolation in the same way. Crew members with a military pilot background and those with an academic science background or teachers and politicians may have problems understanding each other's jargon and worldview.

===Medical===
[[File:Frank De Winne on treadmill cropped.jpg|thumb|Astronaut [[Frank De Winne]] is attached to the [[Treadmill with Vibration Isolation System|TVIS treadmill]] with bungee cords aboard the International Space Station|alt=Astronaut Frank De Winne is attached to the TVIS treadmill with bungee cords aboard the International Space Station]]
Medical effects of long-term weightlessness include [[muscle atrophy]], deterioration of the skeleton [[spaceflight osteopenia|(osteopenia)]], fluid redistribution, a slowing of the cardiovascular system, decreased production of red blood cells, balance disorders, and a weakening of the immune system. Lesser symptoms include loss of body mass, and puffiness of the face.<ref name="JCB" />

Sleep is disturbed on the ISS regularly due to mission demands, such as incoming or departing ships. Sound levels in the station are unavoidably high; because the atmosphere is unable to [[thermosiphon]], fans are required at all times to allow processing of the atmosphere which would stagnate in the freefall (zero-g) environment.

To prevent some of these adverse [[physiological]] effects, the station is equipped with two treadmills (including the [[Treadmill with Vibration Isolation System|COLBERT]]), and the aRED (advanced Resistive Exercise Device) which enables various weightlifting exercises which add muscle but do nothing for bone density,<ref>{{cite pmid|14600562}}</ref> and a stationary bicycle; each astronaut spends at least two hours per day exercising on the equipment.<ref name="ESALife" /><ref name="NASACrewEquip" /> Astronauts use bungee cords to strap themselves to the treadmill.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/bungee_running.html|accessdate=23 August 2009|title=Bungee Cords Keep Astronauts Grounded While Running|date=16 June 2009|publisher=NASA}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/colbert_feature.html|accessdate=23 August 2009|title=Do Tread on Me|date=19 August 2009|author=Amiko Kauderer|publisher=NASA}}</ref>

===Microbiological environmental hazards===
{{see also|Mir#Microbiological environmental hazards}}
Hazardous moulds which can foul air and water filters may develop aboard space stations. They can produce acids which degrade metal, glass, and rubber. They can also be harmful for the crew health. Microbiological hazards have led to a development of the [[LOCAD#Portable Test System|LOCAD-PTS]] that can identify common bacteria and moulds faster than standard methods of [[Cell culture|culturing]], which may require a sample to be sent back to Earth.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2007/11may_locad3/|author=Trudy E. Bell|year=2007|title=Preventing "Sick" Spaceships|access-date=March 29, 2015}}</ref> {{As of|2012}}, 76 types of unregulated micro-organisms have been detected on the ISS.<ref>{{cite web|url=http://rt.com/news/iss-bacteria-mir-mutation-765/|title=Mutant space microbes attack ISS: 'Munch' metal, may crack glass |author= |date=April 23, 2012|website=[[RT (TV network)|RT]]|access-date=March 29, 2015}}</ref>

Reduced humidity, paint with mould killing chemical and antiseptic solutions can be used to prevent contamination in space stations. All materials used in the ISS are tested for resistance against fungi.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2000/ast26nov_1/|author=Patrick L. Barry|year=2000|title=Microscopic Stowaways on the ISS|access-date=March 29, 2015}}</ref>

==Threat of orbital debris==
{{Main|Space debris}}
{{Double image|right|SDIO KEW Lexan projectile.jpg|225|Debris-GEO1280.jpg|225|A 7 gram object (shown in centre) shot at 7 km/s (23,000 ft/sec) (the orbital velocity of the ISS) made this 15 cm (5 7/8 in) crater in a solid block of aluminium.|[[Radar]]-trackable objects including debris, with distinct ring of [[Geostationary orbit|geostationary]] satellites||}}
At the low altitudes at which the ISS orbits there is a variety of space debris,<ref>{{cite web|url=http://defensenews.com/blogs/space-symposium/2009/04/03/its-getting-crowded-up-there/#more-155|publisher=Defense News|accessdate=7 October 2009|author=Michael Hoffman|title=National Space Symposium 2009: It's getting crowded up there|date=3 April 2009}}</ref> consisting of many different objects including entire spent rocket stages, defunct satellites, explosion fragments—including materials from [[anti-satellite weapon]] tests, paint flakes, slag from solid rocket motors, and coolant released by [[US-A]] nuclear-powered satellites. These objects, in addition to natural [[micrometeoroid]]s,<ref>{{cite journal|author=F. L. Whipple|year=1949|title=The Theory of Micrometeoroids|journal=Popular Astronomy|volume=57|page=517|bibcode=1949PA.....57..517W}}</ref> are a significant threat. Large objects could destroy the station, but are less of a threat as their orbits can be predicted.<ref name="NSFdebris">{{cite web|publisher=NASASpaceflight.com|accessdate=28 June 2011|date=28 June 2011|author=Chris Bergin|url=http://www.nasaspaceflight.com/2011/06/sts-135-frr-july-8-atlantis-debris-misses-iss/|title=STS-135: FRR sets 8 July Launch Date for Atlantis – Debris misses ISS}}</ref><ref>{{cite web|author=Henry Nahra|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19890016664_1989016664.pdf|title=Effect of Micrometeoroid and Space Debris Impacts on the Space Station Freedom Solar Array Surfaces|date=24–29 April 1989|publisher=NASA|accessdate=7 October 2009}}</ref> Objects too small to be detected by optical and radar instruments, from approximately 1 cm down to microscopic size, number in the trillions. Despite their small size, some of these objects are still a threat because of their [[kinetic energy]] and direction in relation to the station. Spacesuits of spacewalking crew could puncture, causing [[Space exposure|exposure to vacuum]].<ref name=debrisdecomp>{{cite web|title=Space Suit Punctures and Decompression|url=http://www.asi.org/adb/04/03/08/suit-punctures.html|publisher=The Artemis Project|accessdate=20 July 2011}}</ref>

The station's shields and structure are divided between the ROS and the USOS, with completely different designs. On the USOS, a thin aluminium sheet is held apart from the hull, the sheet causes objects to shatter into a cloud before hitting the hull thereby spreading the energy of the impact. On the ROS, a carbon plastic honeycomb screen is spaced from the hull, an aluminium honeycomb screen is spaced from that, with a screen-vacuum thermal insulation covering, and glass cloth over the top. It is about 50% less likely to be punctured,  and crew move to the ROS when the station is under threat. Punctures on the ROS would be contained within the panels which are 70 cm square.

[[File:ISS impact risk.jpg|thumb|left|Example of [[risk management]]: A NASA model showing areas at high risk from impact for the International Space Station.]]

Space debris objects are tracked remotely from the ground, and the station crew can be notified.<ref>{{cite web|url=http://www.orbitaldebris.jsc.nasa.gov/library/EducationPackage.pdf |title=Microsoft PowerPoint – EducationPackage SMALL.ppt |format=PDF |accessdate=1 May 2012}}</ref> This allows for a [[Debris Avoidance Manoeuvre]] (DAM) to be conducted, which uses thrusters on the Russian Orbital Segment to alter the station's orbital altitude, avoiding the debris. DAMs are not uncommon, taking place if computational models show the debris will approach within a certain threat distance. Eight DAMs had been performed prior to March 2009,<ref>{{cite web|url=http://www.newscientist.com/article/dn16777-space-station-may-move-to-dodge-debris.html|title=Space station may move to dodge debris|work=New Scientist|date=16 March 2009|accessdate=20 April 2010|author=Rachel Courtland}}</ref> the first seven between October 1999 and May 2003.<ref name=ODOct08>{{cite journal|url=http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv12i4.pdf|title=ISS Maneuvers to Avoid Russian Fragmentation Debris|publisher=NASA|pages=1&2|journal=Orbital Debris Quarterly News|date=October 2008|accessdate=20 April 2010|volume=12|issue=4}}</ref> Usually the orbit is raised by one or two kilometres by means of an increase in orbital velocity of the order of 1 m/s. Unusually there was a lowering of 1.7 km on 27 August 2008, the first such lowering for 8 years.<ref name=ODOct08 /><ref>{{cite web|url=http://www.esa.int/esaMI/ATV/SEM64X0SAKF_0.html|title=ATV carries out first debris avoidance manoeuvre for the ISS|publisher=ESA|date=28 August 2008|accessdate=26 February 2010}}</ref> There were two DAMs in 2009, on 22 March and 17 July.<ref>{{cite journal|url=http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv14i1.pdf|title=Avoiding satellite collisions in 2009|page=2|journal=Orbital Debris Quarterly News|publisher=NASA|volume=14|date=January 2010|issue=1|accessdate=20 April 2010}}</ref> If a threat from orbital debris is identified too late for a DAM to be safely conducted, the station crew close all the hatches aboard the station and retreat into their [[Soyuz spacecraft]], so that they would be able to evacuate in the event the station was seriously damaged by the debris. This partial station evacuation has occurred on 13 March 2009, 28 June 2011, 24 March 2012 and 16 June 2015.<ref>{{cite news| url=http://www.bbc.co.uk/news/science-environment-17497766| title=ISS crew take to escape capsules in space junk alert| accessdate=24 March 2012 |work=BBC News |date=24 March 2012}}</ref><ref>{{cite news| url=https://blogs.nasa.gov/spacestation/2015/07/16/station-crew-takes-precautions-for-close-pass-of-space-debris/| title=Station Crew Takes Precautions for Close Pass of Space Debris| accessdate=16 June 2015 |work=NASA Blog |date=16 June 2015}}</ref>
Ballistic panels, also called micrometeorite shielding, are incorporated into the station to protect pressurised sections and critical systems. The type and thickness of these panels varies depending upon their predicted exposure to damage.

==End of mission==
[[File:Jules Verne Automated Transfer Vehicle re-enters Earth's atmosphere.jpg|thumb|right|Many ISS resupply spacecraft have already undergone [[Atmospheric entry|atmospheric re-entry]], such as [[Jules Verne ATV]]]]
According to a 2009 report, [[S.P. Korolev Rocket and Space Corporation Energia|Space Corporation Energia]] is considering methods to remove from the station some modules of the Russian Orbital Segment when the end of mission is reached and use them as a basis for a new station, known as the [[Orbital Piloted Assembly and Experiment Complex]] (OPSEK). The modules under consideration for removal from the current ISS include the [[Multipurpose Laboratory Module]] (MLM), currently scheduled to be launched in 2017, with other Russian modules which are currently planned to be attached to the MLM afterwards. Neither the MLM nor any additional modules attached to it would have reached the end of their useful lives in 2016 or 2020. The report presents a statement from an unnamed Russian engineer who believes that, based on the experience from ''Mir'', a thirty-year life should be possible, except for micrometeorite damage, because the Russian modules have been built with on-orbit refurbishment in mind.<ref name="RussiaSave">{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8064060.stm|title=Russia 'to save its ISS modules'|work=BBC News|date=22 May 2009|accessdate=23 May 2009|author=Anatoly Zak}}</ref>

According to the [[Outer Space Treaty]] the United States and Russia are legally responsible for all modules they have launched.<ref>[http://www.unoosa.org/pdf/publications/STSPACE11E.pdf United Nations Treaties and Principles on Outer Space]. (PDF). United Nations. New York. 2002. ISBN 92-1-100900-6. Retrieved 8 October 2011.</ref> In ISS planning, NASA examined options including returning the station to Earth via shuttle missions (deemed too expensive, as the station (USOS) is not designed for disassembly and this would require at least 27 shuttle missions<ref>{{cite book|url=http://search.nap.edu/openbook.php?record_id=9794&page=28|isbn=0-309-06938-6|publisher=National Academies Press|year=2000|pages=28–30|author=Thomas Kelly|title=Engineering Challenges to the Long-Term Operation of the International Space Station|accessdate=12 July 2011}}</ref>), natural orbital decay with random reentry similar to [[Skylab]], boosting the station to a higher altitude (which would delay reentry) and a controlled targeted de-orbit to a remote ocean area.<ref name=ISSEIS>{{cite web|title = Tier 2 EIS for ISS|publisher = NASA|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960053133_1996092350.pdf|accessdate=12 July 2011 }}</ref>

The technical feasibility of a controlled targeted deorbit into a remote ocean was found to be possible only with Russia's assistance.<ref name=ISSEIS /> The Russian Space Agency has experience from de-orbiting the [[Salyut 4]], [[Salyut 5|5]], [[Salyut 6|6]], [[Salyut 7|7]] and [[Mir]] space stations; NASA's first intentional controlled de-orbit of a satellite (the [[Compton Gamma Ray Observatory]]) occurred in 2000.<ref>{{cite web|title=Entry Debris Field estimation methods and application to Compton Gamma Ray Observatory|publisher=Mission Operations Directorate, NASA Johnson Space Center|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010084992_2001127597.pdf|accessdate=12 July 2011}}</ref> As of late 2010, the preferred plan is to use a slightly modified Progress spacecraft to de-orbit the ISS.<ref name=deo>{{cite web|url=http://www.nasa.gov/pdf/578543main_asap_eol_plan_2010_101020.pdf|title=ISS End-of-Life Disposal Plan|last=Suffredini|first=Michael|date=October 2010|publisher=NASA|accessdate=7 March 2012}}</ref> This plan was seen as the simplest, most cost efficient one with the highest margin.<ref name=deo /> [[Skylab]], the only space station built and launched entirely by the US, decayed from orbit slowly over 5 years, and no attempt was made to de-orbit the station using a [[Atmospheric entry|deorbital burn]]. Remains of Skylab hit populated areas of [[Esperance, Western Australia]]<ref name="debris">{{cite web|url=http://www.eclipsetours.com/sat/debris.html|accessdate=28 May 2011|title=Paul Maley's (Skylab spaceflight controller) Space Debris Page}}</ref> without injuries or loss of life.

The [[Exploration Gateway Platform]], a discussion by NASA and Boeing at the end of 2011, suggested using leftover USOS hardware and '[[Zvezda (ISS module)|Zvezda]] 2' {{sic}} as a refuelling depot and servicing station located at one of the Earth Moon [[Lagrange points]], L1 or L2. The entire USOS cannot be reused and will be discarded, but some other Russian modules are planned to be reused. [[Nauka (ISS module)|Nauka]], the [[Uzlovoy Module|Node module]], two science power platforms and Rassvet, launched between 2010 and 2015 and joined to the ROS may be separated to form [[OPSEK]].<ref>{{cite web|url=http://www.russianspaceweb.com/iss_dc.html|title=DC-1 and MIM-2|publisher=Russianspaceweb.com|accessdate=12 July 2011}}</ref> The [[Nauka (ISS module)|Nauka module]] of the ISS will be used in the station, whose main goal is supporting manned deep space exploration. OPSEK will orbit at a higher inclination of 71 degrees, allowing observation to and from all of the Russian Federation.

In February 2015, Roscosmos announced that it would remain a part of the international space station program until 2024.<ref name=sn20150225>{{cite news |last1=de Selding|first1=Peter B. |title=Russia — and Its Modules — To Part Ways with ISS in 2024 |url=http://spacenews.com/russia-and-its-modules-to-part-ways-with-iss-in-2024/ |accessdate=26 February 2015 |work=Space News |date=25 February 2015}}</ref> Nine months earlier—in response to US sanctions against Russia over the [[2014 Crimean crisis|conflict in the Crimea]]—Russian Deputy Prime Minister [[Dmitry Rogozin]] had stated that Russia would reject a US request to prolong the orbiting station's use beyond 2020, and would only supply rocket engines to the US for non-military satellite launches.<ref>{{cite web|url=http://www.telegraph.co.uk/news/worldnews/europe/russia/10828964/Russia-to-ban-US-from-using-Space-Station-over-Ukraine-sanctions.html|title=Russia to ban US from using Space Station over Ukraine sanctions|agency=Reuters|work=The Telegraph|date=13 May 2014|accessdate=14 May 2014}}</ref>

A proposed modification that would allow some of the ISS American and European segments to be reused would be to attach a [[VASIMR]] drive module to the vacated Node with its own onboard power source. It would allow long term reliability testing of the concept for less cost than building a dedicated space station from scratch.<ref name="nbcnews">{{cite web|url=http://www.nbcnews.com/id/48260759/ns/technology_and_science-space/#.U4LaQCjFBdg|title=From the earth to the moon, and then beyond - Technology & science - Space | NBC News|publisher=nbcnews.com|accessdate=27 May 2014}}</ref>

On March 28, 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS.<ref name=":0"/><ref name=":1"/> [[Igor Komarov]], the head of Russia's Roscosmos, made the announcement with NASA administrator Charles Bolden at his side. Komarov said "Roscosmos together with NASA will work on the programme of a future orbital station," "We agreed that the group of countries taking part in the ISS project will work on the future project of a new orbital station," "The first step is that the ISS will operate until 2024," and that Roscosmos and NASA "do not rule out that the station's flight could be extended,"<ref>{{cite web|url=http://www.spacedaily.com/reports/Russia_announces_plan_to_build_new_space_station_with_NASA_999.html|title=Russia announces plan to build new space station with NASA|work=spacedaily.com}}</ref> In a statement provided to SpaceNews March 28, NASA spokesman David Weaver said the agency appreciated the Russian commitment to extending the ISS, but did not confirm any plans for a future space station.<ref name="no plans" />

==Cost==
The ISS is arguably the most expensive single item ever constructed.<ref>{{cite web|author=Zidbits |url=http://zidbits.com/?p=19 |title=What Is The Most Expensive Object Ever Built? |publisher=Zidbits.com |date=6 November 2010 |accessdate=22 October 2013}}</ref> In 2010 the cost was expected to be $150 billion. It includes NASA's budget of $58.7 billion (inflation unadjusted) for the station from 1985 to 2015 ($72.4 billion in 2010 dollars), Russia's $12 billion, Europe's $5 billion, Japan's $5 billion, Canada's $2 billion, and the cost of 36 shuttle flights to build the station; estimated at $1.4 billion each, or $50.4 billion total. Assuming 20,000 person-days of use from 2000 to 2015 by two to six-person crews, each person-day would cost $7.5 million, less than half the inflation adjusted $19.6 million ($5.5 million before inflation) per person-day of Skylab.<ref name="lafleur20100308">{{cite news | url=http://www.thespacereview.com/article/1579/1 | title=Costs of US piloted programs | work=The Space Review | date=8 March 2010 | accessdate=18 February 2012 | author=Lafleur, Claude}} See author correction in comments.</ref>

==International co-operation==
[[File:ISS Agreements.jpg|thumb|right|upright|Dated 29 January 1998]]
{{Main|Politics of the International Space Station|International Space Station program}}
;Participating countries
{{columns-list|colwidth=20em|

* '''{{flagcountry|Canada}}'''
* '''{{flagcountry|Japan}}'''
* '''{{flagcountry|Russia}}'''
* '''{{flagcountry|United States}}'''
* [[File:ESA logo simple.svg|15x15px]] '''[[European Space Agency]]'''
** {{flagcountry|Austria}}
** {{flagcountry|Belgium}}
** {{flagcountry|Czech Republic}}
** {{flagcountry|Denmark}}
** {{flagcountry|Estonia}}
** {{flagcountry|Finland}}
** {{flagcountry|France}}
** {{flagcountry|Germany}}
** {{flagcountry|Greece}}
** {{flagcountry|Hungary}}
** {{flagcountry|Ireland}}
** {{flagcountry|Italy}}
** {{flagcountry|Luxembourg}}
** {{flagcountry|Netherlands}}
** {{flagcountry|Norway}}
** {{flagcountry|Poland}}
** {{flagcountry|Portugal}}
** {{flagcountry|Romania}}
** {{flagcountry|Spain}}
** {{flagcountry|Sweden}}
** {{flagcountry|Switzerland}}
** {{flagcountry|United Kingdom}}
}}

==Sightings from Earth==

===Naked eye===
The ISS is visible to the [[naked eye]] as a slow-moving, bright white dot due to reflected sunlight, and can be seen in the hours after sunset and before sunrise when the station remains sunlit but the ground and sky are dark.<ref name="Price2005">{{cite book |title=The Backyard Stargazer: An Absolute Beginner's Guide to Skywatching With and Without a Telescope |publisher=Quarry Books |location=Gloucester, MA |first=Pat |last=Price |page=140 |year=2005 |isbn=1-59253-148-2}}</ref> The ISS takes about ten minutes to move from one horizon to another, and will only be visible part of that time due to moving into or out of the Earth's shadow. Because of the size of its reflective surface area, the ISS is the brightest man-made object in the sky excluding [[Satellite flare|flares]], with an approximate maximum [[Apparent magnitude|magnitude of −4]] when overhead, similar to Venus. The ISS, like many satellites including the [[Iridium constellation]], can also produce flares of up to 8 or 16 times the brightness of Venus as sunlight glints off reflective surfaces.<ref>{{cite web|url=http://www.calsky.com/cs.cgi/Satellites/8 |title=Artificial Satellites > (Iridium) Flares |publisher=Calsky.com |accessdate=1 May 2012}}</ref><ref name="haydenplanetarium">{{cite web|url=http://www.amnh.org/our-research/hayden-planetarium/blog/how-to-spot-the-international-space-station-and-other-satellites |title=How to Spot the International Space Station (and other satellites) |publisher=Hayden Planetarium |accessdate=12 July 2011}}</ref> The ISS is also visible during broad daylight conditions, albeit with a great deal more effort.

Tools are provided by a number of websites such as [[Heavens-Above]] (see [[#Live viewing|''Live viewing'']] below) as well as [[smartphone]] applications that use the known [[ephemeris|orbital data]] and the observer's longitude and latitude to predict when the ISS will be visible (weather permitting), where the station will appear to rise to the observer, the altitude above the horizon it will reach and the duration of the pass before the station disappears to the observer either by setting below the horizon or entering into Earth's shadow.<ref name="see">{{cite web|url=http://spaceflight.nasa.gov/realdata/sightings/index.html|title=International Space Station Sighting Opportunities|accessdate=28 January 2009|publisher=NASA|date=2 July 2008|author=NASA}}</ref><ref>{{cite web|url=http://www.heavens-above.com/satinfo.aspx?satid=25544&lat=0&lng=0&loc=Unspecified&alt=0&tz=CET|title=ISS – Information|publisher=Heavens-Above.com|accessdate=8 July 2010}}</ref><ref>{{cite journal|author=Harold F. Weaver|title=The Visibility of Stars Without Optical Aid|journal=Publications of the Astronomical Society of the Pacific|volume=59|issue=350|year=1947|doi=10.1086/125956 }}</ref><ref name="daytime visibility">{{cite web|url=http://spaceweather.com/archive.php?view=1&day=05&month=06&year=2009|title=ISS visible during the daytime|accessdate=5 June 2009|work=Spaceweather.com|date=5 June 2009}}</ref>

{{Double image|right|Isshtv120090917200858nm.jpg|223|ISS 2008-01-10.jpg|230|The ISS and HTV photographed using a telescope-mounted camera by [[Ralf Vandebergh]]|A time exposure of a station pass|A fuzzy image of the ISS set against a black background, with a smaller, cylindrical object visible to the left of the station.|A view of a dark blue, starry sky with a white line visible from the bottom-left to the top-right of the image. A tree is visible to the bottom right.}}

In November 2012 NASA launched its 'Spot the Station' service, which sends people text and email alerts when the station is due to fly above their town.<ref>{{cite news| url= http://www.3news.co.nz/Get-notified-when-the-International-Space-Station-is-in-your-area/tabid/1160/articleID/275612/Default.aspx|work=3 News NZ |title= Get notified when the International Space Station is in your area| date=6 November 2012}}</ref>

The station is visible from 95% of the inhabited land on Earth, but is not visible from extreme northern or southern latitudes.<ref name="MCC Answer" />

===Astrophotography=== 
Using a telescope mounted camera to photograph the station is a popular hobby for astronomers, <ref>{{cite web|url=http://www.hobbyspace.com/SatWatching/ |title=Satellite Watching |publisher=HobbySpace |accessdate=1 May 2012}}</ref> whilst using a mounted camera to photograph the Earth and stars is a popular hobby for crew.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2003/24mar_noseprints/ |title=Space StationAstrophotography – NASA Science |publisher=Science.nasa.gov |date=24 March 2003 |accessdate=1 May 2012}}</ref> The use of a telescope or binoculars allows viewing of the ISS during daylight hours.<ref>{{cite web|url=http://www.zmescience.com/space/video-the-iss-and-atlantis-shuttle-as-seen-in-broad-daylight/ |title=[VIDEO] The ISS and Atlantis shuttle as seen in broad daylight |publisher=Zmescience.com |date=20 July 2011 |accessdate=1 May 2012}}</ref>

Parisian engineer and astrophotographer Thierry Legault, known for his photos of spaceships crossing the Sun (called [[occultation]]), travelled to Oman in 2011, to photograph the Sun, moon and space station all lined up.<ref>{{cite news| url=http://www.wired.com/2011/01/double-eclipse/ | work=Wired | first=Lisa | last=Grossman | title=Moon and Space Station Eclipse the Sun}}</ref> Legault, who received the Marius Jacquemetton award from the [[Société astronomique de France]] in 1999, and other hobbyists, use websites that predict when the ISS will pass in front of the Sun or Moon and from what location those passes will be visible.

==See also==
{{Wikipedia books|International Space Station}}
{{Portal|Spaceflight|Space}}
* [[Center for the Advancement of Science in Space]] - operates the US National Laboratory on the ISS
* [[List of space stations]]
* [[Origins of the International Space Station]]
* [[Space architecture]]

==Gallery==
[[File:ISS and Endeavour seen from the Soyuz TMA-20 spacecraft 14.jpg|thumb|left|550px|<center>International Space Station docked with ''Endeavour'' and ''Johannes Kepler'' ]]
{{-}}

==Notes==
{{Reflist|group="note"}}

==References==
{{Reflist|colwidth=25em}}

==External links==
{{Sister project links|wikt=no|n=Category:International Space Station|voy=Space}}

===Agency ISS websites===
{{divcol|20em}}
* {{flagicon|Canada}} [http://www.asc-csa.gc.ca/eng/iss/default.asp Canadian Space Agency]
* [[File:Not the esa logo.png]] [http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station European Space Agency]
* {{flagicon|France}} [http://www.cnes.fr/web/CNES-en/1422-iss-the-international-space-station.php Centre national d'études spatiales (National Centre for Space Studies)]
* {{flagicon|Germany}} [http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10300 German Aerospace Centre]
* {{flagicon|Italy}} [http://www.asi.it/en/flash_en/living Italian Space Agency]
* {{flagicon|Japan}} [http://www.jaxa.jp/projects/iss_human/index_e.html Japan Aerospace Exploration Agency]
* {{flagicon|Russia}} [http://www.energia.ru/eng/iss/iss.html S.P. Korolev Rocket and Space Corporation Energia]
* {{flagicon|Russia}} [http://www.roscosmos.ru/ Russian Federal Space Agency]
* {{flagicon|USA}} [http://www.nasa.gov/mission_pages/station/main/ National Aeronautics and Space Administration]
{{Div col end}}

===Research===
* [https://blogs.nasa.gov/spacestation/ NASA: Daily ISS Reports]
* [http://www.nasa.gov/mission_pages/station/science/index.html NASA: Station Science]
* [http://www.esa.int/Our_Activities/Human_Spaceflight/Columbus ESA: Columbus]
* [http://www.energia.ru/en/iss/researches/iss-researches.html RSC Energia: Science Research on ISS Russian Segment]

===Live viewing===
{{See also|List of satellite pass predictors}}
* [http://www.ustream.tv/channel/live-iss-stream Live ISS webcam] by NASA at uStream.tv
* [http://heavens-above.com/orbit.aspx?satid=25544 Real-time position] at Heavens-above.com
* [http://www.n2yo.com/?s=25544 Real-time position] at N2YO.com
* [http://wheretheiss.at/ Real-time position] at WheretheISS.at

===Multimedia===
* [http://www.nasa.gov/externalflash/ISSRG/index.html Interactive reference guide] at NASA.gov
* [http://spaceflight.nasa.gov/gallery/images/station/ Image gallery search page] at NASA.gov
* [http://i.usatoday.net/tech/graphics/iss_timeline/flash.htm Assembly sequence animation] by ''USA Today'' and NASA
* [https://www.youtube.com/watch?v=doN4t5NKW-k ISS tour with Sunita Williams] by NASA at YouTube.com
* [https://www.youtube.com/watch?v=QF2w2Dx_QMs ISS tour with André Kuipers] by ESA at YouTube.com
* [http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station/Highlights/International_Space_Station_panoramic_tour ISS photo tour with Samantha Cristoforetti] by ESA
* [https://www.youtube.com/watch?v=vMmcLmu3V1k ''The Future of Hope'', Kibo module documentary] by JAXA at YouTube.com
* [https://www.youtube.com/playlist?list=PLbyvawxScNbsoD_tGlw8kWCw3S5htiVKZ Journey to the ISS] by ESA at YouTube.com

{{ISS modules}}
{{International Space Station}}
{{Manned ISS flight}}
{{Unmanned ISS resupply flights}}
{{People currently in space}}
{{Space stations}}
{{US manned space programs}}
{{Russian manned space programs}}
{{European manned spaceflight}}
{{Spaceflight}}
{{Orbital launches in 1998}}

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{{Authority control}}
[[Category:International Space Station| ]]
[[Category:Artificial satellites orbiting Earth]]
[[Category:Populated places established in 1998]]
[[Category:United States Department of Energy national laboratories]]
[[Category:Spacecraft launched in 1998]]
[[Category:1998 in spaceflight]]
[[Category:Articles containing video clips]]

User:WikipediaTutorials/sandbox

2015-08-25T02:21:12Z

WikipediaTutorials: added citation

{{redirect|ISS}}
{{Use British English|date=December 2013}}
{{Use dmy dates|date=February 2015}}
{{Infobox space station
| station = International Space Station
| station_image =International Space Station after undocking of STS-132.jpg
| station_image_alt = A rearward view of the International Space Station backdropped by the limb of the Earth. In view are the station's four large, gold-coloured solar array wings, two on either side of the station, mounted to a central truss structure. Further along the truss are six large, white radiators, three next to each pair of arrays. In between the solar arrays and radiators is a cluster of pressurised modules arranged in an elongated T shape, also attached to the truss. A set of blue solar arrays are mounted to the module at the aft end of the cluster.
| station_image_size = 300px
| extra_image_size = 300px
| extra_image_caption = The International Space Station on 23 May 2010 as seen from the departing {{OV|104}} during [[STS-132]].
| sign = ''Alpha'', ''Station''
| crew = Fully crewed: 6 Currently aboard: 6 ([[Expedition 44]])
| launch = 20 November 1998
| launch_pad = {{nowrap|[[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|1/5]] and [[Baikonur Cosmodrome Site 81|81/23]] [[Kennedy Space Center|Kennedy]] [[Kennedy Space Center Launch Complex 39|LC-39]]}}
| mass = Approximately {{convert|450000|kg|lbs|abbr=on}}
| length = {{convert|72.8|m|ft|abbr=on}}
| width = {{convert|108.5|m|ft|abbr=on}}
| height = c. 20 m (c. 66 ft) nadir–zenith, arrays forward–aft (27 November 2009){{Update after|2010|05|23|reason=MRM-1 & MRM-2}}
| volume = {{convert|916|m3|abbr=on}} (3 November 2014)
| pressure = 101.3 [[pascal (unit)|kPa]] (29.91 [[inch of mercury|inHg]], 1 [[Atmosphere (unit)|atm]])
| apogee = {{convert|{{Orbit|apogee|416}}|km|abbr=on}} [[Above mean sea level|AMSL]]{{Orbit|ref|<ref name="heavens-above">{{cite web|url=http://www.heavens-above.com/orbit.aspx?satid=25544|title=ISS - Orbit|last=Peat|first=Chris|publisher=Heavens-Above|date=25 January 2015|accessdate=25 January 2015}}</ref>}}
| perigee = {{convert|{{Orbit|perigee|409}}|km|abbr=on}} [[Above mean sea level|AMSL]]{{Orbit|ref|<ref name="heavens-above"/>}}
| inclination = {{Orbit|inclination|51.65}} [[degree (angle)|degrees]]{{Orbit|ref|<ref name="heavens-above"/>}}
| speed = {{convert|{{Orbit|speed at epoch|7.66}}|km/s|km/h mph}}{{Orbit|ref|<ref name="heavens-above"/>}}
| period = {{Orbit|period|92.69}} minutes{{Orbit|ref|<ref name="heavens-above"/>}}
| in_orbit = {{age in days|1998|11|20}} ({{date||dmy}})
| occupied = {{age in days|2000|11|02}} ({{date||dmy}})
| orbits = {{Orbit|orbits|92579}}{{Orbit|ref|<ref name="heavens-above"/>}}
| orbit_epoch = {{Orbit|epoch|25 January 2015}}{{Orbit|ref|<ref name="heavens-above"/>}}
| decay = 2 km/month
| NSSDC_ID = 1998-067A
| as_of = 9 March 2011 (unless noted otherwise)
| stats_ref =<ref name="heavens-above" /><ref name="ISStD" /><ref name="OnOrbit" /><ref>{{cite web|format=PDF|url=http://www.nasa.gov/pdf/451029main_sts132_press_kit.pdf|publisher=NASA|accessdate=19 June 2010|title=STS-132 Press Kit|date=7 May 2010}}</ref><ref>{{cite web|url=http://www.nasa.gov/pdf/521138main_fd04_ep.pdf|publisher=NASA|date=27 February 2011|accessdate=27 February 2011|title=STS-133 FD 04 Execute Package}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html|publisher=NASA|date=3 November 2014|accessdate=5 December 2014|title=NASA — Facts and Figures — International Space Station}}</ref>
| configuration_image = ISS configuration 2011-05 en.svg
| configuration_alt = The components of the ISS in an exploded diagram, with modules on-orbit highlighted in orange, and those still awaiting launch in blue or pink
| configuration_caption = Station elements {{As of|2011|12|lc=on}}, but missing ''Pirs'' ([[exploded view]])
| configuration_size = 300px
}}

The '''International Space Station''' ('''ISS''') is a [[space station]], or a habitable [[satellite|artificial satellite]], in [[low Earth orbit]]. Its first component launched into orbit in 1998, and the ISS is now the largest artificial body in orbit and can often be seen with the [[naked eye]] from Earth.<ref>{{cite web|title= Central Research Institute for Machine Building (FGUP TSNIIMASH) Control of manned and unmanned space vehicles from Mission Control Centre Moscow |publisher= Russian Federal Space Agency |url=ftp://130.206.92.88/Espacio/Mesa%20Redonda%205%20-%20R3%20-%20TSNIIMASH%20-%20V%20M%20IVANOV.pdf| accessdate=26 September 2011}}</ref><ref>{{cite web|url=http://spaceflight.nasa.gov/realdata/sightings/help.html |title=NASA Sightings Help Page |publisher=Spaceflight.nasa.gov |date=30 November 2011 |accessdate=1 May 2012}}</ref> The ISS consists of pressurised modules, external trusses, [[solar arrays]] and other components. ISS components have been launched by Russian [[Proton (rocket)|Proton]] and [[Soyuz (rocket family)|Soyuz]] rockets as well as American [[Space Shuttle]]s.<ref name="ISSBook">{{cite book|isbn=978-0-387-78144-0|date=17 June 2008|publisher=Springer-Praxis|author=John E. Catchpole|title=The International Space Station: Building for the Future}}</ref>

The ISS serves as a [[microgravity]] and [[space environment]] research laboratory in which crew members conduct experiments in [[biology]], [[human biology]], [[physics]], [[astronomy]], [[meteorology]] and [[Scientific research on the ISS|other fields]].<ref name="ISS overview">{{cite web|url=http://www.shuttlepresskit.com/ISS_OVR/index.htm|title=International Space Station Overview|publisher=ShuttlePressKit.com|date=3 June 1999|accessdate=17 February 2009}}</ref><ref name="NASA Fields of Research">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/A-fieldsresearch/index.html|archiveurl=https://web.archive.org/web/20080123150641/http://pdlprod3.hosc.msfc.nasa.gov/A-fieldsresearch/index.html|archivedate=25 March 2008|title=Fields of Research|date=26 June 2007|publisher = NASA}}</ref><ref name="NASA ISS Goals">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/B-gettingonboard/index.html|archiveurl=https://web.archive.org/web/20071208091537/http://pdlprod3.hosc.msfc.nasa.gov/B-gettingonboard/index.html|archivedate=8 December 2007| title = Getting on Board|date = 26 June 2007| publisher=NASA}}</ref> The station is suited for the testing of spacecraft systems and equipment required for missions to the [[Moon]] and Mars.<ref name="ResProg">{{cite web|url=http://spaceflightsystems.grc.nasa.gov/Advanced/ISSResearch/|title=ISS Research Program|publisher=NASA|accessdate=27 February 2009}}{{dead link|date=August 2011}}</ref> The ISS [[Orbital station-keeping|maintains an orbit with an altitude]] of between {{convert|330|and|435|km|mi|0|abbr=on}} by means of reboost manoeuvres using the engines of the [[Zvezda (ISS module)|Zvezda module]] or visiting spacecraft. It completes {{Orbit|daily orbits|15.54}} orbits per day.<ref name="tracking" />

ISS is the ninth space station to be inhabited by crews, following the Soviet and later Russian [[Salyut]], [[Almaz]], and [[Mir]] stations as well as [[Skylab]] from the US. The station has been continuously occupied for {{age in years and days|2 Nov 2000|sep=and}} since the arrival of [[Expedition 1]] on 2 November 2000. This is the longest continuous human presence in space, having surpassed the previous record of {{age in years and days|5 Sep 1989|28 Aug 1999|sep=and}} held by Mir. The station is serviced by a variety of visiting spacecraft: [[Soyuz (spacecraft)|Soyuz]], [[Progress (spacecraft)|Progress]], the [[Automated Transfer Vehicle]], the [[H-II Transfer Vehicle]],<ref name="ISSRG" /> [[Dragon (spacecraft)|Dragon]], and [[Cygnus (spacecraft)|Cygnus]]. It has been visited by astronauts, cosmonauts and space tourists from [[List of International Space Station visitors|15 different nations]].<ref name="10th">{{cite web|url=http://www.nasa.gov/mission_pages/station/main/10th_anniversary.html|title=Nations Around the World Mark 10th Anniversary of International Space Station|publisher=NASA|date=17 November 2008|accessdate=6 March 2009}}</ref>

After the US Space Shuttle program ended in 2011, Soyuz rockets became the only provider of transport for astronauts at the International Space Station, and Dragon became the only provider of bulk [[downmass|cargo-return-to-Earth]] services (downmass capability of Soyuz capsules is very limited).

The [[International Space Station program|ISS programme]] is a joint project among five participating space agencies: [[NASA]], [[Russian Federal Space Agency|Roscosmos]], [[Japan Aerospace Exploration Agency|JAXA]], [[European Space Agency|ESA]], and [[Canadian Space Agency|CSA]].<ref name="ISSRG" /><ref name="PartStates">{{cite web|url=http://www.esa.int/esaHS/partstates.html|title=Human Spaceflight and Exploration—European Participating States|accessdate=17 January 2009|publisher=European Space Agency (ESA)|year=2009}}</ref> The ownership and use of the space station is established by intergovernmental treaties and agreements.<ref name="ESA-IGA">{{cite web|url=http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station/International_Space_Station_legal_framework|title=International Space Station legal framework|publisher=European Space Agency (ESA)|accessdate=21 February 2015|date=19 November 2013}}</ref> The station is divided into two sections, the [[Russian Orbital Segment]] (ROS) and the [[US Orbital Segment|United States Orbital Segment]] (USOS), which is shared by many nations. {{asof|2014|January}}, the American portion of ISS was funded until 2024.<ref>{{cite web|url=http://www.washingtonpost.com/national/health-science/nasa-space-station-operation-extended-by-obama-until-2024-at-least/2014/01/08/9819d5c8-788e-11e3-8963-b4b654bcc9b2_story.html|title=NASA: International space station operation extended by Obama until at least 2024|last=Achenbach|first=Joel|publisher=washingtonpost.com|date=8 January 2014|accessdate=8 January 2014}}</ref><ref>{{cite web|url=http://spaceflightnow.com/news/n1003/11station/|title=Space station partners set 2028 as certification goal|last=Clark|first=Stephen|date=11 March 2010|publisher=Spaceflight Now|accessdate=1 June 2011}}</ref><ref>{{cite news| url=http://www.cbc.ca/news/technology/story/2012/02/29/science-international-space-station.html | work=CBC News | title=Canada's space station commitment renewed | date=29 February 2012}}</ref> Roscosmos has endorsed the continued operation of ISS through 2024,<ref name="sn20150225"/> but have proposed using elements of the Russian Orbital Segment to construct a new Russian space station called [[Orbital Piloted Assembly and Experiment Complex|OPSEK]].<ref name="moscow20141117">{{cite news |url=http://www.themoscowtimes.com/business/article/russia-may-be-planning-national-space-station-to-replace-iss/511299.html |title=Russia May Be Planning National Space Station to Replace ISS |work=The Moscow Times |first=Matthew |last=Bodner |date=17 November 2014 |accessdate=3 March 2015}}</ref>

On March 28, 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS.<ref name=":0">{{cite web|url= http://www.independent.co.uk/news/science/russia-and-the-us-will-build-a-new-space-station-together-10140890.html|title=Russia and the US will build a new space station together |publisher=The Independent|date=28 March 2015}}</ref><ref name=":1">{{Cite news|url = http://rt.com/news/244797-russia-us-new-space-station/|title = Russia & US agree to build new space station after ISS, work on joint Mars project|last = |first = |date = March 28, 2015|work = RT|access-date = March 28, 2015}}</ref> NASA later issued a guarded statement expressing thanks for Russia's interest in future cooperation in space exploration, but fell short of confirming the Russian announcement.<ref>{{Cite news|url = http://www.engadget.com/2015/03/28/nasa-is-working-with-russia-on-a-new-space-station/|title = NASA is working with Russia on a new space station (update: not quite) |last = Moon|first = Mariella|date = 28 March 2015|work = Engadget|access-date = 29 March 2015}}</ref><ref name="no plans">{{cite web|url=http://spacenews.com/nasa-says-no-plans-for-iss-replacement-with-russia/|title=NASA Says No Plans for ISS Replacement with Russia|date=March 28, 2015|author=Jeff Foust|publisher=SpaceNews}}</ref>

{{TOC limit|limit=3}}

==Purpose==
[[File:STS-129 Zvezda sunrise.jpg|thumb|Sunrise at ''Zvezda'']]
[[File:STS-134 EVA4 view to the Space Shuttle Endeavour.jpg|thumb|right|Fisheye view of several labs]]
According to the original Memorandum of Understanding between NASA and Rosaviakosmos, the International Space Station was intended to be a laboratory, observatory and factory in [[low Earth orbit]]. It was also planned to provide transportation, maintenance, and act as a staging base for possible future missions to the Moon, Mars and asteroids.<ref name="RSA-MOU">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/nasa_rsa.html|title=Memorandum of Understanding Between the National Aeronautics and Space Administration of the United States of America and the Russian Space Agency Concerning Cooperation on the Civil International Space Station|publisher=NASA|accessdate=19 April 2009|date=29 January 1998}}</ref> In the 2010 United States National Space Policy, the ISS was given additional roles of serving commercial, diplomatic<ref>{{cite journal|last=Payette|first=Julie|title=Research and Diplomacy 350 Kilometers above the Earth: Lessons from the International Space Station|journal=Science & Diplomacy|date=10 December 2012|volume=1|issue=4|url=http://www.sciencediplomacy.org/article/2012/research-and-diplomacy-350-kilometers-above-earth}}</ref> and educational purposes.<ref name=USNSP>{{cite web|title=National Space Policy of the United States of America|url=http://www.whitehouse.gov/sites/default/files/national_space_policy_6-28-10.pdf|publisher=White House; USA Federal government|accessdate=20 July 2011}}</ref>

===Scientific research===
{{Main|Scientific research on the ISS|l1=Scientific research on the ISS}}
The ISS provides a platform to conduct scientific research. Small unmanned spacecraft can provide platforms for zero gravity and exposure to space, but space stations offer a long term environment where studies can be performed potentially for decades, combined with ready access by human researchers over periods that exceed the capabilities of manned spacecraft.<ref name="10th" /><ref name="Worldbook at NASA" />

The Station simplifies individual experiments by eliminating the need for separate rocket launches and research staff. The wide variety of research fields include [[astrobiology]], [[astronomy]], [[Zero g#Health effects of weightlessness|human research]] including [[space medicine]] and [[life science]]s, [[physical science]]s, [[materials science]], [[space weather]], and weather on Earth ([[meteorology]]).<ref name="ISS overview" /><ref name="NASA Fields of Research" /><ref name="NASA ISS Goals" /><ref>{{cite web|url=http://www.isas.jaxa.jp/e/forefront/2009/ueno/index.shtml|title=Monitor of All-sky X-ray Image (MAXI)|year=2008|publisher=JAXA|accessdate=12 March 2011}}</ref><ref>[http://www.spaceref.com/news/viewpr.html?pid=33007 ESA via SPACEREF] "SOLAR: three years observing and ready for solar maximum", 14 March 2011</ref> Scientists on Earth have access to the crew's data and can modify experiments or launch new ones, which are benefits generally unavailable on unmanned spacecraft.<ref name="Worldbook at NASA" /> Crews fly [[List of International Space Station expeditions|expeditions]] of several months duration, providing approximately 160-man-hours per week of labour with a crew of 6.<ref name="ISS overview"/><ref name="Science in School">{{cite web|url=http://www.scienceinschool.org/2008/issue10/iss|title=The International Space Station: life in space|publisher=Science in School|date=10 December 2008|accessdate=17 February 2009}}</ref>

To detect dark matter and answer other fundamental questions about our universe, engineers and scientists from all over the world built the [[Alpha Magnetic Spectrometer]] (AMS), which NASA compares to the [[Hubble space telescope]], and says could not be accommodated on a free flying satellite platform due in part to its power requirements and data bandwidth needs.<ref>[http://www.nasa.gov/mission_pages/shuttle/main/amsprocessing.html NASA – AMS to Focus on Invisible Universe]. Nasa.gov (18 March 2011). Retrieved 8 October 2011.</ref><ref>[http://science.nasa.gov/science-news/science-at-nasa/2009/14aug_ams/ In Search of Antimatter Galaxies – NASA Science]. ''Science''.nasa.gov (16 May 2011). Retrieved 8 October 2011.</ref> On 3 April 2013, [[NASA]] scientists reported that hints of [[dark matter]] may have been detected by the Alpha Magnetic Spectrometer.<ref name="APS-20130403">{{cite journal |authors=Aguilar, M. et al. (AMS Collaboration) |title=First Result from the Alpha Magnetic Spectrometer on the International Space Station: Precision Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–350 GeV|url=http://prl.aps.org/abstract/PRL/v110/i14/e141102 |date=3 April 2013 |journal=[[Physical Review Letters]]|accessdate=3 April 2013 |doi=10.1103/PhysRevLett.110.141102 }}</ref><ref name="AMS-20130403">{{cite web |author=Staff |title=First Result from the Alpha Magnetic Spectrometer Experiment|url=http://www.ams02.org/2013/04/first-results-from-the-alpha-magnetic-spectrometer-ams-experiment/ |date=3 April 2013 |work=AMS Collaboration |accessdate=3 April 2013 }}</ref><ref name="AP-20130403">{{cite news |last1=Heilprin|first1=John |last2=Borenstein |first2=Seth |title=Scientists find hint of dark matter from cosmos|url=http://apnews.excite.com/article/20130403/DA5E6JAG3.html |date=3 April 2013 |agency=Associated Press |accessdate=3 April 2013 }}</ref><ref name="BBC-20130403">{{cite news |last=Amos |first=Jonathan |title=Alpha Magnetic Spectrometer zeroes in on dark matter |url=http://www.bbc.co.uk/news/science-environment-22016504 |date=3 April 2013 |work=[[BBC News]] |accessdate=3 April 2013 }}</ref><ref name="NASA-20130403">{{cite web |last1=Perrotto|first1=Trent J. |last2=Byerly |first2=Josh |title=NASA TV Briefing Discusses Alpha Magnetic Spectrometer Results|url=http://www.nasa.gov/home/hqnews/2013/apr/HQ_M13-054_AMS_Findings_Briefing.html |date=2 April 2013|work=[[NASA]] |accessdate=3 April 2013 }}</ref><ref name="NYT-20130403">{{cite news |last=Overbye |first=Dennis |title=New Clues to the Mystery of Dark Matter |url=http://www.nytimes.com/2013/04/04/science/space/new-clues-to-the-mystery-of-dark-matter.html |date=3 April 2013 |work=[[The New York Times]] |accessdate=3 April 2013 }}</ref> According to the scientists, "[[Alpha Magnetic Spectrometer#First results|The first results]] from the space-borne Alpha Magnetic Spectrometer confirm an unexplained excess of high-energy positrons in Earth-bound cosmic rays."

{{Double image|right|Iss030e015472 Edit.jpg|117|ISS-08 Michael Foale conducts an inspection of the Microgravity Science Glovebox.jpg|241|[[C/2011 W3 (Lovejoy)|Comet Lovejoy]] photographed by [[Expedition 30]] commander [[Dan Burbank]]|[[Expedition 8]] Commander and Science Officer [[Michael Foale]] conducts an inspection of the [[Microgravity Science Glovebox]]}}
The space environment is hostile to life. Unprotected presence in space is characterised by an intense radiation field (consisting primarily of protons and other subatomic charged particles from the [[solar wind]], in addition to [[cosmic ray]]s), high vacuum, extreme temperatures, and microgravity.<ref name="Space Microbiology">{{cite web|url=http://syntheticbiology.arc.nasa.gov/files/SpaceMicrobiology%20MMBR%201.pdf|title=Space Microbiology, section Space Environment (p. 122)|publisher=Microbiology and Molecular Biology Reviews|date=March 2010|accessdate=4 June 2011|author=G Horneck, DM Klaus & RL Mancinelli}}</ref> Some simple forms of life called [[extremophile]]s,<ref name="Beer microbes">{{cite news|url=http://www.bbc.co.uk/news/science-environment-11039206|title=Beer microbes live 553 days outside ISS|work=[[BBC News]]|date=23 August 2010|accessdate=4 June 2011|author=Jonathan Amos}}</ref> including small invertebrates called [[tardigrade]]s<ref name="Waterbears">{{cite web|url=http://www.nature.com/news/2008/080908/full/news.2008.1087.html|title=Spacesuits optional for 'water bears'|work=Nature|date=8 September 2008|accessdate=4 June 2011}}</ref> can survive in this environment in an extremely dry state called [[Desiccation#Biology and ecology|desiccation]].

Medical research improves knowledge about the effects of long-term space exposure on the human body, including [[muscle atrophy]], [[Osteoporosis|bone loss]], and fluid shift. This data will be used to determine whether lengthy [[human spaceflight]] and [[space colonisation]] are feasible. As of 2006, data on bone loss and muscular atrophy suggest that there would be a significant risk of fractures and movement problems if astronauts landed on a planet after a lengthy interplanetary cruise, such as the six-month interval required to [[Manned mission to Mars|travel to Mars]].<ref name="JCB">{{cite book|author=Jay Buckey|title=Space Physiology|publisher=Oxford University Press USA|date=23 February 2006|isbn=978-0-19-513725-5}}</ref><ref>{{cite web|url=http://www.newscientist.com/article/dn17476-ion-engine-could-one-day-power-39day-trips-to-mars.html?full=true|work=New Scientist|accessdate=8 January 2010|date=24 July 2009|author=List Grossman|title=Ion engine could one day power 39-day trips to Mars}}</ref>
Medical studies are conducted aboard the ISS on behalf of the [[National Space Biomedical Research Institute]] (NSBRI). Prominent among these is the [[Advanced Diagnostic Ultrasound in Microgravity]] study in which astronauts perform ultrasound scans under the guidance of remote experts. The study considers the diagnosis and treatment of medical conditions in space. Usually, there is no physician on board the ISS and diagnosis of medical conditions is a challenge. It is anticipated that remotely guided ultrasound scans will have application on Earth in emergency and rural care situations where access to a trained physician is difficult.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/science/experiments/ADUM.html|date=1 May 2009|accessdate=1 October 2009|author=Brooke Boen|publisher=NASA|title=Advanced Diagnostic Ultrasound in Microgravity (ADUM)}}</ref><ref>{{cite journal|author=Sishir Rao|display-authors=etal|year=2008|title=A Pilot Study of Comprehensive Ultrasound Education at the Wayne State University School of Medicine|journal=Journal of Ultrasound in Medicine|volume=27|pages=745–749|pmid=18424650|issue=5}}</ref><ref>{{cite journal|author=Michael Fincke|display-authors=etal|year=2004|title=Evaluation of Shoulder Integrity in Space: First Report of Musculoskeletal US on the International Space Station|journal=Radiology|issue= 2|pages=319–322|pmid=15533948|doi=10.1148/radiol.2342041680|volume=234}}</ref>

====Microgravity====
[[File:Space Fire.jpg|thumb|A comparison between the combustion of a candle on [[Earth]] (left) and in a microgravity environment, such as that found on the ISS (right)]]
The Earth's gravity is only slightly weaker at the altitude of the ISS than at the surface, but objects in orbit are in a continuous state of [[Free fall|freefall]], resulting in an apparent state of weightlessness. This perceived weightlessness is disturbed by five separate effects:<ref name="gravity">{{cite web|url=http://www.esa.int/Our_Activities/Human_Spaceflight/Human_Spaceflight_Research/European_User_Guide_to_Low-Gravity_Platforms
|title=European Users Guide to Low Gravity Platforms|accessdate=22 March 2013|date=6 December 2005|publisher=European Space Agency}}</ref>
* Drag from the residual atmosphere; when the ISS enters the Earth's shadow, the main solar panels are rotated to minimise this aerodynamic drag, helping reduce [[orbital decay]].
* Vibration from movements of mechanical systems and the crew.
* Actuation of the on-board attitude [[control moment gyroscope]]s.
* [[Rocket engine|Thruster]] firings for attitude or orbital changes.
* [[Gravity-gradient stabilization|Gravity-gradient effects]], also known as [[tidal force|tidal]] effects. Items at different locations within the ISS would, if not attached to the station, follow slightly different orbits. Being mechanically interconnected these items experience small forces that keep the station moving as a [[rigid body]].

[[File:ISS-20 Robert Thirsk at the Minus Eighty Degree Laboratory Freezer.jpg|thumb|left|ISS crew member storing samples]]

Researchers are investigating the effect of the station's near-weightless environment on the evolution, development, growth and internal processes of plants and animals. In response to some of this data, NASA wants to investigate [[microgravity]]'s effects on the growth of three-dimensional, human-like tissues, and the unusual [[protein crystal]]s that can be formed in space.<ref name="NASA Fields of Research" />

The investigation of the physics of fluids in microgravity will allow researchers to model the behaviour of fluids better. Because fluids can be almost completely combined in microgravity, physicists investigate fluids that do not mix well on Earth. In addition, an examination of reactions that are slowed by low gravity and temperatures will give scientists a deeper understanding of [[superconductivity]].<ref name="NASA Fields of Research" />

The study of [[materials science]] is an important ISS research activity, with the objective of reaping economic benefits through the improvement of techniques used on the ground.<ref>{{cite web|url=http://science.nasa.gov/newhome/headlines/msad15sep99_1.htm|title=Materials Science 101|publisher=Science@NASA|accessdate=18 June 2009|date=15 September 1999}}</ref> Other areas of interest include the effect of the low gravity environment on combustion, through the study of the efficiency of burning and control of emissions and pollutants. These findings may improve current knowledge about energy production, and lead to economic and environmental benefits. Future plans are for the researchers aboard the ISS to examine [[aerosol]]s, [[ozone]], [[water vapour]], and [[oxide]]s in Earth's atmosphere, as well as [[cosmic ray]]s, [[cosmic dust]], [[antimatter]], and [[dark matter]] in the universe.<ref name="NASA Fields of Research" />

===Exploration===
[[File:Mars500.jpg|thumb|right|A 3D plan of the Russia-based [[MARS-500]] complex, used for ground-based experiments which complement ISS-based preparations for a [[manned mission to Mars]]]]
The ISS provides a location in the relative safety of Low Earth Orbit to test spacecraft systems that will be required for long-duration missions to [[the Moon]] and [[Mars]]. This provides experience in operations, maintenance as well as repair and replacement activities on-orbit, which will be essential skills in operating spacecraft farther from Earth, mission risks can be reduced and the capabilities of interplanetary spacecraft advanced.<ref name="ResProg">{{cite web|url=http://spaceflightsystems.grc.nasa.gov/Advanced/ISSResearch/|title=ISS Research Program|publisher=NASA|accessdate=27 February 2009}}{{dead link|date=August 2011}}</ref> Referring to the [[MARS-500]] experiment, ESA states that "Whereas the ISS is essential for answering questions concerning the possible impact of weightlessness, radiation and other space-specific factors, aspects such as the effect of long-term isolation and confinement can be more appropriately addressed via ground-based simulations".<ref name="esa mars500 ">{{cite web|title=Mars500 study overview | publisher = ESA |date= 4 June 2011| url = http://www.esa.int/esaMI/Mars500/SEM7W9XX3RF_0.html }}</ref> Sergey Krasnov, the head of human space flight programmes for Russia's space agency, Roscosmos, in 2011 suggested a "shorter version" of MARS-500 may be carried out on the ISS. <ref name="Mars thing on ISS">{{cite web| title=Space station may be site for next mock Mars mission| url = http://www.newscientist.com/blogs/shortsharpscience/2011/11/space-station-may-be-site-for.html|date=4 November 2011|work=New Scientist}}</ref>

In 2009, noting the value of the partnership framework itself, Sergey Krasnov wrote, "When compared with partners acting separately, partners developing complementary abilities and resources could give us much more assurance of the success and safety of space exploration. The ISS is helping further advance near-Earth space exploration and realisation of prospective programmes of research and exploration of the Solar system, including the Moon and Mars."<ref name=IAF2009>{{cite web|title=The Sustainable Utilisation of the ISS Beyond 2015|url=http://www.iafastro.org/docs/2009/ISS2015.pdf|publisher=International Astronautical Congress|accessdate=15 December 2011}}</ref> [[Manned mission to Mars|A manned mission to Mars]] may be a multinational effort involving space agencies and countries outside the current ISS partnership. In 2010, ESA Director-General Jean-Jacques Dordain stated his agency was ready to propose to the other four partners that China, India and South Korea be invited to join the ISS partnership.<ref name="ESAproposesInvite">{{cite web|title=ESA Chief Lauds Renewed U.S. Commitment to Space Station, Earth Science | publisher =Peter B. de Selding, Space News. |date=2 March 2010 | url =http://www.spacenews.com/civil/100203-esa-chief-lauds-renewed-commitment-space-station-earth-science.html}}</ref> NASA chief [[Charlie Bolden]] stated in February 2011, "Any mission to Mars is likely to be a global effort".<ref name="Mars a global effort">{{cite web|title= Charlie Bolden | publisher = space.com |date=4 June 2011 | url = http://www.space.com/11335-nasa-mars-exploration-space-station.html }}</ref> Currently, American legislation prevents NASA co-operation with China on space projects.<ref name="justice1">{{citation|first=Virginia|last=Seitz|title=Memorandum Opinion for the General Counsel, Office of Science and Technology Policy|url=http://www.justice.gov/olc/2011/conduct-diplomacy.pdf|journal=Office of Legal Counsel|volume=35|date=11 September 2011|accessdate=23 May 2012|archiveurl=https://web.archive.org/web/20120713080223/http://www.justice.gov/olc/2011/conduct-diplomacy.pdf|archivedate=13 July 2012}}</ref>

===Education and cultural outreach===
[[File:ISS-36 HTV-4 berthing 2.jpg|thumb|Japan's Kounotori 4 docking]]
The ISS crew provides opportunities for students on Earth by running student-developed experiments, making educational demonstrations, allowing for student participation in classroom versions of ISS experiments, and directly engaging students using radio, videolink and email.<ref name="ISSRG" /><ref>{{cite journal|author1=Gro Mjeldheim Sandal |author2=Dietrich Manzey|title=Cross-cultural issues in space operations: A survey study among ground personnel of the European Space Agency|journal=Acta Astronautica|volume=65|date=December 2009|pages=1520–1529|doi=10.1016/j.actaastro.2009.03.074|issue=11–12}}</ref> ESA offers a wide range of free teaching materials that can be downloaded for use in classrooms.<ref>[http://www.esa.int/SPECIALS/Education/SEM0LW4KXMF_0.html ESA – Education – Online material]. Esa.int (7 September 2011). Retrieved 8 October 2011.</ref> In one lesson, students can navigate a 3-D model of the interior and exterior of the ISS, and face spontaneous challenges to solve in real time.<ref>[http://www.esa.int/SPECIALS/Education/SEM1LL3Z2OF_0.html ESA – Education – ISS 3-D Teaching Tool: Spaceflight Challenge I]. Esa.int (24 May 2011). Retrieved 8 October 2011.</ref>

JAXA aims both to "Stimulate the curiosity of children, cultivating their spirits, and encouraging their passion to pursue craftsmanship", and to "Heighten the child's awareness of the importance of life and their responsibilities in society."<ref>[http://www.oosa.unvienna.org/pdf/pres/copuos2010/tech-17E.pdf Building Peace in Young Minds through Space Education]. Committee on the Peaceful Uses of Outer Space, 53rd Session. June 2010, Vienna, Austria; Space Education Center, Japan Aerospace Exploration Agency (JAXA)</ref> Through a series of education guides, a deeper understanding of the past and near-term future of manned space flight, as well as that of Earth and life, will be learned.<ref>[http://www.edu.jaxa.jp/education/international/ISS/SSK/en/ JAXA Space Education Center : JAXA Spaceflight Seeds Kids I : Spaceflight Sunflower seeds – Let's make them flower! and learn freshly the Earth environment just by contrast with the Space one]. Edu.jaxa.jp. Retrieved 8 October 2011.</ref><ref>[http://www.edu.jaxa.jp/education/international/ISS/SIS/en/ JAXA Space Education Center : JAXA Seeds in Space I : Let's Cultivate Spaceflight Asagao, Miyako-gusa Seeds and Identify the Mutants!]. Edu.jaxa.jp. Retrieved 8 October 2011.</ref> In the JAXA Seeds in Space experiments, the mutation effects of spaceflight on plant seeds aboard the ISS is explored. Students grow sunflower seeds which flew on the ISS for about nine months as a start to 'touch the Universe'. In the first phase of Kibō utilisation from 2008 to mid-2010, researchers from more than a dozen Japanese universities conducted experiments in diverse fields.<ref>{{cite web |author=Keiji Murakami |url=http://www.spacepolicyonline.com/pages/images/stories/Micro%20Oct%2009%20JEM.pdf |title=JEM Utilization Overview |publisher=JAXA. Steering Committee for the Decadal Survey on Biological and Physical Sciences in Space |date=14 October 2009}}</ref>

[[Image:Crew in ATV with Jules Verne manuscript.jpg|thumb|left|Original Jules Verne manuscripts displayed by crew inside Jules Verne ATV]]
Cultural activities are another major objective. Tetsuo Tanaka, director of JAXA's Space Environment and Utilization Center, says "There is something about space that touches even people who are not interested in science."<ref name="jaxa2">{{cite web |author=Tetsuo Tanaka |url=http://www.jaxa.jp/article/special/kibo/tanaka01_e.html |title=Kibo: Japan's First Human Space Facility |publisher=JAXA |accessdate=8 October 2011}}</ref>

[[ARISS|Amateur Radio on the ISS]] (ARISS) is a volunteer programme which encourages students worldwide to pursue careers in science, technology, engineering and mathematics through [[amateur radio]] communications opportunities with the ISS crew. ARISS is an international working group, consisting of delegations from 9 countries including several countries in Europe as well as Japan, Russia, Canada, and the United States. In areas where radio equipment cannot be used, speakerphones connect students to ground stations which then connect the calls to the station. <ref>{{cite web|url=http://www.rac.ca/ariss/oindex.htm|title=Amateur Radio on the International Space Station|date=6 June 2011|accessdate=10 June 2011}}</ref>

''[[First Orbit]]'' is a feature-length documentary film about [[Vostok 1]], the first manned space flight around the Earth. By matching the orbit of the International Space Station to that of Vostok 1 as closely as possible, in terms of ground path and time of day, documentary filmmaker Christopher Riley and ESA astronaut [[Paolo Nespoli]] were able to film the view that Yuri Gagarin saw on his pioneering orbital space flight. This new footage was cut together with the original Vostok 1 mission audio recordings sourced from the Russian State Archive. Nespoli, during Expedition 26/27, filmed the majority of the footage for this documentary film, and as a result is credited as its [[Cinematographer|director of photography]].<ref>{{cite news|last=Riley|first=Christopher|title=What Yuri Gagarin saw: First Orbit film to reveal the view from Vostok 1|url=http://www.guardian.co.uk/science/blog/2011/apr/11/yuri-gagarin-first-orbit-vostok|newspaper=The Guardian|date=11 April 2011|location=London}}</ref> The film was streamed through the website firstorbit.org in a global YouTube premiere in 2011, under a free license.<ref>{{cite web|url=http://www.firstorbit.org/first-orbit-faqs |title=Yuri Gagarin's First Orbit – FAQs |publisher=Firstorbit.org |accessdate=1 May 2012}}</ref>

In May 2013, commander [[Chris Hadfield]] shot a music video of [[David Bowie]]'s ''[[Space Oddity (song)|Space Oddity]]'' on board the station; the film was released freely on YouTube.<ref>{{cite web|last=Warr |first=Philippa |url=http://www.wired.co.uk/news/archive/2013-05/13/commander-hadfield-space-oddity |title=Commander Hadfield bids farewell to ISS with Reddit-inspired Bowie cover |publisher=Wired.co.uk |date=13 May 2013 |accessdate=22 October 2013}}</ref> It was the first music video ever to be filmed in space.<ref>{{Cite web|title = Chris Hadfield sings "Space Oddity" in the first music video in space|url = http://io9.com/chris-hadfield-sings-space-oddity-in-the-first-music-503764317|accessdate = 2015-08-25|first = Lauren|last = Davis}}</ref>

==Assembly==
{{Main|Assembly of the International Space Station|List of ISS spacewalks}}
[[File:ISS-with-S0-S1-P1.jpg|thumb|right|alt=S0, S1 and P1 truss structures installed|Partially constructed ISS in December 2002]]
[[File:S3-S4 Truss Installed 2.jpg|thumb|S3-S4 Truss Installed in 2007]]
[[File:Soyuz TMA-19 spacecraft departs the ISS.jpg|thumb|[[Soyuz TMA-19]] departs in 2010]]
[[File:ISS after STS-117 in June 2007.jpg|thumb|ISS in 2007, with fewer solar arrays]]
The assembly of the International Space Station, a major endeavour in [[space architecture]], began in November 1998.<ref name="ISStD" /> Russian modules launched and docked robotically, with the exception of ''[[Rassvet (ISS module)|Rassvet]]''. All other modules were delivered by the Space Shuttle, which required installation by ISS and shuttle crewmembers using the [[Mobile Servicing System#Canadarm2|Canadarm2]] (SSRMS) and [[List of ISS spacewalks|EVAs]]; {{as of|2011|06|05|lc=y}}, they had added 159 components during more than 1,000 hours of EVA. 127 of these spacewalks originated from the station, and the remaining 32 were launched from the airlocks of docked Space Shuttles.<ref name="ISStD" /> The [[beta angle]] of the station had to be considered at all times during construction, as the station's beta angle is directly related to the percentage of its orbit that the station (as well as any docked or docking spacecraft) is exposed to the sun; the Space Shuttle would not perform optimally above a limit called the "beta cutoff".<ref name="mcc">{{cite web|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-113/11_23_20_01_179.html|title=MCC Answers|author=Derek Hassman, NASA Flight Director|date=1 December 2002|publisher=NASA|accessdate=14 June 2009}}</ref>

The first module of the ISS, ''[[Zarya]]'', was launched on 20 November 1998 on an autonomous Russian [[Proton (rocket)|Proton rocket]]. It provided propulsion, attitude control, communications, electrical power, but lacked long-term life support functions. Two weeks later a passive NASA module ''[[Unity (ISS module)|Unity]]'' was launched aboard Space Shuttle flight [[STS-88]] and attached to Zarya by astronauts during EVAs. This module has two [[Pressurized Mating Adapter]]s (PMAs), one connects permanently to Zarya, the other allows the Space Shuttle to dock to the space station. At this time, the Russian station Mir was still inhabited. The ISS remained unmanned for two years, during which time Mir was de-orbited. On 12 July 2000 [[Zvezda (ISS module)|Zvezda]] was launched into orbit. Preprogrammed commands on board deployed its solar arrays and communications antenna. It then became the passive vehicle for a rendezvous with the Zarya and Unity. As a passive "target" vehicle, the Zvezda maintained a stationkeeping orbit as the Zarya-Unity vehicle performed the rendezvous and docking via ground control and the Russian automated rendezvous and docking system. Zarya's computer transferred control of the station to Zvezda's computer soon after docking. Zvezda added sleeping quarters, a toilet, kitchen, CO2 scrubbers, dehumidifier, oxygen generators, exercise equipment, plus data, voice and television communications with mission control. This enabled permanent habitation of the station.<ref>[http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/servmod.pdf NASA Facts. The Service Module: A Cornerstone of Russian International Space Station Modules]. NASA. January 1999</ref><ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/missions/sts-88/mission-sts-88.html |title=STS-88 |publisher=Science.ksc.nasa.gov |accessdate=19 April 2011}}</ref>

The first resident crew, [[Expedition 1]], arrived in November 2000 on [[Soyuz TM-31]]. At the end of the first day on the station, astronaut Bill Shepherd requested the use of the radio call sign "''Alpha''", which he and cosmonaut Krikalev preferred to the more cumbersome "''International Space Station''".<ref name=TIME-Nov2>{{cite news|url=http://www.time.com/time/arts/article/0,8599,59500,00.html|title=Upward Bound: Tales of Space Station Alpha|author=Brad Liston|date=2 November 2000|work=Time|accessdate=5 August 2010}}</ref> The name "''Alpha''" had previously been used for the station in the early 1990s,<ref name=GAO>{{cite web|url=http://archive.gao.gov/t2pbat3/151975.pdf|title=Space Station – Impact on the expanded Russian role of funding and research|date=21 June 1994|publisher=[[Government Accountability Office|United State General Accounting Office]]|accessdate=9 August 2010}}</ref> and following the request, its use was authorised for the whole of Expedition 1.<ref name=SPACE-Nov3>{{cite web|url=http://www.space.com/missionlaunches/missions/alpha_male_001103.html|title=Call Bill Shepherd the Alpha Male of the International Space Station|author=Alan Ladwig|date=3 November 2000|publisher=Space.com|accessdate=9 August 2010}}</ref> Shepherd had been advocating the use of a new name to project managers for some time. Referencing a [[Ship naming and launching|naval tradition]] in a pre-launch news conference he had said: "For thousands of years, humans have been going to sea in ships. People have designed and built these vessels, launched them with a good feeling that a name will bring good fortune to the crew and success to their voyage."<ref name=SPACE-Nov2>{{cite web|url=http://www.space.com/missionlaunches/missions/exp1_alpha_001102.html|title=Expedition One Crew Wins Bid To Name Space Station Alpha|date=2 November 2000|author=Todd Halvorson|publisher=Space.com|accessdate=9 August 2010}}</ref> [[Yuri Semenov]], the President of [[S.P. Korolev Rocket and Space Corporation Energia|Russian Space Corporation Energia]] at the time, disapproved of the name "''Alpha''"; he felt that ''Mir'' was the first space station, and so he would have preferred the names "''Beta''" or "''Mir 2''" for the ISS.<ref name=SPACE-Nov3 /><ref>{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=5913|title=Interview with RSC Energia's Yuri Semenov|publisher=Space.com|date=3 September 2001|accessdate=22 August 2010}}</ref><ref>{{cite web|url=http://english.ruvr.ru/2001/03/29/100146.html|title=Interview with Yuri Semenov, general designer of Space Rocket corporation Energy|date=21 March 2001|publisher=[[Voice of Russia]]|accessdate=5 October 2010}}</ref>

[[Expedition 1]] arrived midway between the flights of [[STS-92]] and [[STS-97]]. These two Space Shuttle flights each added segments of the station's [[Integrated Truss Structure]], which provided the station with Ku-band communication for US television, additional attitude support needed for the additional mass of the USOS, and substantial [[solar array]]s supplementing the station's existing 4 solar arrays.<ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/missions/sts-92/mission-sts-92.html |title=STS-92 |publisher=Science.ksc.nasa.gov |accessdate=19 April 2011}}</ref>

Over the next two years the station continued to expand. A [[Soyuz-U]] rocket delivered the [[Pirs (ISS module)|''Pirs'' docking compartment]]. The Space Shuttles ''Discovery'', ''[[Space Shuttle Atlantis|Atlantis]]'', and ''Endeavour'' delivered the [[Destiny (ISS module)|''Destiny'' laboratory]] and [[Quest Joint Airlock|''Quest'' airlock]], in addition to the station's main robot arm, the ''[[Canadarm2]]'', and several more segments of the Integrated Truss Structure.
[[File:Zvezda rear.jpg|thumb|left|Aft view showing a Progress spacecraft docked to Zvezda]]
The expansion schedule was interrupted by the {{OV|102}} [[Space Shuttle Columbia disaster|disaster]] in 2003, with the resulting two year hiatus in the [[Space Shuttle program]]me halting station assembly. The space shuttle was grounded until 2005 with [[STS-114]] flown by ''Discovery''.<ref>{{cite web|url=http://www.nasaspaceflight.com/2005/07/discovery-launches-the-shuttle-is-back/|title=Discovery launches—The Shuttle is back|author=Chris Bergin|publisher=NASASpaceflight.com|accessdate=6 March 2009|date=26 July 2005}}</ref>

Assembly resumed in 2006 with the arrival of [[STS-115]] with ''Atlantis'', which delivered the station's second set of solar arrays. Several more truss segments and a third set of arrays were delivered on [[STS-116]], [[STS-117]], and [[STS-118]]. As a result of the major expansion of the station's power-generating capabilities, more pressurised modules could be accommodated, and the ''[[Harmony (ISS module)|Harmony]]'' node and ''Columbus'' European laboratory were added. These were followed shortly after by the first two components of ''Kibō''. In March 2009, [[STS-119]] completed the Integrated Truss Structure with the installation of the fourth and final set of solar arrays. The final section of ''Kibō'' was delivered in July 2009 on [[STS-127]], followed by the Russian ''[[Poisk (ISS module)|Poisk]]'' module. The third node, ''[[Tranquility (ISS module)|Tranquility]]'', was delivered in February 2010 during [[STS-130]] by the Space Shuttle ''Endeavour'', alongside the [[Cupola (ISS module)|Cupola]], closely followed in May 2010 by the penultimate Russian module, ''[[Rassvet (ISS module)|Rassvet]]''. Rassvet was delivered by Space Shuttle ''Atlantis'' on [[STS-132]] in exchange for the Russian Proton delivery of the Zarya Module in 1998 which had been funded by the United States.<ref>{{cite web|url=http://www.russianspaceweb.com/iss_mim1.html |title=Mini-Research Module 1 (MIM1) Rassvet (MRM-1) |publisher=Russianspaceweb.com |accessdate=12 July 2011}}</ref> The last pressurised module of the USOS, ''Leonardo'', was brought to the station by ''Discovery'' on her final flight, [[STS-133]],<ref name="STS-133">{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/main/index.html |title=STS-133 |publisher=NASA |accessdate=1 September 2014}}</ref> followed by the [[Alpha Magnetic Spectrometer]] on [[STS-134]], delivered by ''Endeavour''.<ref name="STS-134">{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/main/index.html |title=STS-134 |publisher=NASA |accessdate=1 September 2014}}</ref>
[[File:Exterior of Cupola - Exp28.jpg|thumb|The Cupola arrived in 2010]]
{{As of|2011|06}}, the station consisted of fifteen pressurised modules and the [[Integrated Truss Structure]]. Still to be launched are the Russian [[Nauka (ISS module)|Multipurpose Laboratory Module]] ''Nauka'' and a number of external components, including the [[European Robotic Arm]]. Assembly is expected to be completed by April 2014,{{update inline|date=October 2014}} by which point the station will have a mass in excess of 400 [[metric ton|tonnes]] (440 [[short ton]]s).<ref name="OnOrbit">{{cite web|url = http://www.nasa.gov/externalflash/ISSRG/pdfs/on_orbit.pdf|title = On-Orbit Elements|publisher = NASA|author = NASA|date = 18 February 2010|accessdate = 19 June 2010|format = PDF}}</ref><ref name="Manifest">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/iss_manifest.html|title=Consolidated Launch Manifest|accessdate=8 July 2008|publisher=NASA|author=NASA|year=2008}}</ref>

The gross mass of the station changes over time. The total launch mass of the modules on orbit is about {{convert|417289|kg|lbs|abbr=on}} (as of 3 September 2011).<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/isstodate.html |title=NASA – The ISS to Date (03/09/2011) |publisher=Nasa.gov |accessdate=12 July 2011}}</ref> The mass of experiments, spare parts, personal effects, crew, foodstuff, clothing, propellants, water supplies, gas supplies, docked spacecraft, and other items add to the total mass of the station. Hydrogen gas is constantly vented overboard by the oxygen generators.

==Station structure==
{{Double image|right|ROS Windows 0114 complete.jpg|130|USOS window identification.png|160|Russian Orbital Segment Windows|USOS International Space Station window locations}}

The ISS is a third generation<ref>{{cite web|url=http://www.dlr.de/iss/en/desktopdefault.aspx/tabid-1945/2746_read-4182/gallery-1/gallery_read-Image.19.2296/ |title=DLR – International Space Station ISS – From Cold War to international cooperation – the story of the ISS |publisher=Dlr.de |accessdate=1 May 2012}}</ref> modular space station.<ref>{{cite web|url=http://www.astronautix.com/articles/thistems.htm |title=Third Generation Soviet Space Systems |publisher=Astronautix.com |accessdate=1 May 2012}}</ref> Modular stations can allow the mission to be changed over time and new modules can be added or removed from the existing structure, allowing greater flexibility.

Below is a diagram of major station components. The blue areas are pressurised sections accessible by the crew without using spacesuits. The station's unpressurised superstructure is indicated in red. Other unpressurised components are yellow. Note that the Unity node joins directly to the Destiny laboratory. For clarity, they are shown apart.

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PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | |AMS|~|ZVEZDA|~|AMS|
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|SGM2 = [[Poisk (ISS module)|'''Poisk''' (MRM-2) Airlock]]
|PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | | | | | | |!|`|-|SGM1|PORT1|
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|PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | |QUEST|-|UNITY|-|NOD3|PORT2| |
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|QUEST = [[Quest Joint Airlock|'''Quest''' Airlock]]
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|PORT2 = [[Pressurized Mating Adapter#PMA-3|'''PMA 3''' docking port]]
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|FE0 = [[ISS Solar Arrays#Solar arrays|Solar array]]
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{{familytree| |:| | |:|ELC| | |:|FZ1|:| | |ELC3|:| | |:|
ELC = [[ExPRESS Logistics Carrier#ELC-2|ELC 2]], '''[[Alpha Magnetic Spectrometer|AMS]]'''
|FZ1 = '''[[Z1 truss]]'''
|ELC3 = [[ExPRESS Logistics Carrier#ELC-3|ELC 3]]
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FS56 = '''[[P5 Truss Segment|S5/6 Truss]]'''
|FS34 = '''[[Integrated Truss Structure#P3/P4, S3/S4 truss assemblies|S3/S4 Truss]]'''
|FS1 = '''[[S1 Truss]]'''
|FS0 = '''[[S0 Truss]]'''
|FP1 = '''[[S1 Truss|P1 Truss]]'''
|FP34 = '''[[Integrated Truss Structure#P3/P4, S3/S4 truss assemblies|P3/P4 Truss]]'''
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ELC4 = [[ExPRESS Logistics Carrier#ELC-4|ELC 4]], [[External Stowage Platform#ESP-3|ESP 3]]
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{{familytree| | | | | | | | | | | | |!| | | | |}}
{{familytree| | | | | | | | |ESP1|DESTYNY| | |
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KIBOPS = [[Japanese Experiment Module#Experiment Logistics Module|'''Kibō logistics''' Cargo Bay]]
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{{familytree| | | | | | | | | |HTV|!|HTV| |!|
HTV = '''[[H-II Transfer Vehicle|HTV]]'''/'''[[Dragon (spacecraft)|Dragon]]'''/'''[[Cygnus (spacecraft)|Cygnus]]''' berth ([[Common berthing mechanism|docking port]])
|boxstyle_HTV = border: 1px solid #a3ff66; background:#ccddff;}}
{{familytree| | | | | | | | | | | |!|!|!| | | |!|KiboRobo|
KiboRobo = [[Japanese Experiment Module|'''Kibō''' Robotic Arm]]
|boxstyle_KiboRobo = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| | | | |COLEXT|COLUMBUS|-|HARMONY|-|KIBO|KiboPlat|
HARMONY = [[Harmony (ISS module)|'''Harmony''' (Node 2)]]
|KiboPlat = [[Japanese Experiment Module|'''Kibō''' External Platform]]
|COLUMBUS = [[Columbus (ISS module)|'''Columbus''' Laboratory]]
|KIBO = [[JEM-PM|'''Kibō''' Laboratory]]
|COLEXT = External Payloads
|boxstyle_HARMONY = border: 2px solid #6699ff; background:#ccddff;
|boxstyle_COLUMBUS = border: 2px solid #6699ff; background:#ccddff;
|boxstyle_COLEXT = border: 1px solid #fee067; background:#fff4cc;
|boxstyle_KIBO = border: 2px solid #6699ff; background:#ccddff;
|boxstyle_KiboPlat = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| | | | | | | | | | | |PORT2| |
PORT2 = [[Pressurized Mating Adapter#PMA-2|'''PMA 2''' docking port]]
|boxstyle_PORT2 = border: 1px solid #a3ff66; background:#ccddff;}}
{{familytree| | | | | | | | | | | | | | | |}}
{{familytree/end|nocat=1}}

==Pressurised modules==

===Zarya===
[[File:Zarya from STS-88.jpg|thumb|upright|Zarya as seen by [[Space Shuttle Endeavour]] during [[STS-88]]]]
'''''[[Zarya]]''''' (Russian: Заря́; lit. dawn), also known as the [[Functional Cargo Block]] or FGB (from the Russian "Функционально-грузовой блок", Funktsionalno-gruzovoy blok or ФГБ), was the first module of the International Space Station to be launched. The FGB provided electrical power, storage, propulsion, and guidance to the ISS during the initial stage of assembly. With the launch and assembly in orbit of other modules with more specialized functionality, Zarya is now primarily used for storage, both inside the pressurized section and in the externally mounted fuel tanks. The Zarya is a descendant of the [[TKS spacecraft]] designed for the Soviet [[Salyut program]]. The name Zarya was given to the FGB because it signified the dawn of a new era of international cooperation in space. Although it was built by a Russian company, it is owned by the [[United States]]. Zarya weighs {{convert|19300|kg|lb|abbr=on}}, is {{convert|12.55|m|ft|abbr=on}} long and {{convert|4.1|m|ft|abbr=on}} wide, discounting solar arrays.

Built from December 1994 to January 1998 in Russia at the [[Khrunichev State Research and Production Space Center]] (KhSC) in [[Moscow]], Zarya's control system was developed by the Khartron Corp. ([[Kharkiv, Ukraine]]).

Zarya was launched on 20 November 1998, on a Russian [[Proton-K|Proton rocket]] from [[Baikonur Cosmodrome Site 81]] in [[Kazakhstan]] to a {{convert|400|km|mi|abbr=on}} high orbit with a designed lifetime of at least 15 years. After Zarya reached orbit, STS-88 launched on 4 December 1998, to attach the Unity Module.

Although only designed to fly autonomously for six to eight months, Zarya did so for almost two years due to delays with the Russian Service Module, Zvezda, which finally launched on 12 July 2000, and docked with Zarya on 26 July using the Russian [[Kurs (docking system)|Kurs docking system]].

===Unity===
[[File:ISS Unity module.jpg|thumb|Unity as pictured by Space Shuttle Endeavour]]
'''''[[Unity (ISS module)|Unity]]''''', or Node 1, is one of three nodes, or passive connecting modules, in the [[US Orbital Segment]] of the station. It was the first US-built component of the Station to be launched. Cylindrical in shape, with six berthing locations facilitating connections to other modules, Unity was carried into orbit by {{OV|105}} as the primary cargo of [[STS-88]] in 1998. Essential space station resources such as fluids, environmental control and life support systems, electrical and data systems are routed through Unity to supply work and living areas of the station. More than 50,000 mechanical items, 216 lines to carry fluids and gases, and 121 internal and external electrical cables using six miles of wire were installed in the Unity node. Unity is made of aluminum. Prior to its launch aboard Endeavour, conical Pressurized Mating Adapters (PMAs) were attached to the aft and forward berthing mechanisms of Unity. Unity and the two mating adapters together weighed about {{convert|25600|lb|kg|disp=flip|abbr=on}}. The adapters allow the docking systems used by the Space Shuttle and by Russian modules to attach to the node's hatches and berthing mechanisms.

Unity was carried into orbit as the primary cargo of the Space Shuttle Endeavour on STS-88, the first Space Shuttle mission dedicated to assembly of the station. On 6 December 1998, the STS-88 crew mated the aft berthing port of Unity with the forward hatch of the already orbiting Zarya module.

===Zvezda===
'''''[[Zvezda (ISS module)|Zvezda]]''''' ({{lang-ru|link=no|Звезда́}}, meaning "star"), also known as DOS-8, Service Module or SM ({{lang-ru|link=no|СМ}}). It provides all of the station's critical systems,{{clarify|date=August 2013}} its addition rendered the station permanently habitable for the first time, adding life support for up to six crew and living quarters for two. Zvezda's DMS-R computer handles guidance, navigation and control for the entire space station.<ref name="Navigation" /> A second computer which performs the same functions will be installed in the [[Nauka (ISS module)|Nauka]] module, FGB-2.

The hull of Zvezda was completed in February 1985, with major internal equipment installed by October 1986. The module was launched by a Proton-K rocket from Site 81/23 at Baikonur, on 12 July 2000. Zvezda is at the rear of the station according to its normal direction of travel and orientation, its engines are used to boost the station's orbit. Alternatively Russian and European spacecraft can dock to Zvezda's aft port and use their engines to boost the station.

===Destiny===
[[File:Destiny as just installed.jpg|thumb|''Destiny'' interior in 2001]]
'''''[[Destiny (ISS module)|Destiny]]''''' is the primary research facility for United States payloads aboard the ISS. In 2011, NASA solicited proposals for a not-for-profit group to manage all American science on the station which does not relate to manned exploration. The module houses 24 [[International Standard Payload Rack]]s, some of which are used for environmental systems and crew daily living equipment. ''Destiny'' also serves as the mounting point for the station's Truss Structure.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/destiny.html|title=NASA—US Destiny Laboratory|date=26 March 2007|accessdate=26 June 2007|publisher = NASA}}</ref>

===Quest===
'''''[[Quest Joint Airlock|Quest]]''''' is the only USOS airlock, and hosts spacewalks with both United States [[Extravehicular Mobility Unit|EMU]] and Russian [[Orlan space suit|Orlan]] [[Space suit|spacesuits]]. It consists of two segments: the equipment lock, which stores spacesuits and equipment, and the crew lock, from which astronauts can exit into space. This module has a separately controlled atmosphere. Crew sleep in this module, breathing a low nitrogen mixture the night before scheduled EVAs, to avoid [[decompression sickness]] (known as "the bends") in the low-pressure suits.<ref>{{cite web|url=http://spaceflight.nasa.gov/station/eva/outside.html|title=Space Station Extravehicular Activity|accessdate=11 March 2009|publisher=[[NASA]]|date=4 April 2004}}</ref>

===Pirs and Poisk===
'''''[[Pirs (ISS module)|Pirs]]''''' ({{lang-ru|link=no|Пирс}}, meaning "[[pier]]"), ({{lang-ru|link=no|Стыковочный отсек}}), "docking module", SO-1 or DC-1 (docking compartment), and '''''[[Poisk (ISS module)|Poisk]]''''' ({{lang-ru|link=no|По́иск}}; lit. ''Search''), also known as the [[Mini-Research Module]] 2 (MRM 2), {{lang|ru|''Малый исследовательский модуль 2''}}, or МИМ 2. Pirs and Poisk are Russian airlock modules. Each of these modules have 2 identical hatches. An outward opening hatch on the MIR space station failed after it swung open too fast after unlatching, due to a small amount of air pressure remaining in the airlock.<ref>{{cite web|url=http://www.russianspaceweb.com/mir_close_calls.html |title=Mir close calls |publisher=Russianspaceweb.com |accessdate=1 May 2012}}</ref> A different entry was used, and the hatch repaired. All EVA hatches on the ISS open inwards and are pressure sealing. Pirs was used to store, service, and refurbish Russian [[Orlan suits]] and provided contingency entry for crew using the slightly bulkier American suits. The outermost docking ports on both airlocks allow docking of Soyuz and Progress spacecraft, and the automatic transfer of propellants to and from storage on the ROS.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/pirs.html|title=Pirs Docking Compartment|publisher=NASA|accessdate=28 March 2009|date=10 May 2006}}</ref>

{{multiple image |align=right |image1=Node 2 - STS-134.jpg |width1=171 |image2=Node 3 - Isolated view.jpg |width2=190 |caption1=''Harmony'' node in 2011 |caption2=''Tranquility'' node in 2011}}

===Harmony===
'''''[[Harmony (ISS module)|Harmony]]''''' is the second of the station's node modules and the utility hub of the USOS. The module contains four racks that provide electrical power, bus electronic data, and acts as a central connecting point for several other components via its six Common Berthing Mechanisms (CBMs). The European Columbus and Japanese Kibō laboratories are permanently berthed to the starboard and port radial ports respectively. The nadir and zenith ports can be used for docking visiting spacecraft including HTV, Dragon, and Cygnus, with the nadir port serving as the primary docking port. American Shuttle Orbiters docked with the ISS via PMA-2, attached to the forward port.

===Tranquility===
'''''[[Tranquility (ISS module)|Tranquility]]''''' is the third and last of the station's US nodes, it contains an additional life support system to recycle waste water for crew use and supplements oxygen generation. Two of the four berthing locations are not used. One location has the ''[[Cupola (ISS module)|Cupola]]'' installed, one has the docking port adapter, and the third one is occupied by the [[Leonardo (ISS module)|''Leonardo'' PMM]].

[[File:S122e008264.jpg|thumb|left|Columbus module in 2008]]

===Columbus===
'''''[[Columbus (ISS module)|Columbus]]''''', the primary research facility for European payloads aboard the ISS, provides a [[European Drawer Rack|generic laboratory]] as well as facilities specifically designed for [[Biolab|biology]], [[European Physiology Modules|biomedical research]] and [[Fluid Science Laboratory|fluid physics]]. Several mounting locations are affixed to the exterior of the module, which provide power and data to external experiments such as the [[European Technology Exposure Facility]] (EuTEF), [[Solar Monitoring Observatory]], [[Materials International Space Station Experiment]], and [[Atomic Clock Ensemble in Space]]. A number of expansions are planned for the module to study [[quantum physics]] and [[cosmology]].<ref>{{cite news|url=http://www.nasaspaceflight.com/2008/01/prcb-plan-sts-122-for-net-feb-7-three-launches-in-10-11-weeks/|title=PRCB plan STS-122 for NET Feb 7—three launches in 10–11 weeks|accessdate=12 January 2008|author=Chris Bergin|date=10 January 2008|publisher=[[NASASpaceflight.com]]}}</ref><ref>{{cite web|url=http://www.esa.int/esaHS/ESAAYI0VMOC_iss_0.html|title=Columbus laboratory|publisher=[[European Space Agency]] (ESA)|accessdate=6 March 2009|date=10 January 2009}}</ref> ESA's development of technologies on all the main areas of life support has been ongoing for more than 20 years and are/have been used in modules such as Columbus and the ATV. The German Aerospace Center [[German Aerospace Center|DLR]] manages ground control operations for Columbus and the ATV is controlled from the French [[CNES]] [[Toulouse Space Center]].

===Kibō===
[[File:きぼうエアロック Kibo airlock.jpg|thumb|Not large enough for crew using spacesuits, the airlock on Kibō has a sliding drawer for external experiments.]]
'''''[[Kibo (ISS module)|Kibō]]''''' ({{lang-ja|きぼう}}, "[[hope]]") is the largest single ISS module. This laboratory is used to carry out research in space medicine, biology, Earth observations, materials production, biotechnology, communications research, and has facilities for growing plants and fish. During August 2011, an observatory mounted on Kibō, which utilises the ISS's orbital motion to image the whole sky in the X-ray spectrum, detected for the first time the moment a star was swallowed by a black hole.<ref>{{cite web|author=[[JAXA]] |url=http://kibo.jaxa.jp/en/experiment/ef/maxi/ |title=Monitor of All-sky X-ray Image (MAXI):Experiment – Kibo Japanese Experimental Module – JAXA |publisher=Kibo.jaxa.jp |date=30 March 2007 |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://www.jaxa.jp/press/2011/08/20110825_maxi_e.html |title=JAXA | Scientific paper in Nature using the Monitor of All-sky X-ray Image (MAXI) on Kibo and the Swift satellite (USA) observations – First observation of a massive black hole swallowing a star |publisher=Jaxa.jp |accessdate=1 May 2012}}</ref> The laboratory contains a total of 23 racks, including 10 experiment racks and has a dedicated airlock for experiments. In a 'shirt sleeves' environment, crew attach an experiment to the sliding drawer within the airlock, close the inner, and then open the outer hatch. By extending the drawer and removing the experiment using the dedicated robotic arm, payloads are placed on the external platform. The process can be reversed and repeated quickly, allowing access to maintain external experiments without the delays caused by EVAs.

<gallery widths="115px" mode="nolines">
File:Kibo - Pressurized Module.jpg|Pressurized Module
File:Kibo - Experiment Logistics Module (Pressurized Section).jpg|Experiment Logistics Module
File:Kibo - Exposed Facility.jpg|Exposed Facility
File:Kibo - Experiment Logistics Module (Exposed Section).jpg|Experiment Logistics Module
File:Kibo - Remote Manipulator System.jpg|Remote Manipulator System
</gallery>

A smaller pressurised module is attached to the top of Kibō, serving as a cargo bay. The dedicated Interorbital communications system allows large amounts of data to be beamed from Kibō's ICS, first to the Japanese KODAMA satellite in geostationary orbit, then to Japanese ground stations. When a direct communication link is used, contact time between the ISS and a ground station is limited to approximately 10 minutes per visible pass. When KODAMA relays data between a LEO spacecraft and a ground station, real-time communications are possible in 60% of the flight path of the spacecraft. Ground staff use [[telepresence robotics]] to conduct on-orbit research without crew intervention.

===Cupola===
{{multiple image |align=right |image1=STS130 cupola view1.jpg |width1=190 |image2=ISS-27 Dmitri Kondratyev and Paolo Nespoli photograph the Earth through the Cupola.jpg |width2=190 |caption1=The [[Cupola (ISS module)|Cupola]]'s design has been compared to the ''[[Millennium Falcon]]'' from ''[[Star Wars (film)|Star Wars]]''. |caption2=[[Dmitri Kondratyev]] and [[Paolo A. Nespoli|Paolo Nespoli]] in the Cupola. Background left to right, [[Progress M-09M]], [[Soyuz TMA-20]], the [[Leonardo (ISS module)|Leonardo]] module and [[Kounotori 2|HTV-2]].}}
'''[[Cupola (ISS module)|Cupola]]''' is a seven window observatory, used to view Earth and docking spacecraft. Its name derives from the Italian word cupola, which means "dome". The Cupola project was started by NASA and Boeing, but cancelled due to budget cuts. A barter agreement between NASA and the ESA resulted in the Cupola's development being resumed in 1998 by the ESA. It was built by Thales Alenia Space in Torino, Italy. The module comes equipped with robotic workstations for operating the station's main robotic arm and shutters to protect its windows from damage caused by micrometeorites. It features 7 windows, with an {{convert|80|cm|in|adj=on}} round window, the largest window on the station (and the largest flown in space to date). The distinctive design has been compared to the 'turret' of the fictitious ''[[Millennium Falcon]]'' from the motion picture ''[[Star Wars (film)|Star Wars]]'';<ref>{{cite web|url=http://www.space.com/7932-astronauts-bask-spectacular-views-space-windows.html |title=Astronauts Bask in Spectacular Views From New Space Windows |publisher=Space.com |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://news.nationalgeographic.com/news/2010/02/photogalleries/100218-international-space-station-cupola-iss-obama-nasa-pictures/ |title=First Photos: Space Station's Observation Deck Unveiled |work=National Geographic |accessdate=1 May 2012}}</ref> the original prop [[lightsaber]] used by actor [[Mark Hamill]] as [[Luke Skywalker]] in the 1977 film was flown to the station in 2007.<ref>{{cite web|url=http://www.space.com/4283-nasa-shuttle-launch-luke-skywalker-lightsaber.html |title=NASA Shuttle to Launch Luke Skywalker's Lightsaber |publisher=Space.com |date=28 August 2007 |accessdate=1 May 2012}}</ref>

===Rassvet===
'''''[[Rassvet (ISS module)|Rassvet]]''''' ({{lang-ru|link=no|Рассве́т}}; lit. "dawn"), also known as the Mini-Research Module 1 (MRM-1) ({{lang-ru|link=no|Ма́лый иссле́довательский модуль}}, {{lang|ru|МИМ 1}}) and formerly known as the Docking Cargo Module (DCM), is similar in design to the [[Mir Docking Module]] launched on [[STS-74]] in 1995. ''Rassvet'' is primarily used for cargo storage and as a docking port for visiting spacecraft. It was flown to the ISS aboard NASA's {{OV|104}} on the [[STS-132]] mission and connected in May 2010,<ref>{{cite web|url=http://www.nasaspaceflight.com/2009/04/sts-132-prcb-baselines-mission-to-deliver-russias-mrm-1/|title=STS-132: PRCB baselines Atlantis' mission to deliver Russia's MRM-1|author=Chris Gebhardt|publisher=NASAspaceflight.com|date=9 April 2009|accessdate=12 November 2009}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts132/news/STS-132-09.html|author=NASA|date=18 May 2010|accessdate=7 July 2010|title=STS-132 MCC Status Report #09}}</ref> Rassvet is the only Russian owned module launched by NASA, to repay for the launch of Zarya, which is Russian designed and built, but partially paid for by NASA.<ref>[http://www.russianspaceweb.com/iss_mim1.html MIM1]. russianspaceweb.com</ref>  Rassvet was launched with the Russian Nauka Laboratory's Experiments airlock temporarily attached to it, and spare parts for the European Robotic Arm.

===Leonardo===
[[File:STS-133 Installation PMM 3.jpg|thumb|''Leonardo'' installed]]
'''''[[Leonardo (ISS module)|Leonardo]]'' Permanent Multipurpose Module''' (PMM) is a storage module attached to the ''[[Tranquility (ISS module)|Tranquility]]'' node.<ref name="leo-esa20110301">{{cite news |url=http://www.esa.int/Our_Activities/Human_Spaceflight/MagISStra/Leonardo_attached_to_Space_Station |title=Leonardo Attached to Space Station |work=ESA.int |date=1 March 2011 |accessdate=11 June 2013}}</ref><ref>{{cite web |url=http://blogs.nasa.gov/spacestation/2015/05/27/module-relocated-prepping-station-for-commercial-crew/ |title=Module Relocated Prepping Station for Commercial Crew |publisher=NASA |first=Mark |last=Garcia |date=27 May 2015 |accessdate=27 May 2015}}</ref> The three NASA Space Shuttle [[Multi-Purpose Logistics Module|MPLM]] cargo containers—Leonardo, Raffaello and Donatello—were built for NASA in [[Turin]], Italy by Alcatel Alenia Space, now [[Thales Alenia Space]].<ref>[http://www.thalesaleniaspace-issmodules.com/ Thales Alenia Space and ISS modules – Thales Alenia Space and ISS modules]. Thalesaleniaspace-issmodules.com. Retrieved 8 October 2011.</ref> The MPLMs were provided to NASA's ISS programme by Italy (independent of their role as a member state of ESA) and are considered to be US elements. In a bartered exchange for providing these containers, the US gave Italy research time aboard the ISS out of the US allotment in addition to that which Italy receives as a member of ESA.<ref>[http://www.spaceref.com/iss/elements/mplm.html Space Station User's Guide]. SpaceRef (3 April 2001). Retrieved 8 October 2011.</ref> The Permanent Multipurpose Module was created by converting Leonardo into a module that could be permanently attached to the station.<ref name="PLM1">{{cite news|url=http://www.nasaspaceflight.com/2009/08/sts-133-five-crew-one-eva-mission-leave-mpm-on-iss|title=STS-133 refined to a five crew, one EVA mission—will leave MPLM on ISS|publisher=NASASpaceflight.com|author=Chris Gebhardt|date=5 August 2009}}</ref><ref name="PLM2">{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8226309.stm|title=Europe looks to buy Soyuz craft|work=BBC News|last=Amos|first=Jonathan|date=29 August 2009}}</ref><ref>{{cite web|url=http://forum.nasaspaceflight.com/index.php?topic=17437.msg483604#msg483604|publisher=NASASpaceflight.com|accessdate=12 October 2009|title=Shuttle Q&A Part 5|date=27 September 2009}}</ref>

===Scheduled additional modules===

====Nauka====
'''''[[Nauka (ISS module)|Nauka]]''''' ({{lang-ru|link=no|Нау́ка}}; lit. "science"), also known as the Multipurpose Laboratory Module (MLM) or FGB-2 ({{lang-ru|link=no|Многофункциональный лабораторный модуль}}, {{lang|ru|МЛМ}}), is the major Russian laboratory module. It was scheduled to arrive at the station in 2014, docking to the port that was occupied by the Pirs module.<ref>{{cite web|url=http://www.aviationweek.com/Article.aspx?id=/article-xml/asd_05_23_2012_p05-01-460939.xml|title=Russia Sees Moon Base As Logical Next Step| last=Morring| first=Frank| date=23 May 2012| publisher=Aviation Week|accessdate=29 May 2012}}</ref> The date has been postponed to February 2017.<ref>{{cite web|url=http://www.russianspaceweb.com/iss_fgb2.html|title=MLM (FGB-2)|author=Anatoly Zak|publisher=Russian Space Web|date=29 April 2014|accessdate=14 May 2014}}</ref> Prior to the arrival of the Nauka module, a Progress spacecraft was used to remove Pirs from the station, deorbiting it to reenter over the Pacific Ocean. Nauka contains an additional set of life support systems and attitude control. Originally it would have routed power from the single Science-and-Power Platform, but that single module design changed over the first ten years of the ISS mission, and the two science modules, which attach to Nauka via the [[Uzlovoy Module]], or Russian node, each incorporate their own large solar arrays to power Russian science experiments in the ROS.

Nauka's mission has changed over time. During the mid-1990s, it was intended as a backup for the FGB, and later as a universal docking module (UDM); its docking ports will be able to support automatic docking of both spacecraft, additional modules and fuel transfer. Nauka has its own engines. Smaller Russian modules such as Pirs and Poisk were delivered by modified [[Progress (spacecraft)|Progress]] spacecraft, and the larger modules; Zvezda, Zarya, and Nauka, were launched by Proton rockets. Russia plans to separate Nauka, along with the rest of the Russian Orbital Segment, before the ISS is deorbited, to form the [[OPSEK]] space station.

====Uzlovoy Module====
The '''[[Uzlovoy Module]]''' (UM), or Node Module is a 4 metric ton<ref name=Zak>{{cite web|last1=Zak|first1=Anatoly|title=Node Module|url=http://www.russianspaceweb.com/iss_node.html|website=RussianSpaceWeb.com|accessdate=7 January 2015}}</ref> ball shaped module that will support the docking of two scientific and power modules during the final stage of the station assembly and provide the Russian segment additional docking ports to receive Soyuz TMA and Progress M spacecraft. UM is to be incorporated into the ISS in 2016. It will be integrated with a special version of the Progress cargo ship and launched by a standard Soyuz rocket. The Progress would use its own propulsion and flight control system to deliver and dock the Node Module to the nadir (Earth-facing) docking port of the Nauka MLM/FGB-2 module. One port is equipped with an active hybrid docking port, which enables docking with the MLM module. The remaining five ports are passive hybrids, enabling docking of Soyuz and Progress vehicles, as well as heavier modules and future spacecraft with modified docking systems. The node module was conceived to serve as the only permanent element of the future Russian successor to the ISS, [[Orbital Piloted Assembly and Experiment Complex|OPSEK]]. Equipped with six docking ports, the Node Module would serve as a single permanent core of the future station with all other modules coming and going as their life span and mission required.<ref>[http://www.energia.ru/en/news/news-2011/news_01-13.html S.P. Korolev RSC Energia – News]. Energia.ru (13 January 2011). Retrieved 8 October 2011.</ref><ref>[http://www.russianspaceweb.com/iss_node.html Node Module]. Russianspaceweb.com. Retrieved 8 October 2011.</ref> This would be a progression beyond the ISS and Russia's modular MIR space station, which are in turn more advanced than early monolithic first generation stations such as Skylab, and early Salyut and Almaz stations.

'''Science Power Modules 1 & 2''' (NEM-1, NEM-2) ({{lang-ru|link=no|Нау́чно-Энергетический Модуль-1 и -2}})

====Bigelow Expandable Activity Module====
On 16 January 2013, [[Bigelow Aerospace]] was contracted by NASA to provide a [[Bigelow Expandable Activity Module]] (BEAM), scheduled to arrive at the space station in 2015 for a two-year technology demonstration.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/station/news/beam_feature.html |title=NASA to Test Bigelow Expandable Module on Space Station |publisher=NASA |date=16 January 2013 |accessdate=17 January 2013}}</ref> BEAM is an inflatable module that will be attached to the aft hatch of the port-side Tranquility module of the International Space Station. During its two-year test run, instruments will measure its structural integrity and leak rate, along with temperature and radiation levels. The hatch leading into the module will remain mostly closed except for periodic visits by space station crew members for inspections and data collection. Following the test run, the module will be detached and jettisoned from the station.<ref>{{cite web | url=http://www.spaceflightnow.com/news/n1301/16bigelow/ | title=Bigelow inflatable module bound for space station | last=Harwood | first=William | date=16 January 2013 | publisher=Spaceflightnow | accessdate=17 January 2013}}</ref>

[[image:ISS Habitation module.jpg|thumb|left|The cancelled Habitation module under construction in 1997]]

===Cancelled components===
Several modules planned for the station have been cancelled over the course of the ISS programme, whether for budgetary reasons, because the modules became unnecessary, or following a redesign of the station after the 2003 [[Space Shuttle Columbia disaster|''Columbia'' disaster]]. The US [[Centrifuge Accommodations Module]] was intended to host science experiments in varying levels of [[artificial gravity]].<ref>{{cite web|url=http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=12560&mid=269666|title=Where is the Centrifuge Accommodation Module (CAM)?|publisher=NASASpaceflight.com|accessdate=12 October 2009}}</ref> The US [[Habitation Module]] would have served as the station's living quarters. Instead, the sleep stations are now spread throughout the station.<ref>{{cite web|url=http://www.space.com/missionlaunches/060214_iss_module.html|title=NASA Recycles Former ISS Module for Life Support Research|author=Tariq Malik|accessdate=11 March 2009|publisher=Space.com|date=14 February 2006}}</ref> The US [[Interim Control Module]] and [[ISS Propulsion Module]] were intended to replace functions of ''Zvezda'' in case of a launch failure.<ref>{{cite web|title=ICM Interim Control Module|publisher=U.S. Naval Center for Space Technology|url=http://code8200.nrl.navy.mil/icm.html|archiveurl=https://web.archive.org/web/20070208164211/http://code8200.nrl.navy.mil/icm.html|archivedate=8 February 2007}}</ref> The Russian [[Universal Docking Module]], to which the cancelled Russian Research modules and spacecraft would have docked.<ref name="Zak">{{cite web|url=http://www.russianspaceweb.com/iss_russia.html|accessdate=3 October 2009|publisher=russianspaceweb.com|author=Anatoly Zak|title=Russian segment of the ISS}}</ref> The Russian [[Science Power Platform]] would have provided the [[Russian Orbital Segment]] with a power supply independent of the ITS solar arrays,<ref name="Zak" /> and two [[Russian Research Module]]s that were planned to be used for scientific research.<ref>{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/components/russian_laboratory.html|title=Russian Research Modules|publisher=Boeing|accessdate=21 June 2009}}</ref>

==Unpressurised elements==
[[File:Truss breakdown.png|thumb|right|ISS Truss Components breakdown showing Trusses and all ORUs in situ]]
The ISS features a large number of external components that do not require pressurisation. The largest such component is the [[Integrated Truss Structure]] (ITS), to which the station's main solar arrays and thermal radiators are mounted.<ref name="Arrays" /> The ITS consists of ten separate segments forming a structure 108.5 m (356 ft) long.<ref name="OnOrbit" />

The station in its complete form has several smaller external components, such as the six robotic arms, the three [[External Stowage Platform]]s (ESPs) and four [[ExPRESS Logistics Carrier]]s (ELCs).<ref name="Manifest" /><ref>{{cite web|url=http://www.nasa.gov/centers/marshall/news/background/facts/expressrack.html|title=EXPRESS Racks 1 and 2 fact sheet|accessdate=4 October 2009|date=12 April 2008|publisher=NASA}}</ref> Whilst these platforms allow experiments (including [[MISSE]], the STP-H3 and the [[Robotic Refueling Mission]]) to be deployed and conducted in the vacuum of space by providing electricity and processing experimental data locally, the platforms' primary function is to store [[Orbital Replacement Unit]]s (ORUs). ORUs are spare parts that can be replaced when the item either passes its design life or fails. Examples of ORUs include pumps, storage tanks, antennas and battery units. Such units are replaced either by astronauts during EVA or by robotic arms. Spare parts were routinely transported to and from the station via Space Shuttle resupply missions, with a heavy emphasis on ORU transport once the NASA Shuttle approached retirement.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/12/soyuz-tma-03m-docks-iss-returns-station-six-crewmembers-future-ops/ |title=Soyuz TMA-03M docks to ISS, returns station to six crewmembers for future ops |publisher=NASASpaceFlight.com |date=23 December 2011 |accessdate=1 May 2012}}</ref> Several shuttle missions were dedicated to the delivery of ORUs, including [[STS-129]],<ref name="EVA129">{{cite web|url=http://www.nasa.gov/centers/johnson/pdf/404493main_EVA_129_F_E1.pdf|title=EVA Checklist: STS-129 Flight Supplement|author=L. D. Welsch|publisher=NASA|date=30 October 2009}}</ref> [[STS-133]]<ref name="STS-133">{{cite web|url=http://www.nasa.gov/pdf/491387main_STS-133%20Press%20Kit.pdf|title=Space Shuttle Mission: STS-131|date=February 2011|publisher=NASA}}</ref> and [[STS-134]].<ref name="STS-134">{{cite web|url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf|title=Space Shuttle Mission: STS-134|publisher=NASA|date=April 2011}}</ref> {{asof|2011|01}}, only one other mode of transportation of ORUs had been utilised – the Japanese cargo vessel [[H-II Transfer Vehicle|HTV-2]] – which delivered an FHRC and CTC-2 via its Exposed Pallet (EP).<ref name="HTV2">{{cite web|url=http://iss.jaxa.jp/en/htv/mission/htv-2/library/presskit/htv2_presskit_en.pdf|title=HTV2: Mission Press Kit|publisher=Japan Aerospace Exploration Agency|date=20 January 2011}}</ref>{{update after|2013|1|28}}

[[File:STS-116 spacewalk 1.jpg|left|thumb|Construction of the [[Integrated Truss Structure]] over New Zealand.]]
There are also smaller exposure facilities mounted directly to laboratory modules; the JEM [[Japanese Experiment Module#Exposed Facility|Exposed Facility]] serves as an external '[[porch]]' for the Japanese Experiment Module complex,<ref>{{cite web|url=http://kibo.jaxa.jp/en/about/kibo/jef/|title=Exposed Facility:About Kibo|publisher=JAXA|date=29 August 2008|accessdate=9 October 2009}}</ref> and a facility on the European ''Columbus'' laboratory provides power and data connections for experiments such as the [[European Technology Exposure Facility]]<ref name="NASA">{{cite web|url=http://www.nasa.gov/mission_pages/station/science/experiments/EuTEF.html|title=NASA—European Technology Exposure Facility (EuTEF)|publisher=NASA|date=6 October 2008|accessdate=28 February 2009}}</ref><ref name="ESA">{{cite web|url=http://www.esa.int/esaMI/Columbus/SEM7ZTEMKBF_0.html|title=ESA—Columbus—European Technology Exposure Facility (EuTEF)|publisher=ESA|date=13 January 2009|accessdate=28 February 2009}}</ref> and the [[Atomic Clock Ensemble in Space]].<ref>{{cite web|url=http://www.esa.int/SPECIALS/HSF_Research/SEMJSK0YDUF_0.html|publisher=ESA|accessdate=9 October 2009|title=Atomic Clock Ensemble in Space (ACES)}}</ref> A [[remote sensing]] instrument, [[Stratospheric Aerosol and Gas Experiment|SAGE III-ISS]], is due to be delivered to the station in 2014 aboard a [[Dragon (spacecraft)|Dragon capsule]], and the [[Neutron star Interior Composition ExploreR|NICER]] experiment in 2016.<ref>{{cite web |url=http://heasarc.gsfc.nasa.gov/docs/nicer/papers/NICER-SPIE-July2012-v4.pdf | publisher=Goddard Space Flight Center |title=The Neutron star Interior Composition ExploreR (NICER): an Explorer mission of opportunity for soft x-ray timing spectroscopy |accessdate=8 April 2013 |author=NICER Team }}</ref><ref>{{cite web|url=http://www.nasa.gov/topics/earth/features/sage3.html|date=1 March 2011|accessdate=12 March 2011|publisher=NASA|title=Time to Fly: SAGE III — ISS Prepped for Space Station|author=Michael Finneran}}</ref> The largest such scientific payload externally mounted to the ISS is the [[Alpha Magnetic Spectrometer]] (AMS), a particle physics experiment launched on [[STS-134]] in May 2011, and mounted externally on the ITS. The AMS measures [[cosmic ray]]s to look for evidence of [[dark matter]] and [[antimatter]].<ref>{{cite web|url=http://ams.cern.ch/|title=The Alpha Magnetic Spectrometer Experiment|publisher=[[CERN]]|date=21 January 2009|accessdate=6 March 2009}}</ref>

===Robotic arms and cargo cranes===
{{Double image|right|Iss017e011097.jpg|250|Dextrereallyhasnohead.jpg|250|Commander [[Sergey Alexandrovich Volkov|Volkov]] stands on Pirs with his back to the [[Soyuz spacecraft|Soyuz]] whilst operating the manual [[Strela (crane)|Strela crane]] holding photographer [[Oleg Kononenko|Kononenko]]. [[Zarya]] is seen to the left and [[Zvezda (ISS module)|Zvezda]] across the bottom of the image.|[[Dextre]], like many of the station's experiments and robotic arms, can be operated from Earth and perform tasks while the crew sleeps.||}}

The [[Integrated Truss Structure]] serves as a base for the station's primary remote manipulator system, called the [[Mobile Servicing System]] (MSS), which is composed of three main components. [[Canadarm2]], the largest robotic arm on the ISS, has a mass of {{convert|1800|kg|lb}} and is used to dock and manipulate spacecraft and modules on the USOS, hold crew members and equipment in place during EVAs and move Dextre around to perform tasks.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/station/structure/elements/mss.html |title=Canadarm2 and the Mobile Servicing System |publisher=NASA |date=8 January 2013 |accessdate=22 June 2015}}</ref> [[Dextre]] is a {{convert|1560|kg|lb|abbr=on}} robotic manipulator with two arms, a rotating torso and has power tools, lights and video for replacing [[orbital replacement unit]]s (ORUs) and performing other tasks requiring fine control.<ref>{{cite web |url=http://www.asc-csa.gc.ca/eng/iss/dextre/default.asp |title=Dextre, the International Space Station's Robotic Handyman |publisher=Canadian Space Agency |accessdate=22 June 2015}}</ref> The [[Mobile Base System]] (MBS) is 2 platforms which rides on rails along the length of the station's main truss. It serves as a mobile base for Canadarm2 and Dextre, allowing the robotic arms to reach all parts of the USOS.<ref>{{cite web |url=http://www.asc-csa.gc.ca/eng/iss/mobile-base/default.asp |title=Mobile Base System |publisher=Canadian Space Agency |accessdate=22 June 2015}}</ref> To gain access to the Russian Segment a [[Grapple Fixture|grapple fixture]] was added to Zarya on [[STS-134]], so that Canadarm2 can inchworm itself onto the ROS.<ref name="presskit134">{{cite web |url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf |title=Space Shuttle Mission STS-134: Final Flight of ''Endeavour'' - Press Kit |format=PDF |publisher=NASA |pages=51-53 |date=April 2011 |accessdate=22 June 2015}}</ref> Also installed during STS-134 was the {{convert|50|ft|m|abbr=on|order=flip}} [[Orbiter Boom Sensor System]] (OBSS), which had been used to inspect head shield tiles on Space Shuttle missions and can be used on station to increase the reach of the MSS.<ref name="presskit134"/> Staff on Earth or the station can operate the MSS components via remote control, performing work outside the station without space walks.

Japan's [[Kibo (ISS module)#Remote Manipulator System|Remote Manipulator System]], which services the JEM Exposed Facility,<ref>{{cite web |url=http://kibo.jaxa.jp/en/about/kibo/rms/ |title=Remote Manipulator System: About Kibo |publisher=JAXA |date=29 August 2008 |accessdate=4 October 2009}}</ref> was launched on [[STS-124]] and is attached to the JEM Pressurised Module.<ref>{{cite web |url=http://www.nasa.gov/centers/johnson/news/station/2002/iss02-03.txt |title=International Space Station Status Report #02-03 |publisher=NASA |date=14 January 2002 |accessdate=4 October 2009}}</ref> The arm is similar to the Space Shuttle arm as it is permanently attached at one end and has a latching end effector for standard grapple fixtures at the other.

The [[European Robotic Arm]], which will service the Russian Orbital Segment, will be launched alongside the [[Multipurpose Laboratory Module]] in 2017.<ref>{{cite web |url=http://www.russianspaceweb.com/iss_fgb2.html |title=MLM (FGB-2) module of the ISS |publisher=RussianSpaceWeb |accessdate=16 June 2014}}</ref> The ROS does not require spacecraft or modules to be manipulated, as all spacecraft and modules dock automatically and may be discarded the same way. Crew use the two ''[[Strela (crane)|Strela]]'' ({{lang-ru|link=no|Стрела́}}; lit. Arrow) cargo cranes during EVAs for moving crew and equipment around the ROS. Each Strela crane has a mass of {{convert|45|kg|lb|abbr=on}}.

===Comparison===
The ISS follows [[Salyut]] and [[Almaz]] series, [[Cosmos 557]], [[Skylab]], and [[Mir]] as the 11th space station launched, as the [[Genesis II|Genesis]] prototypes were never intended to be manned. Other examples of modular station projects include the Soviet/Russian Mir and the planned Russian OPSEK and [[Chinese space station]]. The first space station, [[Salyut 1]], and other one-piece or 'monolithic' first generation space stations, such as Salyut 2,3,4,5, DOS 2, Kosmos 557, Almaz and NASA's [[Skylab]] stations were not designed for re-supply.<ref>http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/history.pdf</ref> Generally, each crew had to depart the station to free the only docking port for the next crew to arrive, Skylab had more than one docking port but was not designed for resupply. Salyut 6 and 7 had more than one docking port and were designed to be resupplied routinely during crewed operation.<ref>{{cite web|url=http://www.pbs.org/spacestation/station/russian.htm |title=Space Station | Russian Space History |publisher=Pbs.org |accessdate=1 May 2012}}</ref>

==Station systems==

===Life support===
{{Main|ISS ECLSS|Chemical oxygen generator}}
The critical systems are the atmosphere control system, the water supply system, the food supply facilities, the sanitation and hygiene equipment, and fire detection and suppression equipment. The Russian Orbital Segment's life support systems are contained in the Service Module Zvezda. Some of these systems are supplemented by equipment in the USOS. The MLM Nauka laboratory has a complete set of life support systems.

====Atmospheric control systems====
[[Image:SpaceStationCycle.svg|thumb|The interactions between the components of the ISS Environmental Control and Life Support System (ECLSS)|alt=A flowchart diagram showing the components of the ISS life support system.]]
The atmosphere on board the ISS is similar to the [[Atmosphere of Earth|Earth's]].<ref>{{cite web|url=http://science.howstuffworks.com/space-station2.htm |title=How Space Stations Work|first=Craig|last=Freudenrich|publisher=Howstuffworks|date=20 November 2000|accessdate=23 November 2008}}</ref> Normal air pressure on the ISS is 101.3 [[kilopascal|kPa]] (14.7 [[Pounds per square inch|psi]]);<ref>{{cite web |url=http://nasaexplores.com/show2_5_8a.php?id=04-032&gl=58|archiveurl=https://web.archive.org/web/20061114010931/http://www.nasaexplores.com/show2_5_8a.php?id=04-032&gl=58|archivedate=14 November 2006|work=NASAexplores|title=5–8: The Air Up There|publisher=NASA|accessdate=31 October 2008}}</ref> the same as at sea level on Earth. An Earth-like atmosphere offers benefits for crew comfort, and is much safer than the alternative, a pure oxygen atmosphere, because of the increased risk of a fire such as that responsible for the deaths of the [[Apollo 1]] crew.<ref>{{cite book|author=Clinton Anderson|display-authors=etal|publisher=US Government Printing Office|title=Report of the Committee on Aeronautical and Space Sciences, United States Senate—Apollo 204 Accident|date=30 January 1968|location=Washington, DC|page=8|url=http://klabs.org/richcontent/Reports/Failure_Reports/as-204/senate_956/as204_senate_956.pdf}}</ref> Earth-like atmospheric conditions have been maintained on all Russian and Soviet spacecraft.<ref name=spacemed>{{Citation | last1=Davis | first1=Jeffrey R. | last2=Johnson | first2=Robert | last3=Stepanek | first3=Jan | lastauthoramp=yes | title=Fundamentals of Aerospace Medicine | publisher=Lippincott Williams & Wilkins | place=Philadelphia PA, USA | volume=XII | pages=261–264 | year=2008}}</ref>

The ''[[Elektron (ISS)|Elektron]]'' system aboard ''Zvezda'' and a similar system in ''Destiny'' generate oxygen aboard the station.<ref name="OGS">{{cite web|url=http://www.space.com/businesstechnology/060215_techwed_iss_oxygen.html|title=Air Apparent: New Oxygen Systems for the ISS|author=Tariq Malik|publisher=Space.com|date=15 February 2006|accessdate=21 November 2008}}</ref> The crew has a backup option in the form of bottled oxygen and [[Vika oxygen generator|Solid Fuel Oxygen Generation]] (SFOG) canisters, a [[chemical oxygen generator]] system.<ref name="breath easy">{{cite web|url=http://science.nasa.gov/headlines/y2000/ast13nov_1.htm|title=Breathing Easy on the Space Station|author=Patrick L. Barry|publisher=NASA|date=13 November 2000|accessdate=21 November 2008}}</ref> Carbon dioxide is removed from the air by the [[Vozdukh]] system in ''Zvezda''. Other by-products of human metabolism, such as methane from the intestines and ammonia from sweat, are removed by [[Activated carbon|activated charcoal]] filters.<ref name="breath easy" />

Part of the ROS atmosphere control system is the oxygen supply, triple-redundancy is provided by the Elektron unit, solid fuel generators, and stored oxygen. The Elektron unit is the primary oxygen supply, {{chem|O|2}} and {{chem|H|2}} are produced by [[electrolysis]], with the {{chem|H|2}} being vented overboard. The 1 kW system uses approximately 1 litre of water per crew member per day from stored water from Earth, or water recycled from other systems. MIR was the first spacecraft to use recycled water for oxygen production. The secondary oxygen supply is provided by burning {{chem|O|2}}-producing [[Vika oxygen generator|Vika]] cartridges (see also [[ISS ECLSS]]). Each 'candle' takes 5–20 minutes to decompose at 450–500 °C, producing 600 litres of {{chem|O|2}}. This unit is manually operated.<ref>[http://suzymchale.com/ruspace/issrslss.html RuSpace | ISS Russian Segment Life Support System]. Suzymchale.com. Retrieved 8 October 2011.</ref>

The US Orbital Segment has redundant supplies of oxygen, from a pressurised storage tank on the Quest airlock module delivered in 2001, supplemented ten years later by ESA built Advanced Closed-Loop System (ACLS) in the Tranquility module (Node 3), which produces {{chem|O|2}} by electrolysis.<ref>[http://science.nasa.gov/science-news/science-at-nasa/2000/ast13nov_1/ Breathing Easy on the Space Station – NASA Science]. ''Science''.nasa.gov (13 November 2000). Retrieved 8 October 2011.</ref> Hydrogen produced is combined with carbon dioxide from the cabin atmosphere and converted to water and methane.

===Power and thermal control===
{{Main|Electrical system of the International Space Station|External Active Thermal Control System}}

{{Double image|left|ROSSA.jpg|200|P4 deployed.jpg|200|Russian solar arrays, backlit by sunset.|One of the eight truss mounted pairs of USOS solar arrays}}
Double-sided solar, or [[Photovoltaic]] arrays, provide [[Electric power|electrical power]] for the ISS. These bifacial cells are more efficient and operate at a lower temperature than single-sided cells commonly used on Earth, by collecting sunlight on one side and light [[Albedo|reflected off]] the Earth on the other.<ref>{{cite web |url=http://wenku.baidu.com/view/a815121ffc4ffe473368ab7a.html |title=The early history of bifacial solar cell_百度文库 |publisher=Wenku.baidu.com |date=25 October 2010 |accessdate=14 August 2012}}</ref> 

The Russian segment of the station, like the Space Shuttle and most spacecraft, uses 28 [[volt]] [[direct current|DC]] from four rotating solar arrays mounted on ''Zarya'' and ''Zvezda''. The USOS uses 130–180 V DC from the USOS PV array, power is stabilised and distributed at 160 V DC and converted to the user-required 124 V DC. The [[High voltage|higher distribution voltage]] allows smaller, lighter conductors, at the expense of crew safety. The ROS uses [[Extra-low voltage|low voltage]]. The two station segments share power with converters.<ref name="Arrays" />

The USOS solar arrays are arranged as four wing pairs, with each wing producing nearly 32.8 kW.<ref name="Arrays">{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/truss_segment.html|title=Spread Your Wings, It's Time to Fly|publisher=NASA|date=26 July 2006|accessdate=21 September 2006}}</ref> These arrays normally track the sun to maximise power generation. Each array is about 375 m2 (450 yd2) in area and {{convert|58|m|yd|0}} long. In the complete configuration, the solar arrays track the sun by rotating the ''alpha [[gimbal]]'' once per orbit; the ''beta gimbal'' follows slower changes in the angle of the sun to the orbital plane. The [[Night Glider mode]] aligns the solar arrays parallel to the ground at night to reduce the significant aerodynamic drag at the station's relatively low orbital altitude.<ref>{{cite journal|author=G. Landis and C-Y. Lu|year=1991|title=Solar Array Orientation Options for a Space Station in Low Earth Orbit|journal=Journal of Propulsion and Power|volume=7|issue=1|pages=123–125|doi=10.2514/3.23302}}</ref>

The station uses rechargeable [[Nickel hydrogen battery|nickel-hydrogen batteries]] (NiH2) for continuous power during the 35 minutes of every 90-minute orbit that it is eclipsed by the Earth. The batteries are recharged on the day side of the Earth. They have a 6.5-year lifetime (over 37,000 charge/discharge cycles) and will be regularly replaced over the anticipated 20-year life of the station.<ref>{{cite web|url=http://www.grc.nasa.gov/WWW/RT/RT1999/5000/5420miller.html|title=Nickel-Hydrogen Battery Cell Life Test Program Update for the International Space Station|accessdate=27 November 2009|publisher=NASA|author=Thomas B. Miller|date=24 April 2000}}</ref>

The station's large solar panels generate a high potential voltage difference between the station and the ionosphere. This could cause arcing through insulating surfaces and sputtering of conductive surfaces as ions are accelerated by the spacecraft plasma sheath. To mitigate this, plasma contactor units (PCU)s create current paths between the station and the ambient plasma field.<ref>[http://www.grc.nasa.gov/WWW/RT/RT1998/5000/5430patterson.html Cathodes Delivered for Space Station Plasma Contactor System]. Grc.nasa.gov (18 June 1999). Retrieved 8 October 2011.</ref>

[[File:EATCS.png|thumb|ISS External Active Thermal Control System (EATCS) diagram]]
The large amount of electrical power consumed by the station's systems and experiments is turned almost entirely into heat. The heat which can be dissipated through the walls of the stations modules is insufficient to keep the internal ambient temperature within comfortable, workable limits. [[Ammonia]] is continuously pumped through pipework throughout the station to collect heat, then into external radiators exposed to the cold of space, and back into the station.

The International Space Station (ISS) External Active Thermal Control System (EATCS) maintains an equilibrium when the ISS environment or heat loads exceed the capabilities of the Passive Thermal Control System (PTCS). Note Elements of the PTCS are external surface materials, insulation such as MLI, or Heat Pipes. The EATCS provides heat rejection capabilities for all the US pressurised modules, including the JEM and COF as well as the main power distribution electronics of the S0, S1 and P1 Trusses. The EATCS consists an internal, non-toxic, water coolant loop used to cool and dehumidify the atmosphere, which transfers collected heat into an external liquid ammonia loop capable of withstanding the much lower temperature of space, which is then circulated through radiators to remove the heat. The EATCS is capable of rejecting up to 70 kW, and provides a substantial upgrade in heat rejection capacity from the 14 kW capability of the Early External Active Thermal Control System (EEATCS) via the Early Ammonia Servicer (EAS), which was launched on [[STS-105]] and installed onto the P6 Truss.<ref>[http://www.nasa.gov/pdf/473486main_iss_atcs_overview.pdf ATCS Team Overview]. (PDF). Retrieved 8 October 2011.</ref>

===Communications and computers===
{{Main|Tracking and Data Relay Satellite|Luch (satellite)}}
{{See also2|[[ThinkPad#Use in space|ThinkPad use in space]]}}
[[File:ISS Communication Systems.png|thumb|The communications systems used by the ISS * Luch satellite not currently in use|alt=Diagram showing communications links between the ISS and other elements.]]
Radio communications provide [[telemetry]] and scientific data links between the station and [[Mission Control Center|Mission Control Centres]]. Radio links are also used during [[Space rendezvous|rendezvous and docking procedures]] and for audio and video communication between crewmembers, flight controllers and family members. As a result, the ISS is equipped with internal and external communication systems used for different purposes.<ref name="BoeingComm" />


The Russian Orbital Segment communicates directly with the ground via the ''[[Lira (ISS)|Lira]]'' [[Antenna (radio)|antenna]] mounted to ''Zvezda''.<ref name="ISSRG" /><ref>{{cite web|url=http://www.nasa.gov/home/hqnews/2005/mar/HQ_ss05015_ISS_status_report.html|title=International Space Station Status Report: SS05-015|last=Mathews|first=Melissa|author2=James Hartsfield|date=25 March 2005|work=NASA News|publisher=NASA|accessdate=11 January 2010}}</ref> The ''Lira'' antenna also has the capability to use the ''[[Luch (satellite)|Luch]]'' data relay satellite system.<ref name="ISSRG" /> This system, used for communications with ''Mir'', fell into disrepair during the 1990s, and as a result is no longer in use,<ref name="ISSRG" /><ref name="SSSM">{{cite book|first=David|last=Harland|title=The Story of Space Station Mir|publisher=Springer-Verlag New York Inc|date=30 November 2004|location=New York|isbn=978-0-387-23011-5}}</ref><ref name="Harvey">{{cite book|last=Harvey|first=Brian|title=The rebirth of the Russian space program: 50 years after Sputnik, new frontiers|publisher=Springer Praxis Books|year=2007|page=263|isbn=0-387-71354-9}}</ref> although two new ''Luch'' satellites—''Luch''-5A and ''Luch''-5B—were launched in 2011 and 2012 respectively to restore the operational capability of the system.<ref>{{cite web|publisher=RussianSpaceWeb|url=http://www.russianspaceweb.com/2011.html|accessdate=12 January 2010|title=Space exploration in 2011|date=4 January 2010|author=Anatoly Zak}}</ref> Another Russian communications system is the [[Voskhod-M]], which enables internal telephone communications between ''Zvezda'', ''Zarya'', ''Pirs'', ''Poisk'' and the USOS, and also provides a VHF radio link to ground control centres via antennas on ''Zvezda''{{'s}} exterior.<ref>{{cite web|url=http://www.nasa.gov/directorates/somd/reports/iss_reports/2010/05022010.html|date=2 May 2010|accessdate=7 July 2010|publisher=NASA|title=ISS On-Orbit Status 05/02/10}}</ref>

The [[US Orbital Segment]] (USOS) makes use of two separate radio links mounted in the [[Z1 truss]] structure: the [[S band]] (used for audio) and [[Ku band|Ku band]] (used for audio, video and data) systems. These transmissions are routed via the United States [[Tracking and Data Relay Satellite]] System (TDRSS) in [[geostationary orbit]], which allows for almost continuous real-time communications with [[Christopher C. Kraft Jr. Mission Control Center|NASA's Mission Control Center]] (MCC-H) in [[Houston]].<ref name="ISSBook" /><ref name="ISSRG" /><ref name="BoeingComm">{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/systems/communications_tracking.html|publisher=Boeing|accessdate=30 November 2009|title=Communications and Tracking|archiveurl = https://web.archive.org/web/20080611115319/http://www.boeing.com/defense-space/space/spacestation/systems/communications_tracking.html |archivedate = 11 June 2008}}</ref> Data channels for the Canadarm2, European ''Columbus'' laboratory and Japanese ''Kibō'' modules are routed via the S band and Ku band systems, although the [[European Data Relay System]] and a similar Japanese system will eventually complement the TDRSS in this role.<ref name="ISSBook" /><ref name="JAXA-MOU">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/nasa_japan.html|title=Memorandum of Understanding Between the National Aeronautics and Space Administration of the United States of America and the Government of Japan Concerning Cooperation on the Civil International Space Station|publisher=NASA|accessdate=19 April 2009|date=24 February 1998}}</ref> Communications between modules are carried on an internal digital [[wireless network]].<ref>{{cite web|title=Operations Local Area Network (OPS LAN) Interface Control Document|format=PDF|publisher=NASA|url=http://www.spaceref.com/iss/computer/iss.ops.lan.icd.pdf|accessdate=30 November 2009|date=February 2000}}</ref>

[[File:STS-128 ISS-20 Destiny Canadarm2.jpg|thumb|left|Laptop computers surround the Canadarm2 console.]]
[[Ultra high frequency|UHF radio]] is used by astronauts and cosmonauts conducting [[Extra-vehicular activity|EVAs]]. UHF is employed by other spacecraft that dock to or undock from the station, such as Soyuz, Progress, HTV, ATV and the Space Shuttle (except the shuttle also makes use of the S band and Ku band systems via TDRSS), to receive commands from Mission Control and ISS crewmembers.<ref name="ISSRG" /> Automated spacecraft are fitted with their own communications equipment; the ATV uses a [[laser]] attached to the spacecraft and equipment attached to ''Zvezda'', known as the Proximity Communications Equipment, to accurately dock to the station.<ref>{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=16247|title=ISS/ATV communication system flight on Soyuz|accessdate=30 November 2009|publisher=[[EADS Astrium]]|date=28 February 2005}}</ref><ref>{{cite web|publisher=NASASpaceflight.com|author=Chris Bergin|url=http://www.nasaspaceflight.com/2009/11/sts-129-support-dragon-communication-demo-iss/|date=10 November 2009|accessdate=30 November 2009|title=STS-129 ready to support Dragon communication demo with ISS}}</ref>

The ISS is equipped with approximately 100 [[IBM]] and [[Lenovo]] [[ThinkPad#Use in space|ThinkPad]] model A31 and T61P laptop computers. Each computer is a [[commercial off-the-shelf]] purchase which is then modified for safety and operation including updates to connectors, cooling and power to accommodate the station's 28V DC power system and weightless environment. Heat generated by the laptops does not rise, but stagnates surrounding the laptop, so additional forced ventilation is required. Laptops aboard the ISS are connected to the station's [[wireless LAN]] via [[Wi-Fi]] and to the ground via Ku band. This provides speeds of 10 [[Megabit per second|Mbit/s]] to and 3 Mbit/s from the station, comparable to home [[digital subscriber line|DSL]] connection speeds.<ref name="issit">{{cite news |url=http://bits.blogs.nytimes.com/2010/01/22/first-tweet-from-space/ |title=First Tweet From Space |work=[[The New York Times]] |first=Nick |last=Bilton |date=22 January 2010 |accessdate=29 April 2014}}</ref><ref name="tested20121019">{{cite news |url=http://www.tested.com/science/space/449539-how-fast-isss-internet-and-other-space-questions-answered/ |title=How Fast is the ISS's Internet? (and Other Space Questions Answered) |work=Tested.com |first=Will |last=Smith |date=19 October 2012 |accessdate=29 April 2014}}</ref>

The operating system used for key station functions is the [[Debian]] [[GNU/Linux distribution]].<ref>{{cite news|last=Thomson|first=Iain|title=Penguins in spa-a-a-ce! ISS dumps Windows for Linux on laptops|url=http://www.theregister.co.uk/2013/05/10/iss_linux_debian_deployment/|accessdate=15 May 2013|newspaper=The Register|date=10 May 2013}}</ref> The migration from [[Microsoft Windows]] was made in May 2013 for reasons of reliability, stability and flexibility.<ref>{{cite news|last=Gunter|first=Joel|title=International Space Station to boldly go with Linux over Windows|url=http://www.telegraph.co.uk/technology/news/10049444/International-Space-Station-to-boldly-go-with-Linux-over-Windows.html|accessdate=15 May 2013|newspaper=The Daily Telegraph|date=10 May 2013}}</ref>

==Station operations==

===Expeditions and private flights===
[[File:Sts088-703-019e.jpg|thumb|Zarya and Unity were entered for the first time on 10 December 1998.]]
[[File:Soyuz tm-31 transported to launch pad.jpg|right|thumb|Soyuz TM-31 being prepared to bring the first resident crew to the station in October 2000]]
[[File:STS-115 ISS after undocking.jpg|thumb|right|ISS was slowly assembled over a decade of spaceflights and crews]]
[[File:Tracy Caldwell Dyson in Cupola ISS.jpg|thumb|Expeditions have included male and female crew-members from many nations]]
''See also the [[list of International Space Station expeditions]] (professional crew), [[space tourism]] (private travellers), and the [[list of human spaceflights to the ISS]] (both).''

Each permanent crew is given an expedition number. Expeditions run up to six months, from launch until undocking, an 'increment' covers the same time period, but includes cargo ships and all activities. Expeditions 1 to 6 consisted of 3 person crews, Expeditions 7 to 12 were reduced to the safe minimum of two following the destruction of the NASA Shuttle Columbia. From Expedition 13 the crew gradually increased to 6 around 2010.<ref name="ISSEx">{{cite web|title=International Space Station Expeditions|publisher=NASA|url=http://www.nasa.gov/mission_pages/station/expeditions/index.html|date=10 April 2009|accessdate=13 April 2009}}</ref><ref name="current">{{cite web|url=http://www.nasa.gov/mission_pages/station/main/index.html|title=International Space Station|accessdate=22 October 2008|publisher=NASA|year=2008|author=NASA}}</ref> With the arrival of the American [[Commercial Crew Development|Commercial Crew]] vehicles in the middle of the 2010s, expedition size may be increased to seven crew members, the number ISS is designed for.<ref>{{cite web|url=http://www.aviationweek.com/article.aspx?id=/article-xml/asd_07_26_2012_p01-02-480253.xml|title=ISS Research Hampered By Crew Availability|last=Morring|first=Frank|date=27 July 2012|quote=A commercial capability would allow the station's crew to grow from six to seven by providing a four-seat vehicle for emergency departures in addition to the three-seat Russian Soyuz capsules in use today.|publisher=Aviation Week|accessdate=30 July 2012}}</ref><ref>{{cite web|url=http://www.airspacemag.com/space-exploration/AS-Interview-Mike-Suffredini.html|title=Assembly (Nearly) Complete |last=Hoversten|first=Paul|date=1 May 2011|publisher=Air & Space Magazine|quote=In fact, we're designed on the U.S. side to take four crew. The ISS design is actually for seven. We operate with six because first, we can get all our work done with six, and second, we don't have a vehicle that allows us to fly a seventh crew member. Our requirement for the new vehicles being designed is for four seats. So I don't expect us to go down in crew size. I would expect us to increase it.|accessdate=8 May 2011}}</ref>

[[Sergei Krikalev]], member of [[Expedition 1]] and Commander of [[Expedition 11]] has spent more time in space than anyone else, a total of 803 days and 9 hours and 39 minutes. His awards include the [[Order of Lenin]], [[Hero of the Soviet Union]], [[Hero of the Russian Federation]], and 4 NASA medals. On 16 August 2005 at 1:44 am EDT he passed the record of 748 days held by [[Sergei Avdeyev]], who had 'time travelled' 1/50th of a second into the future on board MIR.<ref>{{cite web|url=http://www.popsci.com/scitech/article/2002-02/lets-do-time-warp-again?page=2 |archiveurl=https://web.archive.org/web/20100628190931/http://www.popsci.com/scitech/article/2002-02/lets-do-time-warp-again?page=2 |archivedate=28 June 2010 |title=Let's Do the Time Warp Again |publisher=Web.archive.org |date=28 June 2010 |accessdate=1 May 2012}}</ref> He participated in psychosocial experiment SFINCSS-99 (Simulation of Flight of International Crew on Space Station), which examined inter-cultural and other stress factors affecting integration of crew in preparation for the ISS spaceflights. Commander [[Michael Fincke]] has spent a total of 382 days in space – more than any other American astronaut.

Travellers who pay for their own passage into space are termed spaceflight participants by Roscosmos and NASA, and are sometimes informally referred to as space tourists, a term they generally dislike.{{refn|Privately funded travellers who have objected to the term include Dennis Tito, the first such traveller (''Associated Press'', 8 May 2001), [[Mark Shuttleworth]], founder of [[Ubuntu (operating system)|Ubuntu]] (''Associated Press, The Spokesman Review, 6 January 2002, p. A4''), Gregory Olsen and Richard Garriott.<ref>{{cite news|last=Schwartz|first=John|title=Russia Leads Way in Space Tourism With Paid Trips into Orbit|url=http://www.nytimes.com/2008/10/11/science/space/11space.html|newspaper=The New York Times|date=10 October 2008}}</ref><ref>{{cite web|last=Boyle|first=Alan|title=Space passenger Olsen to pull his own weight|url=http://msnbc.msn.com/id/9323509/#.Tz5lcFE-qr4|publisher=MSNBC}}</ref> Canadian astronaut Bob Thirsk said the term does not seem appropriate, referring to his crewmate, [[Guy Laliberté]], founder of [[Cirque du Soleil]].<ref>{{cite web|url=http://www.stcatharinesstandard.ca/ArticleDisplay.aspx?e=1975186&archive=true |title=Flight to space ignited dreams | St. Catharines Standard |publisher=Stcatharinesstandard.ca |accessdate=1 May 2012}}</ref> Anousheh Ansari denied being a tourist<ref>{{cite web|url=http://www.esa.int/esaHS/SEMD58BE8YE_business_0.html |title=ESA – Human Spaceflight and Exploration – Business – "I am NOT a tourist" |publisher=Esa.int |date=18 September 2006 |accessdate=1 May 2012}}</ref> and took offence at the term.<ref>{{cite web|url=http://www.space.com/2889-interview-anousheh-ansari-female-space-tourist.html |title=Interview with Anousheh Ansari, the First Female Space Tourist |publisher=Space.com |date=15 September 2006 |accessdate=1 May 2012}}</ref>|group=note|name}} All seven were transported to the ISS on Russian Soyuz spacecraft. When professional crews change over in numbers not divisible by the three seats in a Soyuz, and a short-stay crewmember is not sent, the spare seat is sold by MirCorp through Space Adventures. When the space shuttle retired in 2011, and the station's crew size was reduced to 6, space tourism was halted, as the partners relied on Russian transport seats for access to the station. Soyuz flight schedules increase after 2013, allowing 5 Soyuz flights (15 seats) with only two expeditions (12 seats) required.<ref>{{cite web|url=http://www.spaceflightnow.com/news/n1101/12soyuz/ |title=Breaking News | Resumption of Soyuz tourist flights announced |publisher=Spaceflight Now |accessdate=1 May 2012}}</ref> The remaining seats are sold for around {{US$|40 million}} to members of the public who can pass a medical. ESA and NASA criticised private spaceflight at the beginning of the ISS, and NASA initially resisted training [[Dennis Tito]], the first man to pay for his own passage to the ISS.{{refn|ESA director Jörg Feustel-Büechl said in 2001 that Russia had no right to send 'amateurs' to the ISS. A 'stand-off' occurred at the Johnson Space Centre between Commander Talgat Musabayev and NASA manager Robert Cabana. Cabana refused to train Dennis Tito, a member of Musabayev's crew along with Yuri Baturin. The commander argued that Tito had trained 700 hours in the last year and was as qualified as any NASA astronaut, and refused to allow his crew to be trained on the American portions of the station without Tito. Cabana stated training could not begin, and the commander returned with his crew to their hotel.|group=note|name}}  [[Toyohiro Akiyama]] was flown to Mir for a week, he was classed as a business traveller, as his employer, [[Tokyo Broadcasting System]], paid for his ticket, and he gave a daily TV broadcast from orbit.

[[Anousheh Ansari]] ({{lang-fa|انوشه انصاری}}) became the first Iranian in space and the first self-funded woman to fly to the station. Officials reported that her education and experience make her much more than a tourist, and her performance in training had been "excellent."<ref>{{cite web|last=Maher |first=Heather |url=http://www.rferl.org/content/article/1071358.html |title=U.S.: Iranian-American To Be First Female Civilian in Space |publisher=Radio Free Europe/Radio Liberty |date=15 September 2006 |accessdate=1 May 2012}}</ref> Ansari herself dismisses the idea that she is a tourist. She did Russian and European studies involving medicine and microbiology during her 10-day stay. The documentary ''[[Space Tourists]]'' follows her journey to the station, where she fulfilled "an age-old dream of man: to leave our planet as a «normal person» and travel into outer space."<ref>{{cite web|url=http://www.space-tourists-film.com/en/film_synopsis.php |title=Space Tourists | A Film By Christian Frei |publisher=Space-tourists-film.com |accessdate=1 May 2012}}</ref> In the film, some Kazakhs are shown waiting in the middle of the steppes for four rocket stages to literally fall from the sky. Film-maker Christian Frei states "Filming the work of the Kazakh scrap metal collectors was anything but easy. The Russian authorities finally gave us a film permit in principle, but they imposed crippling preconditions on our activities. The real daily routine of the scrap metal collectors could definitely not be shown. Secret service agents and military personnel dressed in overalls and helmets were willing to ''re-enact'' their work for the cameras – in an idealised way that officials in Moscow deemed to be presentable, but not at all how it takes place in reality."

Spaceflight participant [[Richard Garriott]] placed a [[Geocaching|geocache]] aboard the ISS during his flight.<ref>{{cite web|url=http://www.geocaching.com/seek/cache_details.aspx?wp=GC1BE91|title=International Space Station Traditional Geocache}}</ref> This is currently the only non-terrestrial geocache in existence.<ref>{{cite web |url=http://www.geekwire.com/2011/outer-space-ocean-floor-15m-geocaches-counting/|accessdate=27 February 2013|last=Cook|first=John|title=From outer space to the ocean floor, Geocaching.com now boasts more than 1.5 million hidden treasures|date=29 August 2011}}</ref>

===Orbit===
{{Double image|right|Internationale Raumstation Bahnhöhe (dumb version).png|300|Iss.ogg|235|Graph showing the changing altitude of the ISS from November 1998 until January 2009|Animation of ISS orbit from a North American geostationary point of view (sped up 1800 times)}}
The ISS is maintained in a nearly circular orbit with a minimum mean altitude of 330 km (205 mi) and a maximum of 410 km (255 mi), in the centre of the [[thermosphere]], at an [[inclination]] of 51.6 degrees to Earth's equator, necessary to ensure that Russian [[Soyuz (spacecraft)|Soyuz]] and [[Progress (spacecraft)|Progress]] spacecraft launched from the [[Baikonur Cosmodrome]] may be safely launched to reach the station. Spent rocket stages must be dropped into uninhabited areas and this limits the directions rockets can be launched from the spaceport.<ref name="MCC Answer">{{cite web|last=Cooney|first=Jim|title=Mission Control Answers Your Questions|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-112/09_04_12_54_17.html|location=Houston, TX|quote=Jim Cooney ISS Trajectory Operations Officer}}</ref><ref>{{cite book|last=Pelt|first=Michel van|title=Into the Solar System on a String : Space Tethers and Space Elevators|year=2009|publisher=Springer New York|location=New York, NY|isbn=0-387-76555-7|page=133|edition=1.}}</ref> The orbital inclination chosen was also low enough to allow American space shuttles launched from Florida to reach the ISS.

It travels at an average speed of 27,724 kilometres (17,227 mi) per hour, and completes {{Orbit|daily orbits|15.54}} orbits per day (93 minutes per orbit).{{Orbit|ref|<ref name="heavens-above"/>}}<ref name="tracking">{{cite web|url=http://spaceflight.nasa.gov/realdata/tracking/index.html|title=Current ISS Tracking data|accessdate=28 January 2009|publisher=NASA|date=15 December 2008|author=NASA}}</ref> The station's altitude was allowed to fall around the time of each NASA shuttle mission. Orbital boost burns would generally be delayed until after the shuttle's departure. This allowed shuttle payloads to be lifted with the station's engines during the routine firings, rather than have the shuttle lift itself and the payload together to a higher orbit. This trade-off allowed heavier loads to be transferred to the station. After the retirement of the NASA shuttle, the nominal orbit of the space station was raised in altitude.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/06/europes-atv-2-depart-iss-make-way-russias-progress-m-11m/ |title=Europe's ATV-2 departs ISS to make way for Russia's Progress M-11M |publisher=NASASpaceFlight.com |date=20 June 2011 |accessdate=1 May 2012}}</ref><ref name="Popular Mechanics">{{cite web|url=http://www.popularmechanics.com/science/air_space/4275571.html|title=The Uncertain Future of the International Space Station: Analysis|author=Rand Simberg|date=29 July 2008|accessdate=6 March 2009|publisher=[[Popular Mechanics]]}}</ref> Other, more frequent supply ships do not require this adjustment as they are substantially lighter vehicles.<ref name="Worldbook at NASA">{{cite web|url=http://www.nasa.gov/worldbook/intspacestation_worldbook.html|title = International Space Station|year=2005|accessdate=14 June 2008|publisher=World Book, Inc|author=James Oberg|work=World Book Online Reference Center}}{{dead link|date=May 2012}}</ref><ref name="nasa.gov-iss-environment">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archiveurl=https://web.archive.org/web/20080213164432/http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archivedate=13 February 2008|title=ISS Environment|accessdate=15 October 2007|publisher=[[Johnson Space Center]]}}</ref>
[[File:ISS orbits 04132013.jpg|thumbnail|Orbits of the ISS, shown in April 2013]]
Orbital boosting can be performed by the station's two main engines on the ''[[Zvezda (ISS module)|Zvezda]]'' service module, or Russian or European spacecraft docked to Zvezda's aft port. The ATV has been designed with the possibility of adding a [[Automated Transfer Vehicle#ATV evolution proposals|second docking port]] to its other end, allowing it to remain at the ISS and still allow other craft to dock and boost the station. It takes approximately two orbits (three hours) for the boost to a higher altitude to be completed.<ref name="nasa.gov-iss-environment" /> In December 2008 NASA signed an agreement with the [[Ad Astra Rocket Company]] which may result in the testing on the ISS of a [[VASIMR]] plasma propulsion engine.<ref name="vasimr">{{cite web|url=http://www.adastrarocket.com/AdAstra-NASA_PR12Dec08.pdf|publisher=AdAstra Rocket Company|title=Press Release 121208|accessdate=7 December 2009|date=12 December 2008|format=PDF}}</ref> This technology could allow [[Orbital station-keeping|station-keeping]] to be done more economically than at present.<ref name="future-prop">{{cite web|url=http://www.nasa.gov/vision/space/travelinginspace/future_propulsion.html|title=Propulsion Systems of the Future|accessdate=29 May 2009|publisher=NASA}}</ref><ref>{{cite web|work=New Scientist|accessdate=7 October 2009|url=http://www.newscientist.com/article/dn17918-rocket-company-tests-worlds-most-powerful-ion-engine.html|title=Rocket company tests world's most powerful ion engine|author=David Shiga|date=5 October 2009}}</ref>

The Russian Orbital Segment contains the station's engines and control [[Bridge (nautical)|bridge]], which handles Guidance, Navigation and Control (ROS GNC) for the entire station.<ref name="Navigation">{{cite web|url=http://www.esa.int/export/esaHS/ESAOXX0VMOC_iss_0.html|title=DMS-R: ESA's Data Management System for the Russian Segment of the ISS}}</ref> Initially, Zarya, the first module of the station, controlled the station until a short time after the Russian service module Zvezda docked and was transferred control. Zvezda contains the ESA built DMS-R Data Management System.<ref name="EsaComputer">{{cite web|url=http://www.esa.int/esapub/onstation/onstation17/os17_chapter6.pdf|title=Exercising Control 49 months of DMS-R Operations}}</ref> Using two fault-tolerant computers (FTC), Zvezda computes the station's position and orbital trajectory using redundant Earth horizon sensors, Solar horizon sensors as well as Sun and star trackers. The FTCs each contain three identical processing units working in parallel and provide advanced fault-masking by majority voting. Zvezda uses gyroscopes and thrusters to turn itself around. Gyroscopes do not require propellant, rather they use electricity to 'store' momentum in flywheels by turning in the opposite direction to the station's movement. The USOS has its own computer controlled gyroscopes to handle the extra mass of that section. When gyroscopes 'saturate', reaching their maximum speed, thrusters are used to cancel out the stored momentum. During [[Expedition 10]], an incorrect command was sent to the station's computer, using about 14 kilograms of propellant before the fault was noticed and fixed. When attitude control computers in the ROS and USOS fail to communicate properly, it can result in a rare 'force fight' where the ROS GNC computer must ignore the USOS counterpart, which has no thrusters.<ref>{{cite web|url=http://pims.grc.nasa.gov/pimsdocs/public/ISS%20Handbook/hb_qs_vehicle_RussianUSGNCForceFight.pdf |title=Microsoft Word – hb_qs_vehicle_RussianUSGNCForceFight_pg1.doc |format=PDF |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://spaceflight.nasa.gov/spacenews/reports/issreports/2005/iss05-7.html|title = International Space Station Status Report #05-7|date=11 February 2005|publisher=NASA|accessdate=23 November 2008}}</ref><ref>{{cite book|title=Dynamics and Control of Attitude, Power, and Momentum for a Spacecraft Using Flywheels and Control Moment Gyroscopes|author=Carlos Roithmayr|format=PDF|year=2003|publisher=NASA|location=Langley Research Center|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030038806_2003038772.pdf|accessdate=12 July 2011}}</ref> When an ATV, NASA Shuttle, or Soyuz is docked to the station, it can also be used to maintain station attitude such as for troubleshooting. Shuttle control was used exclusively during [[STS-117|installation]] of the S3/S4 truss, which provides electrical power and data interfaces for the station's electronics.<ref>{{cite web|url=http://www.nasaspaceflight.com/2007/06/atlantis-ready-to-support-iss-troubleshooting/|title=Atlantis ready to support ISS troubleshooting|publisher=NASASPaceflight.com|author=Chris Bergin|accessdate=6 March 2009|date=14 June 2007}}</ref>

==Mission controls==
The components of the ISS are operated and monitored by their respective space agencies at [[Mission Control Center|mission control centres]] across the globe, including:
* Roscosmos's [[Mission Control Center#RKA Mission Control Center|Mission Control Center]] at [[Korolyov (city)|Korolyov]], Moscow Oblast, controls the [[Russian Orbital Segment]] which handles Guidance, Navigation & Control for the entire Station.,<ref name="Navigation" /><ref name="EsaComputer" /> in addition to individual Soyuz and Progress missions.<ref name="ISSRG" />
* ESA's [[ATV Control Centre]], at the [[Toulouse Space Centre]] (CST) in [[Toulouse]], France, controls flights of the unmanned European [[Automated Transfer Vehicle]].<ref name="ISSRG" />
* JAXA's [[JEM Control Center]] and [[HTV Control Center]] at [[Tsukuba Space Center]] (TKSC) in [[Tsukuba]], Japan, are responsible for operating the Japanese Experiment Module complex and all flights of the 'White Stork' HTV Cargo spacecraft, respectively.<ref name="ISSRG" />
* NASA's [[Christopher C. Kraft Jr. Mission Control Center|Mission Control Center]] at [[Lyndon B. Johnson Space Center]] in Houston, Texas, serves as the primary control facility for the United States segment of the ISS and also controlled the Space Shuttle missions that visited the station.<ref name="ISSRG">{{cite book|author=Gary Kitmacher|title=Reference Guide to the International Space Station| publisher =[[Apogee Books]]|location=Canada|year=2006|isbn=978-1-894959-34-6|issn=1496-6921|pages=71–80}}</ref>
* NASA's [[Payload Operations and Integration Center]] at [[Marshall Space Flight Center]] in [[Huntsville, Alabama]], coordinates payload operations in the USOS.<ref name="ISSRG" />
* ESA's [[Columbus Control Center|Columbus Control Centre]] at the [[German Aerospace Center|German Aerospace Centre]] (DLR) in [[Oberpfaffenhofen]], Germany, manages the European ''Columbus'' research laboratory.<ref name="ISSRG" />
* CSA's [[MSS Control]] at [[Saint-Hubert, Quebec]], Canada, controls and monitors the [[Mobile Servicing System]], or Canadarm2.<ref name="ISSRG" />
{{wide image|ISS Centers.svg|880px|Space centres involved with the ISS programme|alt=A world map highlighting the locations of space centres. See adjacent text for details.}}

===Repairs===
{{Main|Orbital Replacement Units|International Space Station maintenance}}
'''[[Orbital Replacement Units]]''' ('''ORUs''') are spare parts that can be readily replaced when a unit either passes its design life or fails. Examples of ORUs are pumps, storage tanks, controller boxes, antennas, and battery units. Some units can be replaced using robotic arms. Many are stored outside the station, either on small pallets called [[ExPRESS Logistics Carrier]]s (ELCs) or share larger platforms called [[External Stowage Platform]]s which also hold science experiments. Both kinds of pallets have electricity as many parts which could be damaged by the cold of space require heating. The larger logistics carriers also have computer local area network connections (LAN) and telemetry to connect experiments. A heavy emphasis on stocking the USOS with ORU's occurred around 2011, before the end of the NASA shuttle programme, as its commercial replacements, [[Cygnus (spacecraft)|Cygnus]] and [[Dragon (spacecraft)|Dragon]], carry one tenth to one quarter the payload.

[[File:ISS Unpressurized Platforms.png|thumb|Spare parts are called [[Orbit Replaceable Unit|ORU]]s; some are externally stored on pallets called [[ExPRESS Logistics Carrier|ELC]]s and [[External stowage platform|ESP]]s.]]

Unexpected problems and failures have impacted the station's assembly time-line and work schedules leading to periods of reduced capabilities and, in some cases, could have forced abandonment of the station for safety reasons, had these problems not been resolved. During [[STS-120]] in 2007, following the relocation of the P6 truss and solar arrays, it was noted during the redeployment of the array that it had become torn and was not deploying properly.<ref name="Astronauts notice tear in solar panel">{{cite news|url=http://www.redorbit.com/news/space/1123767/astronauts_notice_tear_in_solar_panel/index.html |title=Astronauts notice tear in solar panel|accessdate=30 October 2007|agency=Associated Press|date=30 October 2007|author=Liz Austin Peterson}}</ref> An EVA was carried out by [[Scott E. Parazynski|Scott Parazynski]], assisted by [[Douglas H. Wheelock|Douglas Wheelock]]. The men took extra precautions to reduce the risk of electric shock, as the repairs were carried out with the solar array exposed to sunlight.<ref name="Space Station's Damaged Panel Is Fixed">{{cite news|url=http://www.washingtonpost.com/wp-dyn/content/article/2007/11/03/AR2007110300227.html|title=Space Station's Damaged Panel Is Fixed|accessdate=4 November 2007|work=The Washington Post|date=4 November 2007|first=Rob|last=Stein}}</ref> The issues with the array were followed in the same year by problems with the starboard Solar Alpha Rotary Joint (SARJ), which rotates the arrays on the starboard side of the station. Excessive vibration and high-current spikes in the array drive motor were noted, resulting in a decision to substantially curtail motion of the starboard SARJ until the cause was understood. Inspections during EVAs on STS-120 and [[STS-123]] showed extensive contamination from metallic shavings and debris in the large drive gear and confirmed damage to the large metallic race ring at the heart of the joint, and so the joint was locked to prevent further damage.<ref name="joint-update">{{cite news|url=http://spaceflightnow.com/shuttle/sts123/080325sarj/index.html|title=Station chief gives detailed update on joint problem|accessdate=5 November 2008|author=William Harwood|publisher=CBS News & SpaceflightNow.com|date=25 March 2008}}</ref> Repairs to the joint were carried out during [[STS-126]] with lubrication of both joints and the replacement of 11 out of 12 trundle bearings on the joint.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts126/126_overview.html|title=Crew Expansion Prep, SARJ Repair Focus of STS-126|accessdate=5 November 2008|publisher=NASA|date=30 October 2008}}</ref><ref>{{cite news|url=http://www.spaceflightnow.com/shuttle/sts126/081118fd5/index.html|title=Astronauts prepare for first spacewalk of shuttle flight|date=18 November 2008|author=William Harwood|publisher=CBS News & SpaceflightNow.com|accessdate=22 November 2008}}</ref>

[[File:STS-120 EVA Scott Parazynski.jpg|thumb|While anchored on the end of the [[Orbiter Boom Sensor System|OBSS]], astronaut [[Scott Parazynski]] performs makeshift repairs to a US Solar array which damaged itself when unfolding, during [[STS-120]].|alt=Two black and orange solar arrays, shown uneven and with a large tear visible. A crew member in a spacesuit, attached to the end of a robotic arm, holds a latticework between two solar sails.]]
2009 saw damage to the S1 radiator, one of the components of the station's cooling system. The problem was first noticed in [[Soyuz spacecraft|Soyuz]] imagery in September 2008, but was not thought to be serious.<ref name="Radiator">{{cite web|url=http://www.nasaspaceflight.com/2009/04/iss-concern-s1-radiator-may-require-replacement-shuttle-mission/|author=Chris Bergin|date=1 April 2009|publisher=NASASpaceflight.com|title=ISS concern over S1 Radiator – may require replacement via shuttle mission|accessdate=3 April 2009}}</ref> The imagery showed that the surface of one sub-panel has peeled back from the underlying central structure, possibly due to micro-meteoroid or debris impact. It is also known that a Service Module thruster cover, jettisoned during an EVA in 2008, had struck the S1 radiator, but its effect, if any, has not been determined. On 15 May 2009 the damaged radiator panel's ammonia tubing was mechanically shut off from the rest of the cooling system by the computer-controlled closure of a valve. The same valve was used immediately afterwards to vent the ammonia from the damaged panel, eliminating the possibility of an ammonia leak from the cooling system via the damaged panel.<ref name="Radiator" />

Early on 1 August 2010, a failure in cooling Loop A (starboard side), one of two external cooling loops, left the station with only half of its normal cooling capacity and zero redundancy in some systems.<ref>{{cite web|url=http://spaceflightnow.com/news/n1007/31station/ |title=Problem forces partial powerdown aboard station |publisher=Spaceflightnow.com |date=31 July 2010 |accessdate=16 November 2010}}</ref><ref>{{cite web|url=http://www.spaceref.com/news/viewsr.html?pid=34622 |title=NASA ISS On-Orbit Status 1 August 2010 (early edition) |publisher=Spaceref.com |date=31 July 2010 |accessdate=16 November 2010}}</ref><ref>{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/systems/atcs.html |title=ISS Active Control System |publisher=Boeing |date=21 November 2006 |accessdate=16 November 2010}}</ref> The problem appeared to be in the ammonia pump module that circulates the ammonia cooling fluid. Several subsystems, including two of the four CMGs, were shut down.

Planned operations on the ISS were interrupted through a series of EVAs to address the cooling system issue. A first EVA on 7 August 2010, to replace the failed pump module, was not fully completed due to an ammonia leak in one of four quick-disconnects. A second EVA on 11 August successfully removed the failed pump module.<ref>[http://spaceflightnow.com/station/exp24/100810evapre/index.html Spaceflight Now] "Wednesday spacewalk to remove failed coolant pump"</ref><ref>[http://www.nasaspaceflight.com/2010/08/live-second-eva-with-pump-module-changeout/ NASA spaceflight 11 August] "Large success for second EVA as failed Pump Module is removed"</ref> A third EVA was required to restore Loop A to normal functionality.<ref>[http://spaceflightnow.com/station/exp24/100811eva2/index5.html Spaceflight Now 12 August] "Station's bad pump removed; more spacewalking ahead"</ref><ref>[http://www.nasaspaceflight.com/2010/08/iss-cooling-returning-normal-confirming-etcs-pm-success/ Spaceflight Now, 18 August] ISS cooling configuration returning to normal confirming ETCS PM success</ref>

The USOS's cooling system is largely built by the American company [[Boeing]],<ref>{{cite web|url=http://www.space.com/businesstechnology/international-space-station-complexities-100802.html|title=Cooling System Malfunction Highlights Space Station's Complexity|publisher=Space.com|date=2 August 2010}}</ref> which is also the manufacturer of the failed pump.<ref>{{cite web|url=http://spaceflightnow.com/news/n1007/31station/|title=Spacewalks needed to fix station cooling problem|publisher=Spaceflightnow|date=31 July 2010}}</ref>

An air leak from the USOS in 2004,<ref>{{cite news|url=http://www.msnbc.msn.com/id/3882962/|title=Crew finds 'culprit' in space station leak|publisher=MSNBC|date=11 January 2004|author=James Oberg|accessdate=22 August 2010}}</ref> the venting of fumes from an ''[[Elektron (ISS)|Elektron]]'' oxygen generator in 2006,<ref>{{cite news|url=http://spaceflightnow.com/station/exp13/060918elektron.html|title=Oxygen Generator Problem Triggers Station Alarm|publisher = CBS News through Spaceflight Now|date=18 September 2006|author=William Harwood|accessdate=24 November 2008}}</ref> and the failure of the computers in the ROS in 2007 during [[STS-117]] left the station without thruster, ''Elektron'', ''[[Vozdukh]]'' and other environmental control system operations, the root cause of which was found to be condensation inside the electrical connectors leading to a short-circuit.{{Citation needed|date=June 2011}}
[[File:STS-134 EVA4 view to the Russian Orbital Segment.jpg|thumb|right|In the foreground, a set of heat radiators]]
The four Main Bus Switching Units (MBSUs, located in the S0 truss), control the routing of power from the four solar array wings to the rest of the ISS. In late 2011 MBSU-1, while still routing power correctly, ceased responding to commands or sending data confirming its health, and was scheduled to be swapped out at the next available EVA. In each MBSU, two power channels feed 160V DC from the arrays to two DC-to-DC power converters (DDCUs) that supply the 124V power used in the station. A spare MBSU was already on board, but 30 August 2012 EVA failed to be completed when a bolt being tightened to finish installation of the spare unit jammed before electrical connection was secured.<ref>{{cite web|author=30 August 2012 by Pete Harding |url=http://www.nasaspaceflight.com/2012/08/astronaut-perform-first-post-shuttle-spacewalk-iss |title=Astronaut duo complete challenging first post-Shuttle US spacewalk on ISS |publisher=Nasaspaceflight.com |date=30 August 2012 |accessdate=22 October 2013}}</ref> The loss of MBSU-1 limits the station to 75% of its normal power capacity, requiring minor limitations in normal operations until the problem can be addressed.

On 5 September 2012, in a second, 6 hr, EVA to replace MBSU-1, astronauts Sunita Williams and Akihiko Hoshide successfully restored the ISS to 100% power.<ref>[http://spaceref.com/international-space-station/critical-space-station-spacewalk-a-success.html Spaceref.com Sept 5, 2012] Marc Boucher "Critical Space Station spacewalk a Success".</ref>
[[File:Astronaut Mike Hopkins on Dec. 24 Spacewalk.jpg|thumb|Mike Hopkins on his Christmas Eve spacewalk]]
On 24 December 2013, astronauts made a rare Christmas Eve space walk, installing a new ammonia pump for the station's cooling system. The faulty cooling system had failed earlier in the month, halting many of the station's science experiments. Astronauts had to brave a "mini blizzard" of ammonia while installing the new pump. It was only the second Christmas Eve spacewalk in NASA history.<ref>{{cite web|last=AP|title=Astronauts Complete Rare Christmas Eve Spacewalk|url=http://www.leaker.com/astronauts-complete-rare-christmas-eve-spacewalk/|publisher=Leaker|accessdate=24 December 2013|date=24 December 2013}}</ref>

[[File:Iss orbit and expeditions.png|thumb|Iss orbit with calendar of expeditions and modules]]

==Fleet operations==
:{{See also|List of human spaceflights to the International Space Station|List of unmanned spaceflights to the International Space Station}}
A wide variety of manned and unmanned spacecraft have supported the station's activities. 
[[Progress M-28M]] (ISS-60P) was the 62nd Progress spacecraft planned to arrive at the ISS, including [[Progress M-MIM2|M-MIM2]] and [[Progress M-SO1|M-SO1]] which installed modules. 35 flights of the retired NASA Space Shuttle were made to the station.<ref name="ISStD">{{cite web|url=http://spaceflight.nasa.gov/station/isstodate.html|title=The ISS to Date|accessdate=21 March 2011|publisher=NASA|date=9 March 2011|author=NASA}}</ref> [[Soyuz TMA-16M|TMA-16M]] is the 42nd Soyuz flight, and there have been 5 [[Automated Transfer Vehicle|European ATV]], 4 Japanese [[H-II Transfer Vehicle|Kounotori]] 'White Stork', 8 [[SpaceX]] [[Dragon (spacecraft)|Dragon]] and 4 OSC [[Cygnus (spacecraft)|Cygnus]] planned arrivals.

===Currently docked/berthed===
''See also the list of [[List of International Space Station expeditions|professional]] crew, [[Space tourism|private]] travellers, [[List of human spaceflights to the ISS|both]] or just [[List of unmanned spaceflights to the ISS|unmanned spaceflights]].''

;Key
{{legend|lightblue|Uncrewed cargoships are in light blue}}
{{legend|#cfc|Crewed spacecraft are in light green}}

{| class="wikitable" style="margin: 1em auto 1em auto;text-align: left; font-size: 95%;"
|-Currently Docked
|style="text-align:center; background:#BBB" colspan="3" | '''Spacecraft and mission'''
|style="text-align:center; background:#BBB"|'''Location'''
|style="text-align:center; background:#BBB"|'''Arrived''' ([[UTC]])
|style="text-align:center; background:#BBB"|'''Departure date'''
|- style="background:#cfc;"
| {{flagicon|RUS}}
| [[Soyuz TMA-16M]]
| [[Expedition 43]]/[[Expedition 44|44]]
| [[Poisk (ISS module)|Poisk]] zenith
| 28 March 2015
| 11 September 2015
|- style="background:lightblue;"
| {{flagicon|RUS}}
| [[Progress M-28M]]
| Progress 60 Cargo
| [[Pirs (ISS module)|Pirs]] nadir
| 5 July 2015
| 19 November 2015
|- style="background:#cfc;"
| {{flagicon|RUS}}
| [[Soyuz TMA-17M]]
| [[Expedition 44]]/[[Expedition 45|45]]
| [[Rassvet (ISS module)|Rassvet]] nadir
| 23 July 2015
| 22 December 2015
|}

===Scheduled launches and dockings/berthings===
* All dates are [[UTC]]. Dates are the earliest possible dates and may change.
* Forward ports are at the front of the station according to its normal direction of travel and orientation ([[Yaw, pitch and roll#Aircraft attitudes|attitude]]). Aft is at the rear of the station, used by spacecraft boosting the station's orbit. [[Nadir]] is closest the Earth, [[Zenith]] is on top.
* Spacecraft operated by government agencies are indicated with 'Gov' and under commercial arrangements are indicated with 'Com'.

;Key
{{legend|lightblue|Uncrewed cargoships are in light blue colour}}
{{legend|#cfc|Crewed spacecraft are in light green colour}}
{{legend|wheat|Modules are in wheat colour}}

{| class="wikitable" style="margin: 1em auto 1em auto;text-align: left; font-size: 95%;"
|+Planned Missions
|style="text-align:center; background:#BBB"|'''Launch''' ({{abbr|NET|Not Earlier Than}})
|style="text-align:center; background:#BBB"|'''Launch Vehicle'''
|style="text-align:center; background:#BBB"|'''Launch Site'''
|style="text-align:center; background:#BBB" colspan="3"| '''Launch Service Provider'''
|style="text-align:center; background:#BBB"|'''Payload'''
|style="text-align:center; background:#BBB"|'''Spacecraft'''
|style="text-align:center; background:#BBB"|'''Mission'''
|style="text-align:center; background:#BBB"|'''Docking / Berthing Port'''
|style="text-align:center; background:#BBB"|'''Ref.'''
|-
| nowrap| 19 August 2015
| nowrap| [[H-IIB]]
| nowrap| {{flagicon|JPN}} [[Tanegashima Space Center|Tanegashima]] [[Yoshinobu Launch Complex|LA-Y2]]
| nowrap| {{flagicon|JPN}}
| nowrap| Gov
| nowrap| [[JAXA]]
| style="background:lightblue;" nowrap| [[Kounotori 5|HTV-5]]
| nowrap| [[H-II Transfer Vehicle|HTV]]
| ISS Resupply
| nowrap| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule">{{cite web |url=http://spaceflightnow.com/launch-schedule/ |title=Launch Calendar |work=Spaceflight Now |date=28 March 2015 |accessdate=28 March 2015}}</ref><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 2 September 2015
| nowrap| [[Soyuz-FG]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:#cfc;" nowrap| [[Soyuz TMA-18M]]
| nowrap| [[Soyuz (spacecraft)|Soyuz]]
| [[Expedition 45]]/[[Expedition 46|46]] including [[European Space Agency|ESA]] [[Denmark|Danish]] Astronaut [[Andreas Mogensen]] and [[Kazakhstan]] cosmonaut [[Aydyn Aimbetov]].
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 1 October 2015
| nowrap| [[Soyuz-U]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:lightblue;" nowrap| [[Progress M-29M]]
| nowrap| [[Progress (spacecraft)|Progress]]
| ISS Resupply
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| NET September 2015 (TBD)
| nowrap|[[Falcon 9 v1.1]]
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 40|SLC-40]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[SpaceX]]
| style="background:lightblue;" nowrap| [[SpaceX CRS-8]]
| nowrap| [[Dragon (spacecraft)|Dragon]]
| ISS resupply. Will deliver [[Bigelow Expandable Activity Module|Bigelow Expandable Activity Module (BEAM)]] to the ISS.
| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| 21 November 2015
| nowrap| [[Soyuz-2 (rocket)|Soyuz-2.1a]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:lightblue;" nowrap| [[Progress MS-1]]
| nowrap| [[Progress (spacecraft)|Progress]]
| ISS Resupply. First launch of the new [[Progress (spacecraft)#Progress MS|Progress-MS]] variant.
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 3 December 2015
| nowrap| [[Atlas V]] 401
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 41|SLC-41]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[United Launch Alliance|ULA]]
| style="background:lightblue;" nowrap| [[Cygnus CRS Orb-4]]
| nowrap| [[Cygnus (spacecraft)|Cygnus]]
| ISS Resupply
| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/><ref>{{cite web|url=http://www.space.com/27962-cygnus-cargo-spacecraft-new-rocket.html |title=Private Cargo Spacecraft Gets New Rocket Ride After Accident |publisher=Space.com |date= |accessdate=2015-04-04}}</ref>
|-
| nowrap| 15 December 2015
| nowrap| [[Soyuz-FG]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:#cfc;" nowrap| [[Soyuz TMA-19M]]
| nowrap| [[Soyuz (spacecraft)|Soyuz]]
| [[Expedition 46]]/[[Expedition 47|47]]
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| NET December 2015 (TBD)
| nowrap|[[Falcon 9 v1.1]]
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[SpaceX]]
| style="background:lightblue;" nowrap| [[SpaceX CRS-9]]
| nowrap| [[Dragon (spacecraft)|Dragon]]
| ISS resupply. Will deliver the IDA-2 segment of the [[NASA Docking System]] to the ISS.
| nowrap| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |
url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|}

===Docking===
{{See also|Docking and berthing of spacecraft}}
[[File:Progress M-14M.jpg|thumb|The [[Progress M-14M]] resupply vehicle as it approaches the ISS in 2012. Over 50 unpiloted [[Progress (spacecraft)|Progress]] spacecraft have been sent with supplies during the lifetime of the station.]]
All Russian spacecraft and self-propelled modules are able to rendezvous and dock to the space station without human intervention using the [[Kurs (docking system)|Kurs]] docking system. Radar allows these vehicles to detect and intercept ISS from over 200 kilometres away. The European ATV uses star sensors and GPS to determine its intercept course. When it catches up it then uses laser equipment to [[Computer vision|optically]] recognise Zvezda, along with the Kurs system for redundancy.  Crew supervise these craft, but do not intervene except to send abort commands in emergencies. The Japanese [[H-II Transfer Vehicle]] parks itself in progressively closer orbits to the station, and then awaits 'approach' commands from the crew, until it is close enough for a robotic arm to grapple and berth the vehicle to the USOS. The American Space Shuttle was manually docked, and on missions with a [[Multi-Purpose Logistics Module|cargo container]], the container would be berthed to the Station with the use of manual robotic arms. Berthed craft can transfer [[International Standard Payload Rack]]s. Japanese spacecraft berth for one to two months. Russian and European Supply craft can remain at the ISS for six months,<ref>{{cite web|url=http://www.esa.int/esaMI/ATV/SEMBW0PR4CF_0.html |title=ESA — ATV — Crew role in mission control |publisher=Esa.int |date=2 March 2011 |accessdate=23 May 2011}}</ref><ref>{{cite web|url=http://www.esa.int/esaHS/ESA4ZJ0VMOC_iss_0.html |title=ESA — Human Spaceflight and Exploration — International Space Station — Automated Transfer Vehicle (ATV) |publisher=Esa.int |date=16 January 2009 |accessdate=23 May 2011}}</ref> allowing great flexibility in crew time for loading and unloading of supplies and trash. NASA Shuttles could remain docked for 11–12 days.<ref>{{cite web|url=http://www.boeing.com/news/frontiers/archive/2005/july/i_ids4.html|title=Space Shuttle upgrade lets astronauts at ISS stay in space longer|last=Memi|first=Ed|publisher=Boeing|accessdate=17 September 2011}}</ref>

The American manual approach to docking allows greater initial flexibility and less complexity. The downside to this mode of operation is that each mission becomes unique and requires specialised training and planning, making the process more labour-intensive and expensive. The Russians pursued an automated methodology that used the crew in override or monitoring roles. Although the initial development costs were high, the system has become very reliable with standardisations that provide significant cost benefits in repetitive routine operations.<ref>David C. Wo±nden and David K. Geller [http://www.usu.edu/mae/aerospace/publications/JDSC_RoadToAutonomy.pdf The Road to Autonomous Orbital Rendezvous]. Utah State University, Logan, Utah</ref> An automated approach could allow assembly of modules orbiting other worlds prior to crew arrival.

[[File:ISS and Endeavour seen from the Soyuz TMA-20 spacecraft 27.jpg|thumb|left|{{OV|105}}, [[ATV-2]], [[Soyuz TMA-21]] and [[Progress M-10M]] docked to the ISS during [[STS-134]], as seen from the departing [[Soyuz TMA-20]]|alt=A side-on view of the ISS showing a Space Shuttle docked to the forward end, an ATV to the aft end and Soyuz & Progress spacecraft projecting from the Russian segment.]]
Soyuz spacecraft used for crew rotation also serve as lifeboats for emergency evacuation; they are replaced every six months and have been used once to remove excess crew after the [[Space Shuttle Columbia disaster|Columbia disaster]].<ref>{{cite web|url=http://www.astronautix.com/flights/isseo6.htm |title=ISS EO-6 |publisher=Astronautix.com |accessdate=1 May 2012}}</ref> Expeditions require, on average, {{nowrap|2 722 kg}} of supplies, and {{As of|2011|03|09|lc=yes}}, crews had consumed a total of around {{nowrap|22 000 meals}}.<ref name="ISStD" /> Soyuz crew rotation flights and Progress resupply flights visit the station on average two and three times respectively each year,<ref name="Livelist">{{cite web|url=http://www.nasa.gov/mission_pages/station/resupply/index.html|archiveurl=https://web.archive.org/web/20080803015945/http://www.nasa.gov/mission_pages/station/resupply/index.html|archivedate=3 August 2008|title=Live listing of spacecraft operations|publisher=NASA|date=1 December 2009|accessdate=8 December 2009}}</ref> with the ATV and HTV planned to visit annually from 2010 onwards.{{Citation needed|date=January 2012}} Following retirement of the NASA Shuttle [[Cygnus spacecraft|Cygnus]] and [[SpaceX Dragon|Dragon]] were contracted to fly cargo to the station.<ref>{{cite web|author=Space Operations Mission Directorate|title=Human Space Flight Transition Plan|publisher=NASA|date=30 August 2006|url=http://www.nasa.gov/pdf/315546main_space_flight_transition_plan.pdf}}</ref><ref>{{cite press release|publisher=NASA|date=18 January 2006|title=NASA Seeks Proposals for Crew and Cargo Transportation to Orbit|url=http://www.spaceref.com/news/viewpr.html?pid=18791|accessdate=21 November 2006}}</ref>

From 26 February 2011 to 7 March 2011 four of the governmental partners (United States, ESA, Japan and Russia) had their spacecraft (NASA Shuttle, ATV, HTV, Progress and Soyuz) docked at the ISS, the only time this has happened to date.<ref>{{cite news|title=NASA proposes Soyuz photo op; shuttle launch readiness reviewed (UPDATED)|url=http://www.cbsnews.com/network/news/space/home/spacenews/files/b0e194a8338c336e823c03601f046707-157.html|publisher=CBS|accessdate=11 February 2011}}</ref> On 25 May 2012, [[SpaceX]] became the world's first privately held company to send cargo, via the [[Dragon (spacecraft)|Dragon spacecraft]], to the International Space Station.<ref name="NYT-20120525">{{cite news |last=Chang |first=Kenneth |title=Space X Capsule Docks at Space Station |url=http://www.nytimes.com/2012/05/26/science/space/space-x-capsule-docks-at-space-station.html |date=25 May 2012 |work=[[The New York Times]] |accessdate=25 May 2012 }}</ref>

===Launch and docking windows===
Prior to a ship's docking to the ISS, navigation and attitude control (GNC) is handed over to the ground control of the ships' country of origin. GNC is set to allow the station to drift in space, rather than fire its thrusters or turn using gyroscopes. The solar panels of the station are turned edge-on to the incoming ships, so residue from its thrusters does not damage the cells. When a NASA shuttle docked to the station, other ships were grounded, as the carbon wingtips, cameras, windows, and instruments aboard the shuttle were at too much risk from damage from thruster residue from other ships movements.

Approximately 30% of NASA shuttle launch delays were caused by poor weather. Occasional priority was given to the Soyuz arrivals at the station where the Soyuz carried crew with time-critical cargoes such as biological experiment materials, also causing shuttle delays. Departure of the NASA shuttle was often delayed or prioritised according to weather over its two landing sites.<ref>{{cite web |url=http://www.nasa.gov/home/hqnews/2009/may/HQ_09-118_Shuttle_Landing_Delayed.html |title=NASA's Space Shuttle Landing Delayed by Weather |publisher=NASA |first1=Katherine |last1=Trinidad |first2=Candrea |last2=Thomas |date=22 May 2009 |accessdate=26 June 2015}}</ref> Whilst the Soyuz is capable of landing anywhere, anytime, its planned landing time and place is chosen to give consideration to helicopter pilots and ground recovery crew, to give acceptable flying weather and lighting conditions. Soyuz launches occur in adverse weather conditions, but the cosmodrome has been shut down on occasions when buried by snow drifts up to 6 metres in depth, hampering ground operations.

==Life aboard==

===Crew activities===
[[File:Exp18home nasa big.jpg|thumb|Crewmember peers out of a window]]

A typical day for the crew begins with a wake-up at 06:00, followed by post-sleep activities and a morning inspection of the station. The crew then eats breakfast and takes part in a daily planning conference with Mission Control before starting work at around 08:10. The first scheduled exercise of the day follows, after which the crew continues work until 13:05. Following a one-hour lunch break, the afternoon consists of more exercise and work before the crew carries out its pre-sleep activities beginning at 19:30, including dinner and a crew conference. The scheduled sleep period begins at 21:30. In general, the crew works ten hours per day on a weekday, and five hours on Saturdays, with the rest of the time their own for relaxation or work catch-up.<ref>{{cite web|url=http://www.nasa.gov/pdf/287386main_110508_tl.pdf|title=ISS Crew Timeline|date=5 November 2008|accessdate=5 November 2008|publisher=NASA|format=PDF}}</ref>

The time zone used on board the ISS is [[Coordinated Universal Time]] (UTC). The windows are covered at night hours to give the impression of darkness because the station experiences 16 sunrises and sunsets a day. During visiting space shuttle missions, the ISS crew will mostly follow the shuttle's [[Mission Elapsed Time]] (MET), which is a flexible time zone based on the launch time of the shuttle mission.<ref>{{Cite web|title = NASA - Time in Space, A Space in Time|url = https://www.nasa.gov/mission_pages/station/research/news/time_in_space.html|website = www.nasa.gov|accessdate = 2015-05-05}}</ref><ref>{{Cite web|title = A Slice of Time Pie|url = https://web.archive.org/web/20130317075600/http://blogs.nasa.gov/cm/blog/ISS%20Science%20Blog/posts/post_1340820317951.html|date = 2013-03-17|accessdate = 2015-05-05}}</ref><ref>{{Cite web|title = Human Space Flight (HSF) - Crew Answers|url = http://spaceflight.nasa.gov/feedback/expert/answer/crew/sts-113/index_2.html|website = spaceflight.nasa.gov|accessdate = 2015-05-05}}</ref>

The station provides crew quarters for each member of the expedition's crew, with two 'sleep stations' in the ''Zvezda'' and four more installed in ''Harmony''.<ref>{{cite web|url=https://www.youtube.com/watch?v=Q4dG9vSyUFQ|title=At Home with Commander Scott Kelly (Video)|date=6 December 2010|publisher=NASA|accessdate=8 May 2011|location=International Space Station}}</ref><ref>{{cite web|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080013462_2008012884.pdf|title=International Space Station USOS Crew Quarters Development|first1=James Lee |last1=Broyan |first2=Melissa Ann |last2=Borrego |first3=Juergen F. |last3=Bahr|year=2008|publisher=SAE International|accessdate=8 May 2011}}</ref> The American quarters are private, approximately person-sized soundproof booths. The Russian crew quarters include a small window, but do not provide the same amount of ventilation or block the same amount of noise as their American counterparts. A crewmember can sleep in a crew quarter in a tethered sleeping bag, listen to music, use a laptop, and store personal items in a large drawer or in nets attached to the module's walls. The module also provides a reading lamp, a shelf and a desktop.<ref name="ESALife">{{cite web|url=http://www.esa.int/esaHS/ESAH1V0VMOC_astronauts_0.html|publisher=ESA|accessdate=28 October 2009|date=19 July 2004|title=Daily life}}</ref><ref name="NASACrewEquip">{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/126_payload.html|title=Station Prepares for Expanding Crew|publisher=NASA|first=Cheryl L. |last=Mansfield|date=7 November 2008|accessdate=17 September 2009}}</ref><ref name="CSALife">{{cite web|url=http://www.asc-csa.gc.ca/pdf/educator-liv_wor_iss.pdf|title=Living and Working on the International Space Station|accessdate=28 October 2009|publisher=CSA}}</ref> Visiting crews have no allocated sleep module, and attach a sleeping bag to an available space on a wall—it is possible to sleep floating freely through the station, but this is generally avoided because of the possibility of bumping into sensitive equipment.<ref name="SRLife">{{cite web|url=http://www.space.com/missionlaunches/090827-sts127-space-sleeping.html|title=Sleeping in Space is Easy, But There's No Shower|first=Tariq|last=Malik|accessdate=29 October 2009|date=27 July 2009|publisher=Space.com}}</ref> It is important that crew accommodations be well ventilated; otherwise, astronauts can wake up oxygen-deprived and gasping for air, because a bubble of their own exhaled carbon dioxide has formed around their heads.<ref name="ESALife" />
{{See also|Christmas on the International Space Station}}

===Food===
[[File:Meal STS127.jpg|thumb|alt=Nine astronauts seated around a table covered in open cans of food strapped down to the table. In the background a selection of equipment is visible, as well as the salmon-coloured walls of the Unity node.|The crews of [[STS-127]] and [[Expedition 20]] enjoy a meal inside ''Unity''.]]
{{See also|Space food}}

Most of the food on board is vacuum sealed in plastic bags. Cans are heavy and expensive to transport, so there are not as many. The preserved food is generally not held in high regard by the crew, and when combined with the reduced sense of taste in a microgravity environment,<ref name="ESALife" /> a great deal of effort is made to make the food more palatable. More spices are used than in regular cooking, and the crew looks forward to the arrival of any ships from Earth, as they bring fresh fruit and vegetables with them. Care is taken that foods do not create crumbs. Sauces are often used to ensure station equipment is not contaminated. Each crew member has individual food packages and cooks them using the on-board galley. The galley features two food warmers, a refrigerator added in November 2008, and a water dispenser that provides both heated and unheated water.<ref name="NASACrewEquip" /> Drinks are provided in dehydrated powder form and are mixed with water before consumption.<ref name="NASACrewEquip" /><ref name="CSALife" /> Drinks and soups are sipped from plastic bags with straws; solid food is eaten with a knife and fork, which are attached to a tray with magnets to prevent them from floating away. Any food that floats away, including crumbs, must be collected to prevent it from clogging up the station's air filters and other equipment.<ref name="CSALife" />

===Hygiene===
[[File:Zvezda toilet.jpg|thumb|right|upright|Space toilet in the [[Zvezda (ISS module)|Zvezda Service Module]]]]

Showers on space stations were introduced in the early 1970s on Skylab and Salyut 3.<ref name="livingandworking">Benson, Charles Dunlap and William David Compton. ''[http://history.nasa.gov/SP-4208/contents.htm Living and Working in Space: A History of Skylab]''. NASA publication SP-4208.</ref>{{rp|139}} By Salyut 6, in the early 1980s, the crew complained of the complexity of showering in space, which was a monthly activity.<ref name="Portree1995-86">{{cite book |url=http://history.nasa.gov/SP-4225/documentation/mhh/mirheritage.pdf |title=Mir Hardware Heritage |publisher=NASA |first=David S. F. |last=Portree |page=86 |date=March 1995 |id=Reference Publication 1357 |oclc=755272548}}</ref> The ISS does not feature a shower; instead, crewmembers wash using a water jet and wet wipes, with soap dispensed from a toothpaste tube-like container. Crews are also provided with rinseless shampoo and edible toothpaste to save water.<ref name="SRLife" /><ref>{{cite AV media |url=https://www.youtube.com/watch?v=uIjNfZbUYu8 |title=Karen Nyberg Shows How You Wash Hair in Space |publisher=NASA |work=YouTube.com |first=Karen |last=Nyberg |date=12 July 2013 |accessdate=6 June 2015}}</ref>

There are two [[space toilet]]s on the ISS, both of Russian design, located in ''[[Zvezda (ISS module)|Zvezda]]'' and ''[[Tranquility (ISS module)|Tranquility]]''.<ref name="NASACrewEquip" /> These Waste and Hygiene Compartments use a fan-driven suction system similar to the Space Shuttle Waste Collection System. Astronauts first fasten themselves to the toilet seat, which is equipped with spring-loaded restraining bars to ensure a good seal.<ref name="ESALife" /> A lever operates a powerful fan and a suction hole slides open: the air stream carries the waste away. Solid waste is collected in individual bags which are stored in an aluminium container. Full containers are transferred to Progress spacecraft for disposal.<ref name="NASACrewEquip" /><ref>{{cite web |first=Ed |last=Lu |title=Greetings Earthling |url=http://spaceflight.nasa.gov/station/crew/exp7/luletters/lu_letter9.html |date=8 September 2003 |accessdate=1 November 2009 |publisher=NASA}}</ref> Liquid waste is evacuated by a hose connected to the front of the toilet, with anatomically correct "urine funnel adapters" attached to the tube so both men and women can use the same toilet. Waste is collected and transferred to the Water Recovery System, where it is recycled back into drinking water.<ref name="CSALife" />

==Crew health and safety==
{{Main|Effect of spaceflight on the human body}}

===Radiation===
The ISS is partially protected from the space environment by the Earth's magnetic field. From an average distance of about {{convert|70,000|km|abbr=on}}, depending on Solar activity, the [[magnetosphere]] begins to deflect solar wind around the Earth and ISS. [[coronal mass ejection|Solar flares]] are still a hazard to the crew, who may receive only a few minutes warning. The crew of [[Expedition 10]] took shelter as a precaution in 2005 in a more heavily shielded part of the ROS designed for this purpose during the initial 'proton storm' of an X-3 class solar flare,<ref>{{cite web|title=Solar Flare Hits Earth and Mars|author=Ker Than|publisher=Space.com|date=23 February 2006|url=http://www.space.com/2080-solar-flare-hits-earth-mars.html}}</ref><ref>{{cite web|title=A new kind of solar storm|publisher=NASA|date=10 June 2005|url=http://science.nasa.gov/science-news/science-at-nasa/2005/10jun_newstorm/}}</ref> but without the limited protection of the Earth's [[magnetosphere]], interplanetary manned missions are especially vulnerable.

[[File:Aurora Australis.ogv|thumb|left|Video of the [[Aurora Australis]] taken by the crew of [[Expedition 28]] on an ascending pass from south of [[Madagascar]] to just north of Australia over the Indian Ocean.]]

Subatomic charged particles, primarily protons from [[cosmic ray]]s and [[solar wind]], are normally absorbed by the Earth's atmosphere. When they interact in sufficient quantity, their effect becomes visible to the naked eye in a phenomenon called an aurora. Without the protection of the Earth's atmosphere, which absorbs this radiation, crews are exposed to about 1 [[millisievert]] each day, which is about the same as someone would get in a year on Earth from natural sources. This results in a higher risk of astronauts developing cancer. Radiation can penetrate living tissue, damage DNA, and cause damage to the [[chromosome]]s of [[lymphocytes]]. These cells are central to the [[immune system]], and so any damage to them could contribute to the lowered [[immunity (medical)|immunity]] experienced by astronauts. Radiation has also been linked to a higher incidence of [[cataracts]] in astronauts. Protective shielding and protective drugs may lower the risks to an acceptable level.<ref name="JCB"/>

The radiation levels experienced on the ISS are about five times greater than those experienced by airline passengers and crew. The Earth's electromagnetic field provides almost the same level of protection against solar and other radiation in low Earth orbit as in the stratosphere. Airline passengers experience this level of radiation for no more than 15 hours for the longest intercontinental flights. For example, on a 12-hour flight an airline passenger would experience 0.1 millisieverts of radiation, or a rate of 0.2 millisieverts per day; only 1/5 the rate experienced by an astronaut in LEO.<ref>{{cite web|url=http://jag.cami.jccbi.gov./cariprofile.asp|title=Galactic Radiation Received in Flight|accessdate=20 May 2010|publisher=FAA Civil Aeromedical Institute}}</ref>
{{See also|Coronal mass ejection|Aurora (astronomy)}}

===Stress===
[[File:Nikolai Budarin in a sleep station in Zvezda.jpg|thumb|Cosmonaut [[Nikolai Budarin]] at work inside [[Zvezda (ISS module)|Zvezda]] service module crew quarters]]
There has been considerable evidence that psychosocial stressors are among the most important impediments to optimal crew morale and performance.<ref>{{cite book| author1 =Peter Suedfeld1| author2 = Kasia E. Wilk| author3 = Lindi Cassel| title = Flying with Strangers: Postmission Reflections of Multinational Space Crews}}</ref> Cosmonaut [[Valery Ryumin]], wrote in his journal during a particularly difficult period on board the [[Salyut 6]] space station: "All the conditions necessary for murder are met if you shut two men in a cabin measuring 18 feet by 20 and leave them together for two months."

NASA's interest in psychological stress caused by space travel, initially studied when their manned missions began, was rekindled when astronauts joined cosmonauts on the Russian space station Mir. Common sources of stress in early American missions included maintaining high performance under public scrutiny, as well as isolation from peers and family. The latter is still often a cause of stress on the ISS, such as when the mother of NASA Astronaut [[Daniel M. Tani|Daniel Tani]] died in a car accident, and when Michael Fincke was forced to miss the birth of his second child.


A study of the longest spaceflight concluded that the first three weeks represent a critical period where attention is adversely affected because of the demand to adjust to the extreme change of environment.<ref>{{cite doi|10.1080/001401398186991}}</ref> Skylab's 3 crews remained one, two, and three months respectively, long term crews on Salyut 6, [[Salyut 7]], and the ISS last about five to six months and Mir's expeditions often lasted longer. The ISS working environment includes further stress caused by living and working in cramped conditions with people from very different cultures who speak a different language. First generation space stations had crews who spoke a single language; second and third-generation stations have crew from many cultures who speak many languages. The ISS is unique because visitors are not classed automatically into 'host' or 'guest' categories as with previous stations and spacecraft, and may not suffer from feelings of isolation in the same way. Crew members with a military pilot background and those with an academic science background or teachers and politicians may have problems understanding each other's jargon and worldview.

===Medical===
[[File:Frank De Winne on treadmill cropped.jpg|thumb|Astronaut [[Frank De Winne]] is attached to the [[Treadmill with Vibration Isolation System|TVIS treadmill]] with bungee cords aboard the International Space Station|alt=Astronaut Frank De Winne is attached to the TVIS treadmill with bungee cords aboard the International Space Station]]
Medical effects of long-term weightlessness include [[muscle atrophy]], deterioration of the skeleton [[spaceflight osteopenia|(osteopenia)]], fluid redistribution, a slowing of the cardiovascular system, decreased production of red blood cells, balance disorders, and a weakening of the immune system. Lesser symptoms include loss of body mass, and puffiness of the face.<ref name="JCB" />

Sleep is disturbed on the ISS regularly due to mission demands, such as incoming or departing ships. Sound levels in the station are unavoidably high; because the atmosphere is unable to [[thermosiphon]], fans are required at all times to allow processing of the atmosphere which would stagnate in the freefall (zero-g) environment.

To prevent some of these adverse [[physiological]] effects, the station is equipped with two treadmills (including the [[Treadmill with Vibration Isolation System|COLBERT]]), and the aRED (advanced Resistive Exercise Device) which enables various weightlifting exercises which add muscle but do nothing for bone density,<ref>{{cite pmid|14600562}}</ref> and a stationary bicycle; each astronaut spends at least two hours per day exercising on the equipment.<ref name="ESALife" /><ref name="NASACrewEquip" /> Astronauts use bungee cords to strap themselves to the treadmill.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/bungee_running.html|accessdate=23 August 2009|title=Bungee Cords Keep Astronauts Grounded While Running|date=16 June 2009|publisher=NASA}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/colbert_feature.html|accessdate=23 August 2009|title=Do Tread on Me|date=19 August 2009|author=Amiko Kauderer|publisher=NASA}}</ref>

===Microbiological environmental hazards===
{{see also|Mir#Microbiological environmental hazards}}
Hazardous moulds which can foul air and water filters may develop aboard space stations. They can produce acids which degrade metal, glass, and rubber. They can also be harmful for the crew health. Microbiological hazards have led to a development of the [[LOCAD#Portable Test System|LOCAD-PTS]] that can identify common bacteria and moulds faster than standard methods of [[Cell culture|culturing]], which may require a sample to be sent back to Earth.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2007/11may_locad3/|author=Trudy E. Bell|year=2007|title=Preventing "Sick" Spaceships|access-date=March 29, 2015}}</ref> {{As of|2012}}, 76 types of unregulated micro-organisms have been detected on the ISS.<ref>{{cite web|url=http://rt.com/news/iss-bacteria-mir-mutation-765/|title=Mutant space microbes attack ISS: 'Munch' metal, may crack glass |author= |date=April 23, 2012|website=[[RT (TV network)|RT]]|access-date=March 29, 2015}}</ref>

Reduced humidity, paint with mould killing chemical and antiseptic solutions can be used to prevent contamination in space stations. All materials used in the ISS are tested for resistance against fungi.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2000/ast26nov_1/|author=Patrick L. Barry|year=2000|title=Microscopic Stowaways on the ISS|access-date=March 29, 2015}}</ref>

==Threat of orbital debris==
{{Main|Space debris}}
{{Double image|right|SDIO KEW Lexan projectile.jpg|225|Debris-GEO1280.jpg|225|A 7 gram object (shown in centre) shot at 7 km/s (23,000 ft/sec) (the orbital velocity of the ISS) made this 15 cm (5 7/8 in) crater in a solid block of aluminium.|[[Radar]]-trackable objects including debris, with distinct ring of [[Geostationary orbit|geostationary]] satellites||}}
At the low altitudes at which the ISS orbits there is a variety of space debris,<ref>{{cite web|url=http://defensenews.com/blogs/space-symposium/2009/04/03/its-getting-crowded-up-there/#more-155|publisher=Defense News|accessdate=7 October 2009|author=Michael Hoffman|title=National Space Symposium 2009: It's getting crowded up there|date=3 April 2009}}</ref> consisting of many different objects including entire spent rocket stages, defunct satellites, explosion fragments—including materials from [[anti-satellite weapon]] tests, paint flakes, slag from solid rocket motors, and coolant released by [[US-A]] nuclear-powered satellites. These objects, in addition to natural [[micrometeoroid]]s,<ref>{{cite journal|author=F. L. Whipple|year=1949|title=The Theory of Micrometeoroids|journal=Popular Astronomy|volume=57|page=517|bibcode=1949PA.....57..517W}}</ref> are a significant threat. Large objects could destroy the station, but are less of a threat as their orbits can be predicted.<ref name="NSFdebris">{{cite web|publisher=NASASpaceflight.com|accessdate=28 June 2011|date=28 June 2011|author=Chris Bergin|url=http://www.nasaspaceflight.com/2011/06/sts-135-frr-july-8-atlantis-debris-misses-iss/|title=STS-135: FRR sets 8 July Launch Date for Atlantis – Debris misses ISS}}</ref><ref>{{cite web|author=Henry Nahra|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19890016664_1989016664.pdf|title=Effect of Micrometeoroid and Space Debris Impacts on the Space Station Freedom Solar Array Surfaces|date=24–29 April 1989|publisher=NASA|accessdate=7 October 2009}}</ref> Objects too small to be detected by optical and radar instruments, from approximately 1 cm down to microscopic size, number in the trillions. Despite their small size, some of these objects are still a threat because of their [[kinetic energy]] and direction in relation to the station. Spacesuits of spacewalking crew could puncture, causing [[Space exposure|exposure to vacuum]].<ref name=debrisdecomp>{{cite web|title=Space Suit Punctures and Decompression|url=http://www.asi.org/adb/04/03/08/suit-punctures.html|publisher=The Artemis Project|accessdate=20 July 2011}}</ref>

The station's shields and structure are divided between the ROS and the USOS, with completely different designs. On the USOS, a thin aluminium sheet is held apart from the hull, the sheet causes objects to shatter into a cloud before hitting the hull thereby spreading the energy of the impact. On the ROS, a carbon plastic honeycomb screen is spaced from the hull, an aluminium honeycomb screen is spaced from that, with a screen-vacuum thermal insulation covering, and glass cloth over the top. It is about 50% less likely to be punctured,  and crew move to the ROS when the station is under threat. Punctures on the ROS would be contained within the panels which are 70 cm square.

[[File:ISS impact risk.jpg|thumb|left|Example of [[risk management]]: A NASA model showing areas at high risk from impact for the International Space Station.]]

Space debris objects are tracked remotely from the ground, and the station crew can be notified.<ref>{{cite web|url=http://www.orbitaldebris.jsc.nasa.gov/library/EducationPackage.pdf |title=Microsoft PowerPoint – EducationPackage SMALL.ppt |format=PDF |accessdate=1 May 2012}}</ref> This allows for a [[Debris Avoidance Manoeuvre]] (DAM) to be conducted, which uses thrusters on the Russian Orbital Segment to alter the station's orbital altitude, avoiding the debris. DAMs are not uncommon, taking place if computational models show the debris will approach within a certain threat distance. Eight DAMs had been performed prior to March 2009,<ref>{{cite web|url=http://www.newscientist.com/article/dn16777-space-station-may-move-to-dodge-debris.html|title=Space station may move to dodge debris|work=New Scientist|date=16 March 2009|accessdate=20 April 2010|author=Rachel Courtland}}</ref> the first seven between October 1999 and May 2003.<ref name=ODOct08>{{cite journal|url=http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv12i4.pdf|title=ISS Maneuvers to Avoid Russian Fragmentation Debris|publisher=NASA|pages=1&2|journal=Orbital Debris Quarterly News|date=October 2008|accessdate=20 April 2010|volume=12|issue=4}}</ref> Usually the orbit is raised by one or two kilometres by means of an increase in orbital velocity of the order of 1 m/s. Unusually there was a lowering of 1.7 km on 27 August 2008, the first such lowering for 8 years.<ref name=ODOct08 /><ref>{{cite web|url=http://www.esa.int/esaMI/ATV/SEM64X0SAKF_0.html|title=ATV carries out first debris avoidance manoeuvre for the ISS|publisher=ESA|date=28 August 2008|accessdate=26 February 2010}}</ref> There were two DAMs in 2009, on 22 March and 17 July.<ref>{{cite journal|url=http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv14i1.pdf|title=Avoiding satellite collisions in 2009|page=2|journal=Orbital Debris Quarterly News|publisher=NASA|volume=14|date=January 2010|issue=1|accessdate=20 April 2010}}</ref> If a threat from orbital debris is identified too late for a DAM to be safely conducted, the station crew close all the hatches aboard the station and retreat into their [[Soyuz spacecraft]], so that they would be able to evacuate in the event the station was seriously damaged by the debris. This partial station evacuation has occurred on 13 March 2009, 28 June 2011, 24 March 2012 and 16 June 2015.<ref>{{cite news| url=http://www.bbc.co.uk/news/science-environment-17497766| title=ISS crew take to escape capsules in space junk alert| accessdate=24 March 2012 |work=BBC News |date=24 March 2012}}</ref><ref>{{cite news| url=https://blogs.nasa.gov/spacestation/2015/07/16/station-crew-takes-precautions-for-close-pass-of-space-debris/| title=Station Crew Takes Precautions for Close Pass of Space Debris| accessdate=16 June 2015 |work=NASA Blog |date=16 June 2015}}</ref>
Ballistic panels, also called micrometeorite shielding, are incorporated into the station to protect pressurised sections and critical systems. The type and thickness of these panels varies depending upon their predicted exposure to damage.

==End of mission==
[[File:Jules Verne Automated Transfer Vehicle re-enters Earth's atmosphere.jpg|thumb|right|Many ISS resupply spacecraft have already undergone [[Atmospheric entry|atmospheric re-entry]], such as [[Jules Verne ATV]]]]
According to a 2009 report, [[S.P. Korolev Rocket and Space Corporation Energia|Space Corporation Energia]] is considering methods to remove from the station some modules of the Russian Orbital Segment when the end of mission is reached and use them as a basis for a new station, known as the [[Orbital Piloted Assembly and Experiment Complex]] (OPSEK). The modules under consideration for removal from the current ISS include the [[Multipurpose Laboratory Module]] (MLM), currently scheduled to be launched in 2017, with other Russian modules which are currently planned to be attached to the MLM afterwards. Neither the MLM nor any additional modules attached to it would have reached the end of their useful lives in 2016 or 2020. The report presents a statement from an unnamed Russian engineer who believes that, based on the experience from ''Mir'', a thirty-year life should be possible, except for micrometeorite damage, because the Russian modules have been built with on-orbit refurbishment in mind.<ref name="RussiaSave">{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8064060.stm|title=Russia 'to save its ISS modules'|work=BBC News|date=22 May 2009|accessdate=23 May 2009|author=Anatoly Zak}}</ref>

According to the [[Outer Space Treaty]] the United States and Russia are legally responsible for all modules they have launched.<ref>[http://www.unoosa.org/pdf/publications/STSPACE11E.pdf United Nations Treaties and Principles on Outer Space]. (PDF). United Nations. New York. 2002. ISBN 92-1-100900-6. Retrieved 8 October 2011.</ref> In ISS planning, NASA examined options including returning the station to Earth via shuttle missions (deemed too expensive, as the station (USOS) is not designed for disassembly and this would require at least 27 shuttle missions<ref>{{cite book|url=http://search.nap.edu/openbook.php?record_id=9794&page=28|isbn=0-309-06938-6|publisher=National Academies Press|year=2000|pages=28–30|author=Thomas Kelly|title=Engineering Challenges to the Long-Term Operation of the International Space Station|accessdate=12 July 2011}}</ref>), natural orbital decay with random reentry similar to [[Skylab]], boosting the station to a higher altitude (which would delay reentry) and a controlled targeted de-orbit to a remote ocean area.<ref name=ISSEIS>{{cite web|title = Tier 2 EIS for ISS|publisher = NASA|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960053133_1996092350.pdf|accessdate=12 July 2011 }}</ref>

The technical feasibility of a controlled targeted deorbit into a remote ocean was found to be possible only with Russia's assistance.<ref name=ISSEIS /> The Russian Space Agency has experience from de-orbiting the [[Salyut 4]], [[Salyut 5|5]], [[Salyut 6|6]], [[Salyut 7|7]] and [[Mir]] space stations; NASA's first intentional controlled de-orbit of a satellite (the [[Compton Gamma Ray Observatory]]) occurred in 2000.<ref>{{cite web|title=Entry Debris Field estimation methods and application to Compton Gamma Ray Observatory|publisher=Mission Operations Directorate, NASA Johnson Space Center|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010084992_2001127597.pdf|accessdate=12 July 2011}}</ref> As of late 2010, the preferred plan is to use a slightly modified Progress spacecraft to de-orbit the ISS.<ref name=deo>{{cite web|url=http://www.nasa.gov/pdf/578543main_asap_eol_plan_2010_101020.pdf|title=ISS End-of-Life Disposal Plan|last=Suffredini|first=Michael|date=October 2010|publisher=NASA|accessdate=7 March 2012}}</ref> This plan was seen as the simplest, most cost efficient one with the highest margin.<ref name=deo /> [[Skylab]], the only space station built and launched entirely by the US, decayed from orbit slowly over 5 years, and no attempt was made to de-orbit the station using a [[Atmospheric entry|deorbital burn]]. Remains of Skylab hit populated areas of [[Esperance, Western Australia]]<ref name="debris">{{cite web|url=http://www.eclipsetours.com/sat/debris.html|accessdate=28 May 2011|title=Paul Maley's (Skylab spaceflight controller) Space Debris Page}}</ref> without injuries or loss of life.

The [[Exploration Gateway Platform]], a discussion by NASA and Boeing at the end of 2011, suggested using leftover USOS hardware and '[[Zvezda (ISS module)|Zvezda]] 2' {{sic}} as a refuelling depot and servicing station located at one of the Earth Moon [[Lagrange points]], L1 or L2. The entire USOS cannot be reused and will be discarded, but some other Russian modules are planned to be reused. [[Nauka (ISS module)|Nauka]], the [[Uzlovoy Module|Node module]], two science power platforms and Rassvet, launched between 2010 and 2015 and joined to the ROS may be separated to form [[OPSEK]].<ref>{{cite web|url=http://www.russianspaceweb.com/iss_dc.html|title=DC-1 and MIM-2|publisher=Russianspaceweb.com|accessdate=12 July 2011}}</ref> The [[Nauka (ISS module)|Nauka module]] of the ISS will be used in the station, whose main goal is supporting manned deep space exploration. OPSEK will orbit at a higher inclination of 71 degrees, allowing observation to and from all of the Russian Federation.

In February 2015, Roscosmos announced that it would remain a part of the international space station program until 2024.<ref name=sn20150225>{{cite news |last1=de Selding|first1=Peter B. |title=Russia — and Its Modules — To Part Ways with ISS in 2024 |url=http://spacenews.com/russia-and-its-modules-to-part-ways-with-iss-in-2024/ |accessdate=26 February 2015 |work=Space News |date=25 February 2015}}</ref> Nine months earlier—in response to US sanctions against Russia over the [[2014 Crimean crisis|conflict in the Crimea]]—Russian Deputy Prime Minister [[Dmitry Rogozin]] had stated that Russia would reject a US request to prolong the orbiting station's use beyond 2020, and would only supply rocket engines to the US for non-military satellite launches.<ref>{{cite web|url=http://www.telegraph.co.uk/news/worldnews/europe/russia/10828964/Russia-to-ban-US-from-using-Space-Station-over-Ukraine-sanctions.html|title=Russia to ban US from using Space Station over Ukraine sanctions|agency=Reuters|work=The Telegraph|date=13 May 2014|accessdate=14 May 2014}}</ref>

A proposed modification that would allow some of the ISS American and European segments to be reused would be to attach a [[VASIMR]] drive module to the vacated Node with its own onboard power source. It would allow long term reliability testing of the concept for less cost than building a dedicated space station from scratch.<ref name="nbcnews">{{cite web|url=http://www.nbcnews.com/id/48260759/ns/technology_and_science-space/#.U4LaQCjFBdg|title=From the earth to the moon, and then beyond - Technology & science - Space | NBC News|publisher=nbcnews.com|accessdate=27 May 2014}}</ref>

On March 28, 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS.<ref name=":0"/><ref name=":1"/> [[Igor Komarov]], the head of Russia's Roscosmos, made the announcement with NASA administrator Charles Bolden at his side. Komarov said "Roscosmos together with NASA will work on the programme of a future orbital station," "We agreed that the group of countries taking part in the ISS project will work on the future project of a new orbital station," "The first step is that the ISS will operate until 2024," and that Roscosmos and NASA "do not rule out that the station's flight could be extended,"<ref>{{cite web|url=http://www.spacedaily.com/reports/Russia_announces_plan_to_build_new_space_station_with_NASA_999.html|title=Russia announces plan to build new space station with NASA|work=spacedaily.com}}</ref> In a statement provided to SpaceNews March 28, NASA spokesman David Weaver said the agency appreciated the Russian commitment to extending the ISS, but did not confirm any plans for a future space station.<ref name="no plans" />

==Cost==
The ISS is arguably the most expensive single item ever constructed.<ref>{{cite web|author=Zidbits |url=http://zidbits.com/?p=19 |title=What Is The Most Expensive Object Ever Built? |publisher=Zidbits.com |date=6 November 2010 |accessdate=22 October 2013}}</ref> In 2010 the cost was expected to be $150 billion. It includes NASA's budget of $58.7 billion (inflation unadjusted) for the station from 1985 to 2015 ($72.4 billion in 2010 dollars), Russia's $12 billion, Europe's $5 billion, Japan's $5 billion, Canada's $2 billion, and the cost of 36 shuttle flights to build the station; estimated at $1.4 billion each, or $50.4 billion total. Assuming 20,000 person-days of use from 2000 to 2015 by two to six-person crews, each person-day would cost $7.5 million, less than half the inflation adjusted $19.6 million ($5.5 million before inflation) per person-day of Skylab.<ref name="lafleur20100308">{{cite news | url=http://www.thespacereview.com/article/1579/1 | title=Costs of US piloted programs | work=The Space Review | date=8 March 2010 | accessdate=18 February 2012 | author=Lafleur, Claude}} See author correction in comments.</ref>

==International co-operation==
[[File:ISS Agreements.jpg|thumb|right|upright|Dated 29 January 1998]]
{{Main|Politics of the International Space Station|International Space Station program}}
;Participating countries
{{columns-list|colwidth=20em|

* '''{{flagcountry|Canada}}'''
* '''{{flagcountry|Japan}}'''
* '''{{flagcountry|Russia}}'''
* '''{{flagcountry|United States}}'''
* [[File:ESA logo simple.svg|15x15px]] '''[[European Space Agency]]'''
** {{flagcountry|Austria}}
** {{flagcountry|Belgium}}
** {{flagcountry|Czech Republic}}
** {{flagcountry|Denmark}}
** {{flagcountry|Estonia}}
** {{flagcountry|Finland}}
** {{flagcountry|France}}
** {{flagcountry|Germany}}
** {{flagcountry|Greece}}
** {{flagcountry|Hungary}}
** {{flagcountry|Ireland}}
** {{flagcountry|Italy}}
** {{flagcountry|Luxembourg}}
** {{flagcountry|Netherlands}}
** {{flagcountry|Norway}}
** {{flagcountry|Poland}}
** {{flagcountry|Portugal}}
** {{flagcountry|Romania}}
** {{flagcountry|Spain}}
** {{flagcountry|Sweden}}
** {{flagcountry|Switzerland}}
** {{flagcountry|United Kingdom}}
}}

==Sightings from Earth==

===Naked eye===
The ISS is visible to the [[naked eye]] as a slow-moving, bright white dot due to reflected sunlight, and can be seen in the hours after sunset and before sunrise when the station remains sunlit but the ground and sky are dark.<ref name="Price2005">{{cite book |title=The Backyard Stargazer: An Absolute Beginner's Guide to Skywatching With and Without a Telescope |publisher=Quarry Books |location=Gloucester, MA |first=Pat |last=Price |page=140 |year=2005 |isbn=1-59253-148-2}}</ref> The ISS takes about ten minutes to move from one horizon to another, and will only be visible part of that time due to moving into or out of the Earth's shadow. Because of the size of its reflective surface area, the ISS is the brightest man-made object in the sky excluding [[Satellite flare|flares]], with an approximate maximum [[Apparent magnitude|magnitude of −4]] when overhead, similar to Venus. The ISS, like many satellites including the [[Iridium constellation]], can also produce flares of up to 8 or 16 times the brightness of Venus as sunlight glints off reflective surfaces.<ref>{{cite web|url=http://www.calsky.com/cs.cgi/Satellites/8 |title=Artificial Satellites > (Iridium) Flares |publisher=Calsky.com |accessdate=1 May 2012}}</ref><ref name="haydenplanetarium">{{cite web|url=http://www.amnh.org/our-research/hayden-planetarium/blog/how-to-spot-the-international-space-station-and-other-satellites |title=How to Spot the International Space Station (and other satellites) |publisher=Hayden Planetarium |accessdate=12 July 2011}}</ref> The ISS is also visible during broad daylight conditions, albeit with a great deal more effort.

Tools are provided by a number of websites such as [[Heavens-Above]] (see [[#Live viewing|''Live viewing'']] below) as well as [[smartphone]] applications that use the known [[ephemeris|orbital data]] and the observer's longitude and latitude to predict when the ISS will be visible (weather permitting), where the station will appear to rise to the observer, the altitude above the horizon it will reach and the duration of the pass before the station disappears to the observer either by setting below the horizon or entering into Earth's shadow.<ref name="see">{{cite web|url=http://spaceflight.nasa.gov/realdata/sightings/index.html|title=International Space Station Sighting Opportunities|accessdate=28 January 2009|publisher=NASA|date=2 July 2008|author=NASA}}</ref><ref>{{cite web|url=http://www.heavens-above.com/satinfo.aspx?satid=25544&lat=0&lng=0&loc=Unspecified&alt=0&tz=CET|title=ISS – Information|publisher=Heavens-Above.com|accessdate=8 July 2010}}</ref><ref>{{cite journal|author=Harold F. Weaver|title=The Visibility of Stars Without Optical Aid|journal=Publications of the Astronomical Society of the Pacific|volume=59|issue=350|year=1947|doi=10.1086/125956 }}</ref><ref name="daytime visibility">{{cite web|url=http://spaceweather.com/archive.php?view=1&day=05&month=06&year=2009|title=ISS visible during the daytime|accessdate=5 June 2009|work=Spaceweather.com|date=5 June 2009}}</ref>

{{Double image|right|Isshtv120090917200858nm.jpg|223|ISS 2008-01-10.jpg|230|The ISS and HTV photographed using a telescope-mounted camera by [[Ralf Vandebergh]]|A time exposure of a station pass|A fuzzy image of the ISS set against a black background, with a smaller, cylindrical object visible to the left of the station.|A view of a dark blue, starry sky with a white line visible from the bottom-left to the top-right of the image. A tree is visible to the bottom right.}}

In November 2012 NASA launched its 'Spot the Station' service, which sends people text and email alerts when the station is due to fly above their town.<ref>{{cite news| url= http://www.3news.co.nz/Get-notified-when-the-International-Space-Station-is-in-your-area/tabid/1160/articleID/275612/Default.aspx|work=3 News NZ |title= Get notified when the International Space Station is in your area| date=6 November 2012}}</ref>

The station is visible from 95% of the inhabited land on Earth, but is not visible from extreme northern or southern latitudes.<ref name="MCC Answer" />

===Astrophotography=== 
Using a telescope mounted camera to photograph the station is a popular hobby for astronomers, <ref>{{cite web|url=http://www.hobbyspace.com/SatWatching/ |title=Satellite Watching |publisher=HobbySpace |accessdate=1 May 2012}}</ref> whilst using a mounted camera to photograph the Earth and stars is a popular hobby for crew.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2003/24mar_noseprints/ |title=Space StationAstrophotography – NASA Science |publisher=Science.nasa.gov |date=24 March 2003 |accessdate=1 May 2012}}</ref> The use of a telescope or binoculars allows viewing of the ISS during daylight hours.<ref>{{cite web|url=http://www.zmescience.com/space/video-the-iss-and-atlantis-shuttle-as-seen-in-broad-daylight/ |title=[VIDEO] The ISS and Atlantis shuttle as seen in broad daylight |publisher=Zmescience.com |date=20 July 2011 |accessdate=1 May 2012}}</ref>

Parisian engineer and astrophotographer Thierry Legault, known for his photos of spaceships crossing the Sun (called [[occultation]]), travelled to Oman in 2011, to photograph the Sun, moon and space station all lined up.<ref>{{cite news| url=http://www.wired.com/2011/01/double-eclipse/ | work=Wired | first=Lisa | last=Grossman | title=Moon and Space Station Eclipse the Sun}}</ref> Legault, who received the Marius Jacquemetton award from the [[Société astronomique de France]] in 1999, and other hobbyists, use websites that predict when the ISS will pass in front of the Sun or Moon and from what location those passes will be visible.

==See also==
{{Wikipedia books|International Space Station}}
{{Portal|Spaceflight|Space}}
* [[Center for the Advancement of Science in Space]] - operates the US National Laboratory on the ISS
* [[List of space stations]]
* [[Origins of the International Space Station]]
* [[Space architecture]]

==Gallery==
[[File:ISS and Endeavour seen from the Soyuz TMA-20 spacecraft 14.jpg|thumb|left|550px|<center>International Space Station docked with ''Endeavour'' and ''Johannes Kepler'' ]]
{{-}}

==Notes==
{{Reflist|group="note"}}

==References==
{{Reflist|colwidth=25em}}

==External links==
{{Sister project links|wikt=no|n=Category:International Space Station|voy=Space}}

===Agency ISS websites===
{{divcol|20em}}
* {{flagicon|Canada}} [http://www.asc-csa.gc.ca/eng/iss/default.asp Canadian Space Agency]
* [[File:Not the esa logo.png]] [http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station European Space Agency]
* {{flagicon|France}} [http://www.cnes.fr/web/CNES-en/1422-iss-the-international-space-station.php Centre national d'études spatiales (National Centre for Space Studies)]
* {{flagicon|Germany}} [http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10300 German Aerospace Centre]
* {{flagicon|Italy}} [http://www.asi.it/en/flash_en/living Italian Space Agency]
* {{flagicon|Japan}} [http://www.jaxa.jp/projects/iss_human/index_e.html Japan Aerospace Exploration Agency]
* {{flagicon|Russia}} [http://www.energia.ru/eng/iss/iss.html S.P. Korolev Rocket and Space Corporation Energia]
* {{flagicon|Russia}} [http://www.roscosmos.ru/ Russian Federal Space Agency]
* {{flagicon|USA}} [http://www.nasa.gov/mission_pages/station/main/ National Aeronautics and Space Administration]
{{Div col end}}

===Research===
* [https://blogs.nasa.gov/spacestation/ NASA: Daily ISS Reports]
* [http://www.nasa.gov/mission_pages/station/science/index.html NASA: Station Science]
* [http://www.esa.int/Our_Activities/Human_Spaceflight/Columbus ESA: Columbus]
* [http://www.energia.ru/en/iss/researches/iss-researches.html RSC Energia: Science Research on ISS Russian Segment]

===Live viewing===
{{See also|List of satellite pass predictors}}
* [http://www.ustream.tv/channel/live-iss-stream Live ISS webcam] by NASA at uStream.tv
* [http://heavens-above.com/orbit.aspx?satid=25544 Real-time position] at Heavens-above.com
* [http://www.n2yo.com/?s=25544 Real-time position] at N2YO.com
* [http://wheretheiss.at/ Real-time position] at WheretheISS.at

===Multimedia===
* [http://www.nasa.gov/externalflash/ISSRG/index.html Interactive reference guide] at NASA.gov
* [http://spaceflight.nasa.gov/gallery/images/station/ Image gallery search page] at NASA.gov
* [http://i.usatoday.net/tech/graphics/iss_timeline/flash.htm Assembly sequence animation] by ''USA Today'' and NASA
* [https://www.youtube.com/watch?v=doN4t5NKW-k ISS tour with Sunita Williams] by NASA at YouTube.com
* [https://www.youtube.com/watch?v=QF2w2Dx_QMs ISS tour with André Kuipers] by ESA at YouTube.com
* [http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station/Highlights/International_Space_Station_panoramic_tour ISS photo tour with Samantha Cristoforetti] by ESA
* [https://www.youtube.com/watch?v=vMmcLmu3V1k ''The Future of Hope'', Kibo module documentary] by JAXA at YouTube.com
* [https://www.youtube.com/playlist?list=PLbyvawxScNbsoD_tGlw8kWCw3S5htiVKZ Journey to the ISS] by ESA at YouTube.com

{{ISS modules}}
{{International Space Station}}
{{Manned ISS flight}}
{{Unmanned ISS resupply flights}}
{{People currently in space}}
{{Space stations}}
{{US manned space programs}}
{{Russian manned space programs}}
{{European manned spaceflight}}
{{Spaceflight}}
{{Orbital launches in 1998}}

{{Orbit|satcat|25544|hide}}{{Orbit|datasource|HN}}
{{active editnotice}}

{{Authority control}}
[[Category:International Space Station| ]]
[[Category:Artificial satellites orbiting Earth]]
[[Category:Populated places established in 1998]]
[[Category:United States Department of Energy national laboratories]]
[[Category:Spacecraft launched in 1998]]
[[Category:1998 in spaceflight]]
[[Category:Articles containing video clips]]

User:WikipediaTutorials/sandbox

2015-08-25T01:40:28Z

WikipediaTutorials: added link

{{redirect|ISS}}
{{Use British English|date=December 2013}}
{{Use dmy dates|date=February 2015}}
{{Infobox space station
| station = International Space Station
| station_image =International Space Station after undocking of STS-132.jpg
| station_image_alt = A rearward view of the International Space Station backdropped by the limb of the Earth. In view are the station's four large, gold-coloured solar array wings, two on either side of the station, mounted to a central truss structure. Further along the truss are six large, white radiators, three next to each pair of arrays. In between the solar arrays and radiators is a cluster of pressurised modules arranged in an elongated T shape, also attached to the truss. A set of blue solar arrays are mounted to the module at the aft end of the cluster.
| station_image_size = 300px
| extra_image_size = 300px
| extra_image_caption = The International Space Station on 23 May 2010 as seen from the departing {{OV|104}} during [[STS-132]].
| sign = ''Alpha'', ''Station''
| crew = Fully crewed: 6 Currently aboard: 6 ([[Expedition 44]])
| launch = 20 November 1998
| launch_pad = {{nowrap|[[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|1/5]] and [[Baikonur Cosmodrome Site 81|81/23]] [[Kennedy Space Center|Kennedy]] [[Kennedy Space Center Launch Complex 39|LC-39]]}}
| mass = Approximately {{convert|450000|kg|lbs|abbr=on}}
| length = {{convert|72.8|m|ft|abbr=on}}
| width = {{convert|108.5|m|ft|abbr=on}}
| height = c. 20 m (c. 66 ft) nadir–zenith, arrays forward–aft (27 November 2009){{Update after|2010|05|23|reason=MRM-1 & MRM-2}}
| volume = {{convert|916|m3|abbr=on}} (3 November 2014)
| pressure = 101.3 [[pascal (unit)|kPa]] (29.91 [[inch of mercury|inHg]], 1 [[Atmosphere (unit)|atm]])
| apogee = {{convert|{{Orbit|apogee|416}}|km|abbr=on}} [[Above mean sea level|AMSL]]{{Orbit|ref|<ref name="heavens-above">{{cite web|url=http://www.heavens-above.com/orbit.aspx?satid=25544|title=ISS - Orbit|last=Peat|first=Chris|publisher=Heavens-Above|date=25 January 2015|accessdate=25 January 2015}}</ref>}}
| perigee = {{convert|{{Orbit|perigee|409}}|km|abbr=on}} [[Above mean sea level|AMSL]]{{Orbit|ref|<ref name="heavens-above"/>}}
| inclination = {{Orbit|inclination|51.65}} [[degree (angle)|degrees]]{{Orbit|ref|<ref name="heavens-above"/>}}
| speed = {{convert|{{Orbit|speed at epoch|7.66}}|km/s|km/h mph}}{{Orbit|ref|<ref name="heavens-above"/>}}
| period = {{Orbit|period|92.69}} minutes{{Orbit|ref|<ref name="heavens-above"/>}}
| in_orbit = {{age in days|1998|11|20}} ({{date||dmy}})
| occupied = {{age in days|2000|11|02}} ({{date||dmy}})
| orbits = {{Orbit|orbits|92579}}{{Orbit|ref|<ref name="heavens-above"/>}}
| orbit_epoch = {{Orbit|epoch|25 January 2015}}{{Orbit|ref|<ref name="heavens-above"/>}}
| decay = 2 km/month
| NSSDC_ID = 1998-067A
| as_of = 9 March 2011 (unless noted otherwise)
| stats_ref =<ref name="heavens-above" /><ref name="ISStD" /><ref name="OnOrbit" /><ref>{{cite web|format=PDF|url=http://www.nasa.gov/pdf/451029main_sts132_press_kit.pdf|publisher=NASA|accessdate=19 June 2010|title=STS-132 Press Kit|date=7 May 2010}}</ref><ref>{{cite web|url=http://www.nasa.gov/pdf/521138main_fd04_ep.pdf|publisher=NASA|date=27 February 2011|accessdate=27 February 2011|title=STS-133 FD 04 Execute Package}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html|publisher=NASA|date=3 November 2014|accessdate=5 December 2014|title=NASA — Facts and Figures — International Space Station}}</ref>
| configuration_image = ISS configuration 2011-05 en.svg
| configuration_alt = The components of the ISS in an exploded diagram, with modules on-orbit highlighted in orange, and those still awaiting launch in blue or pink
| configuration_caption = Station elements {{As of|2011|12|lc=on}}, but missing ''Pirs'' ([[exploded view]])
| configuration_size = 300px
}}

The '''International Space Station''' ('''ISS''') is a [[space station]], or a habitable [[satellite|artificial satellite]], in [[low Earth orbit]]. Its first component launched into orbit in 1998, and the ISS is now the largest artificial body in orbit and can often be seen with the [[naked eye]] from Earth.<ref>{{cite web|title= Central Research Institute for Machine Building (FGUP TSNIIMASH) Control of manned and unmanned space vehicles from Mission Control Centre Moscow |publisher= Russian Federal Space Agency |url=ftp://130.206.92.88/Espacio/Mesa%20Redonda%205%20-%20R3%20-%20TSNIIMASH%20-%20V%20M%20IVANOV.pdf| accessdate=26 September 2011}}</ref><ref>{{cite web|url=http://spaceflight.nasa.gov/realdata/sightings/help.html |title=NASA Sightings Help Page |publisher=Spaceflight.nasa.gov |date=30 November 2011 |accessdate=1 May 2012}}</ref> The ISS consists of pressurised modules, external trusses, [[solar arrays]] and other components. ISS components have been launched by Russian [[Proton (rocket)|Proton]] and [[Soyuz (rocket family)|Soyuz]] rockets as well as American [[Space Shuttle]]s.<ref name="ISSBook">{{cite book|isbn=978-0-387-78144-0|date=17 June 2008|publisher=Springer-Praxis|author=John E. Catchpole|title=The International Space Station: Building for the Future}}</ref>

The ISS serves as a [[microgravity]] and [[space environment]] research laboratory in which crew members conduct experiments in [[biology]], [[human biology]], [[physics]], [[astronomy]], [[meteorology]] and [[Scientific research on the ISS|other fields]].<ref name="ISS overview">{{cite web|url=http://www.shuttlepresskit.com/ISS_OVR/index.htm|title=International Space Station Overview|publisher=ShuttlePressKit.com|date=3 June 1999|accessdate=17 February 2009}}</ref><ref name="NASA Fields of Research">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/A-fieldsresearch/index.html|archiveurl=https://web.archive.org/web/20080123150641/http://pdlprod3.hosc.msfc.nasa.gov/A-fieldsresearch/index.html|archivedate=25 March 2008|title=Fields of Research|date=26 June 2007|publisher = NASA}}</ref><ref name="NASA ISS Goals">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/B-gettingonboard/index.html|archiveurl=https://web.archive.org/web/20071208091537/http://pdlprod3.hosc.msfc.nasa.gov/B-gettingonboard/index.html|archivedate=8 December 2007| title = Getting on Board|date = 26 June 2007| publisher=NASA}}</ref> The station is suited for the testing of spacecraft systems and equipment required for missions to the [[Moon]] and Mars.<ref name="ResProg">{{cite web|url=http://spaceflightsystems.grc.nasa.gov/Advanced/ISSResearch/|title=ISS Research Program|publisher=NASA|accessdate=27 February 2009}}{{dead link|date=August 2011}}</ref> The ISS [[Orbital station-keeping|maintains an orbit with an altitude]] of between {{convert|330|and|435|km|mi|0|abbr=on}} by means of reboost manoeuvres using the engines of the [[Zvezda (ISS module)|Zvezda module]] or visiting spacecraft. It completes {{Orbit|daily orbits|15.54}} orbits per day.<ref name="tracking" />

ISS is the ninth space station to be inhabited by crews, following the Soviet and later Russian [[Salyut]], [[Almaz]], and [[Mir]] stations as well as [[Skylab]] from the US. The station has been continuously occupied for {{age in years and days|2 Nov 2000|sep=and}} since the arrival of [[Expedition 1]] on 2 November 2000. This is the longest continuous human presence in space, having surpassed the previous record of {{age in years and days|5 Sep 1989|28 Aug 1999|sep=and}} held by Mir. The station is serviced by a variety of visiting spacecraft: [[Soyuz (spacecraft)|Soyuz]], [[Progress (spacecraft)|Progress]], the [[Automated Transfer Vehicle]], the [[H-II Transfer Vehicle]],<ref name="ISSRG" /> [[Dragon (spacecraft)|Dragon]], and [[Cygnus (spacecraft)|Cygnus]]. It has been visited by astronauts, cosmonauts and space tourists from [[List of International Space Station visitors|15 different nations]].<ref name="10th">{{cite web|url=http://www.nasa.gov/mission_pages/station/main/10th_anniversary.html|title=Nations Around the World Mark 10th Anniversary of International Space Station|publisher=NASA|date=17 November 2008|accessdate=6 March 2009}}</ref>

After the US Space Shuttle program ended in 2011, Soyuz rockets became the only provider of transport for astronauts at the International Space Station, and Dragon became the only provider of bulk [[downmass|cargo-return-to-Earth]] services (downmass capability of Soyuz capsules is very limited).

The [[International Space Station program|ISS programme]] is a joint project among five participating space agencies: [[NASA]], [[Russian Federal Space Agency|Roscosmos]], [[Japan Aerospace Exploration Agency|JAXA]], [[European Space Agency|ESA]], and [[Canadian Space Agency|CSA]].<ref name="ISSRG" /><ref name="PartStates">{{cite web|url=http://www.esa.int/esaHS/partstates.html|title=Human Spaceflight and Exploration—European Participating States|accessdate=17 January 2009|publisher=European Space Agency (ESA)|year=2009}}</ref> The ownership and use of the space station is established by intergovernmental treaties and agreements.<ref name="ESA-IGA">{{cite web|url=http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station/International_Space_Station_legal_framework|title=International Space Station legal framework|publisher=European Space Agency (ESA)|accessdate=21 February 2015|date=19 November 2013}}</ref> The station is divided into two sections, the [[Russian Orbital Segment]] (ROS) and the [[US Orbital Segment|United States Orbital Segment]] (USOS), which is shared by many nations. {{asof|2014|January}}, the American portion of ISS was funded until 2024.<ref>{{cite web|url=http://www.washingtonpost.com/national/health-science/nasa-space-station-operation-extended-by-obama-until-2024-at-least/2014/01/08/9819d5c8-788e-11e3-8963-b4b654bcc9b2_story.html|title=NASA: International space station operation extended by Obama until at least 2024|last=Achenbach|first=Joel|publisher=washingtonpost.com|date=8 January 2014|accessdate=8 January 2014}}</ref><ref>{{cite web|url=http://spaceflightnow.com/news/n1003/11station/|title=Space station partners set 2028 as certification goal|last=Clark|first=Stephen|date=11 March 2010|publisher=Spaceflight Now|accessdate=1 June 2011}}</ref><ref>{{cite news| url=http://www.cbc.ca/news/technology/story/2012/02/29/science-international-space-station.html | work=CBC News | title=Canada's space station commitment renewed | date=29 February 2012}}</ref> Roscosmos has endorsed the continued operation of ISS through 2024,<ref name="sn20150225"/> but have proposed using elements of the Russian Orbital Segment to construct a new Russian space station called [[Orbital Piloted Assembly and Experiment Complex|OPSEK]].<ref name="moscow20141117">{{cite news |url=http://www.themoscowtimes.com/business/article/russia-may-be-planning-national-space-station-to-replace-iss/511299.html |title=Russia May Be Planning National Space Station to Replace ISS |work=The Moscow Times |first=Matthew |last=Bodner |date=17 November 2014 |accessdate=3 March 2015}}</ref>

On March 28, 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS.<ref name=":0">{{cite web|url= http://www.independent.co.uk/news/science/russia-and-the-us-will-build-a-new-space-station-together-10140890.html|title=Russia and the US will build a new space station together |publisher=The Independent|date=28 March 2015}}</ref><ref name=":1">{{Cite news|url = http://rt.com/news/244797-russia-us-new-space-station/|title = Russia & US agree to build new space station after ISS, work on joint Mars project|last = |first = |date = March 28, 2015|work = RT|access-date = March 28, 2015}}</ref> NASA later issued a guarded statement expressing thanks for Russia's interest in future cooperation in space exploration, but fell short of confirming the Russian announcement.<ref>{{Cite news|url = http://www.engadget.com/2015/03/28/nasa-is-working-with-russia-on-a-new-space-station/|title = NASA is working with Russia on a new space station (update: not quite) |last = Moon|first = Mariella|date = 28 March 2015|work = Engadget|access-date = 29 March 2015}}</ref><ref name="no plans">{{cite web|url=http://spacenews.com/nasa-says-no-plans-for-iss-replacement-with-russia/|title=NASA Says No Plans for ISS Replacement with Russia|date=March 28, 2015|author=Jeff Foust|publisher=SpaceNews}}</ref>

{{TOC limit|limit=3}}

==Purpose==
[[File:STS-129 Zvezda sunrise.jpg|thumb|Sunrise at ''Zvezda'']]
[[File:STS-134 EVA4 view to the Space Shuttle Endeavour.jpg|thumb|right|Fisheye view of several labs]]
According to the original Memorandum of Understanding between NASA and Rosaviakosmos, the International Space Station was intended to be a laboratory, observatory and factory in [[low Earth orbit]]. It was also planned to provide transportation, maintenance, and act as a staging base for possible future missions to the Moon, Mars and asteroids.<ref name="RSA-MOU">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/nasa_rsa.html|title=Memorandum of Understanding Between the National Aeronautics and Space Administration of the United States of America and the Russian Space Agency Concerning Cooperation on the Civil International Space Station|publisher=NASA|accessdate=19 April 2009|date=29 January 1998}}</ref> In the 2010 United States National Space Policy, the ISS was given additional roles of serving commercial, diplomatic<ref>{{cite journal|last=Payette|first=Julie|title=Research and Diplomacy 350 Kilometers above the Earth: Lessons from the International Space Station|journal=Science & Diplomacy|date=10 December 2012|volume=1|issue=4|url=http://www.sciencediplomacy.org/article/2012/research-and-diplomacy-350-kilometers-above-earth}}</ref> and educational purposes.<ref name=USNSP>{{cite web|title=National Space Policy of the United States of America|url=http://www.whitehouse.gov/sites/default/files/national_space_policy_6-28-10.pdf|publisher=White House; USA Federal government|accessdate=20 July 2011}}</ref>

===Scientific research===
{{Main|Scientific research on the ISS|l1=Scientific research on the ISS}}
The ISS provides a platform to conduct scientific research. Small unmanned spacecraft can provide platforms for zero gravity and exposure to space, but space stations offer a long term environment where studies can be performed potentially for decades, combined with ready access by human researchers over periods that exceed the capabilities of manned spacecraft.<ref name="10th" /><ref name="Worldbook at NASA" />

The Station simplifies individual experiments by eliminating the need for separate rocket launches and research staff. The wide variety of research fields include [[astrobiology]], [[astronomy]], [[Zero g#Health effects of weightlessness|human research]] including [[space medicine]] and [[life science]]s, [[physical science]]s, [[materials science]], [[space weather]], and weather on Earth ([[meteorology]]).<ref name="ISS overview" /><ref name="NASA Fields of Research" /><ref name="NASA ISS Goals" /><ref>{{cite web|url=http://www.isas.jaxa.jp/e/forefront/2009/ueno/index.shtml|title=Monitor of All-sky X-ray Image (MAXI)|year=2008|publisher=JAXA|accessdate=12 March 2011}}</ref><ref>[http://www.spaceref.com/news/viewpr.html?pid=33007 ESA via SPACEREF] "SOLAR: three years observing and ready for solar maximum", 14 March 2011</ref> Scientists on Earth have access to the crew's data and can modify experiments or launch new ones, which are benefits generally unavailable on unmanned spacecraft.<ref name="Worldbook at NASA" /> Crews fly [[List of International Space Station expeditions|expeditions]] of several months duration, providing approximately 160-man-hours per week of labour with a crew of 6.<ref name="ISS overview"/><ref name="Science in School">{{cite web|url=http://www.scienceinschool.org/2008/issue10/iss|title=The International Space Station: life in space|publisher=Science in School|date=10 December 2008|accessdate=17 February 2009}}</ref>

To detect dark matter and answer other fundamental questions about our universe, engineers and scientists from all over the world built the [[Alpha Magnetic Spectrometer]] (AMS), which NASA compares to the [[Hubble space telescope]], and says could not be accommodated on a free flying satellite platform due in part to its power requirements and data bandwidth needs.<ref>[http://www.nasa.gov/mission_pages/shuttle/main/amsprocessing.html NASA – AMS to Focus on Invisible Universe]. Nasa.gov (18 March 2011). Retrieved 8 October 2011.</ref><ref>[http://science.nasa.gov/science-news/science-at-nasa/2009/14aug_ams/ In Search of Antimatter Galaxies – NASA Science]. ''Science''.nasa.gov (16 May 2011). Retrieved 8 October 2011.</ref> On 3 April 2013, [[NASA]] scientists reported that hints of [[dark matter]] may have been detected by the Alpha Magnetic Spectrometer.<ref name="APS-20130403">{{cite journal |authors=Aguilar, M. et al. (AMS Collaboration) |title=First Result from the Alpha Magnetic Spectrometer on the International Space Station: Precision Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–350 GeV|url=http://prl.aps.org/abstract/PRL/v110/i14/e141102 |date=3 April 2013 |journal=[[Physical Review Letters]]|accessdate=3 April 2013 |doi=10.1103/PhysRevLett.110.141102 }}</ref><ref name="AMS-20130403">{{cite web |author=Staff |title=First Result from the Alpha Magnetic Spectrometer Experiment|url=http://www.ams02.org/2013/04/first-results-from-the-alpha-magnetic-spectrometer-ams-experiment/ |date=3 April 2013 |work=AMS Collaboration |accessdate=3 April 2013 }}</ref><ref name="AP-20130403">{{cite news |last1=Heilprin|first1=John |last2=Borenstein |first2=Seth |title=Scientists find hint of dark matter from cosmos|url=http://apnews.excite.com/article/20130403/DA5E6JAG3.html |date=3 April 2013 |agency=Associated Press |accessdate=3 April 2013 }}</ref><ref name="BBC-20130403">{{cite news |last=Amos |first=Jonathan |title=Alpha Magnetic Spectrometer zeroes in on dark matter |url=http://www.bbc.co.uk/news/science-environment-22016504 |date=3 April 2013 |work=[[BBC News]] |accessdate=3 April 2013 }}</ref><ref name="NASA-20130403">{{cite web |last1=Perrotto|first1=Trent J. |last2=Byerly |first2=Josh |title=NASA TV Briefing Discusses Alpha Magnetic Spectrometer Results|url=http://www.nasa.gov/home/hqnews/2013/apr/HQ_M13-054_AMS_Findings_Briefing.html |date=2 April 2013|work=[[NASA]] |accessdate=3 April 2013 }}</ref><ref name="NYT-20130403">{{cite news |last=Overbye |first=Dennis |title=New Clues to the Mystery of Dark Matter |url=http://www.nytimes.com/2013/04/04/science/space/new-clues-to-the-mystery-of-dark-matter.html |date=3 April 2013 |work=[[The New York Times]] |accessdate=3 April 2013 }}</ref> According to the scientists, "[[Alpha Magnetic Spectrometer#First results|The first results]] from the space-borne Alpha Magnetic Spectrometer confirm an unexplained excess of high-energy positrons in Earth-bound cosmic rays."

{{Double image|right|Iss030e015472 Edit.jpg|117|ISS-08 Michael Foale conducts an inspection of the Microgravity Science Glovebox.jpg|241|[[C/2011 W3 (Lovejoy)|Comet Lovejoy]] photographed by [[Expedition 30]] commander [[Dan Burbank]]|[[Expedition 8]] Commander and Science Officer [[Michael Foale]] conducts an inspection of the [[Microgravity Science Glovebox]]}}
The space environment is hostile to life. Unprotected presence in space is characterised by an intense radiation field (consisting primarily of protons and other subatomic charged particles from the [[solar wind]], in addition to [[cosmic ray]]s), high vacuum, extreme temperatures, and microgravity.<ref name="Space Microbiology">{{cite web|url=http://syntheticbiology.arc.nasa.gov/files/SpaceMicrobiology%20MMBR%201.pdf|title=Space Microbiology, section Space Environment (p. 122)|publisher=Microbiology and Molecular Biology Reviews|date=March 2010|accessdate=4 June 2011|author=G Horneck, DM Klaus & RL Mancinelli}}</ref> Some simple forms of life called [[extremophile]]s,<ref name="Beer microbes">{{cite news|url=http://www.bbc.co.uk/news/science-environment-11039206|title=Beer microbes live 553 days outside ISS|work=[[BBC News]]|date=23 August 2010|accessdate=4 June 2011|author=Jonathan Amos}}</ref> including small invertebrates called [[tardigrade]]s<ref name="Waterbears">{{cite web|url=http://www.nature.com/news/2008/080908/full/news.2008.1087.html|title=Spacesuits optional for 'water bears'|work=Nature|date=8 September 2008|accessdate=4 June 2011}}</ref> can survive in this environment in an extremely dry state called [[Desiccation#Biology and ecology|desiccation]].

Medical research improves knowledge about the effects of long-term space exposure on the human body, including [[muscle atrophy]], [[Osteoporosis|bone loss]], and fluid shift. This data will be used to determine whether lengthy [[human spaceflight]] and [[space colonisation]] are feasible. As of 2006, data on bone loss and muscular atrophy suggest that there would be a significant risk of fractures and movement problems if astronauts landed on a planet after a lengthy interplanetary cruise, such as the six-month interval required to [[Manned mission to Mars|travel to Mars]].<ref name="JCB">{{cite book|author=Jay Buckey|title=Space Physiology|publisher=Oxford University Press USA|date=23 February 2006|isbn=978-0-19-513725-5}}</ref><ref>{{cite web|url=http://www.newscientist.com/article/dn17476-ion-engine-could-one-day-power-39day-trips-to-mars.html?full=true|work=New Scientist|accessdate=8 January 2010|date=24 July 2009|author=List Grossman|title=Ion engine could one day power 39-day trips to Mars}}</ref>
Medical studies are conducted aboard the ISS on behalf of the [[National Space Biomedical Research Institute]] (NSBRI). Prominent among these is the [[Advanced Diagnostic Ultrasound in Microgravity]] study in which astronauts perform ultrasound scans under the guidance of remote experts. The study considers the diagnosis and treatment of medical conditions in space. Usually, there is no physician on board the ISS and diagnosis of medical conditions is a challenge. It is anticipated that remotely guided ultrasound scans will have application on Earth in emergency and rural care situations where access to a trained physician is difficult.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/science/experiments/ADUM.html|date=1 May 2009|accessdate=1 October 2009|author=Brooke Boen|publisher=NASA|title=Advanced Diagnostic Ultrasound in Microgravity (ADUM)}}</ref><ref>{{cite journal|author=Sishir Rao|display-authors=etal|year=2008|title=A Pilot Study of Comprehensive Ultrasound Education at the Wayne State University School of Medicine|journal=Journal of Ultrasound in Medicine|volume=27|pages=745–749|pmid=18424650|issue=5}}</ref><ref>{{cite journal|author=Michael Fincke|display-authors=etal|year=2004|title=Evaluation of Shoulder Integrity in Space: First Report of Musculoskeletal US on the International Space Station|journal=Radiology|issue= 2|pages=319–322|pmid=15533948|doi=10.1148/radiol.2342041680|volume=234}}</ref>

====Microgravity====
[[File:Space Fire.jpg|thumb|A comparison between the combustion of a candle on [[Earth]] (left) and in a microgravity environment, such as that found on the ISS (right)]]
The Earth's gravity is only slightly weaker at the altitude of the ISS than at the surface, but objects in orbit are in a continuous state of [[Free fall|freefall]], resulting in an apparent state of weightlessness. This perceived weightlessness is disturbed by five separate effects:<ref name="gravity">{{cite web|url=http://www.esa.int/Our_Activities/Human_Spaceflight/Human_Spaceflight_Research/European_User_Guide_to_Low-Gravity_Platforms
|title=European Users Guide to Low Gravity Platforms|accessdate=22 March 2013|date=6 December 2005|publisher=European Space Agency}}</ref>
* Drag from the residual atmosphere; when the ISS enters the Earth's shadow, the main solar panels are rotated to minimise this aerodynamic drag, helping reduce [[orbital decay]].
* Vibration from movements of mechanical systems and the crew.
* Actuation of the on-board attitude [[control moment gyroscope]]s.
* [[Rocket engine|Thruster]] firings for attitude or orbital changes.
* [[Gravity-gradient stabilization|Gravity-gradient effects]], also known as [[tidal force|tidal]] effects. Items at different locations within the ISS would, if not attached to the station, follow slightly different orbits. Being mechanically interconnected these items experience small forces that keep the station moving as a [[rigid body]].

[[File:ISS-20 Robert Thirsk at the Minus Eighty Degree Laboratory Freezer.jpg|thumb|left|ISS crew member storing samples]]

Researchers are investigating the effect of the station's near-weightless environment on the evolution, development, growth and internal processes of plants and animals. In response to some of this data, NASA wants to investigate [[microgravity]]'s effects on the growth of three-dimensional, human-like tissues, and the unusual [[protein crystal]]s that can be formed in space.<ref name="NASA Fields of Research" />

The investigation of the physics of fluids in microgravity will allow researchers to model the behaviour of fluids better. Because fluids can be almost completely combined in microgravity, physicists investigate fluids that do not mix well on Earth. In addition, an examination of reactions that are slowed by low gravity and temperatures will give scientists a deeper understanding of [[superconductivity]].<ref name="NASA Fields of Research" />

The study of [[materials science]] is an important ISS research activity, with the objective of reaping economic benefits through the improvement of techniques used on the ground.<ref>{{cite web|url=http://science.nasa.gov/newhome/headlines/msad15sep99_1.htm|title=Materials Science 101|publisher=Science@NASA|accessdate=18 June 2009|date=15 September 1999}}</ref> Other areas of interest include the effect of the low gravity environment on combustion, through the study of the efficiency of burning and control of emissions and pollutants. These findings may improve current knowledge about energy production, and lead to economic and environmental benefits. Future plans are for the researchers aboard the ISS to examine [[aerosol]]s, [[ozone]], [[water vapour]], and [[oxide]]s in Earth's atmosphere, as well as [[cosmic ray]]s, [[cosmic dust]], [[antimatter]], and [[dark matter]] in the universe.<ref name="NASA Fields of Research" />

===Exploration===
[[File:Mars500.jpg|thumb|right|A 3D plan of the Russia-based [[MARS-500]] complex, used for ground-based experiments which complement ISS-based preparations for a [[manned mission to Mars]]]]
The ISS provides a location in the relative safety of Low Earth Orbit to test spacecraft systems that will be required for long-duration missions to [[the Moon]] and [[Mars]]. This provides experience in operations, maintenance as well as repair and replacement activities on-orbit, which will be essential skills in operating spacecraft farther from Earth, mission risks can be reduced and the capabilities of interplanetary spacecraft advanced.<ref name="ResProg">{{cite web|url=http://spaceflightsystems.grc.nasa.gov/Advanced/ISSResearch/|title=ISS Research Program|publisher=NASA|accessdate=27 February 2009}}{{dead link|date=August 2011}}</ref> Referring to the [[MARS-500]] experiment, ESA states that "Whereas the ISS is essential for answering questions concerning the possible impact of weightlessness, radiation and other space-specific factors, aspects such as the effect of long-term isolation and confinement can be more appropriately addressed via ground-based simulations".<ref name="esa mars500 ">{{cite web|title=Mars500 study overview | publisher = ESA |date= 4 June 2011| url = http://www.esa.int/esaMI/Mars500/SEM7W9XX3RF_0.html }}</ref> Sergey Krasnov, the head of human space flight programmes for Russia's space agency, Roscosmos, in 2011 suggested a "shorter version" of MARS-500 may be carried out on the ISS. <ref name="Mars thing on ISS">{{cite web| title=Space station may be site for next mock Mars mission| url = http://www.newscientist.com/blogs/shortsharpscience/2011/11/space-station-may-be-site-for.html|date=4 November 2011|work=New Scientist}}</ref>

In 2009, noting the value of the partnership framework itself, Sergey Krasnov wrote, "When compared with partners acting separately, partners developing complementary abilities and resources could give us much more assurance of the success and safety of space exploration. The ISS is helping further advance near-Earth space exploration and realisation of prospective programmes of research and exploration of the Solar system, including the Moon and Mars."<ref name=IAF2009>{{cite web|title=The Sustainable Utilisation of the ISS Beyond 2015|url=http://www.iafastro.org/docs/2009/ISS2015.pdf|publisher=International Astronautical Congress|accessdate=15 December 2011}}</ref> [[Manned mission to Mars|A manned mission to Mars]] may be a multinational effort involving space agencies and countries outside the current ISS partnership. In 2010, ESA Director-General Jean-Jacques Dordain stated his agency was ready to propose to the other four partners that China, India and South Korea be invited to join the ISS partnership.<ref name="ESAproposesInvite">{{cite web|title=ESA Chief Lauds Renewed U.S. Commitment to Space Station, Earth Science | publisher =Peter B. de Selding, Space News. |date=2 March 2010 | url =http://www.spacenews.com/civil/100203-esa-chief-lauds-renewed-commitment-space-station-earth-science.html}}</ref> NASA chief [[Charlie Bolden]] stated in February 2011, "Any mission to Mars is likely to be a global effort".<ref name="Mars a global effort">{{cite web|title= Charlie Bolden | publisher = space.com |date=4 June 2011 | url = http://www.space.com/11335-nasa-mars-exploration-space-station.html }}</ref> Currently, American legislation prevents NASA co-operation with China on space projects.<ref name="justice1">{{citation|first=Virginia|last=Seitz|title=Memorandum Opinion for the General Counsel, Office of Science and Technology Policy|url=http://www.justice.gov/olc/2011/conduct-diplomacy.pdf|journal=Office of Legal Counsel|volume=35|date=11 September 2011|accessdate=23 May 2012|archiveurl=https://web.archive.org/web/20120713080223/http://www.justice.gov/olc/2011/conduct-diplomacy.pdf|archivedate=13 July 2012}}</ref>

===Education and cultural outreach===
[[File:ISS-36 HTV-4 berthing 2.jpg|thumb|Japan's Kounotori 4 docking]]
The ISS crew provides opportunities for students on Earth by running student-developed experiments, making educational demonstrations, allowing for student participation in classroom versions of ISS experiments, and directly engaging students using radio, videolink and email.<ref name="ISSRG" /><ref>{{cite journal|author1=Gro Mjeldheim Sandal |author2=Dietrich Manzey|title=Cross-cultural issues in space operations: A survey study among ground personnel of the European Space Agency|journal=Acta Astronautica|volume=65|date=December 2009|pages=1520–1529|doi=10.1016/j.actaastro.2009.03.074|issue=11–12}}</ref> ESA offers a wide range of free teaching materials that can be downloaded for use in classrooms.<ref>[http://www.esa.int/SPECIALS/Education/SEM0LW4KXMF_0.html ESA – Education – Online material]. Esa.int (7 September 2011). Retrieved 8 October 2011.</ref> In one lesson, students can navigate a 3-D model of the interior and exterior of the ISS, and face spontaneous challenges to solve in real time.<ref>[http://www.esa.int/SPECIALS/Education/SEM1LL3Z2OF_0.html ESA – Education – ISS 3-D Teaching Tool: Spaceflight Challenge I]. Esa.int (24 May 2011). Retrieved 8 October 2011.</ref>

JAXA aims both to "Stimulate the curiosity of children, cultivating their spirits, and encouraging their passion to pursue craftsmanship", and to "Heighten the child's awareness of the importance of life and their responsibilities in society."<ref>[http://www.oosa.unvienna.org/pdf/pres/copuos2010/tech-17E.pdf Building Peace in Young Minds through Space Education]. Committee on the Peaceful Uses of Outer Space, 53rd Session. June 2010, Vienna, Austria; Space Education Center, Japan Aerospace Exploration Agency (JAXA)</ref> Through a series of education guides, a deeper understanding of the past and near-term future of manned space flight, as well as that of Earth and life, will be learned.<ref>[http://www.edu.jaxa.jp/education/international/ISS/SSK/en/ JAXA Space Education Center : JAXA Spaceflight Seeds Kids I : Spaceflight Sunflower seeds – Let's make them flower! and learn freshly the Earth environment just by contrast with the Space one]. Edu.jaxa.jp. Retrieved 8 October 2011.</ref><ref>[http://www.edu.jaxa.jp/education/international/ISS/SIS/en/ JAXA Space Education Center : JAXA Seeds in Space I : Let's Cultivate Spaceflight Asagao, Miyako-gusa Seeds and Identify the Mutants!]. Edu.jaxa.jp. Retrieved 8 October 2011.</ref> In the JAXA Seeds in Space experiments, the mutation effects of spaceflight on plant seeds aboard the ISS is explored. Students grow sunflower seeds which flew on the ISS for about nine months as a start to 'touch the Universe'. In the first phase of Kibō utilisation from 2008 to mid-2010, researchers from more than a dozen Japanese universities conducted experiments in diverse fields.<ref>{{cite web |author=Keiji Murakami |url=http://www.spacepolicyonline.com/pages/images/stories/Micro%20Oct%2009%20JEM.pdf |title=JEM Utilization Overview |publisher=JAXA. Steering Committee for the Decadal Survey on Biological and Physical Sciences in Space |date=14 October 2009}}</ref>

[[Image:Crew in ATV with Jules Verne manuscript.jpg|thumb|left|Original Jules Verne manuscripts displayed by crew inside Jules Verne ATV]]
Cultural activities are another major objective. Tetsuo Tanaka, director of JAXA's Space Environment and Utilization Center, says "There is something about space that touches even people who are not interested in science."<ref name="jaxa2">{{cite web |author=Tetsuo Tanaka |url=http://www.jaxa.jp/article/special/kibo/tanaka01_e.html |title=Kibo: Japan's First Human Space Facility |publisher=JAXA |accessdate=8 October 2011}}</ref>

[[ARISS|Amateur Radio on the ISS]] (ARISS) is a volunteer programme which encourages students worldwide to pursue careers in science, technology, engineering and mathematics through [[amateur radio]] communications opportunities with the ISS crew. ARISS is an international working group, consisting of delegations from 9 countries including several countries in Europe as well as Japan, Russia, Canada, and the United States. In areas where radio equipment cannot be used, speakerphones connect students to ground stations which then connect the calls to the station. <ref>{{cite web|url=http://www.rac.ca/ariss/oindex.htm|title=Amateur Radio on the International Space Station|date=6 June 2011|accessdate=10 June 2011}}</ref>

''[[First Orbit]]'' is a feature-length documentary film about [[Vostok 1]], the first manned space flight around the Earth. By matching the orbit of the International Space Station to that of Vostok 1 as closely as possible, in terms of ground path and time of day, documentary filmmaker Christopher Riley and ESA astronaut [[Paolo Nespoli]] were able to film the view that Yuri Gagarin saw on his pioneering orbital space flight. This new footage was cut together with the original Vostok 1 mission audio recordings sourced from the Russian State Archive. Nespoli, during Expedition 26/27, filmed the majority of the footage for this documentary film, and as a result is credited as its [[Cinematographer|director of photography]].<ref>{{cite news|last=Riley|first=Christopher|title=What Yuri Gagarin saw: First Orbit film to reveal the view from Vostok 1|url=http://www.guardian.co.uk/science/blog/2011/apr/11/yuri-gagarin-first-orbit-vostok|newspaper=The Guardian|date=11 April 2011|location=London}}</ref> The film was streamed through the website firstorbit.org in a global YouTube premiere in 2011, under a free license.<ref>{{cite web|url=http://www.firstorbit.org/first-orbit-faqs |title=Yuri Gagarin's First Orbit – FAQs |publisher=Firstorbit.org |accessdate=1 May 2012}}</ref>

In May 2013, commander [[Chris Hadfield]] shot a music video of [[David Bowie]]'s ''[[Space Oddity (song)|Space Oddity]]'' on board the station; the film was released freely on YouTube.<ref>{{cite web|last=Warr |first=Philippa |url=http://www.wired.co.uk/news/archive/2013-05/13/commander-hadfield-space-oddity |title=Commander Hadfield bids farewell to ISS with Reddit-inspired Bowie cover |publisher=Wired.co.uk |date=13 May 2013 |accessdate=22 October 2013}}</ref> It was the first music video ever to be filmed in space.<ref>{{cite web|last=Davis|first=Lauren|title=Chris Hadfield sings 'Space Oddity' in the first music video in space|url=http://io9.com/chris-hadfield-sings-space-oddity-in-the-first-music-503764317|publisher=io9}}</ref>

==Assembly==
{{Main|Assembly of the International Space Station|List of ISS spacewalks}}
[[File:ISS-with-S0-S1-P1.jpg|thumb|right|alt=S0, S1 and P1 truss structures installed|Partially constructed ISS in December 2002]]
[[File:S3-S4 Truss Installed 2.jpg|thumb|S3-S4 Truss Installed in 2007]]
[[File:Soyuz TMA-19 spacecraft departs the ISS.jpg|thumb|[[Soyuz TMA-19]] departs in 2010]]
[[File:ISS after STS-117 in June 2007.jpg|thumb|ISS in 2007, with fewer solar arrays]]
The assembly of the International Space Station, a major endeavour in [[space architecture]], began in November 1998.<ref name="OnOrbit">{{cite web|url=http://www.nasa.gov/externalflash/ISSRG/pdfs/on_orbit.pdf|title=On-Orbit Elements|publisher=NASA|author=NASA|date=18 February 2010|accessdate=19 June 2010|format=PDF}}</ref> Russian modules launched and docked robotically, with the exception of ''[[Rassvet (ISS module)|Rassvet]]''. All other modules were delivered by the Space Shuttle, which required installation by ISS and shuttle crewmembers using the [[Mobile Servicing System#Canadarm2|Canadarm2]] (SSRMS) and [[List of ISS spacewalks|EVAs]]; {{as of|2011|06|05|lc=y}}, they had added 159 components during more than 1,000 hours of EVA. 127 of these spacewalks originated from the station, and the remaining 32 were launched from the airlocks of docked Space Shuttles.<ref name="ISStD" /> The [[beta angle]] of the station had to be considered at all times during construction, as the station's beta angle is directly related to the percentage of its orbit that the station (as well as any docked or docking spacecraft) is exposed to the sun; the Space Shuttle would not perform optimally above a limit called the "beta cutoff".<ref name="mcc">{{cite web|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-113/11_23_20_01_179.html|title=MCC Answers|author=Derek Hassman, NASA Flight Director|date=1 December 2002|publisher=NASA|accessdate=14 June 2009}}</ref>

The first module of the ISS, ''[[Zarya]]'', was launched on 20 November 1998 on an autonomous Russian [[Proton (rocket)|Proton rocket]]. It provided propulsion, attitude control, communications, electrical power, but lacked long-term life support functions. Two weeks later a passive NASA module ''[[Unity (ISS module)|Unity]]'' was launched aboard Space Shuttle flight [[STS-88]] and attached to Zarya by astronauts during EVAs. This module has two [[Pressurized Mating Adapter]]s (PMAs), one connects permanently to Zarya, the other allows the Space Shuttle to dock to the space station. At this time, the Russian station Mir was still inhabited. The ISS remained unmanned for two years, during which time Mir was de-orbited. On 12 July 2000 [[Zvezda (ISS module)|Zvezda]] was launched into orbit. Preprogrammed commands on board deployed its solar arrays and communications antenna. It then became the passive vehicle for a rendezvous with the Zarya and Unity. As a passive "target" vehicle, the Zvezda maintained a stationkeeping orbit as the Zarya-Unity vehicle performed the rendezvous and docking via ground control and the Russian automated rendezvous and docking system. Zarya's computer transferred control of the station to Zvezda's computer soon after docking. Zvezda added sleeping quarters, a toilet, kitchen, CO2 scrubbers, dehumidifier, oxygen generators, exercise equipment, plus data, voice and television communications with mission control. This enabled permanent habitation of the station.<ref>[http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/servmod.pdf NASA Facts. The Service Module: A Cornerstone of Russian International Space Station Modules]. NASA. January 1999</ref><ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/missions/sts-88/mission-sts-88.html |title=STS-88 |publisher=Science.ksc.nasa.gov |accessdate=19 April 2011}}</ref>

The first resident crew, [[Expedition 1]], arrived in November 2000 on [[Soyuz TM-31]]. At the end of the first day on the station, astronaut Bill Shepherd requested the use of the radio call sign "''Alpha''", which he and cosmonaut Krikalev preferred to the more cumbersome "''International Space Station''".<ref name=TIME-Nov2>{{cite news|url=http://www.time.com/time/arts/article/0,8599,59500,00.html|title=Upward Bound: Tales of Space Station Alpha|author=Brad Liston|date=2 November 2000|work=Time|accessdate=5 August 2010}}</ref> The name "''Alpha''" had previously been used for the station in the early 1990s,<ref name=GAO>{{cite web|url=http://archive.gao.gov/t2pbat3/151975.pdf|title=Space Station – Impact on the expanded Russian role of funding and research|date=21 June 1994|publisher=[[Government Accountability Office|United State General Accounting Office]]|accessdate=9 August 2010}}</ref> and following the request, its use was authorised for the whole of Expedition 1.<ref name=SPACE-Nov3>{{cite web|url=http://www.space.com/missionlaunches/missions/alpha_male_001103.html|title=Call Bill Shepherd the Alpha Male of the International Space Station|author=Alan Ladwig|date=3 November 2000|publisher=Space.com|accessdate=9 August 2010}}</ref> Shepherd had been advocating the use of a new name to project managers for some time. Referencing a [[Ship naming and launching|naval tradition]] in a pre-launch news conference he had said: "For thousands of years, humans have been going to sea in ships. People have designed and built these vessels, launched them with a good feeling that a name will bring good fortune to the crew and success to their voyage."<ref name=SPACE-Nov2>{{cite web|url=http://www.space.com/missionlaunches/missions/exp1_alpha_001102.html|title=Expedition One Crew Wins Bid To Name Space Station Alpha|date=2 November 2000|author=Todd Halvorson|publisher=Space.com|accessdate=9 August 2010}}</ref> [[Yuri Semenov]], the President of [[S.P. Korolev Rocket and Space Corporation Energia|Russian Space Corporation Energia]] at the time, disapproved of the name "''Alpha''"; he felt that ''Mir'' was the first space station, and so he would have preferred the names "''Beta''" or "''Mir 2''" for the ISS.<ref name=SPACE-Nov3 /><ref>{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=5913|title=Interview with RSC Energia's Yuri Semenov|publisher=Space.com|date=3 September 2001|accessdate=22 August 2010}}</ref><ref>{{cite web|url=http://english.ruvr.ru/2001/03/29/100146.html|title=Interview with Yuri Semenov, general designer of Space Rocket corporation Energy|date=21 March 2001|publisher=[[Voice of Russia]]|accessdate=5 October 2010}}</ref>

[[Expedition 1]] arrived midway between the flights of [[STS-92]] and [[STS-97]]. These two Space Shuttle flights each added segments of the station's [[Integrated Truss Structure]], which provided the station with Ku-band communication for US television, additional attitude support needed for the additional mass of the USOS, and substantial [[solar array]]s supplementing the station's existing 4 solar arrays.<ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/missions/sts-92/mission-sts-92.html |title=STS-92 |publisher=Science.ksc.nasa.gov |accessdate=19 April 2011}}</ref>

Over the next two years the station continued to expand. A [[Soyuz-U]] rocket delivered the [[Pirs (ISS module)|''Pirs'' docking compartment]]. The Space Shuttles ''Discovery'', ''[[Space Shuttle Atlantis|Atlantis]]'', and ''Endeavour'' delivered the [[Destiny (ISS module)|''Destiny'' laboratory]] and [[Quest Joint Airlock|''Quest'' airlock]], in addition to the station's main robot arm, the ''[[Canadarm2]]'', and several more segments of the Integrated Truss Structure.
[[File:Zvezda rear.jpg|thumb|left|Aft view showing a Progress spacecraft docked to Zvezda]]
The expansion schedule was interrupted by the {{OV|102}} [[Space Shuttle Columbia disaster|disaster]] in 2003, with the resulting two year hiatus in the [[Space Shuttle program]]me halting station assembly. The space shuttle was grounded until 2005 with [[STS-114]] flown by ''Discovery''.<ref>{{cite web|url=http://www.nasaspaceflight.com/2005/07/discovery-launches-the-shuttle-is-back/|title=Discovery launches—The Shuttle is back|author=Chris Bergin|publisher=NASASpaceflight.com|accessdate=6 March 2009|date=26 July 2005}}</ref>

Assembly resumed in 2006 with the arrival of [[STS-115]] with ''Atlantis'', which delivered the station's second set of solar arrays. Several more truss segments and a third set of arrays were delivered on [[STS-116]], [[STS-117]], and [[STS-118]]. As a result of the major expansion of the station's power-generating capabilities, more pressurised modules could be accommodated, and the ''[[Harmony (ISS module)|Harmony]]'' node and ''Columbus'' European laboratory were added. These were followed shortly after by the first two components of ''Kibō''. In March 2009, [[STS-119]] completed the Integrated Truss Structure with the installation of the fourth and final set of solar arrays. The final section of ''Kibō'' was delivered in July 2009 on [[STS-127]], followed by the Russian ''[[Poisk (ISS module)|Poisk]]'' module. The third node, ''[[Tranquility (ISS module)|Tranquility]]'', was delivered in February 2010 during [[STS-130]] by the Space Shuttle ''Endeavour'', alongside the [[Cupola (ISS module)|Cupola]], closely followed in May 2010 by the penultimate Russian module, ''[[Rassvet (ISS module)|Rassvet]]''. Rassvet was delivered by Space Shuttle ''Atlantis'' on [[STS-132]] in exchange for the Russian Proton delivery of the Zarya Module in 1998 which had been funded by the United States.<ref>{{cite web|url=http://www.russianspaceweb.com/iss_mim1.html |title=Mini-Research Module 1 (MIM1) Rassvet (MRM-1) |publisher=Russianspaceweb.com |accessdate=12 July 2011}}</ref> The last pressurised module of the USOS, ''Leonardo'', was brought to the station by ''Discovery'' on her final flight, [[STS-133]],<ref name="STS-133">{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/main/index.html |title=STS-133 |publisher=NASA |accessdate=1 September 2014}}</ref> followed by the [[Alpha Magnetic Spectrometer]] on [[STS-134]], delivered by ''Endeavour''.<ref name="STS-134">{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/main/index.html |title=STS-134 |publisher=NASA |accessdate=1 September 2014}}</ref>
[[File:Exterior of Cupola - Exp28.jpg|thumb|The Cupola arrived in 2010]]
{{As of|2011|06}}, the station consisted of fifteen pressurised modules and the [[Integrated Truss Structure]]. Still to be launched are the Russian [[Nauka (ISS module)|Multipurpose Laboratory Module]] ''Nauka'' and a number of external components, including the [[European Robotic Arm]]. Assembly is expected to be completed by April 2014,{{update inline|date=October 2014}} by which point the station will have a mass in excess of 400 [[metric ton|tonnes]] (440 [[short ton]]s).<ref name="OnOrbit" /><ref name="Manifest">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/iss_manifest.html|title=Consolidated Launch Manifest|accessdate=8 July 2008|publisher=NASA|author=NASA|year=2008}}</ref>

The gross mass of the station changes over time. The total launch mass of the modules on orbit is about {{convert|417289|kg|lbs|abbr=on}} (as of 3 September 2011).<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/isstodate.html |title=NASA – The ISS to Date (03/09/2011) |publisher=Nasa.gov |accessdate=12 July 2011}}</ref> The mass of experiments, spare parts, personal effects, crew, foodstuff, clothing, propellants, water supplies, gas supplies, docked spacecraft, and other items add to the total mass of the station. Hydrogen gas is constantly vented overboard by the oxygen generators.

==Station structure==
{{Double image|right|ROS Windows 0114 complete.jpg|130|USOS window identification.png|160|Russian Orbital Segment Windows|USOS International Space Station window locations}}

The ISS is a third generation<ref>{{cite web|url=http://www.dlr.de/iss/en/desktopdefault.aspx/tabid-1945/2746_read-4182/gallery-1/gallery_read-Image.19.2296/ |title=DLR – International Space Station ISS – From Cold War to international cooperation – the story of the ISS |publisher=Dlr.de |accessdate=1 May 2012}}</ref> modular space station.<ref>{{cite web|url=http://www.astronautix.com/articles/thistems.htm |title=Third Generation Soviet Space Systems |publisher=Astronautix.com |accessdate=1 May 2012}}</ref> Modular stations can allow the mission to be changed over time and new modules can be added or removed from the existing structure, allowing greater flexibility.

Below is a diagram of major station components. The blue areas are pressurised sections accessible by the crew without using spacesuits. The station's unpressurised superstructure is indicated in red. Other unpressurised components are yellow. Note that the Unity node joins directly to the Destiny laboratory. For clarity, they are shown apart.

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{{familytree| | | | | | | | | | | | | | | |}}
{{familytree| | | | | | | | | | | |PORT1| | |
PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | |AMS|~|ZVEZDA|~|AMS|
AMS = [[Zvezda (ISS module)|Solar array]]
|ZVEZDA = [[Zvezda (ISS module)|'''Zvezda DOS-8''' Service Module]]
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{{familytree| | | | | | | | | | | |!|!|!| |}}
{{familytree| | | | |PORT1|SGM2|-|'|!|)|-|PIRS|PORT1|
PIRS = [[Pirs (ISS module)|'''Pirs''' Airlock]]
|SGM2 = [[Poisk (ISS module)|'''Poisk''' (MRM-2) Airlock]]
|PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | | | | | | |!|!|}}
{{familytree| | | | | | | | | | | | |!|`|-|MLM|~|ERA| | |
MLM = [[Nauka (ISS module)|'''Nauka lab''' to Replace Pirs]]
| ERA = '''[[European Robotic Arm|European Robotic Arm]]'''
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{{familytree| | | | | | | | | | | | |!| | | | | | | | |}}
{{familytree| | | | | | | |SA|~|ZARYA|~|SA| | | |
SA = [[Zarya (ISS module)|Solar array]]
| ZARYA = [[Zarya (ISS module)|'''Zarya FGB''' (first module)]]
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{{familytree| | | | | | | | | | | | |!|!|}}
{{familytree| | | | | | | | | | | | |!|`|-|SGM1|PORT1|
SGM1 = [[Rassvet (ISS module)|'''Rassvet''' (MRM-1)]]
|PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | | | | | | |!| | | | | | | | |}}
{{familytree| | | | | | | | | | | | |!| | |PMM| | |
PMM = [[Leonardo (ISS module)|'''Leonardo''' cargo bay]]
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{{familytree| | | | | | | | | | | |PMA| | |!|
PMA = [[Pressurized Mating Adapter#PMA-1|PMA 1]]
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{{familytree| | | | | | | |QUEST|-|UNITY|-|NOD3|PORT2| |
UNITY = [[Unity (ISS module)|'''Unity''' Node 1]]
|QUEST = [[Quest Joint Airlock|'''Quest''' Airlock]]
|NOD3 = [[Tranquility (ISS module)|'''Tranquility''' Node 3]]
|PORT2 = [[Pressurized Mating Adapter#PMA-3|'''PMA 3''' docking port]]
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{{familytree| | | | | | | |ESP2| | |!| | |CUPOLA|
ESP2 = '''[[External Stowage Platform#ESP-2|ESP-2]]'''
|CUPOLA = '''[[Cupola (ISS module)|Cupola]]'''
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{{familytree| | | | | | | | | | | | |!|}}
{{familytree| |FE0|F|FE| |RADIATOR|!|RADIATOR| |FE|7|FE| | | |
RADIATOR = [[External Active Thermal Control System|Heat Radiator]]
|FE = [[ISS Solar Arrays#Solar arrays|Solar array]]
|FE0 = [[ISS Solar Arrays#Solar arrays|Solar array]]
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|boxstyle_FE = border: 1px solid #fee067; background:#fff4cc;
|boxstyle_FE0 = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| |:| | |:| | | | | |:| |!| |:| | | | | |:| | |:|}}
{{familytree| |:| | |:|ELC| | |:|FZ1|:| | |ELC3|:| | |:|
ELC = [[ExPRESS Logistics Carrier#ELC-2|ELC 2]], '''[[Alpha Magnetic Spectrometer|AMS]]'''
|FZ1 = '''[[Z1 truss]]'''
|ELC3 = [[ExPRESS Logistics Carrier#ELC-3|ELC 3]]
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|boxstyle_FZ1 = border: 2px solid #ff6666; background:#ffcccc;
|boxstyle_ELC = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| |D|FS56|FS34|FS1|FS0|FP1|FP34|FP56|C|
FS56 = '''[[P5 Truss Segment|S5/6 Truss]]'''
|FS34 = '''[[Integrated Truss Structure#P3/P4, S3/S4 truss assemblies|S3/S4 Truss]]'''
|FS1 = '''[[S1 Truss]]'''
|FS0 = '''[[S0 Truss]]'''
|FP1 = '''[[S1 Truss|P1 Truss]]'''
|FP34 = '''[[Integrated Truss Structure#P3/P4, S3/S4 truss assemblies|P3/P4 Truss]]'''
|FP56 = '''[[P5 Truss Segment|P5/6 Truss]]'''
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|boxstyle_FS34 = border: 2px solid #ff6666; background:#ffcccc;
|boxstyle_FS1 = border: 2px solid #ff6666; background:#ffcccc;
|boxstyle_FS0 = border: 2px solid #ff6666; background:#ffcccc;
|boxstyle_FP1 = border: 2px solid #ff6666; background:#ffcccc;
|boxstyle_FP34 = border: 2px solid #ff6666; background:#ffcccc;
|boxstyle_FP56 = border: 2px solid #ff6666; background:#ffcccc;}}
{{familytree| |:| | |:|ELC4| | | |:|!|:| | | |ELC1|:| | |:|
ELC4 = [[ExPRESS Logistics Carrier#ELC-4|ELC 4]], [[External Stowage Platform#ESP-3|ESP 3]]
|ELC1 = [[ExPRESS Logistics Carrier#ELC-1|ELC 1]]
|boxstyle_ELC1 = border: 1px solid #fee067; background:#fff4cc;
|boxstyle_ELC4 = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| |:| | |:| | | | |DEXTR|!|CANADARM| | | | |:| | |:|
CANADARM = '''[[Canadarm2]]'''
|DEXTR = '''[[Dextre]]'''
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|boxstyle_DEXTR = border: 2px solid #fee067; background:#fff4cc;}}
{{familytree| |FE0|L|FE| | | | |!| | | | |FE|J|FE| | | |
FE0 = [[ISS Solar Arrays#Solar arrays|Solar array]]
|FE = [[ISS Solar Arrays#Solar arrays|Solar array]]
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|boxstyle_FE = border: 1px solid #fee067; background:#fff4cc;
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{{familytree| | | | | | | | | | | | |!| | | | |}}
{{familytree| | | | | | | | |ESP1|DESTYNY| | |
DESTYNY = [[Destiny (ISS module)|'''Destiny''' Laboratory]]
|ESP1 = [[External Stowage Platform#ESP-1|External stowage]]
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|boxstyle_ESP1 = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| | | | | | | | | | | | |!| | | | |KIBOPS| | |
KIBOPS = [[Japanese Experiment Module#Experiment Logistics Module|'''Kibō logistics''' Cargo Bay]]
|boxstyle_KIBOPS = border: 2px solid #6699ff; background:#ccddff;}}
{{familytree| | | | | | | | | |HTV|!|HTV| |!|
HTV = '''[[H-II Transfer Vehicle|HTV]]'''/'''[[Dragon (spacecraft)|Dragon]]'''/'''[[Cygnus (spacecraft)|Cygnus]]''' berth ([[Common berthing mechanism|docking port]])
|boxstyle_HTV = border: 1px solid #a3ff66; background:#ccddff;}}
{{familytree| | | | | | | | | | | |!|!|!| | | |!|KiboRobo|
KiboRobo = [[Japanese Experiment Module|'''Kibō''' Robotic Arm]]
|boxstyle_KiboRobo = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| | | | |COLEXT|COLUMBUS|-|HARMONY|-|KIBO|KiboPlat|
HARMONY = [[Harmony (ISS module)|'''Harmony''' (Node 2)]]
|KiboPlat = [[Japanese Experiment Module|'''Kibō''' External Platform]]
|COLUMBUS = [[Columbus (ISS module)|'''Columbus''' Laboratory]]
|KIBO = [[JEM-PM|'''Kibō''' Laboratory]]
|COLEXT = External Payloads
|boxstyle_HARMONY = border: 2px solid #6699ff; background:#ccddff;
|boxstyle_COLUMBUS = border: 2px solid #6699ff; background:#ccddff;
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|boxstyle_KIBO = border: 2px solid #6699ff; background:#ccddff;
|boxstyle_KiboPlat = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| | | | | | | | | | | |PORT2| |
PORT2 = [[Pressurized Mating Adapter#PMA-2|'''PMA 2''' docking port]]
|boxstyle_PORT2 = border: 1px solid #a3ff66; background:#ccddff;}}
{{familytree| | | | | | | | | | | | | | | |}}
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==Pressurised modules==

===Zarya===
[[File:Zarya from STS-88.jpg|thumb|upright|Zarya as seen by [[Space Shuttle Endeavour]] during [[STS-88]]]]
'''''[[Zarya]]''''' (Russian: Заря́; lit. dawn), also known as the [[Functional Cargo Block]] or FGB (from the Russian "Функционально-грузовой блок", Funktsionalno-gruzovoy blok or ФГБ), was the first module of the International Space Station to be launched. The FGB provided electrical power, storage, propulsion, and guidance to the ISS during the initial stage of assembly. With the launch and assembly in orbit of other modules with more specialized functionality, Zarya is now primarily used for storage, both inside the pressurized section and in the externally mounted fuel tanks. The Zarya is a descendant of the [[TKS spacecraft]] designed for the Soviet [[Salyut program]]. The name Zarya was given to the FGB because it signified the dawn of a new era of international cooperation in space. Although it was built by a Russian company, it is owned by the [[United States]]. Zarya weighs {{convert|19300|kg|lb|abbr=on}}, is {{convert|12.55|m|ft|abbr=on}} long and {{convert|4.1|m|ft|abbr=on}} wide, discounting solar arrays.

Built from December 1994 to January 1998 in Russia at the [[Khrunichev State Research and Production Space Center]] (KhSC) in [[Moscow]], Zarya's control system was developed by the Khartron Corp. ([[Kharkiv, Ukraine]]).

Zarya was launched on 20 November 1998, on a Russian [[Proton-K|Proton rocket]] from [[Baikonur Cosmodrome Site 81]] in [[Kazakhstan]] to a {{convert|400|km|mi|abbr=on}} high orbit with a designed lifetime of at least 15 years. After Zarya reached orbit, STS-88 launched on 4 December 1998, to attach the Unity Module.

Although only designed to fly autonomously for six to eight months, Zarya did so for almost two years due to delays with the Russian Service Module, Zvezda, which finally launched on 12 July 2000, and docked with Zarya on 26 July using the Russian [[Kurs (docking system)|Kurs docking system]].

===Unity===
[[File:ISS Unity module.jpg|thumb|Unity as pictured by Space Shuttle Endeavour]]
'''''[[Unity (ISS module)|Unity]]''''', or Node 1, is one of three nodes, or passive connecting modules, in the [[US Orbital Segment]] of the station. It was the first US-built component of the Station to be launched. Cylindrical in shape, with six berthing locations facilitating connections to other modules, Unity was carried into orbit by {{OV|105}} as the primary cargo of [[STS-88]] in 1998. Essential space station resources such as fluids, environmental control and life support systems, electrical and data systems are routed through Unity to supply work and living areas of the station. More than 50,000 mechanical items, 216 lines to carry fluids and gases, and 121 internal and external electrical cables using six miles of wire were installed in the Unity node. Unity is made of aluminum. Prior to its launch aboard Endeavour, conical Pressurized Mating Adapters (PMAs) were attached to the aft and forward berthing mechanisms of Unity. Unity and the two mating adapters together weighed about {{convert|25600|lb|kg|disp=flip|abbr=on}}. The adapters allow the docking systems used by the Space Shuttle and by Russian modules to attach to the node's hatches and berthing mechanisms.

Unity was carried into orbit as the primary cargo of the Space Shuttle Endeavour on STS-88, the first Space Shuttle mission dedicated to assembly of the station. On 6 December 1998, the STS-88 crew mated the aft berthing port of Unity with the forward hatch of the already orbiting Zarya module.

===Zvezda===
'''''[[Zvezda (ISS module)|Zvezda]]''''' ({{lang-ru|link=no|Звезда́}}, meaning "star"), also known as DOS-8, Service Module or SM ({{lang-ru|link=no|СМ}}). It provides all of the station's critical systems,{{clarify|date=August 2013}} its addition rendered the station permanently habitable for the first time, adding life support for up to six crew and living quarters for two. Zvezda's DMS-R computer handles guidance, navigation and control for the entire space station.<ref name="Navigation" /> A second computer which performs the same functions will be installed in the [[Nauka (ISS module)|Nauka]] module, FGB-2.

The hull of Zvezda was completed in February 1985, with major internal equipment installed by October 1986. The module was launched by a Proton-K rocket from Site 81/23 at Baikonur, on 12 July 2000. Zvezda is at the rear of the station according to its normal direction of travel and orientation, its engines are used to boost the station's orbit. Alternatively Russian and European spacecraft can dock to Zvezda's aft port and use their engines to boost the station.

===Destiny===
[[File:Destiny as just installed.jpg|thumb|''Destiny'' interior in 2001]]
'''''[[Destiny (ISS module)|Destiny]]''''' is the primary research facility for United States payloads aboard the ISS. In 2011, NASA solicited proposals for a not-for-profit group to manage all American science on the station which does not relate to manned exploration. The module houses 24 [[International Standard Payload Rack]]s, some of which are used for environmental systems and crew daily living equipment. ''Destiny'' also serves as the mounting point for the station's Truss Structure.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/destiny.html|title=NASA—US Destiny Laboratory|date=26 March 2007|accessdate=26 June 2007|publisher = NASA}}</ref>

===Quest===
'''''[[Quest Joint Airlock|Quest]]''''' is the only USOS airlock, and hosts spacewalks with both United States [[Extravehicular Mobility Unit|EMU]] and Russian [[Orlan space suit|Orlan]] [[Space suit|spacesuits]]. It consists of two segments: the equipment lock, which stores spacesuits and equipment, and the crew lock, from which astronauts can exit into space. This module has a separately controlled atmosphere. Crew sleep in this module, breathing a low nitrogen mixture the night before scheduled EVAs, to avoid [[decompression sickness]] (known as "the bends") in the low-pressure suits.<ref>{{cite web|url=http://spaceflight.nasa.gov/station/eva/outside.html|title=Space Station Extravehicular Activity|accessdate=11 March 2009|publisher=[[NASA]]|date=4 April 2004}}</ref>

===Pirs and Poisk===
'''''[[Pirs (ISS module)|Pirs]]''''' ({{lang-ru|link=no|Пирс}}, meaning "[[pier]]"), ({{lang-ru|link=no|Стыковочный отсек}}), "docking module", SO-1 or DC-1 (docking compartment), and '''''[[Poisk (ISS module)|Poisk]]''''' ({{lang-ru|link=no|По́иск}}; lit. ''Search''), also known as the [[Mini-Research Module]] 2 (MRM 2), {{lang|ru|''Малый исследовательский модуль 2''}}, or МИМ 2. Pirs and Poisk are Russian airlock modules. Each of these modules have 2 identical hatches. An outward opening hatch on the MIR space station failed after it swung open too fast after unlatching, due to a small amount of air pressure remaining in the airlock.<ref>{{cite web|url=http://www.russianspaceweb.com/mir_close_calls.html |title=Mir close calls |publisher=Russianspaceweb.com |accessdate=1 May 2012}}</ref> A different entry was used, and the hatch repaired. All EVA hatches on the ISS open inwards and are pressure sealing. Pirs was used to store, service, and refurbish Russian [[Orlan suits]] and provided contingency entry for crew using the slightly bulkier American suits. The outermost docking ports on both airlocks allow docking of Soyuz and Progress spacecraft, and the automatic transfer of propellants to and from storage on the ROS.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/pirs.html|title=Pirs Docking Compartment|publisher=NASA|accessdate=28 March 2009|date=10 May 2006}}</ref>

{{multiple image |align=right |image1=Node 2 - STS-134.jpg |width1=171 |image2=Node 3 - Isolated view.jpg |width2=190 |caption1=''Harmony'' node in 2011 |caption2=''Tranquility'' node in 2011}}

===Harmony===
'''''[[Harmony (ISS module)|Harmony]]''''' is the second of the station's node modules and the utility hub of the USOS. The module contains four racks that provide electrical power, bus electronic data, and acts as a central connecting point for several other components via its six Common Berthing Mechanisms (CBMs). The European Columbus and Japanese Kibō laboratories are permanently berthed to the starboard and port radial ports respectively. The nadir and zenith ports can be used for docking visiting spacecraft including HTV, Dragon, and Cygnus, with the nadir port serving as the primary docking port. American Shuttle Orbiters docked with the ISS via PMA-2, attached to the forward port.

===Tranquility===
'''''[[Tranquility (ISS module)|Tranquility]]''''' is the third and last of the station's US nodes, it contains an additional life support system to recycle waste water for crew use and supplements oxygen generation. Two of the four berthing locations are not used. One location has the ''[[Cupola (ISS module)|Cupola]]'' installed, one has the docking port adapter, and the third one is occupied by the [[Leonardo (ISS module)|''Leonardo'' PMM]].

[[File:S122e008264.jpg|thumb|left|Columbus module in 2008]]

===Columbus===
'''''[[Columbus (ISS module)|Columbus]]''''', the primary research facility for European payloads aboard the ISS, provides a [[European Drawer Rack|generic laboratory]] as well as facilities specifically designed for [[Biolab|biology]], [[European Physiology Modules|biomedical research]] and [[Fluid Science Laboratory|fluid physics]]. Several mounting locations are affixed to the exterior of the module, which provide power and data to external experiments such as the [[European Technology Exposure Facility]] (EuTEF), [[Solar Monitoring Observatory]], [[Materials International Space Station Experiment]], and [[Atomic Clock Ensemble in Space]]. A number of expansions are planned for the module to study [[quantum physics]] and [[cosmology]].<ref>{{cite news|url=http://www.nasaspaceflight.com/2008/01/prcb-plan-sts-122-for-net-feb-7-three-launches-in-10-11-weeks/|title=PRCB plan STS-122 for NET Feb 7—three launches in 10–11 weeks|accessdate=12 January 2008|author=Chris Bergin|date=10 January 2008|publisher=[[NASASpaceflight.com]]}}</ref><ref>{{cite web|url=http://www.esa.int/esaHS/ESAAYI0VMOC_iss_0.html|title=Columbus laboratory|publisher=[[European Space Agency]] (ESA)|accessdate=6 March 2009|date=10 January 2009}}</ref> ESA's development of technologies on all the main areas of life support has been ongoing for more than 20 years and are/have been used in modules such as Columbus and the ATV. The German Aerospace Center [[German Aerospace Center|DLR]] manages ground control operations for Columbus and the ATV is controlled from the French [[CNES]] [[Toulouse Space Center]].

===Kibō===
[[File:きぼうエアロック Kibo airlock.jpg|thumb|Not large enough for crew using spacesuits, the airlock on Kibō has a sliding drawer for external experiments.]]
'''''[[Kibo (ISS module)|Kibō]]''''' ({{lang-ja|きぼう}}, "[[hope]]") is the largest single ISS module. This laboratory is used to carry out research in space medicine, biology, Earth observations, materials production, biotechnology, communications research, and has facilities for growing plants and fish. During August 2011, an observatory mounted on Kibō, which utilises the ISS's orbital motion to image the whole sky in the X-ray spectrum, detected for the first time the moment a star was swallowed by a black hole.<ref>{{cite web|author=[[JAXA]] |url=http://kibo.jaxa.jp/en/experiment/ef/maxi/ |title=Monitor of All-sky X-ray Image (MAXI):Experiment – Kibo Japanese Experimental Module – JAXA |publisher=Kibo.jaxa.jp |date=30 March 2007 |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://www.jaxa.jp/press/2011/08/20110825_maxi_e.html |title=JAXA | Scientific paper in Nature using the Monitor of All-sky X-ray Image (MAXI) on Kibo and the Swift satellite (USA) observations – First observation of a massive black hole swallowing a star |publisher=Jaxa.jp |accessdate=1 May 2012}}</ref> The laboratory contains a total of 23 racks, including 10 experiment racks and has a dedicated airlock for experiments. In a 'shirt sleeves' environment, crew attach an experiment to the sliding drawer within the airlock, close the inner, and then open the outer hatch. By extending the drawer and removing the experiment using the dedicated robotic arm, payloads are placed on the external platform. The process can be reversed and repeated quickly, allowing access to maintain external experiments without the delays caused by EVAs.

<gallery widths="115px" mode="nolines">
File:Kibo - Pressurized Module.jpg|Pressurized Module
File:Kibo - Experiment Logistics Module (Pressurized Section).jpg|Experiment Logistics Module
File:Kibo - Exposed Facility.jpg|Exposed Facility
File:Kibo - Experiment Logistics Module (Exposed Section).jpg|Experiment Logistics Module
File:Kibo - Remote Manipulator System.jpg|Remote Manipulator System
</gallery>

A smaller pressurised module is attached to the top of Kibō, serving as a cargo bay. The dedicated Interorbital communications system allows large amounts of data to be beamed from Kibō's ICS, first to the Japanese KODAMA satellite in geostationary orbit, then to Japanese ground stations. When a direct communication link is used, contact time between the ISS and a ground station is limited to approximately 10 minutes per visible pass. When KODAMA relays data between a LEO spacecraft and a ground station, real-time communications are possible in 60% of the flight path of the spacecraft. Ground staff use [[telepresence robotics]] to conduct on-orbit research without crew intervention.

===Cupola===
{{multiple image |align=right |image1=STS130 cupola view1.jpg |width1=190 |image2=ISS-27 Dmitri Kondratyev and Paolo Nespoli photograph the Earth through the Cupola.jpg |width2=190 |caption1=The [[Cupola (ISS module)|Cupola]]'s design has been compared to the ''[[Millennium Falcon]]'' from ''[[Star Wars (film)|Star Wars]]''. |caption2=[[Dmitri Kondratyev]] and [[Paolo A. Nespoli|Paolo Nespoli]] in the Cupola. Background left to right, [[Progress M-09M]], [[Soyuz TMA-20]], the [[Leonardo (ISS module)|Leonardo]] module and [[Kounotori 2|HTV-2]].}}
'''[[Cupola (ISS module)|Cupola]]''' is a seven window observatory, used to view Earth and docking spacecraft. Its name derives from the Italian word cupola, which means "dome". The Cupola project was started by NASA and Boeing, but cancelled due to budget cuts. A barter agreement between NASA and the ESA resulted in the Cupola's development being resumed in 1998 by the ESA. It was built by Thales Alenia Space in Torino, Italy. The module comes equipped with robotic workstations for operating the station's main robotic arm and shutters to protect its windows from damage caused by micrometeorites. It features 7 windows, with an {{convert|80|cm|in|adj=on}} round window, the largest window on the station (and the largest flown in space to date). The distinctive design has been compared to the 'turret' of the fictitious ''[[Millennium Falcon]]'' from the motion picture ''[[Star Wars (film)|Star Wars]]'';<ref>{{cite web|url=http://www.space.com/7932-astronauts-bask-spectacular-views-space-windows.html |title=Astronauts Bask in Spectacular Views From New Space Windows |publisher=Space.com |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://news.nationalgeographic.com/news/2010/02/photogalleries/100218-international-space-station-cupola-iss-obama-nasa-pictures/ |title=First Photos: Space Station's Observation Deck Unveiled |work=National Geographic |accessdate=1 May 2012}}</ref> the original prop [[lightsaber]] used by actor [[Mark Hamill]] as [[Luke Skywalker]] in the 1977 film was flown to the station in 2007.<ref>{{cite web|url=http://www.space.com/4283-nasa-shuttle-launch-luke-skywalker-lightsaber.html |title=NASA Shuttle to Launch Luke Skywalker's Lightsaber |publisher=Space.com |date=28 August 2007 |accessdate=1 May 2012}}</ref>

===Rassvet===
'''''[[Rassvet (ISS module)|Rassvet]]''''' ({{lang-ru|link=no|Рассве́т}}; lit. "dawn"), also known as the Mini-Research Module 1 (MRM-1) ({{lang-ru|link=no|Ма́лый иссле́довательский модуль}}, {{lang|ru|МИМ 1}}) and formerly known as the Docking Cargo Module (DCM), is similar in design to the [[Mir Docking Module]] launched on [[STS-74]] in 1995. ''Rassvet'' is primarily used for cargo storage and as a docking port for visiting spacecraft. It was flown to the ISS aboard NASA's {{OV|104}} on the [[STS-132]] mission and connected in May 2010,<ref>{{cite web|url=http://www.nasaspaceflight.com/2009/04/sts-132-prcb-baselines-mission-to-deliver-russias-mrm-1/|title=STS-132: PRCB baselines Atlantis' mission to deliver Russia's MRM-1|author=Chris Gebhardt|publisher=NASAspaceflight.com|date=9 April 2009|accessdate=12 November 2009}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts132/news/STS-132-09.html|author=NASA|date=18 May 2010|accessdate=7 July 2010|title=STS-132 MCC Status Report #09}}</ref> Rassvet is the only Russian owned module launched by NASA, to repay for the launch of Zarya, which is Russian designed and built, but partially paid for by NASA.<ref>[http://www.russianspaceweb.com/iss_mim1.html MIM1]. russianspaceweb.com</ref>  Rassvet was launched with the Russian Nauka Laboratory's Experiments airlock temporarily attached to it, and spare parts for the European Robotic Arm.

===Leonardo===
[[File:STS-133 Installation PMM 3.jpg|thumb|''Leonardo'' installed]]
'''''[[Leonardo (ISS module)|Leonardo]]'' Permanent Multipurpose Module''' (PMM) is a storage module attached to the ''[[Tranquility (ISS module)|Tranquility]]'' node.<ref name="leo-esa20110301">{{cite news |url=http://www.esa.int/Our_Activities/Human_Spaceflight/MagISStra/Leonardo_attached_to_Space_Station |title=Leonardo Attached to Space Station |work=ESA.int |date=1 March 2011 |accessdate=11 June 2013}}</ref><ref>{{cite web |url=http://blogs.nasa.gov/spacestation/2015/05/27/module-relocated-prepping-station-for-commercial-crew/ |title=Module Relocated Prepping Station for Commercial Crew |publisher=NASA |first=Mark |last=Garcia |date=27 May 2015 |accessdate=27 May 2015}}</ref> The three NASA Space Shuttle [[Multi-Purpose Logistics Module|MPLM]] cargo containers—Leonardo, Raffaello and Donatello—were built for NASA in [[Turin]], Italy by Alcatel Alenia Space, now [[Thales Alenia Space]].<ref>[http://www.thalesaleniaspace-issmodules.com/ Thales Alenia Space and ISS modules – Thales Alenia Space and ISS modules]. Thalesaleniaspace-issmodules.com. Retrieved 8 October 2011.</ref> The MPLMs were provided to NASA's ISS programme by Italy (independent of their role as a member state of ESA) and are considered to be US elements. In a bartered exchange for providing these containers, the US gave Italy research time aboard the ISS out of the US allotment in addition to that which Italy receives as a member of ESA.<ref>[http://www.spaceref.com/iss/elements/mplm.html Space Station User's Guide]. SpaceRef (3 April 2001). Retrieved 8 October 2011.</ref> The Permanent Multipurpose Module was created by converting Leonardo into a module that could be permanently attached to the station.<ref name="PLM1">{{cite news|url=http://www.nasaspaceflight.com/2009/08/sts-133-five-crew-one-eva-mission-leave-mpm-on-iss|title=STS-133 refined to a five crew, one EVA mission—will leave MPLM on ISS|publisher=NASASpaceflight.com|author=Chris Gebhardt|date=5 August 2009}}</ref><ref name="PLM2">{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8226309.stm|title=Europe looks to buy Soyuz craft|work=BBC News|last=Amos|first=Jonathan|date=29 August 2009}}</ref><ref>{{cite web|url=http://forum.nasaspaceflight.com/index.php?topic=17437.msg483604#msg483604|publisher=NASASpaceflight.com|accessdate=12 October 2009|title=Shuttle Q&A Part 5|date=27 September 2009}}</ref>

===Scheduled additional modules===

====Nauka====
'''''[[Nauka (ISS module)|Nauka]]''''' ({{lang-ru|link=no|Нау́ка}}; lit. "science"), also known as the Multipurpose Laboratory Module (MLM) or FGB-2 ({{lang-ru|link=no|Многофункциональный лабораторный модуль}}, {{lang|ru|МЛМ}}), is the major Russian laboratory module. It was scheduled to arrive at the station in 2014, docking to the port that was occupied by the Pirs module.<ref>{{cite web|url=http://www.aviationweek.com/Article.aspx?id=/article-xml/asd_05_23_2012_p05-01-460939.xml|title=Russia Sees Moon Base As Logical Next Step| last=Morring| first=Frank| date=23 May 2012| publisher=Aviation Week|accessdate=29 May 2012}}</ref> The date has been postponed to February 2017.<ref>{{cite web|url=http://www.russianspaceweb.com/iss_fgb2.html|title=MLM (FGB-2)|author=Anatoly Zak|publisher=Russian Space Web|date=29 April 2014|accessdate=14 May 2014}}</ref> Prior to the arrival of the Nauka module, a Progress spacecraft was used to remove Pirs from the station, deorbiting it to reenter over the Pacific Ocean. Nauka contains an additional set of life support systems and attitude control. Originally it would have routed power from the single Science-and-Power Platform, but that single module design changed over the first ten years of the ISS mission, and the two science modules, which attach to Nauka via the [[Uzlovoy Module]], or Russian node, each incorporate their own large solar arrays to power Russian science experiments in the ROS.

Nauka's mission has changed over time. During the mid-1990s, it was intended as a backup for the FGB, and later as a universal docking module (UDM); its docking ports will be able to support automatic docking of both spacecraft, additional modules and fuel transfer. Nauka has its own engines. Smaller Russian modules such as Pirs and Poisk were delivered by modified [[Progress (spacecraft)|Progress]] spacecraft, and the larger modules; Zvezda, Zarya, and Nauka, were launched by Proton rockets. Russia plans to separate Nauka, along with the rest of the Russian Orbital Segment, before the ISS is deorbited, to form the [[OPSEK]] space station.

====Uzlovoy Module====
The '''[[Uzlovoy Module]]''' (UM), or Node Module is a 4 metric ton<ref name=Zak>{{cite web|last1=Zak|first1=Anatoly|title=Node Module|url=http://www.russianspaceweb.com/iss_node.html|website=RussianSpaceWeb.com|accessdate=7 January 2015}}</ref> ball shaped module that will support the docking of two scientific and power modules during the final stage of the station assembly and provide the Russian segment additional docking ports to receive Soyuz TMA and Progress M spacecraft. UM is to be incorporated into the ISS in 2016. It will be integrated with a special version of the Progress cargo ship and launched by a standard Soyuz rocket. The Progress would use its own propulsion and flight control system to deliver and dock the Node Module to the nadir (Earth-facing) docking port of the Nauka MLM/FGB-2 module. One port is equipped with an active hybrid docking port, which enables docking with the MLM module. The remaining five ports are passive hybrids, enabling docking of Soyuz and Progress vehicles, as well as heavier modules and future spacecraft with modified docking systems. The node module was conceived to serve as the only permanent element of the future Russian successor to the ISS, [[Orbital Piloted Assembly and Experiment Complex|OPSEK]]. Equipped with six docking ports, the Node Module would serve as a single permanent core of the future station with all other modules coming and going as their life span and mission required.<ref>[http://www.energia.ru/en/news/news-2011/news_01-13.html S.P. Korolev RSC Energia – News]. Energia.ru (13 January 2011). Retrieved 8 October 2011.</ref><ref>[http://www.russianspaceweb.com/iss_node.html Node Module]. Russianspaceweb.com. Retrieved 8 October 2011.</ref> This would be a progression beyond the ISS and Russia's modular MIR space station, which are in turn more advanced than early monolithic first generation stations such as Skylab, and early Salyut and Almaz stations.

'''Science Power Modules 1 & 2''' (NEM-1, NEM-2) ({{lang-ru|link=no|Нау́чно-Энергетический Модуль-1 и -2}})

====Bigelow Expandable Activity Module====
On 16 January 2013, [[Bigelow Aerospace]] was contracted by NASA to provide a [[Bigelow Expandable Activity Module]] (BEAM), scheduled to arrive at the space station in 2015 for a two-year technology demonstration.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/station/news/beam_feature.html |title=NASA to Test Bigelow Expandable Module on Space Station |publisher=NASA |date=16 January 2013 |accessdate=17 January 2013}}</ref> BEAM is an inflatable module that will be attached to the aft hatch of the port-side Tranquility module of the International Space Station. During its two-year test run, instruments will measure its structural integrity and leak rate, along with temperature and radiation levels. The hatch leading into the module will remain mostly closed except for periodic visits by space station crew members for inspections and data collection. Following the test run, the module will be detached and jettisoned from the station.<ref>{{cite web | url=http://www.spaceflightnow.com/news/n1301/16bigelow/ | title=Bigelow inflatable module bound for space station | last=Harwood | first=William | date=16 January 2013 | publisher=Spaceflightnow | accessdate=17 January 2013}}</ref>

[[image:ISS Habitation module.jpg|thumb|left|The cancelled Habitation module under construction in 1997]]

===Cancelled components===
Several modules planned for the station have been cancelled over the course of the ISS programme, whether for budgetary reasons, because the modules became unnecessary, or following a redesign of the station after the 2003 [[Space Shuttle Columbia disaster|''Columbia'' disaster]]. The US [[Centrifuge Accommodations Module]] was intended to host science experiments in varying levels of [[artificial gravity]].<ref>{{cite web|url=http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=12560&mid=269666|title=Where is the Centrifuge Accommodation Module (CAM)?|publisher=NASASpaceflight.com|accessdate=12 October 2009}}</ref> The US [[Habitation Module]] would have served as the station's living quarters. Instead, the sleep stations are now spread throughout the station.<ref>{{cite web|url=http://www.space.com/missionlaunches/060214_iss_module.html|title=NASA Recycles Former ISS Module for Life Support Research|author=Tariq Malik|accessdate=11 March 2009|publisher=Space.com|date=14 February 2006}}</ref> The US [[Interim Control Module]] and [[ISS Propulsion Module]] were intended to replace functions of ''Zvezda'' in case of a launch failure.<ref>{{cite web|title=ICM Interim Control Module|publisher=U.S. Naval Center for Space Technology|url=http://code8200.nrl.navy.mil/icm.html|archiveurl=https://web.archive.org/web/20070208164211/http://code8200.nrl.navy.mil/icm.html|archivedate=8 February 2007}}</ref> The Russian [[Universal Docking Module]], to which the cancelled Russian Research modules and spacecraft would have docked.<ref name="Zak">{{cite web|url=http://www.russianspaceweb.com/iss_russia.html|accessdate=3 October 2009|publisher=russianspaceweb.com|author=Anatoly Zak|title=Russian segment of the ISS}}</ref> The Russian [[Science Power Platform]] would have provided the [[Russian Orbital Segment]] with a power supply independent of the ITS solar arrays,<ref name="Zak" /> and two [[Russian Research Module]]s that were planned to be used for scientific research.<ref>{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/components/russian_laboratory.html|title=Russian Research Modules|publisher=Boeing|accessdate=21 June 2009}}</ref>

==Unpressurised elements==
[[File:Truss breakdown.png|thumb|right|ISS Truss Components breakdown showing Trusses and all ORUs in situ]]
The ISS features a large number of external components that do not require pressurisation. The largest such component is the [[Integrated Truss Structure]] (ITS), to which the station's main solar arrays and thermal radiators are mounted.<ref name="Arrays" /> The ITS consists of ten separate segments forming a structure 108.5 m (356 ft) long.<ref name="OnOrbit" />

The station in its complete form has several smaller external components, such as the six robotic arms, the three [[External Stowage Platform]]s (ESPs) and four [[ExPRESS Logistics Carrier]]s (ELCs).<ref name="Manifest" /><ref>{{cite web|url=http://www.nasa.gov/centers/marshall/news/background/facts/expressrack.html|title=EXPRESS Racks 1 and 2 fact sheet|accessdate=4 October 2009|date=12 April 2008|publisher=NASA}}</ref> Whilst these platforms allow experiments (including [[MISSE]], the STP-H3 and the [[Robotic Refueling Mission]]) to be deployed and conducted in the vacuum of space by providing electricity and processing experimental data locally, the platforms' primary function is to store [[Orbital Replacement Unit]]s (ORUs). ORUs are spare parts that can be replaced when the item either passes its design life or fails. Examples of ORUs include pumps, storage tanks, antennas and battery units. Such units are replaced either by astronauts during EVA or by robotic arms. Spare parts were routinely transported to and from the station via Space Shuttle resupply missions, with a heavy emphasis on ORU transport once the NASA Shuttle approached retirement.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/12/soyuz-tma-03m-docks-iss-returns-station-six-crewmembers-future-ops/ |title=Soyuz TMA-03M docks to ISS, returns station to six crewmembers for future ops |publisher=NASASpaceFlight.com |date=23 December 2011 |accessdate=1 May 2012}}</ref> Several shuttle missions were dedicated to the delivery of ORUs, including [[STS-129]],<ref name="EVA129">{{cite web|url=http://www.nasa.gov/centers/johnson/pdf/404493main_EVA_129_F_E1.pdf|title=EVA Checklist: STS-129 Flight Supplement|author=L. D. Welsch|publisher=NASA|date=30 October 2009}}</ref> [[STS-133]]<ref name="STS-133">{{cite web|url=http://www.nasa.gov/pdf/491387main_STS-133%20Press%20Kit.pdf|title=Space Shuttle Mission: STS-131|date=February 2011|publisher=NASA}}</ref> and [[STS-134]].<ref name="STS-134">{{cite web|url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf|title=Space Shuttle Mission: STS-134|publisher=NASA|date=April 2011}}</ref> {{asof|2011|01}}, only one other mode of transportation of ORUs had been utilised – the Japanese cargo vessel [[H-II Transfer Vehicle|HTV-2]] – which delivered an FHRC and CTC-2 via its Exposed Pallet (EP).<ref name="HTV2">{{cite web|url=http://iss.jaxa.jp/en/htv/mission/htv-2/library/presskit/htv2_presskit_en.pdf|title=HTV2: Mission Press Kit|publisher=Japan Aerospace Exploration Agency|date=20 January 2011}}</ref>{{update after|2013|1|28}}

[[File:STS-116 spacewalk 1.jpg|left|thumb|Construction of the [[Integrated Truss Structure]] over New Zealand.]]
There are also smaller exposure facilities mounted directly to laboratory modules; the JEM [[Japanese Experiment Module#Exposed Facility|Exposed Facility]] serves as an external '[[porch]]' for the Japanese Experiment Module complex,<ref>{{cite web|url=http://kibo.jaxa.jp/en/about/kibo/jef/|title=Exposed Facility:About Kibo|publisher=JAXA|date=29 August 2008|accessdate=9 October 2009}}</ref> and a facility on the European ''Columbus'' laboratory provides power and data connections for experiments such as the [[European Technology Exposure Facility]]<ref name="NASA">{{cite web|url=http://www.nasa.gov/mission_pages/station/science/experiments/EuTEF.html|title=NASA—European Technology Exposure Facility (EuTEF)|publisher=NASA|date=6 October 2008|accessdate=28 February 2009}}</ref><ref name="ESA">{{cite web|url=http://www.esa.int/esaMI/Columbus/SEM7ZTEMKBF_0.html|title=ESA—Columbus—European Technology Exposure Facility (EuTEF)|publisher=ESA|date=13 January 2009|accessdate=28 February 2009}}</ref> and the [[Atomic Clock Ensemble in Space]].<ref>{{cite web|url=http://www.esa.int/SPECIALS/HSF_Research/SEMJSK0YDUF_0.html|publisher=ESA|accessdate=9 October 2009|title=Atomic Clock Ensemble in Space (ACES)}}</ref> A [[remote sensing]] instrument, [[Stratospheric Aerosol and Gas Experiment|SAGE III-ISS]], is due to be delivered to the station in 2014 aboard a [[Dragon (spacecraft)|Dragon capsule]], and the [[Neutron star Interior Composition ExploreR|NICER]] experiment in 2016.<ref>{{cite web |url=http://heasarc.gsfc.nasa.gov/docs/nicer/papers/NICER-SPIE-July2012-v4.pdf | publisher=Goddard Space Flight Center |title=The Neutron star Interior Composition ExploreR (NICER): an Explorer mission of opportunity for soft x-ray timing spectroscopy |accessdate=8 April 2013 |author=NICER Team }}</ref><ref>{{cite web|url=http://www.nasa.gov/topics/earth/features/sage3.html|date=1 March 2011|accessdate=12 March 2011|publisher=NASA|title=Time to Fly: SAGE III — ISS Prepped for Space Station|author=Michael Finneran}}</ref> The largest such scientific payload externally mounted to the ISS is the [[Alpha Magnetic Spectrometer]] (AMS), a particle physics experiment launched on [[STS-134]] in May 2011, and mounted externally on the ITS. The AMS measures [[cosmic ray]]s to look for evidence of [[dark matter]] and [[antimatter]].<ref>{{cite web|url=http://ams.cern.ch/|title=The Alpha Magnetic Spectrometer Experiment|publisher=[[CERN]]|date=21 January 2009|accessdate=6 March 2009}}</ref>

===Robotic arms and cargo cranes===
{{Double image|right|Iss017e011097.jpg|250|Dextrereallyhasnohead.jpg|250|Commander [[Sergey Alexandrovich Volkov|Volkov]] stands on Pirs with his back to the [[Soyuz spacecraft|Soyuz]] whilst operating the manual [[Strela (crane)|Strela crane]] holding photographer [[Oleg Kononenko|Kononenko]]. [[Zarya]] is seen to the left and [[Zvezda (ISS module)|Zvezda]] across the bottom of the image.|[[Dextre]], like many of the station's experiments and robotic arms, can be operated from Earth and perform tasks while the crew sleeps.||}}

The [[Integrated Truss Structure]] serves as a base for the station's primary remote manipulator system, called the [[Mobile Servicing System]] (MSS), which is composed of three main components. [[Canadarm2]], the largest robotic arm on the ISS, has a mass of {{convert|1800|kg|lb}} and is used to dock and manipulate spacecraft and modules on the USOS, hold crew members and equipment in place during EVAs and move Dextre around to perform tasks.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/station/structure/elements/mss.html |title=Canadarm2 and the Mobile Servicing System |publisher=NASA |date=8 January 2013 |accessdate=22 June 2015}}</ref> [[Dextre]] is a {{convert|1560|kg|lb|abbr=on}} robotic manipulator with two arms, a rotating torso and has power tools, lights and video for replacing [[orbital replacement unit]]s (ORUs) and performing other tasks requiring fine control.<ref>{{cite web |url=http://www.asc-csa.gc.ca/eng/iss/dextre/default.asp |title=Dextre, the International Space Station's Robotic Handyman |publisher=Canadian Space Agency |accessdate=22 June 2015}}</ref> The [[Mobile Base System]] (MBS) is 2 platforms which rides on rails along the length of the station's main truss. It serves as a mobile base for Canadarm2 and Dextre, allowing the robotic arms to reach all parts of the USOS.<ref>{{cite web |url=http://www.asc-csa.gc.ca/eng/iss/mobile-base/default.asp |title=Mobile Base System |publisher=Canadian Space Agency |accessdate=22 June 2015}}</ref> To gain access to the Russian Segment a [[Grapple Fixture|grapple fixture]] was added to Zarya on [[STS-134]], so that Canadarm2 can inchworm itself onto the ROS.<ref name="presskit134">{{cite web |url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf |title=Space Shuttle Mission STS-134: Final Flight of ''Endeavour'' - Press Kit |format=PDF |publisher=NASA |pages=51-53 |date=April 2011 |accessdate=22 June 2015}}</ref> Also installed during STS-134 was the {{convert|50|ft|m|abbr=on|order=flip}} [[Orbiter Boom Sensor System]] (OBSS), which had been used to inspect head shield tiles on Space Shuttle missions and can be used on station to increase the reach of the MSS.<ref name="presskit134"/> Staff on Earth or the station can operate the MSS components via remote control, performing work outside the station without space walks.

Japan's [[Kibo (ISS module)#Remote Manipulator System|Remote Manipulator System]], which services the JEM Exposed Facility,<ref>{{cite web |url=http://kibo.jaxa.jp/en/about/kibo/rms/ |title=Remote Manipulator System: About Kibo |publisher=JAXA |date=29 August 2008 |accessdate=4 October 2009}}</ref> was launched on [[STS-124]] and is attached to the JEM Pressurised Module.<ref>{{cite web |url=http://www.nasa.gov/centers/johnson/news/station/2002/iss02-03.txt |title=International Space Station Status Report #02-03 |publisher=NASA |date=14 January 2002 |accessdate=4 October 2009}}</ref> The arm is similar to the Space Shuttle arm as it is permanently attached at one end and has a latching end effector for standard grapple fixtures at the other.

The [[European Robotic Arm]], which will service the Russian Orbital Segment, will be launched alongside the [[Multipurpose Laboratory Module]] in 2017.<ref>{{cite web |url=http://www.russianspaceweb.com/iss_fgb2.html |title=MLM (FGB-2) module of the ISS |publisher=RussianSpaceWeb |accessdate=16 June 2014}}</ref> The ROS does not require spacecraft or modules to be manipulated, as all spacecraft and modules dock automatically and may be discarded the same way. Crew use the two ''[[Strela (crane)|Strela]]'' ({{lang-ru|link=no|Стрела́}}; lit. Arrow) cargo cranes during EVAs for moving crew and equipment around the ROS. Each Strela crane has a mass of {{convert|45|kg|lb|abbr=on}}.

===Comparison===
The ISS follows [[Salyut]] and [[Almaz]] series, [[Cosmos 557]], [[Skylab]], and [[Mir]] as the 11th space station launched, as the [[Genesis II|Genesis]] prototypes were never intended to be manned. Other examples of modular station projects include the Soviet/Russian Mir and the planned Russian OPSEK and [[Chinese space station]]. The first space station, [[Salyut 1]], and other one-piece or 'monolithic' first generation space stations, such as Salyut 2,3,4,5, DOS 2, Kosmos 557, Almaz and NASA's [[Skylab]] stations were not designed for re-supply.<ref>http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/history.pdf</ref> Generally, each crew had to depart the station to free the only docking port for the next crew to arrive, Skylab had more than one docking port but was not designed for resupply. Salyut 6 and 7 had more than one docking port and were designed to be resupplied routinely during crewed operation.<ref>{{cite web|url=http://www.pbs.org/spacestation/station/russian.htm |title=Space Station | Russian Space History |publisher=Pbs.org |accessdate=1 May 2012}}</ref>

==Station systems==

===Life support===
{{Main|ISS ECLSS|Chemical oxygen generator}}
The critical systems are the atmosphere control system, the water supply system, the food supply facilities, the sanitation and hygiene equipment, and fire detection and suppression equipment. The Russian Orbital Segment's life support systems are contained in the Service Module Zvezda. Some of these systems are supplemented by equipment in the USOS. The MLM Nauka laboratory has a complete set of life support systems.

====Atmospheric control systems====
[[Image:SpaceStationCycle.svg|thumb|The interactions between the components of the ISS Environmental Control and Life Support System (ECLSS)|alt=A flowchart diagram showing the components of the ISS life support system.]]
The atmosphere on board the ISS is similar to the [[Atmosphere of Earth|Earth's]].<ref>{{cite web|url=http://science.howstuffworks.com/space-station2.htm |title=How Space Stations Work|first=Craig|last=Freudenrich|publisher=Howstuffworks|date=20 November 2000|accessdate=23 November 2008}}</ref> Normal air pressure on the ISS is 101.3 [[kilopascal|kPa]] (14.7 [[Pounds per square inch|psi]]);<ref>{{cite web |url=http://nasaexplores.com/show2_5_8a.php?id=04-032&gl=58|archiveurl=https://web.archive.org/web/20061114010931/http://www.nasaexplores.com/show2_5_8a.php?id=04-032&gl=58|archivedate=14 November 2006|work=NASAexplores|title=5–8: The Air Up There|publisher=NASA|accessdate=31 October 2008}}</ref> the same as at sea level on Earth. An Earth-like atmosphere offers benefits for crew comfort, and is much safer than the alternative, a pure oxygen atmosphere, because of the increased risk of a fire such as that responsible for the deaths of the [[Apollo 1]] crew.<ref>{{cite book|author=Clinton Anderson|display-authors=etal|publisher=US Government Printing Office|title=Report of the Committee on Aeronautical and Space Sciences, United States Senate—Apollo 204 Accident|date=30 January 1968|location=Washington, DC|page=8|url=http://klabs.org/richcontent/Reports/Failure_Reports/as-204/senate_956/as204_senate_956.pdf}}</ref> Earth-like atmospheric conditions have been maintained on all Russian and Soviet spacecraft.<ref name=spacemed>{{Citation | last1=Davis | first1=Jeffrey R. | last2=Johnson | first2=Robert | last3=Stepanek | first3=Jan | lastauthoramp=yes | title=Fundamentals of Aerospace Medicine | publisher=Lippincott Williams & Wilkins | place=Philadelphia PA, USA | volume=XII | pages=261–264 | year=2008}}</ref>

The ''[[Elektron (ISS)|Elektron]]'' system aboard ''Zvezda'' and a similar system in ''Destiny'' generate oxygen aboard the station.<ref name="OGS">{{cite web|url=http://www.space.com/businesstechnology/060215_techwed_iss_oxygen.html|title=Air Apparent: New Oxygen Systems for the ISS|author=Tariq Malik|publisher=Space.com|date=15 February 2006|accessdate=21 November 2008}}</ref> The crew has a backup option in the form of bottled oxygen and [[Vika oxygen generator|Solid Fuel Oxygen Generation]] (SFOG) canisters, a [[chemical oxygen generator]] system.<ref name="breath easy">{{cite web|url=http://science.nasa.gov/headlines/y2000/ast13nov_1.htm|title=Breathing Easy on the Space Station|author=Patrick L. Barry|publisher=NASA|date=13 November 2000|accessdate=21 November 2008}}</ref> Carbon dioxide is removed from the air by the [[Vozdukh]] system in ''Zvezda''. Other by-products of human metabolism, such as methane from the intestines and ammonia from sweat, are removed by [[Activated carbon|activated charcoal]] filters.<ref name="breath easy" />

Part of the ROS atmosphere control system is the oxygen supply, triple-redundancy is provided by the Elektron unit, solid fuel generators, and stored oxygen. The Elektron unit is the primary oxygen supply, {{chem|O|2}} and {{chem|H|2}} are produced by [[electrolysis]], with the {{chem|H|2}} being vented overboard. The 1 kW system uses approximately 1 litre of water per crew member per day from stored water from Earth, or water recycled from other systems. MIR was the first spacecraft to use recycled water for oxygen production. The secondary oxygen supply is provided by burning {{chem|O|2}}-producing [[Vika oxygen generator|Vika]] cartridges (see also [[ISS ECLSS]]). Each 'candle' takes 5–20 minutes to decompose at 450–500 °C, producing 600 litres of {{chem|O|2}}. This unit is manually operated.<ref>[http://suzymchale.com/ruspace/issrslss.html RuSpace | ISS Russian Segment Life Support System]. Suzymchale.com. Retrieved 8 October 2011.</ref>

The US Orbital Segment has redundant supplies of oxygen, from a pressurised storage tank on the Quest airlock module delivered in 2001, supplemented ten years later by ESA built Advanced Closed-Loop System (ACLS) in the Tranquility module (Node 3), which produces {{chem|O|2}} by electrolysis.<ref>[http://science.nasa.gov/science-news/science-at-nasa/2000/ast13nov_1/ Breathing Easy on the Space Station – NASA Science]. ''Science''.nasa.gov (13 November 2000). Retrieved 8 October 2011.</ref> Hydrogen produced is combined with carbon dioxide from the cabin atmosphere and converted to water and methane.

===Power and thermal control===
{{Main|Electrical system of the International Space Station|External Active Thermal Control System}}

{{Double image|left|ROSSA.jpg|200|P4 deployed.jpg|200|Russian solar arrays, backlit by sunset.|One of the eight truss mounted pairs of USOS solar arrays}}
Double-sided solar, or [[Photovoltaic]] arrays, provide [[Electric power|electrical power]] for the ISS. These bifacial cells are more efficient and operate at a lower temperature than single-sided cells commonly used on Earth, by collecting sunlight on one side and light [[Albedo|reflected off]] the Earth on the other.<ref>{{cite web |url=http://wenku.baidu.com/view/a815121ffc4ffe473368ab7a.html |title=The early history of bifacial solar cell_百度文库 |publisher=Wenku.baidu.com |date=25 October 2010 |accessdate=14 August 2012}}</ref> 

The Russian segment of the station, like the Space Shuttle and most spacecraft, uses 28 [[volt]] [[direct current|DC]] from four rotating solar arrays mounted on ''Zarya'' and ''Zvezda''. The USOS uses 130–180 V DC from the USOS PV array, power is stabilised and distributed at 160 V DC and converted to the user-required 124 V DC. The [[High voltage|higher distribution voltage]] allows smaller, lighter conductors, at the expense of crew safety. The ROS uses [[Extra-low voltage|low voltage]]. The two station segments share power with converters.<ref name="Arrays" />

The USOS solar arrays are arranged as four wing pairs, with each wing producing nearly 32.8 kW.<ref name="Arrays">{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/truss_segment.html|title=Spread Your Wings, It's Time to Fly|publisher=NASA|date=26 July 2006|accessdate=21 September 2006}}</ref> These arrays normally track the sun to maximise power generation. Each array is about 375 m2 (450 yd2) in area and {{convert|58|m|yd|0}} long. In the complete configuration, the solar arrays track the sun by rotating the ''alpha [[gimbal]]'' once per orbit; the ''beta gimbal'' follows slower changes in the angle of the sun to the orbital plane. The [[Night Glider mode]] aligns the solar arrays parallel to the ground at night to reduce the significant aerodynamic drag at the station's relatively low orbital altitude.<ref>{{cite journal|author=G. Landis and C-Y. Lu|year=1991|title=Solar Array Orientation Options for a Space Station in Low Earth Orbit|journal=Journal of Propulsion and Power|volume=7|issue=1|pages=123–125|doi=10.2514/3.23302}}</ref>

The station uses rechargeable [[Nickel hydrogen battery|nickel-hydrogen batteries]] (NiH2) for continuous power during the 35 minutes of every 90-minute orbit that it is eclipsed by the Earth. The batteries are recharged on the day side of the Earth. They have a 6.5-year lifetime (over 37,000 charge/discharge cycles) and will be regularly replaced over the anticipated 20-year life of the station.<ref>{{cite web|url=http://www.grc.nasa.gov/WWW/RT/RT1999/5000/5420miller.html|title=Nickel-Hydrogen Battery Cell Life Test Program Update for the International Space Station|accessdate=27 November 2009|publisher=NASA|author=Thomas B. Miller|date=24 April 2000}}</ref>

The station's large solar panels generate a high potential voltage difference between the station and the ionosphere. This could cause arcing through insulating surfaces and sputtering of conductive surfaces as ions are accelerated by the spacecraft plasma sheath. To mitigate this, plasma contactor units (PCU)s create current paths between the station and the ambient plasma field.<ref>[http://www.grc.nasa.gov/WWW/RT/RT1998/5000/5430patterson.html Cathodes Delivered for Space Station Plasma Contactor System]. Grc.nasa.gov (18 June 1999). Retrieved 8 October 2011.</ref>

[[File:EATCS.png|thumb|ISS External Active Thermal Control System (EATCS) diagram]]
The large amount of electrical power consumed by the station's systems and experiments is turned almost entirely into heat. The heat which can be dissipated through the walls of the stations modules is insufficient to keep the internal ambient temperature within comfortable, workable limits. [[Ammonia]] is continuously pumped through pipework throughout the station to collect heat, then into external radiators exposed to the cold of space, and back into the station.

The International Space Station (ISS) External Active Thermal Control System (EATCS) maintains an equilibrium when the ISS environment or heat loads exceed the capabilities of the Passive Thermal Control System (PTCS). Note Elements of the PTCS are external surface materials, insulation such as MLI, or Heat Pipes. The EATCS provides heat rejection capabilities for all the US pressurised modules, including the JEM and COF as well as the main power distribution electronics of the S0, S1 and P1 Trusses. The EATCS consists an internal, non-toxic, water coolant loop used to cool and dehumidify the atmosphere, which transfers collected heat into an external liquid ammonia loop capable of withstanding the much lower temperature of space, which is then circulated through radiators to remove the heat. The EATCS is capable of rejecting up to 70 kW, and provides a substantial upgrade in heat rejection capacity from the 14 kW capability of the Early External Active Thermal Control System (EEATCS) via the Early Ammonia Servicer (EAS), which was launched on [[STS-105]] and installed onto the P6 Truss.<ref>[http://www.nasa.gov/pdf/473486main_iss_atcs_overview.pdf ATCS Team Overview]. (PDF). Retrieved 8 October 2011.</ref>

===Communications and computers===
{{Main|Tracking and Data Relay Satellite|Luch (satellite)}}
{{See also2|[[ThinkPad#Use in space|ThinkPad use in space]]}}
[[File:ISS Communication Systems.png|thumb|The communications systems used by the ISS * Luch satellite not currently in use|alt=Diagram showing communications links between the ISS and other elements.]]
Radio communications provide [[telemetry]] and scientific data links between the station and [[Mission Control Center|Mission Control Centres]]. Radio links are also used during [[Space rendezvous|rendezvous and docking procedures]] and for audio and video communication between crewmembers, flight controllers and family members. As a result, the ISS is equipped with internal and external communication systems used for different purposes.<ref name="BoeingComm" />


The Russian Orbital Segment communicates directly with the ground via the ''[[Lira (ISS)|Lira]]'' [[Antenna (radio)|antenna]] mounted to ''Zvezda''.<ref name="ISSRG" /><ref>{{cite web|url=http://www.nasa.gov/home/hqnews/2005/mar/HQ_ss05015_ISS_status_report.html|title=International Space Station Status Report: SS05-015|last=Mathews|first=Melissa|author2=James Hartsfield|date=25 March 2005|work=NASA News|publisher=NASA|accessdate=11 January 2010}}</ref> The ''Lira'' antenna also has the capability to use the ''[[Luch (satellite)|Luch]]'' data relay satellite system.<ref name="ISSRG" /> This system, used for communications with ''Mir'', fell into disrepair during the 1990s, and as a result is no longer in use,<ref name="ISSRG" /><ref name="SSSM">{{cite book|first=David|last=Harland|title=The Story of Space Station Mir|publisher=Springer-Verlag New York Inc|date=30 November 2004|location=New York|isbn=978-0-387-23011-5}}</ref><ref name="Harvey">{{cite book|last=Harvey|first=Brian|title=The rebirth of the Russian space program: 50 years after Sputnik, new frontiers|publisher=Springer Praxis Books|year=2007|page=263|isbn=0-387-71354-9}}</ref> although two new ''Luch'' satellites—''Luch''-5A and ''Luch''-5B—were launched in 2011 and 2012 respectively to restore the operational capability of the system.<ref>{{cite web|publisher=RussianSpaceWeb|url=http://www.russianspaceweb.com/2011.html|accessdate=12 January 2010|title=Space exploration in 2011|date=4 January 2010|author=Anatoly Zak}}</ref> Another Russian communications system is the [[Voskhod-M]], which enables internal telephone communications between ''Zvezda'', ''Zarya'', ''Pirs'', ''Poisk'' and the USOS, and also provides a VHF radio link to ground control centres via antennas on ''Zvezda''{{'s}} exterior.<ref>{{cite web|url=http://www.nasa.gov/directorates/somd/reports/iss_reports/2010/05022010.html|date=2 May 2010|accessdate=7 July 2010|publisher=NASA|title=ISS On-Orbit Status 05/02/10}}</ref>

The [[US Orbital Segment]] (USOS) makes use of two separate radio links mounted in the [[Z1 truss]] structure: the [[S band]] (used for audio) and [[Ku band|Ku band]] (used for audio, video and data) systems. These transmissions are routed via the United States [[Tracking and Data Relay Satellite]] System (TDRSS) in [[geostationary orbit]], which allows for almost continuous real-time communications with [[Christopher C. Kraft Jr. Mission Control Center|NASA's Mission Control Center]] (MCC-H) in [[Houston]].<ref name="ISSBook" /><ref name="ISSRG" /><ref name="BoeingComm">{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/systems/communications_tracking.html|publisher=Boeing|accessdate=30 November 2009|title=Communications and Tracking|archiveurl = https://web.archive.org/web/20080611115319/http://www.boeing.com/defense-space/space/spacestation/systems/communications_tracking.html |archivedate = 11 June 2008}}</ref> Data channels for the Canadarm2, European ''Columbus'' laboratory and Japanese ''Kibō'' modules are routed via the S band and Ku band systems, although the [[European Data Relay System]] and a similar Japanese system will eventually complement the TDRSS in this role.<ref name="ISSBook" /><ref name="JAXA-MOU">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/nasa_japan.html|title=Memorandum of Understanding Between the National Aeronautics and Space Administration of the United States of America and the Government of Japan Concerning Cooperation on the Civil International Space Station|publisher=NASA|accessdate=19 April 2009|date=24 February 1998}}</ref> Communications between modules are carried on an internal digital [[wireless network]].<ref>{{cite web|title=Operations Local Area Network (OPS LAN) Interface Control Document|format=PDF|publisher=NASA|url=http://www.spaceref.com/iss/computer/iss.ops.lan.icd.pdf|accessdate=30 November 2009|date=February 2000}}</ref>

[[File:STS-128 ISS-20 Destiny Canadarm2.jpg|thumb|left|Laptop computers surround the Canadarm2 console.]]
[[Ultra high frequency|UHF radio]] is used by astronauts and cosmonauts conducting [[Extra-vehicular activity|EVAs]]. UHF is employed by other spacecraft that dock to or undock from the station, such as Soyuz, Progress, HTV, ATV and the Space Shuttle (except the shuttle also makes use of the S band and Ku band systems via TDRSS), to receive commands from Mission Control and ISS crewmembers.<ref name="ISSRG" /> Automated spacecraft are fitted with their own communications equipment; the ATV uses a [[laser]] attached to the spacecraft and equipment attached to ''Zvezda'', known as the Proximity Communications Equipment, to accurately dock to the station.<ref>{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=16247|title=ISS/ATV communication system flight on Soyuz|accessdate=30 November 2009|publisher=[[EADS Astrium]]|date=28 February 2005}}</ref><ref>{{cite web|publisher=NASASpaceflight.com|author=Chris Bergin|url=http://www.nasaspaceflight.com/2009/11/sts-129-support-dragon-communication-demo-iss/|date=10 November 2009|accessdate=30 November 2009|title=STS-129 ready to support Dragon communication demo with ISS}}</ref>

The ISS is equipped with approximately 100 [[IBM]] and [[Lenovo]] [[ThinkPad#Use in space|ThinkPad]] model A31 and T61P laptop computers. Each computer is a [[commercial off-the-shelf]] purchase which is then modified for safety and operation including updates to connectors, cooling and power to accommodate the station's 28V DC power system and weightless environment. Heat generated by the laptops does not rise, but stagnates surrounding the laptop, so additional forced ventilation is required. Laptops aboard the ISS are connected to the station's [[wireless LAN]] via [[Wi-Fi]] and to the ground via Ku band. This provides speeds of 10 [[Megabit per second|Mbit/s]] to and 3 Mbit/s from the station, comparable to home [[digital subscriber line|DSL]] connection speeds.<ref name="issit">{{cite news |url=http://bits.blogs.nytimes.com/2010/01/22/first-tweet-from-space/ |title=First Tweet From Space |work=[[The New York Times]] |first=Nick |last=Bilton |date=22 January 2010 |accessdate=29 April 2014}}</ref><ref name="tested20121019">{{cite news |url=http://www.tested.com/science/space/449539-how-fast-isss-internet-and-other-space-questions-answered/ |title=How Fast is the ISS's Internet? (and Other Space Questions Answered) |work=Tested.com |first=Will |last=Smith |date=19 October 2012 |accessdate=29 April 2014}}</ref>

The operating system used for key station functions is the [[Debian]] [[GNU/Linux distribution]].<ref>{{cite news|last=Thomson|first=Iain|title=Penguins in spa-a-a-ce! ISS dumps Windows for Linux on laptops|url=http://www.theregister.co.uk/2013/05/10/iss_linux_debian_deployment/|accessdate=15 May 2013|newspaper=The Register|date=10 May 2013}}</ref> The migration from [[Microsoft Windows]] was made in May 2013 for reasons of reliability, stability and flexibility.<ref>{{cite news|last=Gunter|first=Joel|title=International Space Station to boldly go with Linux over Windows|url=http://www.telegraph.co.uk/technology/news/10049444/International-Space-Station-to-boldly-go-with-Linux-over-Windows.html|accessdate=15 May 2013|newspaper=The Daily Telegraph|date=10 May 2013}}</ref>

==Station operations==

===Expeditions and private flights===
[[File:Sts088-703-019e.jpg|thumb|Zarya and Unity were entered for the first time on 10 December 1998.]]
[[File:Soyuz tm-31 transported to launch pad.jpg|right|thumb|Soyuz TM-31 being prepared to bring the first resident crew to the station in October 2000]]
[[File:STS-115 ISS after undocking.jpg|thumb|right|ISS was slowly assembled over a decade of spaceflights and crews]]
[[File:Tracy Caldwell Dyson in Cupola ISS.jpg|thumb|Expeditions have included male and female crew-members from many nations]]
''See also the [[list of International Space Station expeditions]] (professional crew), [[space tourism]] (private travellers), and the [[list of human spaceflights to the ISS]] (both).''

Each permanent crew is given an expedition number. Expeditions run up to six months, from launch until undocking, an 'increment' covers the same time period, but includes cargo ships and all activities. Expeditions 1 to 6 consisted of 3 person crews, Expeditions 7 to 12 were reduced to the safe minimum of two following the destruction of the NASA Shuttle Columbia. From Expedition 13 the crew gradually increased to 6 around 2010.<ref name="ISSEx">{{cite web|title=International Space Station Expeditions|publisher=NASA|url=http://www.nasa.gov/mission_pages/station/expeditions/index.html|date=10 April 2009|accessdate=13 April 2009}}</ref><ref name="current">{{cite web|url=http://www.nasa.gov/mission_pages/station/main/index.html|title=International Space Station|accessdate=22 October 2008|publisher=NASA|year=2008|author=NASA}}</ref> With the arrival of the American [[Commercial Crew Development|Commercial Crew]] vehicles in the middle of the 2010s, expedition size may be increased to seven crew members, the number ISS is designed for.<ref>{{cite web|url=http://www.aviationweek.com/article.aspx?id=/article-xml/asd_07_26_2012_p01-02-480253.xml|title=ISS Research Hampered By Crew Availability|last=Morring|first=Frank|date=27 July 2012|quote=A commercial capability would allow the station's crew to grow from six to seven by providing a four-seat vehicle for emergency departures in addition to the three-seat Russian Soyuz capsules in use today.|publisher=Aviation Week|accessdate=30 July 2012}}</ref><ref>{{cite web|url=http://www.airspacemag.com/space-exploration/AS-Interview-Mike-Suffredini.html|title=Assembly (Nearly) Complete |last=Hoversten|first=Paul|date=1 May 2011|publisher=Air & Space Magazine|quote=In fact, we're designed on the U.S. side to take four crew. The ISS design is actually for seven. We operate with six because first, we can get all our work done with six, and second, we don't have a vehicle that allows us to fly a seventh crew member. Our requirement for the new vehicles being designed is for four seats. So I don't expect us to go down in crew size. I would expect us to increase it.|accessdate=8 May 2011}}</ref>

[[Sergei Krikalev]], member of [[Expedition 1]] and Commander of [[Expedition 11]] has spent more time in space than anyone else, a total of 803 days and 9 hours and 39 minutes. His awards include the [[Order of Lenin]], [[Hero of the Soviet Union]], [[Hero of the Russian Federation]], and 4 NASA medals. On 16 August 2005 at 1:44 am EDT he passed the record of 748 days held by [[Sergei Avdeyev]], who had 'time travelled' 1/50th of a second into the future on board MIR.<ref>{{cite web|url=http://www.popsci.com/scitech/article/2002-02/lets-do-time-warp-again?page=2 |archiveurl=https://web.archive.org/web/20100628190931/http://www.popsci.com/scitech/article/2002-02/lets-do-time-warp-again?page=2 |archivedate=28 June 2010 |title=Let's Do the Time Warp Again |publisher=Web.archive.org |date=28 June 2010 |accessdate=1 May 2012}}</ref> He participated in psychosocial experiment SFINCSS-99 (Simulation of Flight of International Crew on Space Station), which examined inter-cultural and other stress factors affecting integration of crew in preparation for the ISS spaceflights. Commander [[Michael Fincke]] has spent a total of 382 days in space – more than any other American astronaut.

Travellers who pay for their own passage into space are termed spaceflight participants by Roscosmos and NASA, and are sometimes informally referred to as space tourists, a term they generally dislike.{{refn|Privately funded travellers who have objected to the term include Dennis Tito, the first such traveller (''Associated Press'', 8 May 2001), [[Mark Shuttleworth]], founder of [[Ubuntu (operating system)|Ubuntu]] (''Associated Press, The Spokesman Review, 6 January 2002, p. A4''), Gregory Olsen and Richard Garriott.<ref>{{cite news|last=Schwartz|first=John|title=Russia Leads Way in Space Tourism With Paid Trips into Orbit|url=http://www.nytimes.com/2008/10/11/science/space/11space.html|newspaper=The New York Times|date=10 October 2008}}</ref><ref>{{cite web|last=Boyle|first=Alan|title=Space passenger Olsen to pull his own weight|url=http://msnbc.msn.com/id/9323509/#.Tz5lcFE-qr4|publisher=MSNBC}}</ref> Canadian astronaut Bob Thirsk said the term does not seem appropriate, referring to his crewmate, [[Guy Laliberté]], founder of [[Cirque du Soleil]].<ref>{{cite web|url=http://www.stcatharinesstandard.ca/ArticleDisplay.aspx?e=1975186&archive=true |title=Flight to space ignited dreams | St. Catharines Standard |publisher=Stcatharinesstandard.ca |accessdate=1 May 2012}}</ref> Anousheh Ansari denied being a tourist<ref>{{cite web|url=http://www.esa.int/esaHS/SEMD58BE8YE_business_0.html |title=ESA – Human Spaceflight and Exploration – Business – "I am NOT a tourist" |publisher=Esa.int |date=18 September 2006 |accessdate=1 May 2012}}</ref> and took offence at the term.<ref>{{cite web|url=http://www.space.com/2889-interview-anousheh-ansari-female-space-tourist.html |title=Interview with Anousheh Ansari, the First Female Space Tourist |publisher=Space.com |date=15 September 2006 |accessdate=1 May 2012}}</ref>|group=note|name}} All seven were transported to the ISS on Russian Soyuz spacecraft. When professional crews change over in numbers not divisible by the three seats in a Soyuz, and a short-stay crewmember is not sent, the spare seat is sold by MirCorp through Space Adventures. When the space shuttle retired in 2011, and the station's crew size was reduced to 6, space tourism was halted, as the partners relied on Russian transport seats for access to the station. Soyuz flight schedules increase after 2013, allowing 5 Soyuz flights (15 seats) with only two expeditions (12 seats) required.<ref>{{cite web|url=http://www.spaceflightnow.com/news/n1101/12soyuz/ |title=Breaking News | Resumption of Soyuz tourist flights announced |publisher=Spaceflight Now |accessdate=1 May 2012}}</ref> The remaining seats are sold for around {{US$|40 million}} to members of the public who can pass a medical. ESA and NASA criticised private spaceflight at the beginning of the ISS, and NASA initially resisted training [[Dennis Tito]], the first man to pay for his own passage to the ISS.{{refn|ESA director Jörg Feustel-Büechl said in 2001 that Russia had no right to send 'amateurs' to the ISS. A 'stand-off' occurred at the Johnson Space Centre between Commander Talgat Musabayev and NASA manager Robert Cabana. Cabana refused to train Dennis Tito, a member of Musabayev's crew along with Yuri Baturin. The commander argued that Tito had trained 700 hours in the last year and was as qualified as any NASA astronaut, and refused to allow his crew to be trained on the American portions of the station without Tito. Cabana stated training could not begin, and the commander returned with his crew to their hotel.|group=note|name}}  [[Toyohiro Akiyama]] was flown to Mir for a week, he was classed as a business traveller, as his employer, [[Tokyo Broadcasting System]], paid for his ticket, and he gave a daily TV broadcast from orbit.

[[Anousheh Ansari]] ({{lang-fa|انوشه انصاری}}) became the first Iranian in space and the first self-funded woman to fly to the station. Officials reported that her education and experience make her much more than a tourist, and her performance in training had been "excellent."<ref>{{cite web|last=Maher |first=Heather |url=http://www.rferl.org/content/article/1071358.html |title=U.S.: Iranian-American To Be First Female Civilian in Space |publisher=Radio Free Europe/Radio Liberty |date=15 September 2006 |accessdate=1 May 2012}}</ref> Ansari herself dismisses the idea that she is a tourist. She did Russian and European studies involving medicine and microbiology during her 10-day stay. The documentary ''[[Space Tourists]]'' follows her journey to the station, where she fulfilled "an age-old dream of man: to leave our planet as a «normal person» and travel into outer space."<ref>{{cite web|url=http://www.space-tourists-film.com/en/film_synopsis.php |title=Space Tourists | A Film By Christian Frei |publisher=Space-tourists-film.com |accessdate=1 May 2012}}</ref> In the film, some Kazakhs are shown waiting in the middle of the steppes for four rocket stages to literally fall from the sky. Film-maker Christian Frei states "Filming the work of the Kazakh scrap metal collectors was anything but easy. The Russian authorities finally gave us a film permit in principle, but they imposed crippling preconditions on our activities. The real daily routine of the scrap metal collectors could definitely not be shown. Secret service agents and military personnel dressed in overalls and helmets were willing to ''re-enact'' their work for the cameras – in an idealised way that officials in Moscow deemed to be presentable, but not at all how it takes place in reality."

Spaceflight participant [[Richard Garriott]] placed a [[Geocaching|geocache]] aboard the ISS during his flight.<ref>{{cite web|url=http://www.geocaching.com/seek/cache_details.aspx?wp=GC1BE91|title=International Space Station Traditional Geocache}}</ref> This is currently the only non-terrestrial geocache in existence.<ref>{{cite web |url=http://www.geekwire.com/2011/outer-space-ocean-floor-15m-geocaches-counting/|accessdate=27 February 2013|last=Cook|first=John|title=From outer space to the ocean floor, Geocaching.com now boasts more than 1.5 million hidden treasures|date=29 August 2011}}</ref>

===Orbit===
{{Double image|right|Internationale Raumstation Bahnhöhe (dumb version).png|300|Iss.ogg|235|Graph showing the changing altitude of the ISS from November 1998 until January 2009|Animation of ISS orbit from a North American geostationary point of view (sped up 1800 times)}}
The ISS is maintained in a nearly circular orbit with a minimum mean altitude of 330 km (205 mi) and a maximum of 410 km (255 mi), in the centre of the [[thermosphere]], at an [[inclination]] of 51.6 degrees to Earth's equator, necessary to ensure that Russian [[Soyuz (spacecraft)|Soyuz]] and [[Progress (spacecraft)|Progress]] spacecraft launched from the [[Baikonur Cosmodrome]] may be safely launched to reach the station. Spent rocket stages must be dropped into uninhabited areas and this limits the directions rockets can be launched from the spaceport.<ref name="MCC Answer">{{cite web|last=Cooney|first=Jim|title=Mission Control Answers Your Questions|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-112/09_04_12_54_17.html|location=Houston, TX|quote=Jim Cooney ISS Trajectory Operations Officer}}</ref><ref>{{cite book|last=Pelt|first=Michel van|title=Into the Solar System on a String : Space Tethers and Space Elevators|year=2009|publisher=Springer New York|location=New York, NY|isbn=0-387-76555-7|page=133|edition=1.}}</ref> The orbital inclination chosen was also low enough to allow American space shuttles launched from Florida to reach the ISS.

It travels at an average speed of 27,724 kilometres (17,227 mi) per hour, and completes {{Orbit|daily orbits|15.54}} orbits per day (93 minutes per orbit).{{Orbit|ref|<ref name="heavens-above"/>}}<ref name="tracking">{{cite web|url=http://spaceflight.nasa.gov/realdata/tracking/index.html|title=Current ISS Tracking data|accessdate=28 January 2009|publisher=NASA|date=15 December 2008|author=NASA}}</ref> The station's altitude was allowed to fall around the time of each NASA shuttle mission. Orbital boost burns would generally be delayed until after the shuttle's departure. This allowed shuttle payloads to be lifted with the station's engines during the routine firings, rather than have the shuttle lift itself and the payload together to a higher orbit. This trade-off allowed heavier loads to be transferred to the station. After the retirement of the NASA shuttle, the nominal orbit of the space station was raised in altitude.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/06/europes-atv-2-depart-iss-make-way-russias-progress-m-11m/ |title=Europe's ATV-2 departs ISS to make way for Russia's Progress M-11M |publisher=NASASpaceFlight.com |date=20 June 2011 |accessdate=1 May 2012}}</ref><ref name="Popular Mechanics">{{cite web|url=http://www.popularmechanics.com/science/air_space/4275571.html|title=The Uncertain Future of the International Space Station: Analysis|author=Rand Simberg|date=29 July 2008|accessdate=6 March 2009|publisher=[[Popular Mechanics]]}}</ref> Other, more frequent supply ships do not require this adjustment as they are substantially lighter vehicles.<ref name="Worldbook at NASA">{{cite web|url=http://www.nasa.gov/worldbook/intspacestation_worldbook.html|title = International Space Station|year=2005|accessdate=14 June 2008|publisher=World Book, Inc|author=James Oberg|work=World Book Online Reference Center}}{{dead link|date=May 2012}}</ref><ref name="nasa.gov-iss-environment">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archiveurl=https://web.archive.org/web/20080213164432/http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archivedate=13 February 2008|title=ISS Environment|accessdate=15 October 2007|publisher=[[Johnson Space Center]]}}</ref>
[[File:ISS orbits 04132013.jpg|thumbnail|Orbits of the ISS, shown in April 2013]]
Orbital boosting can be performed by the station's two main engines on the ''[[Zvezda (ISS module)|Zvezda]]'' service module, or Russian or European spacecraft docked to Zvezda's aft port. The ATV has been designed with the possibility of adding a [[Automated Transfer Vehicle#ATV evolution proposals|second docking port]] to its other end, allowing it to remain at the ISS and still allow other craft to dock and boost the station. It takes approximately two orbits (three hours) for the boost to a higher altitude to be completed.<ref name="nasa.gov-iss-environment" /> In December 2008 NASA signed an agreement with the [[Ad Astra Rocket Company]] which may result in the testing on the ISS of a [[VASIMR]] plasma propulsion engine.<ref name="vasimr">{{cite web|url=http://www.adastrarocket.com/AdAstra-NASA_PR12Dec08.pdf|publisher=AdAstra Rocket Company|title=Press Release 121208|accessdate=7 December 2009|date=12 December 2008|format=PDF}}</ref> This technology could allow [[Orbital station-keeping|station-keeping]] to be done more economically than at present.<ref name="future-prop">{{cite web|url=http://www.nasa.gov/vision/space/travelinginspace/future_propulsion.html|title=Propulsion Systems of the Future|accessdate=29 May 2009|publisher=NASA}}</ref><ref>{{cite web|work=New Scientist|accessdate=7 October 2009|url=http://www.newscientist.com/article/dn17918-rocket-company-tests-worlds-most-powerful-ion-engine.html|title=Rocket company tests world's most powerful ion engine|author=David Shiga|date=5 October 2009}}</ref>

The Russian Orbital Segment contains the station's engines and control [[Bridge (nautical)|bridge]], which handles Guidance, Navigation and Control (ROS GNC) for the entire station.<ref name="Navigation">{{cite web|url=http://www.esa.int/export/esaHS/ESAOXX0VMOC_iss_0.html|title=DMS-R: ESA's Data Management System for the Russian Segment of the ISS}}</ref> Initially, Zarya, the first module of the station, controlled the station until a short time after the Russian service module Zvezda docked and was transferred control. Zvezda contains the ESA built DMS-R Data Management System.<ref name="EsaComputer">{{cite web|url=http://www.esa.int/esapub/onstation/onstation17/os17_chapter6.pdf|title=Exercising Control 49 months of DMS-R Operations}}</ref> Using two fault-tolerant computers (FTC), Zvezda computes the station's position and orbital trajectory using redundant Earth horizon sensors, Solar horizon sensors as well as Sun and star trackers. The FTCs each contain three identical processing units working in parallel and provide advanced fault-masking by majority voting. Zvezda uses gyroscopes and thrusters to turn itself around. Gyroscopes do not require propellant, rather they use electricity to 'store' momentum in flywheels by turning in the opposite direction to the station's movement. The USOS has its own computer controlled gyroscopes to handle the extra mass of that section. When gyroscopes 'saturate', reaching their maximum speed, thrusters are used to cancel out the stored momentum. During [[Expedition 10]], an incorrect command was sent to the station's computer, using about 14 kilograms of propellant before the fault was noticed and fixed. When attitude control computers in the ROS and USOS fail to communicate properly, it can result in a rare 'force fight' where the ROS GNC computer must ignore the USOS counterpart, which has no thrusters.<ref>{{cite web|url=http://pims.grc.nasa.gov/pimsdocs/public/ISS%20Handbook/hb_qs_vehicle_RussianUSGNCForceFight.pdf |title=Microsoft Word – hb_qs_vehicle_RussianUSGNCForceFight_pg1.doc |format=PDF |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://spaceflight.nasa.gov/spacenews/reports/issreports/2005/iss05-7.html|title = International Space Station Status Report #05-7|date=11 February 2005|publisher=NASA|accessdate=23 November 2008}}</ref><ref>{{cite book|title=Dynamics and Control of Attitude, Power, and Momentum for a Spacecraft Using Flywheels and Control Moment Gyroscopes|author=Carlos Roithmayr|format=PDF|year=2003|publisher=NASA|location=Langley Research Center|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030038806_2003038772.pdf|accessdate=12 July 2011}}</ref> When an ATV, NASA Shuttle, or Soyuz is docked to the station, it can also be used to maintain station attitude such as for troubleshooting. Shuttle control was used exclusively during [[STS-117|installation]] of the S3/S4 truss, which provides electrical power and data interfaces for the station's electronics.<ref>{{cite web|url=http://www.nasaspaceflight.com/2007/06/atlantis-ready-to-support-iss-troubleshooting/|title=Atlantis ready to support ISS troubleshooting|publisher=NASASPaceflight.com|author=Chris Bergin|accessdate=6 March 2009|date=14 June 2007}}</ref>

==Mission controls==
The components of the ISS are operated and monitored by their respective space agencies at [[Mission Control Center|mission control centres]] across the globe, including:
* Roscosmos's [[Mission Control Center#RKA Mission Control Center|Mission Control Center]] at [[Korolyov (city)|Korolyov]], Moscow Oblast, controls the [[Russian Orbital Segment]] which handles Guidance, Navigation & Control for the entire Station.,<ref name="Navigation" /><ref name="EsaComputer" /> in addition to individual Soyuz and Progress missions.<ref name="ISSRG" />
* ESA's [[ATV Control Centre]], at the [[Toulouse Space Centre]] (CST) in [[Toulouse]], France, controls flights of the unmanned European [[Automated Transfer Vehicle]].<ref name="ISSRG" />
* JAXA's [[JEM Control Center]] and [[HTV Control Center]] at [[Tsukuba Space Center]] (TKSC) in [[Tsukuba]], Japan, are responsible for operating the Japanese Experiment Module complex and all flights of the 'White Stork' HTV Cargo spacecraft, respectively.<ref name="ISSRG" />
* NASA's [[Christopher C. Kraft Jr. Mission Control Center|Mission Control Center]] at [[Lyndon B. Johnson Space Center]] in Houston, Texas, serves as the primary control facility for the United States segment of the ISS and also controlled the Space Shuttle missions that visited the station.<ref name="ISSRG">{{cite book|author=Gary Kitmacher|title=Reference Guide to the International Space Station| publisher =[[Apogee Books]]|location=Canada|year=2006|isbn=978-1-894959-34-6|issn=1496-6921|pages=71–80}}</ref>
* NASA's [[Payload Operations and Integration Center]] at [[Marshall Space Flight Center]] in [[Huntsville, Alabama]], coordinates payload operations in the USOS.<ref name="ISSRG" />
* ESA's [[Columbus Control Center|Columbus Control Centre]] at the [[German Aerospace Center|German Aerospace Centre]] (DLR) in [[Oberpfaffenhofen]], Germany, manages the European ''Columbus'' research laboratory.<ref name="ISSRG" />
* CSA's [[MSS Control]] at [[Saint-Hubert, Quebec]], Canada, controls and monitors the [[Mobile Servicing System]], or Canadarm2.<ref name="ISSRG" />
{{wide image|ISS Centers.svg|880px|Space centres involved with the ISS programme|alt=A world map highlighting the locations of space centres. See adjacent text for details.}}

===Repairs===
{{Main|Orbital Replacement Units|International Space Station maintenance}}
'''[[Orbital Replacement Units]]''' ('''ORUs''') are spare parts that can be readily replaced when a unit either passes its design life or fails. Examples of ORUs are pumps, storage tanks, controller boxes, antennas, and battery units. Some units can be replaced using robotic arms. Many are stored outside the station, either on small pallets called [[ExPRESS Logistics Carrier]]s (ELCs) or share larger platforms called [[External Stowage Platform]]s which also hold science experiments. Both kinds of pallets have electricity as many parts which could be damaged by the cold of space require heating. The larger logistics carriers also have computer local area network connections (LAN) and telemetry to connect experiments. A heavy emphasis on stocking the USOS with ORU's occurred around 2011, before the end of the NASA shuttle programme, as its commercial replacements, [[Cygnus (spacecraft)|Cygnus]] and [[Dragon (spacecraft)|Dragon]], carry one tenth to one quarter the payload.

[[File:ISS Unpressurized Platforms.png|thumb|Spare parts are called [[Orbit Replaceable Unit|ORU]]s; some are externally stored on pallets called [[ExPRESS Logistics Carrier|ELC]]s and [[External stowage platform|ESP]]s.]]

Unexpected problems and failures have impacted the station's assembly time-line and work schedules leading to periods of reduced capabilities and, in some cases, could have forced abandonment of the station for safety reasons, had these problems not been resolved. During [[STS-120]] in 2007, following the relocation of the P6 truss and solar arrays, it was noted during the redeployment of the array that it had become torn and was not deploying properly.<ref name="Astronauts notice tear in solar panel">{{cite news|url=http://www.redorbit.com/news/space/1123767/astronauts_notice_tear_in_solar_panel/index.html |title=Astronauts notice tear in solar panel|accessdate=30 October 2007|agency=Associated Press|date=30 October 2007|author=Liz Austin Peterson}}</ref> An EVA was carried out by [[Scott E. Parazynski|Scott Parazynski]], assisted by [[Douglas H. Wheelock|Douglas Wheelock]]. The men took extra precautions to reduce the risk of electric shock, as the repairs were carried out with the solar array exposed to sunlight.<ref name="Space Station's Damaged Panel Is Fixed">{{cite news|url=http://www.washingtonpost.com/wp-dyn/content/article/2007/11/03/AR2007110300227.html|title=Space Station's Damaged Panel Is Fixed|accessdate=4 November 2007|work=The Washington Post|date=4 November 2007|first=Rob|last=Stein}}</ref> The issues with the array were followed in the same year by problems with the starboard Solar Alpha Rotary Joint (SARJ), which rotates the arrays on the starboard side of the station. Excessive vibration and high-current spikes in the array drive motor were noted, resulting in a decision to substantially curtail motion of the starboard SARJ until the cause was understood. Inspections during EVAs on STS-120 and [[STS-123]] showed extensive contamination from metallic shavings and debris in the large drive gear and confirmed damage to the large metallic race ring at the heart of the joint, and so the joint was locked to prevent further damage.<ref name="joint-update">{{cite news|url=http://spaceflightnow.com/shuttle/sts123/080325sarj/index.html|title=Station chief gives detailed update on joint problem|accessdate=5 November 2008|author=William Harwood|publisher=CBS News & SpaceflightNow.com|date=25 March 2008}}</ref> Repairs to the joint were carried out during [[STS-126]] with lubrication of both joints and the replacement of 11 out of 12 trundle bearings on the joint.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts126/126_overview.html|title=Crew Expansion Prep, SARJ Repair Focus of STS-126|accessdate=5 November 2008|publisher=NASA|date=30 October 2008}}</ref><ref>{{cite news|url=http://www.spaceflightnow.com/shuttle/sts126/081118fd5/index.html|title=Astronauts prepare for first spacewalk of shuttle flight|date=18 November 2008|author=William Harwood|publisher=CBS News & SpaceflightNow.com|accessdate=22 November 2008}}</ref>

[[File:STS-120 EVA Scott Parazynski.jpg|thumb|While anchored on the end of the [[Orbiter Boom Sensor System|OBSS]], astronaut [[Scott Parazynski]] performs makeshift repairs to a US Solar array which damaged itself when unfolding, during [[STS-120]].|alt=Two black and orange solar arrays, shown uneven and with a large tear visible. A crew member in a spacesuit, attached to the end of a robotic arm, holds a latticework between two solar sails.]]
2009 saw damage to the S1 radiator, one of the components of the station's cooling system. The problem was first noticed in [[Soyuz spacecraft|Soyuz]] imagery in September 2008, but was not thought to be serious.<ref name="Radiator">{{cite web|url=http://www.nasaspaceflight.com/2009/04/iss-concern-s1-radiator-may-require-replacement-shuttle-mission/|author=Chris Bergin|date=1 April 2009|publisher=NASASpaceflight.com|title=ISS concern over S1 Radiator – may require replacement via shuttle mission|accessdate=3 April 2009}}</ref> The imagery showed that the surface of one sub-panel has peeled back from the underlying central structure, possibly due to micro-meteoroid or debris impact. It is also known that a Service Module thruster cover, jettisoned during an EVA in 2008, had struck the S1 radiator, but its effect, if any, has not been determined. On 15 May 2009 the damaged radiator panel's ammonia tubing was mechanically shut off from the rest of the cooling system by the computer-controlled closure of a valve. The same valve was used immediately afterwards to vent the ammonia from the damaged panel, eliminating the possibility of an ammonia leak from the cooling system via the damaged panel.<ref name="Radiator" />

Early on 1 August 2010, a failure in cooling Loop A (starboard side), one of two external cooling loops, left the station with only half of its normal cooling capacity and zero redundancy in some systems.<ref>{{cite web|url=http://spaceflightnow.com/news/n1007/31station/ |title=Problem forces partial powerdown aboard station |publisher=Spaceflightnow.com |date=31 July 2010 |accessdate=16 November 2010}}</ref><ref>{{cite web|url=http://www.spaceref.com/news/viewsr.html?pid=34622 |title=NASA ISS On-Orbit Status 1 August 2010 (early edition) |publisher=Spaceref.com |date=31 July 2010 |accessdate=16 November 2010}}</ref><ref>{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/systems/atcs.html |title=ISS Active Control System |publisher=Boeing |date=21 November 2006 |accessdate=16 November 2010}}</ref> The problem appeared to be in the ammonia pump module that circulates the ammonia cooling fluid. Several subsystems, including two of the four CMGs, were shut down.

Planned operations on the ISS were interrupted through a series of EVAs to address the cooling system issue. A first EVA on 7 August 2010, to replace the failed pump module, was not fully completed due to an ammonia leak in one of four quick-disconnects. A second EVA on 11 August successfully removed the failed pump module.<ref>[http://spaceflightnow.com/station/exp24/100810evapre/index.html Spaceflight Now] "Wednesday spacewalk to remove failed coolant pump"</ref><ref>[http://www.nasaspaceflight.com/2010/08/live-second-eva-with-pump-module-changeout/ NASA spaceflight 11 August] "Large success for second EVA as failed Pump Module is removed"</ref> A third EVA was required to restore Loop A to normal functionality.<ref>[http://spaceflightnow.com/station/exp24/100811eva2/index5.html Spaceflight Now 12 August] "Station's bad pump removed; more spacewalking ahead"</ref><ref>[http://www.nasaspaceflight.com/2010/08/iss-cooling-returning-normal-confirming-etcs-pm-success/ Spaceflight Now, 18 August] ISS cooling configuration returning to normal confirming ETCS PM success</ref>

The USOS's cooling system is largely built by the American company [[Boeing]],<ref>{{cite web|url=http://www.space.com/businesstechnology/international-space-station-complexities-100802.html|title=Cooling System Malfunction Highlights Space Station's Complexity|publisher=Space.com|date=2 August 2010}}</ref> which is also the manufacturer of the failed pump.<ref>{{cite web|url=http://spaceflightnow.com/news/n1007/31station/|title=Spacewalks needed to fix station cooling problem|publisher=Spaceflightnow|date=31 July 2010}}</ref>

An air leak from the USOS in 2004,<ref>{{cite news|url=http://www.msnbc.msn.com/id/3882962/|title=Crew finds 'culprit' in space station leak|publisher=MSNBC|date=11 January 2004|author=James Oberg|accessdate=22 August 2010}}</ref> the venting of fumes from an ''[[Elektron (ISS)|Elektron]]'' oxygen generator in 2006,<ref>{{cite news|url=http://spaceflightnow.com/station/exp13/060918elektron.html|title=Oxygen Generator Problem Triggers Station Alarm|publisher = CBS News through Spaceflight Now|date=18 September 2006|author=William Harwood|accessdate=24 November 2008}}</ref> and the failure of the computers in the ROS in 2007 during [[STS-117]] left the station without thruster, ''Elektron'', ''[[Vozdukh]]'' and other environmental control system operations, the root cause of which was found to be condensation inside the electrical connectors leading to a short-circuit.{{Citation needed|date=June 2011}}
[[File:STS-134 EVA4 view to the Russian Orbital Segment.jpg|thumb|right|In the foreground, a set of heat radiators]]
The four Main Bus Switching Units (MBSUs, located in the S0 truss), control the routing of power from the four solar array wings to the rest of the ISS. In late 2011 MBSU-1, while still routing power correctly, ceased responding to commands or sending data confirming its health, and was scheduled to be swapped out at the next available EVA. In each MBSU, two power channels feed 160V DC from the arrays to two DC-to-DC power converters (DDCUs) that supply the 124V power used in the station. A spare MBSU was already on board, but 30 August 2012 EVA failed to be completed when a bolt being tightened to finish installation of the spare unit jammed before electrical connection was secured.<ref>{{cite web|author=30 August 2012 by Pete Harding |url=http://www.nasaspaceflight.com/2012/08/astronaut-perform-first-post-shuttle-spacewalk-iss |title=Astronaut duo complete challenging first post-Shuttle US spacewalk on ISS |publisher=Nasaspaceflight.com |date=30 August 2012 |accessdate=22 October 2013}}</ref> The loss of MBSU-1 limits the station to 75% of its normal power capacity, requiring minor limitations in normal operations until the problem can be addressed.

On 5 September 2012, in a second, 6 hr, EVA to replace MBSU-1, astronauts Sunita Williams and Akihiko Hoshide successfully restored the ISS to 100% power.<ref>[http://spaceref.com/international-space-station/critical-space-station-spacewalk-a-success.html Spaceref.com Sept 5, 2012] Marc Boucher "Critical Space Station spacewalk a Success".</ref>
[[File:Astronaut Mike Hopkins on Dec. 24 Spacewalk.jpg|thumb|Mike Hopkins on his Christmas Eve spacewalk]]
On 24 December 2013, astronauts made a rare Christmas Eve space walk, installing a new ammonia pump for the station's cooling system. The faulty cooling system had failed earlier in the month, halting many of the station's science experiments. Astronauts had to brave a "mini blizzard" of ammonia while installing the new pump. It was only the second Christmas Eve spacewalk in NASA history.<ref>{{cite web|last=AP|title=Astronauts Complete Rare Christmas Eve Spacewalk|url=http://www.leaker.com/astronauts-complete-rare-christmas-eve-spacewalk/|publisher=Leaker|accessdate=24 December 2013|date=24 December 2013}}</ref>

[[File:Iss orbit and expeditions.png|thumb|Iss orbit with calendar of expeditions and modules]]

==Fleet operations==
:{{See also|List of human spaceflights to the International Space Station|List of unmanned spaceflights to the International Space Station}}
A wide variety of manned and unmanned spacecraft have supported the station's activities. 
[[Progress M-28M]] (ISS-60P) was the 62nd Progress spacecraft planned to arrive at the ISS, including [[Progress M-MIM2|M-MIM2]] and [[Progress M-SO1|M-SO1]] which installed modules. 35 flights of the retired NASA Space Shuttle were made to the station.<ref name="ISStD">{{cite web|url=http://spaceflight.nasa.gov/station/isstodate.html|title=The ISS to Date|accessdate=21 March 2011|publisher=NASA|date=9 March 2011|author=NASA}}</ref> [[Soyuz TMA-16M|TMA-16M]] is the 42nd Soyuz flight, and there have been 5 [[Automated Transfer Vehicle|European ATV]], 4 Japanese [[H-II Transfer Vehicle|Kounotori]] 'White Stork', 8 [[SpaceX]] [[Dragon (spacecraft)|Dragon]] and 4 OSC [[Cygnus (spacecraft)|Cygnus]] planned arrivals.

===Currently docked/berthed===
''See also the list of [[List of International Space Station expeditions|professional]] crew, [[Space tourism|private]] travellers, [[List of human spaceflights to the ISS|both]] or just [[List of unmanned spaceflights to the ISS|unmanned spaceflights]].''

;Key
{{legend|lightblue|Uncrewed cargoships are in light blue}}
{{legend|#cfc|Crewed spacecraft are in light green}}

{| class="wikitable" style="margin: 1em auto 1em auto;text-align: left; font-size: 95%;"
|-Currently Docked
|style="text-align:center; background:#BBB" colspan="3" | '''Spacecraft and mission'''
|style="text-align:center; background:#BBB"|'''Location'''
|style="text-align:center; background:#BBB"|'''Arrived''' ([[UTC]])
|style="text-align:center; background:#BBB"|'''Departure date'''
|- style="background:#cfc;"
| {{flagicon|RUS}}
| [[Soyuz TMA-16M]]
| [[Expedition 43]]/[[Expedition 44|44]]
| [[Poisk (ISS module)|Poisk]] zenith
| 28 March 2015
| 11 September 2015
|- style="background:lightblue;"
| {{flagicon|RUS}}
| [[Progress M-28M]]
| Progress 60 Cargo
| [[Pirs (ISS module)|Pirs]] nadir
| 5 July 2015
| 19 November 2015
|- style="background:#cfc;"
| {{flagicon|RUS}}
| [[Soyuz TMA-17M]]
| [[Expedition 44]]/[[Expedition 45|45]]
| [[Rassvet (ISS module)|Rassvet]] nadir
| 23 July 2015
| 22 December 2015
|}

===Scheduled launches and dockings/berthings===
* All dates are [[UTC]]. Dates are the earliest possible dates and may change.
* Forward ports are at the front of the station according to its normal direction of travel and orientation ([[Yaw, pitch and roll#Aircraft attitudes|attitude]]). Aft is at the rear of the station, used by spacecraft boosting the station's orbit. [[Nadir]] is closest the Earth, [[Zenith]] is on top.
* Spacecraft operated by government agencies are indicated with 'Gov' and under commercial arrangements are indicated with 'Com'.

;Key
{{legend|lightblue|Uncrewed cargoships are in light blue colour}}
{{legend|#cfc|Crewed spacecraft are in light green colour}}
{{legend|wheat|Modules are in wheat colour}}

{| class="wikitable" style="margin: 1em auto 1em auto;text-align: left; font-size: 95%;"
|+Planned Missions
|style="text-align:center; background:#BBB"|'''Launch''' ({{abbr|NET|Not Earlier Than}})
|style="text-align:center; background:#BBB"|'''Launch Vehicle'''
|style="text-align:center; background:#BBB"|'''Launch Site'''
|style="text-align:center; background:#BBB" colspan="3"| '''Launch Service Provider'''
|style="text-align:center; background:#BBB"|'''Payload'''
|style="text-align:center; background:#BBB"|'''Spacecraft'''
|style="text-align:center; background:#BBB"|'''Mission'''
|style="text-align:center; background:#BBB"|'''Docking / Berthing Port'''
|style="text-align:center; background:#BBB"|'''Ref.'''
|-
| nowrap| 19 August 2015
| nowrap| [[H-IIB]]
| nowrap| {{flagicon|JPN}} [[Tanegashima Space Center|Tanegashima]] [[Yoshinobu Launch Complex|LA-Y2]]
| nowrap| {{flagicon|JPN}}
| nowrap| Gov
| nowrap| [[JAXA]]
| style="background:lightblue;" nowrap| [[Kounotori 5|HTV-5]]
| nowrap| [[H-II Transfer Vehicle|HTV]]
| ISS Resupply
| nowrap| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule">{{cite web |url=http://spaceflightnow.com/launch-schedule/ |title=Launch Calendar |work=Spaceflight Now |date=28 March 2015 |accessdate=28 March 2015}}</ref><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 2 September 2015
| nowrap| [[Soyuz-FG]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:#cfc;" nowrap| [[Soyuz TMA-18M]]
| nowrap| [[Soyuz (spacecraft)|Soyuz]]
| [[Expedition 45]]/[[Expedition 46|46]] including [[European Space Agency|ESA]] [[Denmark|Danish]] Astronaut [[Andreas Mogensen]] and [[Kazakhstan]] cosmonaut [[Aydyn Aimbetov]].
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 1 October 2015
| nowrap| [[Soyuz-U]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:lightblue;" nowrap| [[Progress M-29M]]
| nowrap| [[Progress (spacecraft)|Progress]]
| ISS Resupply
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| NET September 2015 (TBD)
| nowrap|[[Falcon 9 v1.1]]
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 40|SLC-40]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[SpaceX]]
| style="background:lightblue;" nowrap| [[SpaceX CRS-8]]
| nowrap| [[Dragon (spacecraft)|Dragon]]
| ISS resupply. Will deliver [[Bigelow Expandable Activity Module|Bigelow Expandable Activity Module (BEAM)]] to the ISS.
| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| 21 November 2015
| nowrap| [[Soyuz-2 (rocket)|Soyuz-2.1a]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:lightblue;" nowrap| [[Progress MS-1]]
| nowrap| [[Progress (spacecraft)|Progress]]
| ISS Resupply. First launch of the new [[Progress (spacecraft)#Progress MS|Progress-MS]] variant.
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 3 December 2015
| nowrap| [[Atlas V]] 401
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 41|SLC-41]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[United Launch Alliance|ULA]]
| style="background:lightblue;" nowrap| [[Cygnus CRS Orb-4]]
| nowrap| [[Cygnus (spacecraft)|Cygnus]]
| ISS Resupply
| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/><ref>{{cite web|url=http://www.space.com/27962-cygnus-cargo-spacecraft-new-rocket.html |title=Private Cargo Spacecraft Gets New Rocket Ride After Accident |publisher=Space.com |date= |accessdate=2015-04-04}}</ref>
|-
| nowrap| 15 December 2015
| nowrap| [[Soyuz-FG]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:#cfc;" nowrap| [[Soyuz TMA-19M]]
| nowrap| [[Soyuz (spacecraft)|Soyuz]]
| [[Expedition 46]]/[[Expedition 47|47]]
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| NET December 2015 (TBD)
| nowrap|[[Falcon 9 v1.1]]
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[SpaceX]]
| style="background:lightblue;" nowrap| [[SpaceX CRS-9]]
| nowrap| [[Dragon (spacecraft)|Dragon]]
| ISS resupply. Will deliver the IDA-2 segment of the [[NASA Docking System]] to the ISS.
| nowrap| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |
url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|}

===Docking===
{{See also|Docking and berthing of spacecraft}}
[[File:Progress M-14M.jpg|thumb|The [[Progress M-14M]] resupply vehicle as it approaches the ISS in 2012. Over 50 unpiloted [[Progress (spacecraft)|Progress]] spacecraft have been sent with supplies during the lifetime of the station.]]
All Russian spacecraft and self-propelled modules are able to rendezvous and dock to the space station without human intervention using the [[Kurs (docking system)|Kurs]] docking system. Radar allows these vehicles to detect and intercept ISS from over 200 kilometres away. The European ATV uses star sensors and GPS to determine its intercept course. When it catches up it then uses laser equipment to [[Computer vision|optically]] recognise Zvezda, along with the Kurs system for redundancy.  Crew supervise these craft, but do not intervene except to send abort commands in emergencies. The Japanese [[H-II Transfer Vehicle]] parks itself in progressively closer orbits to the station, and then awaits 'approach' commands from the crew, until it is close enough for a robotic arm to grapple and berth the vehicle to the USOS. The American Space Shuttle was manually docked, and on missions with a [[Multi-Purpose Logistics Module|cargo container]], the container would be berthed to the Station with the use of manual robotic arms. Berthed craft can transfer [[International Standard Payload Rack]]s. Japanese spacecraft berth for one to two months. Russian and European Supply craft can remain at the ISS for six months,<ref>{{cite web|url=http://www.esa.int/esaMI/ATV/SEMBW0PR4CF_0.html |title=ESA — ATV — Crew role in mission control |publisher=Esa.int |date=2 March 2011 |accessdate=23 May 2011}}</ref><ref>{{cite web|url=http://www.esa.int/esaHS/ESA4ZJ0VMOC_iss_0.html |title=ESA — Human Spaceflight and Exploration — International Space Station — Automated Transfer Vehicle (ATV) |publisher=Esa.int |date=16 January 2009 |accessdate=23 May 2011}}</ref> allowing great flexibility in crew time for loading and unloading of supplies and trash. NASA Shuttles could remain docked for 11–12 days.<ref>{{cite web|url=http://www.boeing.com/news/frontiers/archive/2005/july/i_ids4.html|title=Space Shuttle upgrade lets astronauts at ISS stay in space longer|last=Memi|first=Ed|publisher=Boeing|accessdate=17 September 2011}}</ref>

The American manual approach to docking allows greater initial flexibility and less complexity. The downside to this mode of operation is that each mission becomes unique and requires specialised training and planning, making the process more labour-intensive and expensive. The Russians pursued an automated methodology that used the crew in override or monitoring roles. Although the initial development costs were high, the system has become very reliable with standardisations that provide significant cost benefits in repetitive routine operations.<ref>David C. Wo±nden and David K. Geller [http://www.usu.edu/mae/aerospace/publications/JDSC_RoadToAutonomy.pdf The Road to Autonomous Orbital Rendezvous]. Utah State University, Logan, Utah</ref> An automated approach could allow assembly of modules orbiting other worlds prior to crew arrival.

[[File:ISS and Endeavour seen from the Soyuz TMA-20 spacecraft 27.jpg|thumb|left|{{OV|105}}, [[ATV-2]], [[Soyuz TMA-21]] and [[Progress M-10M]] docked to the ISS during [[STS-134]], as seen from the departing [[Soyuz TMA-20]]|alt=A side-on view of the ISS showing a Space Shuttle docked to the forward end, an ATV to the aft end and Soyuz & Progress spacecraft projecting from the Russian segment.]]
Soyuz spacecraft used for crew rotation also serve as lifeboats for emergency evacuation; they are replaced every six months and have been used once to remove excess crew after the [[Space Shuttle Columbia disaster|Columbia disaster]].<ref>{{cite web|url=http://www.astronautix.com/flights/isseo6.htm |title=ISS EO-6 |publisher=Astronautix.com |accessdate=1 May 2012}}</ref> Expeditions require, on average, {{nowrap|2 722 kg}} of supplies, and {{As of|2011|03|09|lc=yes}}, crews had consumed a total of around {{nowrap|22 000 meals}}.<ref name="ISStD" /> Soyuz crew rotation flights and Progress resupply flights visit the station on average two and three times respectively each year,<ref name="Livelist">{{cite web|url=http://www.nasa.gov/mission_pages/station/resupply/index.html|archiveurl=https://web.archive.org/web/20080803015945/http://www.nasa.gov/mission_pages/station/resupply/index.html|archivedate=3 August 2008|title=Live listing of spacecraft operations|publisher=NASA|date=1 December 2009|accessdate=8 December 2009}}</ref> with the ATV and HTV planned to visit annually from 2010 onwards.{{Citation needed|date=January 2012}} Following retirement of the NASA Shuttle [[Cygnus spacecraft|Cygnus]] and [[SpaceX Dragon|Dragon]] were contracted to fly cargo to the station.<ref>{{cite web|author=Space Operations Mission Directorate|title=Human Space Flight Transition Plan|publisher=NASA|date=30 August 2006|url=http://www.nasa.gov/pdf/315546main_space_flight_transition_plan.pdf}}</ref><ref>{{cite press release|publisher=NASA|date=18 January 2006|title=NASA Seeks Proposals for Crew and Cargo Transportation to Orbit|url=http://www.spaceref.com/news/viewpr.html?pid=18791|accessdate=21 November 2006}}</ref>

From 26 February 2011 to 7 March 2011 four of the governmental partners (United States, ESA, Japan and Russia) had their spacecraft (NASA Shuttle, ATV, HTV, Progress and Soyuz) docked at the ISS, the only time this has happened to date.<ref>{{cite news|title=NASA proposes Soyuz photo op; shuttle launch readiness reviewed (UPDATED)|url=http://www.cbsnews.com/network/news/space/home/spacenews/files/b0e194a8338c336e823c03601f046707-157.html|publisher=CBS|accessdate=11 February 2011}}</ref> On 25 May 2012, [[SpaceX]] became the world's first privately held company to send cargo, via the [[Dragon (spacecraft)|Dragon spacecraft]], to the International Space Station.<ref name="NYT-20120525">{{cite news |last=Chang |first=Kenneth |title=Space X Capsule Docks at Space Station |url=http://www.nytimes.com/2012/05/26/science/space/space-x-capsule-docks-at-space-station.html |date=25 May 2012 |work=[[The New York Times]] |accessdate=25 May 2012 }}</ref>

===Launch and docking windows===
Prior to a ship's docking to the ISS, navigation and attitude control (GNC) is handed over to the ground control of the ships' country of origin. GNC is set to allow the station to drift in space, rather than fire its thrusters or turn using gyroscopes. The solar panels of the station are turned edge-on to the incoming ships, so residue from its thrusters does not damage the cells. When a NASA shuttle docked to the station, other ships were grounded, as the carbon wingtips, cameras, windows, and instruments aboard the shuttle were at too much risk from damage from thruster residue from other ships movements.

Approximately 30% of NASA shuttle launch delays were caused by poor weather. Occasional priority was given to the Soyuz arrivals at the station where the Soyuz carried crew with time-critical cargoes such as biological experiment materials, also causing shuttle delays. Departure of the NASA shuttle was often delayed or prioritised according to weather over its two landing sites.<ref>{{cite web |url=http://www.nasa.gov/home/hqnews/2009/may/HQ_09-118_Shuttle_Landing_Delayed.html |title=NASA's Space Shuttle Landing Delayed by Weather |publisher=NASA |first1=Katherine |last1=Trinidad |first2=Candrea |last2=Thomas |date=22 May 2009 |accessdate=26 June 2015}}</ref> Whilst the Soyuz is capable of landing anywhere, anytime, its planned landing time and place is chosen to give consideration to helicopter pilots and ground recovery crew, to give acceptable flying weather and lighting conditions. Soyuz launches occur in adverse weather conditions, but the cosmodrome has been shut down on occasions when buried by snow drifts up to 6 metres in depth, hampering ground operations.

==Life aboard==

===Crew activities===
[[File:Exp18home nasa big.jpg|thumb|Crewmember peers out of a window]]

A typical day for the crew begins with a wake-up at 06:00, followed by post-sleep activities and a morning inspection of the station. The crew then eats breakfast and takes part in a daily planning conference with Mission Control before starting work at around 08:10. The first scheduled exercise of the day follows, after which the crew continues work until 13:05. Following a one-hour lunch break, the afternoon consists of more exercise and work before the crew carries out its pre-sleep activities beginning at 19:30, including dinner and a crew conference. The scheduled sleep period begins at 21:30. In general, the crew works ten hours per day on a weekday, and five hours on Saturdays, with the rest of the time their own for relaxation or work catch-up.<ref>{{cite web|url=http://www.nasa.gov/pdf/287386main_110508_tl.pdf|title=ISS Crew Timeline|date=5 November 2008|accessdate=5 November 2008|publisher=NASA|format=PDF}}</ref>

The time zone used on board the ISS is [[Coordinated Universal Time]] (UTC). The windows are covered at night hours to give the impression of darkness because the station experiences 16 sunrises and sunsets a day. During visiting space shuttle missions, the ISS crew will mostly follow the shuttle's [[Mission Elapsed Time]] (MET), which is a flexible time zone based on the launch time of the shuttle mission.<ref>{{Cite web|title = NASA - Time in Space, A Space in Time|url = https://www.nasa.gov/mission_pages/station/research/news/time_in_space.html|website = www.nasa.gov|accessdate = 2015-05-05}}</ref><ref>{{Cite web|title = A Slice of Time Pie|url = https://web.archive.org/web/20130317075600/http://blogs.nasa.gov/cm/blog/ISS%20Science%20Blog/posts/post_1340820317951.html|date = 2013-03-17|accessdate = 2015-05-05}}</ref><ref>{{Cite web|title = Human Space Flight (HSF) - Crew Answers|url = http://spaceflight.nasa.gov/feedback/expert/answer/crew/sts-113/index_2.html|website = spaceflight.nasa.gov|accessdate = 2015-05-05}}</ref>

The station provides crew quarters for each member of the expedition's crew, with two 'sleep stations' in the ''Zvezda'' and four more installed in ''Harmony''.<ref>{{cite web|url=https://www.youtube.com/watch?v=Q4dG9vSyUFQ|title=At Home with Commander Scott Kelly (Video)|date=6 December 2010|publisher=NASA|accessdate=8 May 2011|location=International Space Station}}</ref><ref>{{cite web|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080013462_2008012884.pdf|title=International Space Station USOS Crew Quarters Development|first1=James Lee |last1=Broyan |first2=Melissa Ann |last2=Borrego |first3=Juergen F. |last3=Bahr|year=2008|publisher=SAE International|accessdate=8 May 2011}}</ref> The American quarters are private, approximately person-sized soundproof booths. The Russian crew quarters include a small window, but do not provide the same amount of ventilation or block the same amount of noise as their American counterparts. A crewmember can sleep in a crew quarter in a tethered sleeping bag, listen to music, use a laptop, and store personal items in a large drawer or in nets attached to the module's walls. The module also provides a reading lamp, a shelf and a desktop.<ref name="ESALife">{{cite web|url=http://www.esa.int/esaHS/ESAH1V0VMOC_astronauts_0.html|publisher=ESA|accessdate=28 October 2009|date=19 July 2004|title=Daily life}}</ref><ref name="NASACrewEquip">{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/126_payload.html|title=Station Prepares for Expanding Crew|publisher=NASA|first=Cheryl L. |last=Mansfield|date=7 November 2008|accessdate=17 September 2009}}</ref><ref name="CSALife">{{cite web|url=http://www.asc-csa.gc.ca/pdf/educator-liv_wor_iss.pdf|title=Living and Working on the International Space Station|accessdate=28 October 2009|publisher=CSA}}</ref> Visiting crews have no allocated sleep module, and attach a sleeping bag to an available space on a wall—it is possible to sleep floating freely through the station, but this is generally avoided because of the possibility of bumping into sensitive equipment.<ref name="SRLife">{{cite web|url=http://www.space.com/missionlaunches/090827-sts127-space-sleeping.html|title=Sleeping in Space is Easy, But There's No Shower|first=Tariq|last=Malik|accessdate=29 October 2009|date=27 July 2009|publisher=Space.com}}</ref> It is important that crew accommodations be well ventilated; otherwise, astronauts can wake up oxygen-deprived and gasping for air, because a bubble of their own exhaled carbon dioxide has formed around their heads.<ref name="ESALife" />
{{See also|Christmas on the International Space Station}}

===Food===
[[File:Meal STS127.jpg|thumb|alt=Nine astronauts seated around a table covered in open cans of food strapped down to the table. In the background a selection of equipment is visible, as well as the salmon-coloured walls of the Unity node.|The crews of [[STS-127]] and [[Expedition 20]] enjoy a meal inside ''Unity''.]]
{{See also|Space food}}

Most of the food on board is vacuum sealed in plastic bags. Cans are heavy and expensive to transport, so there are not as many. The preserved food is generally not held in high regard by the crew, and when combined with the reduced sense of taste in a microgravity environment,<ref name="ESALife" /> a great deal of effort is made to make the food more palatable. More spices are used than in regular cooking, and the crew looks forward to the arrival of any ships from Earth, as they bring fresh fruit and vegetables with them. Care is taken that foods do not create crumbs. Sauces are often used to ensure station equipment is not contaminated. Each crew member has individual food packages and cooks them using the on-board galley. The galley features two food warmers, a refrigerator added in November 2008, and a water dispenser that provides both heated and unheated water.<ref name="NASACrewEquip" /> Drinks are provided in dehydrated powder form and are mixed with water before consumption.<ref name="NASACrewEquip" /><ref name="CSALife" /> Drinks and soups are sipped from plastic bags with straws; solid food is eaten with a knife and fork, which are attached to a tray with magnets to prevent them from floating away. Any food that floats away, including crumbs, must be collected to prevent it from clogging up the station's air filters and other equipment.<ref name="CSALife" />

===Hygiene===
[[File:Zvezda toilet.jpg|thumb|right|upright|Space toilet in the [[Zvezda (ISS module)|Zvezda Service Module]]]]

Showers on space stations were introduced in the early 1970s on Skylab and Salyut 3.<ref name="livingandworking">Benson, Charles Dunlap and William David Compton. ''[http://history.nasa.gov/SP-4208/contents.htm Living and Working in Space: A History of Skylab]''. NASA publication SP-4208.</ref>{{rp|139}} By Salyut 6, in the early 1980s, the crew complained of the complexity of showering in space, which was a monthly activity.<ref name="Portree1995-86">{{cite book |url=http://history.nasa.gov/SP-4225/documentation/mhh/mirheritage.pdf |title=Mir Hardware Heritage |publisher=NASA |first=David S. F. |last=Portree |page=86 |date=March 1995 |id=Reference Publication 1357 |oclc=755272548}}</ref> The ISS does not feature a shower; instead, crewmembers wash using a water jet and wet wipes, with soap dispensed from a toothpaste tube-like container. Crews are also provided with rinseless shampoo and edible toothpaste to save water.<ref name="SRLife" /><ref>{{cite AV media |url=https://www.youtube.com/watch?v=uIjNfZbUYu8 |title=Karen Nyberg Shows How You Wash Hair in Space |publisher=NASA |work=YouTube.com |first=Karen |last=Nyberg |date=12 July 2013 |accessdate=6 June 2015}}</ref>

There are two [[space toilet]]s on the ISS, both of Russian design, located in ''[[Zvezda (ISS module)|Zvezda]]'' and ''[[Tranquility (ISS module)|Tranquility]]''.<ref name="NASACrewEquip" /> These Waste and Hygiene Compartments use a fan-driven suction system similar to the Space Shuttle Waste Collection System. Astronauts first fasten themselves to the toilet seat, which is equipped with spring-loaded restraining bars to ensure a good seal.<ref name="ESALife" /> A lever operates a powerful fan and a suction hole slides open: the air stream carries the waste away. Solid waste is collected in individual bags which are stored in an aluminium container. Full containers are transferred to Progress spacecraft for disposal.<ref name="NASACrewEquip" /><ref>{{cite web |first=Ed |last=Lu |title=Greetings Earthling |url=http://spaceflight.nasa.gov/station/crew/exp7/luletters/lu_letter9.html |date=8 September 2003 |accessdate=1 November 2009 |publisher=NASA}}</ref> Liquid waste is evacuated by a hose connected to the front of the toilet, with anatomically correct "urine funnel adapters" attached to the tube so both men and women can use the same toilet. Waste is collected and transferred to the Water Recovery System, where it is recycled back into drinking water.<ref name="CSALife" />

==Crew health and safety==
{{Main|Effect of spaceflight on the human body}}

===Radiation===
The ISS is partially protected from the space environment by the Earth's magnetic field. From an average distance of about {{convert|70,000|km|abbr=on}}, depending on Solar activity, the [[magnetosphere]] begins to deflect solar wind around the Earth and ISS. [[coronal mass ejection|Solar flares]] are still a hazard to the crew, who may receive only a few minutes warning. The crew of [[Expedition 10]] took shelter as a precaution in 2005 in a more heavily shielded part of the ROS designed for this purpose during the initial 'proton storm' of an X-3 class solar flare,<ref>{{cite web|title=Solar Flare Hits Earth and Mars|author=Ker Than|publisher=Space.com|date=23 February 2006|url=http://www.space.com/2080-solar-flare-hits-earth-mars.html}}</ref><ref>{{cite web|title=A new kind of solar storm|publisher=NASA|date=10 June 2005|url=http://science.nasa.gov/science-news/science-at-nasa/2005/10jun_newstorm/}}</ref> but without the limited protection of the Earth's [[magnetosphere]], interplanetary manned missions are especially vulnerable.

[[File:Aurora Australis.ogv|thumb|left|Video of the [[Aurora Australis]] taken by the crew of [[Expedition 28]] on an ascending pass from south of [[Madagascar]] to just north of Australia over the Indian Ocean.]]

Subatomic charged particles, primarily protons from [[cosmic ray]]s and [[solar wind]], are normally absorbed by the Earth's atmosphere. When they interact in sufficient quantity, their effect becomes visible to the naked eye in a phenomenon called an aurora. Without the protection of the Earth's atmosphere, which absorbs this radiation, crews are exposed to about 1 [[millisievert]] each day, which is about the same as someone would get in a year on Earth from natural sources. This results in a higher risk of astronauts developing cancer. Radiation can penetrate living tissue, damage DNA, and cause damage to the [[chromosome]]s of [[lymphocytes]]. These cells are central to the [[immune system]], and so any damage to them could contribute to the lowered [[immunity (medical)|immunity]] experienced by astronauts. Radiation has also been linked to a higher incidence of [[cataracts]] in astronauts. Protective shielding and protective drugs may lower the risks to an acceptable level.<ref name="JCB"/>

The radiation levels experienced on the ISS are about five times greater than those experienced by airline passengers and crew. The Earth's electromagnetic field provides almost the same level of protection against solar and other radiation in low Earth orbit as in the stratosphere. Airline passengers experience this level of radiation for no more than 15 hours for the longest intercontinental flights. For example, on a 12-hour flight an airline passenger would experience 0.1 millisieverts of radiation, or a rate of 0.2 millisieverts per day; only 1/5 the rate experienced by an astronaut in LEO.<ref>{{cite web|url=http://jag.cami.jccbi.gov./cariprofile.asp|title=Galactic Radiation Received in Flight|accessdate=20 May 2010|publisher=FAA Civil Aeromedical Institute}}</ref>
{{See also|Coronal mass ejection|Aurora (astronomy)}}

===Stress===
[[File:Nikolai Budarin in a sleep station in Zvezda.jpg|thumb|Cosmonaut [[Nikolai Budarin]] at work inside [[Zvezda (ISS module)|Zvezda]] service module crew quarters]]
There has been considerable evidence that psychosocial stressors are among the most important impediments to optimal crew morale and performance.<ref>{{cite book| author1 =Peter Suedfeld1| author2 = Kasia E. Wilk| author3 = Lindi Cassel| title = Flying with Strangers: Postmission Reflections of Multinational Space Crews}}</ref> Cosmonaut [[Valery Ryumin]], wrote in his journal during a particularly difficult period on board the [[Salyut 6]] space station: "All the conditions necessary for murder are met if you shut two men in a cabin measuring 18 feet by 20 and leave them together for two months."

NASA's interest in psychological stress caused by space travel, initially studied when their manned missions began, was rekindled when astronauts joined cosmonauts on the Russian space station Mir. Common sources of stress in early American missions included maintaining high performance under public scrutiny, as well as isolation from peers and family. The latter is still often a cause of stress on the ISS, such as when the mother of NASA Astronaut [[Daniel M. Tani|Daniel Tani]] died in a car accident, and when Michael Fincke was forced to miss the birth of his second child.


A study of the longest spaceflight concluded that the first three weeks represent a critical period where attention is adversely affected because of the demand to adjust to the extreme change of environment.<ref>{{cite doi|10.1080/001401398186991}}</ref> Skylab's 3 crews remained one, two, and three months respectively, long term crews on Salyut 6, [[Salyut 7]], and the ISS last about five to six months and Mir's expeditions often lasted longer. The ISS working environment includes further stress caused by living and working in cramped conditions with people from very different cultures who speak a different language. First generation space stations had crews who spoke a single language; second and third-generation stations have crew from many cultures who speak many languages. The ISS is unique because visitors are not classed automatically into 'host' or 'guest' categories as with previous stations and spacecraft, and may not suffer from feelings of isolation in the same way. Crew members with a military pilot background and those with an academic science background or teachers and politicians may have problems understanding each other's jargon and worldview.

===Medical===
[[File:Frank De Winne on treadmill cropped.jpg|thumb|Astronaut [[Frank De Winne]] is attached to the [[Treadmill with Vibration Isolation System|TVIS treadmill]] with bungee cords aboard the International Space Station|alt=Astronaut Frank De Winne is attached to the TVIS treadmill with bungee cords aboard the International Space Station]]
Medical effects of long-term weightlessness include [[muscle atrophy]], deterioration of the skeleton [[spaceflight osteopenia|(osteopenia)]], fluid redistribution, a slowing of the cardiovascular system, decreased production of red blood cells, balance disorders, and a weakening of the immune system. Lesser symptoms include loss of body mass, and puffiness of the face.<ref name="JCB" />

Sleep is disturbed on the ISS regularly due to mission demands, such as incoming or departing ships. Sound levels in the station are unavoidably high; because the atmosphere is unable to [[thermosiphon]], fans are required at all times to allow processing of the atmosphere which would stagnate in the freefall (zero-g) environment.

To prevent some of these adverse [[physiological]] effects, the station is equipped with two treadmills (including the [[Treadmill with Vibration Isolation System|COLBERT]]), and the aRED (advanced Resistive Exercise Device) which enables various weightlifting exercises which add muscle but do nothing for bone density,<ref>{{cite pmid|14600562}}</ref> and a stationary bicycle; each astronaut spends at least two hours per day exercising on the equipment.<ref name="ESALife" /><ref name="NASACrewEquip" /> Astronauts use bungee cords to strap themselves to the treadmill.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/bungee_running.html|accessdate=23 August 2009|title=Bungee Cords Keep Astronauts Grounded While Running|date=16 June 2009|publisher=NASA}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/colbert_feature.html|accessdate=23 August 2009|title=Do Tread on Me|date=19 August 2009|author=Amiko Kauderer|publisher=NASA}}</ref>

===Microbiological environmental hazards===
{{see also|Mir#Microbiological environmental hazards}}
Hazardous moulds which can foul air and water filters may develop aboard space stations. They can produce acids which degrade metal, glass, and rubber. They can also be harmful for the crew health. Microbiological hazards have led to a development of the [[LOCAD#Portable Test System|LOCAD-PTS]] that can identify common bacteria and moulds faster than standard methods of [[Cell culture|culturing]], which may require a sample to be sent back to Earth.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2007/11may_locad3/|author=Trudy E. Bell|year=2007|title=Preventing "Sick" Spaceships|access-date=March 29, 2015}}</ref> {{As of|2012}}, 76 types of unregulated micro-organisms have been detected on the ISS.<ref>{{cite web|url=http://rt.com/news/iss-bacteria-mir-mutation-765/|title=Mutant space microbes attack ISS: 'Munch' metal, may crack glass |author= |date=April 23, 2012|website=[[RT (TV network)|RT]]|access-date=March 29, 2015}}</ref>

Reduced humidity, paint with mould killing chemical and antiseptic solutions can be used to prevent contamination in space stations. All materials used in the ISS are tested for resistance against fungi.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2000/ast26nov_1/|author=Patrick L. Barry|year=2000|title=Microscopic Stowaways on the ISS|access-date=March 29, 2015}}</ref>

==Threat of orbital debris==
{{Main|Space debris}}
{{Double image|right|SDIO KEW Lexan projectile.jpg|225|Debris-GEO1280.jpg|225|A 7 gram object (shown in centre) shot at 7 km/s (23,000 ft/sec) (the orbital velocity of the ISS) made this 15 cm (5 7/8 in) crater in a solid block of aluminium.|[[Radar]]-trackable objects including debris, with distinct ring of [[Geostationary orbit|geostationary]] satellites||}}
At the low altitudes at which the ISS orbits there is a variety of space debris,<ref>{{cite web|url=http://defensenews.com/blogs/space-symposium/2009/04/03/its-getting-crowded-up-there/#more-155|publisher=Defense News|accessdate=7 October 2009|author=Michael Hoffman|title=National Space Symposium 2009: It's getting crowded up there|date=3 April 2009}}</ref> consisting of many different objects including entire spent rocket stages, defunct satellites, explosion fragments—including materials from [[anti-satellite weapon]] tests, paint flakes, slag from solid rocket motors, and coolant released by [[US-A]] nuclear-powered satellites. These objects, in addition to natural [[micrometeoroid]]s,<ref>{{cite journal|author=F. L. Whipple|year=1949|title=The Theory of Micrometeoroids|journal=Popular Astronomy|volume=57|page=517|bibcode=1949PA.....57..517W}}</ref> are a significant threat. Large objects could destroy the station, but are less of a threat as their orbits can be predicted.<ref name="NSFdebris">{{cite web|publisher=NASASpaceflight.com|accessdate=28 June 2011|date=28 June 2011|author=Chris Bergin|url=http://www.nasaspaceflight.com/2011/06/sts-135-frr-july-8-atlantis-debris-misses-iss/|title=STS-135: FRR sets 8 July Launch Date for Atlantis – Debris misses ISS}}</ref><ref>{{cite web|author=Henry Nahra|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19890016664_1989016664.pdf|title=Effect of Micrometeoroid and Space Debris Impacts on the Space Station Freedom Solar Array Surfaces|date=24–29 April 1989|publisher=NASA|accessdate=7 October 2009}}</ref> Objects too small to be detected by optical and radar instruments, from approximately 1 cm down to microscopic size, number in the trillions. Despite their small size, some of these objects are still a threat because of their [[kinetic energy]] and direction in relation to the station. Spacesuits of spacewalking crew could puncture, causing [[Space exposure|exposure to vacuum]].<ref name=debrisdecomp>{{cite web|title=Space Suit Punctures and Decompression|url=http://www.asi.org/adb/04/03/08/suit-punctures.html|publisher=The Artemis Project|accessdate=20 July 2011}}</ref>

The station's shields and structure are divided between the ROS and the USOS, with completely different designs. On the USOS, a thin aluminium sheet is held apart from the hull, the sheet causes objects to shatter into a cloud before hitting the hull thereby spreading the energy of the impact. On the ROS, a carbon plastic honeycomb screen is spaced from the hull, an aluminium honeycomb screen is spaced from that, with a screen-vacuum thermal insulation covering, and glass cloth over the top. It is about 50% less likely to be punctured,  and crew move to the ROS when the station is under threat. Punctures on the ROS would be contained within the panels which are 70 cm square.

[[File:ISS impact risk.jpg|thumb|left|Example of [[risk management]]: A NASA model showing areas at high risk from impact for the International Space Station.]]

Space debris objects are tracked remotely from the ground, and the station crew can be notified.<ref>{{cite web|url=http://www.orbitaldebris.jsc.nasa.gov/library/EducationPackage.pdf |title=Microsoft PowerPoint – EducationPackage SMALL.ppt |format=PDF |accessdate=1 May 2012}}</ref> This allows for a [[Debris Avoidance Manoeuvre]] (DAM) to be conducted, which uses thrusters on the Russian Orbital Segment to alter the station's orbital altitude, avoiding the debris. DAMs are not uncommon, taking place if computational models show the debris will approach within a certain threat distance. Eight DAMs had been performed prior to March 2009,<ref>{{cite web|url=http://www.newscientist.com/article/dn16777-space-station-may-move-to-dodge-debris.html|title=Space station may move to dodge debris|work=New Scientist|date=16 March 2009|accessdate=20 April 2010|author=Rachel Courtland}}</ref> the first seven between October 1999 and May 2003.<ref name=ODOct08>{{cite journal|url=http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv12i4.pdf|title=ISS Maneuvers to Avoid Russian Fragmentation Debris|publisher=NASA|pages=1&2|journal=Orbital Debris Quarterly News|date=October 2008|accessdate=20 April 2010|volume=12|issue=4}}</ref> Usually the orbit is raised by one or two kilometres by means of an increase in orbital velocity of the order of 1 m/s. Unusually there was a lowering of 1.7 km on 27 August 2008, the first such lowering for 8 years.<ref name=ODOct08 /><ref>{{cite web|url=http://www.esa.int/esaMI/ATV/SEM64X0SAKF_0.html|title=ATV carries out first debris avoidance manoeuvre for the ISS|publisher=ESA|date=28 August 2008|accessdate=26 February 2010}}</ref> There were two DAMs in 2009, on 22 March and 17 July.<ref>{{cite journal|url=http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv14i1.pdf|title=Avoiding satellite collisions in 2009|page=2|journal=Orbital Debris Quarterly News|publisher=NASA|volume=14|date=January 2010|issue=1|accessdate=20 April 2010}}</ref> If a threat from orbital debris is identified too late for a DAM to be safely conducted, the station crew close all the hatches aboard the station and retreat into their [[Soyuz spacecraft]], so that they would be able to evacuate in the event the station was seriously damaged by the debris. This partial station evacuation has occurred on 13 March 2009, 28 June 2011, 24 March 2012 and 16 June 2015.<ref>{{cite news| url=http://www.bbc.co.uk/news/science-environment-17497766| title=ISS crew take to escape capsules in space junk alert| accessdate=24 March 2012 |work=BBC News |date=24 March 2012}}</ref><ref>{{cite news| url=https://blogs.nasa.gov/spacestation/2015/07/16/station-crew-takes-precautions-for-close-pass-of-space-debris/| title=Station Crew Takes Precautions for Close Pass of Space Debris| accessdate=16 June 2015 |work=NASA Blog |date=16 June 2015}}</ref>
Ballistic panels, also called micrometeorite shielding, are incorporated into the station to protect pressurised sections and critical systems. The type and thickness of these panels varies depending upon their predicted exposure to damage.

==End of mission==
[[File:Jules Verne Automated Transfer Vehicle re-enters Earth's atmosphere.jpg|thumb|right|Many ISS resupply spacecraft have already undergone [[Atmospheric entry|atmospheric re-entry]], such as [[Jules Verne ATV]]]]
According to a 2009 report, [[S.P. Korolev Rocket and Space Corporation Energia|Space Corporation Energia]] is considering methods to remove from the station some modules of the Russian Orbital Segment when the end of mission is reached and use them as a basis for a new station, known as the [[Orbital Piloted Assembly and Experiment Complex]] (OPSEK). The modules under consideration for removal from the current ISS include the [[Multipurpose Laboratory Module]] (MLM), currently scheduled to be launched in 2017, with other Russian modules which are currently planned to be attached to the MLM afterwards. Neither the MLM nor any additional modules attached to it would have reached the end of their useful lives in 2016 or 2020. The report presents a statement from an unnamed Russian engineer who believes that, based on the experience from ''Mir'', a thirty-year life should be possible, except for micrometeorite damage, because the Russian modules have been built with on-orbit refurbishment in mind.<ref name="RussiaSave">{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8064060.stm|title=Russia 'to save its ISS modules'|work=BBC News|date=22 May 2009|accessdate=23 May 2009|author=Anatoly Zak}}</ref>

According to the [[Outer Space Treaty]] the United States and Russia are legally responsible for all modules they have launched.<ref>[http://www.unoosa.org/pdf/publications/STSPACE11E.pdf United Nations Treaties and Principles on Outer Space]. (PDF). United Nations. New York. 2002. ISBN 92-1-100900-6. Retrieved 8 October 2011.</ref> In ISS planning, NASA examined options including returning the station to Earth via shuttle missions (deemed too expensive, as the station (USOS) is not designed for disassembly and this would require at least 27 shuttle missions<ref>{{cite book|url=http://search.nap.edu/openbook.php?record_id=9794&page=28|isbn=0-309-06938-6|publisher=National Academies Press|year=2000|pages=28–30|author=Thomas Kelly|title=Engineering Challenges to the Long-Term Operation of the International Space Station|accessdate=12 July 2011}}</ref>), natural orbital decay with random reentry similar to [[Skylab]], boosting the station to a higher altitude (which would delay reentry) and a controlled targeted de-orbit to a remote ocean area.<ref name=ISSEIS>{{cite web|title = Tier 2 EIS for ISS|publisher = NASA|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960053133_1996092350.pdf|accessdate=12 July 2011 }}</ref>

The technical feasibility of a controlled targeted deorbit into a remote ocean was found to be possible only with Russia's assistance.<ref name=ISSEIS /> The Russian Space Agency has experience from de-orbiting the [[Salyut 4]], [[Salyut 5|5]], [[Salyut 6|6]], [[Salyut 7|7]] and [[Mir]] space stations; NASA's first intentional controlled de-orbit of a satellite (the [[Compton Gamma Ray Observatory]]) occurred in 2000.<ref>{{cite web|title=Entry Debris Field estimation methods and application to Compton Gamma Ray Observatory|publisher=Mission Operations Directorate, NASA Johnson Space Center|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010084992_2001127597.pdf|accessdate=12 July 2011}}</ref> As of late 2010, the preferred plan is to use a slightly modified Progress spacecraft to de-orbit the ISS.<ref name=deo>{{cite web|url=http://www.nasa.gov/pdf/578543main_asap_eol_plan_2010_101020.pdf|title=ISS End-of-Life Disposal Plan|last=Suffredini|first=Michael|date=October 2010|publisher=NASA|accessdate=7 March 2012}}</ref> This plan was seen as the simplest, most cost efficient one with the highest margin.<ref name=deo /> [[Skylab]], the only space station built and launched entirely by the US, decayed from orbit slowly over 5 years, and no attempt was made to de-orbit the station using a [[Atmospheric entry|deorbital burn]]. Remains of Skylab hit populated areas of [[Esperance, Western Australia]]<ref name="debris">{{cite web|url=http://www.eclipsetours.com/sat/debris.html|accessdate=28 May 2011|title=Paul Maley's (Skylab spaceflight controller) Space Debris Page}}</ref> without injuries or loss of life.

The [[Exploration Gateway Platform]], a discussion by NASA and Boeing at the end of 2011, suggested using leftover USOS hardware and '[[Zvezda (ISS module)|Zvezda]] 2' {{sic}} as a refuelling depot and servicing station located at one of the Earth Moon [[Lagrange points]], L1 or L2. The entire USOS cannot be reused and will be discarded, but some other Russian modules are planned to be reused. [[Nauka (ISS module)|Nauka]], the [[Uzlovoy Module|Node module]], two science power platforms and Rassvet, launched between 2010 and 2015 and joined to the ROS may be separated to form [[OPSEK]].<ref>{{cite web|url=http://www.russianspaceweb.com/iss_dc.html|title=DC-1 and MIM-2|publisher=Russianspaceweb.com|accessdate=12 July 2011}}</ref> The [[Nauka (ISS module)|Nauka module]] of the ISS will be used in the station, whose main goal is supporting manned deep space exploration. OPSEK will orbit at a higher inclination of 71 degrees, allowing observation to and from all of the Russian Federation.

In February 2015, Roscosmos announced that it would remain a part of the international space station program until 2024.<ref name=sn20150225>{{cite news |last1=de Selding|first1=Peter B. |title=Russia — and Its Modules — To Part Ways with ISS in 2024 |url=http://spacenews.com/russia-and-its-modules-to-part-ways-with-iss-in-2024/ |accessdate=26 February 2015 |work=Space News |date=25 February 2015}}</ref> Nine months earlier—in response to US sanctions against Russia over the [[2014 Crimean crisis|conflict in the Crimea]]—Russian Deputy Prime Minister [[Dmitry Rogozin]] had stated that Russia would reject a US request to prolong the orbiting station's use beyond 2020, and would only supply rocket engines to the US for non-military satellite launches.<ref>{{cite web|url=http://www.telegraph.co.uk/news/worldnews/europe/russia/10828964/Russia-to-ban-US-from-using-Space-Station-over-Ukraine-sanctions.html|title=Russia to ban US from using Space Station over Ukraine sanctions|agency=Reuters|work=The Telegraph|date=13 May 2014|accessdate=14 May 2014}}</ref>

A proposed modification that would allow some of the ISS American and European segments to be reused would be to attach a [[VASIMR]] drive module to the vacated Node with its own onboard power source. It would allow long term reliability testing of the concept for less cost than building a dedicated space station from scratch.<ref name="nbcnews">{{cite web|url=http://www.nbcnews.com/id/48260759/ns/technology_and_science-space/#.U4LaQCjFBdg|title=From the earth to the moon, and then beyond - Technology & science - Space | NBC News|publisher=nbcnews.com|accessdate=27 May 2014}}</ref>

On March 28, 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS.<ref name=":0"/><ref name=":1"/> [[Igor Komarov]], the head of Russia's Roscosmos, made the announcement with NASA administrator Charles Bolden at his side. Komarov said "Roscosmos together with NASA will work on the programme of a future orbital station," "We agreed that the group of countries taking part in the ISS project will work on the future project of a new orbital station," "The first step is that the ISS will operate until 2024," and that Roscosmos and NASA "do not rule out that the station's flight could be extended,"<ref>{{cite web|url=http://www.spacedaily.com/reports/Russia_announces_plan_to_build_new_space_station_with_NASA_999.html|title=Russia announces plan to build new space station with NASA|work=spacedaily.com}}</ref> In a statement provided to SpaceNews March 28, NASA spokesman David Weaver said the agency appreciated the Russian commitment to extending the ISS, but did not confirm any plans for a future space station.<ref name="no plans" />

==Cost==
The ISS is arguably the most expensive single item ever constructed.<ref>{{cite web|author=Zidbits |url=http://zidbits.com/?p=19 |title=What Is The Most Expensive Object Ever Built? |publisher=Zidbits.com |date=6 November 2010 |accessdate=22 October 2013}}</ref> In 2010 the cost was expected to be $150 billion. It includes NASA's budget of $58.7 billion (inflation unadjusted) for the station from 1985 to 2015 ($72.4 billion in 2010 dollars), Russia's $12 billion, Europe's $5 billion, Japan's $5 billion, Canada's $2 billion, and the cost of 36 shuttle flights to build the station; estimated at $1.4 billion each, or $50.4 billion total. Assuming 20,000 person-days of use from 2000 to 2015 by two to six-person crews, each person-day would cost $7.5 million, less than half the inflation adjusted $19.6 million ($5.5 million before inflation) per person-day of Skylab.<ref name="lafleur20100308">{{cite news | url=http://www.thespacereview.com/article/1579/1 | title=Costs of US piloted programs | work=The Space Review | date=8 March 2010 | accessdate=18 February 2012 | author=Lafleur, Claude}} See author correction in comments.</ref>

==International co-operation==
[[File:ISS Agreements.jpg|thumb|right|upright|Dated 29 January 1998]]
{{Main|Politics of the International Space Station|International Space Station program}}
;Participating countries
{{columns-list|colwidth=20em|

* '''{{flagcountry|Canada}}'''
* '''{{flagcountry|Japan}}'''
* '''{{flagcountry|Russia}}'''
* '''{{flagcountry|United States}}'''
* [[File:ESA logo simple.svg|15x15px]] '''[[European Space Agency]]'''
** {{flagcountry|Austria}}
** {{flagcountry|Belgium}}
** {{flagcountry|Czech Republic}}
** {{flagcountry|Denmark}}
** {{flagcountry|Estonia}}
** {{flagcountry|Finland}}
** {{flagcountry|France}}
** {{flagcountry|Germany}}
** {{flagcountry|Greece}}
** {{flagcountry|Hungary}}
** {{flagcountry|Ireland}}
** {{flagcountry|Italy}}
** {{flagcountry|Luxembourg}}
** {{flagcountry|Netherlands}}
** {{flagcountry|Norway}}
** {{flagcountry|Poland}}
** {{flagcountry|Portugal}}
** {{flagcountry|Romania}}
** {{flagcountry|Spain}}
** {{flagcountry|Sweden}}
** {{flagcountry|Switzerland}}
** {{flagcountry|United Kingdom}}
}}

==Sightings from Earth==

===Naked eye===
The ISS is visible to the [[naked eye]] as a slow-moving, bright white dot due to reflected sunlight, and can be seen in the hours after sunset and before sunrise when the station remains sunlit but the ground and sky are dark.<ref name="Price2005">{{cite book |title=The Backyard Stargazer: An Absolute Beginner's Guide to Skywatching With and Without a Telescope |publisher=Quarry Books |location=Gloucester, MA |first=Pat |last=Price |page=140 |year=2005 |isbn=1-59253-148-2}}</ref> The ISS takes about ten minutes to move from one horizon to another, and will only be visible part of that time due to moving into or out of the Earth's shadow. Because of the size of its reflective surface area, the ISS is the brightest man-made object in the sky excluding [[Satellite flare|flares]], with an approximate maximum [[Apparent magnitude|magnitude of −4]] when overhead, similar to Venus. The ISS, like many satellites including the [[Iridium constellation]], can also produce flares of up to 8 or 16 times the brightness of Venus as sunlight glints off reflective surfaces.<ref>{{cite web|url=http://www.calsky.com/cs.cgi/Satellites/8 |title=Artificial Satellites > (Iridium) Flares |publisher=Calsky.com |accessdate=1 May 2012}}</ref><ref name="haydenplanetarium">{{cite web|url=http://www.amnh.org/our-research/hayden-planetarium/blog/how-to-spot-the-international-space-station-and-other-satellites |title=How to Spot the International Space Station (and other satellites) |publisher=Hayden Planetarium |accessdate=12 July 2011}}</ref> The ISS is also visible during broad daylight conditions, albeit with a great deal more effort.

Tools are provided by a number of websites such as [[Heavens-Above]] (see [[#Live viewing|''Live viewing'']] below) as well as [[smartphone]] applications that use the known [[ephemeris|orbital data]] and the observer's longitude and latitude to predict when the ISS will be visible (weather permitting), where the station will appear to rise to the observer, the altitude above the horizon it will reach and the duration of the pass before the station disappears to the observer either by setting below the horizon or entering into Earth's shadow.<ref name="see">{{cite web|url=http://spaceflight.nasa.gov/realdata/sightings/index.html|title=International Space Station Sighting Opportunities|accessdate=28 January 2009|publisher=NASA|date=2 July 2008|author=NASA}}</ref><ref>{{cite web|url=http://www.heavens-above.com/satinfo.aspx?satid=25544&lat=0&lng=0&loc=Unspecified&alt=0&tz=CET|title=ISS – Information|publisher=Heavens-Above.com|accessdate=8 July 2010}}</ref><ref>{{cite journal|author=Harold F. Weaver|title=The Visibility of Stars Without Optical Aid|journal=Publications of the Astronomical Society of the Pacific|volume=59|issue=350|year=1947|doi=10.1086/125956 }}</ref><ref name="daytime visibility">{{cite web|url=http://spaceweather.com/archive.php?view=1&day=05&month=06&year=2009|title=ISS visible during the daytime|accessdate=5 June 2009|work=Spaceweather.com|date=5 June 2009}}</ref>

{{Double image|right|Isshtv120090917200858nm.jpg|223|ISS 2008-01-10.jpg|230|The ISS and HTV photographed using a telescope-mounted camera by [[Ralf Vandebergh]]|A time exposure of a station pass|A fuzzy image of the ISS set against a black background, with a smaller, cylindrical object visible to the left of the station.|A view of a dark blue, starry sky with a white line visible from the bottom-left to the top-right of the image. A tree is visible to the bottom right.}}

In November 2012 NASA launched its 'Spot the Station' service, which sends people text and email alerts when the station is due to fly above their town.<ref>{{cite news| url= http://www.3news.co.nz/Get-notified-when-the-International-Space-Station-is-in-your-area/tabid/1160/articleID/275612/Default.aspx|work=3 News NZ |title= Get notified when the International Space Station is in your area| date=6 November 2012}}</ref>

The station is visible from 95% of the inhabited land on Earth, but is not visible from extreme northern or southern latitudes.<ref name="MCC Answer" />

===Astrophotography=== 
Using a telescope mounted camera to photograph the station is a popular hobby for astronomers, <ref>{{cite web|url=http://www.hobbyspace.com/SatWatching/ |title=Satellite Watching |publisher=HobbySpace |accessdate=1 May 2012}}</ref> whilst using a mounted camera to photograph the Earth and stars is a popular hobby for crew.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2003/24mar_noseprints/ |title=Space StationAstrophotography – NASA Science |publisher=Science.nasa.gov |date=24 March 2003 |accessdate=1 May 2012}}</ref> The use of a telescope or binoculars allows viewing of the ISS during daylight hours.<ref>{{cite web|url=http://www.zmescience.com/space/video-the-iss-and-atlantis-shuttle-as-seen-in-broad-daylight/ |title=[VIDEO] The ISS and Atlantis shuttle as seen in broad daylight |publisher=Zmescience.com |date=20 July 2011 |accessdate=1 May 2012}}</ref>

Parisian engineer and astrophotographer Thierry Legault, known for his photos of spaceships crossing the Sun (called [[occultation]]), travelled to Oman in 2011, to photograph the Sun, moon and space station all lined up.<ref>{{cite news| url=http://www.wired.com/2011/01/double-eclipse/ | work=Wired | first=Lisa | last=Grossman | title=Moon and Space Station Eclipse the Sun}}</ref> Legault, who received the Marius Jacquemetton award from the [[Société astronomique de France]] in 1999, and other hobbyists, use websites that predict when the ISS will pass in front of the Sun or Moon and from what location those passes will be visible.

==See also==
{{Wikipedia books|International Space Station}}
{{Portal|Spaceflight|Space}}
* [[Center for the Advancement of Science in Space]] - operates the US National Laboratory on the ISS
* [[List of space stations]]
* [[Origins of the International Space Station]]
* [[Space architecture]]

==Gallery==
[[File:ISS and Endeavour seen from the Soyuz TMA-20 spacecraft 14.jpg|thumb|left|550px|<center>International Space Station docked with ''Endeavour'' and ''Johannes Kepler'' ]]
{{-}}

==Notes==
{{Reflist|group="note"}}

==References==
{{Reflist|colwidth=25em}}

==External links==
{{Sister project links|wikt=no|n=Category:International Space Station|voy=Space}}

===Agency ISS websites===
{{divcol|20em}}
* {{flagicon|Canada}} [http://www.asc-csa.gc.ca/eng/iss/default.asp Canadian Space Agency]
* [[File:Not the esa logo.png]] [http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station European Space Agency]
* {{flagicon|France}} [http://www.cnes.fr/web/CNES-en/1422-iss-the-international-space-station.php Centre national d'études spatiales (National Centre for Space Studies)]
* {{flagicon|Germany}} [http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10300 German Aerospace Centre]
* {{flagicon|Italy}} [http://www.asi.it/en/flash_en/living Italian Space Agency]
* {{flagicon|Japan}} [http://www.jaxa.jp/projects/iss_human/index_e.html Japan Aerospace Exploration Agency]
* {{flagicon|Russia}} [http://www.energia.ru/eng/iss/iss.html S.P. Korolev Rocket and Space Corporation Energia]
* {{flagicon|Russia}} [http://www.roscosmos.ru/ Russian Federal Space Agency]
* {{flagicon|USA}} [http://www.nasa.gov/mission_pages/station/main/ National Aeronautics and Space Administration]
{{Div col end}}

===Research===
* [https://blogs.nasa.gov/spacestation/ NASA: Daily ISS Reports]
* [http://www.nasa.gov/mission_pages/station/science/index.html NASA: Station Science]
* [http://www.esa.int/Our_Activities/Human_Spaceflight/Columbus ESA: Columbus]
* [http://www.energia.ru/en/iss/researches/iss-researches.html RSC Energia: Science Research on ISS Russian Segment]

===Live viewing===
{{See also|List of satellite pass predictors}}
* [http://www.ustream.tv/channel/live-iss-stream Live ISS webcam] by NASA at uStream.tv
* [http://heavens-above.com/orbit.aspx?satid=25544 Real-time position] at Heavens-above.com
* [http://www.n2yo.com/?s=25544 Real-time position] at N2YO.com
* [http://wheretheiss.at/ Real-time position] at WheretheISS.at

===Multimedia===
* [http://www.nasa.gov/externalflash/ISSRG/index.html Interactive reference guide] at NASA.gov
* [http://spaceflight.nasa.gov/gallery/images/station/ Image gallery search page] at NASA.gov
* [http://i.usatoday.net/tech/graphics/iss_timeline/flash.htm Assembly sequence animation] by ''USA Today'' and NASA
* [https://www.youtube.com/watch?v=doN4t5NKW-k ISS tour with Sunita Williams] by NASA at YouTube.com
* [https://www.youtube.com/watch?v=QF2w2Dx_QMs ISS tour with André Kuipers] by ESA at YouTube.com
* [http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station/Highlights/International_Space_Station_panoramic_tour ISS photo tour with Samantha Cristoforetti] by ESA
* [https://www.youtube.com/watch?v=vMmcLmu3V1k ''The Future of Hope'', Kibo module documentary] by JAXA at YouTube.com
* [https://www.youtube.com/playlist?list=PLbyvawxScNbsoD_tGlw8kWCw3S5htiVKZ Journey to the ISS] by ESA at YouTube.com

{{ISS modules}}
{{International Space Station}}
{{Manned ISS flight}}
{{Unmanned ISS resupply flights}}
{{People currently in space}}
{{Space stations}}
{{US manned space programs}}
{{Russian manned space programs}}
{{European manned spaceflight}}
{{Spaceflight}}
{{Orbital launches in 1998}}

{{Orbit|satcat|25544|hide}}{{Orbit|datasource|HN}}
{{active editnotice}}

{{Authority control}}
[[Category:International Space Station| ]]
[[Category:Artificial satellites orbiting Earth]]
[[Category:Populated places established in 1998]]
[[Category:United States Department of Energy national laboratories]]
[[Category:Spacecraft launched in 1998]]
[[Category:1998 in spaceflight]]
[[Category:Articles containing video clips]]

User:WikipediaTutorials/sandbox

2015-08-25T01:30:14Z

WikipediaTutorials:

{{redirect|ISS}}
{{Use British English|date=December 2013}}
{{Use dmy dates|date=February 2015}}
{{Infobox space station
| station = International Space Station
| station_image =International Space Station after undocking of STS-132.jpg
| station_image_alt = A rearward view of the International Space Station backdropped by the limb of the Earth. In view are the station's four large, gold-coloured solar array wings, two on either side of the station, mounted to a central truss structure. Further along the truss are six large, white radiators, three next to each pair of arrays. In between the solar arrays and radiators is a cluster of pressurised modules arranged in an elongated T shape, also attached to the truss. A set of blue solar arrays are mounted to the module at the aft end of the cluster.
| station_image_size = 300px
| extra_image_size = 300px
| extra_image_caption = The International Space Station on 23 May 2010 as seen from the departing {{OV|104}} during [[STS-132]].
| sign = ''Alpha'', ''Station''
| crew = Fully crewed: 6 Currently aboard: 6 ([[Expedition 44]])
| launch = 20 November 1998
| launch_pad = {{nowrap|[[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|1/5]] and [[Baikonur Cosmodrome Site 81|81/23]] [[Kennedy Space Center|Kennedy]] [[Kennedy Space Center Launch Complex 39|LC-39]]}}
| mass = Approximately {{convert|450000|kg|lbs|abbr=on}}
| length = {{convert|72.8|m|ft|abbr=on}}
| width = {{convert|108.5|m|ft|abbr=on}}
| height = c. 20 m (c. 66 ft) nadir–zenith, arrays forward–aft (27 November 2009){{Update after|2010|05|23|reason=MRM-1 & MRM-2}}
| volume = {{convert|916|m3|abbr=on}} (3 November 2014)
| pressure = 101.3 [[pascal (unit)|kPa]] (29.91 [[inch of mercury|inHg]], 1 [[Atmosphere (unit)|atm]])
| apogee = {{convert|{{Orbit|apogee|416}}|km|abbr=on}} [[Above mean sea level|AMSL]]{{Orbit|ref|<ref name="heavens-above">{{cite web|url=http://www.heavens-above.com/orbit.aspx?satid=25544|title=ISS - Orbit|last=Peat|first=Chris|publisher=Heavens-Above|date=25 January 2015|accessdate=25 January 2015}}</ref>}}
| perigee = {{convert|{{Orbit|perigee|409}}|km|abbr=on}} [[Above mean sea level|AMSL]]{{Orbit|ref|<ref name="heavens-above"/>}}
| inclination = {{Orbit|inclination|51.65}} [[degree (angle)|degrees]]{{Orbit|ref|<ref name="heavens-above"/>}}
| speed = {{convert|{{Orbit|speed at epoch|7.66}}|km/s|km/h mph}}{{Orbit|ref|<ref name="heavens-above"/>}}
| period = {{Orbit|period|92.69}} minutes{{Orbit|ref|<ref name="heavens-above"/>}}
| in_orbit = {{age in days|1998|11|20}} ({{date||dmy}})
| occupied = {{age in days|2000|11|02}} ({{date||dmy}})
| orbits = {{Orbit|orbits|92579}}{{Orbit|ref|<ref name="heavens-above"/>}}
| orbit_epoch = {{Orbit|epoch|25 January 2015}}{{Orbit|ref|<ref name="heavens-above"/>}}
| decay = 2 km/month
| NSSDC_ID = 1998-067A
| as_of = 9 March 2011 (unless noted otherwise)
| stats_ref =<ref name="heavens-above" /><ref name="ISStD" /><ref name="OnOrbit" /><ref>{{cite web|format=PDF|url=http://www.nasa.gov/pdf/451029main_sts132_press_kit.pdf|publisher=NASA|accessdate=19 June 2010|title=STS-132 Press Kit|date=7 May 2010}}</ref><ref>{{cite web|url=http://www.nasa.gov/pdf/521138main_fd04_ep.pdf|publisher=NASA|date=27 February 2011|accessdate=27 February 2011|title=STS-133 FD 04 Execute Package}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html|publisher=NASA|date=3 November 2014|accessdate=5 December 2014|title=NASA — Facts and Figures — International Space Station}}</ref>
| configuration_image = ISS configuration 2011-05 en.svg
| configuration_alt = The components of the ISS in an exploded diagram, with modules on-orbit highlighted in orange, and those still awaiting launch in blue or pink
| configuration_caption = Station elements {{As of|2011|12|lc=on}}, but missing ''Pirs'' ([[exploded view]])
| configuration_size = 300px
}}

The '''International Space Station''' ('''ISS''') is a [[space station]], or a habitable [[satellite|artificial satellite]], in [[low Earth orbit]]. Its first component launched into orbit in 1998, and the ISS is now the largest artificial body in orbit and can often be seen with the [[naked eye]] from Earth.<ref>{{cite web|title= Central Research Institute for Machine Building (FGUP TSNIIMASH) Control of manned and unmanned space vehicles from Mission Control Centre Moscow |publisher= Russian Federal Space Agency |url=ftp://130.206.92.88/Espacio/Mesa%20Redonda%205%20-%20R3%20-%20TSNIIMASH%20-%20V%20M%20IVANOV.pdf| accessdate=26 September 2011}}</ref><ref>{{cite web|url=http://spaceflight.nasa.gov/realdata/sightings/help.html |title=NASA Sightings Help Page |publisher=Spaceflight.nasa.gov |date=30 November 2011 |accessdate=1 May 2012}}</ref> The ISS consists of pressurised modules, external trusses, [[solar arrays]] and other components. ISS components have been launched by Russian [[Proton (rocket)|Proton]] and [[Soyuz (rocket family)|Soyuz]] rockets as well as American [[Space Shuttle]]s.<ref name="ISSBook">{{cite book|isbn=978-0-387-78144-0|date=17 June 2008|publisher=Springer-Praxis|author=John E. Catchpole|title=The International Space Station: Building for the Future}}</ref>

The ISS serves as a [[microgravity]] and [[space environment]] research laboratory in which crew members conduct experiments in [[biology]], [[human biology]], [[physics]], [[astronomy]], [[meteorology]] and [[Scientific research on the ISS|other fields]].<ref name="ISS overview">{{cite web|url=http://www.shuttlepresskit.com/ISS_OVR/index.htm|title=International Space Station Overview|publisher=ShuttlePressKit.com|date=3 June 1999|accessdate=17 February 2009}}</ref><ref name="NASA Fields of Research">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/A-fieldsresearch/index.html|archiveurl=https://web.archive.org/web/20080123150641/http://pdlprod3.hosc.msfc.nasa.gov/A-fieldsresearch/index.html|archivedate=25 March 2008|title=Fields of Research|date=26 June 2007|publisher = NASA}}</ref><ref name="NASA ISS Goals">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/B-gettingonboard/index.html|archiveurl=https://web.archive.org/web/20071208091537/http://pdlprod3.hosc.msfc.nasa.gov/B-gettingonboard/index.html|archivedate=8 December 2007| title = Getting on Board|date = 26 June 2007| publisher=NASA}}</ref> The station is suited for the testing of spacecraft systems and equipment required for missions to the Moon and Mars.<ref name="ResProg">{{cite web|url=http://spaceflightsystems.grc.nasa.gov/Advanced/ISSResearch/|title=ISS Research Program|publisher=NASA|accessdate=27 February 2009}}{{dead link|date=August 2011}}</ref> The ISS [[Orbital station-keeping|maintains an orbit with an altitude]] of between {{convert|330|and|435|km|mi|0|abbr=on}} by means of reboost manoeuvres using the engines of the [[Zvezda (ISS module)|Zvezda module]] or visiting spacecraft. It completes {{Orbit|daily orbits|15.54}} orbits per day.<ref name="tracking" />

ISS is the ninth space station to be inhabited by crews, following the Soviet and later Russian [[Salyut]], [[Almaz]], and [[Mir]] stations as well as [[Skylab]] from the US. The station has been continuously occupied for {{age in years and days|2 Nov 2000|sep=and}} since the arrival of [[Expedition 1]] on 2 November 2000. This is the longest continuous human presence in space, having surpassed the previous record of {{age in years and days|5 Sep 1989|28 Aug 1999|sep=and}} held by Mir. The station is serviced by a variety of visiting spacecraft: [[Soyuz (spacecraft)|Soyuz]], [[Progress (spacecraft)|Progress]], the [[Automated Transfer Vehicle]], the [[H-II Transfer Vehicle]],<ref name="ISSRG" /> [[Dragon (spacecraft)|Dragon]], and [[Cygnus (spacecraft)|Cygnus]]. It has been visited by astronauts, cosmonauts and space tourists from [[List of International Space Station visitors|15 different nations]].<ref name="10th">{{cite web|url=http://www.nasa.gov/mission_pages/station/main/10th_anniversary.html|title=Nations Around the World Mark 10th Anniversary of International Space Station|publisher=NASA|date=17 November 2008|accessdate=6 March 2009}}</ref>

After the US Space Shuttle program ended in 2011, Soyuz rockets became the only provider of transport for astronauts at the International Space Station, and Dragon became the only provider of bulk [[downmass|cargo-return-to-Earth]] services (downmass capability of Soyuz capsules is very limited).

The [[International Space Station program|ISS programme]] is a joint project among five participating space agencies: [[NASA]], [[Russian Federal Space Agency|Roscosmos]], [[Japan Aerospace Exploration Agency|JAXA]], [[European Space Agency|ESA]], and [[Canadian Space Agency|CSA]].<ref name="ISSRG" /><ref name="PartStates">{{cite web|url=http://www.esa.int/esaHS/partstates.html|title=Human Spaceflight and Exploration—European Participating States|accessdate=17 January 2009|publisher=European Space Agency (ESA)|year=2009}}</ref> The ownership and use of the space station is established by intergovernmental treaties and agreements.<ref name="ESA-IGA">{{cite web|url=http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station/International_Space_Station_legal_framework|title=International Space Station legal framework|publisher=European Space Agency (ESA)|accessdate=21 February 2015|date=19 November 2013}}</ref> The station is divided into two sections, the [[Russian Orbital Segment]] (ROS) and the [[US Orbital Segment|United States Orbital Segment]] (USOS), which is shared by many nations. {{asof|2014|January}}, the American portion of ISS was funded until 2024.<ref>{{cite web|url=http://www.washingtonpost.com/national/health-science/nasa-space-station-operation-extended-by-obama-until-2024-at-least/2014/01/08/9819d5c8-788e-11e3-8963-b4b654bcc9b2_story.html|title=NASA: International space station operation extended by Obama until at least 2024|last=Achenbach|first=Joel|publisher=washingtonpost.com|date=8 January 2014|accessdate=8 January 2014}}</ref><ref>{{cite web|url=http://spaceflightnow.com/news/n1003/11station/|title=Space station partners set 2028 as certification goal|last=Clark|first=Stephen|date=11 March 2010|publisher=Spaceflight Now|accessdate=1 June 2011}}</ref><ref>{{cite news| url=http://www.cbc.ca/news/technology/story/2012/02/29/science-international-space-station.html | work=CBC News | title=Canada's space station commitment renewed | date=29 February 2012}}</ref> Roscosmos has endorsed the continued operation of ISS through 2024,<ref name="sn20150225"/> but have proposed using elements of the Russian Orbital Segment to construct a new Russian space station called [[Orbital Piloted Assembly and Experiment Complex|OPSEK]].<ref name="moscow20141117">{{cite news |url=http://www.themoscowtimes.com/business/article/russia-may-be-planning-national-space-station-to-replace-iss/511299.html |title=Russia May Be Planning National Space Station to Replace ISS |work=The Moscow Times |first=Matthew |last=Bodner |date=17 November 2014 |accessdate=3 March 2015}}</ref>

On March 28, 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS.<ref name=":0">{{cite web|url= http://www.independent.co.uk/news/science/russia-and-the-us-will-build-a-new-space-station-together-10140890.html|title=Russia and the US will build a new space station together |publisher=The Independent|date=28 March 2015}}</ref><ref name=":1">{{Cite news|url = http://rt.com/news/244797-russia-us-new-space-station/|title = Russia & US agree to build new space station after ISS, work on joint Mars project|last = |first = |date = March 28, 2015|work = RT|access-date = March 28, 2015}}</ref> NASA later issued a guarded statement expressing thanks for Russia's interest in future cooperation in space exploration, but fell short of confirming the Russian announcement.<ref>{{Cite news|url = http://www.engadget.com/2015/03/28/nasa-is-working-with-russia-on-a-new-space-station/|title = NASA is working with Russia on a new space station (update: not quite) |last = Moon|first = Mariella|date = 28 March 2015|work = Engadget|access-date = 29 March 2015}}</ref><ref name="no plans">{{cite web|url=http://spacenews.com/nasa-says-no-plans-for-iss-replacement-with-russia/|title=NASA Says No Plans for ISS Replacement with Russia|date=March 28, 2015|author=Jeff Foust|publisher=SpaceNews}}</ref>

{{TOC limit|limit=3}}

==Purpose==
[[File:STS-129 Zvezda sunrise.jpg|thumb|Sunrise at ''Zvezda'']]
[[File:STS-134 EVA4 view to the Space Shuttle Endeavour.jpg|thumb|right|Fisheye view of several labs]]
According to the original Memorandum of Understanding between NASA and Rosaviakosmos, the International Space Station was intended to be a laboratory, observatory and factory in [[low Earth orbit]]. It was also planned to provide transportation, maintenance, and act as a staging base for possible future missions to the Moon, Mars and asteroids.<ref name="RSA-MOU">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/nasa_rsa.html|title=Memorandum of Understanding Between the National Aeronautics and Space Administration of the United States of America and the Russian Space Agency Concerning Cooperation on the Civil International Space Station|publisher=NASA|accessdate=19 April 2009|date=29 January 1998}}</ref> In the 2010 United States National Space Policy, the ISS was given additional roles of serving commercial, diplomatic<ref>{{cite journal|last=Payette|first=Julie|title=Research and Diplomacy 350 Kilometers above the Earth: Lessons from the International Space Station|journal=Science & Diplomacy|date=10 December 2012|volume=1|issue=4|url=http://www.sciencediplomacy.org/article/2012/research-and-diplomacy-350-kilometers-above-earth}}</ref> and educational purposes.<ref name=USNSP>{{cite web|title=National Space Policy of the United States of America|url=http://www.whitehouse.gov/sites/default/files/national_space_policy_6-28-10.pdf|publisher=White House; USA Federal government|accessdate=20 July 2011}}</ref>

===Scientific research===
{{Main|Scientific research on the ISS|l1=Scientific research on the ISS}}
The ISS provides a platform to conduct scientific research. Small unmanned spacecraft can provide platforms for zero gravity and exposure to space, but space stations offer a long term environment where studies can be performed potentially for decades, combined with ready access by human researchers over periods that exceed the capabilities of manned spacecraft.<ref name="10th" /><ref name="Worldbook at NASA" />

The Station simplifies individual experiments by eliminating the need for separate rocket launches and research staff. The wide variety of research fields include [[astrobiology]], [[astronomy]], [[Zero g#Health effects of weightlessness|human research]] including [[space medicine]] and [[life science]]s, [[physical science]]s, [[materials science]], [[space weather]], and weather on Earth ([[meteorology]]).<ref name="ISS overview" /><ref name="NASA Fields of Research" /><ref name="NASA ISS Goals" /><ref>{{cite web|url=http://www.isas.jaxa.jp/e/forefront/2009/ueno/index.shtml|title=Monitor of All-sky X-ray Image (MAXI)|year=2008|publisher=JAXA|accessdate=12 March 2011}}</ref><ref>[http://www.spaceref.com/news/viewpr.html?pid=33007 ESA via SPACEREF] "SOLAR: three years observing and ready for solar maximum", 14 March 2011</ref> Scientists on Earth have access to the crew's data and can modify experiments or launch new ones, which are benefits generally unavailable on unmanned spacecraft.<ref name="Worldbook at NASA" /> Crews fly [[List of International Space Station expeditions|expeditions]] of several months duration, providing approximately 160-man-hours per week of labour with a crew of 6.<ref name="ISS overview"/><ref name="Science in School">{{cite web|url=http://www.scienceinschool.org/2008/issue10/iss|title=The International Space Station: life in space|publisher=Science in School|date=10 December 2008|accessdate=17 February 2009}}</ref>

To detect dark matter and answer other fundamental questions about our universe, engineers and scientists from all over the world built the [[Alpha Magnetic Spectrometer]] (AMS), which NASA compares to the [[Hubble space telescope]], and says could not be accommodated on a free flying satellite platform due in part to its power requirements and data bandwidth needs.<ref>[http://www.nasa.gov/mission_pages/shuttle/main/amsprocessing.html NASA – AMS to Focus on Invisible Universe]. Nasa.gov (18 March 2011). Retrieved 8 October 2011.</ref><ref>[http://science.nasa.gov/science-news/science-at-nasa/2009/14aug_ams/ In Search of Antimatter Galaxies – NASA Science]. ''Science''.nasa.gov (16 May 2011). Retrieved 8 October 2011.</ref> On 3 April 2013, [[NASA]] scientists reported that hints of [[dark matter]] may have been detected by the Alpha Magnetic Spectrometer.<ref name="APS-20130403">{{cite journal |authors=Aguilar, M. et al. (AMS Collaboration) |title=First Result from the Alpha Magnetic Spectrometer on the International Space Station: Precision Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–350 GeV|url=http://prl.aps.org/abstract/PRL/v110/i14/e141102 |date=3 April 2013 |journal=[[Physical Review Letters]]|accessdate=3 April 2013 |doi=10.1103/PhysRevLett.110.141102 }}</ref><ref name="AMS-20130403">{{cite web |author=Staff |title=First Result from the Alpha Magnetic Spectrometer Experiment|url=http://www.ams02.org/2013/04/first-results-from-the-alpha-magnetic-spectrometer-ams-experiment/ |date=3 April 2013 |work=AMS Collaboration |accessdate=3 April 2013 }}</ref><ref name="AP-20130403">{{cite news |last1=Heilprin|first1=John |last2=Borenstein |first2=Seth |title=Scientists find hint of dark matter from cosmos|url=http://apnews.excite.com/article/20130403/DA5E6JAG3.html |date=3 April 2013 |agency=Associated Press |accessdate=3 April 2013 }}</ref><ref name="BBC-20130403">{{cite news |last=Amos |first=Jonathan |title=Alpha Magnetic Spectrometer zeroes in on dark matter |url=http://www.bbc.co.uk/news/science-environment-22016504 |date=3 April 2013 |work=[[BBC News]] |accessdate=3 April 2013 }}</ref><ref name="NASA-20130403">{{cite web |last1=Perrotto|first1=Trent J. |last2=Byerly |first2=Josh |title=NASA TV Briefing Discusses Alpha Magnetic Spectrometer Results|url=http://www.nasa.gov/home/hqnews/2013/apr/HQ_M13-054_AMS_Findings_Briefing.html |date=2 April 2013|work=[[NASA]] |accessdate=3 April 2013 }}</ref><ref name="NYT-20130403">{{cite news |last=Overbye |first=Dennis |title=New Clues to the Mystery of Dark Matter |url=http://www.nytimes.com/2013/04/04/science/space/new-clues-to-the-mystery-of-dark-matter.html |date=3 April 2013 |work=[[The New York Times]] |accessdate=3 April 2013 }}</ref> According to the scientists, "[[Alpha Magnetic Spectrometer#First results|The first results]] from the space-borne Alpha Magnetic Spectrometer confirm an unexplained excess of high-energy positrons in Earth-bound cosmic rays."

{{Double image|right|Iss030e015472 Edit.jpg|117|ISS-08 Michael Foale conducts an inspection of the Microgravity Science Glovebox.jpg|241|[[C/2011 W3 (Lovejoy)|Comet Lovejoy]] photographed by [[Expedition 30]] commander [[Dan Burbank]]|[[Expedition 8]] Commander and Science Officer [[Michael Foale]] conducts an inspection of the [[Microgravity Science Glovebox]]}}
The space environment is hostile to life. Unprotected presence in space is characterised by an intense radiation field (consisting primarily of protons and other subatomic charged particles from the [[solar wind]], in addition to [[cosmic ray]]s), high vacuum, extreme temperatures, and microgravity.<ref name="Space Microbiology">{{cite web|url=http://syntheticbiology.arc.nasa.gov/files/SpaceMicrobiology%20MMBR%201.pdf|title=Space Microbiology, section Space Environment (p. 122)|publisher=Microbiology and Molecular Biology Reviews|date=March 2010|accessdate=4 June 2011|author=G Horneck, DM Klaus & RL Mancinelli}}</ref> Some simple forms of life called [[extremophile]]s,<ref name="Beer microbes">{{cite news|url=http://www.bbc.co.uk/news/science-environment-11039206|title=Beer microbes live 553 days outside ISS|work=[[BBC News]]|date=23 August 2010|accessdate=4 June 2011|author=Jonathan Amos}}</ref> including small invertebrates called [[tardigrade]]s<ref name="Waterbears">{{cite web|url=http://www.nature.com/news/2008/080908/full/news.2008.1087.html|title=Spacesuits optional for 'water bears'|work=Nature|date=8 September 2008|accessdate=4 June 2011}}</ref> can survive in this environment in an extremely dry state called [[Desiccation#Biology and ecology|desiccation]].

Medical research improves knowledge about the effects of long-term space exposure on the human body, including [[muscle atrophy]], [[Osteoporosis|bone loss]], and fluid shift. This data will be used to determine whether lengthy [[human spaceflight]] and [[space colonisation]] are feasible. As of 2006, data on bone loss and muscular atrophy suggest that there would be a significant risk of fractures and movement problems if astronauts landed on a planet after a lengthy interplanetary cruise, such as the six-month interval required to [[Manned mission to Mars|travel to Mars]].<ref name="JCB">{{cite book|author=Jay Buckey|title=Space Physiology|publisher=Oxford University Press USA|date=23 February 2006|isbn=978-0-19-513725-5}}</ref><ref>{{cite web|url=http://www.newscientist.com/article/dn17476-ion-engine-could-one-day-power-39day-trips-to-mars.html?full=true|work=New Scientist|accessdate=8 January 2010|date=24 July 2009|author=List Grossman|title=Ion engine could one day power 39-day trips to Mars}}</ref>
Medical studies are conducted aboard the ISS on behalf of the [[National Space Biomedical Research Institute]] (NSBRI). Prominent among these is the [[Advanced Diagnostic Ultrasound in Microgravity]] study in which astronauts perform ultrasound scans under the guidance of remote experts. The study considers the diagnosis and treatment of medical conditions in space. Usually, there is no physician on board the ISS and diagnosis of medical conditions is a challenge. It is anticipated that remotely guided ultrasound scans will have application on Earth in emergency and rural care situations where access to a trained physician is difficult.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/science/experiments/ADUM.html|date=1 May 2009|accessdate=1 October 2009|author=Brooke Boen|publisher=NASA|title=Advanced Diagnostic Ultrasound in Microgravity (ADUM)}}</ref><ref>{{cite journal|author=Sishir Rao|display-authors=etal|year=2008|title=A Pilot Study of Comprehensive Ultrasound Education at the Wayne State University School of Medicine|journal=Journal of Ultrasound in Medicine|volume=27|pages=745–749|pmid=18424650|issue=5}}</ref><ref>{{cite journal|author=Michael Fincke|display-authors=etal|year=2004|title=Evaluation of Shoulder Integrity in Space: First Report of Musculoskeletal US on the International Space Station|journal=Radiology|issue= 2|pages=319–322|pmid=15533948|doi=10.1148/radiol.2342041680|volume=234}}</ref>

====Microgravity====
[[File:Space Fire.jpg|thumb|A comparison between the combustion of a candle on [[Earth]] (left) and in a microgravity environment, such as that found on the ISS (right)]]
The Earth's gravity is only slightly weaker at the altitude of the ISS than at the surface, but objects in orbit are in a continuous state of [[Free fall|freefall]], resulting in an apparent state of weightlessness. This perceived weightlessness is disturbed by five separate effects:<ref name="gravity">{{cite web|url=http://www.esa.int/Our_Activities/Human_Spaceflight/Human_Spaceflight_Research/European_User_Guide_to_Low-Gravity_Platforms
|title=European Users Guide to Low Gravity Platforms|accessdate=22 March 2013|date=6 December 2005|publisher=European Space Agency}}</ref>
* Drag from the residual atmosphere; when the ISS enters the Earth's shadow, the main solar panels are rotated to minimise this aerodynamic drag, helping reduce [[orbital decay]].
* Vibration from movements of mechanical systems and the crew.
* Actuation of the on-board attitude [[control moment gyroscope]]s.
* [[Rocket engine|Thruster]] firings for attitude or orbital changes.
* [[Gravity-gradient stabilization|Gravity-gradient effects]], also known as [[tidal force|tidal]] effects. Items at different locations within the ISS would, if not attached to the station, follow slightly different orbits. Being mechanically interconnected these items experience small forces that keep the station moving as a [[rigid body]].

[[File:ISS-20 Robert Thirsk at the Minus Eighty Degree Laboratory Freezer.jpg|thumb|left|ISS crew member storing samples]]

Researchers are investigating the effect of the station's near-weightless environment on the evolution, development, growth and internal processes of plants and animals. In response to some of this data, NASA wants to investigate [[microgravity]]'s effects on the growth of three-dimensional, human-like tissues, and the unusual [[protein crystal]]s that can be formed in space.<ref name="NASA Fields of Research" />

The investigation of the physics of fluids in microgravity will allow researchers to model the behaviour of fluids better. Because fluids can be almost completely combined in microgravity, physicists investigate fluids that do not mix well on Earth. In addition, an examination of reactions that are slowed by low gravity and temperatures will give scientists a deeper understanding of [[superconductivity]].<ref name="NASA Fields of Research" />

The study of [[materials science]] is an important ISS research activity, with the objective of reaping economic benefits through the improvement of techniques used on the ground.<ref>{{cite web|url=http://science.nasa.gov/newhome/headlines/msad15sep99_1.htm|title=Materials Science 101|publisher=Science@NASA|accessdate=18 June 2009|date=15 September 1999}}</ref> Other areas of interest include the effect of the low gravity environment on combustion, through the study of the efficiency of burning and control of emissions and pollutants. These findings may improve current knowledge about energy production, and lead to economic and environmental benefits. Future plans are for the researchers aboard the ISS to examine [[aerosol]]s, [[ozone]], [[water vapour]], and [[oxide]]s in Earth's atmosphere, as well as [[cosmic ray]]s, [[cosmic dust]], [[antimatter]], and [[dark matter]] in the universe.<ref name="NASA Fields of Research" />

===Exploration===
[[File:Mars500.jpg|thumb|right|A 3D plan of the Russia-based [[MARS-500]] complex, used for ground-based experiments which complement ISS-based preparations for a [[manned mission to Mars]]]]
The ISS provides a location in the relative safety of Low Earth Orbit to test spacecraft systems that will be required for long-duration missions to [[the Moon]] and [[Mars]]. This provides experience in operations, maintenance as well as repair and replacement activities on-orbit, which will be essential skills in operating spacecraft farther from Earth, mission risks can be reduced and the capabilities of interplanetary spacecraft advanced.<ref name="ResProg">{{cite web|url=http://spaceflightsystems.grc.nasa.gov/Advanced/ISSResearch/|title=ISS Research Program|publisher=NASA|accessdate=27 February 2009}}{{dead link|date=August 2011}}</ref> Referring to the [[MARS-500]] experiment, ESA states that "Whereas the ISS is essential for answering questions concerning the possible impact of weightlessness, radiation and other space-specific factors, aspects such as the effect of long-term isolation and confinement can be more appropriately addressed via ground-based simulations".<ref name="esa mars500 ">{{cite web|title=Mars500 study overview | publisher = ESA |date= 4 June 2011| url = http://www.esa.int/esaMI/Mars500/SEM7W9XX3RF_0.html }}</ref> Sergey Krasnov, the head of human space flight programmes for Russia's space agency, Roscosmos, in 2011 suggested a "shorter version" of MARS-500 may be carried out on the ISS. <ref name="Mars thing on ISS">{{cite web| title=Space station may be site for next mock Mars mission| url = http://www.newscientist.com/blogs/shortsharpscience/2011/11/space-station-may-be-site-for.html|date=4 November 2011|work=New Scientist}}</ref>

In 2009, noting the value of the partnership framework itself, Sergey Krasnov wrote, "When compared with partners acting separately, partners developing complementary abilities and resources could give us much more assurance of the success and safety of space exploration. The ISS is helping further advance near-Earth space exploration and realisation of prospective programmes of research and exploration of the Solar system, including the Moon and Mars."<ref name=IAF2009>{{cite web|title=The Sustainable Utilisation of the ISS Beyond 2015|url=http://www.iafastro.org/docs/2009/ISS2015.pdf|publisher=International Astronautical Congress|accessdate=15 December 2011}}</ref> [[Manned mission to Mars|A manned mission to Mars]] may be a multinational effort involving space agencies and countries outside the current ISS partnership. In 2010, ESA Director-General Jean-Jacques Dordain stated his agency was ready to propose to the other four partners that China, India and South Korea be invited to join the ISS partnership.<ref name="ESAproposesInvite">{{cite web|title=ESA Chief Lauds Renewed U.S. Commitment to Space Station, Earth Science | publisher =Peter B. de Selding, Space News. |date=2 March 2010 | url =http://www.spacenews.com/civil/100203-esa-chief-lauds-renewed-commitment-space-station-earth-science.html}}</ref> NASA chief [[Charlie Bolden]] stated in February 2011, "Any mission to Mars is likely to be a global effort".<ref name="Mars a global effort">{{cite web|title= Charlie Bolden | publisher = space.com |date=4 June 2011 | url = http://www.space.com/11335-nasa-mars-exploration-space-station.html }}</ref> Currently, American legislation prevents NASA co-operation with China on space projects.<ref name="justice1">{{citation|first=Virginia|last=Seitz|title=Memorandum Opinion for the General Counsel, Office of Science and Technology Policy|url=http://www.justice.gov/olc/2011/conduct-diplomacy.pdf|journal=Office of Legal Counsel|volume=35|date=11 September 2011|accessdate=23 May 2012|archiveurl=https://web.archive.org/web/20120713080223/http://www.justice.gov/olc/2011/conduct-diplomacy.pdf|archivedate=13 July 2012}}</ref>

===Education and cultural outreach===
[[File:ISS-36 HTV-4 berthing 2.jpg|thumb|Japan's Kounotori 4 docking]]
The ISS crew provides opportunities for students on Earth by running student-developed experiments, making educational demonstrations, allowing for student participation in classroom versions of ISS experiments, and directly engaging students using radio, videolink and email.<ref name="ISSRG" /><ref>{{cite journal|author1=Gro Mjeldheim Sandal |author2=Dietrich Manzey|title=Cross-cultural issues in space operations: A survey study among ground personnel of the European Space Agency|journal=Acta Astronautica|volume=65|date=December 2009|pages=1520–1529|doi=10.1016/j.actaastro.2009.03.074|issue=11–12}}</ref> ESA offers a wide range of free teaching materials that can be downloaded for use in classrooms.<ref>[http://www.esa.int/SPECIALS/Education/SEM0LW4KXMF_0.html ESA – Education – Online material]. Esa.int (7 September 2011). Retrieved 8 October 2011.</ref> In one lesson, students can navigate a 3-D model of the interior and exterior of the ISS, and face spontaneous challenges to solve in real time.<ref>[http://www.esa.int/SPECIALS/Education/SEM1LL3Z2OF_0.html ESA – Education – ISS 3-D Teaching Tool: Spaceflight Challenge I]. Esa.int (24 May 2011). Retrieved 8 October 2011.</ref>

JAXA aims both to "Stimulate the curiosity of children, cultivating their spirits, and encouraging their passion to pursue craftsmanship", and to "Heighten the child's awareness of the importance of life and their responsibilities in society."<ref>[http://www.oosa.unvienna.org/pdf/pres/copuos2010/tech-17E.pdf Building Peace in Young Minds through Space Education]. Committee on the Peaceful Uses of Outer Space, 53rd Session. June 2010, Vienna, Austria; Space Education Center, Japan Aerospace Exploration Agency (JAXA)</ref> Through a series of education guides, a deeper understanding of the past and near-term future of manned space flight, as well as that of Earth and life, will be learned.<ref>[http://www.edu.jaxa.jp/education/international/ISS/SSK/en/ JAXA Space Education Center : JAXA Spaceflight Seeds Kids I : Spaceflight Sunflower seeds – Let's make them flower! and learn freshly the Earth environment just by contrast with the Space one]. Edu.jaxa.jp. Retrieved 8 October 2011.</ref><ref>[http://www.edu.jaxa.jp/education/international/ISS/SIS/en/ JAXA Space Education Center : JAXA Seeds in Space I : Let's Cultivate Spaceflight Asagao, Miyako-gusa Seeds and Identify the Mutants!]. Edu.jaxa.jp. Retrieved 8 October 2011.</ref> In the JAXA Seeds in Space experiments, the mutation effects of spaceflight on plant seeds aboard the ISS is explored. Students grow sunflower seeds which flew on the ISS for about nine months as a start to 'touch the Universe'. In the first phase of Kibō utilisation from 2008 to mid-2010, researchers from more than a dozen Japanese universities conducted experiments in diverse fields.<ref>{{cite web |author=Keiji Murakami |url=http://www.spacepolicyonline.com/pages/images/stories/Micro%20Oct%2009%20JEM.pdf |title=JEM Utilization Overview |publisher=JAXA. Steering Committee for the Decadal Survey on Biological and Physical Sciences in Space |date=14 October 2009}}</ref>

[[Image:Crew in ATV with Jules Verne manuscript.jpg|thumb|left|Original Jules Verne manuscripts displayed by crew inside Jules Verne ATV]]
Cultural activities are another major objective. Tetsuo Tanaka, director of JAXA's Space Environment and Utilization Center, says "There is something about space that touches even people who are not interested in science."<ref name="jaxa2">{{cite web |author=Tetsuo Tanaka |url=http://www.jaxa.jp/article/special/kibo/tanaka01_e.html |title=Kibo: Japan's First Human Space Facility |publisher=JAXA |accessdate=8 October 2011}}</ref>

[[ARISS|Amateur Radio on the ISS]] (ARISS) is a volunteer programme which encourages students worldwide to pursue careers in science, technology, engineering and mathematics through [[amateur radio]] communications opportunities with the ISS crew. ARISS is an international working group, consisting of delegations from 9 countries including several countries in Europe as well as Japan, Russia, Canada, and the United States. In areas where radio equipment cannot be used, speakerphones connect students to ground stations which then connect the calls to the station. <ref>{{cite web|url=http://www.rac.ca/ariss/oindex.htm|title=Amateur Radio on the International Space Station|date=6 June 2011|accessdate=10 June 2011}}</ref>

''[[First Orbit]]'' is a feature-length documentary film about [[Vostok 1]], the first manned space flight around the Earth. By matching the orbit of the International Space Station to that of Vostok 1 as closely as possible, in terms of ground path and time of day, documentary filmmaker Christopher Riley and ESA astronaut [[Paolo Nespoli]] were able to film the view that Yuri Gagarin saw on his pioneering orbital space flight. This new footage was cut together with the original Vostok 1 mission audio recordings sourced from the Russian State Archive. Nespoli, during Expedition 26/27, filmed the majority of the footage for this documentary film, and as a result is credited as its [[Cinematographer|director of photography]].<ref>{{cite news|last=Riley|first=Christopher|title=What Yuri Gagarin saw: First Orbit film to reveal the view from Vostok 1|url=http://www.guardian.co.uk/science/blog/2011/apr/11/yuri-gagarin-first-orbit-vostok|newspaper=The Guardian|date=11 April 2011|location=London}}</ref> The film was streamed through the website firstorbit.org in a global YouTube premiere in 2011, under a free license.<ref>{{cite web|url=http://www.firstorbit.org/first-orbit-faqs |title=Yuri Gagarin's First Orbit – FAQs |publisher=Firstorbit.org |accessdate=1 May 2012}}</ref>

In May 2013, commander [[Chris Hadfield]] shot a music video of [[David Bowie]]'s ''[[Space Oddity (song)|Space Oddity]]'' on board the station; the film was released freely on YouTube.<ref>{{cite web|last=Warr |first=Philippa |url=http://www.wired.co.uk/news/archive/2013-05/13/commander-hadfield-space-oddity |title=Commander Hadfield bids farewell to ISS with Reddit-inspired Bowie cover |publisher=Wired.co.uk |date=13 May 2013 |accessdate=22 October 2013}}</ref> It was the first music video ever to be filmed in space.<ref>{{cite web|last=Davis|first=Lauren|title=Chris Hadfield sings 'Space Oddity' in the first music video in space|url=http://io9.com/chris-hadfield-sings-space-oddity-in-the-first-music-503764317|publisher=io9}}</ref>

==Assembly==
{{Main|Assembly of the International Space Station|List of ISS spacewalks}}
[[File:ISS-with-S0-S1-P1.jpg|thumb|right|alt=S0, S1 and P1 truss structures installed|Partially constructed ISS in December 2002]]
[[File:S3-S4 Truss Installed 2.jpg|thumb|S3-S4 Truss Installed in 2007]]
[[File:Soyuz TMA-19 spacecraft departs the ISS.jpg|thumb|[[Soyuz TMA-19]] departs in 2010]]
[[File:ISS after STS-117 in June 2007.jpg|thumb|ISS in 2007, with fewer solar arrays]]
The assembly of the International Space Station, a major endeavour in [[space architecture]], began in November 1998.<ref name="OnOrbit">{{cite web|url=http://www.nasa.gov/externalflash/ISSRG/pdfs/on_orbit.pdf|title=On-Orbit Elements|publisher=NASA|author=NASA|date=18 February 2010|accessdate=19 June 2010|format=PDF}}</ref> Russian modules launched and docked robotically, with the exception of ''[[Rassvet (ISS module)|Rassvet]]''. All other modules were delivered by the Space Shuttle, which required installation by ISS and shuttle crewmembers using the [[Mobile Servicing System#Canadarm2|Canadarm2]] (SSRMS) and [[List of ISS spacewalks|EVAs]]; {{as of|2011|06|05|lc=y}}, they had added 159 components during more than 1,000 hours of EVA. 127 of these spacewalks originated from the station, and the remaining 32 were launched from the airlocks of docked Space Shuttles.<ref name="ISStD" /> The [[beta angle]] of the station had to be considered at all times during construction, as the station's beta angle is directly related to the percentage of its orbit that the station (as well as any docked or docking spacecraft) is exposed to the sun; the Space Shuttle would not perform optimally above a limit called the "beta cutoff".<ref name="mcc">{{cite web|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-113/11_23_20_01_179.html|title=MCC Answers|author=Derek Hassman, NASA Flight Director|date=1 December 2002|publisher=NASA|accessdate=14 June 2009}}</ref>

The first module of the ISS, ''[[Zarya]]'', was launched on 20 November 1998 on an autonomous Russian [[Proton (rocket)|Proton rocket]]. It provided propulsion, attitude control, communications, electrical power, but lacked long-term life support functions. Two weeks later a passive NASA module ''[[Unity (ISS module)|Unity]]'' was launched aboard Space Shuttle flight [[STS-88]] and attached to Zarya by astronauts during EVAs. This module has two [[Pressurized Mating Adapter]]s (PMAs), one connects permanently to Zarya, the other allows the Space Shuttle to dock to the space station. At this time, the Russian station Mir was still inhabited. The ISS remained unmanned for two years, during which time Mir was de-orbited. On 12 July 2000 [[Zvezda (ISS module)|Zvezda]] was launched into orbit. Preprogrammed commands on board deployed its solar arrays and communications antenna. It then became the passive vehicle for a rendezvous with the Zarya and Unity. As a passive "target" vehicle, the Zvezda maintained a stationkeeping orbit as the Zarya-Unity vehicle performed the rendezvous and docking via ground control and the Russian automated rendezvous and docking system. Zarya's computer transferred control of the station to Zvezda's computer soon after docking. Zvezda added sleeping quarters, a toilet, kitchen, CO2 scrubbers, dehumidifier, oxygen generators, exercise equipment, plus data, voice and television communications with mission control. This enabled permanent habitation of the station.<ref>[http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/servmod.pdf NASA Facts. The Service Module: A Cornerstone of Russian International Space Station Modules]. NASA. January 1999</ref><ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/missions/sts-88/mission-sts-88.html |title=STS-88 |publisher=Science.ksc.nasa.gov |accessdate=19 April 2011}}</ref>

The first resident crew, [[Expedition 1]], arrived in November 2000 on [[Soyuz TM-31]]. At the end of the first day on the station, astronaut Bill Shepherd requested the use of the radio call sign "''Alpha''", which he and cosmonaut Krikalev preferred to the more cumbersome "''International Space Station''".<ref name=TIME-Nov2>{{cite news|url=http://www.time.com/time/arts/article/0,8599,59500,00.html|title=Upward Bound: Tales of Space Station Alpha|author=Brad Liston|date=2 November 2000|work=Time|accessdate=5 August 2010}}</ref> The name "''Alpha''" had previously been used for the station in the early 1990s,<ref name=GAO>{{cite web|url=http://archive.gao.gov/t2pbat3/151975.pdf|title=Space Station – Impact on the expanded Russian role of funding and research|date=21 June 1994|publisher=[[Government Accountability Office|United State General Accounting Office]]|accessdate=9 August 2010}}</ref> and following the request, its use was authorised for the whole of Expedition 1.<ref name=SPACE-Nov3>{{cite web|url=http://www.space.com/missionlaunches/missions/alpha_male_001103.html|title=Call Bill Shepherd the Alpha Male of the International Space Station|author=Alan Ladwig|date=3 November 2000|publisher=Space.com|accessdate=9 August 2010}}</ref> Shepherd had been advocating the use of a new name to project managers for some time. Referencing a [[Ship naming and launching|naval tradition]] in a pre-launch news conference he had said: "For thousands of years, humans have been going to sea in ships. People have designed and built these vessels, launched them with a good feeling that a name will bring good fortune to the crew and success to their voyage."<ref name=SPACE-Nov2>{{cite web|url=http://www.space.com/missionlaunches/missions/exp1_alpha_001102.html|title=Expedition One Crew Wins Bid To Name Space Station Alpha|date=2 November 2000|author=Todd Halvorson|publisher=Space.com|accessdate=9 August 2010}}</ref> [[Yuri Semenov]], the President of [[S.P. Korolev Rocket and Space Corporation Energia|Russian Space Corporation Energia]] at the time, disapproved of the name "''Alpha''"; he felt that ''Mir'' was the first space station, and so he would have preferred the names "''Beta''" or "''Mir 2''" for the ISS.<ref name=SPACE-Nov3 /><ref>{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=5913|title=Interview with RSC Energia's Yuri Semenov|publisher=Space.com|date=3 September 2001|accessdate=22 August 2010}}</ref><ref>{{cite web|url=http://english.ruvr.ru/2001/03/29/100146.html|title=Interview with Yuri Semenov, general designer of Space Rocket corporation Energy|date=21 March 2001|publisher=[[Voice of Russia]]|accessdate=5 October 2010}}</ref>

[[Expedition 1]] arrived midway between the flights of [[STS-92]] and [[STS-97]]. These two Space Shuttle flights each added segments of the station's [[Integrated Truss Structure]], which provided the station with Ku-band communication for US television, additional attitude support needed for the additional mass of the USOS, and substantial [[solar array]]s supplementing the station's existing 4 solar arrays.<ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/missions/sts-92/mission-sts-92.html |title=STS-92 |publisher=Science.ksc.nasa.gov |accessdate=19 April 2011}}</ref>

Over the next two years the station continued to expand. A [[Soyuz-U]] rocket delivered the [[Pirs (ISS module)|''Pirs'' docking compartment]]. The Space Shuttles ''Discovery'', ''[[Space Shuttle Atlantis|Atlantis]]'', and ''Endeavour'' delivered the [[Destiny (ISS module)|''Destiny'' laboratory]] and [[Quest Joint Airlock|''Quest'' airlock]], in addition to the station's main robot arm, the ''[[Canadarm2]]'', and several more segments of the Integrated Truss Structure.
[[File:Zvezda rear.jpg|thumb|left|Aft view showing a Progress spacecraft docked to Zvezda]]
The expansion schedule was interrupted by the {{OV|102}} [[Space Shuttle Columbia disaster|disaster]] in 2003, with the resulting two year hiatus in the [[Space Shuttle program]]me halting station assembly. The space shuttle was grounded until 2005 with [[STS-114]] flown by ''Discovery''.<ref>{{cite web|url=http://www.nasaspaceflight.com/2005/07/discovery-launches-the-shuttle-is-back/|title=Discovery launches—The Shuttle is back|author=Chris Bergin|publisher=NASASpaceflight.com|accessdate=6 March 2009|date=26 July 2005}}</ref>

Assembly resumed in 2006 with the arrival of [[STS-115]] with ''Atlantis'', which delivered the station's second set of solar arrays. Several more truss segments and a third set of arrays were delivered on [[STS-116]], [[STS-117]], and [[STS-118]]. As a result of the major expansion of the station's power-generating capabilities, more pressurised modules could be accommodated, and the ''[[Harmony (ISS module)|Harmony]]'' node and ''Columbus'' European laboratory were added. These were followed shortly after by the first two components of ''Kibō''. In March 2009, [[STS-119]] completed the Integrated Truss Structure with the installation of the fourth and final set of solar arrays. The final section of ''Kibō'' was delivered in July 2009 on [[STS-127]], followed by the Russian ''[[Poisk (ISS module)|Poisk]]'' module. The third node, ''[[Tranquility (ISS module)|Tranquility]]'', was delivered in February 2010 during [[STS-130]] by the Space Shuttle ''Endeavour'', alongside the [[Cupola (ISS module)|Cupola]], closely followed in May 2010 by the penultimate Russian module, ''[[Rassvet (ISS module)|Rassvet]]''. Rassvet was delivered by Space Shuttle ''Atlantis'' on [[STS-132]] in exchange for the Russian Proton delivery of the Zarya Module in 1998 which had been funded by the United States.<ref>{{cite web|url=http://www.russianspaceweb.com/iss_mim1.html |title=Mini-Research Module 1 (MIM1) Rassvet (MRM-1) |publisher=Russianspaceweb.com |accessdate=12 July 2011}}</ref> The last pressurised module of the USOS, ''Leonardo'', was brought to the station by ''Discovery'' on her final flight, [[STS-133]],<ref name="STS-133">{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/main/index.html |title=STS-133 |publisher=NASA |accessdate=1 September 2014}}</ref> followed by the [[Alpha Magnetic Spectrometer]] on [[STS-134]], delivered by ''Endeavour''.<ref name="STS-134">{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/main/index.html |title=STS-134 |publisher=NASA |accessdate=1 September 2014}}</ref>
[[File:Exterior of Cupola - Exp28.jpg|thumb|The Cupola arrived in 2010]]
{{As of|2011|06}}, the station consisted of fifteen pressurised modules and the [[Integrated Truss Structure]]. Still to be launched are the Russian [[Nauka (ISS module)|Multipurpose Laboratory Module]] ''Nauka'' and a number of external components, including the [[European Robotic Arm]]. Assembly is expected to be completed by April 2014,{{update inline|date=October 2014}} by which point the station will have a mass in excess of 400 [[metric ton|tonnes]] (440 [[short ton]]s).<ref name="OnOrbit" /><ref name="Manifest">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/iss_manifest.html|title=Consolidated Launch Manifest|accessdate=8 July 2008|publisher=NASA|author=NASA|year=2008}}</ref>

The gross mass of the station changes over time. The total launch mass of the modules on orbit is about {{convert|417289|kg|lbs|abbr=on}} (as of 3 September 2011).<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/isstodate.html |title=NASA – The ISS to Date (03/09/2011) |publisher=Nasa.gov |accessdate=12 July 2011}}</ref> The mass of experiments, spare parts, personal effects, crew, foodstuff, clothing, propellants, water supplies, gas supplies, docked spacecraft, and other items add to the total mass of the station. Hydrogen gas is constantly vented overboard by the oxygen generators.

==Station structure==
{{Double image|right|ROS Windows 0114 complete.jpg|130|USOS window identification.png|160|Russian Orbital Segment Windows|USOS International Space Station window locations}}

The ISS is a third generation<ref>{{cite web|url=http://www.dlr.de/iss/en/desktopdefault.aspx/tabid-1945/2746_read-4182/gallery-1/gallery_read-Image.19.2296/ |title=DLR – International Space Station ISS – From Cold War to international cooperation – the story of the ISS |publisher=Dlr.de |accessdate=1 May 2012}}</ref> modular space station.<ref>{{cite web|url=http://www.astronautix.com/articles/thistems.htm |title=Third Generation Soviet Space Systems |publisher=Astronautix.com |accessdate=1 May 2012}}</ref> Modular stations can allow the mission to be changed over time and new modules can be added or removed from the existing structure, allowing greater flexibility.

Below is a diagram of major station components. The blue areas are pressurised sections accessible by the crew without using spacesuits. The station's unpressurised superstructure is indicated in red. Other unpressurised components are yellow. Note that the Unity node joins directly to the Destiny laboratory. For clarity, they are shown apart.

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PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | |AMS|~|ZVEZDA|~|AMS|
AMS = [[Zvezda (ISS module)|Solar array]]
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PIRS = [[Pirs (ISS module)|'''Pirs''' Airlock]]
|SGM2 = [[Poisk (ISS module)|'''Poisk''' (MRM-2) Airlock]]
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{{familytree| | | | | | | | | | | | |!|!|}}
{{familytree| | | | | | | | | | | | |!|`|-|MLM|~|ERA| | |
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| ERA = '''[[European Robotic Arm|European Robotic Arm]]'''
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{{familytree| | | | | | | |SA|~|ZARYA|~|SA| | | |
SA = [[Zarya (ISS module)|Solar array]]
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{{familytree| | | | | | | | | | | | |!|!|}}
{{familytree| | | | | | | | | | | | |!|`|-|SGM1|PORT1|
SGM1 = [[Rassvet (ISS module)|'''Rassvet''' (MRM-1)]]
|PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | | | | | | |!| | |PMM| | |
PMM = [[Leonardo (ISS module)|'''Leonardo''' cargo bay]]
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{{familytree| | | | | | | |QUEST|-|UNITY|-|NOD3|PORT2| |
UNITY = [[Unity (ISS module)|'''Unity''' Node 1]]
|QUEST = [[Quest Joint Airlock|'''Quest''' Airlock]]
|NOD3 = [[Tranquility (ISS module)|'''Tranquility''' Node 3]]
|PORT2 = [[Pressurized Mating Adapter#PMA-3|'''PMA 3''' docking port]]
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{{familytree| |FE0|F|FE| |RADIATOR|!|RADIATOR| |FE|7|FE| | | |
RADIATOR = [[External Active Thermal Control System|Heat Radiator]]
|FE = [[ISS Solar Arrays#Solar arrays|Solar array]]
|FE0 = [[ISS Solar Arrays#Solar arrays|Solar array]]
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{{familytree| |:| | |:| | | | | |:| |!| |:| | | | | |:| | |:|}}
{{familytree| |:| | |:|ELC| | |:|FZ1|:| | |ELC3|:| | |:|
ELC = [[ExPRESS Logistics Carrier#ELC-2|ELC 2]], '''[[Alpha Magnetic Spectrometer|AMS]]'''
|FZ1 = '''[[Z1 truss]]'''
|ELC3 = [[ExPRESS Logistics Carrier#ELC-3|ELC 3]]
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FS56 = '''[[P5 Truss Segment|S5/6 Truss]]'''
|FS34 = '''[[Integrated Truss Structure#P3/P4, S3/S4 truss assemblies|S3/S4 Truss]]'''
|FS1 = '''[[S1 Truss]]'''
|FS0 = '''[[S0 Truss]]'''
|FP1 = '''[[S1 Truss|P1 Truss]]'''
|FP34 = '''[[Integrated Truss Structure#P3/P4, S3/S4 truss assemblies|P3/P4 Truss]]'''
|FP56 = '''[[P5 Truss Segment|P5/6 Truss]]'''
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{{familytree| |:| | |:|ELC4| | | |:|!|:| | | |ELC1|:| | |:|
ELC4 = [[ExPRESS Logistics Carrier#ELC-4|ELC 4]], [[External Stowage Platform#ESP-3|ESP 3]]
|ELC1 = [[ExPRESS Logistics Carrier#ELC-1|ELC 1]]
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CANADARM = '''[[Canadarm2]]'''
|DEXTR = '''[[Dextre]]'''
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|boxstyle_DEXTR = border: 2px solid #fee067; background:#fff4cc;}}
{{familytree| |FE0|L|FE| | | | |!| | | | |FE|J|FE| | | |
FE0 = [[ISS Solar Arrays#Solar arrays|Solar array]]
|FE = [[ISS Solar Arrays#Solar arrays|Solar array]]
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{{familytree| | | | | | | | | | | | |!| | | | |}}
{{familytree| | | | | | | | |ESP1|DESTYNY| | |
DESTYNY = [[Destiny (ISS module)|'''Destiny''' Laboratory]]
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KIBOPS = [[Japanese Experiment Module#Experiment Logistics Module|'''Kibō logistics''' Cargo Bay]]
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{{familytree| | | | | | | | | |HTV|!|HTV| |!|
HTV = '''[[H-II Transfer Vehicle|HTV]]'''/'''[[Dragon (spacecraft)|Dragon]]'''/'''[[Cygnus (spacecraft)|Cygnus]]''' berth ([[Common berthing mechanism|docking port]])
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{{familytree| | | | | | | | | | | |!|!|!| | | |!|KiboRobo|
KiboRobo = [[Japanese Experiment Module|'''Kibō''' Robotic Arm]]
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{{familytree| | | | |COLEXT|COLUMBUS|-|HARMONY|-|KIBO|KiboPlat|
HARMONY = [[Harmony (ISS module)|'''Harmony''' (Node 2)]]
|KiboPlat = [[Japanese Experiment Module|'''Kibō''' External Platform]]
|COLUMBUS = [[Columbus (ISS module)|'''Columbus''' Laboratory]]
|KIBO = [[JEM-PM|'''Kibō''' Laboratory]]
|COLEXT = External Payloads
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PORT2 = [[Pressurized Mating Adapter#PMA-2|'''PMA 2''' docking port]]
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==Pressurised modules==

===Zarya===
[[File:Zarya from STS-88.jpg|thumb|upright|Zarya as seen by [[Space Shuttle Endeavour]] during [[STS-88]]]]
'''''[[Zarya]]''''' (Russian: Заря́; lit. dawn), also known as the [[Functional Cargo Block]] or FGB (from the Russian "Функционально-грузовой блок", Funktsionalno-gruzovoy blok or ФГБ), was the first module of the International Space Station to be launched. The FGB provided electrical power, storage, propulsion, and guidance to the ISS during the initial stage of assembly. With the launch and assembly in orbit of other modules with more specialized functionality, Zarya is now primarily used for storage, both inside the pressurized section and in the externally mounted fuel tanks. The Zarya is a descendant of the [[TKS spacecraft]] designed for the Soviet [[Salyut program]]. The name Zarya was given to the FGB because it signified the dawn of a new era of international cooperation in space. Although it was built by a Russian company, it is owned by the [[United States]]. Zarya weighs {{convert|19300|kg|lb|abbr=on}}, is {{convert|12.55|m|ft|abbr=on}} long and {{convert|4.1|m|ft|abbr=on}} wide, discounting solar arrays.

Built from December 1994 to January 1998 in Russia at the [[Khrunichev State Research and Production Space Center]] (KhSC) in [[Moscow]], Zarya's control system was developed by the Khartron Corp. ([[Kharkiv, Ukraine]]).

Zarya was launched on 20 November 1998, on a Russian [[Proton-K|Proton rocket]] from [[Baikonur Cosmodrome Site 81]] in [[Kazakhstan]] to a {{convert|400|km|mi|abbr=on}} high orbit with a designed lifetime of at least 15 years. After Zarya reached orbit, STS-88 launched on 4 December 1998, to attach the Unity Module.

Although only designed to fly autonomously for six to eight months, Zarya did so for almost two years due to delays with the Russian Service Module, Zvezda, which finally launched on 12 July 2000, and docked with Zarya on 26 July using the Russian [[Kurs (docking system)|Kurs docking system]].

===Unity===
[[File:ISS Unity module.jpg|thumb|Unity as pictured by Space Shuttle Endeavour]]
'''''[[Unity (ISS module)|Unity]]''''', or Node 1, is one of three nodes, or passive connecting modules, in the [[US Orbital Segment]] of the station. It was the first US-built component of the Station to be launched. Cylindrical in shape, with six berthing locations facilitating connections to other modules, Unity was carried into orbit by {{OV|105}} as the primary cargo of [[STS-88]] in 1998. Essential space station resources such as fluids, environmental control and life support systems, electrical and data systems are routed through Unity to supply work and living areas of the station. More than 50,000 mechanical items, 216 lines to carry fluids and gases, and 121 internal and external electrical cables using six miles of wire were installed in the Unity node. Unity is made of aluminum. Prior to its launch aboard Endeavour, conical Pressurized Mating Adapters (PMAs) were attached to the aft and forward berthing mechanisms of Unity. Unity and the two mating adapters together weighed about {{convert|25600|lb|kg|disp=flip|abbr=on}}. The adapters allow the docking systems used by the Space Shuttle and by Russian modules to attach to the node's hatches and berthing mechanisms.

Unity was carried into orbit as the primary cargo of the Space Shuttle Endeavour on STS-88, the first Space Shuttle mission dedicated to assembly of the station. On 6 December 1998, the STS-88 crew mated the aft berthing port of Unity with the forward hatch of the already orbiting Zarya module.

===Zvezda===
'''''[[Zvezda (ISS module)|Zvezda]]''''' ({{lang-ru|link=no|Звезда́}}, meaning "star"), also known as DOS-8, Service Module or SM ({{lang-ru|link=no|СМ}}). It provides all of the station's critical systems,{{clarify|date=August 2013}} its addition rendered the station permanently habitable for the first time, adding life support for up to six crew and living quarters for two. Zvezda's DMS-R computer handles guidance, navigation and control for the entire space station.<ref name="Navigation" /> A second computer which performs the same functions will be installed in the [[Nauka (ISS module)|Nauka]] module, FGB-2.

The hull of Zvezda was completed in February 1985, with major internal equipment installed by October 1986. The module was launched by a Proton-K rocket from Site 81/23 at Baikonur, on 12 July 2000. Zvezda is at the rear of the station according to its normal direction of travel and orientation, its engines are used to boost the station's orbit. Alternatively Russian and European spacecraft can dock to Zvezda's aft port and use their engines to boost the station.

===Destiny===
[[File:Destiny as just installed.jpg|thumb|''Destiny'' interior in 2001]]
'''''[[Destiny (ISS module)|Destiny]]''''' is the primary research facility for United States payloads aboard the ISS. In 2011, NASA solicited proposals for a not-for-profit group to manage all American science on the station which does not relate to manned exploration. The module houses 24 [[International Standard Payload Rack]]s, some of which are used for environmental systems and crew daily living equipment. ''Destiny'' also serves as the mounting point for the station's Truss Structure.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/destiny.html|title=NASA—US Destiny Laboratory|date=26 March 2007|accessdate=26 June 2007|publisher = NASA}}</ref>

===Quest===
'''''[[Quest Joint Airlock|Quest]]''''' is the only USOS airlock, and hosts spacewalks with both United States [[Extravehicular Mobility Unit|EMU]] and Russian [[Orlan space suit|Orlan]] [[Space suit|spacesuits]]. It consists of two segments: the equipment lock, which stores spacesuits and equipment, and the crew lock, from which astronauts can exit into space. This module has a separately controlled atmosphere. Crew sleep in this module, breathing a low nitrogen mixture the night before scheduled EVAs, to avoid [[decompression sickness]] (known as "the bends") in the low-pressure suits.<ref>{{cite web|url=http://spaceflight.nasa.gov/station/eva/outside.html|title=Space Station Extravehicular Activity|accessdate=11 March 2009|publisher=[[NASA]]|date=4 April 2004}}</ref>

===Pirs and Poisk===
'''''[[Pirs (ISS module)|Pirs]]''''' ({{lang-ru|link=no|Пирс}}, meaning "[[pier]]"), ({{lang-ru|link=no|Стыковочный отсек}}), "docking module", SO-1 or DC-1 (docking compartment), and '''''[[Poisk (ISS module)|Poisk]]''''' ({{lang-ru|link=no|По́иск}}; lit. ''Search''), also known as the [[Mini-Research Module]] 2 (MRM 2), {{lang|ru|''Малый исследовательский модуль 2''}}, or МИМ 2. Pirs and Poisk are Russian airlock modules. Each of these modules have 2 identical hatches. An outward opening hatch on the MIR space station failed after it swung open too fast after unlatching, due to a small amount of air pressure remaining in the airlock.<ref>{{cite web|url=http://www.russianspaceweb.com/mir_close_calls.html |title=Mir close calls |publisher=Russianspaceweb.com |accessdate=1 May 2012}}</ref> A different entry was used, and the hatch repaired. All EVA hatches on the ISS open inwards and are pressure sealing. Pirs was used to store, service, and refurbish Russian [[Orlan suits]] and provided contingency entry for crew using the slightly bulkier American suits. The outermost docking ports on both airlocks allow docking of Soyuz and Progress spacecraft, and the automatic transfer of propellants to and from storage on the ROS.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/pirs.html|title=Pirs Docking Compartment|publisher=NASA|accessdate=28 March 2009|date=10 May 2006}}</ref>

{{multiple image |align=right |image1=Node 2 - STS-134.jpg |width1=171 |image2=Node 3 - Isolated view.jpg |width2=190 |caption1=''Harmony'' node in 2011 |caption2=''Tranquility'' node in 2011}}

===Harmony===
'''''[[Harmony (ISS module)|Harmony]]''''' is the second of the station's node modules and the utility hub of the USOS. The module contains four racks that provide electrical power, bus electronic data, and acts as a central connecting point for several other components via its six Common Berthing Mechanisms (CBMs). The European Columbus and Japanese Kibō laboratories are permanently berthed to the starboard and port radial ports respectively. The nadir and zenith ports can be used for docking visiting spacecraft including HTV, Dragon, and Cygnus, with the nadir port serving as the primary docking port. American Shuttle Orbiters docked with the ISS via PMA-2, attached to the forward port.

===Tranquility===
'''''[[Tranquility (ISS module)|Tranquility]]''''' is the third and last of the station's US nodes, it contains an additional life support system to recycle waste water for crew use and supplements oxygen generation. Two of the four berthing locations are not used. One location has the ''[[Cupola (ISS module)|Cupola]]'' installed, one has the docking port adapter, and the third one is occupied by the [[Leonardo (ISS module)|''Leonardo'' PMM]].

[[File:S122e008264.jpg|thumb|left|Columbus module in 2008]]

===Columbus===
'''''[[Columbus (ISS module)|Columbus]]''''', the primary research facility for European payloads aboard the ISS, provides a [[European Drawer Rack|generic laboratory]] as well as facilities specifically designed for [[Biolab|biology]], [[European Physiology Modules|biomedical research]] and [[Fluid Science Laboratory|fluid physics]]. Several mounting locations are affixed to the exterior of the module, which provide power and data to external experiments such as the [[European Technology Exposure Facility]] (EuTEF), [[Solar Monitoring Observatory]], [[Materials International Space Station Experiment]], and [[Atomic Clock Ensemble in Space]]. A number of expansions are planned for the module to study [[quantum physics]] and [[cosmology]].<ref>{{cite news|url=http://www.nasaspaceflight.com/2008/01/prcb-plan-sts-122-for-net-feb-7-three-launches-in-10-11-weeks/|title=PRCB plan STS-122 for NET Feb 7—three launches in 10–11 weeks|accessdate=12 January 2008|author=Chris Bergin|date=10 January 2008|publisher=[[NASASpaceflight.com]]}}</ref><ref>{{cite web|url=http://www.esa.int/esaHS/ESAAYI0VMOC_iss_0.html|title=Columbus laboratory|publisher=[[European Space Agency]] (ESA)|accessdate=6 March 2009|date=10 January 2009}}</ref> ESA's development of technologies on all the main areas of life support has been ongoing for more than 20 years and are/have been used in modules such as Columbus and the ATV. The German Aerospace Center [[German Aerospace Center|DLR]] manages ground control operations for Columbus and the ATV is controlled from the French [[CNES]] [[Toulouse Space Center]].

===Kibō===
[[File:きぼうエアロック Kibo airlock.jpg|thumb|Not large enough for crew using spacesuits, the airlock on Kibō has a sliding drawer for external experiments.]]
'''''[[Kibo (ISS module)|Kibō]]''''' ({{lang-ja|きぼう}}, "[[hope]]") is the largest single ISS module. This laboratory is used to carry out research in space medicine, biology, Earth observations, materials production, biotechnology, communications research, and has facilities for growing plants and fish. During August 2011, an observatory mounted on Kibō, which utilises the ISS's orbital motion to image the whole sky in the X-ray spectrum, detected for the first time the moment a star was swallowed by a black hole.<ref>{{cite web|author=[[JAXA]] |url=http://kibo.jaxa.jp/en/experiment/ef/maxi/ |title=Monitor of All-sky X-ray Image (MAXI):Experiment – Kibo Japanese Experimental Module – JAXA |publisher=Kibo.jaxa.jp |date=30 March 2007 |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://www.jaxa.jp/press/2011/08/20110825_maxi_e.html |title=JAXA | Scientific paper in Nature using the Monitor of All-sky X-ray Image (MAXI) on Kibo and the Swift satellite (USA) observations – First observation of a massive black hole swallowing a star |publisher=Jaxa.jp |accessdate=1 May 2012}}</ref> The laboratory contains a total of 23 racks, including 10 experiment racks and has a dedicated airlock for experiments. In a 'shirt sleeves' environment, crew attach an experiment to the sliding drawer within the airlock, close the inner, and then open the outer hatch. By extending the drawer and removing the experiment using the dedicated robotic arm, payloads are placed on the external platform. The process can be reversed and repeated quickly, allowing access to maintain external experiments without the delays caused by EVAs.

<gallery widths="115px" mode="nolines">
File:Kibo - Pressurized Module.jpg|Pressurized Module
File:Kibo - Experiment Logistics Module (Pressurized Section).jpg|Experiment Logistics Module
File:Kibo - Exposed Facility.jpg|Exposed Facility
File:Kibo - Experiment Logistics Module (Exposed Section).jpg|Experiment Logistics Module
File:Kibo - Remote Manipulator System.jpg|Remote Manipulator System
</gallery>

A smaller pressurised module is attached to the top of Kibō, serving as a cargo bay. The dedicated Interorbital communications system allows large amounts of data to be beamed from Kibō's ICS, first to the Japanese KODAMA satellite in geostationary orbit, then to Japanese ground stations. When a direct communication link is used, contact time between the ISS and a ground station is limited to approximately 10 minutes per visible pass. When KODAMA relays data between a LEO spacecraft and a ground station, real-time communications are possible in 60% of the flight path of the spacecraft. Ground staff use [[telepresence robotics]] to conduct on-orbit research without crew intervention.

===Cupola===
{{multiple image |align=right |image1=STS130 cupola view1.jpg |width1=190 |image2=ISS-27 Dmitri Kondratyev and Paolo Nespoli photograph the Earth through the Cupola.jpg |width2=190 |caption1=The [[Cupola (ISS module)|Cupola]]'s design has been compared to the ''[[Millennium Falcon]]'' from ''[[Star Wars (film)|Star Wars]]''. |caption2=[[Dmitri Kondratyev]] and [[Paolo A. Nespoli|Paolo Nespoli]] in the Cupola. Background left to right, [[Progress M-09M]], [[Soyuz TMA-20]], the [[Leonardo (ISS module)|Leonardo]] module and [[Kounotori 2|HTV-2]].}}
'''[[Cupola (ISS module)|Cupola]]''' is a seven window observatory, used to view Earth and docking spacecraft. Its name derives from the Italian word cupola, which means "dome". The Cupola project was started by NASA and Boeing, but cancelled due to budget cuts. A barter agreement between NASA and the ESA resulted in the Cupola's development being resumed in 1998 by the ESA. It was built by Thales Alenia Space in Torino, Italy. The module comes equipped with robotic workstations for operating the station's main robotic arm and shutters to protect its windows from damage caused by micrometeorites. It features 7 windows, with an {{convert|80|cm|in|adj=on}} round window, the largest window on the station (and the largest flown in space to date). The distinctive design has been compared to the 'turret' of the fictitious ''[[Millennium Falcon]]'' from the motion picture ''[[Star Wars (film)|Star Wars]]'';<ref>{{cite web|url=http://www.space.com/7932-astronauts-bask-spectacular-views-space-windows.html |title=Astronauts Bask in Spectacular Views From New Space Windows |publisher=Space.com |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://news.nationalgeographic.com/news/2010/02/photogalleries/100218-international-space-station-cupola-iss-obama-nasa-pictures/ |title=First Photos: Space Station's Observation Deck Unveiled |work=National Geographic |accessdate=1 May 2012}}</ref> the original prop [[lightsaber]] used by actor [[Mark Hamill]] as [[Luke Skywalker]] in the 1977 film was flown to the station in 2007.<ref>{{cite web|url=http://www.space.com/4283-nasa-shuttle-launch-luke-skywalker-lightsaber.html |title=NASA Shuttle to Launch Luke Skywalker's Lightsaber |publisher=Space.com |date=28 August 2007 |accessdate=1 May 2012}}</ref>

===Rassvet===
'''''[[Rassvet (ISS module)|Rassvet]]''''' ({{lang-ru|link=no|Рассве́т}}; lit. "dawn"), also known as the Mini-Research Module 1 (MRM-1) ({{lang-ru|link=no|Ма́лый иссле́довательский модуль}}, {{lang|ru|МИМ 1}}) and formerly known as the Docking Cargo Module (DCM), is similar in design to the [[Mir Docking Module]] launched on [[STS-74]] in 1995. ''Rassvet'' is primarily used for cargo storage and as a docking port for visiting spacecraft. It was flown to the ISS aboard NASA's {{OV|104}} on the [[STS-132]] mission and connected in May 2010,<ref>{{cite web|url=http://www.nasaspaceflight.com/2009/04/sts-132-prcb-baselines-mission-to-deliver-russias-mrm-1/|title=STS-132: PRCB baselines Atlantis' mission to deliver Russia's MRM-1|author=Chris Gebhardt|publisher=NASAspaceflight.com|date=9 April 2009|accessdate=12 November 2009}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts132/news/STS-132-09.html|author=NASA|date=18 May 2010|accessdate=7 July 2010|title=STS-132 MCC Status Report #09}}</ref> Rassvet is the only Russian owned module launched by NASA, to repay for the launch of Zarya, which is Russian designed and built, but partially paid for by NASA.<ref>[http://www.russianspaceweb.com/iss_mim1.html MIM1]. russianspaceweb.com</ref>  Rassvet was launched with the Russian Nauka Laboratory's Experiments airlock temporarily attached to it, and spare parts for the European Robotic Arm.

===Leonardo===
[[File:STS-133 Installation PMM 3.jpg|thumb|''Leonardo'' installed]]
'''''[[Leonardo (ISS module)|Leonardo]]'' Permanent Multipurpose Module''' (PMM) is a storage module attached to the ''[[Tranquility (ISS module)|Tranquility]]'' node.<ref name="leo-esa20110301">{{cite news |url=http://www.esa.int/Our_Activities/Human_Spaceflight/MagISStra/Leonardo_attached_to_Space_Station |title=Leonardo Attached to Space Station |work=ESA.int |date=1 March 2011 |accessdate=11 June 2013}}</ref><ref>{{cite web |url=http://blogs.nasa.gov/spacestation/2015/05/27/module-relocated-prepping-station-for-commercial-crew/ |title=Module Relocated Prepping Station for Commercial Crew |publisher=NASA |first=Mark |last=Garcia |date=27 May 2015 |accessdate=27 May 2015}}</ref> The three NASA Space Shuttle [[Multi-Purpose Logistics Module|MPLM]] cargo containers—Leonardo, Raffaello and Donatello—were built for NASA in [[Turin]], Italy by Alcatel Alenia Space, now [[Thales Alenia Space]].<ref>[http://www.thalesaleniaspace-issmodules.com/ Thales Alenia Space and ISS modules – Thales Alenia Space and ISS modules]. Thalesaleniaspace-issmodules.com. Retrieved 8 October 2011.</ref> The MPLMs were provided to NASA's ISS programme by Italy (independent of their role as a member state of ESA) and are considered to be US elements. In a bartered exchange for providing these containers, the US gave Italy research time aboard the ISS out of the US allotment in addition to that which Italy receives as a member of ESA.<ref>[http://www.spaceref.com/iss/elements/mplm.html Space Station User's Guide]. SpaceRef (3 April 2001). Retrieved 8 October 2011.</ref> The Permanent Multipurpose Module was created by converting Leonardo into a module that could be permanently attached to the station.<ref name="PLM1">{{cite news|url=http://www.nasaspaceflight.com/2009/08/sts-133-five-crew-one-eva-mission-leave-mpm-on-iss|title=STS-133 refined to a five crew, one EVA mission—will leave MPLM on ISS|publisher=NASASpaceflight.com|author=Chris Gebhardt|date=5 August 2009}}</ref><ref name="PLM2">{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8226309.stm|title=Europe looks to buy Soyuz craft|work=BBC News|last=Amos|first=Jonathan|date=29 August 2009}}</ref><ref>{{cite web|url=http://forum.nasaspaceflight.com/index.php?topic=17437.msg483604#msg483604|publisher=NASASpaceflight.com|accessdate=12 October 2009|title=Shuttle Q&A Part 5|date=27 September 2009}}</ref>

===Scheduled additional modules===

====Nauka====
'''''[[Nauka (ISS module)|Nauka]]''''' ({{lang-ru|link=no|Нау́ка}}; lit. "science"), also known as the Multipurpose Laboratory Module (MLM) or FGB-2 ({{lang-ru|link=no|Многофункциональный лабораторный модуль}}, {{lang|ru|МЛМ}}), is the major Russian laboratory module. It was scheduled to arrive at the station in 2014, docking to the port that was occupied by the Pirs module.<ref>{{cite web|url=http://www.aviationweek.com/Article.aspx?id=/article-xml/asd_05_23_2012_p05-01-460939.xml|title=Russia Sees Moon Base As Logical Next Step| last=Morring| first=Frank| date=23 May 2012| publisher=Aviation Week|accessdate=29 May 2012}}</ref> The date has been postponed to February 2017.<ref>{{cite web|url=http://www.russianspaceweb.com/iss_fgb2.html|title=MLM (FGB-2)|author=Anatoly Zak|publisher=Russian Space Web|date=29 April 2014|accessdate=14 May 2014}}</ref> Prior to the arrival of the Nauka module, a Progress spacecraft was used to remove Pirs from the station, deorbiting it to reenter over the Pacific Ocean. Nauka contains an additional set of life support systems and attitude control. Originally it would have routed power from the single Science-and-Power Platform, but that single module design changed over the first ten years of the ISS mission, and the two science modules, which attach to Nauka via the [[Uzlovoy Module]], or Russian node, each incorporate their own large solar arrays to power Russian science experiments in the ROS.

Nauka's mission has changed over time. During the mid-1990s, it was intended as a backup for the FGB, and later as a universal docking module (UDM); its docking ports will be able to support automatic docking of both spacecraft, additional modules and fuel transfer. Nauka has its own engines. Smaller Russian modules such as Pirs and Poisk were delivered by modified [[Progress (spacecraft)|Progress]] spacecraft, and the larger modules; Zvezda, Zarya, and Nauka, were launched by Proton rockets. Russia plans to separate Nauka, along with the rest of the Russian Orbital Segment, before the ISS is deorbited, to form the [[OPSEK]] space station.

====Uzlovoy Module====
The '''[[Uzlovoy Module]]''' (UM), or Node Module is a 4 metric ton<ref name=Zak>{{cite web|last1=Zak|first1=Anatoly|title=Node Module|url=http://www.russianspaceweb.com/iss_node.html|website=RussianSpaceWeb.com|accessdate=7 January 2015}}</ref> ball shaped module that will support the docking of two scientific and power modules during the final stage of the station assembly and provide the Russian segment additional docking ports to receive Soyuz TMA and Progress M spacecraft. UM is to be incorporated into the ISS in 2016. It will be integrated with a special version of the Progress cargo ship and launched by a standard Soyuz rocket. The Progress would use its own propulsion and flight control system to deliver and dock the Node Module to the nadir (Earth-facing) docking port of the Nauka MLM/FGB-2 module. One port is equipped with an active hybrid docking port, which enables docking with the MLM module. The remaining five ports are passive hybrids, enabling docking of Soyuz and Progress vehicles, as well as heavier modules and future spacecraft with modified docking systems. The node module was conceived to serve as the only permanent element of the future Russian successor to the ISS, [[Orbital Piloted Assembly and Experiment Complex|OPSEK]]. Equipped with six docking ports, the Node Module would serve as a single permanent core of the future station with all other modules coming and going as their life span and mission required.<ref>[http://www.energia.ru/en/news/news-2011/news_01-13.html S.P. Korolev RSC Energia – News]. Energia.ru (13 January 2011). Retrieved 8 October 2011.</ref><ref>[http://www.russianspaceweb.com/iss_node.html Node Module]. Russianspaceweb.com. Retrieved 8 October 2011.</ref> This would be a progression beyond the ISS and Russia's modular MIR space station, which are in turn more advanced than early monolithic first generation stations such as Skylab, and early Salyut and Almaz stations.

'''Science Power Modules 1 & 2''' (NEM-1, NEM-2) ({{lang-ru|link=no|Нау́чно-Энергетический Модуль-1 и -2}})

====Bigelow Expandable Activity Module====
On 16 January 2013, [[Bigelow Aerospace]] was contracted by NASA to provide a [[Bigelow Expandable Activity Module]] (BEAM), scheduled to arrive at the space station in 2015 for a two-year technology demonstration.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/station/news/beam_feature.html |title=NASA to Test Bigelow Expandable Module on Space Station |publisher=NASA |date=16 January 2013 |accessdate=17 January 2013}}</ref> BEAM is an inflatable module that will be attached to the aft hatch of the port-side Tranquility module of the International Space Station. During its two-year test run, instruments will measure its structural integrity and leak rate, along with temperature and radiation levels. The hatch leading into the module will remain mostly closed except for periodic visits by space station crew members for inspections and data collection. Following the test run, the module will be detached and jettisoned from the station.<ref>{{cite web | url=http://www.spaceflightnow.com/news/n1301/16bigelow/ | title=Bigelow inflatable module bound for space station | last=Harwood | first=William | date=16 January 2013 | publisher=Spaceflightnow | accessdate=17 January 2013}}</ref>

[[image:ISS Habitation module.jpg|thumb|left|The cancelled Habitation module under construction in 1997]]

===Cancelled components===
Several modules planned for the station have been cancelled over the course of the ISS programme, whether for budgetary reasons, because the modules became unnecessary, or following a redesign of the station after the 2003 [[Space Shuttle Columbia disaster|''Columbia'' disaster]]. The US [[Centrifuge Accommodations Module]] was intended to host science experiments in varying levels of [[artificial gravity]].<ref>{{cite web|url=http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=12560&mid=269666|title=Where is the Centrifuge Accommodation Module (CAM)?|publisher=NASASpaceflight.com|accessdate=12 October 2009}}</ref> The US [[Habitation Module]] would have served as the station's living quarters. Instead, the sleep stations are now spread throughout the station.<ref>{{cite web|url=http://www.space.com/missionlaunches/060214_iss_module.html|title=NASA Recycles Former ISS Module for Life Support Research|author=Tariq Malik|accessdate=11 March 2009|publisher=Space.com|date=14 February 2006}}</ref> The US [[Interim Control Module]] and [[ISS Propulsion Module]] were intended to replace functions of ''Zvezda'' in case of a launch failure.<ref>{{cite web|title=ICM Interim Control Module|publisher=U.S. Naval Center for Space Technology|url=http://code8200.nrl.navy.mil/icm.html|archiveurl=https://web.archive.org/web/20070208164211/http://code8200.nrl.navy.mil/icm.html|archivedate=8 February 2007}}</ref> The Russian [[Universal Docking Module]], to which the cancelled Russian Research modules and spacecraft would have docked.<ref name="Zak">{{cite web|url=http://www.russianspaceweb.com/iss_russia.html|accessdate=3 October 2009|publisher=russianspaceweb.com|author=Anatoly Zak|title=Russian segment of the ISS}}</ref> The Russian [[Science Power Platform]] would have provided the [[Russian Orbital Segment]] with a power supply independent of the ITS solar arrays,<ref name="Zak" /> and two [[Russian Research Module]]s that were planned to be used for scientific research.<ref>{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/components/russian_laboratory.html|title=Russian Research Modules|publisher=Boeing|accessdate=21 June 2009}}</ref>

==Unpressurised elements==
[[File:Truss breakdown.png|thumb|right|ISS Truss Components breakdown showing Trusses and all ORUs in situ]]
The ISS features a large number of external components that do not require pressurisation. The largest such component is the [[Integrated Truss Structure]] (ITS), to which the station's main solar arrays and thermal radiators are mounted.<ref name="Arrays" /> The ITS consists of ten separate segments forming a structure 108.5 m (356 ft) long.<ref name="OnOrbit" />

The station in its complete form has several smaller external components, such as the six robotic arms, the three [[External Stowage Platform]]s (ESPs) and four [[ExPRESS Logistics Carrier]]s (ELCs).<ref name="Manifest" /><ref>{{cite web|url=http://www.nasa.gov/centers/marshall/news/background/facts/expressrack.html|title=EXPRESS Racks 1 and 2 fact sheet|accessdate=4 October 2009|date=12 April 2008|publisher=NASA}}</ref> Whilst these platforms allow experiments (including [[MISSE]], the STP-H3 and the [[Robotic Refueling Mission]]) to be deployed and conducted in the vacuum of space by providing electricity and processing experimental data locally, the platforms' primary function is to store [[Orbital Replacement Unit]]s (ORUs). ORUs are spare parts that can be replaced when the item either passes its design life or fails. Examples of ORUs include pumps, storage tanks, antennas and battery units. Such units are replaced either by astronauts during EVA or by robotic arms. Spare parts were routinely transported to and from the station via Space Shuttle resupply missions, with a heavy emphasis on ORU transport once the NASA Shuttle approached retirement.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/12/soyuz-tma-03m-docks-iss-returns-station-six-crewmembers-future-ops/ |title=Soyuz TMA-03M docks to ISS, returns station to six crewmembers for future ops |publisher=NASASpaceFlight.com |date=23 December 2011 |accessdate=1 May 2012}}</ref> Several shuttle missions were dedicated to the delivery of ORUs, including [[STS-129]],<ref name="EVA129">{{cite web|url=http://www.nasa.gov/centers/johnson/pdf/404493main_EVA_129_F_E1.pdf|title=EVA Checklist: STS-129 Flight Supplement|author=L. D. Welsch|publisher=NASA|date=30 October 2009}}</ref> [[STS-133]]<ref name="STS-133">{{cite web|url=http://www.nasa.gov/pdf/491387main_STS-133%20Press%20Kit.pdf|title=Space Shuttle Mission: STS-131|date=February 2011|publisher=NASA}}</ref> and [[STS-134]].<ref name="STS-134">{{cite web|url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf|title=Space Shuttle Mission: STS-134|publisher=NASA|date=April 2011}}</ref> {{asof|2011|01}}, only one other mode of transportation of ORUs had been utilised – the Japanese cargo vessel [[H-II Transfer Vehicle|HTV-2]] – which delivered an FHRC and CTC-2 via its Exposed Pallet (EP).<ref name="HTV2">{{cite web|url=http://iss.jaxa.jp/en/htv/mission/htv-2/library/presskit/htv2_presskit_en.pdf|title=HTV2: Mission Press Kit|publisher=Japan Aerospace Exploration Agency|date=20 January 2011}}</ref>{{update after|2013|1|28}}

[[File:STS-116 spacewalk 1.jpg|left|thumb|Construction of the [[Integrated Truss Structure]] over New Zealand.]]
There are also smaller exposure facilities mounted directly to laboratory modules; the JEM [[Japanese Experiment Module#Exposed Facility|Exposed Facility]] serves as an external '[[porch]]' for the Japanese Experiment Module complex,<ref>{{cite web|url=http://kibo.jaxa.jp/en/about/kibo/jef/|title=Exposed Facility:About Kibo|publisher=JAXA|date=29 August 2008|accessdate=9 October 2009}}</ref> and a facility on the European ''Columbus'' laboratory provides power and data connections for experiments such as the [[European Technology Exposure Facility]]<ref name="NASA">{{cite web|url=http://www.nasa.gov/mission_pages/station/science/experiments/EuTEF.html|title=NASA—European Technology Exposure Facility (EuTEF)|publisher=NASA|date=6 October 2008|accessdate=28 February 2009}}</ref><ref name="ESA">{{cite web|url=http://www.esa.int/esaMI/Columbus/SEM7ZTEMKBF_0.html|title=ESA—Columbus—European Technology Exposure Facility (EuTEF)|publisher=ESA|date=13 January 2009|accessdate=28 February 2009}}</ref> and the [[Atomic Clock Ensemble in Space]].<ref>{{cite web|url=http://www.esa.int/SPECIALS/HSF_Research/SEMJSK0YDUF_0.html|publisher=ESA|accessdate=9 October 2009|title=Atomic Clock Ensemble in Space (ACES)}}</ref> A [[remote sensing]] instrument, [[Stratospheric Aerosol and Gas Experiment|SAGE III-ISS]], is due to be delivered to the station in 2014 aboard a [[Dragon (spacecraft)|Dragon capsule]], and the [[Neutron star Interior Composition ExploreR|NICER]] experiment in 2016.<ref>{{cite web |url=http://heasarc.gsfc.nasa.gov/docs/nicer/papers/NICER-SPIE-July2012-v4.pdf | publisher=Goddard Space Flight Center |title=The Neutron star Interior Composition ExploreR (NICER): an Explorer mission of opportunity for soft x-ray timing spectroscopy |accessdate=8 April 2013 |author=NICER Team }}</ref><ref>{{cite web|url=http://www.nasa.gov/topics/earth/features/sage3.html|date=1 March 2011|accessdate=12 March 2011|publisher=NASA|title=Time to Fly: SAGE III — ISS Prepped for Space Station|author=Michael Finneran}}</ref> The largest such scientific payload externally mounted to the ISS is the [[Alpha Magnetic Spectrometer]] (AMS), a particle physics experiment launched on [[STS-134]] in May 2011, and mounted externally on the ITS. The AMS measures [[cosmic ray]]s to look for evidence of [[dark matter]] and [[antimatter]].<ref>{{cite web|url=http://ams.cern.ch/|title=The Alpha Magnetic Spectrometer Experiment|publisher=[[CERN]]|date=21 January 2009|accessdate=6 March 2009}}</ref>

===Robotic arms and cargo cranes===
{{Double image|right|Iss017e011097.jpg|250|Dextrereallyhasnohead.jpg|250|Commander [[Sergey Alexandrovich Volkov|Volkov]] stands on Pirs with his back to the [[Soyuz spacecraft|Soyuz]] whilst operating the manual [[Strela (crane)|Strela crane]] holding photographer [[Oleg Kononenko|Kononenko]]. [[Zarya]] is seen to the left and [[Zvezda (ISS module)|Zvezda]] across the bottom of the image.|[[Dextre]], like many of the station's experiments and robotic arms, can be operated from Earth and perform tasks while the crew sleeps.||}}

The [[Integrated Truss Structure]] serves as a base for the station's primary remote manipulator system, called the [[Mobile Servicing System]] (MSS), which is composed of three main components. [[Canadarm2]], the largest robotic arm on the ISS, has a mass of {{convert|1800|kg|lb}} and is used to dock and manipulate spacecraft and modules on the USOS, hold crew members and equipment in place during EVAs and move Dextre around to perform tasks.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/station/structure/elements/mss.html |title=Canadarm2 and the Mobile Servicing System |publisher=NASA |date=8 January 2013 |accessdate=22 June 2015}}</ref> [[Dextre]] is a {{convert|1560|kg|lb|abbr=on}} robotic manipulator with two arms, a rotating torso and has power tools, lights and video for replacing [[orbital replacement unit]]s (ORUs) and performing other tasks requiring fine control.<ref>{{cite web |url=http://www.asc-csa.gc.ca/eng/iss/dextre/default.asp |title=Dextre, the International Space Station's Robotic Handyman |publisher=Canadian Space Agency |accessdate=22 June 2015}}</ref> The [[Mobile Base System]] (MBS) is 2 platforms which rides on rails along the length of the station's main truss. It serves as a mobile base for Canadarm2 and Dextre, allowing the robotic arms to reach all parts of the USOS.<ref>{{cite web |url=http://www.asc-csa.gc.ca/eng/iss/mobile-base/default.asp |title=Mobile Base System |publisher=Canadian Space Agency |accessdate=22 June 2015}}</ref> To gain access to the Russian Segment a [[Grapple Fixture|grapple fixture]] was added to Zarya on [[STS-134]], so that Canadarm2 can inchworm itself onto the ROS.<ref name="presskit134">{{cite web |url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf |title=Space Shuttle Mission STS-134: Final Flight of ''Endeavour'' - Press Kit |format=PDF |publisher=NASA |pages=51-53 |date=April 2011 |accessdate=22 June 2015}}</ref> Also installed during STS-134 was the {{convert|50|ft|m|abbr=on|order=flip}} [[Orbiter Boom Sensor System]] (OBSS), which had been used to inspect head shield tiles on Space Shuttle missions and can be used on station to increase the reach of the MSS.<ref name="presskit134"/> Staff on Earth or the station can operate the MSS components via remote control, performing work outside the station without space walks.

Japan's [[Kibo (ISS module)#Remote Manipulator System|Remote Manipulator System]], which services the JEM Exposed Facility,<ref>{{cite web |url=http://kibo.jaxa.jp/en/about/kibo/rms/ |title=Remote Manipulator System: About Kibo |publisher=JAXA |date=29 August 2008 |accessdate=4 October 2009}}</ref> was launched on [[STS-124]] and is attached to the JEM Pressurised Module.<ref>{{cite web |url=http://www.nasa.gov/centers/johnson/news/station/2002/iss02-03.txt |title=International Space Station Status Report #02-03 |publisher=NASA |date=14 January 2002 |accessdate=4 October 2009}}</ref> The arm is similar to the Space Shuttle arm as it is permanently attached at one end and has a latching end effector for standard grapple fixtures at the other.

The [[European Robotic Arm]], which will service the Russian Orbital Segment, will be launched alongside the [[Multipurpose Laboratory Module]] in 2017.<ref>{{cite web |url=http://www.russianspaceweb.com/iss_fgb2.html |title=MLM (FGB-2) module of the ISS |publisher=RussianSpaceWeb |accessdate=16 June 2014}}</ref> The ROS does not require spacecraft or modules to be manipulated, as all spacecraft and modules dock automatically and may be discarded the same way. Crew use the two ''[[Strela (crane)|Strela]]'' ({{lang-ru|link=no|Стрела́}}; lit. Arrow) cargo cranes during EVAs for moving crew and equipment around the ROS. Each Strela crane has a mass of {{convert|45|kg|lb|abbr=on}}.

===Comparison===
The ISS follows [[Salyut]] and [[Almaz]] series, [[Cosmos 557]], [[Skylab]], and [[Mir]] as the 11th space station launched, as the [[Genesis II|Genesis]] prototypes were never intended to be manned. Other examples of modular station projects include the Soviet/Russian Mir and the planned Russian OPSEK and [[Chinese space station]]. The first space station, [[Salyut 1]], and other one-piece or 'monolithic' first generation space stations, such as Salyut 2,3,4,5, DOS 2, Kosmos 557, Almaz and NASA's [[Skylab]] stations were not designed for re-supply.<ref>http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/history.pdf</ref> Generally, each crew had to depart the station to free the only docking port for the next crew to arrive, Skylab had more than one docking port but was not designed for resupply. Salyut 6 and 7 had more than one docking port and were designed to be resupplied routinely during crewed operation.<ref>{{cite web|url=http://www.pbs.org/spacestation/station/russian.htm |title=Space Station | Russian Space History |publisher=Pbs.org |accessdate=1 May 2012}}</ref>

==Station systems==

===Life support===
{{Main|ISS ECLSS|Chemical oxygen generator}}
The critical systems are the atmosphere control system, the water supply system, the food supply facilities, the sanitation and hygiene equipment, and fire detection and suppression equipment. The Russian Orbital Segment's life support systems are contained in the Service Module Zvezda. Some of these systems are supplemented by equipment in the USOS. The MLM Nauka laboratory has a complete set of life support systems.

====Atmospheric control systems====
[[Image:SpaceStationCycle.svg|thumb|The interactions between the components of the ISS Environmental Control and Life Support System (ECLSS)|alt=A flowchart diagram showing the components of the ISS life support system.]]
The atmosphere on board the ISS is similar to the [[Atmosphere of Earth|Earth's]].<ref>{{cite web|url=http://science.howstuffworks.com/space-station2.htm |title=How Space Stations Work|first=Craig|last=Freudenrich|publisher=Howstuffworks|date=20 November 2000|accessdate=23 November 2008}}</ref> Normal air pressure on the ISS is 101.3 [[kilopascal|kPa]] (14.7 [[Pounds per square inch|psi]]);<ref>{{cite web |url=http://nasaexplores.com/show2_5_8a.php?id=04-032&gl=58|archiveurl=https://web.archive.org/web/20061114010931/http://www.nasaexplores.com/show2_5_8a.php?id=04-032&gl=58|archivedate=14 November 2006|work=NASAexplores|title=5–8: The Air Up There|publisher=NASA|accessdate=31 October 2008}}</ref> the same as at sea level on Earth. An Earth-like atmosphere offers benefits for crew comfort, and is much safer than the alternative, a pure oxygen atmosphere, because of the increased risk of a fire such as that responsible for the deaths of the [[Apollo 1]] crew.<ref>{{cite book|author=Clinton Anderson|display-authors=etal|publisher=US Government Printing Office|title=Report of the Committee on Aeronautical and Space Sciences, United States Senate—Apollo 204 Accident|date=30 January 1968|location=Washington, DC|page=8|url=http://klabs.org/richcontent/Reports/Failure_Reports/as-204/senate_956/as204_senate_956.pdf}}</ref> Earth-like atmospheric conditions have been maintained on all Russian and Soviet spacecraft.<ref name=spacemed>{{Citation | last1=Davis | first1=Jeffrey R. | last2=Johnson | first2=Robert | last3=Stepanek | first3=Jan | lastauthoramp=yes | title=Fundamentals of Aerospace Medicine | publisher=Lippincott Williams & Wilkins | place=Philadelphia PA, USA | volume=XII | pages=261–264 | year=2008}}</ref>

The ''[[Elektron (ISS)|Elektron]]'' system aboard ''Zvezda'' and a similar system in ''Destiny'' generate oxygen aboard the station.<ref name="OGS">{{cite web|url=http://www.space.com/businesstechnology/060215_techwed_iss_oxygen.html|title=Air Apparent: New Oxygen Systems for the ISS|author=Tariq Malik|publisher=Space.com|date=15 February 2006|accessdate=21 November 2008}}</ref> The crew has a backup option in the form of bottled oxygen and [[Vika oxygen generator|Solid Fuel Oxygen Generation]] (SFOG) canisters, a [[chemical oxygen generator]] system.<ref name="breath easy">{{cite web|url=http://science.nasa.gov/headlines/y2000/ast13nov_1.htm|title=Breathing Easy on the Space Station|author=Patrick L. Barry|publisher=NASA|date=13 November 2000|accessdate=21 November 2008}}</ref> Carbon dioxide is removed from the air by the [[Vozdukh]] system in ''Zvezda''. Other by-products of human metabolism, such as methane from the intestines and ammonia from sweat, are removed by [[Activated carbon|activated charcoal]] filters.<ref name="breath easy" />

Part of the ROS atmosphere control system is the oxygen supply, triple-redundancy is provided by the Elektron unit, solid fuel generators, and stored oxygen. The Elektron unit is the primary oxygen supply, {{chem|O|2}} and {{chem|H|2}} are produced by [[electrolysis]], with the {{chem|H|2}} being vented overboard. The 1 kW system uses approximately 1 litre of water per crew member per day from stored water from Earth, or water recycled from other systems. MIR was the first spacecraft to use recycled water for oxygen production. The secondary oxygen supply is provided by burning {{chem|O|2}}-producing [[Vika oxygen generator|Vika]] cartridges (see also [[ISS ECLSS]]). Each 'candle' takes 5–20 minutes to decompose at 450–500 °C, producing 600 litres of {{chem|O|2}}. This unit is manually operated.<ref>[http://suzymchale.com/ruspace/issrslss.html RuSpace | ISS Russian Segment Life Support System]. Suzymchale.com. Retrieved 8 October 2011.</ref>

The US Orbital Segment has redundant supplies of oxygen, from a pressurised storage tank on the Quest airlock module delivered in 2001, supplemented ten years later by ESA built Advanced Closed-Loop System (ACLS) in the Tranquility module (Node 3), which produces {{chem|O|2}} by electrolysis.<ref>[http://science.nasa.gov/science-news/science-at-nasa/2000/ast13nov_1/ Breathing Easy on the Space Station – NASA Science]. ''Science''.nasa.gov (13 November 2000). Retrieved 8 October 2011.</ref> Hydrogen produced is combined with carbon dioxide from the cabin atmosphere and converted to water and methane.

===Power and thermal control===
{{Main|Electrical system of the International Space Station|External Active Thermal Control System}}

{{Double image|left|ROSSA.jpg|200|P4 deployed.jpg|200|Russian solar arrays, backlit by sunset.|One of the eight truss mounted pairs of USOS solar arrays}}
Double-sided solar, or [[Photovoltaic]] arrays, provide [[Electric power|electrical power]] for the ISS. These bifacial cells are more efficient and operate at a lower temperature than single-sided cells commonly used on Earth, by collecting sunlight on one side and light [[Albedo|reflected off]] the Earth on the other.<ref>{{cite web |url=http://wenku.baidu.com/view/a815121ffc4ffe473368ab7a.html |title=The early history of bifacial solar cell_百度文库 |publisher=Wenku.baidu.com |date=25 October 2010 |accessdate=14 August 2012}}</ref> 

The Russian segment of the station, like the Space Shuttle and most spacecraft, uses 28 [[volt]] [[direct current|DC]] from four rotating solar arrays mounted on ''Zarya'' and ''Zvezda''. The USOS uses 130–180 V DC from the USOS PV array, power is stabilised and distributed at 160 V DC and converted to the user-required 124 V DC. The [[High voltage|higher distribution voltage]] allows smaller, lighter conductors, at the expense of crew safety. The ROS uses [[Extra-low voltage|low voltage]]. The two station segments share power with converters.<ref name="Arrays" />

The USOS solar arrays are arranged as four wing pairs, with each wing producing nearly 32.8 kW.<ref name="Arrays">{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/truss_segment.html|title=Spread Your Wings, It's Time to Fly|publisher=NASA|date=26 July 2006|accessdate=21 September 2006}}</ref> These arrays normally track the sun to maximise power generation. Each array is about 375 m2 (450 yd2) in area and {{convert|58|m|yd|0}} long. In the complete configuration, the solar arrays track the sun by rotating the ''alpha [[gimbal]]'' once per orbit; the ''beta gimbal'' follows slower changes in the angle of the sun to the orbital plane. The [[Night Glider mode]] aligns the solar arrays parallel to the ground at night to reduce the significant aerodynamic drag at the station's relatively low orbital altitude.<ref>{{cite journal|author=G. Landis and C-Y. Lu|year=1991|title=Solar Array Orientation Options for a Space Station in Low Earth Orbit|journal=Journal of Propulsion and Power|volume=7|issue=1|pages=123–125|doi=10.2514/3.23302}}</ref>

The station uses rechargeable [[Nickel hydrogen battery|nickel-hydrogen batteries]] (NiH2) for continuous power during the 35 minutes of every 90-minute orbit that it is eclipsed by the Earth. The batteries are recharged on the day side of the Earth. They have a 6.5-year lifetime (over 37,000 charge/discharge cycles) and will be regularly replaced over the anticipated 20-year life of the station.<ref>{{cite web|url=http://www.grc.nasa.gov/WWW/RT/RT1999/5000/5420miller.html|title=Nickel-Hydrogen Battery Cell Life Test Program Update for the International Space Station|accessdate=27 November 2009|publisher=NASA|author=Thomas B. Miller|date=24 April 2000}}</ref>

The station's large solar panels generate a high potential voltage difference between the station and the ionosphere. This could cause arcing through insulating surfaces and sputtering of conductive surfaces as ions are accelerated by the spacecraft plasma sheath. To mitigate this, plasma contactor units (PCU)s create current paths between the station and the ambient plasma field.<ref>[http://www.grc.nasa.gov/WWW/RT/RT1998/5000/5430patterson.html Cathodes Delivered for Space Station Plasma Contactor System]. Grc.nasa.gov (18 June 1999). Retrieved 8 October 2011.</ref>

[[File:EATCS.png|thumb|ISS External Active Thermal Control System (EATCS) diagram]]
The large amount of electrical power consumed by the station's systems and experiments is turned almost entirely into heat. The heat which can be dissipated through the walls of the stations modules is insufficient to keep the internal ambient temperature within comfortable, workable limits. [[Ammonia]] is continuously pumped through pipework throughout the station to collect heat, then into external radiators exposed to the cold of space, and back into the station.

The International Space Station (ISS) External Active Thermal Control System (EATCS) maintains an equilibrium when the ISS environment or heat loads exceed the capabilities of the Passive Thermal Control System (PTCS). Note Elements of the PTCS are external surface materials, insulation such as MLI, or Heat Pipes. The EATCS provides heat rejection capabilities for all the US pressurised modules, including the JEM and COF as well as the main power distribution electronics of the S0, S1 and P1 Trusses. The EATCS consists an internal, non-toxic, water coolant loop used to cool and dehumidify the atmosphere, which transfers collected heat into an external liquid ammonia loop capable of withstanding the much lower temperature of space, which is then circulated through radiators to remove the heat. The EATCS is capable of rejecting up to 70 kW, and provides a substantial upgrade in heat rejection capacity from the 14 kW capability of the Early External Active Thermal Control System (EEATCS) via the Early Ammonia Servicer (EAS), which was launched on [[STS-105]] and installed onto the P6 Truss.<ref>[http://www.nasa.gov/pdf/473486main_iss_atcs_overview.pdf ATCS Team Overview]. (PDF). Retrieved 8 October 2011.</ref>

===Communications and computers===
{{Main|Tracking and Data Relay Satellite|Luch (satellite)}}
{{See also2|[[ThinkPad#Use in space|ThinkPad use in space]]}}
[[File:ISS Communication Systems.png|thumb|The communications systems used by the ISS * Luch satellite not currently in use|alt=Diagram showing communications links between the ISS and other elements.]]
Radio communications provide [[telemetry]] and scientific data links between the station and [[Mission Control Center|Mission Control Centres]]. Radio links are also used during [[Space rendezvous|rendezvous and docking procedures]] and for audio and video communication between crewmembers, flight controllers and family members. As a result, the ISS is equipped with internal and external communication systems used for different purposes.<ref name="BoeingComm" />


The Russian Orbital Segment communicates directly with the ground via the ''[[Lira (ISS)|Lira]]'' [[Antenna (radio)|antenna]] mounted to ''Zvezda''.<ref name="ISSRG" /><ref>{{cite web|url=http://www.nasa.gov/home/hqnews/2005/mar/HQ_ss05015_ISS_status_report.html|title=International Space Station Status Report: SS05-015|last=Mathews|first=Melissa|author2=James Hartsfield|date=25 March 2005|work=NASA News|publisher=NASA|accessdate=11 January 2010}}</ref> The ''Lira'' antenna also has the capability to use the ''[[Luch (satellite)|Luch]]'' data relay satellite system.<ref name="ISSRG" /> This system, used for communications with ''Mir'', fell into disrepair during the 1990s, and as a result is no longer in use,<ref name="ISSRG" /><ref name="SSSM">{{cite book|first=David|last=Harland|title=The Story of Space Station Mir|publisher=Springer-Verlag New York Inc|date=30 November 2004|location=New York|isbn=978-0-387-23011-5}}</ref><ref name="Harvey">{{cite book|last=Harvey|first=Brian|title=The rebirth of the Russian space program: 50 years after Sputnik, new frontiers|publisher=Springer Praxis Books|year=2007|page=263|isbn=0-387-71354-9}}</ref> although two new ''Luch'' satellites—''Luch''-5A and ''Luch''-5B—were launched in 2011 and 2012 respectively to restore the operational capability of the system.<ref>{{cite web|publisher=RussianSpaceWeb|url=http://www.russianspaceweb.com/2011.html|accessdate=12 January 2010|title=Space exploration in 2011|date=4 January 2010|author=Anatoly Zak}}</ref> Another Russian communications system is the [[Voskhod-M]], which enables internal telephone communications between ''Zvezda'', ''Zarya'', ''Pirs'', ''Poisk'' and the USOS, and also provides a VHF radio link to ground control centres via antennas on ''Zvezda''{{'s}} exterior.<ref>{{cite web|url=http://www.nasa.gov/directorates/somd/reports/iss_reports/2010/05022010.html|date=2 May 2010|accessdate=7 July 2010|publisher=NASA|title=ISS On-Orbit Status 05/02/10}}</ref>

The [[US Orbital Segment]] (USOS) makes use of two separate radio links mounted in the [[Z1 truss]] structure: the [[S band]] (used for audio) and [[Ku band|Ku band]] (used for audio, video and data) systems. These transmissions are routed via the United States [[Tracking and Data Relay Satellite]] System (TDRSS) in [[geostationary orbit]], which allows for almost continuous real-time communications with [[Christopher C. Kraft Jr. Mission Control Center|NASA's Mission Control Center]] (MCC-H) in [[Houston]].<ref name="ISSBook" /><ref name="ISSRG" /><ref name="BoeingComm">{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/systems/communications_tracking.html|publisher=Boeing|accessdate=30 November 2009|title=Communications and Tracking|archiveurl = https://web.archive.org/web/20080611115319/http://www.boeing.com/defense-space/space/spacestation/systems/communications_tracking.html |archivedate = 11 June 2008}}</ref> Data channels for the Canadarm2, European ''Columbus'' laboratory and Japanese ''Kibō'' modules are routed via the S band and Ku band systems, although the [[European Data Relay System]] and a similar Japanese system will eventually complement the TDRSS in this role.<ref name="ISSBook" /><ref name="JAXA-MOU">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/nasa_japan.html|title=Memorandum of Understanding Between the National Aeronautics and Space Administration of the United States of America and the Government of Japan Concerning Cooperation on the Civil International Space Station|publisher=NASA|accessdate=19 April 2009|date=24 February 1998}}</ref> Communications between modules are carried on an internal digital [[wireless network]].<ref>{{cite web|title=Operations Local Area Network (OPS LAN) Interface Control Document|format=PDF|publisher=NASA|url=http://www.spaceref.com/iss/computer/iss.ops.lan.icd.pdf|accessdate=30 November 2009|date=February 2000}}</ref>

[[File:STS-128 ISS-20 Destiny Canadarm2.jpg|thumb|left|Laptop computers surround the Canadarm2 console.]]
[[Ultra high frequency|UHF radio]] is used by astronauts and cosmonauts conducting [[Extra-vehicular activity|EVAs]]. UHF is employed by other spacecraft that dock to or undock from the station, such as Soyuz, Progress, HTV, ATV and the Space Shuttle (except the shuttle also makes use of the S band and Ku band systems via TDRSS), to receive commands from Mission Control and ISS crewmembers.<ref name="ISSRG" /> Automated spacecraft are fitted with their own communications equipment; the ATV uses a [[laser]] attached to the spacecraft and equipment attached to ''Zvezda'', known as the Proximity Communications Equipment, to accurately dock to the station.<ref>{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=16247|title=ISS/ATV communication system flight on Soyuz|accessdate=30 November 2009|publisher=[[EADS Astrium]]|date=28 February 2005}}</ref><ref>{{cite web|publisher=NASASpaceflight.com|author=Chris Bergin|url=http://www.nasaspaceflight.com/2009/11/sts-129-support-dragon-communication-demo-iss/|date=10 November 2009|accessdate=30 November 2009|title=STS-129 ready to support Dragon communication demo with ISS}}</ref>

The ISS is equipped with approximately 100 [[IBM]] and [[Lenovo]] [[ThinkPad#Use in space|ThinkPad]] model A31 and T61P laptop computers. Each computer is a [[commercial off-the-shelf]] purchase which is then modified for safety and operation including updates to connectors, cooling and power to accommodate the station's 28V DC power system and weightless environment. Heat generated by the laptops does not rise, but stagnates surrounding the laptop, so additional forced ventilation is required. Laptops aboard the ISS are connected to the station's [[wireless LAN]] via [[Wi-Fi]] and to the ground via Ku band. This provides speeds of 10 [[Megabit per second|Mbit/s]] to and 3 Mbit/s from the station, comparable to home [[digital subscriber line|DSL]] connection speeds.<ref name="issit">{{cite news |url=http://bits.blogs.nytimes.com/2010/01/22/first-tweet-from-space/ |title=First Tweet From Space |work=[[The New York Times]] |first=Nick |last=Bilton |date=22 January 2010 |accessdate=29 April 2014}}</ref><ref name="tested20121019">{{cite news |url=http://www.tested.com/science/space/449539-how-fast-isss-internet-and-other-space-questions-answered/ |title=How Fast is the ISS's Internet? (and Other Space Questions Answered) |work=Tested.com |first=Will |last=Smith |date=19 October 2012 |accessdate=29 April 2014}}</ref>

The operating system used for key station functions is the [[Debian]] [[GNU/Linux distribution]].<ref>{{cite news|last=Thomson|first=Iain|title=Penguins in spa-a-a-ce! ISS dumps Windows for Linux on laptops|url=http://www.theregister.co.uk/2013/05/10/iss_linux_debian_deployment/|accessdate=15 May 2013|newspaper=The Register|date=10 May 2013}}</ref> The migration from [[Microsoft Windows]] was made in May 2013 for reasons of reliability, stability and flexibility.<ref>{{cite news|last=Gunter|first=Joel|title=International Space Station to boldly go with Linux over Windows|url=http://www.telegraph.co.uk/technology/news/10049444/International-Space-Station-to-boldly-go-with-Linux-over-Windows.html|accessdate=15 May 2013|newspaper=The Daily Telegraph|date=10 May 2013}}</ref>

==Station operations==

===Expeditions and private flights===
[[File:Sts088-703-019e.jpg|thumb|Zarya and Unity were entered for the first time on 10 December 1998.]]
[[File:Soyuz tm-31 transported to launch pad.jpg|right|thumb|Soyuz TM-31 being prepared to bring the first resident crew to the station in October 2000]]
[[File:STS-115 ISS after undocking.jpg|thumb|right|ISS was slowly assembled over a decade of spaceflights and crews]]
[[File:Tracy Caldwell Dyson in Cupola ISS.jpg|thumb|Expeditions have included male and female crew-members from many nations]]
''See also the [[list of International Space Station expeditions]] (professional crew), [[space tourism]] (private travellers), and the [[list of human spaceflights to the ISS]] (both).''

Each permanent crew is given an expedition number. Expeditions run up to six months, from launch until undocking, an 'increment' covers the same time period, but includes cargo ships and all activities. Expeditions 1 to 6 consisted of 3 person crews, Expeditions 7 to 12 were reduced to the safe minimum of two following the destruction of the NASA Shuttle Columbia. From Expedition 13 the crew gradually increased to 6 around 2010.<ref name="ISSEx">{{cite web|title=International Space Station Expeditions|publisher=NASA|url=http://www.nasa.gov/mission_pages/station/expeditions/index.html|date=10 April 2009|accessdate=13 April 2009}}</ref><ref name="current">{{cite web|url=http://www.nasa.gov/mission_pages/station/main/index.html|title=International Space Station|accessdate=22 October 2008|publisher=NASA|year=2008|author=NASA}}</ref> With the arrival of the American [[Commercial Crew Development|Commercial Crew]] vehicles in the middle of the 2010s, expedition size may be increased to seven crew members, the number ISS is designed for.<ref>{{cite web|url=http://www.aviationweek.com/article.aspx?id=/article-xml/asd_07_26_2012_p01-02-480253.xml|title=ISS Research Hampered By Crew Availability|last=Morring|first=Frank|date=27 July 2012|quote=A commercial capability would allow the station's crew to grow from six to seven by providing a four-seat vehicle for emergency departures in addition to the three-seat Russian Soyuz capsules in use today.|publisher=Aviation Week|accessdate=30 July 2012}}</ref><ref>{{cite web|url=http://www.airspacemag.com/space-exploration/AS-Interview-Mike-Suffredini.html|title=Assembly (Nearly) Complete |last=Hoversten|first=Paul|date=1 May 2011|publisher=Air & Space Magazine|quote=In fact, we're designed on the U.S. side to take four crew. The ISS design is actually for seven. We operate with six because first, we can get all our work done with six, and second, we don't have a vehicle that allows us to fly a seventh crew member. Our requirement for the new vehicles being designed is for four seats. So I don't expect us to go down in crew size. I would expect us to increase it.|accessdate=8 May 2011}}</ref>

[[Sergei Krikalev]], member of [[Expedition 1]] and Commander of [[Expedition 11]] has spent more time in space than anyone else, a total of 803 days and 9 hours and 39 minutes. His awards include the [[Order of Lenin]], [[Hero of the Soviet Union]], [[Hero of the Russian Federation]], and 4 NASA medals. On 16 August 2005 at 1:44 am EDT he passed the record of 748 days held by [[Sergei Avdeyev]], who had 'time travelled' 1/50th of a second into the future on board MIR.<ref>{{cite web|url=http://www.popsci.com/scitech/article/2002-02/lets-do-time-warp-again?page=2 |archiveurl=https://web.archive.org/web/20100628190931/http://www.popsci.com/scitech/article/2002-02/lets-do-time-warp-again?page=2 |archivedate=28 June 2010 |title=Let's Do the Time Warp Again |publisher=Web.archive.org |date=28 June 2010 |accessdate=1 May 2012}}</ref> He participated in psychosocial experiment SFINCSS-99 (Simulation of Flight of International Crew on Space Station), which examined inter-cultural and other stress factors affecting integration of crew in preparation for the ISS spaceflights. Commander [[Michael Fincke]] has spent a total of 382 days in space – more than any other American astronaut.

Travellers who pay for their own passage into space are termed spaceflight participants by Roscosmos and NASA, and are sometimes informally referred to as space tourists, a term they generally dislike.{{refn|Privately funded travellers who have objected to the term include Dennis Tito, the first such traveller (''Associated Press'', 8 May 2001), [[Mark Shuttleworth]], founder of [[Ubuntu (operating system)|Ubuntu]] (''Associated Press, The Spokesman Review, 6 January 2002, p. A4''), Gregory Olsen and Richard Garriott.<ref>{{cite news|last=Schwartz|first=John|title=Russia Leads Way in Space Tourism With Paid Trips into Orbit|url=http://www.nytimes.com/2008/10/11/science/space/11space.html|newspaper=The New York Times|date=10 October 2008}}</ref><ref>{{cite web|last=Boyle|first=Alan|title=Space passenger Olsen to pull his own weight|url=http://msnbc.msn.com/id/9323509/#.Tz5lcFE-qr4|publisher=MSNBC}}</ref> Canadian astronaut Bob Thirsk said the term does not seem appropriate, referring to his crewmate, [[Guy Laliberté]], founder of [[Cirque du Soleil]].<ref>{{cite web|url=http://www.stcatharinesstandard.ca/ArticleDisplay.aspx?e=1975186&archive=true |title=Flight to space ignited dreams | St. Catharines Standard |publisher=Stcatharinesstandard.ca |accessdate=1 May 2012}}</ref> Anousheh Ansari denied being a tourist<ref>{{cite web|url=http://www.esa.int/esaHS/SEMD58BE8YE_business_0.html |title=ESA – Human Spaceflight and Exploration – Business – "I am NOT a tourist" |publisher=Esa.int |date=18 September 2006 |accessdate=1 May 2012}}</ref> and took offence at the term.<ref>{{cite web|url=http://www.space.com/2889-interview-anousheh-ansari-female-space-tourist.html |title=Interview with Anousheh Ansari, the First Female Space Tourist |publisher=Space.com |date=15 September 2006 |accessdate=1 May 2012}}</ref>|group=note|name}} All seven were transported to the ISS on Russian Soyuz spacecraft. When professional crews change over in numbers not divisible by the three seats in a Soyuz, and a short-stay crewmember is not sent, the spare seat is sold by MirCorp through Space Adventures. When the space shuttle retired in 2011, and the station's crew size was reduced to 6, space tourism was halted, as the partners relied on Russian transport seats for access to the station. Soyuz flight schedules increase after 2013, allowing 5 Soyuz flights (15 seats) with only two expeditions (12 seats) required.<ref>{{cite web|url=http://www.spaceflightnow.com/news/n1101/12soyuz/ |title=Breaking News | Resumption of Soyuz tourist flights announced |publisher=Spaceflight Now |accessdate=1 May 2012}}</ref> The remaining seats are sold for around {{US$|40 million}} to members of the public who can pass a medical. ESA and NASA criticised private spaceflight at the beginning of the ISS, and NASA initially resisted training [[Dennis Tito]], the first man to pay for his own passage to the ISS.{{refn|ESA director Jörg Feustel-Büechl said in 2001 that Russia had no right to send 'amateurs' to the ISS. A 'stand-off' occurred at the Johnson Space Centre between Commander Talgat Musabayev and NASA manager Robert Cabana. Cabana refused to train Dennis Tito, a member of Musabayev's crew along with Yuri Baturin. The commander argued that Tito had trained 700 hours in the last year and was as qualified as any NASA astronaut, and refused to allow his crew to be trained on the American portions of the station without Tito. Cabana stated training could not begin, and the commander returned with his crew to their hotel.|group=note|name}}  [[Toyohiro Akiyama]] was flown to Mir for a week, he was classed as a business traveller, as his employer, [[Tokyo Broadcasting System]], paid for his ticket, and he gave a daily TV broadcast from orbit.

[[Anousheh Ansari]] ({{lang-fa|انوشه انصاری}}) became the first Iranian in space and the first self-funded woman to fly to the station. Officials reported that her education and experience make her much more than a tourist, and her performance in training had been "excellent."<ref>{{cite web|last=Maher |first=Heather |url=http://www.rferl.org/content/article/1071358.html |title=U.S.: Iranian-American To Be First Female Civilian in Space |publisher=Radio Free Europe/Radio Liberty |date=15 September 2006 |accessdate=1 May 2012}}</ref> Ansari herself dismisses the idea that she is a tourist. She did Russian and European studies involving medicine and microbiology during her 10-day stay. The documentary ''[[Space Tourists]]'' follows her journey to the station, where she fulfilled "an age-old dream of man: to leave our planet as a «normal person» and travel into outer space."<ref>{{cite web|url=http://www.space-tourists-film.com/en/film_synopsis.php |title=Space Tourists | A Film By Christian Frei |publisher=Space-tourists-film.com |accessdate=1 May 2012}}</ref> In the film, some Kazakhs are shown waiting in the middle of the steppes for four rocket stages to literally fall from the sky. Film-maker Christian Frei states "Filming the work of the Kazakh scrap metal collectors was anything but easy. The Russian authorities finally gave us a film permit in principle, but they imposed crippling preconditions on our activities. The real daily routine of the scrap metal collectors could definitely not be shown. Secret service agents and military personnel dressed in overalls and helmets were willing to ''re-enact'' their work for the cameras – in an idealised way that officials in Moscow deemed to be presentable, but not at all how it takes place in reality."

Spaceflight participant [[Richard Garriott]] placed a [[Geocaching|geocache]] aboard the ISS during his flight.<ref>{{cite web|url=http://www.geocaching.com/seek/cache_details.aspx?wp=GC1BE91|title=International Space Station Traditional Geocache}}</ref> This is currently the only non-terrestrial geocache in existence.<ref>{{cite web |url=http://www.geekwire.com/2011/outer-space-ocean-floor-15m-geocaches-counting/|accessdate=27 February 2013|last=Cook|first=John|title=From outer space to the ocean floor, Geocaching.com now boasts more than 1.5 million hidden treasures|date=29 August 2011}}</ref>

===Orbit===
{{Double image|right|Internationale Raumstation Bahnhöhe (dumb version).png|300|Iss.ogg|235|Graph showing the changing altitude of the ISS from November 1998 until January 2009|Animation of ISS orbit from a North American geostationary point of view (sped up 1800 times)}}
The ISS is maintained in a nearly circular orbit with a minimum mean altitude of 330 km (205 mi) and a maximum of 410 km (255 mi), in the centre of the [[thermosphere]], at an [[inclination]] of 51.6 degrees to Earth's equator, necessary to ensure that Russian [[Soyuz (spacecraft)|Soyuz]] and [[Progress (spacecraft)|Progress]] spacecraft launched from the [[Baikonur Cosmodrome]] may be safely launched to reach the station. Spent rocket stages must be dropped into uninhabited areas and this limits the directions rockets can be launched from the spaceport.<ref name="MCC Answer">{{cite web|last=Cooney|first=Jim|title=Mission Control Answers Your Questions|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-112/09_04_12_54_17.html|location=Houston, TX|quote=Jim Cooney ISS Trajectory Operations Officer}}</ref><ref>{{cite book|last=Pelt|first=Michel van|title=Into the Solar System on a String : Space Tethers and Space Elevators|year=2009|publisher=Springer New York|location=New York, NY|isbn=0-387-76555-7|page=133|edition=1.}}</ref> The orbital inclination chosen was also low enough to allow American space shuttles launched from Florida to reach the ISS.

It travels at an average speed of 27,724 kilometres (17,227 mi) per hour, and completes {{Orbit|daily orbits|15.54}} orbits per day (93 minutes per orbit).{{Orbit|ref|<ref name="heavens-above"/>}}<ref name="tracking">{{cite web|url=http://spaceflight.nasa.gov/realdata/tracking/index.html|title=Current ISS Tracking data|accessdate=28 January 2009|publisher=NASA|date=15 December 2008|author=NASA}}</ref> The station's altitude was allowed to fall around the time of each NASA shuttle mission. Orbital boost burns would generally be delayed until after the shuttle's departure. This allowed shuttle payloads to be lifted with the station's engines during the routine firings, rather than have the shuttle lift itself and the payload together to a higher orbit. This trade-off allowed heavier loads to be transferred to the station. After the retirement of the NASA shuttle, the nominal orbit of the space station was raised in altitude.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/06/europes-atv-2-depart-iss-make-way-russias-progress-m-11m/ |title=Europe's ATV-2 departs ISS to make way for Russia's Progress M-11M |publisher=NASASpaceFlight.com |date=20 June 2011 |accessdate=1 May 2012}}</ref><ref name="Popular Mechanics">{{cite web|url=http://www.popularmechanics.com/science/air_space/4275571.html|title=The Uncertain Future of the International Space Station: Analysis|author=Rand Simberg|date=29 July 2008|accessdate=6 March 2009|publisher=[[Popular Mechanics]]}}</ref> Other, more frequent supply ships do not require this adjustment as they are substantially lighter vehicles.<ref name="Worldbook at NASA">{{cite web|url=http://www.nasa.gov/worldbook/intspacestation_worldbook.html|title = International Space Station|year=2005|accessdate=14 June 2008|publisher=World Book, Inc|author=James Oberg|work=World Book Online Reference Center}}{{dead link|date=May 2012}}</ref><ref name="nasa.gov-iss-environment">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archiveurl=https://web.archive.org/web/20080213164432/http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archivedate=13 February 2008|title=ISS Environment|accessdate=15 October 2007|publisher=[[Johnson Space Center]]}}</ref>
[[File:ISS orbits 04132013.jpg|thumbnail|Orbits of the ISS, shown in April 2013]]
Orbital boosting can be performed by the station's two main engines on the ''[[Zvezda (ISS module)|Zvezda]]'' service module, or Russian or European spacecraft docked to Zvezda's aft port. The ATV has been designed with the possibility of adding a [[Automated Transfer Vehicle#ATV evolution proposals|second docking port]] to its other end, allowing it to remain at the ISS and still allow other craft to dock and boost the station. It takes approximately two orbits (three hours) for the boost to a higher altitude to be completed.<ref name="nasa.gov-iss-environment" /> In December 2008 NASA signed an agreement with the [[Ad Astra Rocket Company]] which may result in the testing on the ISS of a [[VASIMR]] plasma propulsion engine.<ref name="vasimr">{{cite web|url=http://www.adastrarocket.com/AdAstra-NASA_PR12Dec08.pdf|publisher=AdAstra Rocket Company|title=Press Release 121208|accessdate=7 December 2009|date=12 December 2008|format=PDF}}</ref> This technology could allow [[Orbital station-keeping|station-keeping]] to be done more economically than at present.<ref name="future-prop">{{cite web|url=http://www.nasa.gov/vision/space/travelinginspace/future_propulsion.html|title=Propulsion Systems of the Future|accessdate=29 May 2009|publisher=NASA}}</ref><ref>{{cite web|work=New Scientist|accessdate=7 October 2009|url=http://www.newscientist.com/article/dn17918-rocket-company-tests-worlds-most-powerful-ion-engine.html|title=Rocket company tests world's most powerful ion engine|author=David Shiga|date=5 October 2009}}</ref>

The Russian Orbital Segment contains the station's engines and control [[Bridge (nautical)|bridge]], which handles Guidance, Navigation and Control (ROS GNC) for the entire station.<ref name="Navigation">{{cite web|url=http://www.esa.int/export/esaHS/ESAOXX0VMOC_iss_0.html|title=DMS-R: ESA's Data Management System for the Russian Segment of the ISS}}</ref> Initially, Zarya, the first module of the station, controlled the station until a short time after the Russian service module Zvezda docked and was transferred control. Zvezda contains the ESA built DMS-R Data Management System.<ref name="EsaComputer">{{cite web|url=http://www.esa.int/esapub/onstation/onstation17/os17_chapter6.pdf|title=Exercising Control 49 months of DMS-R Operations}}</ref> Using two fault-tolerant computers (FTC), Zvezda computes the station's position and orbital trajectory using redundant Earth horizon sensors, Solar horizon sensors as well as Sun and star trackers. The FTCs each contain three identical processing units working in parallel and provide advanced fault-masking by majority voting. Zvezda uses gyroscopes and thrusters to turn itself around. Gyroscopes do not require propellant, rather they use electricity to 'store' momentum in flywheels by turning in the opposite direction to the station's movement. The USOS has its own computer controlled gyroscopes to handle the extra mass of that section. When gyroscopes 'saturate', reaching their maximum speed, thrusters are used to cancel out the stored momentum. During [[Expedition 10]], an incorrect command was sent to the station's computer, using about 14 kilograms of propellant before the fault was noticed and fixed. When attitude control computers in the ROS and USOS fail to communicate properly, it can result in a rare 'force fight' where the ROS GNC computer must ignore the USOS counterpart, which has no thrusters.<ref>{{cite web|url=http://pims.grc.nasa.gov/pimsdocs/public/ISS%20Handbook/hb_qs_vehicle_RussianUSGNCForceFight.pdf |title=Microsoft Word – hb_qs_vehicle_RussianUSGNCForceFight_pg1.doc |format=PDF |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://spaceflight.nasa.gov/spacenews/reports/issreports/2005/iss05-7.html|title = International Space Station Status Report #05-7|date=11 February 2005|publisher=NASA|accessdate=23 November 2008}}</ref><ref>{{cite book|title=Dynamics and Control of Attitude, Power, and Momentum for a Spacecraft Using Flywheels and Control Moment Gyroscopes|author=Carlos Roithmayr|format=PDF|year=2003|publisher=NASA|location=Langley Research Center|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030038806_2003038772.pdf|accessdate=12 July 2011}}</ref> When an ATV, NASA Shuttle, or Soyuz is docked to the station, it can also be used to maintain station attitude such as for troubleshooting. Shuttle control was used exclusively during [[STS-117|installation]] of the S3/S4 truss, which provides electrical power and data interfaces for the station's electronics.<ref>{{cite web|url=http://www.nasaspaceflight.com/2007/06/atlantis-ready-to-support-iss-troubleshooting/|title=Atlantis ready to support ISS troubleshooting|publisher=NASASPaceflight.com|author=Chris Bergin|accessdate=6 March 2009|date=14 June 2007}}</ref>

==Mission controls==
The components of the ISS are operated and monitored by their respective space agencies at [[Mission Control Center|mission control centres]] across the globe, including:
* Roscosmos's [[Mission Control Center#RKA Mission Control Center|Mission Control Center]] at [[Korolyov (city)|Korolyov]], Moscow Oblast, controls the [[Russian Orbital Segment]] which handles Guidance, Navigation & Control for the entire Station.,<ref name="Navigation" /><ref name="EsaComputer" /> in addition to individual Soyuz and Progress missions.<ref name="ISSRG" />
* ESA's [[ATV Control Centre]], at the [[Toulouse Space Centre]] (CST) in [[Toulouse]], France, controls flights of the unmanned European [[Automated Transfer Vehicle]].<ref name="ISSRG" />
* JAXA's [[JEM Control Center]] and [[HTV Control Center]] at [[Tsukuba Space Center]] (TKSC) in [[Tsukuba]], Japan, are responsible for operating the Japanese Experiment Module complex and all flights of the 'White Stork' HTV Cargo spacecraft, respectively.<ref name="ISSRG" />
* NASA's [[Christopher C. Kraft Jr. Mission Control Center|Mission Control Center]] at [[Lyndon B. Johnson Space Center]] in Houston, Texas, serves as the primary control facility for the United States segment of the ISS and also controlled the Space Shuttle missions that visited the station.<ref name="ISSRG">{{cite book|author=Gary Kitmacher|title=Reference Guide to the International Space Station| publisher =[[Apogee Books]]|location=Canada|year=2006|isbn=978-1-894959-34-6|issn=1496-6921|pages=71–80}}</ref>
* NASA's [[Payload Operations and Integration Center]] at [[Marshall Space Flight Center]] in [[Huntsville, Alabama]], coordinates payload operations in the USOS.<ref name="ISSRG" />
* ESA's [[Columbus Control Center|Columbus Control Centre]] at the [[German Aerospace Center|German Aerospace Centre]] (DLR) in [[Oberpfaffenhofen]], Germany, manages the European ''Columbus'' research laboratory.<ref name="ISSRG" />
* CSA's [[MSS Control]] at [[Saint-Hubert, Quebec]], Canada, controls and monitors the [[Mobile Servicing System]], or Canadarm2.<ref name="ISSRG" />
{{wide image|ISS Centers.svg|880px|Space centres involved with the ISS programme|alt=A world map highlighting the locations of space centres. See adjacent text for details.}}

===Repairs===
{{Main|Orbital Replacement Units|International Space Station maintenance}}
'''[[Orbital Replacement Units]]''' ('''ORUs''') are spare parts that can be readily replaced when a unit either passes its design life or fails. Examples of ORUs are pumps, storage tanks, controller boxes, antennas, and battery units. Some units can be replaced using robotic arms. Many are stored outside the station, either on small pallets called [[ExPRESS Logistics Carrier]]s (ELCs) or share larger platforms called [[External Stowage Platform]]s which also hold science experiments. Both kinds of pallets have electricity as many parts which could be damaged by the cold of space require heating. The larger logistics carriers also have computer local area network connections (LAN) and telemetry to connect experiments. A heavy emphasis on stocking the USOS with ORU's occurred around 2011, before the end of the NASA shuttle programme, as its commercial replacements, [[Cygnus (spacecraft)|Cygnus]] and [[Dragon (spacecraft)|Dragon]], carry one tenth to one quarter the payload.

[[File:ISS Unpressurized Platforms.png|thumb|Spare parts are called [[Orbit Replaceable Unit|ORU]]s; some are externally stored on pallets called [[ExPRESS Logistics Carrier|ELC]]s and [[External stowage platform|ESP]]s.]]

Unexpected problems and failures have impacted the station's assembly time-line and work schedules leading to periods of reduced capabilities and, in some cases, could have forced abandonment of the station for safety reasons, had these problems not been resolved. During [[STS-120]] in 2007, following the relocation of the P6 truss and solar arrays, it was noted during the redeployment of the array that it had become torn and was not deploying properly.<ref name="Astronauts notice tear in solar panel">{{cite news|url=http://www.redorbit.com/news/space/1123767/astronauts_notice_tear_in_solar_panel/index.html |title=Astronauts notice tear in solar panel|accessdate=30 October 2007|agency=Associated Press|date=30 October 2007|author=Liz Austin Peterson}}</ref> An EVA was carried out by [[Scott E. Parazynski|Scott Parazynski]], assisted by [[Douglas H. Wheelock|Douglas Wheelock]]. The men took extra precautions to reduce the risk of electric shock, as the repairs were carried out with the solar array exposed to sunlight.<ref name="Space Station's Damaged Panel Is Fixed">{{cite news|url=http://www.washingtonpost.com/wp-dyn/content/article/2007/11/03/AR2007110300227.html|title=Space Station's Damaged Panel Is Fixed|accessdate=4 November 2007|work=The Washington Post|date=4 November 2007|first=Rob|last=Stein}}</ref> The issues with the array were followed in the same year by problems with the starboard Solar Alpha Rotary Joint (SARJ), which rotates the arrays on the starboard side of the station. Excessive vibration and high-current spikes in the array drive motor were noted, resulting in a decision to substantially curtail motion of the starboard SARJ until the cause was understood. Inspections during EVAs on STS-120 and [[STS-123]] showed extensive contamination from metallic shavings and debris in the large drive gear and confirmed damage to the large metallic race ring at the heart of the joint, and so the joint was locked to prevent further damage.<ref name="joint-update">{{cite news|url=http://spaceflightnow.com/shuttle/sts123/080325sarj/index.html|title=Station chief gives detailed update on joint problem|accessdate=5 November 2008|author=William Harwood|publisher=CBS News & SpaceflightNow.com|date=25 March 2008}}</ref> Repairs to the joint were carried out during [[STS-126]] with lubrication of both joints and the replacement of 11 out of 12 trundle bearings on the joint.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts126/126_overview.html|title=Crew Expansion Prep, SARJ Repair Focus of STS-126|accessdate=5 November 2008|publisher=NASA|date=30 October 2008}}</ref><ref>{{cite news|url=http://www.spaceflightnow.com/shuttle/sts126/081118fd5/index.html|title=Astronauts prepare for first spacewalk of shuttle flight|date=18 November 2008|author=William Harwood|publisher=CBS News & SpaceflightNow.com|accessdate=22 November 2008}}</ref>

[[File:STS-120 EVA Scott Parazynski.jpg|thumb|While anchored on the end of the [[Orbiter Boom Sensor System|OBSS]], astronaut [[Scott Parazynski]] performs makeshift repairs to a US Solar array which damaged itself when unfolding, during [[STS-120]].|alt=Two black and orange solar arrays, shown uneven and with a large tear visible. A crew member in a spacesuit, attached to the end of a robotic arm, holds a latticework between two solar sails.]]
2009 saw damage to the S1 radiator, one of the components of the station's cooling system. The problem was first noticed in [[Soyuz spacecraft|Soyuz]] imagery in September 2008, but was not thought to be serious.<ref name="Radiator">{{cite web|url=http://www.nasaspaceflight.com/2009/04/iss-concern-s1-radiator-may-require-replacement-shuttle-mission/|author=Chris Bergin|date=1 April 2009|publisher=NASASpaceflight.com|title=ISS concern over S1 Radiator – may require replacement via shuttle mission|accessdate=3 April 2009}}</ref> The imagery showed that the surface of one sub-panel has peeled back from the underlying central structure, possibly due to micro-meteoroid or debris impact. It is also known that a Service Module thruster cover, jettisoned during an EVA in 2008, had struck the S1 radiator, but its effect, if any, has not been determined. On 15 May 2009 the damaged radiator panel's ammonia tubing was mechanically shut off from the rest of the cooling system by the computer-controlled closure of a valve. The same valve was used immediately afterwards to vent the ammonia from the damaged panel, eliminating the possibility of an ammonia leak from the cooling system via the damaged panel.<ref name="Radiator" />

Early on 1 August 2010, a failure in cooling Loop A (starboard side), one of two external cooling loops, left the station with only half of its normal cooling capacity and zero redundancy in some systems.<ref>{{cite web|url=http://spaceflightnow.com/news/n1007/31station/ |title=Problem forces partial powerdown aboard station |publisher=Spaceflightnow.com |date=31 July 2010 |accessdate=16 November 2010}}</ref><ref>{{cite web|url=http://www.spaceref.com/news/viewsr.html?pid=34622 |title=NASA ISS On-Orbit Status 1 August 2010 (early edition) |publisher=Spaceref.com |date=31 July 2010 |accessdate=16 November 2010}}</ref><ref>{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/systems/atcs.html |title=ISS Active Control System |publisher=Boeing |date=21 November 2006 |accessdate=16 November 2010}}</ref> The problem appeared to be in the ammonia pump module that circulates the ammonia cooling fluid. Several subsystems, including two of the four CMGs, were shut down.

Planned operations on the ISS were interrupted through a series of EVAs to address the cooling system issue. A first EVA on 7 August 2010, to replace the failed pump module, was not fully completed due to an ammonia leak in one of four quick-disconnects. A second EVA on 11 August successfully removed the failed pump module.<ref>[http://spaceflightnow.com/station/exp24/100810evapre/index.html Spaceflight Now] "Wednesday spacewalk to remove failed coolant pump"</ref><ref>[http://www.nasaspaceflight.com/2010/08/live-second-eva-with-pump-module-changeout/ NASA spaceflight 11 August] "Large success for second EVA as failed Pump Module is removed"</ref> A third EVA was required to restore Loop A to normal functionality.<ref>[http://spaceflightnow.com/station/exp24/100811eva2/index5.html Spaceflight Now 12 August] "Station's bad pump removed; more spacewalking ahead"</ref><ref>[http://www.nasaspaceflight.com/2010/08/iss-cooling-returning-normal-confirming-etcs-pm-success/ Spaceflight Now, 18 August] ISS cooling configuration returning to normal confirming ETCS PM success</ref>

The USOS's cooling system is largely built by the American company [[Boeing]],<ref>{{cite web|url=http://www.space.com/businesstechnology/international-space-station-complexities-100802.html|title=Cooling System Malfunction Highlights Space Station's Complexity|publisher=Space.com|date=2 August 2010}}</ref> which is also the manufacturer of the failed pump.<ref>{{cite web|url=http://spaceflightnow.com/news/n1007/31station/|title=Spacewalks needed to fix station cooling problem|publisher=Spaceflightnow|date=31 July 2010}}</ref>

An air leak from the USOS in 2004,<ref>{{cite news|url=http://www.msnbc.msn.com/id/3882962/|title=Crew finds 'culprit' in space station leak|publisher=MSNBC|date=11 January 2004|author=James Oberg|accessdate=22 August 2010}}</ref> the venting of fumes from an ''[[Elektron (ISS)|Elektron]]'' oxygen generator in 2006,<ref>{{cite news|url=http://spaceflightnow.com/station/exp13/060918elektron.html|title=Oxygen Generator Problem Triggers Station Alarm|publisher = CBS News through Spaceflight Now|date=18 September 2006|author=William Harwood|accessdate=24 November 2008}}</ref> and the failure of the computers in the ROS in 2007 during [[STS-117]] left the station without thruster, ''Elektron'', ''[[Vozdukh]]'' and other environmental control system operations, the root cause of which was found to be condensation inside the electrical connectors leading to a short-circuit.{{Citation needed|date=June 2011}}
[[File:STS-134 EVA4 view to the Russian Orbital Segment.jpg|thumb|right|In the foreground, a set of heat radiators]]
The four Main Bus Switching Units (MBSUs, located in the S0 truss), control the routing of power from the four solar array wings to the rest of the ISS. In late 2011 MBSU-1, while still routing power correctly, ceased responding to commands or sending data confirming its health, and was scheduled to be swapped out at the next available EVA. In each MBSU, two power channels feed 160V DC from the arrays to two DC-to-DC power converters (DDCUs) that supply the 124V power used in the station. A spare MBSU was already on board, but 30 August 2012 EVA failed to be completed when a bolt being tightened to finish installation of the spare unit jammed before electrical connection was secured.<ref>{{cite web|author=30 August 2012 by Pete Harding |url=http://www.nasaspaceflight.com/2012/08/astronaut-perform-first-post-shuttle-spacewalk-iss |title=Astronaut duo complete challenging first post-Shuttle US spacewalk on ISS |publisher=Nasaspaceflight.com |date=30 August 2012 |accessdate=22 October 2013}}</ref> The loss of MBSU-1 limits the station to 75% of its normal power capacity, requiring minor limitations in normal operations until the problem can be addressed.

On 5 September 2012, in a second, 6 hr, EVA to replace MBSU-1, astronauts Sunita Williams and Akihiko Hoshide successfully restored the ISS to 100% power.<ref>[http://spaceref.com/international-space-station/critical-space-station-spacewalk-a-success.html Spaceref.com Sept 5, 2012] Marc Boucher "Critical Space Station spacewalk a Success".</ref>
[[File:Astronaut Mike Hopkins on Dec. 24 Spacewalk.jpg|thumb|Mike Hopkins on his Christmas Eve spacewalk]]
On 24 December 2013, astronauts made a rare Christmas Eve space walk, installing a new ammonia pump for the station's cooling system. The faulty cooling system had failed earlier in the month, halting many of the station's science experiments. Astronauts had to brave a "mini blizzard" of ammonia while installing the new pump. It was only the second Christmas Eve spacewalk in NASA history.<ref>{{cite web|last=AP|title=Astronauts Complete Rare Christmas Eve Spacewalk|url=http://www.leaker.com/astronauts-complete-rare-christmas-eve-spacewalk/|publisher=Leaker|accessdate=24 December 2013|date=24 December 2013}}</ref>

[[File:Iss orbit and expeditions.png|thumb|Iss orbit with calendar of expeditions and modules]]

==Fleet operations==
:{{See also|List of human spaceflights to the International Space Station|List of unmanned spaceflights to the International Space Station}}
A wide variety of manned and unmanned spacecraft have supported the station's activities. 
[[Progress M-28M]] (ISS-60P) was the 62nd Progress spacecraft planned to arrive at the ISS, including [[Progress M-MIM2|M-MIM2]] and [[Progress M-SO1|M-SO1]] which installed modules. 35 flights of the retired NASA Space Shuttle were made to the station.<ref name="ISStD">{{cite web|url=http://spaceflight.nasa.gov/station/isstodate.html|title=The ISS to Date|accessdate=21 March 2011|publisher=NASA|date=9 March 2011|author=NASA}}</ref> [[Soyuz TMA-16M|TMA-16M]] is the 42nd Soyuz flight, and there have been 5 [[Automated Transfer Vehicle|European ATV]], 4 Japanese [[H-II Transfer Vehicle|Kounotori]] 'White Stork', 8 [[SpaceX]] [[Dragon (spacecraft)|Dragon]] and 4 OSC [[Cygnus (spacecraft)|Cygnus]] planned arrivals.

===Currently docked/berthed===
''See also the list of [[List of International Space Station expeditions|professional]] crew, [[Space tourism|private]] travellers, [[List of human spaceflights to the ISS|both]] or just [[List of unmanned spaceflights to the ISS|unmanned spaceflights]].''

;Key
{{legend|lightblue|Uncrewed cargoships are in light blue}}
{{legend|#cfc|Crewed spacecraft are in light green}}

{| class="wikitable" style="margin: 1em auto 1em auto;text-align: left; font-size: 95%;"
|-Currently Docked
|style="text-align:center; background:#BBB" colspan="3" | '''Spacecraft and mission'''
|style="text-align:center; background:#BBB"|'''Location'''
|style="text-align:center; background:#BBB"|'''Arrived''' ([[UTC]])
|style="text-align:center; background:#BBB"|'''Departure date'''
|- style="background:#cfc;"
| {{flagicon|RUS}}
| [[Soyuz TMA-16M]]
| [[Expedition 43]]/[[Expedition 44|44]]
| [[Poisk (ISS module)|Poisk]] zenith
| 28 March 2015
| 11 September 2015
|- style="background:lightblue;"
| {{flagicon|RUS}}
| [[Progress M-28M]]
| Progress 60 Cargo
| [[Pirs (ISS module)|Pirs]] nadir
| 5 July 2015
| 19 November 2015
|- style="background:#cfc;"
| {{flagicon|RUS}}
| [[Soyuz TMA-17M]]
| [[Expedition 44]]/[[Expedition 45|45]]
| [[Rassvet (ISS module)|Rassvet]] nadir
| 23 July 2015
| 22 December 2015
|}

===Scheduled launches and dockings/berthings===
* All dates are [[UTC]]. Dates are the earliest possible dates and may change.
* Forward ports are at the front of the station according to its normal direction of travel and orientation ([[Yaw, pitch and roll#Aircraft attitudes|attitude]]). Aft is at the rear of the station, used by spacecraft boosting the station's orbit. [[Nadir]] is closest the Earth, [[Zenith]] is on top.
* Spacecraft operated by government agencies are indicated with 'Gov' and under commercial arrangements are indicated with 'Com'.

;Key
{{legend|lightblue|Uncrewed cargoships are in light blue colour}}
{{legend|#cfc|Crewed spacecraft are in light green colour}}
{{legend|wheat|Modules are in wheat colour}}

{| class="wikitable" style="margin: 1em auto 1em auto;text-align: left; font-size: 95%;"
|+Planned Missions
|style="text-align:center; background:#BBB"|'''Launch''' ({{abbr|NET|Not Earlier Than}})
|style="text-align:center; background:#BBB"|'''Launch Vehicle'''
|style="text-align:center; background:#BBB"|'''Launch Site'''
|style="text-align:center; background:#BBB" colspan="3"| '''Launch Service Provider'''
|style="text-align:center; background:#BBB"|'''Payload'''
|style="text-align:center; background:#BBB"|'''Spacecraft'''
|style="text-align:center; background:#BBB"|'''Mission'''
|style="text-align:center; background:#BBB"|'''Docking / Berthing Port'''
|style="text-align:center; background:#BBB"|'''Ref.'''
|-
| nowrap| 19 August 2015
| nowrap| [[H-IIB]]
| nowrap| {{flagicon|JPN}} [[Tanegashima Space Center|Tanegashima]] [[Yoshinobu Launch Complex|LA-Y2]]
| nowrap| {{flagicon|JPN}}
| nowrap| Gov
| nowrap| [[JAXA]]
| style="background:lightblue;" nowrap| [[Kounotori 5|HTV-5]]
| nowrap| [[H-II Transfer Vehicle|HTV]]
| ISS Resupply
| nowrap| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule">{{cite web |url=http://spaceflightnow.com/launch-schedule/ |title=Launch Calendar |work=Spaceflight Now |date=28 March 2015 |accessdate=28 March 2015}}</ref><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 2 September 2015
| nowrap| [[Soyuz-FG]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:#cfc;" nowrap| [[Soyuz TMA-18M]]
| nowrap| [[Soyuz (spacecraft)|Soyuz]]
| [[Expedition 45]]/[[Expedition 46|46]] including [[European Space Agency|ESA]] [[Denmark|Danish]] Astronaut [[Andreas Mogensen]] and [[Kazakhstan]] cosmonaut [[Aydyn Aimbetov]].
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 1 October 2015
| nowrap| [[Soyuz-U]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:lightblue;" nowrap| [[Progress M-29M]]
| nowrap| [[Progress (spacecraft)|Progress]]
| ISS Resupply
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| NET September 2015 (TBD)
| nowrap|[[Falcon 9 v1.1]]
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 40|SLC-40]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[SpaceX]]
| style="background:lightblue;" nowrap| [[SpaceX CRS-8]]
| nowrap| [[Dragon (spacecraft)|Dragon]]
| ISS resupply. Will deliver [[Bigelow Expandable Activity Module|Bigelow Expandable Activity Module (BEAM)]] to the ISS.
| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| 21 November 2015
| nowrap| [[Soyuz-2 (rocket)|Soyuz-2.1a]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:lightblue;" nowrap| [[Progress MS-1]]
| nowrap| [[Progress (spacecraft)|Progress]]
| ISS Resupply. First launch of the new [[Progress (spacecraft)#Progress MS|Progress-MS]] variant.
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 3 December 2015
| nowrap| [[Atlas V]] 401
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 41|SLC-41]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[United Launch Alliance|ULA]]
| style="background:lightblue;" nowrap| [[Cygnus CRS Orb-4]]
| nowrap| [[Cygnus (spacecraft)|Cygnus]]
| ISS Resupply
| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/><ref>{{cite web|url=http://www.space.com/27962-cygnus-cargo-spacecraft-new-rocket.html |title=Private Cargo Spacecraft Gets New Rocket Ride After Accident |publisher=Space.com |date= |accessdate=2015-04-04}}</ref>
|-
| nowrap| 15 December 2015
| nowrap| [[Soyuz-FG]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:#cfc;" nowrap| [[Soyuz TMA-19M]]
| nowrap| [[Soyuz (spacecraft)|Soyuz]]
| [[Expedition 46]]/[[Expedition 47|47]]
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| NET December 2015 (TBD)
| nowrap|[[Falcon 9 v1.1]]
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[SpaceX]]
| style="background:lightblue;" nowrap| [[SpaceX CRS-9]]
| nowrap| [[Dragon (spacecraft)|Dragon]]
| ISS resupply. Will deliver the IDA-2 segment of the [[NASA Docking System]] to the ISS.
| nowrap| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |
url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|}

===Docking===
{{See also|Docking and berthing of spacecraft}}
[[File:Progress M-14M.jpg|thumb|The [[Progress M-14M]] resupply vehicle as it approaches the ISS in 2012. Over 50 unpiloted [[Progress (spacecraft)|Progress]] spacecraft have been sent with supplies during the lifetime of the station.]]
All Russian spacecraft and self-propelled modules are able to rendezvous and dock to the space station without human intervention using the [[Kurs (docking system)|Kurs]] docking system. Radar allows these vehicles to detect and intercept ISS from over 200 kilometres away. The European ATV uses star sensors and GPS to determine its intercept course. When it catches up it then uses laser equipment to [[Computer vision|optically]] recognise Zvezda, along with the Kurs system for redundancy.  Crew supervise these craft, but do not intervene except to send abort commands in emergencies. The Japanese [[H-II Transfer Vehicle]] parks itself in progressively closer orbits to the station, and then awaits 'approach' commands from the crew, until it is close enough for a robotic arm to grapple and berth the vehicle to the USOS. The American Space Shuttle was manually docked, and on missions with a [[Multi-Purpose Logistics Module|cargo container]], the container would be berthed to the Station with the use of manual robotic arms. Berthed craft can transfer [[International Standard Payload Rack]]s. Japanese spacecraft berth for one to two months. Russian and European Supply craft can remain at the ISS for six months,<ref>{{cite web|url=http://www.esa.int/esaMI/ATV/SEMBW0PR4CF_0.html |title=ESA — ATV — Crew role in mission control |publisher=Esa.int |date=2 March 2011 |accessdate=23 May 2011}}</ref><ref>{{cite web|url=http://www.esa.int/esaHS/ESA4ZJ0VMOC_iss_0.html |title=ESA — Human Spaceflight and Exploration — International Space Station — Automated Transfer Vehicle (ATV) |publisher=Esa.int |date=16 January 2009 |accessdate=23 May 2011}}</ref> allowing great flexibility in crew time for loading and unloading of supplies and trash. NASA Shuttles could remain docked for 11–12 days.<ref>{{cite web|url=http://www.boeing.com/news/frontiers/archive/2005/july/i_ids4.html|title=Space Shuttle upgrade lets astronauts at ISS stay in space longer|last=Memi|first=Ed|publisher=Boeing|accessdate=17 September 2011}}</ref>

The American manual approach to docking allows greater initial flexibility and less complexity. The downside to this mode of operation is that each mission becomes unique and requires specialised training and planning, making the process more labour-intensive and expensive. The Russians pursued an automated methodology that used the crew in override or monitoring roles. Although the initial development costs were high, the system has become very reliable with standardisations that provide significant cost benefits in repetitive routine operations.<ref>David C. Wo±nden and David K. Geller [http://www.usu.edu/mae/aerospace/publications/JDSC_RoadToAutonomy.pdf The Road to Autonomous Orbital Rendezvous]. Utah State University, Logan, Utah</ref> An automated approach could allow assembly of modules orbiting other worlds prior to crew arrival.

[[File:ISS and Endeavour seen from the Soyuz TMA-20 spacecraft 27.jpg|thumb|left|{{OV|105}}, [[ATV-2]], [[Soyuz TMA-21]] and [[Progress M-10M]] docked to the ISS during [[STS-134]], as seen from the departing [[Soyuz TMA-20]]|alt=A side-on view of the ISS showing a Space Shuttle docked to the forward end, an ATV to the aft end and Soyuz & Progress spacecraft projecting from the Russian segment.]]
Soyuz spacecraft used for crew rotation also serve as lifeboats for emergency evacuation; they are replaced every six months and have been used once to remove excess crew after the [[Space Shuttle Columbia disaster|Columbia disaster]].<ref>{{cite web|url=http://www.astronautix.com/flights/isseo6.htm |title=ISS EO-6 |publisher=Astronautix.com |accessdate=1 May 2012}}</ref> Expeditions require, on average, {{nowrap|2 722 kg}} of supplies, and {{As of|2011|03|09|lc=yes}}, crews had consumed a total of around {{nowrap|22 000 meals}}.<ref name="ISStD" /> Soyuz crew rotation flights and Progress resupply flights visit the station on average two and three times respectively each year,<ref name="Livelist">{{cite web|url=http://www.nasa.gov/mission_pages/station/resupply/index.html|archiveurl=https://web.archive.org/web/20080803015945/http://www.nasa.gov/mission_pages/station/resupply/index.html|archivedate=3 August 2008|title=Live listing of spacecraft operations|publisher=NASA|date=1 December 2009|accessdate=8 December 2009}}</ref> with the ATV and HTV planned to visit annually from 2010 onwards.{{Citation needed|date=January 2012}} Following retirement of the NASA Shuttle [[Cygnus spacecraft|Cygnus]] and [[SpaceX Dragon|Dragon]] were contracted to fly cargo to the station.<ref>{{cite web|author=Space Operations Mission Directorate|title=Human Space Flight Transition Plan|publisher=NASA|date=30 August 2006|url=http://www.nasa.gov/pdf/315546main_space_flight_transition_plan.pdf}}</ref><ref>{{cite press release|publisher=NASA|date=18 January 2006|title=NASA Seeks Proposals for Crew and Cargo Transportation to Orbit|url=http://www.spaceref.com/news/viewpr.html?pid=18791|accessdate=21 November 2006}}</ref>

From 26 February 2011 to 7 March 2011 four of the governmental partners (United States, ESA, Japan and Russia) had their spacecraft (NASA Shuttle, ATV, HTV, Progress and Soyuz) docked at the ISS, the only time this has happened to date.<ref>{{cite news|title=NASA proposes Soyuz photo op; shuttle launch readiness reviewed (UPDATED)|url=http://www.cbsnews.com/network/news/space/home/spacenews/files/b0e194a8338c336e823c03601f046707-157.html|publisher=CBS|accessdate=11 February 2011}}</ref> On 25 May 2012, [[SpaceX]] became the world's first privately held company to send cargo, via the [[Dragon (spacecraft)|Dragon spacecraft]], to the International Space Station.<ref name="NYT-20120525">{{cite news |last=Chang |first=Kenneth |title=Space X Capsule Docks at Space Station |url=http://www.nytimes.com/2012/05/26/science/space/space-x-capsule-docks-at-space-station.html |date=25 May 2012 |work=[[The New York Times]] |accessdate=25 May 2012 }}</ref>

===Launch and docking windows===
Prior to a ship's docking to the ISS, navigation and attitude control (GNC) is handed over to the ground control of the ships' country of origin. GNC is set to allow the station to drift in space, rather than fire its thrusters or turn using gyroscopes. The solar panels of the station are turned edge-on to the incoming ships, so residue from its thrusters does not damage the cells. When a NASA shuttle docked to the station, other ships were grounded, as the carbon wingtips, cameras, windows, and instruments aboard the shuttle were at too much risk from damage from thruster residue from other ships movements.

Approximately 30% of NASA shuttle launch delays were caused by poor weather. Occasional priority was given to the Soyuz arrivals at the station where the Soyuz carried crew with time-critical cargoes such as biological experiment materials, also causing shuttle delays. Departure of the NASA shuttle was often delayed or prioritised according to weather over its two landing sites.<ref>{{cite web |url=http://www.nasa.gov/home/hqnews/2009/may/HQ_09-118_Shuttle_Landing_Delayed.html |title=NASA's Space Shuttle Landing Delayed by Weather |publisher=NASA |first1=Katherine |last1=Trinidad |first2=Candrea |last2=Thomas |date=22 May 2009 |accessdate=26 June 2015}}</ref> Whilst the Soyuz is capable of landing anywhere, anytime, its planned landing time and place is chosen to give consideration to helicopter pilots and ground recovery crew, to give acceptable flying weather and lighting conditions. Soyuz launches occur in adverse weather conditions, but the cosmodrome has been shut down on occasions when buried by snow drifts up to 6 metres in depth, hampering ground operations.

==Life aboard==

===Crew activities===
[[File:Exp18home nasa big.jpg|thumb|Crewmember peers out of a window]]

A typical day for the crew begins with a wake-up at 06:00, followed by post-sleep activities and a morning inspection of the station. The crew then eats breakfast and takes part in a daily planning conference with Mission Control before starting work at around 08:10. The first scheduled exercise of the day follows, after which the crew continues work until 13:05. Following a one-hour lunch break, the afternoon consists of more exercise and work before the crew carries out its pre-sleep activities beginning at 19:30, including dinner and a crew conference. The scheduled sleep period begins at 21:30. In general, the crew works ten hours per day on a weekday, and five hours on Saturdays, with the rest of the time their own for relaxation or work catch-up.<ref>{{cite web|url=http://www.nasa.gov/pdf/287386main_110508_tl.pdf|title=ISS Crew Timeline|date=5 November 2008|accessdate=5 November 2008|publisher=NASA|format=PDF}}</ref>

The time zone used on board the ISS is [[Coordinated Universal Time]] (UTC). The windows are covered at night hours to give the impression of darkness because the station experiences 16 sunrises and sunsets a day. During visiting space shuttle missions, the ISS crew will mostly follow the shuttle's [[Mission Elapsed Time]] (MET), which is a flexible time zone based on the launch time of the shuttle mission.<ref>{{Cite web|title = NASA - Time in Space, A Space in Time|url = https://www.nasa.gov/mission_pages/station/research/news/time_in_space.html|website = www.nasa.gov|accessdate = 2015-05-05}}</ref><ref>{{Cite web|title = A Slice of Time Pie|url = https://web.archive.org/web/20130317075600/http://blogs.nasa.gov/cm/blog/ISS%20Science%20Blog/posts/post_1340820317951.html|date = 2013-03-17|accessdate = 2015-05-05}}</ref><ref>{{Cite web|title = Human Space Flight (HSF) - Crew Answers|url = http://spaceflight.nasa.gov/feedback/expert/answer/crew/sts-113/index_2.html|website = spaceflight.nasa.gov|accessdate = 2015-05-05}}</ref>

The station provides crew quarters for each member of the expedition's crew, with two 'sleep stations' in the ''Zvezda'' and four more installed in ''Harmony''.<ref>{{cite web|url=https://www.youtube.com/watch?v=Q4dG9vSyUFQ|title=At Home with Commander Scott Kelly (Video)|date=6 December 2010|publisher=NASA|accessdate=8 May 2011|location=International Space Station}}</ref><ref>{{cite web|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080013462_2008012884.pdf|title=International Space Station USOS Crew Quarters Development|first1=James Lee |last1=Broyan |first2=Melissa Ann |last2=Borrego |first3=Juergen F. |last3=Bahr|year=2008|publisher=SAE International|accessdate=8 May 2011}}</ref> The American quarters are private, approximately person-sized soundproof booths. The Russian crew quarters include a small window, but do not provide the same amount of ventilation or block the same amount of noise as their American counterparts. A crewmember can sleep in a crew quarter in a tethered sleeping bag, listen to music, use a laptop, and store personal items in a large drawer or in nets attached to the module's walls. The module also provides a reading lamp, a shelf and a desktop.<ref name="ESALife">{{cite web|url=http://www.esa.int/esaHS/ESAH1V0VMOC_astronauts_0.html|publisher=ESA|accessdate=28 October 2009|date=19 July 2004|title=Daily life}}</ref><ref name="NASACrewEquip">{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/126_payload.html|title=Station Prepares for Expanding Crew|publisher=NASA|first=Cheryl L. |last=Mansfield|date=7 November 2008|accessdate=17 September 2009}}</ref><ref name="CSALife">{{cite web|url=http://www.asc-csa.gc.ca/pdf/educator-liv_wor_iss.pdf|title=Living and Working on the International Space Station|accessdate=28 October 2009|publisher=CSA}}</ref> Visiting crews have no allocated sleep module, and attach a sleeping bag to an available space on a wall—it is possible to sleep floating freely through the station, but this is generally avoided because of the possibility of bumping into sensitive equipment.<ref name="SRLife">{{cite web|url=http://www.space.com/missionlaunches/090827-sts127-space-sleeping.html|title=Sleeping in Space is Easy, But There's No Shower|first=Tariq|last=Malik|accessdate=29 October 2009|date=27 July 2009|publisher=Space.com}}</ref> It is important that crew accommodations be well ventilated; otherwise, astronauts can wake up oxygen-deprived and gasping for air, because a bubble of their own exhaled carbon dioxide has formed around their heads.<ref name="ESALife" />
{{See also|Christmas on the International Space Station}}

===Food===
[[File:Meal STS127.jpg|thumb|alt=Nine astronauts seated around a table covered in open cans of food strapped down to the table. In the background a selection of equipment is visible, as well as the salmon-coloured walls of the Unity node.|The crews of [[STS-127]] and [[Expedition 20]] enjoy a meal inside ''Unity''.]]
{{See also|Space food}}

Most of the food on board is vacuum sealed in plastic bags. Cans are heavy and expensive to transport, so there are not as many. The preserved food is generally not held in high regard by the crew, and when combined with the reduced sense of taste in a microgravity environment,<ref name="ESALife" /> a great deal of effort is made to make the food more palatable. More spices are used than in regular cooking, and the crew looks forward to the arrival of any ships from Earth, as they bring fresh fruit and vegetables with them. Care is taken that foods do not create crumbs. Sauces are often used to ensure station equipment is not contaminated. Each crew member has individual food packages and cooks them using the on-board galley. The galley features two food warmers, a refrigerator added in November 2008, and a water dispenser that provides both heated and unheated water.<ref name="NASACrewEquip" /> Drinks are provided in dehydrated powder form and are mixed with water before consumption.<ref name="NASACrewEquip" /><ref name="CSALife" /> Drinks and soups are sipped from plastic bags with straws; solid food is eaten with a knife and fork, which are attached to a tray with magnets to prevent them from floating away. Any food that floats away, including crumbs, must be collected to prevent it from clogging up the station's air filters and other equipment.<ref name="CSALife" />

===Hygiene===
[[File:Zvezda toilet.jpg|thumb|right|upright|Space toilet in the [[Zvezda (ISS module)|Zvezda Service Module]]]]

Showers on space stations were introduced in the early 1970s on Skylab and Salyut 3.<ref name="livingandworking">Benson, Charles Dunlap and William David Compton. ''[http://history.nasa.gov/SP-4208/contents.htm Living and Working in Space: A History of Skylab]''. NASA publication SP-4208.</ref>{{rp|139}} By Salyut 6, in the early 1980s, the crew complained of the complexity of showering in space, which was a monthly activity.<ref name="Portree1995-86">{{cite book |url=http://history.nasa.gov/SP-4225/documentation/mhh/mirheritage.pdf |title=Mir Hardware Heritage |publisher=NASA |first=David S. F. |last=Portree |page=86 |date=March 1995 |id=Reference Publication 1357 |oclc=755272548}}</ref> The ISS does not feature a shower; instead, crewmembers wash using a water jet and wet wipes, with soap dispensed from a toothpaste tube-like container. Crews are also provided with rinseless shampoo and edible toothpaste to save water.<ref name="SRLife" /><ref>{{cite AV media |url=https://www.youtube.com/watch?v=uIjNfZbUYu8 |title=Karen Nyberg Shows How You Wash Hair in Space |publisher=NASA |work=YouTube.com |first=Karen |last=Nyberg |date=12 July 2013 |accessdate=6 June 2015}}</ref>

There are two [[space toilet]]s on the ISS, both of Russian design, located in ''[[Zvezda (ISS module)|Zvezda]]'' and ''[[Tranquility (ISS module)|Tranquility]]''.<ref name="NASACrewEquip" /> These Waste and Hygiene Compartments use a fan-driven suction system similar to the Space Shuttle Waste Collection System. Astronauts first fasten themselves to the toilet seat, which is equipped with spring-loaded restraining bars to ensure a good seal.<ref name="ESALife" /> A lever operates a powerful fan and a suction hole slides open: the air stream carries the waste away. Solid waste is collected in individual bags which are stored in an aluminium container. Full containers are transferred to Progress spacecraft for disposal.<ref name="NASACrewEquip" /><ref>{{cite web |first=Ed |last=Lu |title=Greetings Earthling |url=http://spaceflight.nasa.gov/station/crew/exp7/luletters/lu_letter9.html |date=8 September 2003 |accessdate=1 November 2009 |publisher=NASA}}</ref> Liquid waste is evacuated by a hose connected to the front of the toilet, with anatomically correct "urine funnel adapters" attached to the tube so both men and women can use the same toilet. Waste is collected and transferred to the Water Recovery System, where it is recycled back into drinking water.<ref name="CSALife" />

==Crew health and safety==
{{Main|Effect of spaceflight on the human body}}

===Radiation===
The ISS is partially protected from the space environment by the Earth's magnetic field. From an average distance of about {{convert|70,000|km|abbr=on}}, depending on Solar activity, the [[magnetosphere]] begins to deflect solar wind around the Earth and ISS. [[coronal mass ejection|Solar flares]] are still a hazard to the crew, who may receive only a few minutes warning. The crew of [[Expedition 10]] took shelter as a precaution in 2005 in a more heavily shielded part of the ROS designed for this purpose during the initial 'proton storm' of an X-3 class solar flare,<ref>{{cite web|title=Solar Flare Hits Earth and Mars|author=Ker Than|publisher=Space.com|date=23 February 2006|url=http://www.space.com/2080-solar-flare-hits-earth-mars.html}}</ref><ref>{{cite web|title=A new kind of solar storm|publisher=NASA|date=10 June 2005|url=http://science.nasa.gov/science-news/science-at-nasa/2005/10jun_newstorm/}}</ref> but without the limited protection of the Earth's [[magnetosphere]], interplanetary manned missions are especially vulnerable.

[[File:Aurora Australis.ogv|thumb|left|Video of the [[Aurora Australis]] taken by the crew of [[Expedition 28]] on an ascending pass from south of [[Madagascar]] to just north of Australia over the Indian Ocean.]]

Subatomic charged particles, primarily protons from [[cosmic ray]]s and [[solar wind]], are normally absorbed by the Earth's atmosphere. When they interact in sufficient quantity, their effect becomes visible to the naked eye in a phenomenon called an aurora. Without the protection of the Earth's atmosphere, which absorbs this radiation, crews are exposed to about 1 [[millisievert]] each day, which is about the same as someone would get in a year on Earth from natural sources. This results in a higher risk of astronauts developing cancer. Radiation can penetrate living tissue, damage DNA, and cause damage to the [[chromosome]]s of [[lymphocytes]]. These cells are central to the [[immune system]], and so any damage to them could contribute to the lowered [[immunity (medical)|immunity]] experienced by astronauts. Radiation has also been linked to a higher incidence of [[cataracts]] in astronauts. Protective shielding and protective drugs may lower the risks to an acceptable level.<ref name="JCB"/>

The radiation levels experienced on the ISS are about five times greater than those experienced by airline passengers and crew. The Earth's electromagnetic field provides almost the same level of protection against solar and other radiation in low Earth orbit as in the stratosphere. Airline passengers experience this level of radiation for no more than 15 hours for the longest intercontinental flights. For example, on a 12-hour flight an airline passenger would experience 0.1 millisieverts of radiation, or a rate of 0.2 millisieverts per day; only 1/5 the rate experienced by an astronaut in LEO.<ref>{{cite web|url=http://jag.cami.jccbi.gov./cariprofile.asp|title=Galactic Radiation Received in Flight|accessdate=20 May 2010|publisher=FAA Civil Aeromedical Institute}}</ref>
{{See also|Coronal mass ejection|Aurora (astronomy)}}

===Stress===
[[File:Nikolai Budarin in a sleep station in Zvezda.jpg|thumb|Cosmonaut [[Nikolai Budarin]] at work inside [[Zvezda (ISS module)|Zvezda]] service module crew quarters]]
There has been considerable evidence that psychosocial stressors are among the most important impediments to optimal crew morale and performance.<ref>{{cite book| author1 =Peter Suedfeld1| author2 = Kasia E. Wilk| author3 = Lindi Cassel| title = Flying with Strangers: Postmission Reflections of Multinational Space Crews}}</ref> Cosmonaut [[Valery Ryumin]], wrote in his journal during a particularly difficult period on board the [[Salyut 6]] space station: "All the conditions necessary for murder are met if you shut two men in a cabin measuring 18 feet by 20 and leave them together for two months."

NASA's interest in psychological stress caused by space travel, initially studied when their manned missions began, was rekindled when astronauts joined cosmonauts on the Russian space station Mir. Common sources of stress in early American missions included maintaining high performance under public scrutiny, as well as isolation from peers and family. The latter is still often a cause of stress on the ISS, such as when the mother of NASA Astronaut [[Daniel M. Tani|Daniel Tani]] died in a car accident, and when Michael Fincke was forced to miss the birth of his second child.


A study of the longest spaceflight concluded that the first three weeks represent a critical period where attention is adversely affected because of the demand to adjust to the extreme change of environment.<ref>{{cite doi|10.1080/001401398186991}}</ref> Skylab's 3 crews remained one, two, and three months respectively, long term crews on Salyut 6, [[Salyut 7]], and the ISS last about five to six months and Mir's expeditions often lasted longer. The ISS working environment includes further stress caused by living and working in cramped conditions with people from very different cultures who speak a different language. First generation space stations had crews who spoke a single language; second and third-generation stations have crew from many cultures who speak many languages. The ISS is unique because visitors are not classed automatically into 'host' or 'guest' categories as with previous stations and spacecraft, and may not suffer from feelings of isolation in the same way. Crew members with a military pilot background and those with an academic science background or teachers and politicians may have problems understanding each other's jargon and worldview.

===Medical===
[[File:Frank De Winne on treadmill cropped.jpg|thumb|Astronaut [[Frank De Winne]] is attached to the [[Treadmill with Vibration Isolation System|TVIS treadmill]] with bungee cords aboard the International Space Station|alt=Astronaut Frank De Winne is attached to the TVIS treadmill with bungee cords aboard the International Space Station]]
Medical effects of long-term weightlessness include [[muscle atrophy]], deterioration of the skeleton [[spaceflight osteopenia|(osteopenia)]], fluid redistribution, a slowing of the cardiovascular system, decreased production of red blood cells, balance disorders, and a weakening of the immune system. Lesser symptoms include loss of body mass, and puffiness of the face.<ref name="JCB" />

Sleep is disturbed on the ISS regularly due to mission demands, such as incoming or departing ships. Sound levels in the station are unavoidably high; because the atmosphere is unable to [[thermosiphon]], fans are required at all times to allow processing of the atmosphere which would stagnate in the freefall (zero-g) environment.

To prevent some of these adverse [[physiological]] effects, the station is equipped with two treadmills (including the [[Treadmill with Vibration Isolation System|COLBERT]]), and the aRED (advanced Resistive Exercise Device) which enables various weightlifting exercises which add muscle but do nothing for bone density,<ref>{{cite pmid|14600562}}</ref> and a stationary bicycle; each astronaut spends at least two hours per day exercising on the equipment.<ref name="ESALife" /><ref name="NASACrewEquip" /> Astronauts use bungee cords to strap themselves to the treadmill.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/bungee_running.html|accessdate=23 August 2009|title=Bungee Cords Keep Astronauts Grounded While Running|date=16 June 2009|publisher=NASA}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/colbert_feature.html|accessdate=23 August 2009|title=Do Tread on Me|date=19 August 2009|author=Amiko Kauderer|publisher=NASA}}</ref>

===Microbiological environmental hazards===
{{see also|Mir#Microbiological environmental hazards}}
Hazardous moulds which can foul air and water filters may develop aboard space stations. They can produce acids which degrade metal, glass, and rubber. They can also be harmful for the crew health. Microbiological hazards have led to a development of the [[LOCAD#Portable Test System|LOCAD-PTS]] that can identify common bacteria and moulds faster than standard methods of [[Cell culture|culturing]], which may require a sample to be sent back to Earth.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2007/11may_locad3/|author=Trudy E. Bell|year=2007|title=Preventing "Sick" Spaceships|access-date=March 29, 2015}}</ref> {{As of|2012}}, 76 types of unregulated micro-organisms have been detected on the ISS.<ref>{{cite web|url=http://rt.com/news/iss-bacteria-mir-mutation-765/|title=Mutant space microbes attack ISS: 'Munch' metal, may crack glass |author= |date=April 23, 2012|website=[[RT (TV network)|RT]]|access-date=March 29, 2015}}</ref>

Reduced humidity, paint with mould killing chemical and antiseptic solutions can be used to prevent contamination in space stations. All materials used in the ISS are tested for resistance against fungi.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2000/ast26nov_1/|author=Patrick L. Barry|year=2000|title=Microscopic Stowaways on the ISS|access-date=March 29, 2015}}</ref>

==Threat of orbital debris==
{{Main|Space debris}}
{{Double image|right|SDIO KEW Lexan projectile.jpg|225|Debris-GEO1280.jpg|225|A 7 gram object (shown in centre) shot at 7 km/s (23,000 ft/sec) (the orbital velocity of the ISS) made this 15 cm (5 7/8 in) crater in a solid block of aluminium.|[[Radar]]-trackable objects including debris, with distinct ring of [[Geostationary orbit|geostationary]] satellites||}}
At the low altitudes at which the ISS orbits there is a variety of space debris,<ref>{{cite web|url=http://defensenews.com/blogs/space-symposium/2009/04/03/its-getting-crowded-up-there/#more-155|publisher=Defense News|accessdate=7 October 2009|author=Michael Hoffman|title=National Space Symposium 2009: It's getting crowded up there|date=3 April 2009}}</ref> consisting of many different objects including entire spent rocket stages, defunct satellites, explosion fragments—including materials from [[anti-satellite weapon]] tests, paint flakes, slag from solid rocket motors, and coolant released by [[US-A]] nuclear-powered satellites. These objects, in addition to natural [[micrometeoroid]]s,<ref>{{cite journal|author=F. L. Whipple|year=1949|title=The Theory of Micrometeoroids|journal=Popular Astronomy|volume=57|page=517|bibcode=1949PA.....57..517W}}</ref> are a significant threat. Large objects could destroy the station, but are less of a threat as their orbits can be predicted.<ref name="NSFdebris">{{cite web|publisher=NASASpaceflight.com|accessdate=28 June 2011|date=28 June 2011|author=Chris Bergin|url=http://www.nasaspaceflight.com/2011/06/sts-135-frr-july-8-atlantis-debris-misses-iss/|title=STS-135: FRR sets 8 July Launch Date for Atlantis – Debris misses ISS}}</ref><ref>{{cite web|author=Henry Nahra|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19890016664_1989016664.pdf|title=Effect of Micrometeoroid and Space Debris Impacts on the Space Station Freedom Solar Array Surfaces|date=24–29 April 1989|publisher=NASA|accessdate=7 October 2009}}</ref> Objects too small to be detected by optical and radar instruments, from approximately 1 cm down to microscopic size, number in the trillions. Despite their small size, some of these objects are still a threat because of their [[kinetic energy]] and direction in relation to the station. Spacesuits of spacewalking crew could puncture, causing [[Space exposure|exposure to vacuum]].<ref name=debrisdecomp>{{cite web|title=Space Suit Punctures and Decompression|url=http://www.asi.org/adb/04/03/08/suit-punctures.html|publisher=The Artemis Project|accessdate=20 July 2011}}</ref>

The station's shields and structure are divided between the ROS and the USOS, with completely different designs. On the USOS, a thin aluminium sheet is held apart from the hull, the sheet causes objects to shatter into a cloud before hitting the hull thereby spreading the energy of the impact. On the ROS, a carbon plastic honeycomb screen is spaced from the hull, an aluminium honeycomb screen is spaced from that, with a screen-vacuum thermal insulation covering, and glass cloth over the top. It is about 50% less likely to be punctured,  and crew move to the ROS when the station is under threat. Punctures on the ROS would be contained within the panels which are 70 cm square.

[[File:ISS impact risk.jpg|thumb|left|Example of [[risk management]]: A NASA model showing areas at high risk from impact for the International Space Station.]]

Space debris objects are tracked remotely from the ground, and the station crew can be notified.<ref>{{cite web|url=http://www.orbitaldebris.jsc.nasa.gov/library/EducationPackage.pdf |title=Microsoft PowerPoint – EducationPackage SMALL.ppt |format=PDF |accessdate=1 May 2012}}</ref> This allows for a [[Debris Avoidance Manoeuvre]] (DAM) to be conducted, which uses thrusters on the Russian Orbital Segment to alter the station's orbital altitude, avoiding the debris. DAMs are not uncommon, taking place if computational models show the debris will approach within a certain threat distance. Eight DAMs had been performed prior to March 2009,<ref>{{cite web|url=http://www.newscientist.com/article/dn16777-space-station-may-move-to-dodge-debris.html|title=Space station may move to dodge debris|work=New Scientist|date=16 March 2009|accessdate=20 April 2010|author=Rachel Courtland}}</ref> the first seven between October 1999 and May 2003.<ref name=ODOct08>{{cite journal|url=http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv12i4.pdf|title=ISS Maneuvers to Avoid Russian Fragmentation Debris|publisher=NASA|pages=1&2|journal=Orbital Debris Quarterly News|date=October 2008|accessdate=20 April 2010|volume=12|issue=4}}</ref> Usually the orbit is raised by one or two kilometres by means of an increase in orbital velocity of the order of 1 m/s. Unusually there was a lowering of 1.7 km on 27 August 2008, the first such lowering for 8 years.<ref name=ODOct08 /><ref>{{cite web|url=http://www.esa.int/esaMI/ATV/SEM64X0SAKF_0.html|title=ATV carries out first debris avoidance manoeuvre for the ISS|publisher=ESA|date=28 August 2008|accessdate=26 February 2010}}</ref> There were two DAMs in 2009, on 22 March and 17 July.<ref>{{cite journal|url=http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv14i1.pdf|title=Avoiding satellite collisions in 2009|page=2|journal=Orbital Debris Quarterly News|publisher=NASA|volume=14|date=January 2010|issue=1|accessdate=20 April 2010}}</ref> If a threat from orbital debris is identified too late for a DAM to be safely conducted, the station crew close all the hatches aboard the station and retreat into their [[Soyuz spacecraft]], so that they would be able to evacuate in the event the station was seriously damaged by the debris. This partial station evacuation has occurred on 13 March 2009, 28 June 2011, 24 March 2012 and 16 June 2015.<ref>{{cite news| url=http://www.bbc.co.uk/news/science-environment-17497766| title=ISS crew take to escape capsules in space junk alert| accessdate=24 March 2012 |work=BBC News |date=24 March 2012}}</ref><ref>{{cite news| url=https://blogs.nasa.gov/spacestation/2015/07/16/station-crew-takes-precautions-for-close-pass-of-space-debris/| title=Station Crew Takes Precautions for Close Pass of Space Debris| accessdate=16 June 2015 |work=NASA Blog |date=16 June 2015}}</ref>
Ballistic panels, also called micrometeorite shielding, are incorporated into the station to protect pressurised sections and critical systems. The type and thickness of these panels varies depending upon their predicted exposure to damage.

==End of mission==
[[File:Jules Verne Automated Transfer Vehicle re-enters Earth's atmosphere.jpg|thumb|right|Many ISS resupply spacecraft have already undergone [[Atmospheric entry|atmospheric re-entry]], such as [[Jules Verne ATV]]]]
According to a 2009 report, [[S.P. Korolev Rocket and Space Corporation Energia|Space Corporation Energia]] is considering methods to remove from the station some modules of the Russian Orbital Segment when the end of mission is reached and use them as a basis for a new station, known as the [[Orbital Piloted Assembly and Experiment Complex]] (OPSEK). The modules under consideration for removal from the current ISS include the [[Multipurpose Laboratory Module]] (MLM), currently scheduled to be launched in 2017, with other Russian modules which are currently planned to be attached to the MLM afterwards. Neither the MLM nor any additional modules attached to it would have reached the end of their useful lives in 2016 or 2020. The report presents a statement from an unnamed Russian engineer who believes that, based on the experience from ''Mir'', a thirty-year life should be possible, except for micrometeorite damage, because the Russian modules have been built with on-orbit refurbishment in mind.<ref name="RussiaSave">{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8064060.stm|title=Russia 'to save its ISS modules'|work=BBC News|date=22 May 2009|accessdate=23 May 2009|author=Anatoly Zak}}</ref>

According to the [[Outer Space Treaty]] the United States and Russia are legally responsible for all modules they have launched.<ref>[http://www.unoosa.org/pdf/publications/STSPACE11E.pdf United Nations Treaties and Principles on Outer Space]. (PDF). United Nations. New York. 2002. ISBN 92-1-100900-6. Retrieved 8 October 2011.</ref> In ISS planning, NASA examined options including returning the station to Earth via shuttle missions (deemed too expensive, as the station (USOS) is not designed for disassembly and this would require at least 27 shuttle missions<ref>{{cite book|url=http://search.nap.edu/openbook.php?record_id=9794&page=28|isbn=0-309-06938-6|publisher=National Academies Press|year=2000|pages=28–30|author=Thomas Kelly|title=Engineering Challenges to the Long-Term Operation of the International Space Station|accessdate=12 July 2011}}</ref>), natural orbital decay with random reentry similar to [[Skylab]], boosting the station to a higher altitude (which would delay reentry) and a controlled targeted de-orbit to a remote ocean area.<ref name=ISSEIS>{{cite web|title = Tier 2 EIS for ISS|publisher = NASA|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960053133_1996092350.pdf|accessdate=12 July 2011 }}</ref>

The technical feasibility of a controlled targeted deorbit into a remote ocean was found to be possible only with Russia's assistance.<ref name=ISSEIS /> The Russian Space Agency has experience from de-orbiting the [[Salyut 4]], [[Salyut 5|5]], [[Salyut 6|6]], [[Salyut 7|7]] and [[Mir]] space stations; NASA's first intentional controlled de-orbit of a satellite (the [[Compton Gamma Ray Observatory]]) occurred in 2000.<ref>{{cite web|title=Entry Debris Field estimation methods and application to Compton Gamma Ray Observatory|publisher=Mission Operations Directorate, NASA Johnson Space Center|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010084992_2001127597.pdf|accessdate=12 July 2011}}</ref> As of late 2010, the preferred plan is to use a slightly modified Progress spacecraft to de-orbit the ISS.<ref name=deo>{{cite web|url=http://www.nasa.gov/pdf/578543main_asap_eol_plan_2010_101020.pdf|title=ISS End-of-Life Disposal Plan|last=Suffredini|first=Michael|date=October 2010|publisher=NASA|accessdate=7 March 2012}}</ref> This plan was seen as the simplest, most cost efficient one with the highest margin.<ref name=deo /> [[Skylab]], the only space station built and launched entirely by the US, decayed from orbit slowly over 5 years, and no attempt was made to de-orbit the station using a [[Atmospheric entry|deorbital burn]]. Remains of Skylab hit populated areas of [[Esperance, Western Australia]]<ref name="debris">{{cite web|url=http://www.eclipsetours.com/sat/debris.html|accessdate=28 May 2011|title=Paul Maley's (Skylab spaceflight controller) Space Debris Page}}</ref> without injuries or loss of life.

The [[Exploration Gateway Platform]], a discussion by NASA and Boeing at the end of 2011, suggested using leftover USOS hardware and '[[Zvezda (ISS module)|Zvezda]] 2' {{sic}} as a refuelling depot and servicing station located at one of the Earth Moon [[Lagrange points]], L1 or L2. The entire USOS cannot be reused and will be discarded, but some other Russian modules are planned to be reused. [[Nauka (ISS module)|Nauka]], the [[Uzlovoy Module|Node module]], two science power platforms and Rassvet, launched between 2010 and 2015 and joined to the ROS may be separated to form [[OPSEK]].<ref>{{cite web|url=http://www.russianspaceweb.com/iss_dc.html|title=DC-1 and MIM-2|publisher=Russianspaceweb.com|accessdate=12 July 2011}}</ref> The [[Nauka (ISS module)|Nauka module]] of the ISS will be used in the station, whose main goal is supporting manned deep space exploration. OPSEK will orbit at a higher inclination of 71 degrees, allowing observation to and from all of the Russian Federation.

In February 2015, Roscosmos announced that it would remain a part of the international space station program until 2024.<ref name=sn20150225>{{cite news |last1=de Selding|first1=Peter B. |title=Russia — and Its Modules — To Part Ways with ISS in 2024 |url=http://spacenews.com/russia-and-its-modules-to-part-ways-with-iss-in-2024/ |accessdate=26 February 2015 |work=Space News |date=25 February 2015}}</ref> Nine months earlier—in response to US sanctions against Russia over the [[2014 Crimean crisis|conflict in the Crimea]]—Russian Deputy Prime Minister [[Dmitry Rogozin]] had stated that Russia would reject a US request to prolong the orbiting station's use beyond 2020, and would only supply rocket engines to the US for non-military satellite launches.<ref>{{cite web|url=http://www.telegraph.co.uk/news/worldnews/europe/russia/10828964/Russia-to-ban-US-from-using-Space-Station-over-Ukraine-sanctions.html|title=Russia to ban US from using Space Station over Ukraine sanctions|agency=Reuters|work=The Telegraph|date=13 May 2014|accessdate=14 May 2014}}</ref>

A proposed modification that would allow some of the ISS American and European segments to be reused would be to attach a [[VASIMR]] drive module to the vacated Node with its own onboard power source. It would allow long term reliability testing of the concept for less cost than building a dedicated space station from scratch.<ref name="nbcnews">{{cite web|url=http://www.nbcnews.com/id/48260759/ns/technology_and_science-space/#.U4LaQCjFBdg|title=From the earth to the moon, and then beyond - Technology & science - Space | NBC News|publisher=nbcnews.com|accessdate=27 May 2014}}</ref>

On March 28, 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS.<ref name=":0"/><ref name=":1"/> [[Igor Komarov]], the head of Russia's Roscosmos, made the announcement with NASA administrator Charles Bolden at his side. Komarov said "Roscosmos together with NASA will work on the programme of a future orbital station," "We agreed that the group of countries taking part in the ISS project will work on the future project of a new orbital station," "The first step is that the ISS will operate until 2024," and that Roscosmos and NASA "do not rule out that the station's flight could be extended,"<ref>{{cite web|url=http://www.spacedaily.com/reports/Russia_announces_plan_to_build_new_space_station_with_NASA_999.html|title=Russia announces plan to build new space station with NASA|work=spacedaily.com}}</ref> In a statement provided to SpaceNews March 28, NASA spokesman David Weaver said the agency appreciated the Russian commitment to extending the ISS, but did not confirm any plans for a future space station.<ref name="no plans" />

==Cost==
The ISS is arguably the most expensive single item ever constructed.<ref>{{cite web|author=Zidbits |url=http://zidbits.com/?p=19 |title=What Is The Most Expensive Object Ever Built? |publisher=Zidbits.com |date=6 November 2010 |accessdate=22 October 2013}}</ref> In 2010 the cost was expected to be $150 billion. It includes NASA's budget of $58.7 billion (inflation unadjusted) for the station from 1985 to 2015 ($72.4 billion in 2010 dollars), Russia's $12 billion, Europe's $5 billion, Japan's $5 billion, Canada's $2 billion, and the cost of 36 shuttle flights to build the station; estimated at $1.4 billion each, or $50.4 billion total. Assuming 20,000 person-days of use from 2000 to 2015 by two to six-person crews, each person-day would cost $7.5 million, less than half the inflation adjusted $19.6 million ($5.5 million before inflation) per person-day of Skylab.<ref name="lafleur20100308">{{cite news | url=http://www.thespacereview.com/article/1579/1 | title=Costs of US piloted programs | work=The Space Review | date=8 March 2010 | accessdate=18 February 2012 | author=Lafleur, Claude}} See author correction in comments.</ref>

==International co-operation==
[[File:ISS Agreements.jpg|thumb|right|upright|Dated 29 January 1998]]
{{Main|Politics of the International Space Station|International Space Station program}}
;Participating countries
{{columns-list|colwidth=20em|

* '''{{flagcountry|Canada}}'''
* '''{{flagcountry|Japan}}'''
* '''{{flagcountry|Russia}}'''
* '''{{flagcountry|United States}}'''
* [[File:ESA logo simple.svg|15x15px]] '''[[European Space Agency]]'''
** {{flagcountry|Austria}}
** {{flagcountry|Belgium}}
** {{flagcountry|Czech Republic}}
** {{flagcountry|Denmark}}
** {{flagcountry|Estonia}}
** {{flagcountry|Finland}}
** {{flagcountry|France}}
** {{flagcountry|Germany}}
** {{flagcountry|Greece}}
** {{flagcountry|Hungary}}
** {{flagcountry|Ireland}}
** {{flagcountry|Italy}}
** {{flagcountry|Luxembourg}}
** {{flagcountry|Netherlands}}
** {{flagcountry|Norway}}
** {{flagcountry|Poland}}
** {{flagcountry|Portugal}}
** {{flagcountry|Romania}}
** {{flagcountry|Spain}}
** {{flagcountry|Sweden}}
** {{flagcountry|Switzerland}}
** {{flagcountry|United Kingdom}}
}}

==Sightings from Earth==

===Naked eye===
The ISS is visible to the [[naked eye]] as a slow-moving, bright white dot due to reflected sunlight, and can be seen in the hours after sunset and before sunrise when the station remains sunlit but the ground and sky are dark.<ref name="Price2005">{{cite book |title=The Backyard Stargazer: An Absolute Beginner's Guide to Skywatching With and Without a Telescope |publisher=Quarry Books |location=Gloucester, MA |first=Pat |last=Price |page=140 |year=2005 |isbn=1-59253-148-2}}</ref> The ISS takes about ten minutes to move from one horizon to another, and will only be visible part of that time due to moving into or out of the Earth's shadow. Because of the size of its reflective surface area, the ISS is the brightest man-made object in the sky excluding [[Satellite flare|flares]], with an approximate maximum [[Apparent magnitude|magnitude of −4]] when overhead, similar to Venus. The ISS, like many satellites including the [[Iridium constellation]], can also produce flares of up to 8 or 16 times the brightness of Venus as sunlight glints off reflective surfaces.<ref>{{cite web|url=http://www.calsky.com/cs.cgi/Satellites/8 |title=Artificial Satellites > (Iridium) Flares |publisher=Calsky.com |accessdate=1 May 2012}}</ref><ref name="haydenplanetarium">{{cite web|url=http://www.amnh.org/our-research/hayden-planetarium/blog/how-to-spot-the-international-space-station-and-other-satellites |title=How to Spot the International Space Station (and other satellites) |publisher=Hayden Planetarium |accessdate=12 July 2011}}</ref> The ISS is also visible during broad daylight conditions, albeit with a great deal more effort.

Tools are provided by a number of websites such as [[Heavens-Above]] (see [[#Live viewing|''Live viewing'']] below) as well as [[smartphone]] applications that use the known [[ephemeris|orbital data]] and the observer's longitude and latitude to predict when the ISS will be visible (weather permitting), where the station will appear to rise to the observer, the altitude above the horizon it will reach and the duration of the pass before the station disappears to the observer either by setting below the horizon or entering into Earth's shadow.<ref name="see">{{cite web|url=http://spaceflight.nasa.gov/realdata/sightings/index.html|title=International Space Station Sighting Opportunities|accessdate=28 January 2009|publisher=NASA|date=2 July 2008|author=NASA}}</ref><ref>{{cite web|url=http://www.heavens-above.com/satinfo.aspx?satid=25544&lat=0&lng=0&loc=Unspecified&alt=0&tz=CET|title=ISS – Information|publisher=Heavens-Above.com|accessdate=8 July 2010}}</ref><ref>{{cite journal|author=Harold F. Weaver|title=The Visibility of Stars Without Optical Aid|journal=Publications of the Astronomical Society of the Pacific|volume=59|issue=350|year=1947|doi=10.1086/125956 }}</ref><ref name="daytime visibility">{{cite web|url=http://spaceweather.com/archive.php?view=1&day=05&month=06&year=2009|title=ISS visible during the daytime|accessdate=5 June 2009|work=Spaceweather.com|date=5 June 2009}}</ref>

{{Double image|right|Isshtv120090917200858nm.jpg|223|ISS 2008-01-10.jpg|230|The ISS and HTV photographed using a telescope-mounted camera by [[Ralf Vandebergh]]|A time exposure of a station pass|A fuzzy image of the ISS set against a black background, with a smaller, cylindrical object visible to the left of the station.|A view of a dark blue, starry sky with a white line visible from the bottom-left to the top-right of the image. A tree is visible to the bottom right.}}

In November 2012 NASA launched its 'Spot the Station' service, which sends people text and email alerts when the station is due to fly above their town.<ref>{{cite news| url= http://www.3news.co.nz/Get-notified-when-the-International-Space-Station-is-in-your-area/tabid/1160/articleID/275612/Default.aspx|work=3 News NZ |title= Get notified when the International Space Station is in your area| date=6 November 2012}}</ref>

The station is visible from 95% of the inhabited land on Earth, but is not visible from extreme northern or southern latitudes.<ref name="MCC Answer" />

===Astrophotography=== 
Using a telescope mounted camera to photograph the station is a popular hobby for astronomers, <ref>{{cite web|url=http://www.hobbyspace.com/SatWatching/ |title=Satellite Watching |publisher=HobbySpace |accessdate=1 May 2012}}</ref> whilst using a mounted camera to photograph the Earth and stars is a popular hobby for crew.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2003/24mar_noseprints/ |title=Space StationAstrophotography – NASA Science |publisher=Science.nasa.gov |date=24 March 2003 |accessdate=1 May 2012}}</ref> The use of a telescope or binoculars allows viewing of the ISS during daylight hours.<ref>{{cite web|url=http://www.zmescience.com/space/video-the-iss-and-atlantis-shuttle-as-seen-in-broad-daylight/ |title=[VIDEO] The ISS and Atlantis shuttle as seen in broad daylight |publisher=Zmescience.com |date=20 July 2011 |accessdate=1 May 2012}}</ref>

Parisian engineer and astrophotographer Thierry Legault, known for his photos of spaceships crossing the Sun (called [[occultation]]), travelled to Oman in 2011, to photograph the Sun, moon and space station all lined up.<ref>{{cite news| url=http://www.wired.com/2011/01/double-eclipse/ | work=Wired | first=Lisa | last=Grossman | title=Moon and Space Station Eclipse the Sun}}</ref> Legault, who received the Marius Jacquemetton award from the [[Société astronomique de France]] in 1999, and other hobbyists, use websites that predict when the ISS will pass in front of the Sun or Moon and from what location those passes will be visible.

==See also==
{{Wikipedia books|International Space Station}}
{{Portal|Spaceflight|Space}}
* [[Center for the Advancement of Science in Space]] - operates the US National Laboratory on the ISS
* [[List of space stations]]
* [[Origins of the International Space Station]]
* [[Space architecture]]

==Gallery==
[[File:ISS and Endeavour seen from the Soyuz TMA-20 spacecraft 14.jpg|thumb|left|550px|<center>International Space Station docked with ''Endeavour'' and ''Johannes Kepler'' ]]
{{-}}

==Notes==
{{Reflist|group="note"}}

==References==
{{Reflist|colwidth=25em}}

==External links==
{{Sister project links|wikt=no|n=Category:International Space Station|voy=Space}}

===Agency ISS websites===
{{divcol|20em}}
* {{flagicon|Canada}} [http://www.asc-csa.gc.ca/eng/iss/default.asp Canadian Space Agency]
* [[File:Not the esa logo.png]] [http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station European Space Agency]
* {{flagicon|France}} [http://www.cnes.fr/web/CNES-en/1422-iss-the-international-space-station.php Centre national d'études spatiales (National Centre for Space Studies)]
* {{flagicon|Germany}} [http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10300 German Aerospace Centre]
* {{flagicon|Italy}} [http://www.asi.it/en/flash_en/living Italian Space Agency]
* {{flagicon|Japan}} [http://www.jaxa.jp/projects/iss_human/index_e.html Japan Aerospace Exploration Agency]
* {{flagicon|Russia}} [http://www.energia.ru/eng/iss/iss.html S.P. Korolev Rocket and Space Corporation Energia]
* {{flagicon|Russia}} [http://www.roscosmos.ru/ Russian Federal Space Agency]
* {{flagicon|USA}} [http://www.nasa.gov/mission_pages/station/main/ National Aeronautics and Space Administration]
{{Div col end}}

===Research===
* [https://blogs.nasa.gov/spacestation/ NASA: Daily ISS Reports]
* [http://www.nasa.gov/mission_pages/station/science/index.html NASA: Station Science]
* [http://www.esa.int/Our_Activities/Human_Spaceflight/Columbus ESA: Columbus]
* [http://www.energia.ru/en/iss/researches/iss-researches.html RSC Energia: Science Research on ISS Russian Segment]

===Live viewing===
{{See also|List of satellite pass predictors}}
* [http://www.ustream.tv/channel/live-iss-stream Live ISS webcam] by NASA at uStream.tv
* [http://heavens-above.com/orbit.aspx?satid=25544 Real-time position] at Heavens-above.com
* [http://www.n2yo.com/?s=25544 Real-time position] at N2YO.com
* [http://wheretheiss.at/ Real-time position] at WheretheISS.at

===Multimedia===
* [http://www.nasa.gov/externalflash/ISSRG/index.html Interactive reference guide] at NASA.gov
* [http://spaceflight.nasa.gov/gallery/images/station/ Image gallery search page] at NASA.gov
* [http://i.usatoday.net/tech/graphics/iss_timeline/flash.htm Assembly sequence animation] by ''USA Today'' and NASA
* [https://www.youtube.com/watch?v=doN4t5NKW-k ISS tour with Sunita Williams] by NASA at YouTube.com
* [https://www.youtube.com/watch?v=QF2w2Dx_QMs ISS tour with André Kuipers] by ESA at YouTube.com
* [http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station/Highlights/International_Space_Station_panoramic_tour ISS photo tour with Samantha Cristoforetti] by ESA
* [https://www.youtube.com/watch?v=vMmcLmu3V1k ''The Future of Hope'', Kibo module documentary] by JAXA at YouTube.com
* [https://www.youtube.com/playlist?list=PLbyvawxScNbsoD_tGlw8kWCw3S5htiVKZ Journey to the ISS] by ESA at YouTube.com

{{ISS modules}}
{{International Space Station}}
{{Manned ISS flight}}
{{Unmanned ISS resupply flights}}
{{People currently in space}}
{{Space stations}}
{{US manned space programs}}
{{Russian manned space programs}}
{{European manned spaceflight}}
{{Spaceflight}}
{{Orbital launches in 1998}}

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{{Authority control}}
[[Category:International Space Station| ]]
[[Category:Artificial satellites orbiting Earth]]
[[Category:Populated places established in 1998]]
[[Category:United States Department of Energy national laboratories]]
[[Category:Spacecraft launched in 1998]]
[[Category:1998 in spaceflight]]
[[Category:Articles containing video clips]]

User:WikipediaTutorials/sandbox

2015-08-18T20:08:42Z

WikipediaTutorials: I fixed a typo.

{{About|the astronomical structure|other uses}}
{{Use mdy dates|date=February 2015}}
{{Multiple image |direction=vertical |align=right |width=310|image1=NGC 4414 (NASA-med).jpg|caption1=[[NGC 4414]], a typical spiral galaxy in the [[constellation]] [[Coma Berenices]], is about 55,000 [[light-year]]s in diameter and approximately 60 million light-years away from Earth|image2=M104_ngc4594_sombrero_galaxy_hi-res.jpg|caption2=The [[Sombrero galaxy]] (M104), a bright nearby spiral galaxy.|image3=Irregular_galaxy_NGC_1427A_(captured_by_the_Hubble_Space_Telescope).jpg|caption3=[[NGC 1427A]], an example of an irregular galaxy, 52 million [[light-year]]s away}}

A '''galaxy''' is a [[gravitation|gravitationally]] bound system of [[star]]s, [[stellar remnant]]s, [[interstellar medium|interstellar gas]] and [[cosmic dust|dust]], and [[dark matter]].<ref name="sparkegallagher2000"/><ref name=nasa060812/> The word galxy is derived from the [[Ancient Greek|Greek]] ''{{transl|grc|galaxias}}'' ({{lang|grc|γαλαξίας}}), literally "milky", a refrence to the [[Milky Way]]. Examples of galaxies range from [[dwarf galaxy|dwarfs]] with just a few thousand (103) stars to giants with one hundred [[Trillion (short scale)|trillion]] (1014) stars,<ref name=science250_4980_539/> each orbiting their galaxy's own [[center of mass]]. Galaxies are categorized according to their visual morphology, including [[elliptical galaxy|elliptical]],<ref name=uf030616/> [[Spiral galaxy|spiral]], and [[irregular galaxy|irregular]].<ref name="IRatlas"/> Many galaxies are believed to have [[black hole]]s at their [[active galactic nucleus|active center]]s. The Milky Way's central black hole, known as [[Sagittarius A*]], has a mass four million times that of our Sun.<ref name="smbh"/> As of May 2015, [[EGS-zs8-1]] is the most distant known galaxy, estimated to be 13.1 billion [[light-year]]s away and to have 15% of the mass of the Milky Way.<ref name="ARX-20150503">{{cite journal |authors=Oesch, P.A. et al. |title=A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE |url=http://arxiv.org/abs/1502.05399 |date=May 3, 2015 |journal=[[ArXiv]] |arxiv=1502.05399 |accessdate=May 6, 2015 |bibcode = 2015arXiv150205399O }}
</ref><ref name=p15>{{cite web |author=Staff |title=Astronomers unveil the farthest galaxy |url=http://phys.org/news/2015-05-astronomers-unveil-farthest-galaxy.html |publisher=[[Phys.org]] |accessdate=May 6, 2015|date=May 5, 2015}}</ref><ref name="NYT-20150505">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Astronomers Measure Distance to Farthest Galaxy Yet |url=http://www.nytimes.com/2015/05/06/science/astronomers-measure-distance-to-farthest-galaxy-yet.html |date=May 5, 2015 |work=[[New York Times]] |accessdate=May 6, 2015 }}</ref><ref name="AP-20150505">{{cite news |last=Borenstein |first=Seth |title=Astronomers find farthest galaxy: 13.1 billion light-years |url=http://apnews.excite.com/article/20150505/us-sci--farthest_galaxy-46c792535a.html |date= May 5, 2015 |work=[[AP News]] |accessdate=May 6, 2015 }}</ref>

Approximately 170 billion ({{nowrap|1.7 × 1011}}) galaxies exist in the [[observable universe]].<ref name="apj624_2"/> Most of the galaxies are 1,000 to 100,000 [[parsec]]s in diameter and usually separated by distances on the order of millions of parsecs (or megaparsecs). The [[intergalactic space|space]] between galaxies is filled with a tenuous gas with an average density less than one [[atom]] per cubic meter. The majority of galaxies are gravitationally organized into associations known as [[galaxy group]]s, [[galaxy cluster|clusters]], and [[supercluster]]s. At the [[Large-scale structure of the Cosmos|largest scale]], these associations are generally arranged into [[galaxy filament|sheets and filaments]] that are surrounded by immense [[void (astronomy)|voids]].<ref name=camb_lss/>

==Etymology==
The word ''galaxy'' derives from the [[Greek language|Greek]] term for our own galaxy, ''{{transl|grc|galaxias}}'' (''{{lang|grc|{{linktext|γαλαξίας}}}}'', "milky one"), or ''{{transl|grc|[[kyklos]] galaktikos}}'' ("milky circle")<ref name=oed/> due to its appearance as a "milky" band of light in the sky. In [[Greek mythology]], [[Zeus]] places his son born by a mortal woman, the infant [[Heracles]], on [[Hera]]'s breast while she is asleep so that the baby will drink her divine milk and will thus become immortal. Hera wakes up while breastfeeding and then realizes she is nursing an unknown baby: she pushes the baby away and a jet of her milk sprays the night sky, producing the faint band of light known as the Milky Way.<ref name=waller_hodge2003/><ref name=konean2006/>

In the astronomical literature, the capitalized word "Galaxy" is often used to refer to our galaxy, the [[Milky Way]], to distinguish it from the other galaxies in our [[universe]]. The English term ''Milky Way'' can be traced back to a story by [[Chaucer]] {{circa|1380}}:
{{Quote|"See yonder, lo, the Galaxyë  Which men {{linktext|clepe}}th ''the Milky Wey'',  For hit is whyt."|Geoffrey Chaucer|[[The House of Fame]]''<ref name=oed/>}}

When [[William Herschel]] assembled [[Catalogue of Nebulae|his catalog]] of deep sky objects in 1786, he used the term ''[[spiral nebula]]'' for certain objects such as [[Andromeda Galaxy|M31]]. These would later be recognized as conglomerations of stars when the true distance to these objects began to be appreciated, and they would later be termed ''island universes.'' However, the word ''Universe'' was understood to mean the entirety of existence, so this expression fell into disuse and the objects instead became known as galaxies.<ref name=rao2005/>

==Nomenclature==
Tens of thousands of galaxies have been catalogued, but only a few have well-established names, such as the [[Andromeda Galaxy]], the [[Magellanic clouds]], the [[Whirlpool Galaxy]] and the [[Sombrero Galaxy]]. Astronomers work with numbers from certain catalogues, such as the [[Messier catalogue]], the NGC ([[New General Catalogue]]), the IC ([[Index Catalogue]]), the CGCG ([[Catalogue of Galaxies and of Clusters of Galaxies]]), the MCG ([[Morphological Catalogue of Galaxies]]) and UGC ([[Uppsala General Catalogue|Uppsala General Catalogue of Galaxies]]). All of the well-known galaxies appear in one or more of these catalogues but each time under a different number.
For example, [[Messier 109]] is a spiral galaxy having the number 109 in the catalogue of Messier, but also codes NGC3992, UGC6937, CGCG 269-023, MCG +09-20-044, and PGC 37617.

Because it is customary in science to assign names to most of the studied objects, even to the smallest ones, the Belgian astrophysicist [[Gerard Bodifee]] and the classicist Michel Berger started a new catalogue ([[Gerard Bodifee#Works|CNG-Catalogue of Named Galaxies]])<ref>{{Cite web|url=http://www.bodifee.be/acms/acmsdata/document/9/184_CNG%20catalogue.pdf|title=CNG-Catalogue of Named Galaxies |author=Bodifée G. & Berger M.|date=2010|accessdate=January 17, 2014}}</ref> in which a thousand well-known galaxies are given meaningful, descriptive names in Latin (or Latinized Greek)<ref>{{cite web |title=Contemporary Latin |url=http://www.isnare.com/encyclopedia/Contemporary_Latin#In_science |accessdate= January 22, 2014}}</ref> in accordance with the binomial nomenclature that one uses in other sciences such as biology, anatomy, [[paleontology]] and in other fields of astronomy such as the geography of Mars.
One of the arguments to do so is that these impressive objects deserve better than uninspired codes. For instance, Bodifee and Berger propose the informal, descriptive name ''{{lang|la|Callimorphus Ursae Majoris}}'' for the well-formed barred galaxy Messier 109 in Ursa Major.

==Observation history==
The realization that we live in a galaxy, and that ours is one among many, parallels major discoveries that were made about the Milky Way and other [[nebula]]e in the night sky.

===Milky Way===
{{Main|Milky Way}}
The [[Greek philosophy|Greek]] philosopher [[Democritus]] (450–370 BC) proposed that the bright band on the night sky known as the Milky Way might consist of distant stars.<ref name="Plutarch">{{cite book | title=The Complete Works Volume 3: Essays and Miscellanies | publisher=Echo Library | author=Plutarch | authorlink=Plutarch | date=2006 | location=Chapter 3 | pages=66 | isbn=978-1-4068-3224-2}}</ref>
[[Aristotle]] (384–322 BC), however, believed the Milky Way to be caused by "the ignition of the fiery exhalation of some stars that were large, numerous and close together" and that the "ignition takes place in the upper part of the [[atmosphere]], in the [[Sublunary sphere|region of the World that is continuous with the heavenly motions]]."<ref name=Montada>
{{cite web
| last1=Montada |first1=J. P.
| date=September 28, 2007
| title=Ibn Bajja
| work=[[Stanford Encyclopedia of Philosophy]]
| url=http://plato.stanford.edu/entries/ibn-bajja
| accessdate=July 11, 2008
}}</ref> The [[Neoplatonism|Neoplatonist]] philosopher [[Olympiodorus the Younger]] ({{circa|495}}–570 AD) was critical of this view, arguing that if the Milky Way is [[sublunary]] (situated between Earth and the Moon) it should appear different at different times and places on Earth, and that it should have [[parallax]], which it does not. In his view, the Milky Way is celestial.<ref name=heidarzadeh23/>

According to Mohani Mohamed, the [[Islamic astronomy|Arabian]] astronomer [[Alhazen]] (965–1037) made the first attempt at observing and measuring the Milky Way's parallax,<ref name=mohamed/> and he thus "determined that because the Milky Way had no parallax, it must be remote from the Earth, not belonging to the atmosphere."<ref>
{{cite web
| last1=Bouali |first1=H.-E.
| last2=Zghal |first2=M.
| last3=Lakhdar |first3=Z. B.
| date=2005
| title=Popularisation of Optical Phenomena: Establishing the First Ibn Al-Haytham Workshop on Photography
| publisher=The Education and Training in Optics and Photonics Conference
| url=http://spie.org/etop/ETOP2005_080.pdf
| accessdate=July 8, 2008
}}</ref> The [[Persian people|Persian]] astronomer [[al-Bīrūnī]] (973–1048) proposed the Milky Way galaxy to be "a collection of countless fragments of the nature of nebulous stars."<ref>{{MacTutor Biography|id=Al-Biruni|title=Abu Rayhan Muhammad ibn Ahmad al-Biruni}}</ref><ref name=al_biruni/> The [[Al-Andalus|Andalusian]] astronomer [[Ibn Bajjah]] ("Avempace", {{abbr|d.|died}} 1138) proposed that the Milky Way is made up of many stars that almost touch one another and appear to be a continuous image due to the effect of [[refraction]] from sublunary material,<ref name=Montada/><ref name="heidarzadeh25"/> citing his observation of the [[Conjunction (astronomy and astrology)|conjunction]] of Jupiter and Mars as evidence of this occurring when two objects are near.<ref name=Montada/> In the 14th century, the Syrian-born [[Ibn Qayyim]] proposed the Milky Way galaxy to be "a myriad of tiny stars packed together in the sphere of the fixed stars."<ref name=Livingston>
{{cite journal
|last1=Livingston |first1=J. W.
|date=1971
|title=Ibn Qayyim al-Jawziyyah: A Fourteenth Century Defense against Astrological Divination and Alchemical Transmutation
|journal=[[Journal of the American Oriental Society]]
|volume=91 |issue=1 |pages=96–103 [99]
|doi=10.2307/600445
|jstor=600445
}}</ref>
[[File:Herschel-Galaxy.png|thumb|The shape of the Milky Way as estimated from star counts by [[William Herschel]] in 1785; the solar system was assumed to be near the center.]]
Actual proof of the Milky Way consisting of many stars came in 1610 when the Italian astronomer [[Galileo Galilei]] used a [[optical telescope|telescope]] to study the Milky Way and discovered that it is composed of a huge number of faint stars.<ref>Galileo Galilei, ''Sidereus Nuncius'' (Venice, (Italy): Thomas Baglioni, 1610), [https://archive.org/stream/Sidereusnuncius00Gali#page/n37/mode/2up pages 15 and 16.] 
English translation: Galileo Galilei with Edward Stafford Carlos, trans., ''The Sidereal Messenger'' (London, England: Rivingtons, 1880), [https://archive.org/stream/siderealmessenge80gali#page/42/mode/2up/ pages 42 and 43.]</ref><ref>
{{cite web
|last1=O'Connor |first1=J. J.
|last2=Robertson |first2=E. F.
|date=November 2002
|title=Galileo Galilei
|url=http://www-gap.dcs.st-and.ac.uk/~history/Biographies/Galileo.html
|publisher=[[University of St. Andrews]]
|accessdate=January 8, 2007
}}</ref> In 1750 the English astronomer [[Thomas Wright (astronomer)|Thomas Wright]], in his ''An original theory or new hypothesis of the Universe'', speculated (correctly) that the galaxy might be a rotating body of a huge number of stars held together by [[gravitation|gravitational forces]], akin to the solar system but on a much larger scale. The resulting disk of stars can be seen as a band on the sky from our perspective inside the disk.<ref>Thomas Wright, ''An Original Theory or New Hypothesis of the Universe'' … (London, England: H. Chapelle, 1750). [http://books.google.com/books?id=80VZAAAAcAAJ&pg=PA48#v=onepage&q&f=false From p.48:] " … the stars are not infinitely dispersed and distributed in a promiscuous manner throughout all the mundane space, without order or design, … this phænomenon [is] no other than a certain effect arising from the observer's situation, … To a spectator placed in an indefinite space, … it [i.e., the Milky Way (''Via Lactea'')] [is] a vast ring of stars … " 
[http://books.google.com/books?id=80VZAAAAcAAJ&pg=PA73#v=onepage&q&f=false On page 73], Wright called the Milky Way the ''Vortex Magnus'' (the great whirlpool) and estimated its diameter at 8.64×1012 miles (13.9×1012 km).</ref><ref name="our_galaxy"/> In a treatise in 1755, [[Immanuel Kant]] elaborated on Wright's idea about the structure of the Milky Way.<ref>Immanuel Kant, [http://books.google.com/books?id=nCcaAQAAMAAJ&pg=PP9#v=onepage&q&f=false ''Allgemeine Naturgeschichte und Theorie des Himmels'' …] [Universal Natural History and Theory of the Heavens … ], (Koenigsberg and Leipzig, (Germany): Johann Friederich Petersen, 1755). Available in English translation by Ian Johnston at: [http://records.viu.ca/~johnstoi/kant/kant2e.htm Vancouver Island University, British Columbia, Canada]</ref>

The first project to describe the shape of the Milky Way and the position of the [[Sun]] was undertaken by [[William Herschel]] in 1785 by counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with [[Galactocentrism|the solar system close to the center]].<ref>William Herschel (1785) "On the Construction of the Heavens," ''Philosophical Transactions of the Royal Society of London'', '''75''' : 213-266. Herschel's diagram of the galaxy appears immediately after the article's last page. See:
* [http://books.google.com/books?id=IU9FAAAAcAAJ&pg=PA213#v=onepage&q&f=false Google Books]
* [http://rstl.royalsocietypublishing.org/content/75/213.full.pdf+html The Royal Society of London]</ref><ref name=paul1993/> Using a refined approach, [[Jacobus Kapteyn|Kapteyn]] in 1920 arrived at the picture of a small (diameter about 15 kiloparsecs) ellipsoid galaxy with the Sun close to the center. A different method by [[Harlow Shapley]] based on the cataloguing of [[globular cluster]]s led to a radically different picture: a flat disk with diameter approximately 70 kiloparsecs and the Sun far from the center.<ref name="our_galaxy" /> Both analyses failed to take into account the [[extinction (astronomy)|absorption of light]] by [[cosmic dust|interstellar dust]] present in the [[galactic plane]], but after [[Robert Julius Trumpler]] quantified this effect in 1930 by studying [[open cluster]]s, the present picture of our host galaxy, the Milky Way, emerged.<ref>
{{cite journal
|last1=Trimble |first1=V.
|date=1999
|title=Robert Trumpler and the (Non)transparency of Space
|journal=[[Bulletin of the American Astronomical Society]]
|volume=31 |issue=31 |pages=1479
|bibcode=1999AAS...195.7409T
}}</ref>

[[File:Milky Way Arch.jpg|thumb|center|600px|A [[Fisheye lens|fish-eye]] mosaic of the Milky Way arching at a high inclination across the night sky, shot from a dark-sky location in Chile]]

===Distinction from other nebulae===

A few galaxies outside the Milky Way are visible in the night sky to the unaided eye. In the 10th century, the Persian astronomer [[Al-Sufi]] made the earliest recorded identification of the [[Andromeda Galaxy]], describing it as a "small cloud".<ref name="NSOG"/> In 964, Al-Sufi identified the [[Large Magellanic Cloud]] in his ''[[Book of Fixed Stars]]''; it was not seen by Europeans until [[Ferdinand Magellan|Magellan]]'s voyage in the 16th century.<ref name="obspm">
{{cite web
|title=Abd-al-Rahman Al Sufi (December 7, 903 – May 25, 986 A.D.)
|url=http://messier.obspm.fr/xtra/Bios/alsufi.html
|publisher=[[Observatoire de Paris]]
|accessdate=April 19, 2007
}}</ref><ref name="obspm2">
{{cite web
|title=The Large Magellanic Cloud, LMC
|url=http://messier.obspm.fr/xtra/ngc/lmc.html
|publisher=[[Observatoire de Paris]]
|accessdate=April 19, 2007
}}</ref> The Andromeda Galaxy was independently noted by [[Simon Marius]] in 1612.<ref name="NSOG"/>

In 1750, [[Thomas Wright (astronomer)|Thomas Wright]] speculated (correctly) that the Milky Way is a flattened disk of stars, and that some of the [[nebula]]e visible in the night sky might be separate Milky Ways.<ref name="our_galaxy">
{{cite web
|last1=Evans |first1=J. C.
|date=November 24, 1998
|title=Our Galaxy
|url=http://physics.gmu.edu/~jevans/astr103/CourseNotes/ECText/ch20_txt.htm
|publisher=[[George Mason University]]
|accessdate=January 4, 2007
}}</ref><ref>See text quoted from Wright's ''An original theory or new hypothesis of the Universe'' in {{Cite book
|last1=Dyson |first1=F.
|date=1979
|title=Disturbing the Universe
|page=245
|publisher=[[Pan Books]]
|isbn=0-330-26324-2
}}</ref> In 1755, [[Immanuel Kant]] used the term "island Universe" to describe these distant nebulae.
[[File:Pic iroberts1.jpg|thumb|right|Photograph of the "Great Andromeda Nebula" from 1899, later identified as the [[Andromeda Galaxy]]]]
Toward the end of the 18th century, [[Charles Messier]] compiled a [[Messier object|catalog]] containing the 109 brightest celestial objects having nebulous appearance. Subsequently, William Herschel assembled a catalog of 5,000 nebulae.<ref name="our_galaxy" /> In 1845, [[William Parsons, 3rd Earl of Rosse|Lord Rosse]] constructed a new telescope and was able to distinguish between elliptical and spiral nebulae. He also managed to make out individual point sources in some of these nebulae, lending credence to Kant's earlier conjecture.<ref>[http://parsonstown.info/people/william-rosse "Parsonstown | The genius of the Parsons family | William Rosse"]. ''parsonstown.info''.</ref>

In 1912, [[Vesto Slipher]] made spectrographic studies of the brightest spiral nebulae to determine their composition. Slipher discovered that the spiral nebulae have high [[Doppler shift]]s, indicating that they are moving at a rate exceeding the velocity of the stars he had measured. He found that the majority of these nebulae are moving away from us.<ref>
{{cite journal
|last1=Slipher |first1=V. M.
|date=1913
|title=The radial velocity of the Andromeda Nebula
|journal=Lowell Observatory Bulletin
|volume=1 |pages=56–57
|bibcode=1913LowOB...2...56S
}}</ref><ref>
{{cite journal
|last1=Slipher |first1=V. M.
|date=1915
|title=Spectrographic Observations of Nebulae
|journal=[[Popular Astronomy (US magazine)|Popular Astronomy]]
|volume=23 |pages=21–24
|bibcode=1915PA.....23...21S
}}</ref>

In 1917, [[Heber Curtis]] observed nova [[S Andromedae]] within the "Great [[Andromeda (constellation)|Andromeda]] Nebula" (as the Andromeda Galaxy, [[Messier object]] [[Andromeda Galaxy|M31]], was then known). Searching the photographic record, he found 11 more [[nova]]e. Curtis noticed that these novae were, on average, 10 [[magnitude (astronomy)|magnitudes]] fainter than those that occurred within our galaxy. As a result, he was able to come up with a distance estimate of 150,000 [[parsec]]s. He became a proponent of the so-called "island universes" hypothesis, which holds that spiral nebulae are actually independent galaxies.<ref>
{{cite journal
|last=Curtis |first1=H. D.
|date=1988
|title=Novae in Spiral Nebulae and the Island Universe Theory
|journal=[[Publications of the Astronomical Society of the Pacific]]
|volume=100 |pages=6
|bibcode=1988PASP..100....6C
|doi=10.1086/132128
}}</ref>

In 1920 the so-called [[Great Debate (astronomy)|Great Debate]] took place between [[Harlow Shapley]] and [[Heber Curtis]], concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the Universe. To support his claim that the Great Andromeda Nebula is an external galaxy, Curtis noted the appearance of dark lanes resembling the dust clouds in the Milky Way, as well as the significant Doppler shift.<ref>
{{cite web
|last1=Weaver |first1=H. F.
|title=Robert Julius Trumpler
|url=http://www.nap.edu/readingroom/books/biomems/rtrumpler.html
|publisher=[[United States National Academy of Sciences|US National Academy of Sciences]]
|accessdate=January 5, 2007
}}</ref>

In 1922, the [[Estonia]]n astronomer [[Ernst Öpik]] gave a distance determination that supported the theory that the Andromeda Nebula is indeed a distant extra-galactic object.<ref>
{{cite journal
|last1=Öpik |first1=E.
|date=1922
|title=An estimate of the distance of the Andromeda Nebula
|journal=[[Astrophysical Journal]]
|volume=55 |pages=406
|bibcode=1922ApJ....55..406O
|doi=10.1086/142680
}}</ref> Using the new 100 inch [[Mount Wilson Observatory|Mt. Wilson]] telescope, [[Edwin Hubble]] was able to resolve the outer parts of some spiral nebulae as collections of individual stars and identified some [[Cepheid variable]]s, thus allowing him to estimate the distance to the nebulae: they were far too distant to be part of the Milky Way.<ref>
{{cite journal
|last1=Hubble |first1=E. P.
|date=1929
|title=A spiral nebula as a stellar system, Messier 31
|journal=[[Astrophysical Journal]]
|volume=69 |pages=103–158
|bibcode=1929ApJ....69..103H
|doi=10.1086/143167
}}</ref> In 1936 Hubble produced a classification of [[Galaxy morphological classification|galactic morphology]] that is used to this day.<ref>
{{cite journal
|last1=Sandage |first1=A.
|date=1989
|title=Edwin Hubble, 1889–1953
|journal=[[Journal of the Royal Astronomical Society of Canada]]
|volume=83 |issue=6 |pages=351–362
|url=http://antwrp.gsfc.nasa.gov/diamond_jubilee/1996/sandage_hubble.html
|accessdate=January 8, 2007
|bibcode = 1989JRASC..83..351S }}</ref>

===Modern research===
[[File:GalacticRotation2.svg|thumb|right|200px|[[Galaxy rotation curve|Rotation curve]] of a typical spiral galaxy: predicted based on the visible matter (A) and observed (B). The distance is from the [[Bulge (astronomy)|galactic core]].]]
In 1944, [[Hendrik C. van de Hulst|Hendrik van de Hulst]] predicted that [[microwave]] radiation with [[hydrogen line|wavelength of 21 cm]] would be detectable from interstellar atomic [[hydrogen]] gas;<ref>
{{cite web
|last1=Tenn |first1=J.
|title=Hendrik Christoffel van de Hulst
|url=http://www.phys-astro.sonoma.edu/BruceMedalists/vandeHulst/
|publisher=[[Sonoma State University]]
|accessdate=January 5, 2007
}}</ref> and in 1951 it was observed. This radiation is not affected by dust absorption, and so its Doppler shift can be used to map the motion of the gas in our galaxy. These observations led to the hypothesis of a rotating [[barred spiral galaxy|bar structure]] in the center of our galaxy.<ref>
{{cite journal
|last1=López-Corredoira |first1=M.
|display-authors=etal
|date=2001
|title=Searching for the in-plane Galactic bar and ring in DENIS
|journal=[[Astronomy and Astrophysics]]
|volume=373
|issue=1 |pages=139–152
|bibcode=2001A&A...373..139L
|doi=10.1051/0004-6361:20010560
|arxiv = astro-ph/0104307 }}</ref> With improved [[radio telescope]]s, hydrogen gas could also be traced in other galaxies.
In the 1970s, [[Vera Rubin]] uncovered a discrepancy between observed galactic [[galaxy rotation curve|rotation speed]] and that predicted by the visible mass of stars and gas. Today, the galaxy rotation problem is thought to be explained by the presence of large quantities of unseen [[dark matter]].<ref>
{{cite journal
|last1=Rubin |first1=V. C.
|date=1983
|title=Dark matter in spiral galaxies
|journal=[[Scientific American]]
|volume=248
|issue=6 |pages=96–106
|bibcode=1983SciAm.248...96R
|doi=10.1038/scientificamerican0683-96
}}</ref><ref>
{{cite journal
|last1=Rubin |first1=V. C.
|date=2000
|title=One Hundred Years of Rotating Galaxies
|journal=[[Publications of the Astronomical Society of the Pacific]]
|volume=112 |issue=772 |pages=747–750
|bibcode=2000PASP..112..747R
|doi=10.1086/316573
}}</ref> A concept known as the [[universal rotation curve]] of spirals, moreover, shows that the problem is ubiquitous in these objects.

Beginning in the 1990s, the [[Hubble Space Telescope]] yielded improved observations. Among other things, Hubble data helped establish that the missing dark matter in our galaxy cannot solely consist of inherently faint and small stars.<ref>
{{cite news
|title=Hubble Rules Out a Leading Explanation for Dark Matter
|publisher=Hubble News Desk
|date=October 17, 1994
|url=http://hubblesite.org/newscenter/archive/releases/1994/41/text/
|accessdate=January 8, 2007
}}</ref> The [[Hubble Deep Field]], an extremely long exposure of a relatively empty part of the sky, provided evidence that there are about 125 billion ({{val|1.25|e=11}}) galaxies in the Universe.<ref>
{{cite web
|date=November 27, 2002
|title=How many galaxies are there?
|url=http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/021127a.html
|publisher=[[NASA]]
|accessdate=January 8, 2007
}}</ref> Improved technology in detecting the [[electromagnetic spectrum|spectra]] invisible to humans (radio telescopes, infrared cameras, and [[x-ray astronomy|x-ray telescopes]]) allow detection of other galaxies that are not detected by Hubble. Particularly, galaxy surveys in the [[Zone of Avoidance]] (the region of the sky blocked by the Milky Way) have revealed a number of new galaxies.<ref>
{{cite journal
|last1=Kraan-Korteweg |first1=R. C.
|last2=Juraszek |first2=S.
|date=2000
|title=Mapping the hidden Universe: The galaxy distribution in the Zone of Avoidance
|journal=[[Publications of the Astronomical Society of Australia]]
|volume=17 |issue=1 |pages=6–12
|bibcode=1999astro.ph.10572K
|arxiv = astro-ph/9910572
|doi=10.1071/AS00006 }}</ref>

==Types and morphology==
{{Main|Galaxy morphological classification}}
[[File:Hubble sequence photo.png|thumb|360px|Types of galaxies according to the Hubble classification scheme: an ''E'' indicates a type of elliptical galaxy; an ''S'' is a spiral; and ''SB'' is a barred-spiral galaxy.<ref group=note>Galaxies to the left side of the Hubble classification scheme are sometimes referred to as "early-type", while those to the right are "late-type".</ref>]]
Galaxies come in three main types: ellipticals, spirals, and irregulars. A slightly more extensive description of galaxy types based on their appearance is given by the [[Galaxy morphological classification|Hubble sequence]]. Since the Hubble sequence is entirely based upon visual morphological type, it may miss certain important characteristics of galaxies such as [[star formation]] rate in [[Starburst galaxy|starburst galaxies]] and activity in the cores of [[active galaxy|active galaxies]].<ref name="IRatlas" />

===Ellipticals===
{{Main|Elliptical galaxy}}
The Hubble classification system rates elliptical galaxies on the basis of their ellipticity, ranging from E0, being nearly spherical, up to E7, which is highly elongated. These galaxies have an [[ellipsoid]]al profile, giving them an elliptical appearance regardless of the viewing angle. Their appearance shows little structure and they typically have relatively little [[interstellar medium|interstellar matter]]. Consequently, these galaxies also have a low portion of [[open cluster]]s and a reduced rate of new star formation. Instead they are dominated by generally older, more [[stellar evolution|evolved stars]] that are orbiting the common center of gravity in random directions. The stars contain low abundances of heavy elements because star formation ceases after the initial burst. In this sense they have some similarity to the much smaller [[globular cluster]]s.<ref name="elliptical">
{{cite web
|last1=Barstow |first1=M. A.
|date=2005
|title=Elliptical Galaxies
|url=http://web.archive.org/web/20120729081504/http://www.star.le.ac.uk/edu/Elliptical.shtml
|publisher=[[Leicester University]] Physics Department
|accessdate=June 8, 2006
}}</ref>

The largest galaxies are giant ellipticals. Many elliptical galaxies are believed to form due to the [[interacting galaxy|interaction of galaxies]], resulting in a collision and merger. They can grow to enormous sizes (compared to spiral galaxies, for example), and giant elliptical galaxies are often found near the core of large galaxy clusters.<ref>
{{cite web
|date=October 20, 2005
|title=Galaxies
|url=http://web.archive.org/web/20140629115612/http://curious.astro.cornell.edu/galaxies.php
|publisher=[[Cornell University]]
|accessdate=August 10, 2006
}}</ref> Starburst galaxies are the result of such a galactic collision that can result in the formation of an elliptical galaxy.<ref name="elliptical" />

====Shell galaxy====
[[File:NGC 3923 Elliptical Shell Galaxy.jpg|thumb|NGC 3923 Elliptical Shell Galaxy-Hubble Space Telescope photograph]]
A shell galaxy is a type of elliptical galaxy where the stars in the galaxy's halo are arranged in concentric shells. About 1/10 tenth of elliptical galaxies have a shell-like structure, which has never been observed in spiral galaxies. The shell-like structures are thought to develop when a larger galaxy absorbs a smaller companion galaxy. As the two galaxy centers approach, the centers start to oscillate around a center point, the oscillation creates gravitational ripples forming the shells of stars, similar to ripples spreading on water. For example, galaxy [[NGC 3923]] has over twenty shells.<ref>{{Cite web|title = Galactic onion|url = http://www.spacetelescope.org/images/potw1519a/|website = www.spacetelescope.org|accessdate = 2015-05-11}}</ref>

===Spirals===
{{Main|Spiral galaxy|Barred spiral galaxy}}

[[File:M101 hires STScI-PRC2006-10a.jpg|thumb|right|The [[Pinwheel Galaxy]], NGC 5457.]]

Spiral galaxies resemble spiraling pinwheels. Though the stars and other visible material contained in such a galaxy lie mostly on a plane, the majority of mass in spiral galaxies exists in a roughly spherical halo of [[dark matter]] that extends beyond the visible component, as demonstrated by the universal rotation curve concept.<ref name="Williams2009">{{cite doi|10.1111/j.1365-2966.2009.15582.x}}</ref>

Spiral galaxies consist of a rotating disk of stars and interstellar medium, along with a central bulge of generally older stars. Extending outward from the [[bulge (astronomy)|bulge]] are relatively bright arms. In the Hubble classification scheme, spiral galaxies are listed as type ''S'', followed by a letter (''a'', ''b'', or ''c'') that indicates the degree of tightness of the spiral arms and the size of the central bulge. An ''Sa'' galaxy has tightly wound, poorly defined arms and possesses a relatively large core region. At the other extreme, an ''Sc'' galaxy has open, well-defined arms and a small core region.<ref>
{{cite web
|last1=Smith |first1=G.
|date=March 6, 2000
|url=http://casswww.ucsd.edu/public/tutorial/Galaxies.html
|title=Galaxies — The Spiral Nebulae
|publisher=[[University of California]], San Diego Center for Astrophysics & Space Sciences
|accessdate=November 30, 2006
}}</ref> A galaxy with poorly defined arms is sometimes referred to as a [[flocculent spiral galaxy]]; in contrast to the [[grand design spiral galaxy]] that has prominent and well-defined spiral arms.<ref name=bergh1998/>

It appears the reason that some spiral galaxies are fat and bulging while some are flat discs is because of how fast they rotate.<ref>[http://phys.org/news/2014-02-fat-flat-galaxies.html "Fat or flat: Getting galaxies into shape"]. ''phys.org''. February 2014</ref>
[[File:Hubble2005-01-barred-spiral-galaxy-NGC1300.jpg|right|thumb|300px|[[NGC 1300]], an example of a [[barred spiral galaxy]].]]
In spiral galaxies, the spiral arms do have the shape of approximate [[logarithmic spiral]]s, a pattern that can be theoretically shown to result from a disturbance in a uniformly rotating mass of stars. Like the stars, the spiral arms rotate around the center, but they do so with constant [[angular velocity]]. The spiral arms are thought to be areas of high-density matter, or "[[Density wave theory|density waves]]".<ref name=bertin_lin1996/> As stars move through an arm, the space velocity of each stellar system is modified by the gravitational force of the higher density. (The velocity returns to normal after the stars depart on the other side of the arm.) This effect is akin to a "wave" of slowdowns moving along a highway full of moving cars. The arms are visible because the high density facilitates star formation, and therefore they harbor many bright and young stars.<ref name=belkora355/>
{{multiple image
| align = right
| direction = vertical
| width = 230
| image1 = Hoag's object.jpg
| caption1 = [[Hoag's Object]], an example of a [[ring galaxy]]
| image2 = File-Ngc5866 hst big.png
| caption2 = [[NGC 5866]], an example of a [[lenticular galaxy]]
}}
====Barred Spiral Galaxy====
A majority of spiral galaxies, including our own [[Milky Way]] galaxy, have a linear, bar-shaped band of stars that extends outward to either side of the core, then merges into the spiral arm structure.<ref>
{{cite journal
|last1=Eskridge |first1=P. B.
|last2=Frogel |first2=J. A.
|date=1999
|title=What is the True Fraction of Barred Spiral Galaxies?
|journal=[[Astrophysics and Space Science]]
|volume=269/270 |pages=427–430
|bibcode=1999Ap&SS.269..427E
|doi=10.1023/A:1017025820201
}}</ref> In the Hubble classification scheme, these are designated by an ''SB'', followed by a lower-case letter (''a'', ''b'' or ''c'') that indicates the form of the spiral arms (in the same manner as the categorization of normal spiral galaxies). Bars are thought to be temporary structures that can occur as a result of a density wave radiating outward from the core, or else due to a [[Galactic tide|tidal interaction]] with another galaxy.<ref>
{{cite journal
|last1=Bournaud |first1=F.
|last2=Combes |first2=F.
|date=2002
|title=Gas accretion on spiral galaxies: Bar formation and renewal
|journal=[[Astronomy and Astrophysics]]
|volume=392
|issue=1 |pages=83–102
|bibcode=2002A&A...392...83B
|doi=10.1051/0004-6361:20020920
|arxiv = astro-ph/0206273 }}</ref> Many barred spiral galaxies are active, possibly as a result of gas being channeled into the core along the arms.<ref>
{{cite journal
|last1=Knapen |first1=J. H.
|last2=Perez-Ramirez |first2=D.
|last3=Laine |first3=S.
|date=2002
|title=Circumnuclear regions in barred spiral galaxies — II. Relations to host galaxies
|journal=[[Monthly Notices of the Royal Astronomical Society]]
|volume=337 |issue=3 |pages=808–828
|bibcode=2002MNRAS.337..808K
|doi=10.1046/j.1365-8711.2002.05840.x
|arxiv = astro-ph/0207258 }}</ref>

Our own galaxy, the [[Milky Way]], is a large disk-shaped barred-spiral galaxy<ref>
{{cite journal
|last1=Alard |first1=C.
|date=2001
|title=Another bar in the Bulge
|journal=[[Astronomy and Astrophysics Letters]]
|volume=379 |issue=2 |pages=L44–L47
|bibcode=2001A&A...379L..44A
|doi=10.1051/0004-6361:20011487
|arxiv = astro-ph/0110491 }}</ref> about 30 kiloparsecs in diameter and a kiloparsec thick. It contains about two hundred billion (2×1011)<ref>
{{cite news
|last1=Sanders |first1=R.
|date=January 9, 2006
|title=Milky Way galaxy is warped and vibrating like a drum
|publisher=[[UC Berkeley|UCBerkeley News]]
|url=http://www.berkeley.edu/news/media/releases/2006/01/09_warp.shtml
|accessdate=May 24, 2006
}}</ref> stars and has a total mass of about six hundred billion (6×1011) times the mass of the Sun.<ref>
{{cite journal
|last1=Bell |first1=G. R.
|last2=Levine |first2=S. E.
|date=1997
|title=Mass of the Milky Way and Dwarf Spheroidal Stream Membership
|journal=[[Bulletin of the American Astronomical Society]]
|volume=29 |issue=2 |pages=1384
|bibcode=1997AAS...19110806B
}}</ref>

===Other morphologies===
* [[Peculiar galaxy|Peculiar galaxies]] are galactic formations that develop unusual properties due to tidal interactions with other galaxies. An example of this is the [[ring galaxy]], which possesses a ring-like structure of stars and interstellar medium surrounding a bare core. A ring galaxy is thought to occur when a smaller galaxy passes through the core of a spiral galaxy.<ref>{{cite journal
|last1=Gerber |first1=R. A.
|last2=Lamb |first2=S. A.
|last3=Balsara |first3=D. S.
|date=1994
|title=Ring Galaxy Evolution as a Function of "Intruder" Mass
|journal=[[Bulletin of the American Astronomical Society]]
|volume=26 |pages=911
|bibcode=1994AAS...184.3204G
}}</ref> Such an event may have affected the [[Andromeda Galaxy]], as it displays a multi-ring-like structure when viewed in [[infrared]] radiation.<ref>{{cite press release
|publisher=[[European Space Agency]]
|date=October 14, 1998
|title=ISO unveils the hidden rings of Andromeda
|url=http://www.iso.vilspa.esa.es/outreach/esa_pr/andromed.htm
|accessdate=May 24, 2006
}}</ref>

* A [[lenticular galaxy]] is an intermediate form that has properties of both elliptical and spiral galaxies. These are categorized as Hubble type S0, and they possess ill-defined spiral arms with an elliptical halo of stars<ref>{{cite web
|date=May 31, 2004
|title=Spitzer Reveals What Edwin Hubble Missed
|url=http://web.archive.org/web/20060907042809/http://www.cfa.harvard.edu/press/pr0419.html
|publisher=[[Harvard-Smithsonian Center for Astrophysics]]
|accessdate=December 6, 2006
}}</ref> ([[Barred lenticular galaxy|barred lenticular galaxies]] receive Hubble classification SB0.)

* [[Irregular galaxy|Irregular galaxies]] are galaxies that can not be readily classified into an elliptical or spiral morphology. An Irr-I galaxy has some structure but does not align cleanly with the Hubble classification scheme. Irr-II galaxies do not possess any structure that resembles a Hubble classification, and may have been disrupted.<ref>{{cite web
|last1=Barstow |first1=M. A.
|date=2005
|title=Irregular Galaxies
|url=http://web.archive.org/web/20120227172628/http://www.star.le.ac.uk/edu/Irregular.shtml
|publisher=[[University of Leicester]]
|accessdate=December 5, 2006
}}</ref> Nearby examples of (dwarf) irregular galaxies include the [[Magellanic Clouds]].

* An [[ultra diffuse galaxy]] (UDG) is an extremely-low-density galaxy. The galaxy may be the same size as the Milky Way but has a visible star count of only 1% of the Milky Way. The lack of luminosity is because there is a lack of star-forming gas in the galaxy which results in old stellar populations.

===Dwarfs===
{{Main|Dwarf galaxy}}
Despite the prominence of large elliptical and spiral galaxies, most galaxies in the Universe are dwarf galaxies. These galaxies are relatively small when compared with other galactic formations, being about one hundredth the size of the Milky Way, containing only a few billion stars. Ultra-compact dwarf galaxies have recently been discovered that are only 100 parsecs across.<ref>
{{cite journal
|last1=Phillipps |first1=S.
|last2=Drinkwater |first2=M. J.
|last3=Gregg |first3=M. D.
|last4=Jones |first4=J. B.
|date=2001
|title=Ultracompact Dwarf Galaxies in the Fornax Cluster
|journal=[[Astrophysical Journal]]
|volume=560 |issue=1 |pages=201–206
|bibcode=2001ApJ...560..201P
|doi=10.1086/322517
|arxiv = astro-ph/0106377 }}</ref>

Many dwarf galaxies may orbit a single larger galaxy; the Milky Way has at least a dozen such satellites, with an estimated 300–500 yet to be discovered.<ref>
{{cite news
|last1=Groshong |first1=K.
|date=April 24, 2006
|title=Strange satellite galaxies revealed around Milky Way
|publisher=[[New Scientist]]
|url=http://www.newscientist.com/article/dn9043-strange-satellite-galaxies-revealed-around-milky-way.html
|accessdate=January 10, 2007
}}</ref> Dwarf galaxies may also be classified as [[dwarf elliptical galaxy|elliptical]], [[dwarf spiral galaxy|spiral]], or [[irregular galaxy|irregular]]. Since small dwarf ellipticals bear little resemblance to large ellipticals, they are often called [[dwarf spheroidal galaxy|dwarf spheroidal galaxies]] instead.

A study of 27 Milky Way neighbors found that in all dwarf galaxies, the central mass is approximately 10 million [[solar mass]]es, regardless of whether the galaxy has thousands or millions of stars. This has led to the suggestion that galaxies are largely formed by [[dark matter]], and that the minimum size may indicate a form of [[warm dark matter]] incapable of gravitational coalescence on a smaller scale.<ref>
{{cite web
|last1=Schirber |first1=M.
|date=August 27, 2008
|url=http://news.sciencemag.org/physics/2008/08/no-slimming-down-dwarf-galaxies
|title=No Slimming Down for Dwarf Galaxies
|publisher=[[ScienceNOW]]
|accessdate=August 27, 2008
}}</ref>

==Unusual dynamics and activities==

===Interacting===
{{Main|Interacting galaxy}}
[[File:Antennae galaxies xl.jpg|thumb|right|200px|The [[Antennae Galaxies]] are undergoing a collision that will result in their eventual merger.]]
Interactions between galaxies are relatively frequent, and they can play an important role in [[galaxy formation and evolution|galactic evolution]]. Near misses between galaxies result in warping distortions due to [[galactic tide|tidal interactions]], and may cause some exchange of gas and dust.<ref name="umda">
{{cite web
|url=http://www.astro.umd.edu/education/astro/gal/interact.html
|title=Galaxy Interactions
|publisher=[[University of Maryland]] Department of Astronomy
|accessdate=December 19, 2006
|archiveurl=http://web.archive.org/web/20060509074300/http://www.astro.umd.edu/education/astro/gal/interact.html
|archivedate=May 9, 2006
}}</ref><ref name="suia">
{{cite web
|title=Interacting Galaxies
|url=http://Cosmos.swin.edu.au/entries/interactinggalaxies/interactinggalaxies.html?e=1
|publisher=[[Swinburne University]]
|accessdate=December 19, 2006
}}</ref>
Collisions occur when two galaxies pass directly through each other and have sufficient relative momentum not to merge. The stars of interacting galaxies will usually not collide, but the gas and dust within the two forms will interact, sometimes triggering star formation. A collision can severely distort the shape of the galaxies, forming bars, rings or tail-like structures.<ref name="umda" /><ref name="suia" />

At the extreme of interactions are galactic mergers. In this case the relative momentum of the two galaxies is insufficient to allow the galaxies to pass through each other. Instead, they gradually merge to form a single, larger galaxy. Mergers can result in significant changes to morphology, as compared to the original galaxies. In the case where one of the galaxies is much more massive, however, the result is known as [[Interacting galaxy#Galactic cannibalism|cannibalism]]. In this case the larger galaxy will remain relatively undisturbed by the merger, while the smaller galaxy is torn apart. The Milky Way galaxy is currently in the process of cannibalizing the [[Sagittarius Dwarf Elliptical Galaxy]] and the [[Canis Major Dwarf Galaxy]].<ref name="umda" /><ref name="suia" />

===Starburst===
{{Main|Starburst galaxy}}
[[File:M82 HST ACS 2006-14-a-large web.jpg|thumb|right|200px|[[Messier 82|M82]], a starburst galaxy that has ten times the star formation of a "normal" galaxy.<ref>
{{cite web
|date=April 24, 2006
|url=http://hubblesite.org/newscenter/archive/releases/2006/14/image/a
|title=Happy Sweet Sixteen, Hubble Telescope!
|publisher=[[NASA]]
|accessdate=August 10, 2006
}}</ref>]]

Stars are created within galaxies from a reserve of cold gas that forms into giant [[molecular cloud]]s. Some galaxies have been observed to form stars at an exceptional rate, known as a starburst. Should they continue to do so, however, they would consume their reserve of gas in a time frame lower than the lifespan of the galaxy. Hence starburst activity usually lasts for only about ten million years, a relatively brief period in the history of a galaxy. Starburst galaxies were more common during the early history of the Universe,<ref name="chandra">
{{cite web
|date=August 29, 2006
|url=http://chandra.harvard.edu/xray_sources/starburst.html
|title=Starburst Galaxies
|publisher=[[Harvard-Smithsonian Center for Astrophysics]]
|accessdate=August 10, 2006
}}</ref> and, at present, still contribute an estimated 15% to the total star production rate.<ref>
{{cite conference
|last1=Kennicutt Jr. |first1=R. C.
|display-authors=etal
|date=2005
|title=Demographics and Host Galaxies of Starbursts
|work=Starbursts: From 30 Doradus to Lyman Break Galaxies
|page=187
|publisher=[[Springer (publisher)|Springer]]
|bibcode=2005sdlb.proc..187K
}}</ref>

Starburst galaxies are characterized by dusty concentrations of gas and the appearance of newly formed stars, including massive stars that ionize the surrounding clouds to create [[H II region]]s.<ref>
{{cite web
|last1=Smith |first1=G.
|date=July 13, 2006
|title=Starbursts & Colliding Galaxies
|url=http://casswww.ucsd.edu/public/tutorial/Starbursts.html
|publisher=[[University of California]], San Diego Center for Astrophysics & Space Sciences
|accessdate=August 10, 2006
}}</ref> These massive stars produce [[supernova]] explosions, resulting in expanding [[supernova remnant|remnants]] that interact powerfully with the surrounding gas. These outbursts trigger a chain reaction of star building that spreads throughout the gaseous region. Only when the available gas is nearly consumed or dispersed does the starburst activity come to an end.<ref name="chandra" />

Starbursts are often associated with merging or interacting galaxies. The prototype example of such a starburst-forming interaction is [[Messier 82|M82]], which experienced a close encounter with the larger [[Messier 81|M81]]. Irregular galaxies often exhibit spaced knots of starburst activity.<ref>
{{cite web
|last1=Keel |first1=B.
|date=September 2006
|title=Starburst Galaxies
|url=http://www.astr.ua.edu/keel/galaxies/starburst.html
|publisher=[[University of Alabama]]
|accessdate=December 11, 2006
}}</ref>

===Active nucleus===
{{Main|Active galactic nucleus}}
[[File:M87 jet.jpg|thumb|right|200px|A jet of particles is being emitted from the core of the elliptical radio galaxy [[Messier 87|M87]].]]
A portion of the observable galaxies are classified as active. That is, a significant portion of the total energy output from the galaxy is emitted by a source other than the stars, dust and [[interstellar medium]].

The standard model for an [[active galactic nucleus]] is based upon an [[accretion disc]] that forms around a [[supermassive black hole]] (SMBH) at the core region. The radiation from an active galactic nucleus results from the [[gravitational energy]] of matter as it falls toward the black hole from the disc.<ref name="keel">
{{cite web
|last1=Keel |first1=W. C.
|date=2000
|url=http://www.astr.ua.edu/keel/galaxies/agnintro.html
|title=Introducing Active Galactic Nuclei
|publisher=[[University of Alabama]]
|accessdate=December 6, 2006
}}</ref> In about 10% of these objects, a diametrically opposed pair of energetic jets ejects particles from the core at velocities close to the [[speed of light]]. The mechanism for producing these jets is still not well understood.<ref name="monster">
{{cite web
|last1=Lochner |first1=J.
|last2=Gibb |first2=M.
|title=A Monster in the Middle
|url=http://imagine.gsfc.nasa.gov/docs/science/know_l2/active_galaxies.html
|publisher=[[NASA]]
|accessdate=December 20, 2006
}}</ref>

Active galaxies that emit high-energy radiation in the form of [[x-ray]]s are classified as [[Seyfert galaxy|Seyfert galaxies]] or [[quasar]]s, depending on the luminosity.

====Blazars====
{{Main|Blazars}}
[[Blazar]]s are believed to be an active galaxy with a [[relativistic jet]] that is pointed in the direction of Earth. A [[radio galaxy]] emits radio frequencies from relativistic jets. A unified model of these types of active galaxies explains their differences based on the viewing angle of the observer.<ref name="monster" />

====LINERS====
Possibly related to active galactic nuclei (as well as [[starburst (astronomy)|starburst]] regions) are [[low-ionization nuclear emission-line region]]s (LINERs). The emission from LINER-type galaxies is dominated by weakly [[ion]]ized elements.<ref name="heckman1980">
{{cite journal
|last1=Heckman |first1=T. M.
|date=1980
|title=An optical and radio survey of the nuclei of bright galaxies — Activity in normal galactic nuclei
|journal=[[Astronomy and Astrophysics]]
|volume=87 |pages=152–164
|bibcode=1980A&A....87..152H
}}</ref> Approximately one-third of nearby galaxies are classified as containing LINER nuclei.<ref name="keel" /><ref name="heckman1980" /><ref name="hoetal1997b">
{{cite journal
|last1=Ho |first1=L. C.
|last2=Filippenko |first2=A. V.
|last3=Sargent |first3=W. L. W.
|date=1997
|title=A Search for "Dwarf" Seyfert Nuclei. V. Demographics of Nuclear Activity in Nearby Galaxies
|journal=[[Astrophysical Journal]]
|volume=487
|issue=2 |pages=568–578
|bibcode=1997ApJ...487..568H
|doi=10.1086/304638
|arxiv = astro-ph/9704108 }}</ref>

====Seyfert Galaxy====
{{Main|Seyfert Galaxy}}
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei (very luminous, distant and bright sources of electromagnetic radiation) with very high surface brightnesses but unlike quasars, their host galaxies are clearly detectable. Seyfert galaxies account for about 10% of all galaxies. Seen in visible light, most Seyfert galaxies look like normal spiral galaxies, but when studied under other wavelengths, the luminosity of their cores is equivalent to the luminosity of whole galaxies the size of the Milky Way.

====Quasar====
{{Main|Quasar}}
Quasars (/ˈkweɪzɑr/) or quasi-stellar radio sources are the most energetic and distant members of a class of objects called active galactic nuclei (AGN). Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that appeared to be similar to stars, rather than extended sources similar to galaxies. Their luminosity can be 100 times greater than that of the Milky Way.

===Luminous infrared galaxy===
{{Main|Luminous infrared galaxy}}
Luminous Infrared Galaxies or (LIRG's) are galaxies with luminosities, the measurement of brightness, above 1011 L☉. LIRG's are more abundant than starburst galaxies, Seyfert galaxies and quasi-stellar objects at comparable luminosity. Infrared galaxies emit more energy in the infrared than at all other wavelengths combined. An LIRG's luminosity is 100 billion times that of our sun.

==Formation and evolution==
{{Main|Galaxy formation and evolution}}
Galactic formation and evolution is an active area of research in [[astrophysics]].

===Formation===
[[File:Artist's impression of a protocluster forming in the early Universe.jpg|align=right|thumb|Artist's impression of a protocluster forming in the early Universe.<ref>{{cite web|title=Construction Secrets of a Galactic Metropolis|url=http://www.eso.org/public/news/eso1431/|website=www.eso.org|publisher=ESO Press Release|accessdate=October 15, 2014}}</ref>]]
Current cosmological models of the early Universe are based on the [[Big Bang]] theory. About 300,000 years after this event, atoms of [[hydrogen]] and [[helium]] began to form, in an event called [[Recombination (cosmology)|recombination]]. Nearly all the hydrogen was neutral (non-ionized) and readily absorbed light, and no stars had yet formed. As a result, this period has been called the "[[Timeline of the Big Bang#Dark Ages|dark ages]]". It was from density fluctuations (or [[anisotropy|anisotropic]] irregularities) in this primordial matter that [[structure formation|larger structures]] began to appear. As a result, masses of [[baryon]]ic matter started to condense within [[cold dark matter]] halos.<ref name="hqrdvj">
{{cite web
|date=November 18, 1999
|title=Search for Submillimeter Protogalaxies
|url=http://web.archive.org/web/20080325183740/http://cfa-www.harvard.edu/~aas/tenmeter/proto.htm
|publisher=[[Harvard-Smithsonian Center for Astrophysics]]
|accessdate=January 10, 2007
}}</ref><ref name=rmaa17_107/> These primordial structures would eventually become the galaxies we see today.
[[File:Young Galaxy Accreting Material.jpg|thumb|right|200px|Artist's impression of a young galaxy accreting material.]]

====Early galaxies====
Evidence for the early appearance of galaxies was found in 2006, when it was discovered that the galaxy [[IOK-1]] has an unusually high [[redshift]] of 6.96, corresponding to just 750 million years after the Big Bang and making it the most distant and primordial galaxy yet seen.<ref>
{{cite journal
|last1=McMahon |first1=R.
|date=2006
|title=Journey to the birth of the Universe
|journal=[[Nature (journal)|Nature]]
|volume=443 |issue=7108 |pages=151–2
|doi=10.1038/443151a
|pmid=16971933
|bibcode = 2006Natur.443..151M }}</ref>
While some scientists have claimed other objects (such as [[Galaxy Abell 1835 IR1916|Abell 1835 IR1916]]) have higher redshifts (and therefore are seen in an earlier stage of the Universe's evolution), IOK-1's age and composition have been more reliably established. In December 2012, astronomers reported that the [[UDFj-39546284]] is the most distant object known and has a redshift value of 11.9. The object, is estimated to have existed around "380 million years"<ref name="Space-20121212">{{cite web |last=Wall |first=Mike |title=Ancient Galaxy May Be Most Distant Ever Seen |url=http://www.space.com/18879-hubble-most-distant-galaxy.html |date=December 12, 2012 |publisher=[[Space.com]] |accessdate=December 12, 2012 }}</ref> after the [[Big Bang]] (which was about 13.8 billion years ago),<ref name="Cosmic Detectives">{{cite web
|last =
|first =
|title = Cosmic Detectives
|url=http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives
|authorlink =
|work =
|publisher = The European Space Agency (ESA)
|date = April 2, 2013
|doi =
|accessdate = April 15, 2013}}</ref> is about 13.42 billion light years away. The existence of such early [[protogalaxy|protogalaxies]] suggests that they must have grown in the so-called "dark ages".<ref name="hqrdvj"/> As of May 5, 2015, the galaxy [[EGS-zs8-1]] is the most distant and earliest galaxy measured, forming 670 million years after the [[Big Bang]]. The light from EGS-zs8-1 has taken 13 billion years to reach Earth, and is now 30 billion light-years away, because of the [[expansion of the universe]] during 13 billion years.<ref>{{Cite web|title = HubbleSite - NewsCenter - Astronomers Set a New Galaxy Distance Record (05/05/2015) - Introduction|url = http://hubblesite.org/newscenter/archive/releases/2015/22/|website = hubblesite.org|accessdate = 2015-05-07}}</ref><ref>{{Cite web|title = This Galaxy Far, Far Away Is the Farthest One Yet Found|url = http://www.space.com/29319-farthest-galaxy-ever-found.html?cmpid=NL_SP_weekly_2015-05-06|accessdate = 2015-05-07}}</ref><ref name="phys.org">{{Cite web|title = Astronomers unveil the farthest galaxy|url = http://phys.org/news/2015-05-astronomers-unveil-farthest-galaxy.html|accessdate = 2015-05-07}}</ref><ref name="phys.org"/><ref>{{Cite news|title = Astronomers Measure Distance to Farthest Galaxy Yet|url = http://www.nytimes.com/2015/05/06/science/astronomers-measure-distance-to-farthest-galaxy-yet.html|newspaper = The New York Times|date = 2015-05-05|access-date = 2015-05-07|issn = 0362-4331|first = Dennis|last = Overbye}}</ref><ref>{{Cite journal|title = A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE|url = http://arxiv.org/abs/1502.05399|journal = arXiv:1502.05399 [astro-ph]|date = 2015-02-18|access-date = 2015-05-07|first = P. A.|last = Oesch|first2 = P. G.|last2 = van Dokkum|first3 = G. D.|last3 = Illingworth|first4 = R. J.|last4 = Bouwens|first5 = I.|last5 = Momcheva|first6 = B.|last6 = Holden|first7 = G. W.|last7 = Roberts-Borsani|first8 = R.|last8 = Smit|first9 = M.|last9 = Franx}}</ref>

====Early galaxy formation====
The detailed process by which early galaxies formed is an open question in astrophysics. Theories can be divided into two categories: top-down and bottom-up. In top-down theories (such as the Eggen–Lynden-Bell–Sandage [ELS] model), protogalaxies form in a large-scale simultaneous collapse lasting about one hundred million years.<ref>
{{cite journal
|last1=Eggen |first1=O. J.
|last2=Lynden-Bell |first2=D.
|last3=Sandage |first3=A. R.
|date=1962
|title=Evidence from the motions of old stars that the Galaxy collapsed
|journal=[[Reports on Progress in Physics]]
|volume=136 |pages=748
|bibcode=1962ApJ...136..748E
|doi=10.1086/147433
}}</ref> In bottom-up theories (such as the Searle-Zinn [SZ] model), small structures such as [[globular cluster]]s form first, and then a number of such bodies accrete to form a larger galaxy.<ref>
{{cite journal
|last1=Searle |first1=L.
|last2=Zinn |first2=R.
|date=1978
|title=Compositions of halo clusters and the formation of the galactic halo
|journal=[[Astrophysical Journal]]
|volume=225 |issue=1 |pages=357–379
|bibcode=1978ApJ...225..357S
|doi=10.1086/156499
}}</ref>

Once protogalaxies began to form and contract, the first [[halo star]]s (called [[Metallicity#Population III stars|Population III stars]]) appeared within them. These were composed almost entirely of hydrogen and helium, and may have been massive. If so, these huge stars would have quickly consumed their supply of fuel and became [[supernova]]e, releasing heavy elements into the [[interstellar medium]].<ref>
{{cite journal
|last1=Heger |first1=A.
|last2=Woosley |first2=S. E.
|date=2002
|title=The Nucleosynthetic Signature of Population III
|journal=[[Astrophysical Journal]]
|volume=567 |issue=1 |pages=532–543
|bibcode=2002ApJ...567..532H
|doi=10.1086/338487
|arxiv = astro-ph/0107037 }}</ref> This first generation of stars re-ionized the surrounding neutral hydrogen, creating expanding bubbles of space through which light could readily travel.<ref>
{{cite journal
|last1=Barkana |first1=R.
|last2=Loeb |first2=A.
|date=1999
|title=In the beginning: the first sources of light and the reionization of the Universe
|journal=[[Physics Reports]]
|volume=349 |issue=2 |pages=125–238
|bibcode=2001PhR...349..125B
| arxiv = astro-ph/0010468
|doi=10.1016/S0370-1573(01)00019-9
}}</ref>

In June 2015, astronomers reported evidence for [[Metallicity#Population III stars|Population III stars]] in the [[Cosmos Redshift 7]] [[galaxy]] at {{math|''z'' {{=}} 6.60}}. Such stars are likely to have existed in the very early universe (i.e., at high redshift), and may have started the production of [[chemical element]]s heavier than [[hydrogen]] that are needed for the later formation of [[planet]]s and [[life]] as we know it.<ref name="AJ-20150604">{{cite journal |last1=Sobral |first1=David |last2=Matthee |first2=Jorryt |last3=Darvish |first3=Behnam |last4=Schaerer |first4=Daniel |last5=Mobasher |first5=Bahram |last6=Röttgering |first6=Huub J. A. |last7=Santos |first7=Sérgio |last8=Hemmati |first8=Shoubaneh |title=Evidence For POPIII-Like Stellar Populations In The Most Luminous LYMAN-α Emitters At The Epoch Of Re-Ionisation: Spectroscopic Confirmation |url=http://arxiv.org/pdf/1504.01734.pdf |format=[[PDF]] |date=4 June 2015 |journal=[[The Astrophysical Journal]] |accessdate=17 June 2015 }}</ref><ref name="NYT-20150617">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Astronomers Report Finding Earliest Stars That Enriched Cosmos |url=http://www.nytimes.com/2015/06/18/science/space/astronomers-report-finding-earliest-stars-that-enriched-cosmos.html |date=17 June 2015 |work=[[New York Times]] |accessdate=17 June 2015 }}</ref>

===Evolution===
Within a billion years of a galaxy's formation, key structures begin to appear. [[Globular cluster]]s, the central supermassive black hole, and a [[bulge (astronomy)|galactic bulge]] of metal-poor [[metallicity|Population II stars]] form. The creation of a supermassive black hole appears to play a key role in actively regulating the growth of galaxies by limiting the total amount of additional matter added.<ref>
{{cite news
|date=February 9, 2005
|title=Simulations Show How Growing Black Holes Regulate Galaxy Formation
|url=http://www.cmu.edu/PR/releases05/050209_blackhole.html
|publisher=[[Carnegie Mellon University]]
|accessdate=January 7, 2007
}}</ref> During this early epoch, galaxies undergo a major burst of star formation.<ref>
{{cite news
|last1=Massey |first1=R.
|date=April 21, 2007
|title=Caught in the act; forming galaxies captured in the young Universe
|url=http://web.archive.org/web/20131115031412/http://www.ras.org.uk/index.php?option=com_content&task=view&id=1190&Itemid=2
|publisher=[[Royal Astronomical Society]]
|accessdate=April 20, 2007
}}</ref>

During the following two billion years, the accumulated matter settles into a [[disc (galaxy)|galactic disc]].<ref>
{{cite journal
|last=Noguchi |first=M.
|date=1999
|title=Early Evolution of Disk Galaxies: Formation of Bulges in Clumpy Young Galactic Disks
|journal=[[Astrophysical Journal]]
|volume=514 |issue=1 |pages=77–95
|bibcode=1999ApJ...514...77N
|doi=10.1086/306932
|arxiv = astro-ph/9806355 }}</ref> A galaxy will continue to absorb infalling material from [[high-velocity cloud]]s and [[dwarf galaxy|dwarf galaxies]] throughout its life.<ref>
{{cite web
|last1=Baugh |first1=C.
|last2=Frenk |first2=C.
|date=May 1999
|url=http://web.archive.org/web/20070426043157/http://physicsweb.org/articles/world/12/5/9
|title=How are galaxies made?
|publisher=[[PhysicsWeb]]
|accessdate=January 16, 2007
}}</ref> This matter is mostly hydrogen and helium. The cycle of stellar birth and death slowly increases the abundance of heavy elements, eventually allowing the [[planetary formation|formation]] of [[planet]]s.<ref>
{{cite conference
|last1=Gonzalez |first1=G.
|date=1998
|title=The Stellar Metallicity — Planet Connection
|work=Proceedings of a workshop on brown dwarfs and extrasolar planets
|pages=431
|bibcode=1998bdep.conf..431G
}}</ref>
{{Multiple image |direction=vertical |align=right |width=200 |image1=XDF-scale.jpg|image2=Constellation Fornax, EXtreme Deep Field.jpg |image3=XDF-separated.jpg |caption1=''[[Hubble Extreme Deep Field|XDF]]'' view field compared to the [[angular diameter|angular size]] of the [[Moon]]. Several thousand galaxies, each consisting of billions of [[star]]s, are in this small view. |caption2=''[[Hubble Extreme Deep Field|XDF]]'' (2012) view: Each light speck is a galaxy, some of which are as old as 13.2 billion years<ref name="Space-20120925">{{cite web |last=Moskowitz |first=Clara |title=Hubble Telescope Reveals Farthest View Into Universe Ever|url=http://www.space.com/17755-farthest-universe-view-hubble-space-telescope.html|date=September 25, 2012 |publisher=[[Space.com]] |accessdate=September 26, 2012}}</ref> – the [[observable universe]] is estimated to contain 200 billion galaxies. |caption3=''[[Hubble Extreme Deep Field|XDF]]'' image shows (from left) fully mature galaxies, nearly mature galaxies (from 5 to 9 billion years ago), [[Protogalaxy|protogalaxies]], blazing with [[young star]]s (beyond 9 billion years). |header=''[[Hubble Extreme Deep Field|Hubble eXtreme Deep Field (XDF)]]'' }}

The evolution of galaxies can be significantly affected by interactions and collisions. Mergers of galaxies were common during the early epoch, and the majority of galaxies were peculiar in morphology.<ref name="sa296">
{{cite journal
|last1=Conselice |first1=C. J.
|date=February 2007
|title=The Universe's Invisible Hand
|journal=[[Scientific American]]
|volume=296 |issue=2 |pages=35–41
|doi=10.1038/scientificamerican0207-34
}}</ref> Given the distances between the stars, the great majority of stellar systems in colliding galaxies will be unaffected. However, gravitational stripping of the interstellar gas and dust that makes up the spiral arms produces a long train of stars known as tidal tails. Examples of these formations can be seen in [[NGC 4676]]<ref>
{{cite news
|last1=Ford |first1=H.
|display-authors=etal
|date=April 30, 2002
|title=Hubble's New Camera Delivers Breathtaking Views of the Universe
|url=http://hubblesite.org/newscenter/archive/releases/2002/11/image/d
|publisher=Hubble News Desk
|accessdate=May 8, 2007
}}</ref> or the [[Antennae Galaxies]].<ref>
{{cite journal
|last1=Struck |first1=C.
|date=1999
|title=Galaxy Collisions
|doi=10.1016/S0370-1573(99)00030-7
|journal=Physics Reports
|volume=321
|pages=1
|arxiv=astro-ph/9908269
|bibcode = 1999PhR...321....1S }}</ref>

The Milky Way galaxy and the nearby Andromeda Galaxy are moving toward each other at about 130 [[metre per second|km/s]], and—depending upon the lateral movements—the two might collide in about five to six billion years. Although the Milky Way has never collided with a galaxy as large as Andromeda before, evidence of past collisions of the Milky Way with smaller dwarf galaxies is increasing.<ref>
{{cite news
|last1=Wong |first1=J.
|date=April 14, 2000
|title=Astrophysicist maps out our own galaxy's end
|url=http://www.news.utoronto.ca/bin/000414b.asp
|publisher=[[University of Toronto]]
|accessdate=January 11, 2007
|archiveurl=http://web.archive.org/web/20070108183824/http://www.news.utoronto.ca/bin/000414b.asp
|archivedate=January 8, 2007
}}</ref>

Such large-scale interactions are rare. As time passes, mergers of two systems of equal size become less common. Most bright galaxies have remained fundamentally unchanged for the last few billion years, and the net rate of star formation probably also peaked approximately ten billion years ago.<ref>
{{cite journal
|last1=Panter |first1=B.
|last2=Jimenez |first2=R.
|last3=Heavens |first3=A. F.
|last4=Charlot |first4=S.
|date=2007
|title=The star formation histories of galaxies in the Sloan Digital Sky Survey
|journal=[[Monthly Notices of the Royal Astronomical Society]]
|volume=378 |issue=4 |pages=1550–1564
|arxiv=astro-ph/0608531
|doi=10.1111/j.1365-2966.2007.11909.x |bibcode=2007MNRAS.378.1550P
}}</ref>

===Future trends===
Spiral galaxies, like the Milky Way, produce new generations of stars as long as they have dense [[molecular cloud]]s of interstellar hydrogen in their spiral arms.<ref>
{{cite journal
|last1=Kennicutt Jr. |first1=R. C.
|last2=Tamblyn |first2=P.
|last3=Congdon |first3=C. E.
|date=1994
|title=Past and future star formation in disk galaxies
|journal=[[Astrophysical Journal]]
|volume=435 |issue=1 |pages=22–36
|bibcode=1994ApJ...435...22K
|doi=10.1086/174790
}}</ref> Elliptical galaxies are largely devoid of this gas, and so form few new stars.<ref>
{{cite book
|last1=Knapp |first1=G. R.
|date=1999
|title=Star Formation in Early Type Galaxies
|publisher=[[Astronomical Society of the Pacific]]
|bibcode=1998astro.ph..8266K
|oclc=41302839
|isbn=1-886733-84-8
}}</ref> The supply of star-forming material is finite; once stars have converted the available supply of hydrogen into heavier elements, new star formation will come to an end.<ref name="cosmic_battle">
{{cite web
|last1=Adams |first1=Fred
|last2=Laughlin |first2=Greg
|date=July 13, 2006
|title=The Great Cosmic Battle
|url=http://www.astrosociety.org/pubs/mercury/0001/cosmic.html
|publisher=[[Astronomical Society of the Pacific]]
|accessdate=January 16, 2007
}}</ref><ref>{{Cite web|title = Cosmic 'Murder Mystery' Solved: Galaxies Are 'Strangled to Death'|url = http://www.space.com/29398-galaxy-strangulation-death-mystery.html?cmpid=NL_SP_weekly_2015-05-13|accessdate = 2015-05-14}}</ref>

The current era of star formation is expected to continue for up to one hundred billion years, and then the "stellar age" will wind down after about ten trillion to one hundred trillion years (1013–1014 years), as the smallest, longest-lived stars in our universe, tiny [[red dwarf]]s, begin to fade. At the end of the stellar age, galaxies will be composed of [[compact star|compact objects]]: [[brown dwarf]]s, [[white dwarf]]s that are cooling or cold ("[[black dwarf]]s"), [[neutron star]]s, and [[black hole]]s. Eventually, as a result of [[relaxation time|gravitational relaxation]], all stars will either fall into central supermassive black holes or be flung into intergalactic space as a result of collisions.<ref name="cosmic_battle" /><ref>
{{cite web
|last1=Pobojewski |first1=S.
|date=January 21, 1997
|title=Physics offers glimpse into the dark side of the Universe
|url=http://www.umich.edu/~urecord/9697/Jan21_97/artcl17.htm
|publisher=[[University of Michigan]]
|accessdate=January 13, 2007
}}</ref>

==Larger-scale structures==
{{Main|Observable universe#Large-scale structure|Galaxy filament|Galaxy groups and clusters}}
Deep sky surveys show that galaxies are often found in groups and [[Clusters of galaxies|clusters]]. Solitary galaxies that have not significantly interacted with another galaxy of comparable mass during the past billion years are relatively scarce. Only about 5% of the galaxies surveyed have been found to be truly isolated; however, these isolated formations may have interacted and even merged with other galaxies in the past, and may still be orbited by smaller, satellite galaxies. Isolated galaxies<ref group=note>The term "field galaxy" is sometimes used to mean an isolated galaxy, although the same term is also used to describe galaxies that do not belong to a cluster but may be a member of a group of galaxies.</ref> can produce stars at a higher rate than normal, as their gas is not being stripped by other nearby galaxies.<ref>
{{cite web
|last1=McKee |first1=M.
|date=June 7, 2005
|title=Galactic loners produce more stars
|url=http://www.newscientist.com/article.ns?id=dn7478
|publisher=[[New Scientist]]
|accessdate=January 15, 2007
}}</ref>

On the largest scale, the Universe is continually expanding, resulting in an average increase in the separation between individual galaxies (see [[Hubble's law]]). Associations of galaxies can overcome this expansion on a local scale through their mutual gravitational attraction. These associations formed early in the Universe, as clumps of dark matter pulled their respective galaxies together. Nearby groups later merged to form larger-scale clusters. This on-going merger process (as well as an influx of infalling gas) heats the inter-galactic gas within a cluster to very high temperatures, reaching 30–100 [[megakelvin]]s.<ref>
{{cite web
|url=http://chandra.harvard.edu/xray_sources/galaxy_clusters.html
|title=Groups & Clusters of Galaxies
|publisher=[[NASA]]/[[Chandra]]
|accessdate=January 15, 2007
}}</ref> About 70–80% of the mass in a cluster is in the form of dark matter, with 10–30% consisting of this heated gas and the remaining few percent of the matter in the form of galaxies.<ref>
{{cite web
|last1=Ricker |first1=P.
|title=When Galaxy Clusters Collide
|url=http://www.sdsc.edu/pub/envision/v15.2/ricker.html
|publisher=[[San Diego Supercomputer Center]]
|accessdate=August 27, 2008
}}</ref>
{{multiple image
| align = right
| direction = vertical
| width = 230
| image1 = Seyfert Sextet full.jpg
| width1 =
| alt1 =
| caption1 = [[Seyfert's Sextet]] is an example of a compact galaxy group.
| image2 =
| width2 =
| alt2 =
| caption2 = [[Millennium Simulation]] showing large-scale structure of the Cosmos. The image spans about 400 million light years across.
}}
Most galaxies in the Universe are gravitationally bound to a number of other galaxies. These form a [[fractal]]-like hierarchical distribution of clustered structures, with the smallest such associations being termed groups. A group of galaxies is the most common type of galactic cluster, and these formations contain a majority of the galaxies (as well as most of the [[baryon]]ic mass) in the Universe.<ref>
{{cite web
|last1=Dahlem |first1=M.
|date=November 24, 2006
|title=Optical and radio survey of Southern Compact Groups of galaxies
|url=http://www.atnf.csiro.au/people/mdahlem/sci/SCGs.html
|publisher=[[University of Birmingham]] Astrophysics and Space Research Group
|accessdate=January 15, 2007
|archiveurl=http://web.archive.org/web/20070613151936/http://www.atnf.csiro.au/people/mdahlem/sci/SCGs.html
|archivedate=June 13, 2007
}}</ref><ref>
{{cite web
|last1=Ponman |first1=T.
|date=February 25, 2005
|title=Galaxy Systems: Groups
|url=http://web.archive.org/web/20090215023446/http://www.sr.bham.ac.uk/research/groups.html
|publisher=[[University of Birmingham]] Astrophysics and Space Research Group
|accessdate=January 15, 2007
}}</ref> To remain gravitationally bound to such a group, each member galaxy must have a sufficiently low velocity to prevent it from escaping (see [[Virial theorem]]). If there is insufficient [[kinetic energy]], however, the group may evolve into a smaller number of galaxies through mergers.<ref>
{{cite journal
|last1=Girardi |first1=M.
|last2=Giuricin |first2=G.
|date=2000
|title=The Observational Mass Function of Loose Galaxy Groups
|journal=[[The Astrophysical Journal]]
|volume=540 |issue=1 |pages=45–56
|bibcode=2000ApJ...540...45G
|doi=10.1086/309314
|arxiv = astro-ph/0004149 }}</ref>

Clusters of galaxies consist of hundreds to thousands of galaxies bound together by gravity.<ref name="Hubble protocluster">{{cite news|title=Hubble Pinpoints Furthest Protocluster of Galaxies Ever Seen|url=http://www.spacetelescope.org/news/heic1201/|accessdate=January 22, 2015|newspaper=ESA/Hubble Press Release}}</ref> Clusters of galaxies are often dominated by a single giant elliptical galaxy, known as the [[brightest cluster galaxy]], which, over time, [[tidal force|tidally]] destroys its satellite galaxies and adds their mass to its own.<ref>
{{cite journal
|last=Dubinski |first=J.
|date=1998
|title=The Origin of the Brightest Cluster Galaxies
|url=http://www.cita.utoronto.ca/~dubinski/bcg/
|journal=[[Astrophysical Journal]]
|volume=502 |issue=2 |pages=141–149
|doi=10.1086/305901
|bibcode=1998ApJ...502..141D
|arxiv = astro-ph/9709102 }}</ref>

[[Supercluster]]s contain tens of thousands of galaxies, which are found in clusters, groups and sometimes individually. At the [[large-scale structure of the Cosmos|supercluster scale]], galaxies are arranged into sheets and filaments surrounding vast empty voids.<ref>
{{cite journal
|last1=Bahcall |first1=N. A.
|date=1988
|title=Large-scale structure in the Universe indicated by galaxy clusters
|journal=[[Annual Review of Astronomy and Astrophysics]]
|volume=26
|issue=1 |pages=631–686
|bibcode=1988ARA&A..26..631B
|doi=10.1146/annurev.aa.26.090188.003215
}}</ref> Above this scale, the Universe appears to be the same in all directions ([[isotropy|isotropic]] and [[wikt:Homogeneity|homogeneous]]).<ref>
{{cite journal
|last1=Mandolesi |first1=N.
|display-authors=etal
|date=1986
|title=Large-scale homogeneity of the Universe measured by the microwave background
|journal=[[Letters to Nature]]
|volume=319
|issue=6056 |pages=751–753
|doi=10.1038/319751a0
|bibcode = 1986Natur.319..751M }}</ref>

The Milky Way galaxy is a member of an association named the [[Local Group]], a relatively small group of galaxies that has a diameter of approximately one megaparsec. The Milky Way and the Andromeda Galaxy are the two brightest galaxies within the group; many of the other member galaxies are dwarf companions of these two galaxies.<ref>
{{cite journal
|last1=van den Bergh |first1=S.
|date=2000
|title=Updated Information on the Local Group
|journal=Publications of the Astronomical Society of the Pacific
|volume=112 |issue=770 |pages=529–536
|bibcode=2000PASP..112..529V
|doi=10.1086/316548
|arxiv = astro-ph/0001040 }}</ref> The Local Group itself is a part of a cloud-like structure within the [[Virgo Supercluster]], a large, extended structure of groups and clusters of galaxies centered on the [[Virgo Cluster]].<ref name="tully1982">
{{cite journal
|last1=Tully |first1=R. B.
|date=1982
|title=The Local Supercluster
|journal=[[Astrophysical Journal]]
|volume=257 |pages=389–422
|bibcode=1982ApJ...257..389T
|doi=10.1086/159999
}}</ref> And the Virgo Supercluster itself is a part of the [[Pisces-Cetus Supercluster Complex]], a giant [[galaxy filament]].

==Multi-wavelength observation==
{{See also|Observational astronomy}}
{{multiple image
| align = right
| direction = vertical
| width = 220
| image1 =
| caption1 = A visual light image of [[Andromeda Galaxy]] shows the emission of ordinary stars and the light reflected by dust.
| image2 = Andromeda galaxy.jpg
| caption2 = This ultraviolet image of [[Andromeda Galaxy|Andromeda]] shows blue regions containing young, massive stars.
}}
The peak radiation of most stars lies in the [[visible spectrum]], so the observation of the stars that form galaxies has been a major component of [[optical astronomy]]. It is also a favorable portion of the spectrum for observing ionized [[H II region]]s, and for examining the distribution of dusty arms.

The [[cosmic dust|dust]] present in the interstellar medium is opaque to visual light. It is more transparent to [[far infrared astronomy|far-infrared]], which can be used to observe the interior regions of giant molecular clouds and [[Bulge (astronomy)|galactic cores]] in great detail.<ref>
{{cite web
|title=Near, Mid & Far Infrared
|url=http://www.ipac.caltech.edu/Outreach/Edu/Regions/irregions.html
|publisher=[[Infrared Processing and Analysis Center|IPAC]]/[[NASA]]
|accessdate=January 2, 2007
}}</ref> Infrared is also used to observe distant, [[redshift|red-shifted]] galaxies that were formed much earlier in the history of the Universe. Water vapor and [[carbon dioxide]] absorb a number of useful portions of the infrared spectrum, so high-altitude or space-based telescopes are used for [[infrared astronomy]].

The first non-visual study of galaxies, particularly active galaxies, was made using [[radio astronomy|radio frequencies]]. The atmosphere is nearly transparent to radio between 5 [[Hertz|MHz]] and 30 GHz. (The [[ionosphere]] blocks signals below this range.)<ref>
{{cite web
|title=The Effects of Earth's Upper Atmosphere on Radio Signals
|url=http://radiojove.gsfc.nasa.gov/education/educ/radio/tran-rec/exerc/iono.htm
|publisher=[[NASA]]
|accessdate=August 10, 2006
}}</ref> Large radio [[interferometry|interferometers]] have been used to map the active jets emitted from active nuclei. [[Radio telescope]]s can also be used to observe neutral hydrogen (''via'' [[hydrogen line|21 cm radiation]]), including, potentially, the non-ionized matter in the early Universe that later collapsed to form galaxies.<ref>
{{cite news
|title=Giant Radio Telescope Imaging Could Make Dark Matter Visible
|url=http://www.sciencedaily.com/releases/2006/12/061214135537.htm
|publisher=[[ScienceDaily]]
|date=December 14, 2006
|accessdate=January 2, 2007
}}</ref>

[[UV astronomy|Ultraviolet]] and [[X-ray astronomy|X-ray telescopes]] can observe highly energetic galactic phenomena. An ultraviolet flare was observed when a star in a distant galaxy was torn apart from the tidal forces of a black hole.<ref>
{{cite news
|title=NASA Telescope Sees Black Hole Munch on a Star
|url=http://www.nasa.gov/mission_pages/galex/galex-20061205.html
|publisher=[[NASA]]
|date=December 5, 2006
|accessdate=January 2, 2007
}}</ref> The distribution of hot gas in galactic clusters can be mapped by X-rays. The existence of supermassive black holes at the cores of galaxies was confirmed through X-ray astronomy.<ref>
{{cite web
|last1=Dunn |first1=R.
|title=An Introduction to X-ray Astronomy
|url=http://www-xray.ast.cam.ac.uk/xray_introduction/
|publisher=[[Institute of Astronomy, Cambridge|Institute of Astronomy]] X-Ray Group
|accessdate=January 2, 2007
}}</ref>

==See also==
{{Wikipedia books|Galaxies}}
{{colbegin|2}}
* [[Dark galaxy]]
* [[Galactic orientation]]
* [[Galaxy formation and evolution]]
* [[Illustris project]]
* [[List of galaxies]]
* [[List of nearest galaxies]]
* [[Luminous infrared galaxy]]
* [[Supermassive black hole]]
* [[Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure]]
{{colend}}
{{Portal bar|Astronomy|Space|Cosmology}}

==Notes==
{{reflist|group=note}}

==References==
{{Reflist|colwidth=30em|refs=
<ref name="sparkegallagher2000">{{harvnb|Sparke|Gallagher III|2000|p=i}}</ref>

<ref name="heidarzadeh23">{{harvnb|Heidarzadeh|2008|pp=23–25}}</ref>

<ref name="heidarzadeh25">{{harvnb|Heidarzadeh|2008|p=25, Table 2.1}}</ref>

<ref name=paul1993>{{harvnb|Paul|1993|pp=16–18}}</ref>

<ref name=al_biruni>{{harvnb|Al-Biruni|2004|p=87}}</ref>

<ref name=mohamed>{{harvnb|Mohamed|2000|pp=49–50}}</ref>

<ref name="NSOG">{{harvnb|Kepple|Sanner|1998|p=18}}</ref>

<ref name=bergh1998>{{harvnb|Van den Bergh|1998|p=17}}</ref>

<ref name=waller_hodge2003>{{harvnb|Waller|Hodge|2003|p=91}}</ref>

<ref name=bertin_lin1996>{{harvnb|Bertin|Lin|1996|pp=65–85}}</ref>

<ref name=belkora355>{{harvnb|Belkora|2003|p=355}}</ref>

<ref name=nasa060812>
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<ref name=uf030616>
{{cite news
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|url=http://news.ufl.edu/2003/06/16/galaxies/
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}} Based upon:
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<ref name="IRatlas">
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<ref name=camb_lss>
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<ref name="smbh">
{{cite web
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|date=November 2, 2005
|title=Astronomers Get Closest Look Yet At Milky Way's Mysterious Core
|url=http://www.nrao.edu/pr/2005/sagastar/
|publisher=[[National Radio Astronomy Observatory]]
|accessdate=August 10, 2006
}}</ref>

<ref name="apj624_2">
{{cite journal
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|year=2005
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|title=A Map of the Universe
|journal=[[Astrophysical Journal]]
|volume=624 |issue=2 |pages=463–484
|bibcode=2005ApJ...624..463G
|doi=10.1086/428890
|arxiv = astro-ph/0310571 }}</ref>

<ref name=rmaa17_107>
{{cite journal
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|last2=Avila-Reese |first2=V.
|date=2003
|title=Physical processes behind the morphological Hubble sequence
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|volume=17 |pages=107–120
|bibcode=2003RMxAC..17..107F
|arxiv = astro-ph/0303543
}}</ref>

<ref name=konean2006>
{{cite web
|last1=Koneãn˘ |first1=Lubomír
|url=http://www.udu.cas.cz/collegium/tintoretto.pdf
|title=Emblematics, Agriculture, and Mythography in The Origin of the Milky Way
|publisher=[[Academy of Sciences of the Czech Republic]]
|accessdate=January 5, 2007
|archiveurl=http://web.archive.org/web/20060720204104/http://www.udu.cas.cz/collegium/tintoretto.pdf
|archivedate=July 20, 2006
}}</ref>

<ref name=oed>
{{cite web
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|title=galaxy|work=[[Online Etymology Dictionary]]
|accessdate=November 11, 2011
}}</ref>

<ref name=rao2005>
{{cite web
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|title=Explore the Archer's Realm
|url=http://www.space.com/spacewatch/050902_teapot.html
|publisher=[[Space.com]]
|accessdate=January 3, 2007
}}</ref>


}} 

=== Other references ===
* {{cite web
|date=May 3, 2000
|title=Unveiling the Secret of a Virgo Dwarf Galaxy
|url=http://web.archive.org/web/20090109032310/http://www.eso.org/outreach/press-rel/pr-2000/pr-12-00.html
|publisher=[[ESO]]
|accessdate=January 3, 2007
}}

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|isbn=0-7661-9307-1
}}
*{{Cite book |ref=harv
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|date=2003
|title=Minding the Heavens: the Story of our Discovery of the Milky Way
|publisher=[[CRC Press]]
|isbn=0-7503-0730-7
}}
*{{Cite book |ref=harv
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|last2=Lin |first2=C.-C.
|date=1996
|title=Spiral Structure in Galaxies: a Density Wave Theory
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*{{Cite book
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|last2=Merrifield |first2=M.
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*{{Cite book
|last1=Dickinson |first1=T.
|date=2004
|title=The Universe and Beyond
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*{{Cite book |ref=harv
|last1=Heidarzadeh |first1=T.
|date=2008
|title=A History of Physical Theories of Comets, from Aristotle to Whipple
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}}
* {{Cite book |ref=harv
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|publisher= [[Cambridge University Press]]
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}}
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|title=Galaxies in the Universe: An Introduction
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}}
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|last1=Van den Bergh |first1=S.
|date=1998
|title=Galaxy Morphology and Classification
|publisher=[[Cambridge University Press]]
|isbn=0-521-62335-9
}}
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|last1=Waller |first1=W. H.
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|date=2003
|title=Galaxies and the Cosmic Frontier
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|isbn=0-674-01079-5
}}
{{refend}}

==External links==
{{Sister project links|wikt=galaxy|common=Category:Galaxies|q=no|v=no|s=no|b=High School Earth Science/Galaxies}}
* {{In Our Time|Galaxies|p003c1cn|Galaxies}}
* [http://messier.seds.org/galaxy.html Galaxies, SEDS Messier pages]
* [http://www.atlasoftheuniverse.com/ An Atlas of The Universe]
* [http://www.nightskyinfo.com/galaxies Galaxies — Information and amateur observations]
* [http://science.nasa.gov/headlines/y2002/08feb_gravlens.htm The Oldest Galaxy Yet Found]
* [http://www.galaxyzoo.org Galaxy classification project, harnessing the power of the internet and the human brain]
* [http://www.physics.org/facts/sand-galaxies.asp How many galaxies are in our Universe?]
* [http://www.astronoo.com/en/galaxies.html The most beautiful galaxies on Astronoo]
* [http://www.youtube.com/watch?v=08LBltePDZw 3-D Video (01:46) – Over a Million Galaxies of Billions of Stars each – BerkeleyLab/animated.]

{{Galaxy}}

{{Featured article}}

{{Authority control}}
[[Category:Galaxies| ]]

User:WikipediaTutorials/sandbox

2015-08-18T18:26:16Z

WikipediaTutorials: /* Milky Way */

{{About|the astronomical structure|other uses}}
{{Use mdy dates|date=February 2015}}
{{Multiple image |direction=vertical |align=right |width=310|image1=NGC 4414 (NASA-med).jpg|caption1=[[NGC 4414]], a typical spiral galaxy in the [[constellation]] [[Coma Berenices]], is about 55,000 [[light-year]]s in diameter and approximately 60 million light-years away from Earth|image2=M104_ngc4594_sombrero_galaxy_hi-res.jpg|caption2=The [[Sombrero galaxy]] (M104), a bright nearby spiral galaxy.|image3=Irregular_galaxy_NGC_1427A_(captured_by_the_Hubble_Space_Telescope).jpg|caption3=[[NGC 1427A]], an example of an irregular galaxy, 52 million [[light-year]]s away}}

A '''galaxy''' is a [[gravitation|gravitationally]] bound system of [[star]]s, [[stellar remnant]]s, [[interstellar medium|interstellar gas]] and [[cosmic dust|dust]], and [[dark matter]].<ref name="sparkegallagher2000"/><ref name=nasa060812/> The word galxy is derived from the [[Ancient Greek|Greek]] ''{{transl|grc|galaxias}}'' ({{lang|grc|γαλαξίας}}), literally "milky", a reference to the [[Milky Way]]. Examples of galaxies range from [[dwarf galaxy|dwarfs]] with just a few thousand (103) stars to giants with one hundred [[Trillion (short scale)|trillion]] (1014) stars,<ref name=science250_4980_539/> each orbiting their galaxy's own [[center of mass]]. Galaxies are categorized according to their visual morphology, including [[elliptical galaxy|elliptical]],<ref name=uf030616/> [[Spiral galaxy|spiral]], and [[irregular galaxy|irregular]].<ref name="IRatlas"/> Many galaxies are believed to have [[black hole]]s at their [[active galactic nucleus|active center]]s. The Milky Way's central black hole, known as [[Sagittarius A*]], has a mass four million times that of our Sun.<ref name="smbh"/> As of May 2015, [[EGS-zs8-1]] is the most distant known galaxy, estimated to be 13.1 billion [[light-year]]s away and to have 15% of the mass of the Milky Way.<ref name="ARX-20150503">{{cite journal |authors=Oesch, P.A. et al. |title=A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE |url=http://arxiv.org/abs/1502.05399 |date=May 3, 2015 |journal=[[ArXiv]] |arxiv=1502.05399 |accessdate=May 6, 2015 |bibcode = 2015arXiv150205399O }}
</ref><ref name=p15>{{cite web |author=Staff |title=Astronomers unveil the farthest galaxy |url=http://phys.org/news/2015-05-astronomers-unveil-farthest-galaxy.html |publisher=[[Phys.org]] |accessdate=May 6, 2015|date=May 5, 2015}}</ref><ref name="NYT-20150505">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Astronomers Measure Distance to Farthest Galaxy Yet |url=http://www.nytimes.com/2015/05/06/science/astronomers-measure-distance-to-farthest-galaxy-yet.html |date=May 5, 2015 |work=[[New York Times]] |accessdate=May 6, 2015 }}</ref><ref name="AP-20150505">{{cite news |last=Borenstein |first=Seth |title=Astronomers find farthest galaxy: 13.1 billion light-years |url=http://apnews.excite.com/article/20150505/us-sci--farthest_galaxy-46c792535a.html |date= May 5, 2015 |work=[[AP News]] |accessdate=May 6, 2015 }}</ref>

Approximately 170 billion ({{nowrap|1.7 × 1011}}) galaxies exist in the [[observable universe]].<ref name="apj624_2"/> Most of the galaxies are 1,000 to 100,000 [[parsec]]s in diameter and usually separated by distances on the order of millions of parsecs (or megaparsecs). The [[intergalactic space|space]] between galaxies is filled with a tenuous gas with an average density less than one [[atom]] per cubic meter. The majority of galaxies are gravitationally organized into associations known as [[galaxy group]]s, [[galaxy cluster|clusters]], and [[supercluster]]s. At the [[Large-scale structure of the Cosmos|largest scale]], these associations are generally arranged into [[galaxy filament|sheets and filaments]] that are surrounded by immense [[void (astronomy)|voids]].<ref name=camb_lss/>

==Etymology==
The word ''galaxy'' derives from the [[Greek language|Greek]] term for our own galaxy, ''{{transl|grc|galaxias}}'' (''{{lang|grc|{{linktext|γαλαξίας}}}}'', "milky one"), or ''{{transl|grc|[[kyklos]] galaktikos}}'' ("milky circle")<ref name=oed/> due to its appearance as a "milky" band of light in the sky. In [[Greek mythology]], [[Zeus]] places his son born by a mortal woman, the infant [[Heracles]], on [[Hera]]'s breast while she is asleep so that the baby will drink her divine milk and will thus become immortal. Hera wakes up while breastfeeding and then realizes she is nursing an unknown baby: she pushes the baby away and a jet of her milk sprays the night sky, producing the faint band of light known as the Milky Way.<ref name=waller_hodge2003/><ref name=konean2006/>

In the astronomical literature, the capitalized word "Galaxy" is often used to refer to our galaxy, the [[Milky Way]], to distinguish it from the other galaxies in our [[universe]]. The English term ''Milky Way'' can be traced back to a story by [[Chaucer]] {{circa|1380}}:
{{Quote|"See yonder, lo, the Galaxyë  Which men {{linktext|clepe}}th ''the Milky Wey'',  For hit is whyt."|Geoffrey Chaucer|[[The House of Fame]]''<ref name=oed/>}}

When [[William Herschel]] assembled [[Catalogue of Nebulae|his catalog]] of deep sky objects in 1786, he used the term ''[[spiral nebula]]'' for certain objects such as [[Andromeda Galaxy|M31]]. These would later be recognized as conglomerations of stars when the true distance to these objects began to be appreciated, and they would later be termed ''island universes.'' However, the word ''Universe'' was understood to mean the entirety of existence, so this expression fell into disuse and the objects instead became known as galaxies.<ref name=rao2005/>

==Nomenclature==
Tens of thousands of galaxies have been catalogued, but only a few have well-established names, such as the [[Andromeda Galaxy]], the [[Magellanic clouds]], the [[Whirlpool Galaxy]] and the [[Sombrero Galaxy]]. Astronomers work with numbers from certain catalogues, such as the [[Messier catalogue]], the NGC ([[New General Catalogue]]), the IC ([[Index Catalogue]]), the CGCG ([[Catalogue of Galaxies and of Clusters of Galaxies]]), the MCG ([[Morphological Catalogue of Galaxies]]) and UGC ([[Uppsala General Catalogue|Uppsala General Catalogue of Galaxies]]). All of the well-known galaxies appear in one or more of these catalogues but each time under a different number.
For example, [[Messier 109]] is a spiral galaxy having the number 109 in the catalogue of Messier, but also codes NGC3992, UGC6937, CGCG 269-023, MCG +09-20-044, and PGC 37617.

Because it is customary in science to assign names to most of the studied objects, even to the smallest ones, the Belgian astrophysicist [[Gerard Bodifee]] and the classicist Michel Berger started a new catalogue ([[Gerard Bodifee#Works|CNG-Catalogue of Named Galaxies]])<ref>{{Cite web|url=http://www.bodifee.be/acms/acmsdata/document/9/184_CNG%20catalogue.pdf|title=CNG-Catalogue of Named Galaxies |author=Bodifée G. & Berger M.|date=2010|accessdate=January 17, 2014}}</ref> in which a thousand well-known galaxies are given meaningful, descriptive names in Latin (or Latinized Greek)<ref>{{cite web |title=Contemporary Latin |url=http://www.isnare.com/encyclopedia/Contemporary_Latin#In_science |accessdate= January 22, 2014}}</ref> in accordance with the binomial nomenclature that one uses in other sciences such as biology, anatomy, [[paleontology]] and in other fields of astronomy such as the geography of Mars.
One of the arguments to do so is that these impressive objects deserve better than uninspired codes. For instance, Bodifee and Berger propose the informal, descriptive name ''{{lang|la|Callimorphus Ursae Majoris}}'' for the well-formed barred galaxy Messier 109 in Ursa Major.

==Observation history==
The realization that we live in a galaxy, and that ours is one among many, parallels major discoveries that were made about the Milky Way and other [[nebula]]e in the night sky.

===Milky Way===
{{Main|Milky Way}}
The [[Greek philosophy|Greek]] philosopher [[Democritus]] (450–370 BC) proposed that the bright band on the night sky known as the Milky Way might consist of distant stars.<ref name="Plutarch">{{cite book | title=The Complete Works Volume 3: Essays and Miscellanies | publisher=Echo Library | author=Plutarch | authorlink=Plutarch | date=2006 | location=Chapter 3 | pages=66 | isbn=978-1-4068-3224-2}}</ref>
[[Aristotle]] (384–322 BC), however, believed the Milky Way to be caused by "the ignition of the fiery exhalation of some stars that were large, numerous and close together" and that the "ignition takes place in the upper part of the [[atmosphere]], in the [[Sublunary sphere|region of the World that is continuous with the heavenly motions]]."<ref name=Montada>
{{cite web
| last1=Montada |first1=J. P.
| date=September 28, 2007
| title=Ibn Bajja
| work=[[Stanford Encyclopedia of Philosophy]]
| url=http://plato.stanford.edu/entries/ibn-bajja
| accessdate=July 11, 2008
}}</ref> The [[Neoplatonism|Neoplatonist]] philosopher [[Olympiodorus the Younger]] ({{circa|495}}–570 AD) was critical of this view, arguing that if the Milky Way is [[sublunary]] (situated between Earth and the Moon) it should appear different at different times and places on Earth, and that it should have [[parallax]], which it does not. In his view, the Milky Way is celestial.<ref name=heidarzadeh23/>

According to Mohani Mohamed, the [[Islamic astronomy|Arabian]] astronomer [[Alhazen]] (965–1037) made the first attempt at observing and measuring the Milky Way's parallax,<ref name=mohamed/> and he thus "determined that because the Milky Way had no parallax, it must be remote from the Earth, not belonging to the atmosphere."<ref>
{{cite web
| last1=Bouali |first1=H.-E.
| last2=Zghal |first2=M.
| last3=Lakhdar |first3=Z. B.
| date=2005
| title=Popularisation of Optical Phenomena: Establishing the First Ibn Al-Haytham Workshop on Photography
| publisher=The Education and Training in Optics and Photonics Conference
| url=http://spie.org/etop/ETOP2005_080.pdf
| accessdate=July 8, 2008
}}</ref> The [[Persian people|Persian]] astronomer [[al-Bīrūnī]] (973–1048) proposed the Milky Way galaxy to be "a collection of countless fragments of the nature of nebulous stars."<ref>{{MacTutor Biography|id=Al-Biruni|title=Abu Rayhan Muhammad ibn Ahmad al-Biruni}}</ref><ref name=al_biruni/> The [[Al-Andalus|Andalusian]] astronomer [[Ibn Bajjah]] ("Avempace", {{abbr|d.|died}} 1138) proposed that the Milky Way is made up of many stars that almost touch one another and appear to be a continuous image due to the effect of [[refraction]] from sublunary material,<ref name=Montada/><ref name="heidarzadeh25"/> citing his observation of the [[Conjunction (astronomy and astrology)|conjunction]] of Jupiter and Mars as evidence of this occurring when two objects are near.<ref name=Montada/> In the 14th century, the Syrian-born [[Ibn Qayyim]] proposed the Milky Way galaxy to be "a myriad of tiny stars packed together in the sphere of the fixed stars."<ref name=Livingston>
{{cite journal
|last1=Livingston |first1=J. W.
|date=1971
|title=Ibn Qayyim al-Jawziyyah: A Fourteenth Century Defense against Astrological Divination and Alchemical Transmutation
|journal=[[Journal of the American Oriental Society]]
|volume=91 |issue=1 |pages=96–103 [99]
|doi=10.2307/600445
|jstor=600445
}}</ref>
[[File:Herschel-Galaxy.png|thumb|The shape of the Milky Way as estimated from star counts by [[William Herschel]] in 1785; the solar system was assumed to be near the center.]]
Actual proof of the Milky Way consisting of many stars came in 1610 when the Italian astronomer [[Galileo Galilei]] used a [[optical telescope|telescope]] to study the Milky Way and discovered that it is composed of a huge number of faint stars.<ref>Galileo Galilei, ''Sidereus Nuncius'' (Venice, (Italy): Thomas Baglioni, 1610), [https://archive.org/stream/Sidereusnuncius00Gali#page/n37/mode/2up pages 15 and 16.] 
English translation: Galileo Galilei with Edward Stafford Carlos, trans., ''The Sidereal Messenger'' (London, England: Rivingtons, 1880), [https://archive.org/stream/siderealmessenge80gali#page/42/mode/2up/ pages 42 and 43.]</ref><ref>
{{cite web
|last1=O'Connor |first1=J. J.
|last2=Robertson |first2=E. F.
|date=November 2002
|title=Galileo Galilei
|url=http://www-gap.dcs.st-and.ac.uk/~history/Biographies/Galileo.html
|publisher=[[University of St. Andrews]]
|accessdate=January 8, 2007
}}</ref> In 1750 the English astronomer [[Thomas Wright (astronomer)|Thomas Wright]], in his ''An original theory or new hypothesis of the Universe'', speculated (correctly) that the galaxy might be a rotating body of a huge number of stars held together by [[gravitation|gravitational forces]], akin to the solar system but on a much larger scale. The resulting disk of stars can be seen as a band on the sky from our perspective inside the disk.<ref>Thomas Wright, ''An Original Theory or New Hypothesis of the Universe'' … (London, England: H. Chapelle, 1750). [http://books.google.com/books?id=80VZAAAAcAAJ&pg=PA48#v=onepage&q&f=false From p.48:] " … the stars are not infinitely dispersed and distributed in a promiscuous manner throughout all the mundane space, without order or design, … this phænomenon [is] no other than a certain effect arising from the observer's situation, … To a spectator placed in an indefinite space, … it [i.e., the Milky Way (''Via Lactea'')] [is] a vast ring of stars … " 
[http://books.google.com/books?id=80VZAAAAcAAJ&pg=PA73#v=onepage&q&f=false On page 73], Wright called the Milky Way the ''Vortex Magnus'' (the great whirlpool) and estimated its diameter at 8.64×1012 miles (13.9×1012 km).</ref><ref name="our_galaxy"/> In a treatise in 1755, [[Immanuel Kant]] elaborated on Wright's idea about the structure of the Milky Way.<ref>Immanuel Kant, [http://books.google.com/books?id=nCcaAQAAMAAJ&pg=PP9#v=onepage&q&f=false ''Allgemeine Naturgeschichte und Theorie des Himmels'' …] [Universal Natural History and Theory of the Heavens … ], (Koenigsberg and Leipzig, (Germany): Johann Friederich Petersen, 1755). Available in English translation by Ian Johnston at: [http://records.viu.ca/~johnstoi/kant/kant2e.htm Vancouver Island University, British Columbia, Canada]</ref>

The first project to describe the shape of the Milky Way and the position of the [[Sun]] was undertaken by [[William Herschel]] in 1785 by counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with [[Galactocentrism|the solar system close to the center]].<ref>William Herschel (1785) "On the Construction of the Heavens," ''Philosophical Transactions of the Royal Society of London'', '''75''' : 213-266. Herschel's diagram of the galaxy appears immediately after the article's last page. See:
* [http://books.google.com/books?id=IU9FAAAAcAAJ&pg=PA213#v=onepage&q&f=false Google Books]
* [http://rstl.royalsocietypublishing.org/content/75/213.full.pdf+html The Royal Society of London]</ref><ref name=paul1993/> Using a refined approach, [[Jacobus Kapteyn|Kapteyn]] in 1920 arrived at the picture of a small (diameter about 15 kiloparsecs) ellipsoid galaxy with the Sun close to the center. A different method by [[Harlow Shapley]] based on the cataloguing of [[globular cluster]]s led to a radically different picture: a flat disk with diameter approximately 70 kiloparsecs and the Sun far from the center.<ref name="our_galaxy" /> Both analyses failed to take into account the [[extinction (astronomy)|absorption of light]] by [[cosmic dust|interstellar dust]] present in the [[galactic plane]], but after [[Robert Julius Trumpler]] quantified this effect in 1930 by studying [[open cluster]]s, the present picture of our host galaxy, the Milky Way, emerged.<ref>
{{cite journal
|last1=Trimble |first1=V.
|date=1999
|title=Robert Trumpler and the (Non)transparency of Space
|journal=[[Bulletin of the American Astronomical Society]]
|volume=31 |issue=31 |pages=1479
|bibcode=1999AAS...195.7409T
}}</ref>

[[File:Milky Way Arch.jpg|thumb|center|600px|A [[Fisheye lens|fish-eye]] mosaic of the Milky Way arching at a high inclination across the night sky, shot from a dark-sky location in Chile]]

===Distinction from other nebulae===

A few galaxies outside the Milky Way are visible in the night sky to the unaided eye. In the 10th century, the Persian astronomer [[Al-Sufi]] made the earliest recorded identification of the [[Andromeda Galaxy]], describing it as a "small cloud".<ref name="NSOG"/> In 964, Al-Sufi identified the [[Large Magellanic Cloud]] in his ''[[Book of Fixed Stars]]''; it was not seen by Europeans until [[Ferdinand Magellan|Magellan]]'s voyage in the 16th century.<ref name="obspm">
{{cite web
|title=Abd-al-Rahman Al Sufi (December 7, 903 – May 25, 986 A.D.)
|url=http://messier.obspm.fr/xtra/Bios/alsufi.html
|publisher=[[Observatoire de Paris]]
|accessdate=April 19, 2007
}}</ref><ref name="obspm2">
{{cite web
|title=The Large Magellanic Cloud, LMC
|url=http://messier.obspm.fr/xtra/ngc/lmc.html
|publisher=[[Observatoire de Paris]]
|accessdate=April 19, 2007
}}</ref> The Andromeda Galaxy was independently noted by [[Simon Marius]] in 1612.<ref name="NSOG"/>

In 1750, [[Thomas Wright (astronomer)|Thomas Wright]] speculated (correctly) that the Milky Way is a flattened disk of stars, and that some of the [[nebula]]e visible in the night sky might be separate Milky Ways.<ref name="our_galaxy">
{{cite web
|last1=Evans |first1=J. C.
|date=November 24, 1998
|title=Our Galaxy
|url=http://physics.gmu.edu/~jevans/astr103/CourseNotes/ECText/ch20_txt.htm
|publisher=[[George Mason University]]
|accessdate=January 4, 2007
}}</ref><ref>See text quoted from Wright's ''An original theory or new hypothesis of the Universe'' in {{Cite book
|last1=Dyson |first1=F.
|date=1979
|title=Disturbing the Universe
|page=245
|publisher=[[Pan Books]]
|isbn=0-330-26324-2
}}</ref> In 1755, [[Immanuel Kant]] used the term "island Universe" to describe these distant nebulae.
[[File:Pic iroberts1.jpg|thumb|right|Photograph of the "Great Andromeda Nebula" from 1899, later identified as the [[Andromeda Galaxy]]]]
Toward the end of the 18th century, [[Charles Messier]] compiled a [[Messier object|catalog]] containing the 109 brightest celestial objects having nebulous appearance. Subsequently, William Herschel assembled a catalog of 5,000 nebulae.<ref name="our_galaxy" /> In 1845, [[William Parsons, 3rd Earl of Rosse|Lord Rosse]] constructed a new telescope and was able to distinguish between elliptical and spiral nebulae. He also managed to make out individual point sources in some of these nebulae, lending credence to Kant's earlier conjecture.<ref>[http://parsonstown.info/people/william-rosse "Parsonstown | The genius of the Parsons family | William Rosse"]. ''parsonstown.info''.</ref>

In 1912, [[Vesto Slipher]] made spectrographic studies of the brightest spiral nebulae to determine their composition. Slipher discovered that the spiral nebulae have high [[Doppler shift]]s, indicating that they are moving at a rate exceeding the velocity of the stars he had measured. He found that the majority of these nebulae are moving away from us.<ref>
{{cite journal
|last1=Slipher |first1=V. M.
|date=1913
|title=The radial velocity of the Andromeda Nebula
|journal=Lowell Observatory Bulletin
|volume=1 |pages=56–57
|bibcode=1913LowOB...2...56S
}}</ref><ref>
{{cite journal
|last1=Slipher |first1=V. M.
|date=1915
|title=Spectrographic Observations of Nebulae
|journal=[[Popular Astronomy (US magazine)|Popular Astronomy]]
|volume=23 |pages=21–24
|bibcode=1915PA.....23...21S
}}</ref>

In 1917, [[Heber Curtis]] observed nova [[S Andromedae]] within the "Great [[Andromeda (constellation)|Andromeda]] Nebula" (as the Andromeda Galaxy, [[Messier object]] [[Andromeda Galaxy|M31]], was then known). Searching the photographic record, he found 11 more [[nova]]e. Curtis noticed that these novae were, on average, 10 [[magnitude (astronomy)|magnitudes]] fainter than those that occurred within our galaxy. As a result, he was able to come up with a distance estimate of 150,000 [[parsec]]s. He became a proponent of the so-called "island universes" hypothesis, which holds that spiral nebulae are actually independent galaxies.<ref>
{{cite journal
|last=Curtis |first1=H. D.
|date=1988
|title=Novae in Spiral Nebulae and the Island Universe Theory
|journal=[[Publications of the Astronomical Society of the Pacific]]
|volume=100 |pages=6
|bibcode=1988PASP..100....6C
|doi=10.1086/132128
}}</ref>

In 1920 the so-called [[Great Debate (astronomy)|Great Debate]] took place between [[Harlow Shapley]] and [[Heber Curtis]], concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the Universe. To support his claim that the Great Andromeda Nebula is an external galaxy, Curtis noted the appearance of dark lanes resembling the dust clouds in the Milky Way, as well as the significant Doppler shift.<ref>
{{cite web
|last1=Weaver |first1=H. F.
|title=Robert Julius Trumpler
|url=http://www.nap.edu/readingroom/books/biomems/rtrumpler.html
|publisher=[[United States National Academy of Sciences|US National Academy of Sciences]]
|accessdate=January 5, 2007
}}</ref>

In 1922, the [[Estonia]]n astronomer [[Ernst Öpik]] gave a distance determination that supported the theory that the Andromeda Nebula is indeed a distant extra-galactic object.<ref>
{{cite journal
|last1=Öpik |first1=E.
|date=1922
|title=An estimate of the distance of the Andromeda Nebula
|journal=[[Astrophysical Journal]]
|volume=55 |pages=406
|bibcode=1922ApJ....55..406O
|doi=10.1086/142680
}}</ref> Using the new 100 inch [[Mount Wilson Observatory|Mt. Wilson]] telescope, [[Edwin Hubble]] was able to resolve the outer parts of some spiral nebulae as collections of individual stars and identified some [[Cepheid variable]]s, thus allowing him to estimate the distance to the nebulae: they were far too distant to be part of the Milky Way.<ref>
{{cite journal
|last1=Hubble |first1=E. P.
|date=1929
|title=A spiral nebula as a stellar system, Messier 31
|journal=[[Astrophysical Journal]]
|volume=69 |pages=103–158
|bibcode=1929ApJ....69..103H
|doi=10.1086/143167
}}</ref> In 1936 Hubble produced a classification of [[Galaxy morphological classification|galactic morphology]] that is used to this day.<ref>
{{cite journal
|last1=Sandage |first1=A.
|date=1989
|title=Edwin Hubble, 1889–1953
|journal=[[Journal of the Royal Astronomical Society of Canada]]
|volume=83 |issue=6 |pages=351–362
|url=http://antwrp.gsfc.nasa.gov/diamond_jubilee/1996/sandage_hubble.html
|accessdate=January 8, 2007
|bibcode = 1989JRASC..83..351S }}</ref>

===Modern research===
[[File:GalacticRotation2.svg|thumb|right|200px|[[Galaxy rotation curve|Rotation curve]] of a typical spiral galaxy: predicted based on the visible matter (A) and observed (B). The distance is from the [[Bulge (astronomy)|galactic core]].]]
In 1944, [[Hendrik C. van de Hulst|Hendrik van de Hulst]] predicted that [[microwave]] radiation with [[hydrogen line|wavelength of 21 cm]] would be detectable from interstellar atomic [[hydrogen]] gas;<ref>
{{cite web
|last1=Tenn |first1=J.
|title=Hendrik Christoffel van de Hulst
|url=http://www.phys-astro.sonoma.edu/BruceMedalists/vandeHulst/
|publisher=[[Sonoma State University]]
|accessdate=January 5, 2007
}}</ref> and in 1951 it was observed. This radiation is not affected by dust absorption, and so its Doppler shift can be used to map the motion of the gas in our galaxy. These observations led to the hypothesis of a rotating [[barred spiral galaxy|bar structure]] in the center of our galaxy.<ref>
{{cite journal
|last1=López-Corredoira |first1=M.
|display-authors=etal
|date=2001
|title=Searching for the in-plane Galactic bar and ring in DENIS
|journal=[[Astronomy and Astrophysics]]
|volume=373
|issue=1 |pages=139–152
|bibcode=2001A&A...373..139L
|doi=10.1051/0004-6361:20010560
|arxiv = astro-ph/0104307 }}</ref> With improved [[radio telescope]]s, hydrogen gas could also be traced in other galaxies.
In the 1970s, [[Vera Rubin]] uncovered a discrepancy between observed galactic [[galaxy rotation curve|rotation speed]] and that predicted by the visible mass of stars and gas. Today, the galaxy rotation problem is thought to be explained by the presence of large quantities of unseen [[dark matter]].<ref>
{{cite journal
|last1=Rubin |first1=V. C.
|date=1983
|title=Dark matter in spiral galaxies
|journal=[[Scientific American]]
|volume=248
|issue=6 |pages=96–106
|bibcode=1983SciAm.248...96R
|doi=10.1038/scientificamerican0683-96
}}</ref><ref>
{{cite journal
|last1=Rubin |first1=V. C.
|date=2000
|title=One Hundred Years of Rotating Galaxies
|journal=[[Publications of the Astronomical Society of the Pacific]]
|volume=112 |issue=772 |pages=747–750
|bibcode=2000PASP..112..747R
|doi=10.1086/316573
}}</ref> A concept known as the [[universal rotation curve]] of spirals, moreover, shows that the problem is ubiquitous in these objects.

Beginning in the 1990s, the [[Hubble Space Telescope]] yielded improved observations. Among other things, Hubble data helped establish that the missing dark matter in our galaxy cannot solely consist of inherently faint and small stars.<ref>
{{cite news
|title=Hubble Rules Out a Leading Explanation for Dark Matter
|publisher=Hubble News Desk
|date=October 17, 1994
|url=http://hubblesite.org/newscenter/archive/releases/1994/41/text/
|accessdate=January 8, 2007
}}</ref> The [[Hubble Deep Field]], an extremely long exposure of a relatively empty part of the sky, provided evidence that there are about 125 billion ({{val|1.25|e=11}}) galaxies in the Universe.<ref>
{{cite web
|date=November 27, 2002
|title=How many galaxies are there?
|url=http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/021127a.html
|publisher=[[NASA]]
|accessdate=January 8, 2007
}}</ref> Improved technology in detecting the [[electromagnetic spectrum|spectra]] invisible to humans (radio telescopes, infrared cameras, and [[x-ray astronomy|x-ray telescopes]]) allow detection of other galaxies that are not detected by Hubble. Particularly, galaxy surveys in the [[Zone of Avoidance]] (the region of the sky blocked by the Milky Way) have revealed a number of new galaxies.<ref>
{{cite journal
|last1=Kraan-Korteweg |first1=R. C.
|last2=Juraszek |first2=S.
|date=2000
|title=Mapping the hidden Universe: The galaxy distribution in the Zone of Avoidance
|journal=[[Publications of the Astronomical Society of Australia]]
|volume=17 |issue=1 |pages=6–12
|bibcode=1999astro.ph.10572K
|arxiv = astro-ph/9910572
|doi=10.1071/AS00006 }}</ref>

==Types and morphology==
{{Main|Galaxy morphological classification}}
[[File:Hubble sequence photo.png|thumb|360px|Types of galaxies according to the Hubble classification scheme: an ''E'' indicates a type of elliptical galaxy; an ''S'' is a spiral; and ''SB'' is a barred-spiral galaxy.<ref group=note>Galaxies to the left side of the Hubble classification scheme are sometimes referred to as "early-type", while those to the right are "late-type".</ref>]]
Galaxies come in three main types: ellipticals, spirals, and irregulars. A slightly more extensive description of galaxy types based on their appearance is given by the [[Galaxy morphological classification|Hubble sequence]]. Since the Hubble sequence is entirely based upon visual morphological type, it may miss certain important characteristics of galaxies such as [[star formation]] rate in [[Starburst galaxy|starburst galaxies]] and activity in the cores of [[active galaxy|active galaxies]].<ref name="IRatlas" />

===Ellipticals===
{{Main|Elliptical galaxy}}
The Hubble classification system rates elliptical galaxies on the basis of their ellipticity, ranging from E0, being nearly spherical, up to E7, which is highly elongated. These galaxies have an [[ellipsoid]]al profile, giving them an elliptical appearance regardless of the viewing angle. Their appearance shows little structure and they typically have relatively little [[interstellar medium|interstellar matter]]. Consequently, these galaxies also have a low portion of [[open cluster]]s and a reduced rate of new star formation. Instead they are dominated by generally older, more [[stellar evolution|evolved stars]] that are orbiting the common center of gravity in random directions. The stars contain low abundances of heavy elements because star formation ceases after the initial burst. In this sense they have some similarity to the much smaller [[globular cluster]]s.<ref name="elliptical">
{{cite web
|last1=Barstow |first1=M. A.
|date=2005
|title=Elliptical Galaxies
|url=http://web.archive.org/web/20120729081504/http://www.star.le.ac.uk/edu/Elliptical.shtml
|publisher=[[Leicester University]] Physics Department
|accessdate=June 8, 2006
}}</ref>

The largest galaxies are giant ellipticals. Many elliptical galaxies are believed to form due to the [[interacting galaxy|interaction of galaxies]], resulting in a collision and merger. They can grow to enormous sizes (compared to spiral galaxies, for example), and giant elliptical galaxies are often found near the core of large galaxy clusters.<ref>
{{cite web
|date=October 20, 2005
|title=Galaxies
|url=http://web.archive.org/web/20140629115612/http://curious.astro.cornell.edu/galaxies.php
|publisher=[[Cornell University]]
|accessdate=August 10, 2006
}}</ref> Starburst galaxies are the result of such a galactic collision that can result in the formation of an elliptical galaxy.<ref name="elliptical" />

====Shell galaxy====
[[File:NGC 3923 Elliptical Shell Galaxy.jpg|thumb|NGC 3923 Elliptical Shell Galaxy-Hubble Space Telescope photograph]]
A shell galaxy is a type of elliptical galaxy where the stars in the galaxy's halo are arranged in concentric shells. About 1/10 tenth of elliptical galaxies have a shell-like structure, which has never been observed in spiral galaxies. The shell-like structures are thought to develop when a larger galaxy absorbs a smaller companion galaxy. As the two galaxy centers approach, the centers start to oscillate around a center point, the oscillation creates gravitational ripples forming the shells of stars, similar to ripples spreading on water. For example, galaxy [[NGC 3923]] has over twenty shells.<ref>{{Cite web|title = Galactic onion|url = http://www.spacetelescope.org/images/potw1519a/|website = www.spacetelescope.org|accessdate = 2015-05-11}}</ref>

===Spirals===
{{Main|Spiral galaxy|Barred spiral galaxy}}

[[File:M101 hires STScI-PRC2006-10a.jpg|thumb|right|The [[Pinwheel Galaxy]], NGC 5457.]]

Spiral galaxies resemble spiraling pinwheels. Though the stars and other visible material contained in such a galaxy lie mostly on a plane, the majority of mass in spiral galaxies exists in a roughly spherical halo of [[dark matter]] that extends beyond the visible component, as demonstrated by the universal rotation curve concept.<ref name="Williams2009">{{cite doi|10.1111/j.1365-2966.2009.15582.x}}</ref>

Spiral galaxies consist of a rotating disk of stars and interstellar medium, along with a central bulge of generally older stars. Extending outward from the [[bulge (astronomy)|bulge]] are relatively bright arms. In the Hubble classification scheme, spiral galaxies are listed as type ''S'', followed by a letter (''a'', ''b'', or ''c'') that indicates the degree of tightness of the spiral arms and the size of the central bulge. An ''Sa'' galaxy has tightly wound, poorly defined arms and possesses a relatively large core region. At the other extreme, an ''Sc'' galaxy has open, well-defined arms and a small core region.<ref>
{{cite web
|last1=Smith |first1=G.
|date=March 6, 2000
|url=http://casswww.ucsd.edu/public/tutorial/Galaxies.html
|title=Galaxies — The Spiral Nebulae
|publisher=[[University of California]], San Diego Center for Astrophysics & Space Sciences
|accessdate=November 30, 2006
}}</ref> A galaxy with poorly defined arms is sometimes referred to as a [[flocculent spiral galaxy]]; in contrast to the [[grand design spiral galaxy]] that has prominent and well-defined spiral arms.<ref name=bergh1998/>

It appears the reason that some spiral galaxies are fat and bulging while some are flat discs is because of how fast they rotate.<ref>[http://phys.org/news/2014-02-fat-flat-galaxies.html "Fat or flat: Getting galaxies into shape"]. ''phys.org''. February 2014</ref>
[[File:Hubble2005-01-barred-spiral-galaxy-NGC1300.jpg|right|thumb|300px|[[NGC 1300]], an example of a [[barred spiral galaxy]].]]
In spiral galaxies, the spiral arms do have the shape of approximate [[logarithmic spiral]]s, a pattern that can be theoretically shown to result from a disturbance in a uniformly rotating mass of stars. Like the stars, the spiral arms rotate around the center, but they do so with constant [[angular velocity]]. The spiral arms are thought to be areas of high-density matter, or "[[Density wave theory|density waves]]".<ref name=bertin_lin1996/> As stars move through an arm, the space velocity of each stellar system is modified by the gravitational force of the higher density. (The velocity returns to normal after the stars depart on the other side of the arm.) This effect is akin to a "wave" of slowdowns moving along a highway full of moving cars. The arms are visible because the high density facilitates star formation, and therefore they harbor many bright and young stars.<ref name=belkora355/>
{{multiple image
| align = right
| direction = vertical
| width = 230
| image1 = Hoag's object.jpg
| caption1 = [[Hoag's Object]], an example of a [[ring galaxy]]
| image2 = File-Ngc5866 hst big.png
| caption2 = [[NGC 5866]], an example of a [[lenticular galaxy]]
}}
====Barred Spiral Galaxy====
A majority of spiral galaxies, including our own [[Milky Way]] galaxy, have a linear, bar-shaped band of stars that extends outward to either side of the core, then merges into the spiral arm structure.<ref>
{{cite journal
|last1=Eskridge |first1=P. B.
|last2=Frogel |first2=J. A.
|date=1999
|title=What is the True Fraction of Barred Spiral Galaxies?
|journal=[[Astrophysics and Space Science]]
|volume=269/270 |pages=427–430
|bibcode=1999Ap&SS.269..427E
|doi=10.1023/A:1017025820201
}}</ref> In the Hubble classification scheme, these are designated by an ''SB'', followed by a lower-case letter (''a'', ''b'' or ''c'') that indicates the form of the spiral arms (in the same manner as the categorization of normal spiral galaxies). Bars are thought to be temporary structures that can occur as a result of a density wave radiating outward from the core, or else due to a [[Galactic tide|tidal interaction]] with another galaxy.<ref>
{{cite journal
|last1=Bournaud |first1=F.
|last2=Combes |first2=F.
|date=2002
|title=Gas accretion on spiral galaxies: Bar formation and renewal
|journal=[[Astronomy and Astrophysics]]
|volume=392
|issue=1 |pages=83–102
|bibcode=2002A&A...392...83B
|doi=10.1051/0004-6361:20020920
|arxiv = astro-ph/0206273 }}</ref> Many barred spiral galaxies are active, possibly as a result of gas being channeled into the core along the arms.<ref>
{{cite journal
|last1=Knapen |first1=J. H.
|last2=Perez-Ramirez |first2=D.
|last3=Laine |first3=S.
|date=2002
|title=Circumnuclear regions in barred spiral galaxies — II. Relations to host galaxies
|journal=[[Monthly Notices of the Royal Astronomical Society]]
|volume=337 |issue=3 |pages=808–828
|bibcode=2002MNRAS.337..808K
|doi=10.1046/j.1365-8711.2002.05840.x
|arxiv = astro-ph/0207258 }}</ref>

Our own galaxy, the [[Milky Way]], is a large disk-shaped barred-spiral galaxy<ref>
{{cite journal
|last1=Alard |first1=C.
|date=2001
|title=Another bar in the Bulge
|journal=[[Astronomy and Astrophysics Letters]]
|volume=379 |issue=2 |pages=L44–L47
|bibcode=2001A&A...379L..44A
|doi=10.1051/0004-6361:20011487
|arxiv = astro-ph/0110491 }}</ref> about 30 kiloparsecs in diameter and a kiloparsec thick. It contains about two hundred billion (2×1011)<ref>
{{cite news
|last1=Sanders |first1=R.
|date=January 9, 2006
|title=Milky Way galaxy is warped and vibrating like a drum
|publisher=[[UC Berkeley|UCBerkeley News]]
|url=http://www.berkeley.edu/news/media/releases/2006/01/09_warp.shtml
|accessdate=May 24, 2006
}}</ref> stars and has a total mass of about six hundred billion (6×1011) times the mass of the Sun.<ref>
{{cite journal
|last1=Bell |first1=G. R.
|last2=Levine |first2=S. E.
|date=1997
|title=Mass of the Milky Way and Dwarf Spheroidal Stream Membership
|journal=[[Bulletin of the American Astronomical Society]]
|volume=29 |issue=2 |pages=1384
|bibcode=1997AAS...19110806B
}}</ref>

===Other morphologies===
* [[Peculiar galaxy|Peculiar galaxies]] are galactic formations that develop unusual properties due to tidal interactions with other galaxies. An example of this is the [[ring galaxy]], which possesses a ring-like structure of stars and interstellar medium surrounding a bare core. A ring galaxy is thought to occur when a smaller galaxy passes through the core of a spiral galaxy.<ref>{{cite journal
|last1=Gerber |first1=R. A.
|last2=Lamb |first2=S. A.
|last3=Balsara |first3=D. S.
|date=1994
|title=Ring Galaxy Evolution as a Function of "Intruder" Mass
|journal=[[Bulletin of the American Astronomical Society]]
|volume=26 |pages=911
|bibcode=1994AAS...184.3204G
}}</ref> Such an event may have affected the [[Andromeda Galaxy]], as it displays a multi-ring-like structure when viewed in [[infrared]] radiation.<ref>{{cite press release
|publisher=[[European Space Agency]]
|date=October 14, 1998
|title=ISO unveils the hidden rings of Andromeda
|url=http://www.iso.vilspa.esa.es/outreach/esa_pr/andromed.htm
|accessdate=May 24, 2006
}}</ref>

* A [[lenticular galaxy]] is an intermediate form that has properties of both elliptical and spiral galaxies. These are categorized as Hubble type S0, and they possess ill-defined spiral arms with an elliptical halo of stars<ref>{{cite web
|date=May 31, 2004
|title=Spitzer Reveals What Edwin Hubble Missed
|url=http://web.archive.org/web/20060907042809/http://www.cfa.harvard.edu/press/pr0419.html
|publisher=[[Harvard-Smithsonian Center for Astrophysics]]
|accessdate=December 6, 2006
}}</ref> ([[Barred lenticular galaxy|barred lenticular galaxies]] receive Hubble classification SB0.)

* [[Irregular galaxy|Irregular galaxies]] are galaxies that can not be readily classified into an elliptical or spiral morphology. An Irr-I galaxy has some structure but does not align cleanly with the Hubble classification scheme. Irr-II galaxies do not possess any structure that resembles a Hubble classification, and may have been disrupted.<ref>{{cite web
|last1=Barstow |first1=M. A.
|date=2005
|title=Irregular Galaxies
|url=http://web.archive.org/web/20120227172628/http://www.star.le.ac.uk/edu/Irregular.shtml
|publisher=[[University of Leicester]]
|accessdate=December 5, 2006
}}</ref> Nearby examples of (dwarf) irregular galaxies include the [[Magellanic Clouds]].

* An [[ultra diffuse galaxy]] (UDG) is an extremely-low-density galaxy. The galaxy may be the same size as the Milky Way but has a visible star count of only 1% of the Milky Way. The lack of luminosity is because there is a lack of star-forming gas in the galaxy which results in old stellar populations.

===Dwarfs===
{{Main|Dwarf galaxy}}
Despite the prominence of large elliptical and spiral galaxies, most galaxies in the Universe are dwarf galaxies. These galaxies are relatively small when compared with other galactic formations, being about one hundredth the size of the Milky Way, containing only a few billion stars. Ultra-compact dwarf galaxies have recently been discovered that are only 100 parsecs across.<ref>
{{cite journal
|last1=Phillipps |first1=S.
|last2=Drinkwater |first2=M. J.
|last3=Gregg |first3=M. D.
|last4=Jones |first4=J. B.
|date=2001
|title=Ultracompact Dwarf Galaxies in the Fornax Cluster
|journal=[[Astrophysical Journal]]
|volume=560 |issue=1 |pages=201–206
|bibcode=2001ApJ...560..201P
|doi=10.1086/322517
|arxiv = astro-ph/0106377 }}</ref>

Many dwarf galaxies may orbit a single larger galaxy; the Milky Way has at least a dozen such satellites, with an estimated 300–500 yet to be discovered.<ref>
{{cite news
|last1=Groshong |first1=K.
|date=April 24, 2006
|title=Strange satellite galaxies revealed around Milky Way
|publisher=[[New Scientist]]
|url=http://www.newscientist.com/article/dn9043-strange-satellite-galaxies-revealed-around-milky-way.html
|accessdate=January 10, 2007
}}</ref> Dwarf galaxies may also be classified as [[dwarf elliptical galaxy|elliptical]], [[dwarf spiral galaxy|spiral]], or [[irregular galaxy|irregular]]. Since small dwarf ellipticals bear little resemblance to large ellipticals, they are often called [[dwarf spheroidal galaxy|dwarf spheroidal galaxies]] instead.

A study of 27 Milky Way neighbors found that in all dwarf galaxies, the central mass is approximately 10 million [[solar mass]]es, regardless of whether the galaxy has thousands or millions of stars. This has led to the suggestion that galaxies are largely formed by [[dark matter]], and that the minimum size may indicate a form of [[warm dark matter]] incapable of gravitational coalescence on a smaller scale.<ref>
{{cite web
|last1=Schirber |first1=M.
|date=August 27, 2008
|url=http://news.sciencemag.org/physics/2008/08/no-slimming-down-dwarf-galaxies
|title=No Slimming Down for Dwarf Galaxies
|publisher=[[ScienceNOW]]
|accessdate=August 27, 2008
}}</ref>

==Unusual dynamics and activities==

===Interacting===
{{Main|Interacting galaxy}}
[[File:Antennae galaxies xl.jpg|thumb|right|200px|The [[Antennae Galaxies]] are undergoing a collision that will result in their eventual merger.]]
Interactions between galaxies are relatively frequent, and they can play an important role in [[galaxy formation and evolution|galactic evolution]]. Near misses between galaxies result in warping distortions due to [[galactic tide|tidal interactions]], and may cause some exchange of gas and dust.<ref name="umda">
{{cite web
|url=http://www.astro.umd.edu/education/astro/gal/interact.html
|title=Galaxy Interactions
|publisher=[[University of Maryland]] Department of Astronomy
|accessdate=December 19, 2006
|archiveurl=http://web.archive.org/web/20060509074300/http://www.astro.umd.edu/education/astro/gal/interact.html
|archivedate=May 9, 2006
}}</ref><ref name="suia">
{{cite web
|title=Interacting Galaxies
|url=http://Cosmos.swin.edu.au/entries/interactinggalaxies/interactinggalaxies.html?e=1
|publisher=[[Swinburne University]]
|accessdate=December 19, 2006
}}</ref>
Collisions occur when two galaxies pass directly through each other and have sufficient relative momentum not to merge. The stars of interacting galaxies will usually not collide, but the gas and dust within the two forms will interact, sometimes triggering star formation. A collision can severely distort the shape of the galaxies, forming bars, rings or tail-like structures.<ref name="umda" /><ref name="suia" />

At the extreme of interactions are galactic mergers. In this case the relative momentum of the two galaxies is insufficient to allow the galaxies to pass through each other. Instead, they gradually merge to form a single, larger galaxy. Mergers can result in significant changes to morphology, as compared to the original galaxies. In the case where one of the galaxies is much more massive, however, the result is known as [[Interacting galaxy#Galactic cannibalism|cannibalism]]. In this case the larger galaxy will remain relatively undisturbed by the merger, while the smaller galaxy is torn apart. The Milky Way galaxy is currently in the process of cannibalizing the [[Sagittarius Dwarf Elliptical Galaxy]] and the [[Canis Major Dwarf Galaxy]].<ref name="umda" /><ref name="suia" />

===Starburst===
{{Main|Starburst galaxy}}
[[File:M82 HST ACS 2006-14-a-large web.jpg|thumb|right|200px|[[Messier 82|M82]], a starburst galaxy that has ten times the star formation of a "normal" galaxy.<ref>
{{cite web
|date=April 24, 2006
|url=http://hubblesite.org/newscenter/archive/releases/2006/14/image/a
|title=Happy Sweet Sixteen, Hubble Telescope!
|publisher=[[NASA]]
|accessdate=August 10, 2006
}}</ref>]]

Stars are created within galaxies from a reserve of cold gas that forms into giant [[molecular cloud]]s. Some galaxies have been observed to form stars at an exceptional rate, known as a starburst. Should they continue to do so, however, they would consume their reserve of gas in a time frame lower than the lifespan of the galaxy. Hence starburst activity usually lasts for only about ten million years, a relatively brief period in the history of a galaxy. Starburst galaxies were more common during the early history of the Universe,<ref name="chandra">
{{cite web
|date=August 29, 2006
|url=http://chandra.harvard.edu/xray_sources/starburst.html
|title=Starburst Galaxies
|publisher=[[Harvard-Smithsonian Center for Astrophysics]]
|accessdate=August 10, 2006
}}</ref> and, at present, still contribute an estimated 15% to the total star production rate.<ref>
{{cite conference
|last1=Kennicutt Jr. |first1=R. C.
|display-authors=etal
|date=2005
|title=Demographics and Host Galaxies of Starbursts
|work=Starbursts: From 30 Doradus to Lyman Break Galaxies
|page=187
|publisher=[[Springer (publisher)|Springer]]
|bibcode=2005sdlb.proc..187K
}}</ref>

Starburst galaxies are characterized by dusty concentrations of gas and the appearance of newly formed stars, including massive stars that ionize the surrounding clouds to create [[H II region]]s.<ref>
{{cite web
|last1=Smith |first1=G.
|date=July 13, 2006
|title=Starbursts & Colliding Galaxies
|url=http://casswww.ucsd.edu/public/tutorial/Starbursts.html
|publisher=[[University of California]], San Diego Center for Astrophysics & Space Sciences
|accessdate=August 10, 2006
}}</ref> These massive stars produce [[supernova]] explosions, resulting in expanding [[supernova remnant|remnants]] that interact powerfully with the surrounding gas. These outbursts trigger a chain reaction of star building that spreads throughout the gaseous region. Only when the available gas is nearly consumed or dispersed does the starburst activity come to an end.<ref name="chandra" />

Starbursts are often associated with merging or interacting galaxies. The prototype example of such a starburst-forming interaction is [[Messier 82|M82]], which experienced a close encounter with the larger [[Messier 81|M81]]. Irregular galaxies often exhibit spaced knots of starburst activity.<ref>
{{cite web
|last1=Keel |first1=B.
|date=September 2006
|title=Starburst Galaxies
|url=http://www.astr.ua.edu/keel/galaxies/starburst.html
|publisher=[[University of Alabama]]
|accessdate=December 11, 2006
}}</ref>

===Active nucleus===
{{Main|Active galactic nucleus}}
[[File:M87 jet.jpg|thumb|right|200px|A jet of particles is being emitted from the core of the elliptical radio galaxy [[Messier 87|M87]].]]
A portion of the observable galaxies are classified as active. That is, a significant portion of the total energy output from the galaxy is emitted by a source other than the stars, dust and [[interstellar medium]].

The standard model for an [[active galactic nucleus]] is based upon an [[accretion disc]] that forms around a [[supermassive black hole]] (SMBH) at the core region. The radiation from an active galactic nucleus results from the [[gravitational energy]] of matter as it falls toward the black hole from the disc.<ref name="keel">
{{cite web
|last1=Keel |first1=W. C.
|date=2000
|url=http://www.astr.ua.edu/keel/galaxies/agnintro.html
|title=Introducing Active Galactic Nuclei
|publisher=[[University of Alabama]]
|accessdate=December 6, 2006
}}</ref> In about 10% of these objects, a diametrically opposed pair of energetic jets ejects particles from the core at velocities close to the [[speed of light]]. The mechanism for producing these jets is still not well understood.<ref name="monster">
{{cite web
|last1=Lochner |first1=J.
|last2=Gibb |first2=M.
|title=A Monster in the Middle
|url=http://imagine.gsfc.nasa.gov/docs/science/know_l2/active_galaxies.html
|publisher=[[NASA]]
|accessdate=December 20, 2006
}}</ref>

Active galaxies that emit high-energy radiation in the form of [[x-ray]]s are classified as [[Seyfert galaxy|Seyfert galaxies]] or [[quasar]]s, depending on the luminosity.

====Blazars====
{{Main|Blazars}}
[[Blazar]]s are believed to be an active galaxy with a [[relativistic jet]] that is pointed in the direction of Earth. A [[radio galaxy]] emits radio frequencies from relativistic jets. A unified model of these types of active galaxies explains their differences based on the viewing angle of the observer.<ref name="monster" />

====LINERS====
Possibly related to active galactic nuclei (as well as [[starburst (astronomy)|starburst]] regions) are [[low-ionization nuclear emission-line region]]s (LINERs). The emission from LINER-type galaxies is dominated by weakly [[ion]]ized elements.<ref name="heckman1980">
{{cite journal
|last1=Heckman |first1=T. M.
|date=1980
|title=An optical and radio survey of the nuclei of bright galaxies — Activity in normal galactic nuclei
|journal=[[Astronomy and Astrophysics]]
|volume=87 |pages=152–164
|bibcode=1980A&A....87..152H
}}</ref> Approximately one-third of nearby galaxies are classified as containing LINER nuclei.<ref name="keel" /><ref name="heckman1980" /><ref name="hoetal1997b">
{{cite journal
|last1=Ho |first1=L. C.
|last2=Filippenko |first2=A. V.
|last3=Sargent |first3=W. L. W.
|date=1997
|title=A Search for "Dwarf" Seyfert Nuclei. V. Demographics of Nuclear Activity in Nearby Galaxies
|journal=[[Astrophysical Journal]]
|volume=487
|issue=2 |pages=568–578
|bibcode=1997ApJ...487..568H
|doi=10.1086/304638
|arxiv = astro-ph/9704108 }}</ref>

====Seyfert Galaxy====
{{Main|Seyfert Galaxy}}
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei (very luminous, distant and bright sources of electromagnetic radiation) with very high surface brightnesses but unlike quasars, their host galaxies are clearly detectable. Seyfert galaxies account for about 10% of all galaxies. Seen in visible light, most Seyfert galaxies look like normal spiral galaxies, but when studied under other wavelengths, the luminosity of their cores is equivalent to the luminosity of whole galaxies the size of the Milky Way.

====Quasar====
{{Main|Quasar}}
Quasars (/ˈkweɪzɑr/) or quasi-stellar radio sources are the most energetic and distant members of a class of objects called active galactic nuclei (AGN). Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that appeared to be similar to stars, rather than extended sources similar to galaxies. Their luminosity can be 100 times greater than that of the Milky Way.

===Luminous infrared galaxy===
{{Main|Luminous infrared galaxy}}
Luminous Infrared Galaxies or (LIRG's) are galaxies with luminosities, the measurement of brightness, above 1011 L☉. LIRG's are more abundant than starburst galaxies, Seyfert galaxies and quasi-stellar objects at comparable luminosity. Infrared galaxies emit more energy in the infrared than at all other wavelengths combined. An LIRG's luminosity is 100 billion times that of our sun.

==Formation and evolution==
{{Main|Galaxy formation and evolution}}
Galactic formation and evolution is an active area of research in [[astrophysics]].

===Formation===
[[File:Artist's impression of a protocluster forming in the early Universe.jpg|align=right|thumb|Artist's impression of a protocluster forming in the early Universe.<ref>{{cite web|title=Construction Secrets of a Galactic Metropolis|url=http://www.eso.org/public/news/eso1431/|website=www.eso.org|publisher=ESO Press Release|accessdate=October 15, 2014}}</ref>]]
Current cosmological models of the early Universe are based on the [[Big Bang]] theory. About 300,000 years after this event, atoms of [[hydrogen]] and [[helium]] began to form, in an event called [[Recombination (cosmology)|recombination]]. Nearly all the hydrogen was neutral (non-ionized) and readily absorbed light, and no stars had yet formed. As a result, this period has been called the "[[Timeline of the Big Bang#Dark Ages|dark ages]]". It was from density fluctuations (or [[anisotropy|anisotropic]] irregularities) in this primordial matter that [[structure formation|larger structures]] began to appear. As a result, masses of [[baryon]]ic matter started to condense within [[cold dark matter]] halos.<ref name="hqrdvj">
{{cite web
|date=November 18, 1999
|title=Search for Submillimeter Protogalaxies
|url=http://web.archive.org/web/20080325183740/http://cfa-www.harvard.edu/~aas/tenmeter/proto.htm
|publisher=[[Harvard-Smithsonian Center for Astrophysics]]
|accessdate=January 10, 2007
}}</ref><ref name=rmaa17_107/> These primordial structures would eventually become the galaxies we see today.
[[File:Young Galaxy Accreting Material.jpg|thumb|right|200px|Artist's impression of a young galaxy accreting material.]]

====Early galaxies====
Evidence for the early appearance of galaxies was found in 2006, when it was discovered that the galaxy [[IOK-1]] has an unusually high [[redshift]] of 6.96, corresponding to just 750 million years after the Big Bang and making it the most distant and primordial galaxy yet seen.<ref>
{{cite journal
|last1=McMahon |first1=R.
|date=2006
|title=Journey to the birth of the Universe
|journal=[[Nature (journal)|Nature]]
|volume=443 |issue=7108 |pages=151–2
|doi=10.1038/443151a
|pmid=16971933
|bibcode = 2006Natur.443..151M }}</ref>
While some scientists have claimed other objects (such as [[Galaxy Abell 1835 IR1916|Abell 1835 IR1916]]) have higher redshifts (and therefore are seen in an earlier stage of the Universe's evolution), IOK-1's age and composition have been more reliably established. In December 2012, astronomers reported that the [[UDFj-39546284]] is the most distant object known and has a redshift value of 11.9. The object, is estimated to have existed around "380 million years"<ref name="Space-20121212">{{cite web |last=Wall |first=Mike |title=Ancient Galaxy May Be Most Distant Ever Seen |url=http://www.space.com/18879-hubble-most-distant-galaxy.html |date=December 12, 2012 |publisher=[[Space.com]] |accessdate=December 12, 2012 }}</ref> after the [[Big Bang]] (which was about 13.8 billion years ago),<ref name="Cosmic Detectives">{{cite web
|last =
|first =
|title = Cosmic Detectives
|url=http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives
|authorlink =
|work =
|publisher = The European Space Agency (ESA)
|date = April 2, 2013
|doi =
|accessdate = April 15, 2013}}</ref> is about 13.42 billion light years away. The existence of such early [[protogalaxy|protogalaxies]] suggests that they must have grown in the so-called "dark ages".<ref name="hqrdvj"/> As of May 5, 2015, the galaxy [[EGS-zs8-1]] is the most distant and earliest galaxy measured, forming 670 million years after the [[Big Bang]]. The light from EGS-zs8-1 has taken 13 billion years to reach Earth, and is now 30 billion light-years away, because of the [[expansion of the universe]] during 13 billion years.<ref>{{Cite web|title = HubbleSite - NewsCenter - Astronomers Set a New Galaxy Distance Record (05/05/2015) - Introduction|url = http://hubblesite.org/newscenter/archive/releases/2015/22/|website = hubblesite.org|accessdate = 2015-05-07}}</ref><ref>{{Cite web|title = This Galaxy Far, Far Away Is the Farthest One Yet Found|url = http://www.space.com/29319-farthest-galaxy-ever-found.html?cmpid=NL_SP_weekly_2015-05-06|accessdate = 2015-05-07}}</ref><ref name="phys.org">{{Cite web|title = Astronomers unveil the farthest galaxy|url = http://phys.org/news/2015-05-astronomers-unveil-farthest-galaxy.html|accessdate = 2015-05-07}}</ref><ref name="phys.org"/><ref>{{Cite news|title = Astronomers Measure Distance to Farthest Galaxy Yet|url = http://www.nytimes.com/2015/05/06/science/astronomers-measure-distance-to-farthest-galaxy-yet.html|newspaper = The New York Times|date = 2015-05-05|access-date = 2015-05-07|issn = 0362-4331|first = Dennis|last = Overbye}}</ref><ref>{{Cite journal|title = A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE|url = http://arxiv.org/abs/1502.05399|journal = arXiv:1502.05399 [astro-ph]|date = 2015-02-18|access-date = 2015-05-07|first = P. A.|last = Oesch|first2 = P. G.|last2 = van Dokkum|first3 = G. D.|last3 = Illingworth|first4 = R. J.|last4 = Bouwens|first5 = I.|last5 = Momcheva|first6 = B.|last6 = Holden|first7 = G. W.|last7 = Roberts-Borsani|first8 = R.|last8 = Smit|first9 = M.|last9 = Franx}}</ref>

====Early galaxy formation====
The detailed process by which early galaxies formed is an open question in astrophysics. Theories can be divided into two categories: top-down and bottom-up. In top-down theories (such as the Eggen–Lynden-Bell–Sandage [ELS] model), protogalaxies form in a large-scale simultaneous collapse lasting about one hundred million years.<ref>
{{cite journal
|last1=Eggen |first1=O. J.
|last2=Lynden-Bell |first2=D.
|last3=Sandage |first3=A. R.
|date=1962
|title=Evidence from the motions of old stars that the Galaxy collapsed
|journal=[[Reports on Progress in Physics]]
|volume=136 |pages=748
|bibcode=1962ApJ...136..748E
|doi=10.1086/147433
}}</ref> In bottom-up theories (such as the Searle-Zinn [SZ] model), small structures such as [[globular cluster]]s form first, and then a number of such bodies accrete to form a larger galaxy.<ref>
{{cite journal
|last1=Searle |first1=L.
|last2=Zinn |first2=R.
|date=1978
|title=Compositions of halo clusters and the formation of the galactic halo
|journal=[[Astrophysical Journal]]
|volume=225 |issue=1 |pages=357–379
|bibcode=1978ApJ...225..357S
|doi=10.1086/156499
}}</ref>

Once protogalaxies began to form and contract, the first [[halo star]]s (called [[Metallicity#Population III stars|Population III stars]]) appeared within them. These were composed almost entirely of hydrogen and helium, and may have been massive. If so, these huge stars would have quickly consumed their supply of fuel and became [[supernova]]e, releasing heavy elements into the [[interstellar medium]].<ref>
{{cite journal
|last1=Heger |first1=A.
|last2=Woosley |first2=S. E.
|date=2002
|title=The Nucleosynthetic Signature of Population III
|journal=[[Astrophysical Journal]]
|volume=567 |issue=1 |pages=532–543
|bibcode=2002ApJ...567..532H
|doi=10.1086/338487
|arxiv = astro-ph/0107037 }}</ref> This first generation of stars re-ionized the surrounding neutral hydrogen, creating expanding bubbles of space through which light could readily travel.<ref>
{{cite journal
|last1=Barkana |first1=R.
|last2=Loeb |first2=A.
|date=1999
|title=In the beginning: the first sources of light and the reionization of the Universe
|journal=[[Physics Reports]]
|volume=349 |issue=2 |pages=125–238
|bibcode=2001PhR...349..125B
| arxiv = astro-ph/0010468
|doi=10.1016/S0370-1573(01)00019-9
}}</ref>

In June 2015, astronomers reported evidence for [[Metallicity#Population III stars|Population III stars]] in the [[Cosmos Redshift 7]] [[galaxy]] at {{math|''z'' {{=}} 6.60}}. Such stars are likely to have existed in the very early universe (i.e., at high redshift), and may have started the production of [[chemical element]]s heavier than [[hydrogen]] that are needed for the later formation of [[planet]]s and [[life]] as we know it.<ref name="AJ-20150604">{{cite journal |last1=Sobral |first1=David |last2=Matthee |first2=Jorryt |last3=Darvish |first3=Behnam |last4=Schaerer |first4=Daniel |last5=Mobasher |first5=Bahram |last6=Röttgering |first6=Huub J. A. |last7=Santos |first7=Sérgio |last8=Hemmati |first8=Shoubaneh |title=Evidence For POPIII-Like Stellar Populations In The Most Luminous LYMAN-α Emitters At The Epoch Of Re-Ionisation: Spectroscopic Confirmation |url=http://arxiv.org/pdf/1504.01734.pdf |format=[[PDF]] |date=4 June 2015 |journal=[[The Astrophysical Journal]] |accessdate=17 June 2015 }}</ref><ref name="NYT-20150617">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Astronomers Report Finding Earliest Stars That Enriched Cosmos |url=http://www.nytimes.com/2015/06/18/science/space/astronomers-report-finding-earliest-stars-that-enriched-cosmos.html |date=17 June 2015 |work=[[New York Times]] |accessdate=17 June 2015 }}</ref>

===Evolution===
Within a billion years of a galaxy's formation, key structures begin to appear. [[Globular cluster]]s, the central supermassive black hole, and a [[bulge (astronomy)|galactic bulge]] of metal-poor [[metallicity|Population II stars]] form. The creation of a supermassive black hole appears to play a key role in actively regulating the growth of galaxies by limiting the total amount of additional matter added.<ref>
{{cite news
|date=February 9, 2005
|title=Simulations Show How Growing Black Holes Regulate Galaxy Formation
|url=http://www.cmu.edu/PR/releases05/050209_blackhole.html
|publisher=[[Carnegie Mellon University]]
|accessdate=January 7, 2007
}}</ref> During this early epoch, galaxies undergo a major burst of star formation.<ref>
{{cite news
|last1=Massey |first1=R.
|date=April 21, 2007
|title=Caught in the act; forming galaxies captured in the young Universe
|url=http://web.archive.org/web/20131115031412/http://www.ras.org.uk/index.php?option=com_content&task=view&id=1190&Itemid=2
|publisher=[[Royal Astronomical Society]]
|accessdate=April 20, 2007
}}</ref>

During the following two billion years, the accumulated matter settles into a [[disc (galaxy)|galactic disc]].<ref>
{{cite journal
|last=Noguchi |first=M.
|date=1999
|title=Early Evolution of Disk Galaxies: Formation of Bulges in Clumpy Young Galactic Disks
|journal=[[Astrophysical Journal]]
|volume=514 |issue=1 |pages=77–95
|bibcode=1999ApJ...514...77N
|doi=10.1086/306932
|arxiv = astro-ph/9806355 }}</ref> A galaxy will continue to absorb infalling material from [[high-velocity cloud]]s and [[dwarf galaxy|dwarf galaxies]] throughout its life.<ref>
{{cite web
|last1=Baugh |first1=C.
|last2=Frenk |first2=C.
|date=May 1999
|url=http://web.archive.org/web/20070426043157/http://physicsweb.org/articles/world/12/5/9
|title=How are galaxies made?
|publisher=[[PhysicsWeb]]
|accessdate=January 16, 2007
}}</ref> This matter is mostly hydrogen and helium. The cycle of stellar birth and death slowly increases the abundance of heavy elements, eventually allowing the [[planetary formation|formation]] of [[planet]]s.<ref>
{{cite conference
|last1=Gonzalez |first1=G.
|date=1998
|title=The Stellar Metallicity — Planet Connection
|work=Proceedings of a workshop on brown dwarfs and extrasolar planets
|pages=431
|bibcode=1998bdep.conf..431G
}}</ref>
{{Multiple image |direction=vertical |align=right |width=200 |image1=XDF-scale.jpg|image2=Constellation Fornax, EXtreme Deep Field.jpg |image3=XDF-separated.jpg |caption1=''[[Hubble Extreme Deep Field|XDF]]'' view field compared to the [[angular diameter|angular size]] of the [[Moon]]. Several thousand galaxies, each consisting of billions of [[star]]s, are in this small view. |caption2=''[[Hubble Extreme Deep Field|XDF]]'' (2012) view: Each light speck is a galaxy, some of which are as old as 13.2 billion years<ref name="Space-20120925">{{cite web |last=Moskowitz |first=Clara |title=Hubble Telescope Reveals Farthest View Into Universe Ever|url=http://www.space.com/17755-farthest-universe-view-hubble-space-telescope.html|date=September 25, 2012 |publisher=[[Space.com]] |accessdate=September 26, 2012}}</ref> – the [[observable universe]] is estimated to contain 200 billion galaxies. |caption3=''[[Hubble Extreme Deep Field|XDF]]'' image shows (from left) fully mature galaxies, nearly mature galaxies (from 5 to 9 billion years ago), [[Protogalaxy|protogalaxies]], blazing with [[young star]]s (beyond 9 billion years). |header=''[[Hubble Extreme Deep Field|Hubble eXtreme Deep Field (XDF)]]'' }}

The evolution of galaxies can be significantly affected by interactions and collisions. Mergers of galaxies were common during the early epoch, and the majority of galaxies were peculiar in morphology.<ref name="sa296">
{{cite journal
|last1=Conselice |first1=C. J.
|date=February 2007
|title=The Universe's Invisible Hand
|journal=[[Scientific American]]
|volume=296 |issue=2 |pages=35–41
|doi=10.1038/scientificamerican0207-34
}}</ref> Given the distances between the stars, the great majority of stellar systems in colliding galaxies will be unaffected. However, gravitational stripping of the interstellar gas and dust that makes up the spiral arms produces a long train of stars known as tidal tails. Examples of these formations can be seen in [[NGC 4676]]<ref>
{{cite news
|last1=Ford |first1=H.
|display-authors=etal
|date=April 30, 2002
|title=Hubble's New Camera Delivers Breathtaking Views of the Universe
|url=http://hubblesite.org/newscenter/archive/releases/2002/11/image/d
|publisher=Hubble News Desk
|accessdate=May 8, 2007
}}</ref> or the [[Antennae Galaxies]].<ref>
{{cite journal
|last1=Struck |first1=C.
|date=1999
|title=Galaxy Collisions
|doi=10.1016/S0370-1573(99)00030-7
|journal=Physics Reports
|volume=321
|pages=1
|arxiv=astro-ph/9908269
|bibcode = 1999PhR...321....1S }}</ref>

The Milky Way galaxy and the nearby Andromeda Galaxy are moving toward each other at about 130 [[metre per second|km/s]], and—depending upon the lateral movements—the two might collide in about five to six billion years. Although the Milky Way has never collided with a galaxy as large as Andromeda before, evidence of past collisions of the Milky Way with smaller dwarf galaxies is increasing.<ref>
{{cite news
|last1=Wong |first1=J.
|date=April 14, 2000
|title=Astrophysicist maps out our own galaxy's end
|url=http://www.news.utoronto.ca/bin/000414b.asp
|publisher=[[University of Toronto]]
|accessdate=January 11, 2007
|archiveurl=http://web.archive.org/web/20070108183824/http://www.news.utoronto.ca/bin/000414b.asp
|archivedate=January 8, 2007
}}</ref>

Such large-scale interactions are rare. As time passes, mergers of two systems of equal size become less common. Most bright galaxies have remained fundamentally unchanged for the last few billion years, and the net rate of star formation probably also peaked approximately ten billion years ago.<ref>
{{cite journal
|last1=Panter |first1=B.
|last2=Jimenez |first2=R.
|last3=Heavens |first3=A. F.
|last4=Charlot |first4=S.
|date=2007
|title=The star formation histories of galaxies in the Sloan Digital Sky Survey
|journal=[[Monthly Notices of the Royal Astronomical Society]]
|volume=378 |issue=4 |pages=1550–1564
|arxiv=astro-ph/0608531
|doi=10.1111/j.1365-2966.2007.11909.x |bibcode=2007MNRAS.378.1550P
}}</ref>

===Future trends===
Spiral galaxies, like the Milky Way, produce new generations of stars as long as they have dense [[molecular cloud]]s of interstellar hydrogen in their spiral arms.<ref>
{{cite journal
|last1=Kennicutt Jr. |first1=R. C.
|last2=Tamblyn |first2=P.
|last3=Congdon |first3=C. E.
|date=1994
|title=Past and future star formation in disk galaxies
|journal=[[Astrophysical Journal]]
|volume=435 |issue=1 |pages=22–36
|bibcode=1994ApJ...435...22K
|doi=10.1086/174790
}}</ref> Elliptical galaxies are largely devoid of this gas, and so form few new stars.<ref>
{{cite book
|last1=Knapp |first1=G. R.
|date=1999
|title=Star Formation in Early Type Galaxies
|publisher=[[Astronomical Society of the Pacific]]
|bibcode=1998astro.ph..8266K
|oclc=41302839
|isbn=1-886733-84-8
}}</ref> The supply of star-forming material is finite; once stars have converted the available supply of hydrogen into heavier elements, new star formation will come to an end.<ref name="cosmic_battle">
{{cite web
|last1=Adams |first1=Fred
|last2=Laughlin |first2=Greg
|date=July 13, 2006
|title=The Great Cosmic Battle
|url=http://www.astrosociety.org/pubs/mercury/0001/cosmic.html
|publisher=[[Astronomical Society of the Pacific]]
|accessdate=January 16, 2007
}}</ref><ref>{{Cite web|title = Cosmic 'Murder Mystery' Solved: Galaxies Are 'Strangled to Death'|url = http://www.space.com/29398-galaxy-strangulation-death-mystery.html?cmpid=NL_SP_weekly_2015-05-13|accessdate = 2015-05-14}}</ref>

The current era of star formation is expected to continue for up to one hundred billion years, and then the "stellar age" will wind down after about ten trillion to one hundred trillion years (1013–1014 years), as the smallest, longest-lived stars in our universe, tiny [[red dwarf]]s, begin to fade. At the end of the stellar age, galaxies will be composed of [[compact star|compact objects]]: [[brown dwarf]]s, [[white dwarf]]s that are cooling or cold ("[[black dwarf]]s"), [[neutron star]]s, and [[black hole]]s. Eventually, as a result of [[relaxation time|gravitational relaxation]], all stars will either fall into central supermassive black holes or be flung into intergalactic space as a result of collisions.<ref name="cosmic_battle" /><ref>
{{cite web
|last1=Pobojewski |first1=S.
|date=January 21, 1997
|title=Physics offers glimpse into the dark side of the Universe
|url=http://www.umich.edu/~urecord/9697/Jan21_97/artcl17.htm
|publisher=[[University of Michigan]]
|accessdate=January 13, 2007
}}</ref>

==Larger-scale structures==
{{Main|Observable universe#Large-scale structure|Galaxy filament|Galaxy groups and clusters}}
Deep sky surveys show that galaxies are often found in groups and [[Clusters of galaxies|clusters]]. Solitary galaxies that have not significantly interacted with another galaxy of comparable mass during the past billion years are relatively scarce. Only about 5% of the galaxies surveyed have been found to be truly isolated; however, these isolated formations may have interacted and even merged with other galaxies in the past, and may still be orbited by smaller, satellite galaxies. Isolated galaxies<ref group=note>The term "field galaxy" is sometimes used to mean an isolated galaxy, although the same term is also used to describe galaxies that do not belong to a cluster but may be a member of a group of galaxies.</ref> can produce stars at a higher rate than normal, as their gas is not being stripped by other nearby galaxies.<ref>
{{cite web
|last1=McKee |first1=M.
|date=June 7, 2005
|title=Galactic loners produce more stars
|url=http://www.newscientist.com/article.ns?id=dn7478
|publisher=[[New Scientist]]
|accessdate=January 15, 2007
}}</ref>

On the largest scale, the Universe is continually expanding, resulting in an average increase in the separation between individual galaxies (see [[Hubble's law]]). Associations of galaxies can overcome this expansion on a local scale through their mutual gravitational attraction. These associations formed early in the Universe, as clumps of dark matter pulled their respective galaxies together. Nearby groups later merged to form larger-scale clusters. This on-going merger process (as well as an influx of infalling gas) heats the inter-galactic gas within a cluster to very high temperatures, reaching 30–100 [[megakelvin]]s.<ref>
{{cite web
|url=http://chandra.harvard.edu/xray_sources/galaxy_clusters.html
|title=Groups & Clusters of Galaxies
|publisher=[[NASA]]/[[Chandra]]
|accessdate=January 15, 2007
}}</ref> About 70–80% of the mass in a cluster is in the form of dark matter, with 10–30% consisting of this heated gas and the remaining few percent of the matter in the form of galaxies.<ref>
{{cite web
|last1=Ricker |first1=P.
|title=When Galaxy Clusters Collide
|url=http://www.sdsc.edu/pub/envision/v15.2/ricker.html
|publisher=[[San Diego Supercomputer Center]]
|accessdate=August 27, 2008
}}</ref>
{{multiple image
| align = right
| direction = vertical
| width = 230
| image1 = Seyfert Sextet full.jpg
| width1 =
| alt1 =
| caption1 = [[Seyfert's Sextet]] is an example of a compact galaxy group.
| image2 =
| width2 =
| alt2 =
| caption2 = [[Millennium Simulation]] showing large-scale structure of the Cosmos. The image spans about 400 million light years across.
}}
Most galaxies in the Universe are gravitationally bound to a number of other galaxies. These form a [[fractal]]-like hierarchical distribution of clustered structures, with the smallest such associations being termed groups. A group of galaxies is the most common type of galactic cluster, and these formations contain a majority of the galaxies (as well as most of the [[baryon]]ic mass) in the Universe.<ref>
{{cite web
|last1=Dahlem |first1=M.
|date=November 24, 2006
|title=Optical and radio survey of Southern Compact Groups of galaxies
|url=http://www.atnf.csiro.au/people/mdahlem/sci/SCGs.html
|publisher=[[University of Birmingham]] Astrophysics and Space Research Group
|accessdate=January 15, 2007
|archiveurl=http://web.archive.org/web/20070613151936/http://www.atnf.csiro.au/people/mdahlem/sci/SCGs.html
|archivedate=June 13, 2007
}}</ref><ref>
{{cite web
|last1=Ponman |first1=T.
|date=February 25, 2005
|title=Galaxy Systems: Groups
|url=http://web.archive.org/web/20090215023446/http://www.sr.bham.ac.uk/research/groups.html
|publisher=[[University of Birmingham]] Astrophysics and Space Research Group
|accessdate=January 15, 2007
}}</ref> To remain gravitationally bound to such a group, each member galaxy must have a sufficiently low velocity to prevent it from escaping (see [[Virial theorem]]). If there is insufficient [[kinetic energy]], however, the group may evolve into a smaller number of galaxies through mergers.<ref>
{{cite journal
|last1=Girardi |first1=M.
|last2=Giuricin |first2=G.
|date=2000
|title=The Observational Mass Function of Loose Galaxy Groups
|journal=[[The Astrophysical Journal]]
|volume=540 |issue=1 |pages=45–56
|bibcode=2000ApJ...540...45G
|doi=10.1086/309314
|arxiv = astro-ph/0004149 }}</ref>

Clusters of galaxies consist of hundreds to thousands of galaxies bound together by gravity.<ref name="Hubble protocluster">{{cite news|title=Hubble Pinpoints Furthest Protocluster of Galaxies Ever Seen|url=http://www.spacetelescope.org/news/heic1201/|accessdate=January 22, 2015|newspaper=ESA/Hubble Press Release}}</ref> Clusters of galaxies are often dominated by a single giant elliptical galaxy, known as the [[brightest cluster galaxy]], which, over time, [[tidal force|tidally]] destroys its satellite galaxies and adds their mass to its own.<ref>
{{cite journal
|last=Dubinski |first=J.
|date=1998
|title=The Origin of the Brightest Cluster Galaxies
|url=http://www.cita.utoronto.ca/~dubinski/bcg/
|journal=[[Astrophysical Journal]]
|volume=502 |issue=2 |pages=141–149
|doi=10.1086/305901
|bibcode=1998ApJ...502..141D
|arxiv = astro-ph/9709102 }}</ref>

[[Supercluster]]s contain tens of thousands of galaxies, which are found in clusters, groups and sometimes individually. At the [[large-scale structure of the Cosmos|supercluster scale]], galaxies are arranged into sheets and filaments surrounding vast empty voids.<ref>
{{cite journal
|last1=Bahcall |first1=N. A.
|date=1988
|title=Large-scale structure in the Universe indicated by galaxy clusters
|journal=[[Annual Review of Astronomy and Astrophysics]]
|volume=26
|issue=1 |pages=631–686
|bibcode=1988ARA&A..26..631B
|doi=10.1146/annurev.aa.26.090188.003215
}}</ref> Above this scale, the Universe appears to be the same in all directions ([[isotropy|isotropic]] and [[wikt:Homogeneity|homogeneous]]).<ref>
{{cite journal
|last1=Mandolesi |first1=N.
|display-authors=etal
|date=1986
|title=Large-scale homogeneity of the Universe measured by the microwave background
|journal=[[Letters to Nature]]
|volume=319
|issue=6056 |pages=751–753
|doi=10.1038/319751a0
|bibcode = 1986Natur.319..751M }}</ref>

The Milky Way galaxy is a member of an association named the [[Local Group]], a relatively small group of galaxies that has a diameter of approximately one megaparsec. The Milky Way and the Andromeda Galaxy are the two brightest galaxies within the group; many of the other member galaxies are dwarf companions of these two galaxies.<ref>
{{cite journal
|last1=van den Bergh |first1=S.
|date=2000
|title=Updated Information on the Local Group
|journal=Publications of the Astronomical Society of the Pacific
|volume=112 |issue=770 |pages=529–536
|bibcode=2000PASP..112..529V
|doi=10.1086/316548
|arxiv = astro-ph/0001040 }}</ref> The Local Group itself is a part of a cloud-like structure within the [[Virgo Supercluster]], a large, extended structure of groups and clusters of galaxies centered on the [[Virgo Cluster]].<ref name="tully1982">
{{cite journal
|last1=Tully |first1=R. B.
|date=1982
|title=The Local Supercluster
|journal=[[Astrophysical Journal]]
|volume=257 |pages=389–422
|bibcode=1982ApJ...257..389T
|doi=10.1086/159999
}}</ref> And the Virgo Supercluster itself is a part of the [[Pisces-Cetus Supercluster Complex]], a giant [[galaxy filament]].

==Multi-wavelength observation==
{{See also|Observational astronomy}}
{{multiple image
| align = right
| direction = vertical
| width = 220
| image1 =
| caption1 = A visual light image of [[Andromeda Galaxy]] shows the emission of ordinary stars and the light reflected by dust.
| image2 = Andromeda galaxy.jpg
| caption2 = This ultraviolet image of [[Andromeda Galaxy|Andromeda]] shows blue regions containing young, massive stars.
}}
The peak radiation of most stars lies in the [[visible spectrum]], so the observation of the stars that form galaxies has been a major component of [[optical astronomy]]. It is also a favorable portion of the spectrum for observing ionized [[H II region]]s, and for examining the distribution of dusty arms.

The [[cosmic dust|dust]] present in the interstellar medium is opaque to visual light. It is more transparent to [[far infrared astronomy|far-infrared]], which can be used to observe the interior regions of giant molecular clouds and [[Bulge (astronomy)|galactic cores]] in great detail.<ref>
{{cite web
|title=Near, Mid & Far Infrared
|url=http://www.ipac.caltech.edu/Outreach/Edu/Regions/irregions.html
|publisher=[[Infrared Processing and Analysis Center|IPAC]]/[[NASA]]
|accessdate=January 2, 2007
}}</ref> Infrared is also used to observe distant, [[redshift|red-shifted]] galaxies that were formed much earlier in the history of the Universe. Water vapor and [[carbon dioxide]] absorb a number of useful portions of the infrared spectrum, so high-altitude or space-based telescopes are used for [[infrared astronomy]].

The first non-visual study of galaxies, particularly active galaxies, was made using [[radio astronomy|radio frequencies]]. The atmosphere is nearly transparent to radio between 5 [[Hertz|MHz]] and 30 GHz. (The [[ionosphere]] blocks signals below this range.)<ref>
{{cite web
|title=The Effects of Earth's Upper Atmosphere on Radio Signals
|url=http://radiojove.gsfc.nasa.gov/education/educ/radio/tran-rec/exerc/iono.htm
|publisher=[[NASA]]
|accessdate=August 10, 2006
}}</ref> Large radio [[interferometry|interferometers]] have been used to map the active jets emitted from active nuclei. [[Radio telescope]]s can also be used to observe neutral hydrogen (''via'' [[hydrogen line|21 cm radiation]]), including, potentially, the non-ionized matter in the early Universe that later collapsed to form galaxies.<ref>
{{cite news
|title=Giant Radio Telescope Imaging Could Make Dark Matter Visible
|url=http://www.sciencedaily.com/releases/2006/12/061214135537.htm
|publisher=[[ScienceDaily]]
|date=December 14, 2006
|accessdate=January 2, 2007
}}</ref>

[[UV astronomy|Ultraviolet]] and [[X-ray astronomy|X-ray telescopes]] can observe highly energetic galactic phenomena. An ultraviolet flare was observed when a star in a distant galaxy was torn apart from the tidal forces of a black hole.<ref>
{{cite news
|title=NASA Telescope Sees Black Hole Munch on a Star
|url=http://www.nasa.gov/mission_pages/galex/galex-20061205.html
|publisher=[[NASA]]
|date=December 5, 2006
|accessdate=January 2, 2007
}}</ref> The distribution of hot gas in galactic clusters can be mapped by X-rays. The existence of supermassive black holes at the cores of galaxies was confirmed through X-ray astronomy.<ref>
{{cite web
|last1=Dunn |first1=R.
|title=An Introduction to X-ray Astronomy
|url=http://www-xray.ast.cam.ac.uk/xray_introduction/
|publisher=[[Institute of Astronomy, Cambridge|Institute of Astronomy]] X-Ray Group
|accessdate=January 2, 2007
}}</ref>

==See also==
{{Wikipedia books|Galaxies}}
{{colbegin|2}}
* [[Dark galaxy]]
* [[Galactic orientation]]
* [[Galaxy formation and evolution]]
* [[Illustris project]]
* [[List of galaxies]]
* [[List of nearest galaxies]]
* [[Luminous infrared galaxy]]
* [[Supermassive black hole]]
* [[Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure]]
{{colend}}
{{Portal bar|Astronomy|Space|Cosmology}}

==Notes==
{{reflist|group=note}}

==References==
{{Reflist|colwidth=30em|refs=
<ref name="sparkegallagher2000">{{harvnb|Sparke|Gallagher III|2000|p=i}}</ref>

<ref name="heidarzadeh23">{{harvnb|Heidarzadeh|2008|pp=23–25}}</ref>

<ref name="heidarzadeh25">{{harvnb|Heidarzadeh|2008|p=25, Table 2.1}}</ref>

<ref name=paul1993>{{harvnb|Paul|1993|pp=16–18}}</ref>

<ref name=al_biruni>{{harvnb|Al-Biruni|2004|p=87}}</ref>

<ref name=mohamed>{{harvnb|Mohamed|2000|pp=49–50}}</ref>

<ref name="NSOG">{{harvnb|Kepple|Sanner|1998|p=18}}</ref>

<ref name=bergh1998>{{harvnb|Van den Bergh|1998|p=17}}</ref>

<ref name=waller_hodge2003>{{harvnb|Waller|Hodge|2003|p=91}}</ref>

<ref name=bertin_lin1996>{{harvnb|Bertin|Lin|1996|pp=65–85}}</ref>

<ref name=belkora355>{{harvnb|Belkora|2003|p=355}}</ref>

<ref name=nasa060812>
{{cite web
|last1=Hupp |first1=E.
|last2=Roy |first2=S.
|last3=Watzke |first3=M.
|date=August 12, 2006
|title=NASA Finds Direct Proof of Dark Matter
|url=http://www.nasa.gov/home/hqnews/2006/aug/HQ_06297_CHANDRA_Dark_Matter.html
|publisher=[[NASA]]
|accessdate=April 17, 2007
}}</ref>

<ref name=science250_4980_539>
{{cite journal
|last1=Uson |first1=J. M.
|last2=Boughn |first2=S. P.
|last3=Kuhn |first3=J. R.
|date=1990
|title=The central galaxy in Abell 2029 – An old supergiant
|journal=[[Science (journal)|Science]]
|volume=250 |issue=4980 |pages=539–540
|bibcode=1990Sci...250..539U
|doi=10.1126/science.250.4980.539
}}</ref>

<ref name=uf030616>
{{cite news
|last1=Hoover |first1=A.
|date=June 16, 2003
|title=UF Astronomers: Universe Slightly Simpler Than Expected
|url=http://news.ufl.edu/2003/06/16/galaxies/
|publisher=Hubble News Desk
|accessdate=March 4, 2011
}} Based upon:
*{{Cite journal
|last1=Graham |first1=A. W.
|last2=Guzman |first2=R.
|date=2003
|title=HST Photometry of Dwarf Elliptical Galaxies in Coma, and an Explanation for the Alleged Structural Dichotomy between Dwarf and Bright Elliptical Galaxies
|journal=[[Astronomical Journal]]
|volume=125 |issue=6 |pages=2936–2950
|bibcode=2003AJ....125.2936G
|doi=10.1086/374992
|arxiv = astro-ph/0303391 }}</ref>

<ref name="IRatlas">
{{cite web
|last1=Jarrett |first1=T. H.
|title=Near-Infrared Galaxy Morphology Atlas
|url=http://www.ipac.caltech.edu/2mass/gallery/galmorph/
|publisher=[[California Institute of Technology]]
|accessdate=January 9, 2007
}}</ref>

<ref name=camb_lss>
{{cite web
|title=Galaxy Clusters and Large-Scale Structure
|url=http://www.damtp.cam.ac.uk/user/gr/public/gal_lss.html
|publisher=[[University of Cambridge]]
|accessdate=January 15, 2007
}}</ref>

<ref name="smbh">
{{cite web
|last1=Finley |first1=D.
|last2=Aguilar |first2=D.
|date=November 2, 2005
|title=Astronomers Get Closest Look Yet At Milky Way's Mysterious Core
|url=http://www.nrao.edu/pr/2005/sagastar/
|publisher=[[National Radio Astronomy Observatory]]
|accessdate=August 10, 2006
}}</ref>

<ref name="apj624_2">
{{cite journal
|last1=Gott III |first1=J. R.
|year=2005
|display-authors=etal
|title=A Map of the Universe
|journal=[[Astrophysical Journal]]
|volume=624 |issue=2 |pages=463–484
|bibcode=2005ApJ...624..463G
|doi=10.1086/428890
|arxiv = astro-ph/0310571 }}</ref>

<ref name=rmaa17_107>
{{cite journal
|last1=Firmani |first1=C.
|last2=Avila-Reese |first2=V.
|date=2003
|title=Physical processes behind the morphological Hubble sequence
|journal=Revista Mexicana de Astronomía y Astrofísica
|volume=17 |pages=107–120
|bibcode=2003RMxAC..17..107F
|arxiv = astro-ph/0303543
}}</ref>

<ref name=konean2006>
{{cite web
|last1=Koneãn˘ |first1=Lubomír
|url=http://www.udu.cas.cz/collegium/tintoretto.pdf
|title=Emblematics, Agriculture, and Mythography in The Origin of the Milky Way
|publisher=[[Academy of Sciences of the Czech Republic]]
|accessdate=January 5, 2007
|archiveurl=http://web.archive.org/web/20060720204104/http://www.udu.cas.cz/collegium/tintoretto.pdf
|archivedate=July 20, 2006
}}</ref>

<ref name=oed>
{{cite web
|last1=Harper |first1=D.
|url=http://www.etymonline.com/index.php?term=galaxy
|title=galaxy|work=[[Online Etymology Dictionary]]
|accessdate=November 11, 2011
}}</ref>

<ref name=rao2005>
{{cite web
|last1=Rao |first1=J.
|date=September 2, 2005
|title=Explore the Archer's Realm
|url=http://www.space.com/spacewatch/050902_teapot.html
|publisher=[[Space.com]]
|accessdate=January 3, 2007
}}</ref>


}} 

=== Other references ===
* {{cite web
|date=May 3, 2000
|title=Unveiling the Secret of a Virgo Dwarf Galaxy
|url=http://web.archive.org/web/20090109032310/http://www.eso.org/outreach/press-rel/pr-2000/pr-12-00.html
|publisher=[[ESO]]
|accessdate=January 3, 2007
}}

==Bibliography==
{{refbegin}}
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|last=Al-Biruni
|others=R. Ramsay Wright (transl.)
|date=2004
|title=The Book of Instruction in the Elements of the Art of Astrology
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}}
*{{Cite book |ref=harv
|last1=Belkora |first1=L.
|date=2003
|title=Minding the Heavens: the Story of our Discovery of the Milky Way
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|isbn=0-7503-0730-7
}}
*{{Cite book |ref=harv
|last1=Bertin |first1=G.
|last2=Lin |first2=C.-C.
|date=1996
|title=Spiral Structure in Galaxies: a Density Wave Theory
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}}
*{{Cite book
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|date=1998
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|oclc=39108765
}}
*{{Cite book
|last1=Dickinson |first1=T.
|date=2004
|title=The Universe and Beyond
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*{{Cite book |ref=harv
|last1=Heidarzadeh |first1=T.
|date=2008
|title=A History of Physical Theories of Comets, from Aristotle to Whipple
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}}
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}}
{{refend}}

==External links==
{{Sister project links|wikt=galaxy|common=Category:Galaxies|q=no|v=no|s=no|b=High School Earth Science/Galaxies}}
* {{In Our Time|Galaxies|p003c1cn|Galaxies}}
* [http://messier.seds.org/galaxy.html Galaxies, SEDS Messier pages]
* [http://www.atlasoftheuniverse.com/ An Atlas of The Universe]
* [http://www.nightskyinfo.com/galaxies Galaxies — Information and amateur observations]
* [http://science.nasa.gov/headlines/y2002/08feb_gravlens.htm The Oldest Galaxy Yet Found]
* [http://www.galaxyzoo.org Galaxy classification project, harnessing the power of the internet and the human brain]
* [http://www.physics.org/facts/sand-galaxies.asp How many galaxies are in our Universe?]
* [http://www.astronoo.com/en/galaxies.html The most beautiful galaxies on Astronoo]
* [http://www.youtube.com/watch?v=08LBltePDZw 3-D Video (01:46) – Over a Million Galaxies of Billions of Stars each – BerkeleyLab/animated.]

{{Galaxy}}

{{Featured article}}

{{Authority control}}
[[Category:Galaxies| ]]

User:WikipediaTutorials/sandbox

2015-08-18T18:24:12Z

WikipediaTutorials:

{{About|the astronomical structure|other uses}}
{{Use mdy dates|date=February 2015}}
{{Multiple image |direction=vertical |align=right |width=310|image1=NGC 4414 (NASA-med).jpg|caption1=[[NGC 4414]], a typical spiral galaxy in the [[constellation]] [[Coma Berenices]], is about 55,000 [[light-year]]s in diameter and approximately 60 million light-years away from Earth|image2=M104_ngc4594_sombrero_galaxy_hi-res.jpg|caption2=The [[Sombrero galaxy]] (M104), a bright nearby spiral galaxy.|image3=Irregular_galaxy_NGC_1427A_(captured_by_the_Hubble_Space_Telescope).jpg|caption3=[[NGC 1427A]], an example of an irregular galaxy, 52 million [[light-year]]s away}}

A '''galaxy''' is a [[gravitation|gravitationally]] bound system of [[star]]s, [[stellar remnant]]s, [[interstellar medium|interstellar gas]] and [[cosmic dust|dust]], and [[dark matter]].<ref name="sparkegallagher2000"/><ref name=nasa060812/> The word galaxy is derived from the [[Ancient Greek|Greek]] ''{{transl|grc|galaxias}}'' ({{lang|grc|γαλαξίας}}), literally "milky", a reference to the [[Milky Way]]. Examples of galaxies range from [[dwarf galaxy|dwarfs]] with just a few thousand (103) stars to giants with one hundred [[Trillion (short scale)|trillion]] (1014) stars,<ref name=science250_4980_539/> each orbiting their galaxy's own [[center of mass]]. Galaxies are categorized according to their visual morphology, including [[elliptical galaxy|elliptical]],<ref name=uf030616/> [[Spiral galaxy|spiral]], and [[irregular galaxy|irregular]].<ref name="IRatlas"/> Many galaxies are believed to have [[black hole]]s at their [[active galactic nucleus|active center]]s. The Milky Way's central black hole, known as [[Sagittarius A*]], has a mass four million times that of our Sun.<ref name="smbh"/> As of May 2015, [[EGS-zs8-1]] is the most distant known galaxy, estimated to be 13.1 billion [[light-year]]s away and to have 15% of the mass of the Milky Way.<ref name="ARX-20150503">{{cite journal |authors=Oesch, P.A. et al. |title=A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE |url=http://arxiv.org/abs/1502.05399 |date=May 3, 2015 |journal=[[ArXiv]] |arxiv=1502.05399 |accessdate=May 6, 2015 |bibcode = 2015arXiv150205399O }}
</ref><ref name=p15>{{cite web |author=Staff |title=Astronomers unveil the farthest galaxy |url=http://phys.org/news/2015-05-astronomers-unveil-farthest-galaxy.html |publisher=[[Phys.org]] |accessdate=May 6, 2015|date=May 5, 2015}}</ref><ref name="NYT-20150505">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Astronomers Measure Distance to Farthest Galaxy Yet |url=http://www.nytimes.com/2015/05/06/science/astronomers-measure-distance-to-farthest-galaxy-yet.html |date=May 5, 2015 |work=[[New York Times]] |accessdate=May 6, 2015 }}</ref><ref name="AP-20150505">{{cite news |last=Borenstein |first=Seth |title=Astronomers find farthest galaxy: 13.1 billion light-years |url=http://apnews.excite.com/article/20150505/us-sci--farthest_galaxy-46c792535a.html |date= May 5, 2015 |work=[[AP News]] |accessdate=May 6, 2015 }}</ref>

Approximately 170 billion ({{nowrap|1.7 × 1011}}) galaxies exist in the [[observable universe]].<ref name="apj624_2"/> Most of the galaxies are 1,000 to 100,000 [[parsec]]s in diameter and usually separated by distances on the order of millions of parsecs (or megaparsecs). The [[intergalactic space|space]] between galaxies is filled with a tenuous gas with an average density less than one [[atom]] per cubic meter. The majority of galaxies are gravitationally organized into associations known as [[galaxy group]]s, [[galaxy cluster|clusters]], and [[supercluster]]s. At the [[Large-scale structure of the Cosmos|largest scale]], these associations are generally arranged into [[galaxy filament|sheets and filaments]] that are surrounded by immense [[void (astronomy)|voids]].<ref name=camb_lss/>

==Etymology==
The word ''galaxy'' derives from the [[Greek language|Greek]] term for our own galaxy, ''{{transl|grc|galaxias}}'' (''{{lang|grc|{{linktext|γαλαξίας}}}}'', "milky one"), or ''{{transl|grc|[[kyklos]] galaktikos}}'' ("milky circle")<ref name=oed/> due to its appearance as a "milky" band of light in the sky. In [[Greek mythology]], [[Zeus]] places his son born by a mortal woman, the infant [[Heracles]], on [[Hera]]'s breast while she is asleep so that the baby will drink her divine milk and will thus become immortal. Hera wakes up while breastfeeding and then realizes she is nursing an unknown baby: she pushes the baby away and a jet of her milk sprays the night sky, producing the faint band of light known as the Milky Way.<ref name=waller_hodge2003/><ref name=konean2006/>

In the astronomical literature, the capitalized word "Galaxy" is often used to refer to our galaxy, the [[Milky Way]], to distinguish it from the other galaxies in our [[universe]]. The English term ''Milky Way'' can be traced back to a story by [[Chaucer]] {{circa|1380}}:
{{Quote|"See yonder, lo, the Galaxyë  Which men {{linktext|clepe}}th ''the Milky Wey'',  For hit is whyt."|Geoffrey Chaucer|[[The House of Fame]]''<ref name=oed/>}}

When [[William Herschel]] assembled [[Catalogue of Nebulae|his catalog]] of deep sky objects in 1786, he used the term ''[[spiral nebula]]'' for certain objects such as [[Andromeda Galaxy|M31]]. These would later be recognized as conglomerations of stars when the true distance to these objects began to be appreciated, and they would later be termed ''island universes.'' However, the word ''Universe'' was understood to mean the entirety of existence, so this expression fell into disuse and the objects instead became known as galaxies.<ref name=rao2005/>

==Nomenclature==
Tens of thousands of galaxies have been catalogued, but only a few have well-established names, such as the [[Andromeda Galaxy]], the [[Magellanic clouds]], the [[Whirlpool Galaxy]] and the [[Sombrero Galaxy]]. Astronomers work with numbers from certain catalogues, such as the [[Messier catalogue]], the NGC ([[New General Catalogue]]), the IC ([[Index Catalogue]]), the CGCG ([[Catalogue of Galaxies and of Clusters of Galaxies]]), the MCG ([[Morphological Catalogue of Galaxies]]) and UGC ([[Uppsala General Catalogue|Uppsala General Catalogue of Galaxies]]). All of the well-known galaxies appear in one or more of these catalogues but each time under a different number.
For example, [[Messier 109]] is a spiral galaxy having the number 109 in the catalogue of Messier, but also codes NGC3992, UGC6937, CGCG 269-023, MCG +09-20-044, and PGC 37617.

Because it is customary in science to assign names to most of the studied objects, even to the smallest ones, the Belgian astrophysicist [[Gerard Bodifee]] and the classicist Michel Berger started a new catalogue ([[Gerard Bodifee#Works|CNG-Catalogue of Named Galaxies]])<ref>{{Cite web|url=http://www.bodifee.be/acms/acmsdata/document/9/184_CNG%20catalogue.pdf|title=CNG-Catalogue of Named Galaxies |author=Bodifée G. & Berger M.|date=2010|accessdate=January 17, 2014}}</ref> in which a thousand well-known galaxies are given meaningful, descriptive names in Latin (or Latinized Greek)<ref>{{cite web |title=Contemporary Latin |url=http://www.isnare.com/encyclopedia/Contemporary_Latin#In_science |accessdate= January 22, 2014}}</ref> in accordance with the binomial nomenclature that one uses in other sciences such as biology, anatomy, [[paleontology]] and in other fields of astronomy such as the geography of Mars.
One of the arguments to do so is that these impressive objects deserve better than uninspired codes. For instance, Bodifee and Berger propose the informal, descriptive name ''{{lang|la|Callimorphus Ursae Majoris}}'' for the well-formed barred galaxy Messier 109 in Ursa Major.

==Observation history==
The realization that we live in a galaxy, and that ours is one among many, parallels major discoveries that were made about the Milky Way and other [[nebula]]e in the night sky.

===Milky Way===
{{Main|Milky Way}}
The [[Greek philosophy|Greek]] philosopher [[Democritus]] (450–370 BC) proposed that the bright band on the night sky known as the Milky Way might consist of distant stars.<ref name="Plutarch">{{cite book | title=The Complete Works Volume 3: Essays and Miscellanies | publisher=Echo Library | author=Plutarch | authorlink=Plutarch | date=2006 | location=Chapter 3 | pages=66 | isbn=978-1-4068-3224-2}}</ref>
[[Aristotle]] (384–322 BC), however, believed the Milky Way to be caused by "the ignition of the fiery exhalation of some stars that were large, numerous and close together" and that the "ignition takes place in the upper part of the [[atmosphere]], in the [[Sublunary sphere|region of the World that is continuous with the heavenly motions]]."<ref name=Montada>
{{cite web
| last1=Montada |first1=J. P.
| date=September 28, 2007
| title=Ibn Bajja
| work=[[Stanford Encyclopedia of Philosophy]]
| url=http://plato.stanford.edu/entries/ibn-bajja
| accessdate=July 11, 2008
}}</ref> The [[Neoplatonism|Neoplatonist]] philosopher [[Olympiodorus the Younger]] ({{circa|495}}–570 AD) was critical of this view, arguing that if the Milky Way is [[sublunary]] (situated between Earth and the Moon) it should appear different at different times and places on Earth, and that it should have [[parallax]], which it does not. In his view, the Milky Way is celestial.<ref name=heidarzadeh23/>

According to Mohani Mohamed, the [[Islamic astronomy|Arabian]] astronomer [[Alhazen]] (965–1037) made the first attempt at observing and measuring the Milky Way's parallax,<ref name=mohamed/> and he thus "determined that because the Milky Way had no parallax, it must be remote from the Earth, not belonging to the atmosphere."<ref>
{{cite web
| last1=Bouali |first1=H.-E.
| last2=Zghal |first2=M.
| last3=Lakhdar |first3=Z. B.
| date=2005
| title=Popularisation of Optical Phenomena: Establishing the First Ibn Al-Haytham Workshop on Photography
| publisher=The Education and Training in Optics and Photonics Conference
| url=http://spie.org/etop/ETOP2005_080.pdf
| accessdate=July 8, 2008
}}</ref> The [[Persian people|Persian]] astronomer [[al-Bīrūnī]] (973–1048) proposed the Milky Way galaxy to be "a collection of countless fragments of the nature of nebulous stars."<ref>{{MacTutor Biography|id=Al-Biruni|title=Abu Rayhan Muhammad ibn Ahmad al-Biruni}}</ref><ref name=al_biruni/> The [[Al-Andalus|Andalusian]] astronomer [[Ibn Bajjah]] ("Avempace", {{abbr|d.|died}} 1138) proposed that the Milky Way is made up of many stars that almost touch one another and appear to be a continuous image due to the effect of [[refraction]] from sublunary material,<ref name=Montada/><ref name="heidarzadeh25"/> citing his observation of the [[Conjunction (astronomy and astrology)|conjunction]] of Jupiter and Mars as evidence of this occurring when two objects are near.<ref name=Montada/> In the 14th century, the Syrian-born [[Ibn Qayyim]] proposed the Milky Way galaxy to be "a myriad of tiny stars packed together in the sphere of the fixed stars."<ref name=Livingston>
{{cite journal
|last1=Livingston |first1=J. W.
|date=1971
|title=Ibn Qayyim al-Jawziyyah: A Fourteenth Century Defense against Astrological Divination and Alchemical Transmutation
|journal=[[Journal of the American Oriental Society]]
|volume=91 |issue=1 |pages=96–103 [99]
|doi=10.2307/600445
|jstor=600445
}}</ref>
[[File:Herschel-Galaxy.png|thumb|The shape of the Milky Way as estimated from star counts by [[William Herschel]] in 1785; the solar system was assumed to be near the center.]]
Actual proof of the Milky Way consisting of many stars came in 1610 when the Italian astronomer [[Galileo Galilei]] used a [[optical telescope|telescope]] to study the Milky Way and discovered that it is composed of a huge number of faint stars.<ref>Galileo Galilei, ''Sidereus Nuncius'' (Venice, (Italy): Thomas Baglioni, 1610), [https://archive.org/stream/Sidereusnuncius00Gali#page/n37/mode/2up pages 15 and 16.] 
English translation: Galileo Galilei with Edward Stafford Carlos, trans., ''The Sidereal Messenger'' (London, England: Rivingtons, 1880), [https://archive.org/stream/siderealmessenge80gali#page/42/mode/2up/ pages 42 and 43.]</ref><ref>
{{cite web
|last1=O'Connor |first1=J. J.
|last2=Robertson |first2=E. F.
|date=November 2002
|title=Galileo Galilei
|url=http://www-gap.dcs.st-and.ac.uk/~history/Biographies/Galileo.html
|publisher=[[University of St. Andrews]]
|accessdate=January 8, 2007
}}</ref> In 1750 the English astronomer [[Thomas Wright (astronomer)|Thomas Wright]], in his ''An original theory or new hypothesis of the Universe'', speculated (correctly) that the galaxy might be a rotating body of a huge number of stars held together by [[gravitation|gravitational forces]], akin to the solar system but on a much larger scale. The resulting disk of stars can be seen as a band on the sky from our perspective inside the disk.<ref>Thomas Wright, ''An Original Theory or New Hypothesis of the Universe'' … (London, England: H. Chapelle, 1750). [http://books.google.com/books?id=80VZAAAAcAAJ&pg=PA48#v=onepage&q&f=false From p.48:] " … the stars are not infinitely dispersed and distributed in a promiscuous manner throughout all the mundane space, without order or design, … this phænomenon [is] no other than a certain effect arising from the observer's situation, … To a spectator placed in an indefinite space, … it [i.e., the Milky Way (''Via Lactea'')] [is] a vast ring of stars … " 
[http://books.google.com/books?id=80VZAAAAcAAJ&pg=PA73#v=onepage&q&f=false On page 73], Wright called the Milky Way the ''Vortex Magnus'' (the great whirlpool) and estimated its diameter at 8.64×1012 miles (13.9×1012 km).</ref><ref name="our_galaxy"/> In a treatise in 1755, [[Immanuel Kant]] elaborated on Wright's idea about the structure of the Milky Way.<ref>Immanuel Kant, [http://books.google.com/books?id=nCcaAQAAMAAJ&pg=PP9#v=onepage&q&f=false ''Allgemeine Naturgeschichte und Theorie des Himmels'' …] [Universal Natural History and Theory of the Heavens … ], (Koenigsberg and Leipzig, (Germany): Johann Friederich Petersen, 1755). Available in English translation by Ian Johnston at: [http://records.viu.ca/~johnstoi/kant/kant2e.htm Vancouver Island University, British Columbia, Canada]</ref>

The first project to describe the shape of the Milky Way and the position of the [[Sun]] was undertaken by [[William Herschel]] in 1785 by counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with [[Galactocentrism|the solar system close to the center]].<ref>William Herschel (1785) "On the Construction of the Heavens," ''Philosophical Transactions of the Royal Society of London'', '''75''' : 213-266. Herschel's diagram of the galaxy appears immediately after the article's last page. See:
* [http://books.google.com/books?id=IU9FAAAAcAAJ&pg=PA213#v=onepage&q&f=false Google Books]
* [http://rstl.royalsocietypublishing.org/content/75/213.full.pdf+html The Royal Society of London]</ref><ref name=paul1993/> Using a refined approach, [[Jacobus Kapteyn|Kapteyn]] in 1920 arrived at the picture of a small (diameter about 15 kiloparsecs) ellipsoid galaxy with the Sun close to the center. A different method by [[Harlow Shapley]] based on the cataloguing of [[globular cluster]]s led to a radically different picture: a flat disk with diameter approximately 70 kiloparsecs and the Sun far from the center.<ref name="our_galaxy" /> Both analyses failed to take into account the [[extinction (astronomy)|absorption of light]] by [[cosmic dust|interstellar dust]] present in the [[galactic plane]], but after [[Robert Julius Trumpler]] quantified this effect in 1930 by studying [[open cluster]]s, the present picture of our host galaxy, the Milky Way, emerged.<ref>
{{cite journal
|last1=Trimble |first1=V.
|date=1999
|title=Robert Trumpler and the (Non)transparency of Space
|journal=[[Bulletin of the American Astronomical Society]]
|volume=31 |issue=31 |pages=1479
|bibcode=1999AAS...195.7409T
}}</ref>

[[File:Milky Way Arch.jpg|thumb|center|600px|A [[Fisheye lens|fish-eye]] mosaic of the Milky Way arching at a high inclination across the night sky, shot from a dark-sky location in Chile]]

===Distinction from other nebulae===

A few galaxies outside the Milky Way are visible in the night sky to the unaided eye. In the 10th century, the Persian astronomer [[Al-Sufi]] made the earliest recorded identification of the [[Andromeda Galaxy]], describing it as a "small cloud".<ref name="NSOG"/> In 964, Al-Sufi identified the [[Large Magellanic Cloud]] in his ''[[Book of Fixed Stars]]''; it was not seen by Europeans until [[Ferdinand Magellan|Magellan]]'s voyage in the 16th century.<ref name="obspm">
{{cite web
|title=Abd-al-Rahman Al Sufi (December 7, 903 – May 25, 986 A.D.)
|url=http://messier.obspm.fr/xtra/Bios/alsufi.html
|publisher=[[Observatoire de Paris]]
|accessdate=April 19, 2007
}}</ref><ref name="obspm2">
{{cite web
|title=The Large Magellanic Cloud, LMC
|url=http://messier.obspm.fr/xtra/ngc/lmc.html
|publisher=[[Observatoire de Paris]]
|accessdate=April 19, 2007
}}</ref> The Andromeda Galaxy was independently noted by [[Simon Marius]] in 1612.<ref name="NSOG"/>

In 1750, [[Thomas Wright (astronomer)|Thomas Wright]] speculated (correctly) that the Milky Way is a flattened disk of stars, and that some of the [[nebula]]e visible in the night sky might be separate Milky Ways.<ref name="our_galaxy">
{{cite web
|last1=Evans |first1=J. C.
|date=November 24, 1998
|title=Our Galaxy
|url=http://physics.gmu.edu/~jevans/astr103/CourseNotes/ECText/ch20_txt.htm
|publisher=[[George Mason University]]
|accessdate=January 4, 2007
}}</ref><ref>See text quoted from Wright's ''An original theory or new hypothesis of the Universe'' in {{Cite book
|last1=Dyson |first1=F.
|date=1979
|title=Disturbing the Universe
|page=245
|publisher=[[Pan Books]]
|isbn=0-330-26324-2
}}</ref> In 1755, [[Immanuel Kant]] used the term "island Universe" to describe these distant nebulae.
[[File:Pic iroberts1.jpg|thumb|right|Photograph of the "Great Andromeda Nebula" from 1899, later identified as the [[Andromeda Galaxy]]]]
Toward the end of the 18th century, [[Charles Messier]] compiled a [[Messier object|catalog]] containing the 109 brightest celestial objects having nebulous appearance. Subsequently, William Herschel assembled a catalog of 5,000 nebulae.<ref name="our_galaxy" /> In 1845, [[William Parsons, 3rd Earl of Rosse|Lord Rosse]] constructed a new telescope and was able to distinguish between elliptical and spiral nebulae. He also managed to make out individual point sources in some of these nebulae, lending credence to Kant's earlier conjecture.<ref>[http://parsonstown.info/people/william-rosse "Parsonstown | The genius of the Parsons family | William Rosse"]. ''parsonstown.info''.</ref>

In 1912, [[Vesto Slipher]] made spectrographic studies of the brightest spiral nebulae to determine their composition. Slipher discovered that the spiral nebulae have high [[Doppler shift]]s, indicating that they are moving at a rate exceeding the velocity of the stars he had measured. He found that the majority of these nebulae are moving away from us.<ref>
{{cite journal
|last1=Slipher |first1=V. M.
|date=1913
|title=The radial velocity of the Andromeda Nebula
|journal=Lowell Observatory Bulletin
|volume=1 |pages=56–57
|bibcode=1913LowOB...2...56S
}}</ref><ref>
{{cite journal
|last1=Slipher |first1=V. M.
|date=1915
|title=Spectrographic Observations of Nebulae
|journal=[[Popular Astronomy (US magazine)|Popular Astronomy]]
|volume=23 |pages=21–24
|bibcode=1915PA.....23...21S
}}</ref>

In 1917, [[Heber Curtis]] observed nova [[S Andromedae]] within the "Great [[Andromeda (constellation)|Andromeda]] Nebula" (as the Andromeda Galaxy, [[Messier object]] [[Andromeda Galaxy|M31]], was then known). Searching the photographic record, he found 11 more [[nova]]e. Curtis noticed that these novae were, on average, 10 [[magnitude (astronomy)|magnitudes]] fainter than those that occurred within our galaxy. As a result, he was able to come up with a distance estimate of 150,000 [[parsec]]s. He became a proponent of the so-called "island universes" hypothesis, which holds that spiral nebulae are actually independent galaxies.<ref>
{{cite journal
|last=Curtis |first1=H. D.
|date=1988
|title=Novae in Spiral Nebulae and the Island Universe Theory
|journal=[[Publications of the Astronomical Society of the Pacific]]
|volume=100 |pages=6
|bibcode=1988PASP..100....6C
|doi=10.1086/132128
}}</ref>

In 1920 the so-called [[Great Debate (astronomy)|Great Debate]] took place between [[Harlow Shapley]] and [[Heber Curtis]], concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the Universe. To support his claim that the Great Andromeda Nebula is an external galaxy, Curtis noted the appearance of dark lanes resembling the dust clouds in the Milky Way, as well as the significant Doppler shift.<ref>
{{cite web
|last1=Weaver |first1=H. F.
|title=Robert Julius Trumpler
|url=http://www.nap.edu/readingroom/books/biomems/rtrumpler.html
|publisher=[[United States National Academy of Sciences|US National Academy of Sciences]]
|accessdate=January 5, 2007
}}</ref>

In 1922, the [[Estonia]]n astronomer [[Ernst Öpik]] gave a distance determination that supported the theory that the Andromeda Nebula is indeed a distant extra-galactic object.<ref>
{{cite journal
|last1=Öpik |first1=E.
|date=1922
|title=An estimate of the distance of the Andromeda Nebula
|journal=[[Astrophysical Journal]]
|volume=55 |pages=406
|bibcode=1922ApJ....55..406O
|doi=10.1086/142680
}}</ref> Using the new 100 inch [[Mount Wilson Observatory|Mt. Wilson]] telescope, [[Edwin Hubble]] was able to resolve the outer parts of some spiral nebulae as collections of individual stars and identified some [[Cepheid variable]]s, thus allowing him to estimate the distance to the nebulae: they were far too distant to be part of the Milky Way.<ref>
{{cite journal
|last1=Hubble |first1=E. P.
|date=1929
|title=A spiral nebula as a stellar system, Messier 31
|journal=[[Astrophysical Journal]]
|volume=69 |pages=103–158
|bibcode=1929ApJ....69..103H
|doi=10.1086/143167
}}</ref> In 1936 Hubble produced a classification of [[Galaxy morphological classification|galactic morphology]] that is used to this day.<ref>
{{cite journal
|last1=Sandage |first1=A.
|date=1989
|title=Edwin Hubble, 1889–1953
|journal=[[Journal of the Royal Astronomical Society of Canada]]
|volume=83 |issue=6 |pages=351–362
|url=http://antwrp.gsfc.nasa.gov/diamond_jubilee/1996/sandage_hubble.html
|accessdate=January 8, 2007
|bibcode = 1989JRASC..83..351S }}</ref>

===Modern research===
[[File:GalacticRotation2.svg|thumb|right|200px|[[Galaxy rotation curve|Rotation curve]] of a typical spiral galaxy: predicted based on the visible matter (A) and observed (B). The distance is from the [[Bulge (astronomy)|galactic core]].]]
In 1944, [[Hendrik C. van de Hulst|Hendrik van de Hulst]] predicted that [[microwave]] radiation with [[hydrogen line|wavelength of 21 cm]] would be detectable from interstellar atomic [[hydrogen]] gas;<ref>
{{cite web
|last1=Tenn |first1=J.
|title=Hendrik Christoffel van de Hulst
|url=http://www.phys-astro.sonoma.edu/BruceMedalists/vandeHulst/
|publisher=[[Sonoma State University]]
|accessdate=January 5, 2007
}}</ref> and in 1951 it was observed. This radiation is not affected by dust absorption, and so its Doppler shift can be used to map the motion of the gas in our galaxy. These observations led to the hypothesis of a rotating [[barred spiral galaxy|bar structure]] in the center of our galaxy.<ref>
{{cite journal
|last1=López-Corredoira |first1=M.
|display-authors=etal
|date=2001
|title=Searching for the in-plane Galactic bar and ring in DENIS
|journal=[[Astronomy and Astrophysics]]
|volume=373
|issue=1 |pages=139–152
|bibcode=2001A&A...373..139L
|doi=10.1051/0004-6361:20010560
|arxiv = astro-ph/0104307 }}</ref> With improved [[radio telescope]]s, hydrogen gas could also be traced in other galaxies.
In the 1970s, [[Vera Rubin]] uncovered a discrepancy between observed galactic [[galaxy rotation curve|rotation speed]] and that predicted by the visible mass of stars and gas. Today, the galaxy rotation problem is thought to be explained by the presence of large quantities of unseen [[dark matter]].<ref>
{{cite journal
|last1=Rubin |first1=V. C.
|date=1983
|title=Dark matter in spiral galaxies
|journal=[[Scientific American]]
|volume=248
|issue=6 |pages=96–106
|bibcode=1983SciAm.248...96R
|doi=10.1038/scientificamerican0683-96
}}</ref><ref>
{{cite journal
|last1=Rubin |first1=V. C.
|date=2000
|title=One Hundred Years of Rotating Galaxies
|journal=[[Publications of the Astronomical Society of the Pacific]]
|volume=112 |issue=772 |pages=747–750
|bibcode=2000PASP..112..747R
|doi=10.1086/316573
}}</ref> A concept known as the [[universal rotation curve]] of spirals, moreover, shows that the problem is ubiquitous in these objects.

Beginning in the 1990s, the [[Hubble Space Telescope]] yielded improved observations. Among other things, Hubble data helped establish that the missing dark matter in our galaxy cannot solely consist of inherently faint and small stars.<ref>
{{cite news
|title=Hubble Rules Out a Leading Explanation for Dark Matter
|publisher=Hubble News Desk
|date=October 17, 1994
|url=http://hubblesite.org/newscenter/archive/releases/1994/41/text/
|accessdate=January 8, 2007
}}</ref> The [[Hubble Deep Field]], an extremely long exposure of a relatively empty part of the sky, provided evidence that there are about 125 billion ({{val|1.25|e=11}}) galaxies in the Universe.<ref>
{{cite web
|date=November 27, 2002
|title=How many galaxies are there?
|url=http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/021127a.html
|publisher=[[NASA]]
|accessdate=January 8, 2007
}}</ref> Improved technology in detecting the [[electromagnetic spectrum|spectra]] invisible to humans (radio telescopes, infrared cameras, and [[x-ray astronomy|x-ray telescopes]]) allow detection of other galaxies that are not detected by Hubble. Particularly, galaxy surveys in the [[Zone of Avoidance]] (the region of the sky blocked by the Milky Way) have revealed a number of new galaxies.<ref>
{{cite journal
|last1=Kraan-Korteweg |first1=R. C.
|last2=Juraszek |first2=S.
|date=2000
|title=Mapping the hidden Universe: The galaxy distribution in the Zone of Avoidance
|journal=[[Publications of the Astronomical Society of Australia]]
|volume=17 |issue=1 |pages=6–12
|bibcode=1999astro.ph.10572K
|arxiv = astro-ph/9910572
|doi=10.1071/AS00006 }}</ref>

==Types and morphology==
{{Main|Galaxy morphological classification}}
[[File:Hubble sequence photo.png|thumb|360px|Types of galaxies according to the Hubble classification scheme: an ''E'' indicates a type of elliptical galaxy; an ''S'' is a spiral; and ''SB'' is a barred-spiral galaxy.<ref group=note>Galaxies to the left side of the Hubble classification scheme are sometimes referred to as "early-type", while those to the right are "late-type".</ref>]]
Galaxies come in three main types: ellipticals, spirals, and irregulars. A slightly more extensive description of galaxy types based on their appearance is given by the [[Galaxy morphological classification|Hubble sequence]]. Since the Hubble sequence is entirely based upon visual morphological type, it may miss certain important characteristics of galaxies such as [[star formation]] rate in [[Starburst galaxy|starburst galaxies]] and activity in the cores of [[active galaxy|active galaxies]].<ref name="IRatlas" />

===Ellipticals===
{{Main|Elliptical galaxy}}
The Hubble classification system rates elliptical galaxies on the basis of their ellipticity, ranging from E0, being nearly spherical, up to E7, which is highly elongated. These galaxies have an [[ellipsoid]]al profile, giving them an elliptical appearance regardless of the viewing angle. Their appearance shows little structure and they typically have relatively little [[interstellar medium|interstellar matter]]. Consequently, these galaxies also have a low portion of [[open cluster]]s and a reduced rate of new star formation. Instead they are dominated by generally older, more [[stellar evolution|evolved stars]] that are orbiting the common center of gravity in random directions. The stars contain low abundances of heavy elements because star formation ceases after the initial burst. In this sense they have some similarity to the much smaller [[globular cluster]]s.<ref name="elliptical">
{{cite web
|last1=Barstow |first1=M. A.
|date=2005
|title=Elliptical Galaxies
|url=http://web.archive.org/web/20120729081504/http://www.star.le.ac.uk/edu/Elliptical.shtml
|publisher=[[Leicester University]] Physics Department
|accessdate=June 8, 2006
}}</ref>

The largest galaxies are giant ellipticals. Many elliptical galaxies are believed to form due to the [[interacting galaxy|interaction of galaxies]], resulting in a collision and merger. They can grow to enormous sizes (compared to spiral galaxies, for example), and giant elliptical galaxies are often found near the core of large galaxy clusters.<ref>
{{cite web
|date=October 20, 2005
|title=Galaxies
|url=http://web.archive.org/web/20140629115612/http://curious.astro.cornell.edu/galaxies.php
|publisher=[[Cornell University]]
|accessdate=August 10, 2006
}}</ref> Starburst galaxies are the result of such a galactic collision that can result in the formation of an elliptical galaxy.<ref name="elliptical" />

====Shell galaxy====
[[File:NGC 3923 Elliptical Shell Galaxy.jpg|thumb|NGC 3923 Elliptical Shell Galaxy-Hubble Space Telescope photograph]]
A shell galaxy is a type of elliptical galaxy where the stars in the galaxy's halo are arranged in concentric shells. About 1/10 tenth of elliptical galaxies have a shell-like structure, which has never been observed in spiral galaxies. The shell-like structures are thought to develop when a larger galaxy absorbs a smaller companion galaxy. As the two galaxy centers approach, the centers start to oscillate around a center point, the oscillation creates gravitational ripples forming the shells of stars, similar to ripples spreading on water. For example, galaxy [[NGC 3923]] has over twenty shells.<ref>{{Cite web|title = Galactic onion|url = http://www.spacetelescope.org/images/potw1519a/|website = www.spacetelescope.org|accessdate = 2015-05-11}}</ref>

===Spirals===
{{Main|Spiral galaxy|Barred spiral galaxy}}

[[File:M101 hires STScI-PRC2006-10a.jpg|thumb|right|The [[Pinwheel Galaxy]], NGC 5457.]]

Spiral galaxies resemble spiraling pinwheels. Though the stars and other visible material contained in such a galaxy lie mostly on a plane, the majority of mass in spiral galaxies exists in a roughly spherical halo of [[dark matter]] that extends beyond the visible component, as demonstrated by the universal rotation curve concept.<ref name="Williams2009">{{cite doi|10.1111/j.1365-2966.2009.15582.x}}</ref>

Spiral galaxies consist of a rotating disk of stars and interstellar medium, along with a central bulge of generally older stars. Extending outward from the [[bulge (astronomy)|bulge]] are relatively bright arms. In the Hubble classification scheme, spiral galaxies are listed as type ''S'', followed by a letter (''a'', ''b'', or ''c'') that indicates the degree of tightness of the spiral arms and the size of the central bulge. An ''Sa'' galaxy has tightly wound, poorly defined arms and possesses a relatively large core region. At the other extreme, an ''Sc'' galaxy has open, well-defined arms and a small core region.<ref>
{{cite web
|last1=Smith |first1=G.
|date=March 6, 2000
|url=http://casswww.ucsd.edu/public/tutorial/Galaxies.html
|title=Galaxies — The Spiral Nebulae
|publisher=[[University of California]], San Diego Center for Astrophysics & Space Sciences
|accessdate=November 30, 2006
}}</ref> A galaxy with poorly defined arms is sometimes referred to as a [[flocculent spiral galaxy]]; in contrast to the [[grand design spiral galaxy]] that has prominent and well-defined spiral arms.<ref name=bergh1998/>

It appears the reason that some spiral galaxies are fat and bulging while some are flat discs is because of how fast they rotate.<ref>[http://phys.org/news/2014-02-fat-flat-galaxies.html "Fat or flat: Getting galaxies into shape"]. ''phys.org''. February 2014</ref>
[[File:Hubble2005-01-barred-spiral-galaxy-NGC1300.jpg|right|thumb|300px|[[NGC 1300]], an example of a [[barred spiral galaxy]].]]
In spiral galaxies, the spiral arms do have the shape of approximate [[logarithmic spiral]]s, a pattern that can be theoretically shown to result from a disturbance in a uniformly rotating mass of stars. Like the stars, the spiral arms rotate around the center, but they do so with constant [[angular velocity]]. The spiral arms are thought to be areas of high-density matter, or "[[Density wave theory|density waves]]".<ref name=bertin_lin1996/> As stars move through an arm, the space velocity of each stellar system is modified by the gravitational force of the higher density. (The velocity returns to normal after the stars depart on the other side of the arm.) This effect is akin to a "wave" of slowdowns moving along a highway full of moving cars. The arms are visible because the high density facilitates star formation, and therefore they harbor many bright and young stars.<ref name=belkora355/>
{{multiple image
| align = right
| direction = vertical
| width = 230
| image1 = Hoag's object.jpg
| caption1 = [[Hoag's Object]], an example of a [[ring galaxy]]
| image2 = File-Ngc5866 hst big.png
| caption2 = [[NGC 5866]], an example of a [[lenticular galaxy]]
}}
====Barred Spiral Galaxy====
A majority of spiral galaxies, including our own [[Milky Way]] galaxy, have a linear, bar-shaped band of stars that extends outward to either side of the core, then merges into the spiral arm structure.<ref>
{{cite journal
|last1=Eskridge |first1=P. B.
|last2=Frogel |first2=J. A.
|date=1999
|title=What is the True Fraction of Barred Spiral Galaxies?
|journal=[[Astrophysics and Space Science]]
|volume=269/270 |pages=427–430
|bibcode=1999Ap&SS.269..427E
|doi=10.1023/A:1017025820201
}}</ref> In the Hubble classification scheme, these are designated by an ''SB'', followed by a lower-case letter (''a'', ''b'' or ''c'') that indicates the form of the spiral arms (in the same manner as the categorization of normal spiral galaxies). Bars are thought to be temporary structures that can occur as a result of a density wave radiating outward from the core, or else due to a [[Galactic tide|tidal interaction]] with another galaxy.<ref>
{{cite journal
|last1=Bournaud |first1=F.
|last2=Combes |first2=F.
|date=2002
|title=Gas accretion on spiral galaxies: Bar formation and renewal
|journal=[[Astronomy and Astrophysics]]
|volume=392
|issue=1 |pages=83–102
|bibcode=2002A&A...392...83B
|doi=10.1051/0004-6361:20020920
|arxiv = astro-ph/0206273 }}</ref> Many barred spiral galaxies are active, possibly as a result of gas being channeled into the core along the arms.<ref>
{{cite journal
|last1=Knapen |first1=J. H.
|last2=Perez-Ramirez |first2=D.
|last3=Laine |first3=S.
|date=2002
|title=Circumnuclear regions in barred spiral galaxies — II. Relations to host galaxies
|journal=[[Monthly Notices of the Royal Astronomical Society]]
|volume=337 |issue=3 |pages=808–828
|bibcode=2002MNRAS.337..808K
|doi=10.1046/j.1365-8711.2002.05840.x
|arxiv = astro-ph/0207258 }}</ref>

Our own galaxy, the [[Milky Way]], is a large disk-shaped barred-spiral galaxy<ref>
{{cite journal
|last1=Alard |first1=C.
|date=2001
|title=Another bar in the Bulge
|journal=[[Astronomy and Astrophysics Letters]]
|volume=379 |issue=2 |pages=L44–L47
|bibcode=2001A&A...379L..44A
|doi=10.1051/0004-6361:20011487
|arxiv = astro-ph/0110491 }}</ref> about 30 kiloparsecs in diameter and a kiloparsec thick. It contains about two hundred billion (2×1011)<ref>
{{cite news
|last1=Sanders |first1=R.
|date=January 9, 2006
|title=Milky Way galaxy is warped and vibrating like a drum
|publisher=[[UC Berkeley|UCBerkeley News]]
|url=http://www.berkeley.edu/news/media/releases/2006/01/09_warp.shtml
|accessdate=May 24, 2006
}}</ref> stars and has a total mass of about six hundred billion (6×1011) times the mass of the Sun.<ref>
{{cite journal
|last1=Bell |first1=G. R.
|last2=Levine |first2=S. E.
|date=1997
|title=Mass of the Milky Way and Dwarf Spheroidal Stream Membership
|journal=[[Bulletin of the American Astronomical Society]]
|volume=29 |issue=2 |pages=1384
|bibcode=1997AAS...19110806B
}}</ref>

===Other morphologies===
* [[Peculiar galaxy|Peculiar galaxies]] are galactic formations that develop unusual properties due to tidal interactions with other galaxies. An example of this is the [[ring galaxy]], which possesses a ring-like structure of stars and interstellar medium surrounding a bare core. A ring galaxy is thought to occur when a smaller galaxy passes through the core of a spiral galaxy.<ref>{{cite journal
|last1=Gerber |first1=R. A.
|last2=Lamb |first2=S. A.
|last3=Balsara |first3=D. S.
|date=1994
|title=Ring Galaxy Evolution as a Function of "Intruder" Mass
|journal=[[Bulletin of the American Astronomical Society]]
|volume=26 |pages=911
|bibcode=1994AAS...184.3204G
}}</ref> Such an event may have affected the [[Andromeda Galaxy]], as it displays a multi-ring-like structure when viewed in [[infrared]] radiation.<ref>{{cite press release
|publisher=[[European Space Agency]]
|date=October 14, 1998
|title=ISO unveils the hidden rings of Andromeda
|url=http://www.iso.vilspa.esa.es/outreach/esa_pr/andromed.htm
|accessdate=May 24, 2006
}}</ref>

* A [[lenticular galaxy]] is an intermediate form that has properties of both elliptical and spiral galaxies. These are categorized as Hubble type S0, and they possess ill-defined spiral arms with an elliptical halo of stars<ref>{{cite web
|date=May 31, 2004
|title=Spitzer Reveals What Edwin Hubble Missed
|url=http://web.archive.org/web/20060907042809/http://www.cfa.harvard.edu/press/pr0419.html
|publisher=[[Harvard-Smithsonian Center for Astrophysics]]
|accessdate=December 6, 2006
}}</ref> ([[Barred lenticular galaxy|barred lenticular galaxies]] receive Hubble classification SB0.)

* [[Irregular galaxy|Irregular galaxies]] are galaxies that can not be readily classified into an elliptical or spiral morphology. An Irr-I galaxy has some structure but does not align cleanly with the Hubble classification scheme. Irr-II galaxies do not possess any structure that resembles a Hubble classification, and may have been disrupted.<ref>{{cite web
|last1=Barstow |first1=M. A.
|date=2005
|title=Irregular Galaxies
|url=http://web.archive.org/web/20120227172628/http://www.star.le.ac.uk/edu/Irregular.shtml
|publisher=[[University of Leicester]]
|accessdate=December 5, 2006
}}</ref> Nearby examples of (dwarf) irregular galaxies include the [[Magellanic Clouds]].

* An [[ultra diffuse galaxy]] (UDG) is an extremely-low-density galaxy. The galaxy may be the same size as the Milky Way but has a visible star count of only 1% of the Milky Way. The lack of luminosity is because there is a lack of star-forming gas in the galaxy which results in old stellar populations.

===Dwarfs===
{{Main|Dwarf galaxy}}
Despite the prominence of large elliptical and spiral galaxies, most galaxies in the Universe are dwarf galaxies. These galaxies are relatively small when compared with other galactic formations, being about one hundredth the size of the Milky Way, containing only a few billion stars. Ultra-compact dwarf galaxies have recently been discovered that are only 100 parsecs across.<ref>
{{cite journal
|last1=Phillipps |first1=S.
|last2=Drinkwater |first2=M. J.
|last3=Gregg |first3=M. D.
|last4=Jones |first4=J. B.
|date=2001
|title=Ultracompact Dwarf Galaxies in the Fornax Cluster
|journal=[[Astrophysical Journal]]
|volume=560 |issue=1 |pages=201–206
|bibcode=2001ApJ...560..201P
|doi=10.1086/322517
|arxiv = astro-ph/0106377 }}</ref>

Many dwarf galaxies may orbit a single larger galaxy; the Milky Way has at least a dozen such satellites, with an estimated 300–500 yet to be discovered.<ref>
{{cite news
|last1=Groshong |first1=K.
|date=April 24, 2006
|title=Strange satellite galaxies revealed around Milky Way
|publisher=[[New Scientist]]
|url=http://www.newscientist.com/article/dn9043-strange-satellite-galaxies-revealed-around-milky-way.html
|accessdate=January 10, 2007
}}</ref> Dwarf galaxies may also be classified as [[dwarf elliptical galaxy|elliptical]], [[dwarf spiral galaxy|spiral]], or [[irregular galaxy|irregular]]. Since small dwarf ellipticals bear little resemblance to large ellipticals, they are often called [[dwarf spheroidal galaxy|dwarf spheroidal galaxies]] instead.

A study of 27 Milky Way neighbors found that in all dwarf galaxies, the central mass is approximately 10 million [[solar mass]]es, regardless of whether the galaxy has thousands or millions of stars. This has led to the suggestion that galaxies are largely formed by [[dark matter]], and that the minimum size may indicate a form of [[warm dark matter]] incapable of gravitational coalescence on a smaller scale.<ref>
{{cite web
|last1=Schirber |first1=M.
|date=August 27, 2008
|url=http://news.sciencemag.org/physics/2008/08/no-slimming-down-dwarf-galaxies
|title=No Slimming Down for Dwarf Galaxies
|publisher=[[ScienceNOW]]
|accessdate=August 27, 2008
}}</ref>

==Unusual dynamics and activities==

===Interacting===
{{Main|Interacting galaxy}}
[[File:Antennae galaxies xl.jpg|thumb|right|200px|The [[Antennae Galaxies]] are undergoing a collision that will result in their eventual merger.]]
Interactions between galaxies are relatively frequent, and they can play an important role in [[galaxy formation and evolution|galactic evolution]]. Near misses between galaxies result in warping distortions due to [[galactic tide|tidal interactions]], and may cause some exchange of gas and dust.<ref name="umda">
{{cite web
|url=http://www.astro.umd.edu/education/astro/gal/interact.html
|title=Galaxy Interactions
|publisher=[[University of Maryland]] Department of Astronomy
|accessdate=December 19, 2006
|archiveurl=http://web.archive.org/web/20060509074300/http://www.astro.umd.edu/education/astro/gal/interact.html
|archivedate=May 9, 2006
}}</ref><ref name="suia">
{{cite web
|title=Interacting Galaxies
|url=http://Cosmos.swin.edu.au/entries/interactinggalaxies/interactinggalaxies.html?e=1
|publisher=[[Swinburne University]]
|accessdate=December 19, 2006
}}</ref>
Collisions occur when two galaxies pass directly through each other and have sufficient relative momentum not to merge. The stars of interacting galaxies will usually not collide, but the gas and dust within the two forms will interact, sometimes triggering star formation. A collision can severely distort the shape of the galaxies, forming bars, rings or tail-like structures.<ref name="umda" /><ref name="suia" />

At the extreme of interactions are galactic mergers. In this case the relative momentum of the two galaxies is insufficient to allow the galaxies to pass through each other. Instead, they gradually merge to form a single, larger galaxy. Mergers can result in significant changes to morphology, as compared to the original galaxies. In the case where one of the galaxies is much more massive, however, the result is known as [[Interacting galaxy#Galactic cannibalism|cannibalism]]. In this case the larger galaxy will remain relatively undisturbed by the merger, while the smaller galaxy is torn apart. The Milky Way galaxy is currently in the process of cannibalizing the [[Sagittarius Dwarf Elliptical Galaxy]] and the [[Canis Major Dwarf Galaxy]].<ref name="umda" /><ref name="suia" />

===Starburst===
{{Main|Starburst galaxy}}
[[File:M82 HST ACS 2006-14-a-large web.jpg|thumb|right|200px|[[Messier 82|M82]], a starburst galaxy that has ten times the star formation of a "normal" galaxy.<ref>
{{cite web
|date=April 24, 2006
|url=http://hubblesite.org/newscenter/archive/releases/2006/14/image/a
|title=Happy Sweet Sixteen, Hubble Telescope!
|publisher=[[NASA]]
|accessdate=August 10, 2006
}}</ref>]]

Stars are created within galaxies from a reserve of cold gas that forms into giant [[molecular cloud]]s. Some galaxies have been observed to form stars at an exceptional rate, known as a starburst. Should they continue to do so, however, they would consume their reserve of gas in a time frame lower than the lifespan of the galaxy. Hence starburst activity usually lasts for only about ten million years, a relatively brief period in the history of a galaxy. Starburst galaxies were more common during the early history of the Universe,<ref name="chandra">
{{cite web
|date=August 29, 2006
|url=http://chandra.harvard.edu/xray_sources/starburst.html
|title=Starburst Galaxies
|publisher=[[Harvard-Smithsonian Center for Astrophysics]]
|accessdate=August 10, 2006
}}</ref> and, at present, still contribute an estimated 15% to the total star production rate.<ref>
{{cite conference
|last1=Kennicutt Jr. |first1=R. C.
|display-authors=etal
|date=2005
|title=Demographics and Host Galaxies of Starbursts
|work=Starbursts: From 30 Doradus to Lyman Break Galaxies
|page=187
|publisher=[[Springer (publisher)|Springer]]
|bibcode=2005sdlb.proc..187K
}}</ref>

Starburst galaxies are characterized by dusty concentrations of gas and the appearance of newly formed stars, including massive stars that ionize the surrounding clouds to create [[H II region]]s.<ref>
{{cite web
|last1=Smith |first1=G.
|date=July 13, 2006
|title=Starbursts & Colliding Galaxies
|url=http://casswww.ucsd.edu/public/tutorial/Starbursts.html
|publisher=[[University of California]], San Diego Center for Astrophysics & Space Sciences
|accessdate=August 10, 2006
}}</ref> These massive stars produce [[supernova]] explosions, resulting in expanding [[supernova remnant|remnants]] that interact powerfully with the surrounding gas. These outbursts trigger a chain reaction of star building that spreads throughout the gaseous region. Only when the available gas is nearly consumed or dispersed does the starburst activity come to an end.<ref name="chandra" />

Starbursts are often associated with merging or interacting galaxies. The prototype example of such a starburst-forming interaction is [[Messier 82|M82]], which experienced a close encounter with the larger [[Messier 81|M81]]. Irregular galaxies often exhibit spaced knots of starburst activity.<ref>
{{cite web
|last1=Keel |first1=B.
|date=September 2006
|title=Starburst Galaxies
|url=http://www.astr.ua.edu/keel/galaxies/starburst.html
|publisher=[[University of Alabama]]
|accessdate=December 11, 2006
}}</ref>

===Active nucleus===
{{Main|Active galactic nucleus}}
[[File:M87 jet.jpg|thumb|right|200px|A jet of particles is being emitted from the core of the elliptical radio galaxy [[Messier 87|M87]].]]
A portion of the observable galaxies are classified as active. That is, a significant portion of the total energy output from the galaxy is emitted by a source other than the stars, dust and [[interstellar medium]].

The standard model for an [[active galactic nucleus]] is based upon an [[accretion disc]] that forms around a [[supermassive black hole]] (SMBH) at the core region. The radiation from an active galactic nucleus results from the [[gravitational energy]] of matter as it falls toward the black hole from the disc.<ref name="keel">
{{cite web
|last1=Keel |first1=W. C.
|date=2000
|url=http://www.astr.ua.edu/keel/galaxies/agnintro.html
|title=Introducing Active Galactic Nuclei
|publisher=[[University of Alabama]]
|accessdate=December 6, 2006
}}</ref> In about 10% of these objects, a diametrically opposed pair of energetic jets ejects particles from the core at velocities close to the [[speed of light]]. The mechanism for producing these jets is still not well understood.<ref name="monster">
{{cite web
|last1=Lochner |first1=J.
|last2=Gibb |first2=M.
|title=A Monster in the Middle
|url=http://imagine.gsfc.nasa.gov/docs/science/know_l2/active_galaxies.html
|publisher=[[NASA]]
|accessdate=December 20, 2006
}}</ref>

Active galaxies that emit high-energy radiation in the form of [[x-ray]]s are classified as [[Seyfert galaxy|Seyfert galaxies]] or [[quasar]]s, depending on the luminosity.

====Blazars====
{{Main|Blazars}}
[[Blazar]]s are believed to be an active galaxy with a [[relativistic jet]] that is pointed in the direction of Earth. A [[radio galaxy]] emits radio frequencies from relativistic jets. A unified model of these types of active galaxies explains their differences based on the viewing angle of the observer.<ref name="monster" />

====LINERS====
Possibly related to active galactic nuclei (as well as [[starburst (astronomy)|starburst]] regions) are [[low-ionization nuclear emission-line region]]s (LINERs). The emission from LINER-type galaxies is dominated by weakly [[ion]]ized elements.<ref name="heckman1980">
{{cite journal
|last1=Heckman |first1=T. M.
|date=1980
|title=An optical and radio survey of the nuclei of bright galaxies — Activity in normal galactic nuclei
|journal=[[Astronomy and Astrophysics]]
|volume=87 |pages=152–164
|bibcode=1980A&A....87..152H
}}</ref> Approximately one-third of nearby galaxies are classified as containing LINER nuclei.<ref name="keel" /><ref name="heckman1980" /><ref name="hoetal1997b">
{{cite journal
|last1=Ho |first1=L. C.
|last2=Filippenko |first2=A. V.
|last3=Sargent |first3=W. L. W.
|date=1997
|title=A Search for "Dwarf" Seyfert Nuclei. V. Demographics of Nuclear Activity in Nearby Galaxies
|journal=[[Astrophysical Journal]]
|volume=487
|issue=2 |pages=568–578
|bibcode=1997ApJ...487..568H
|doi=10.1086/304638
|arxiv = astro-ph/9704108 }}</ref>

====Seyfert Galaxy====
{{Main|Seyfert Galaxy}}
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei (very luminous, distant and bright sources of electromagnetic radiation) with very high surface brightnesses but unlike quasars, their host galaxies are clearly detectable. Seyfert galaxies account for about 10% of all galaxies. Seen in visible light, most Seyfert galaxies look like normal spiral galaxies, but when studied under other wavelengths, the luminosity of their cores is equivalent to the luminosity of whole galaxies the size of the Milky Way.

====Quasar====
{{Main|Quasar}}
Quasars (/ˈkweɪzɑr/) or quasi-stellar radio sources are the most energetic and distant members of a class of objects called active galactic nuclei (AGN). Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that appeared to be similar to stars, rather than extended sources similar to galaxies. Their luminosity can be 100 times greater than that of the Milky Way.

===Luminous infrared galaxy===
{{Main|Luminous infrared galaxy}}
Luminous Infrared Galaxies or (LIRG's) are galaxies with luminosities, the measurement of brightness, above 1011 L☉. LIRG's are more abundant than starburst galaxies, Seyfert galaxies and quasi-stellar objects at comparable luminosity. Infrared galaxies emit more energy in the infrared than at all other wavelengths combined. An LIRG's luminosity is 100 billion times that of our sun.

==Formation and evolution==
{{Main|Galaxy formation and evolution}}
Galactic formation and evolution is an active area of research in [[astrophysics]].

===Formation===
[[File:Artist's impression of a protocluster forming in the early Universe.jpg|align=right|thumb|Artist's impression of a protocluster forming in the early Universe.<ref>{{cite web|title=Construction Secrets of a Galactic Metropolis|url=http://www.eso.org/public/news/eso1431/|website=www.eso.org|publisher=ESO Press Release|accessdate=October 15, 2014}}</ref>]]
Current cosmological models of the early Universe are based on the [[Big Bang]] theory. About 300,000 years after this event, atoms of [[hydrogen]] and [[helium]] began to form, in an event called [[Recombination (cosmology)|recombination]]. Nearly all the hydrogen was neutral (non-ionized) and readily absorbed light, and no stars had yet formed. As a result, this period has been called the "[[Timeline of the Big Bang#Dark Ages|dark ages]]". It was from density fluctuations (or [[anisotropy|anisotropic]] irregularities) in this primordial matter that [[structure formation|larger structures]] began to appear. As a result, masses of [[baryon]]ic matter started to condense within [[cold dark matter]] halos.<ref name="hqrdvj">
{{cite web
|date=November 18, 1999
|title=Search for Submillimeter Protogalaxies
|url=http://web.archive.org/web/20080325183740/http://cfa-www.harvard.edu/~aas/tenmeter/proto.htm
|publisher=[[Harvard-Smithsonian Center for Astrophysics]]
|accessdate=January 10, 2007
}}</ref><ref name=rmaa17_107/> These primordial structures would eventually become the galaxies we see today.
[[File:Young Galaxy Accreting Material.jpg|thumb|right|200px|Artist's impression of a young galaxy accreting material.]]

====Early galaxies====
Evidence for the early appearance of galaxies was found in 2006, when it was discovered that the galaxy [[IOK-1]] has an unusually high [[redshift]] of 6.96, corresponding to just 750 million years after the Big Bang and making it the most distant and primordial galaxy yet seen.<ref>
{{cite journal
|last1=McMahon |first1=R.
|date=2006
|title=Journey to the birth of the Universe
|journal=[[Nature (journal)|Nature]]
|volume=443 |issue=7108 |pages=151–2
|doi=10.1038/443151a
|pmid=16971933
|bibcode = 2006Natur.443..151M }}</ref>
While some scientists have claimed other objects (such as [[Galaxy Abell 1835 IR1916|Abell 1835 IR1916]]) have higher redshifts (and therefore are seen in an earlier stage of the Universe's evolution), IOK-1's age and composition have been more reliably established. In December 2012, astronomers reported that the [[UDFj-39546284]] is the most distant object known and has a redshift value of 11.9. The object, is estimated to have existed around "380 million years"<ref name="Space-20121212">{{cite web |last=Wall |first=Mike |title=Ancient Galaxy May Be Most Distant Ever Seen |url=http://www.space.com/18879-hubble-most-distant-galaxy.html |date=December 12, 2012 |publisher=[[Space.com]] |accessdate=December 12, 2012 }}</ref> after the [[Big Bang]] (which was about 13.8 billion years ago),<ref name="Cosmic Detectives">{{cite web
|last =
|first =
|title = Cosmic Detectives
|url=http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives
|authorlink =
|work =
|publisher = The European Space Agency (ESA)
|date = April 2, 2013
|doi =
|accessdate = April 15, 2013}}</ref> is about 13.42 billion light years away. The existence of such early [[protogalaxy|protogalaxies]] suggests that they must have grown in the so-called "dark ages".<ref name="hqrdvj"/> As of May 5, 2015, the galaxy [[EGS-zs8-1]] is the most distant and earliest galaxy measured, forming 670 million years after the [[Big Bang]]. The light from EGS-zs8-1 has taken 13 billion years to reach Earth, and is now 30 billion light-years away, because of the [[expansion of the universe]] during 13 billion years.<ref>{{Cite web|title = HubbleSite - NewsCenter - Astronomers Set a New Galaxy Distance Record (05/05/2015) - Introduction|url = http://hubblesite.org/newscenter/archive/releases/2015/22/|website = hubblesite.org|accessdate = 2015-05-07}}</ref><ref>{{Cite web|title = This Galaxy Far, Far Away Is the Farthest One Yet Found|url = http://www.space.com/29319-farthest-galaxy-ever-found.html?cmpid=NL_SP_weekly_2015-05-06|accessdate = 2015-05-07}}</ref><ref name="phys.org">{{Cite web|title = Astronomers unveil the farthest galaxy|url = http://phys.org/news/2015-05-astronomers-unveil-farthest-galaxy.html|accessdate = 2015-05-07}}</ref><ref name="phys.org"/><ref>{{Cite news|title = Astronomers Measure Distance to Farthest Galaxy Yet|url = http://www.nytimes.com/2015/05/06/science/astronomers-measure-distance-to-farthest-galaxy-yet.html|newspaper = The New York Times|date = 2015-05-05|access-date = 2015-05-07|issn = 0362-4331|first = Dennis|last = Overbye}}</ref><ref>{{Cite journal|title = A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE|url = http://arxiv.org/abs/1502.05399|journal = arXiv:1502.05399 [astro-ph]|date = 2015-02-18|access-date = 2015-05-07|first = P. A.|last = Oesch|first2 = P. G.|last2 = van Dokkum|first3 = G. D.|last3 = Illingworth|first4 = R. J.|last4 = Bouwens|first5 = I.|last5 = Momcheva|first6 = B.|last6 = Holden|first7 = G. W.|last7 = Roberts-Borsani|first8 = R.|last8 = Smit|first9 = M.|last9 = Franx}}</ref>

====Early galaxy formation====
The detailed process by which early galaxies formed is an open question in astrophysics. Theories can be divided into two categories: top-down and bottom-up. In top-down theories (such as the Eggen–Lynden-Bell–Sandage [ELS] model), protogalaxies form in a large-scale simultaneous collapse lasting about one hundred million years.<ref>
{{cite journal
|last1=Eggen |first1=O. J.
|last2=Lynden-Bell |first2=D.
|last3=Sandage |first3=A. R.
|date=1962
|title=Evidence from the motions of old stars that the Galaxy collapsed
|journal=[[Reports on Progress in Physics]]
|volume=136 |pages=748
|bibcode=1962ApJ...136..748E
|doi=10.1086/147433
}}</ref> In bottom-up theories (such as the Searle-Zinn [SZ] model), small structures such as [[globular cluster]]s form first, and then a number of such bodies accrete to form a larger galaxy.<ref>
{{cite journal
|last1=Searle |first1=L.
|last2=Zinn |first2=R.
|date=1978
|title=Compositions of halo clusters and the formation of the galactic halo
|journal=[[Astrophysical Journal]]
|volume=225 |issue=1 |pages=357–379
|bibcode=1978ApJ...225..357S
|doi=10.1086/156499
}}</ref>

Once protogalaxies began to form and contract, the first [[halo star]]s (called [[Metallicity#Population III stars|Population III stars]]) appeared within them. These were composed almost entirely of hydrogen and helium, and may have been massive. If so, these huge stars would have quickly consumed their supply of fuel and became [[supernova]]e, releasing heavy elements into the [[interstellar medium]].<ref>
{{cite journal
|last1=Heger |first1=A.
|last2=Woosley |first2=S. E.
|date=2002
|title=The Nucleosynthetic Signature of Population III
|journal=[[Astrophysical Journal]]
|volume=567 |issue=1 |pages=532–543
|bibcode=2002ApJ...567..532H
|doi=10.1086/338487
|arxiv = astro-ph/0107037 }}</ref> This first generation of stars re-ionized the surrounding neutral hydrogen, creating expanding bubbles of space through which light could readily travel.<ref>
{{cite journal
|last1=Barkana |first1=R.
|last2=Loeb |first2=A.
|date=1999
|title=In the beginning: the first sources of light and the reionization of the Universe
|journal=[[Physics Reports]]
|volume=349 |issue=2 |pages=125–238
|bibcode=2001PhR...349..125B
| arxiv = astro-ph/0010468
|doi=10.1016/S0370-1573(01)00019-9
}}</ref>

In June 2015, astronomers reported evidence for [[Metallicity#Population III stars|Population III stars]] in the [[Cosmos Redshift 7]] [[galaxy]] at {{math|''z'' {{=}} 6.60}}. Such stars are likely to have existed in the very early universe (i.e., at high redshift), and may have started the production of [[chemical element]]s heavier than [[hydrogen]] that are needed for the later formation of [[planet]]s and [[life]] as we know it.<ref name="AJ-20150604">{{cite journal |last1=Sobral |first1=David |last2=Matthee |first2=Jorryt |last3=Darvish |first3=Behnam |last4=Schaerer |first4=Daniel |last5=Mobasher |first5=Bahram |last6=Röttgering |first6=Huub J. A. |last7=Santos |first7=Sérgio |last8=Hemmati |first8=Shoubaneh |title=Evidence For POPIII-Like Stellar Populations In The Most Luminous LYMAN-α Emitters At The Epoch Of Re-Ionisation: Spectroscopic Confirmation |url=http://arxiv.org/pdf/1504.01734.pdf |format=[[PDF]] |date=4 June 2015 |journal=[[The Astrophysical Journal]] |accessdate=17 June 2015 }}</ref><ref name="NYT-20150617">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Astronomers Report Finding Earliest Stars That Enriched Cosmos |url=http://www.nytimes.com/2015/06/18/science/space/astronomers-report-finding-earliest-stars-that-enriched-cosmos.html |date=17 June 2015 |work=[[New York Times]] |accessdate=17 June 2015 }}</ref>

===Evolution===
Within a billion years of a galaxy's formation, key structures begin to appear. [[Globular cluster]]s, the central supermassive black hole, and a [[bulge (astronomy)|galactic bulge]] of metal-poor [[metallicity|Population II stars]] form. The creation of a supermassive black hole appears to play a key role in actively regulating the growth of galaxies by limiting the total amount of additional matter added.<ref>
{{cite news
|date=February 9, 2005
|title=Simulations Show How Growing Black Holes Regulate Galaxy Formation
|url=http://www.cmu.edu/PR/releases05/050209_blackhole.html
|publisher=[[Carnegie Mellon University]]
|accessdate=January 7, 2007
}}</ref> During this early epoch, galaxies undergo a major burst of star formation.<ref>
{{cite news
|last1=Massey |first1=R.
|date=April 21, 2007
|title=Caught in the act; forming galaxies captured in the young Universe
|url=http://web.archive.org/web/20131115031412/http://www.ras.org.uk/index.php?option=com_content&task=view&id=1190&Itemid=2
|publisher=[[Royal Astronomical Society]]
|accessdate=April 20, 2007
}}</ref>

During the following two billion years, the accumulated matter settles into a [[disc (galaxy)|galactic disc]].<ref>
{{cite journal
|last=Noguchi |first=M.
|date=1999
|title=Early Evolution of Disk Galaxies: Formation of Bulges in Clumpy Young Galactic Disks
|journal=[[Astrophysical Journal]]
|volume=514 |issue=1 |pages=77–95
|bibcode=1999ApJ...514...77N
|doi=10.1086/306932
|arxiv = astro-ph/9806355 }}</ref> A galaxy will continue to absorb infalling material from [[high-velocity cloud]]s and [[dwarf galaxy|dwarf galaxies]] throughout its life.<ref>
{{cite web
|last1=Baugh |first1=C.
|last2=Frenk |first2=C.
|date=May 1999
|url=http://web.archive.org/web/20070426043157/http://physicsweb.org/articles/world/12/5/9
|title=How are galaxies made?
|publisher=[[PhysicsWeb]]
|accessdate=January 16, 2007
}}</ref> This matter is mostly hydrogen and helium. The cycle of stellar birth and death slowly increases the abundance of heavy elements, eventually allowing the [[planetary formation|formation]] of [[planet]]s.<ref>
{{cite conference
|last1=Gonzalez |first1=G.
|date=1998
|title=The Stellar Metallicity — Planet Connection
|work=Proceedings of a workshop on brown dwarfs and extrasolar planets
|pages=431
|bibcode=1998bdep.conf..431G
}}</ref>
{{Multiple image |direction=vertical |align=right |width=200 |image1=XDF-scale.jpg|image2=Constellation Fornax, EXtreme Deep Field.jpg |image3=XDF-separated.jpg |caption1=''[[Hubble Extreme Deep Field|XDF]]'' view field compared to the [[angular diameter|angular size]] of the [[Moon]]. Several thousand galaxies, each consisting of billions of [[star]]s, are in this small view. |caption2=''[[Hubble Extreme Deep Field|XDF]]'' (2012) view: Each light speck is a galaxy, some of which are as old as 13.2 billion years<ref name="Space-20120925">{{cite web |last=Moskowitz |first=Clara |title=Hubble Telescope Reveals Farthest View Into Universe Ever|url=http://www.space.com/17755-farthest-universe-view-hubble-space-telescope.html|date=September 25, 2012 |publisher=[[Space.com]] |accessdate=September 26, 2012}}</ref> – the [[observable universe]] is estimated to contain 200 billion galaxies. |caption3=''[[Hubble Extreme Deep Field|XDF]]'' image shows (from left) fully mature galaxies, nearly mature galaxies (from 5 to 9 billion years ago), [[Protogalaxy|protogalaxies]], blazing with [[young star]]s (beyond 9 billion years). |header=''[[Hubble Extreme Deep Field|Hubble eXtreme Deep Field (XDF)]]'' }}

The evolution of galaxies can be significantly affected by interactions and collisions. Mergers of galaxies were common during the early epoch, and the majority of galaxies were peculiar in morphology.<ref name="sa296">
{{cite journal
|last1=Conselice |first1=C. J.
|date=February 2007
|title=The Universe's Invisible Hand
|journal=[[Scientific American]]
|volume=296 |issue=2 |pages=35–41
|doi=10.1038/scientificamerican0207-34
}}</ref> Given the distances between the stars, the great majority of stellar systems in colliding galaxies will be unaffected. However, gravitational stripping of the interstellar gas and dust that makes up the spiral arms produces a long train of stars known as tidal tails. Examples of these formations can be seen in [[NGC 4676]]<ref>
{{cite news
|last1=Ford |first1=H.
|display-authors=etal
|date=April 30, 2002
|title=Hubble's New Camera Delivers Breathtaking Views of the Universe
|url=http://hubblesite.org/newscenter/archive/releases/2002/11/image/d
|publisher=Hubble News Desk
|accessdate=May 8, 2007
}}</ref> or the [[Antennae Galaxies]].<ref>
{{cite journal
|last1=Struck |first1=C.
|date=1999
|title=Galaxy Collisions
|doi=10.1016/S0370-1573(99)00030-7
|journal=Physics Reports
|volume=321
|pages=1
|arxiv=astro-ph/9908269
|bibcode = 1999PhR...321....1S }}</ref>

The Milky Way galaxy and the nearby Andromeda Galaxy are moving toward each other at about 130 [[metre per second|km/s]], and—depending upon the lateral movements—the two might collide in about five to six billion years. Although the Milky Way has never collided with a galaxy as large as Andromeda before, evidence of past collisions of the Milky Way with smaller dwarf galaxies is increasing.<ref>
{{cite news
|last1=Wong |first1=J.
|date=April 14, 2000
|title=Astrophysicist maps out our own galaxy's end
|url=http://www.news.utoronto.ca/bin/000414b.asp
|publisher=[[University of Toronto]]
|accessdate=January 11, 2007
|archiveurl=http://web.archive.org/web/20070108183824/http://www.news.utoronto.ca/bin/000414b.asp
|archivedate=January 8, 2007
}}</ref>

Such large-scale interactions are rare. As time passes, mergers of two systems of equal size become less common. Most bright galaxies have remained fundamentally unchanged for the last few billion years, and the net rate of star formation probably also peaked approximately ten billion years ago.<ref>
{{cite journal
|last1=Panter |first1=B.
|last2=Jimenez |first2=R.
|last3=Heavens |first3=A. F.
|last4=Charlot |first4=S.
|date=2007
|title=The star formation histories of galaxies in the Sloan Digital Sky Survey
|journal=[[Monthly Notices of the Royal Astronomical Society]]
|volume=378 |issue=4 |pages=1550–1564
|arxiv=astro-ph/0608531
|doi=10.1111/j.1365-2966.2007.11909.x |bibcode=2007MNRAS.378.1550P
}}</ref>

===Future trends===
Spiral galaxies, like the Milky Way, produce new generations of stars as long as they have dense [[molecular cloud]]s of interstellar hydrogen in their spiral arms.<ref>
{{cite journal
|last1=Kennicutt Jr. |first1=R. C.
|last2=Tamblyn |first2=P.
|last3=Congdon |first3=C. E.
|date=1994
|title=Past and future star formation in disk galaxies
|journal=[[Astrophysical Journal]]
|volume=435 |issue=1 |pages=22–36
|bibcode=1994ApJ...435...22K
|doi=10.1086/174790
}}</ref> Elliptical galaxies are largely devoid of this gas, and so form few new stars.<ref>
{{cite book
|last1=Knapp |first1=G. R.
|date=1999
|title=Star Formation in Early Type Galaxies
|publisher=[[Astronomical Society of the Pacific]]
|bibcode=1998astro.ph..8266K
|oclc=41302839
|isbn=1-886733-84-8
}}</ref> The supply of star-forming material is finite; once stars have converted the available supply of hydrogen into heavier elements, new star formation will come to an end.<ref name="cosmic_battle">
{{cite web
|last1=Adams |first1=Fred
|last2=Laughlin |first2=Greg
|date=July 13, 2006
|title=The Great Cosmic Battle
|url=http://www.astrosociety.org/pubs/mercury/0001/cosmic.html
|publisher=[[Astronomical Society of the Pacific]]
|accessdate=January 16, 2007
}}</ref><ref>{{Cite web|title = Cosmic 'Murder Mystery' Solved: Galaxies Are 'Strangled to Death'|url = http://www.space.com/29398-galaxy-strangulation-death-mystery.html?cmpid=NL_SP_weekly_2015-05-13|accessdate = 2015-05-14}}</ref>

The current era of star formation is expected to continue for up to one hundred billion years, and then the "stellar age" will wind down after about ten trillion to one hundred trillion years (1013–1014 years), as the smallest, longest-lived stars in our universe, tiny [[red dwarf]]s, begin to fade. At the end of the stellar age, galaxies will be composed of [[compact star|compact objects]]: [[brown dwarf]]s, [[white dwarf]]s that are cooling or cold ("[[black dwarf]]s"), [[neutron star]]s, and [[black hole]]s. Eventually, as a result of [[relaxation time|gravitational relaxation]], all stars will either fall into central supermassive black holes or be flung into intergalactic space as a result of collisions.<ref name="cosmic_battle" /><ref>
{{cite web
|last1=Pobojewski |first1=S.
|date=January 21, 1997
|title=Physics offers glimpse into the dark side of the Universe
|url=http://www.umich.edu/~urecord/9697/Jan21_97/artcl17.htm
|publisher=[[University of Michigan]]
|accessdate=January 13, 2007
}}</ref>

==Larger-scale structures==
{{Main|Observable universe#Large-scale structure|Galaxy filament|Galaxy groups and clusters}}
Deep sky surveys show that galaxies are often found in groups and [[Clusters of galaxies|clusters]]. Solitary galaxies that have not significantly interacted with another galaxy of comparable mass during the past billion years are relatively scarce. Only about 5% of the galaxies surveyed have been found to be truly isolated; however, these isolated formations may have interacted and even merged with other galaxies in the past, and may still be orbited by smaller, satellite galaxies. Isolated galaxies<ref group=note>The term "field galaxy" is sometimes used to mean an isolated galaxy, although the same term is also used to describe galaxies that do not belong to a cluster but may be a member of a group of galaxies.</ref> can produce stars at a higher rate than normal, as their gas is not being stripped by other nearby galaxies.<ref>
{{cite web
|last1=McKee |first1=M.
|date=June 7, 2005
|title=Galactic loners produce more stars
|url=http://www.newscientist.com/article.ns?id=dn7478
|publisher=[[New Scientist]]
|accessdate=January 15, 2007
}}</ref>

On the largest scale, the Universe is continually expanding, resulting in an average increase in the separation between individual galaxies (see [[Hubble's law]]). Associations of galaxies can overcome this expansion on a local scale through their mutual gravitational attraction. These associations formed early in the Universe, as clumps of dark matter pulled their respective galaxies together. Nearby groups later merged to form larger-scale clusters. This on-going merger process (as well as an influx of infalling gas) heats the inter-galactic gas within a cluster to very high temperatures, reaching 30–100 [[megakelvin]]s.<ref>
{{cite web
|url=http://chandra.harvard.edu/xray_sources/galaxy_clusters.html
|title=Groups & Clusters of Galaxies
|publisher=[[NASA]]/[[Chandra]]
|accessdate=January 15, 2007
}}</ref> About 70–80% of the mass in a cluster is in the form of dark matter, with 10–30% consisting of this heated gas and the remaining few percent of the matter in the form of galaxies.<ref>
{{cite web
|last1=Ricker |first1=P.
|title=When Galaxy Clusters Collide
|url=http://www.sdsc.edu/pub/envision/v15.2/ricker.html
|publisher=[[San Diego Supercomputer Center]]
|accessdate=August 27, 2008
}}</ref>
{{multiple image
| align = right
| direction = vertical
| width = 230
| image1 = Seyfert Sextet full.jpg
| width1 =
| alt1 =
| caption1 = [[Seyfert's Sextet]] is an example of a compact galaxy group.
| image2 =
| width2 =
| alt2 =
| caption2 = [[Millennium Simulation]] showing large-scale structure of the Cosmos. The image spans about 400 million light years across.
}}
Most galaxies in the Universe are gravitationally bound to a number of other galaxies. These form a [[fractal]]-like hierarchical distribution of clustered structures, with the smallest such associations being termed groups. A group of galaxies is the most common type of galactic cluster, and these formations contain a majority of the galaxies (as well as most of the [[baryon]]ic mass) in the Universe.<ref>
{{cite web
|last1=Dahlem |first1=M.
|date=November 24, 2006
|title=Optical and radio survey of Southern Compact Groups of galaxies
|url=http://www.atnf.csiro.au/people/mdahlem/sci/SCGs.html
|publisher=[[University of Birmingham]] Astrophysics and Space Research Group
|accessdate=January 15, 2007
|archiveurl=http://web.archive.org/web/20070613151936/http://www.atnf.csiro.au/people/mdahlem/sci/SCGs.html
|archivedate=June 13, 2007
}}</ref><ref>
{{cite web
|last1=Ponman |first1=T.
|date=February 25, 2005
|title=Galaxy Systems: Groups
|url=http://web.archive.org/web/20090215023446/http://www.sr.bham.ac.uk/research/groups.html
|publisher=[[University of Birmingham]] Astrophysics and Space Research Group
|accessdate=January 15, 2007
}}</ref> To remain gravitationally bound to such a group, each member galaxy must have a sufficiently low velocity to prevent it from escaping (see [[Virial theorem]]). If there is insufficient [[kinetic energy]], however, the group may evolve into a smaller number of galaxies through mergers.<ref>
{{cite journal
|last1=Girardi |first1=M.
|last2=Giuricin |first2=G.
|date=2000
|title=The Observational Mass Function of Loose Galaxy Groups
|journal=[[The Astrophysical Journal]]
|volume=540 |issue=1 |pages=45–56
|bibcode=2000ApJ...540...45G
|doi=10.1086/309314
|arxiv = astro-ph/0004149 }}</ref>

Clusters of galaxies consist of hundreds to thousands of galaxies bound together by gravity.<ref name="Hubble protocluster">{{cite news|title=Hubble Pinpoints Furthest Protocluster of Galaxies Ever Seen|url=http://www.spacetelescope.org/news/heic1201/|accessdate=January 22, 2015|newspaper=ESA/Hubble Press Release}}</ref> Clusters of galaxies are often dominated by a single giant elliptical galaxy, known as the [[brightest cluster galaxy]], which, over time, [[tidal force|tidally]] destroys its satellite galaxies and adds their mass to its own.<ref>
{{cite journal
|last=Dubinski |first=J.
|date=1998
|title=The Origin of the Brightest Cluster Galaxies
|url=http://www.cita.utoronto.ca/~dubinski/bcg/
|journal=[[Astrophysical Journal]]
|volume=502 |issue=2 |pages=141–149
|doi=10.1086/305901
|bibcode=1998ApJ...502..141D
|arxiv = astro-ph/9709102 }}</ref>

[[Supercluster]]s contain tens of thousands of galaxies, which are found in clusters, groups and sometimes individually. At the [[large-scale structure of the Cosmos|supercluster scale]], galaxies are arranged into sheets and filaments surrounding vast empty voids.<ref>
{{cite journal
|last1=Bahcall |first1=N. A.
|date=1988
|title=Large-scale structure in the Universe indicated by galaxy clusters
|journal=[[Annual Review of Astronomy and Astrophysics]]
|volume=26
|issue=1 |pages=631–686
|bibcode=1988ARA&A..26..631B
|doi=10.1146/annurev.aa.26.090188.003215
}}</ref> Above this scale, the Universe appears to be the same in all directions ([[isotropy|isotropic]] and [[wikt:Homogeneity|homogeneous]]).<ref>
{{cite journal
|last1=Mandolesi |first1=N.
|display-authors=etal
|date=1986
|title=Large-scale homogeneity of the Universe measured by the microwave background
|journal=[[Letters to Nature]]
|volume=319
|issue=6056 |pages=751–753
|doi=10.1038/319751a0
|bibcode = 1986Natur.319..751M }}</ref>

The Milky Way galaxy is a member of an association named the [[Local Group]], a relatively small group of galaxies that has a diameter of approximately one megaparsec. The Milky Way and the Andromeda Galaxy are the two brightest galaxies within the group; many of the other member galaxies are dwarf companions of these two galaxies.<ref>
{{cite journal
|last1=van den Bergh |first1=S.
|date=2000
|title=Updated Information on the Local Group
|journal=Publications of the Astronomical Society of the Pacific
|volume=112 |issue=770 |pages=529–536
|bibcode=2000PASP..112..529V
|doi=10.1086/316548
|arxiv = astro-ph/0001040 }}</ref> The Local Group itself is a part of a cloud-like structure within the [[Virgo Supercluster]], a large, extended structure of groups and clusters of galaxies centered on the [[Virgo Cluster]].<ref name="tully1982">
{{cite journal
|last1=Tully |first1=R. B.
|date=1982
|title=The Local Supercluster
|journal=[[Astrophysical Journal]]
|volume=257 |pages=389–422
|bibcode=1982ApJ...257..389T
|doi=10.1086/159999
}}</ref> And the Virgo Supercluster itself is a part of the [[Pisces-Cetus Supercluster Complex]], a giant [[galaxy filament]].

==Multi-wavelength observation==
{{See also|Observational astronomy}}
{{multiple image
| align = right
| direction = vertical
| width = 220
| image1 =
| caption1 = A visual light image of [[Andromeda Galaxy]] shows the emission of ordinary stars and the light reflected by dust.
| image2 = Andromeda galaxy.jpg
| caption2 = This ultraviolet image of [[Andromeda Galaxy|Andromeda]] shows blue regions containing young, massive stars.
}}
The peak radiation of most stars lies in the [[visible spectrum]], so the observation of the stars that form galaxies has been a major component of [[optical astronomy]]. It is also a favorable portion of the spectrum for observing ionized [[H II region]]s, and for examining the distribution of dusty arms.

The [[cosmic dust|dust]] present in the interstellar medium is opaque to visual light. It is more transparent to [[far infrared astronomy|far-infrared]], which can be used to observe the interior regions of giant molecular clouds and [[Bulge (astronomy)|galactic cores]] in great detail.<ref>
{{cite web
|title=Near, Mid & Far Infrared
|url=http://www.ipac.caltech.edu/Outreach/Edu/Regions/irregions.html
|publisher=[[Infrared Processing and Analysis Center|IPAC]]/[[NASA]]
|accessdate=January 2, 2007
}}</ref> Infrared is also used to observe distant, [[redshift|red-shifted]] galaxies that were formed much earlier in the history of the Universe. Water vapor and [[carbon dioxide]] absorb a number of useful portions of the infrared spectrum, so high-altitude or space-based telescopes are used for [[infrared astronomy]].

The first non-visual study of galaxies, particularly active galaxies, was made using [[radio astronomy|radio frequencies]]. The atmosphere is nearly transparent to radio between 5 [[Hertz|MHz]] and 30 GHz. (The [[ionosphere]] blocks signals below this range.)<ref>
{{cite web
|title=The Effects of Earth's Upper Atmosphere on Radio Signals
|url=http://radiojove.gsfc.nasa.gov/education/educ/radio/tran-rec/exerc/iono.htm
|publisher=[[NASA]]
|accessdate=August 10, 2006
}}</ref> Large radio [[interferometry|interferometers]] have been used to map the active jets emitted from active nuclei. [[Radio telescope]]s can also be used to observe neutral hydrogen (''via'' [[hydrogen line|21 cm radiation]]), including, potentially, the non-ionized matter in the early Universe that later collapsed to form galaxies.<ref>
{{cite news
|title=Giant Radio Telescope Imaging Could Make Dark Matter Visible
|url=http://www.sciencedaily.com/releases/2006/12/061214135537.htm
|publisher=[[ScienceDaily]]
|date=December 14, 2006
|accessdate=January 2, 2007
}}</ref>

[[UV astronomy|Ultraviolet]] and [[X-ray astronomy|X-ray telescopes]] can observe highly energetic galactic phenomena. An ultraviolet flare was observed when a star in a distant galaxy was torn apart from the tidal forces of a black hole.<ref>
{{cite news
|title=NASA Telescope Sees Black Hole Munch on a Star
|url=http://www.nasa.gov/mission_pages/galex/galex-20061205.html
|publisher=[[NASA]]
|date=December 5, 2006
|accessdate=January 2, 2007
}}</ref> The distribution of hot gas in galactic clusters can be mapped by X-rays. The existence of supermassive black holes at the cores of galaxies was confirmed through X-ray astronomy.<ref>
{{cite web
|last1=Dunn |first1=R.
|title=An Introduction to X-ray Astronomy
|url=http://www-xray.ast.cam.ac.uk/xray_introduction/
|publisher=[[Institute of Astronomy, Cambridge|Institute of Astronomy]] X-Ray Group
|accessdate=January 2, 2007
}}</ref>

==See also==
{{Wikipedia books|Galaxies}}
{{colbegin|2}}
* [[Dark galaxy]]
* [[Galactic orientation]]
* [[Galaxy formation and evolution]]
* [[Illustris project]]
* [[List of galaxies]]
* [[List of nearest galaxies]]
* [[Luminous infrared galaxy]]
* [[Supermassive black hole]]
* [[Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure]]
{{colend}}
{{Portal bar|Astronomy|Space|Cosmology}}

==Notes==
{{reflist|group=note}}

==References==
{{Reflist|colwidth=30em|refs=
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<ref name="heidarzadeh23">{{harvnb|Heidarzadeh|2008|pp=23–25}}</ref>

<ref name="heidarzadeh25">{{harvnb|Heidarzadeh|2008|p=25, Table 2.1}}</ref>

<ref name=paul1993>{{harvnb|Paul|1993|pp=16–18}}</ref>

<ref name=al_biruni>{{harvnb|Al-Biruni|2004|p=87}}</ref>

<ref name=mohamed>{{harvnb|Mohamed|2000|pp=49–50}}</ref>

<ref name="NSOG">{{harvnb|Kepple|Sanner|1998|p=18}}</ref>

<ref name=bergh1998>{{harvnb|Van den Bergh|1998|p=17}}</ref>

<ref name=waller_hodge2003>{{harvnb|Waller|Hodge|2003|p=91}}</ref>

<ref name=bertin_lin1996>{{harvnb|Bertin|Lin|1996|pp=65–85}}</ref>

<ref name=belkora355>{{harvnb|Belkora|2003|p=355}}</ref>

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<ref name=konean2006>
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<ref name=oed>
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<ref name=rao2005>
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}} 

=== Other references ===
* {{cite web
|date=May 3, 2000
|title=Unveiling the Secret of a Virgo Dwarf Galaxy
|url=http://web.archive.org/web/20090109032310/http://www.eso.org/outreach/press-rel/pr-2000/pr-12-00.html
|publisher=[[ESO]]
|accessdate=January 3, 2007
}}

==Bibliography==
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|others=R. Ramsay Wright (transl.)
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|title=The Book of Instruction in the Elements of the Art of Astrology
|url=http://books.google.com/books?id=VbPna7GOoIEC&pg=PA87
|publisher=[[Kessinger Publishing]]
|isbn=0-7661-9307-1
}}
*{{Cite book |ref=harv
|last1=Belkora |first1=L.
|date=2003
|title=Minding the Heavens: the Story of our Discovery of the Milky Way
|publisher=[[CRC Press]]
|isbn=0-7503-0730-7
}}
*{{Cite book |ref=harv
|last1=Bertin |first1=G.
|last2=Lin |first2=C.-C.
|date=1996
|title=Spiral Structure in Galaxies: a Density Wave Theory
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}}
*{{Cite book
|last1=Binney |first1=J.
|last2=Merrifield |first2=M.
|date=1998
|title=Galactic Astronomy
|publisher=[[Princeton University Press]]
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*{{Cite book
|last1=Dickinson |first1=T.
|date=2004
|title=The Universe and Beyond
|edition=4th
|publisher=[[Firefly Books]]
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}}
*{{Cite book |ref=harv
|last1=Heidarzadeh |first1=T.
|date=2008
|title=A History of Physical Theories of Comets, from Aristotle to Whipple
|publisher=[[Springer (publisher)|Springer]]
|isbn=1-4020-8322-X
}}
* {{Cite book |ref=harv
|last=Ho |first= Houjun
|last2=van den Bosch|first2=Frank
|last3=White|first3=Simon
|author3-link=Simon White
|date=2010
|title=Galaxy Formation and Evolution
|publisher= [[Cambridge University Press]]
|edition=1
|isbn= 978-0521857932 }}
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|last1=Kepple |first1=G. R.
|last2=Sanner |first2=G. W.
|date=1998
|title=The Night Sky Observer's Guide, Volume 1
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|last=Merritt |first=D.
|author-link=David Merritt
|date=2013
|title=Dynamics and Evolution of Galactic Nuclei
|publisher=[[Princeton University Press]]
|isbn=9781400846122
}}
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|last1=Mohamed |first1=M.
|date=2000
|title=Great Muslim Mathematicians
|publisher=[[Penerbit UTM]]
|isbn=983-52-0157-9
|oclc=48759017
}}
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|last1=Paul |first1=E. R.
|date=1993
|title=The Milky Way Galaxy and Statistical Cosmology, 1890–1924
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|last1=Sparke |first1=L. S.
|last2=Gallagher III |first2=J. S.
|date=2000
|title=Galaxies in the Universe: An Introduction
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|isbn=0-521-59740-4
}}
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|last1=Van den Bergh |first1=S.
|date=1998
|title=Galaxy Morphology and Classification
|publisher=[[Cambridge University Press]]
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*{{cite book |ref=harv
|last1=Waller |first1=W. H.
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|date=2003
|title=Galaxies and the Cosmic Frontier
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}}
{{refend}}

==External links==
{{Sister project links|wikt=galaxy|common=Category:Galaxies|q=no|v=no|s=no|b=High School Earth Science/Galaxies}}
* {{In Our Time|Galaxies|p003c1cn|Galaxies}}
* [http://messier.seds.org/galaxy.html Galaxies, SEDS Messier pages]
* [http://www.atlasoftheuniverse.com/ An Atlas of The Universe]
* [http://www.nightskyinfo.com/galaxies Galaxies — Information and amateur observations]
* [http://science.nasa.gov/headlines/y2002/08feb_gravlens.htm The Oldest Galaxy Yet Found]
* [http://www.galaxyzoo.org Galaxy classification project, harnessing the power of the internet and the human brain]
* [http://www.physics.org/facts/sand-galaxies.asp How many galaxies are in our Universe?]
* [http://www.astronoo.com/en/galaxies.html The most beautiful galaxies on Astronoo]
* [http://www.youtube.com/watch?v=08LBltePDZw 3-D Video (01:46) – Over a Million Galaxies of Billions of Stars each – BerkeleyLab/animated.]

{{Galaxy}}

{{Featured article}}

{{Authority control}}
[[Category:Galaxies| ]]

User:WikipediaTutorials/sandbox

2015-08-05T04:03:04Z

WikipediaTutorials: /* Exploration */ added link

{{User sandbox}}

{{redirect|ISS}}
{{Use British English|date=December 2013}}
{{Use dmy dates|date=February 2015}}
{{Infobox space station
| station = International Space Station
| station_image =International Space Station after undocking of STS-132.jpg
| station_image_alt = A rearward view of the International Space Station backdropped by the limb of the Earth. In view are the station's four large, gold-coloured solar array wings, two on either side of the station, mounted to a central truss structure. Further along the truss are six large, white radiators, three next to each pair of arrays. In between the solar arrays and radiators is a cluster of pressurised modules arranged in an elongated T shape, also attached to the truss. A set of blue solar arrays are mounted to the module at the aft end of the cluster.
| station_image_size = 300px
| extra_image_size = 300px
| extra_image_caption = The International Space Station on 23 May 2010 as seen from the departing {{OV|104}} during [[STS-132]].
| sign = ''Alpha'', ''Station''
| crew = Fully crewed: 6 Currently aboard: 6 ([[Expedition 44]])
| launch = 20 November 1998
| launch_pad = {{nowrap|[[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|1/5]] and [[Baikonur Cosmodrome Site 81|81/23]] [[Kennedy Space Center|Kennedy]] [[Kennedy Space Center Launch Complex 39|LC-39]]}}
| mass = Approximately {{convert|450000|kg|lbs|abbr=on}}
| length = {{convert|72.8|m|ft|abbr=on}}
| width = {{convert|108.5|m|ft|abbr=on}}
| height = c. 20 m (c. 66 ft) nadir–zenith, arrays forward–aft (27 November 2009){{Update after|2010|05|23|reason=MRM-1 & MRM-2}}
| volume = {{convert|916|m3|abbr=on}} (3 November 2014)
| pressure = 101.3 [[pascal (unit)|kPa]] (29.91 [[inch of mercury|inHg]], 1 [[Atmosphere (unit)|atm]])
| apogee = {{convert|{{Orbit|apogee|416}}|km|abbr=on}} [[Above mean sea level|AMSL]]{{Orbit|ref|<ref name="heavens-above">{{cite web|url=http://www.heavens-above.com/orbit.aspx?satid=25544|title=ISS - Orbit|last=Peat|first=Chris|publisher=Heavens-Above|date=25 January 2015|accessdate=25 January 2015}}</ref>}}
| perigee = {{convert|{{Orbit|perigee|409}}|km|abbr=on}} [[Above mean sea level|AMSL]]{{Orbit|ref|<ref name="heavens-above"/>}}
| inclination = {{Orbit|inclination|51.65}} [[degree (angle)|degrees]]{{Orbit|ref|<ref name="heavens-above"/>}}
| speed = {{convert|{{Orbit|speed at epoch|7.66}}|km/s|km/h mph}}{{Orbit|ref|<ref name="heavens-above"/>}}
| period = {{Orbit|period|92.69}} minutes{{Orbit|ref|<ref name="heavens-above"/>}}
| in_orbit = {{age in days|1998|11|20}} ({{date||dmy}})
| occupied = {{age in days|2000|11|02}} ({{date||dmy}})
| orbits = {{Orbit|orbits|92579}}{{Orbit|ref|<ref name="heavens-above"/>}}
| orbit_epoch = {{Orbit|epoch|25 January 2015}}{{Orbit|ref|<ref name="heavens-above"/>}}
| decay = 2 km/month
| NSSDC_ID = 1998-067A
| as_of = 9 March 2011 (unless noted otherwise)
| stats_ref =<ref name="heavens-above" /><ref name="ISStD" /><ref name="OnOrbit" /><ref>{{cite web|format=PDF|url=http://www.nasa.gov/pdf/451029main_sts132_press_kit.pdf|publisher=NASA|accessdate=19 June 2010|title=STS-132 Press Kit|date=7 May 2010}}</ref><ref>{{cite web|url=http://www.nasa.gov/pdf/521138main_fd04_ep.pdf|publisher=NASA|date=27 February 2011|accessdate=27 February 2011|title=STS-133 FD 04 Execute Package}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html|publisher=NASA|date=3 November 2014|accessdate=5 December 2014|title=NASA — Facts and Figures — International Space Station}}</ref>
| configuration_image = ISS configuration 2011-05 en.svg
| configuration_alt = The components of the ISS in an exploded diagram, with modules on-orbit highlighted in orange, and those still awaiting launch in blue or pink
| configuration_caption = Station elements {{As of|2011|12|lc=on}}, but missing ''Pirs'' ([[exploded view]])
| configuration_size = 300px
}}

The '''International Space Station''' ('''ISS''') is a [[space station]], or a habitable [[satellite|artificial satellite]], in [[low Earth orbit]]. Its first component launched into orbit in 1998, and the ISS is now the largest artificial body in orbit and can often be seen with the [[naked eye]] from Earth.<ref>{{cite web|title= Central Research Institute for Machine Building (FGUP TSNIIMASH) Control of manned and unmanned space vehicles from Mission Control Centre Moscow |publisher= Russian Federal Space Agency |url=ftp://130.206.92.88/Espacio/Mesa%20Redonda%205%20-%20R3%20-%20TSNIIMASH%20-%20V%20M%20IVANOV.pdf| accessdate=26 September 2011}}</ref><ref>{{cite web|url=http://spaceflight.nasa.gov/realdata/sightings/help.html |title=NASA Sightings Help Page |publisher=Spaceflight.nasa.gov |date=30 November 2011 |accessdate=1 May 2012}}</ref> The ISS consists of pressurised modules, external trusses, [[solar arrays]] and other components. ISS components have been launched by Russian [[Proton (rocket)|Proton]] and [[Soyuz (rocket family)|Soyuz]] rockets as well as American [[Space Shuttle]]s.<ref name="ISSBook">{{cite book|isbn=978-0-387-78144-0|date=17 June 2008|publisher=Springer-Praxis|author=John E. Catchpole|title=The International Space Station: Building for the Future}}</ref>

The ISS serves as a [[microgravity]] and [[space environment]] research laboratory in which crew members conduct experiments in [[biology]], [[human biology]], [[physics]], [[astronomy]], [[meteorology]] and [[Scientific research on the ISS|other fields]].<ref name="ISS overview">{{cite web|url=http://www.shuttlepresskit.com/ISS_OVR/index.htm|title=International Space Station Overview|publisher=ShuttlePressKit.com|date=3 June 1999|accessdate=17 February 2009}}</ref><ref name="NASA Fields of Research">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/A-fieldsresearch/index.html|archiveurl=https://web.archive.org/web/20080123150641/http://pdlprod3.hosc.msfc.nasa.gov/A-fieldsresearch/index.html|archivedate=25 March 2008|title=Fields of Research|date=26 June 2007|publisher = NASA}}</ref><ref name="NASA ISS Goals">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/B-gettingonboard/index.html|archiveurl=https://web.archive.org/web/20071208091537/http://pdlprod3.hosc.msfc.nasa.gov/B-gettingonboard/index.html|archivedate=8 December 2007| title = Getting on Board|date = 26 June 2007| publisher=NASA}}</ref> The station is suited for the testing of spacecraft systems and equipment required for missions to the Moon and Mars.<ref name="ResProg">{{cite web|url=http://spaceflightsystems.grc.nasa.gov/Advanced/ISSResearch/|title=ISS Research Program|publisher=NASA|accessdate=27 February 2009}}{{dead link|date=August 2011}}</ref> The ISS [[Orbital station-keeping|maintains an orbit with an altitude]] of between {{convert|330|and|435|km|mi|0|abbr=on}} by means of reboost manoeuvres using the engines of the [[Zvezda (ISS module)|Zvezda module]] or visiting spacecraft. It completes {{Orbit|daily orbits|15.54}} orbits per day.<ref name="tracking" />

ISS is the ninth space station to be inhabited by crews, following the Soviet and later Russian [[Salyut]], [[Almaz]], and [[Mir]] stations as well as [[Skylab]] from the US. The station has been continuously occupied for {{age in years and days|2 Nov 2000|sep=and}} since the arrival of [[Expedition 1]] on 2 November 2000. This is the longest continuous human presence in space, having surpassed the previous record of {{age in years and days|5 Sep 1989|28 Aug 1999|sep=and}} held by Mir. The station is serviced by a variety of visiting spacecraft: [[Soyuz (spacecraft)|Soyuz]], [[Progress (spacecraft)|Progress]], the [[Automated Transfer Vehicle]], the [[H-II Transfer Vehicle]],<ref name="ISSRG" /> [[Dragon (spacecraft)|Dragon]], and [[Cygnus (spacecraft)|Cygnus]]. It has been visited by astronauts, cosmonauts and space tourists from [[List of International Space Station visitors|15 different nations]].<ref name="10th">{{cite web|url=http://www.nasa.gov/mission_pages/station/main/10th_anniversary.html|title=Nations Around the World Mark 10th Anniversary of International Space Station|publisher=NASA|date=17 November 2008|accessdate=6 March 2009}}</ref>

After the US Space Shuttle program ended in 2011, Soyuz rockets became the only provider of transport for astronauts at the International Space Station, and Dragon became the only provider of bulk [[downmass|cargo-return-to-Earth]] services (downmass capability of Soyuz capsules is very limited).

The [[International Space Station program|ISS programme]] is a joint project among five participating space agencies: [[NASA]], [[Russian Federal Space Agency|Roscosmos]], [[Japan Aerospace Exploration Agency|JAXA]], [[European Space Agency|ESA]], and [[Canadian Space Agency|CSA]].<ref name="ISSRG" /><ref name="PartStates">{{cite web|url=http://www.esa.int/esaHS/partstates.html|title=Human Spaceflight and Exploration—European Participating States|accessdate=17 January 2009|publisher=European Space Agency (ESA)|year=2009}}</ref> The ownership and use of the space station is established by intergovernmental treaties and agreements.<ref name="ESA-IGA">{{cite web|url=http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station/International_Space_Station_legal_framework|title=International Space Station legal framework|publisher=European Space Agency (ESA)|accessdate=21 February 2015|date=19 November 2013}}</ref> The station is divided into two sections, the [[Russian Orbital Segment]] (ROS) and the [[US Orbital Segment|United States Orbital Segment]] (USOS), which is shared by many nations. {{asof|2014|January}}, the American portion of ISS was funded until 2024.<ref>{{cite web|url=http://www.washingtonpost.com/national/health-science/nasa-space-station-operation-extended-by-obama-until-2024-at-least/2014/01/08/9819d5c8-788e-11e3-8963-b4b654bcc9b2_story.html|title=NASA: International space station operation extended by Obama until at least 2024|last=Achenbach|first=Joel|publisher=washingtonpost.com|date=8 January 2014|accessdate=8 January 2014}}</ref><ref>{{cite web|url=http://spaceflightnow.com/news/n1003/11station/|title=Space station partners set 2028 as certification goal|last=Clark|first=Stephen|date=11 March 2010|publisher=Spaceflight Now|accessdate=1 June 2011}}</ref><ref>{{cite news| url=http://www.cbc.ca/news/technology/story/2012/02/29/science-international-space-station.html | work=CBC News | title=Canada's space station commitment renewed | date=29 February 2012}}</ref> Roscosmos has endorsed the continued operation of ISS through 2024,<ref name="sn20150225"/> but have proposed using elements of the Russian Orbital Segment to construct a new Russian space station called [[Orbital Piloted Assembly and Experiment Complex|OPSEK]].<ref name="moscow20141117">{{cite news |url=http://www.themoscowtimes.com/business/article/russia-may-be-planning-national-space-station-to-replace-iss/511299.html |title=Russia May Be Planning National Space Station to Replace ISS |work=The Moscow Times |first=Matthew |last=Bodner |date=17 November 2014 |accessdate=3 March 2015}}</ref>

On March 28, 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS.<ref name=":0">{{cite web|url= http://www.independent.co.uk/news/science/russia-and-the-us-will-build-a-new-space-station-together-10140890.html|title=Russia and the US will build a new space station together |publisher=The Independent|date=28 March 2015}}</ref><ref name=":1">{{Cite news|url = http://rt.com/news/244797-russia-us-new-space-station/|title = Russia & US agree to build new space station after ISS, work on joint Mars project|last = |first = |date = March 28, 2015|work = RT|access-date = March 28, 2015}}</ref> NASA later issued a guarded statement expressing thanks for Russia's interest in future cooperation in space exploration, but fell short of confirming the Russian announcement.<ref>{{Cite news|url = http://www.engadget.com/2015/03/28/nasa-is-working-with-russia-on-a-new-space-station/|title = NASA is working with Russia on a new space station (update: not quite) |last = Moon|first = Mariella|date = 28 March 2015|work = Engadget|access-date = 29 March 2015}}</ref><ref name="no plans">{{cite web|url=http://spacenews.com/nasa-says-no-plans-for-iss-replacement-with-russia/|title=NASA Says No Plans for ISS Replacement with Russia|date=March 28, 2015|author=Jeff Foust|publisher=SpaceNews}}</ref>

{{TOC limit|limit=3}}

==Purpose==
[[File:STS-129 Zvezda sunrise.jpg|thumb|Sunrise at ''Zvezda'']]
[[File:STS-134 EVA4 view to the Space Shuttle Endeavour.jpg|thumb|right|Fisheye view of several labs]]
According to the original Memorandum of Understanding between NASA and Rosaviakosmos, the International Space Station was intended to be a laboratory, observatory and factory in [[low Earth orbit]]. It was also planned to provide transportation, maintenance, and act as a staging base for possible future missions to the Moon, Mars and asteroids.<ref name="RSA-MOU">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/nasa_rsa.html|title=Memorandum of Understanding Between the National Aeronautics and Space Administration of the United States of America and the Russian Space Agency Concerning Cooperation on the Civil International Space Station|publisher=NASA|accessdate=19 April 2009|date=29 January 1998}}</ref> In the 2010 United States National Space Policy, the ISS was given additional roles of serving commercial, diplomatic<ref>{{cite journal|last=Payette|first=Julie|title=Research and Diplomacy 350 Kilometers above the Earth: Lessons from the International Space Station|journal=Science & Diplomacy|date=10 December 2012|volume=1|issue=4|url=http://www.sciencediplomacy.org/article/2012/research-and-diplomacy-350-kilometers-above-earth}}</ref> and educational purposes.<ref name=USNSP>{{cite web|title=National Space Policy of the United States of America|url=http://www.whitehouse.gov/sites/default/files/national_space_policy_6-28-10.pdf|publisher=White House; USA Federal government|accessdate=20 July 2011}}</ref>

===Scientific research===
{{Main|Scientific research on the ISS|l1=Scientific research on the ISS}}
The ISS provides a platform to conduct scientific research. Small unmanned spacecraft can provide platforms for zero gravity and exposure to space, but space stations offer a long term environment where studies can be performed potentially for decades, combined with ready access by human researchers over periods that exceed the capabilities of manned spacecraft.<ref name="10th" /><ref name="Worldbook at NASA" />

The Station simplifies individual experiments by eliminating the need for separate rocket launches and research staff. The wide variety of research fields include [[astrobiology]], [[astronomy]], [[Zero g#Health effects of weightlessness|human research]] including [[space medicine]] and [[life science]]s, [[physical science]]s, [[materials science]], [[space weather]], and weather on Earth ([[meteorology]]).<ref name="ISS overview" /><ref name="NASA Fields of Research" /><ref name="NASA ISS Goals" /><ref>{{cite web|url=http://www.isas.jaxa.jp/e/forefront/2009/ueno/index.shtml|title=Monitor of All-sky X-ray Image (MAXI)|year=2008|publisher=JAXA|accessdate=12 March 2011}}</ref><ref>[http://www.spaceref.com/news/viewpr.html?pid=33007 ESA via SPACEREF] "SOLAR: three years observing and ready for solar maximum", 14 March 2011</ref> Scientists on Earth have access to the crew's data and can modify experiments or launch new ones, which are benefits generally unavailable on unmanned spacecraft.<ref name="Worldbook at NASA" /> Crews fly [[List of International Space Station expeditions|expeditions]] of several months duration, providing approximately 160-man-hours per week of labour with a crew of 6.<ref name="ISS overview"/><ref name="Science in School">{{cite web|url=http://www.scienceinschool.org/2008/issue10/iss|title=The International Space Station: life in space|publisher=Science in School|date=10 December 2008|accessdate=17 February 2009}}</ref>

To detect dark matter and answer other fundamental questions about our universe, engineers and scientists from all over the world built the [[Alpha Magnetic Spectrometer]] (AMS), which NASA compares to the [[Hubble space telescope]], and says could not be accommodated on a free flying satellite platform due in part to its power requirements and data bandwidth needs.<ref>[http://www.nasa.gov/mission_pages/shuttle/main/amsprocessing.html NASA – AMS to Focus on Invisible Universe]. Nasa.gov (18 March 2011). Retrieved 8 October 2011.</ref><ref>[http://science.nasa.gov/science-news/science-at-nasa/2009/14aug_ams/ In Search of Antimatter Galaxies – NASA Science]. ''Science''.nasa.gov (16 May 2011). Retrieved 8 October 2011.</ref> On 3 April 2013, [[NASA]] scientists reported that hints of [[dark matter]] may have been detected by the Alpha Magnetic Spectrometer.<ref name="APS-20130403">{{cite journal |authors=Aguilar, M. et al. (AMS Collaboration) |title=First Result from the Alpha Magnetic Spectrometer on the International Space Station: Precision Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–350 GeV|url=http://prl.aps.org/abstract/PRL/v110/i14/e141102 |date=3 April 2013 |journal=[[Physical Review Letters]]|accessdate=3 April 2013 |doi=10.1103/PhysRevLett.110.141102 }}</ref><ref name="AMS-20130403">{{cite web |author=Staff |title=First Result from the Alpha Magnetic Spectrometer Experiment|url=http://www.ams02.org/2013/04/first-results-from-the-alpha-magnetic-spectrometer-ams-experiment/ |date=3 April 2013 |work=AMS Collaboration |accessdate=3 April 2013 }}</ref><ref name="AP-20130403">{{cite news |last1=Heilprin|first1=John |last2=Borenstein |first2=Seth |title=Scientists find hint of dark matter from cosmos|url=http://apnews.excite.com/article/20130403/DA5E6JAG3.html |date=3 April 2013 |agency=Associated Press |accessdate=3 April 2013 }}</ref><ref name="BBC-20130403">{{cite news |last=Amos |first=Jonathan |title=Alpha Magnetic Spectrometer zeroes in on dark matter |url=http://www.bbc.co.uk/news/science-environment-22016504 |date=3 April 2013 |work=[[BBC News]] |accessdate=3 April 2013 }}</ref><ref name="NASA-20130403">{{cite web |last1=Perrotto|first1=Trent J. |last2=Byerly |first2=Josh |title=NASA TV Briefing Discusses Alpha Magnetic Spectrometer Results|url=http://www.nasa.gov/home/hqnews/2013/apr/HQ_M13-054_AMS_Findings_Briefing.html |date=2 April 2013|work=[[NASA]] |accessdate=3 April 2013 }}</ref><ref name="NYT-20130403">{{cite news |last=Overbye |first=Dennis |title=New Clues to the Mystery of Dark Matter |url=http://www.nytimes.com/2013/04/04/science/space/new-clues-to-the-mystery-of-dark-matter.html |date=3 April 2013 |work=[[The New York Times]] |accessdate=3 April 2013 }}</ref> According to the scientists, "[[Alpha Magnetic Spectrometer#First results|The first results]] from the space-borne Alpha Magnetic Spectrometer confirm an unexplained excess of high-energy positrons in Earth-bound cosmic rays."

{{Double image|right|Iss030e015472 Edit.jpg|117|ISS-08 Michael Foale conducts an inspection of the Microgravity Science Glovebox.jpg|241|[[C/2011 W3 (Lovejoy)|Comet Lovejoy]] photographed by [[Expedition 30]] commander [[Dan Burbank]]|[[Expedition 8]] Commander and Science Officer [[Michael Foale]] conducts an inspection of the [[Microgravity Science Glovebox]]}}
The space environment is hostile to life. Unprotected presence in space is characterised by an intense radiation field (consisting primarily of protons and other subatomic charged particles from the [[solar wind]], in addition to [[cosmic ray]]s), high vacuum, extreme temperatures, and microgravity.<ref name="Space Microbiology">{{cite web|url=http://syntheticbiology.arc.nasa.gov/files/SpaceMicrobiology%20MMBR%201.pdf|title=Space Microbiology, section Space Environment (p. 122)|publisher=Microbiology and Molecular Biology Reviews|date=March 2010|accessdate=4 June 2011|author=G Horneck, DM Klaus & RL Mancinelli}}</ref> Some simple forms of life called [[extremophile]]s,<ref name="Beer microbes">{{cite news|url=http://www.bbc.co.uk/news/science-environment-11039206|title=Beer microbes live 553 days outside ISS|work=[[BBC News]]|date=23 August 2010|accessdate=4 June 2011|author=Jonathan Amos}}</ref> including small invertebrates called [[tardigrade]]s<ref name="Waterbears">{{cite web|url=http://www.nature.com/news/2008/080908/full/news.2008.1087.html|title=Spacesuits optional for 'water bears'|work=Nature|date=8 September 2008|accessdate=4 June 2011}}</ref> can survive in this environment in an extremely dry state called [[Desiccation#Biology and ecology|desiccation]].

Medical research improves knowledge about the effects of long-term space exposure on the human body, including [[muscle atrophy]], [[Osteoporosis|bone loss]], and fluid shift. This data will be used to determine whether lengthy [[human spaceflight]] and [[space colonisation]] are feasible. As of 2006, data on bone loss and muscular atrophy suggest that there would be a significant risk of fractures and movement problems if astronauts landed on a planet after a lengthy interplanetary cruise, such as the six-month interval required to [[Manned mission to Mars|travel to Mars]].<ref name="JCB">{{cite book|author=Jay Buckey|title=Space Physiology|publisher=Oxford University Press USA|date=23 February 2006|isbn=978-0-19-513725-5}}</ref><ref>{{cite web|url=http://www.newscientist.com/article/dn17476-ion-engine-could-one-day-power-39day-trips-to-mars.html?full=true|work=New Scientist|accessdate=8 January 2010|date=24 July 2009|author=List Grossman|title=Ion engine could one day power 39-day trips to Mars}}</ref>
Medical studies are conducted aboard the ISS on behalf of the [[National Space Biomedical Research Institute]] (NSBRI). Prominent among these is the [[Advanced Diagnostic Ultrasound in Microgravity]] study in which astronauts perform ultrasound scans under the guidance of remote experts. The study considers the diagnosis and treatment of medical conditions in space. Usually, there is no physician on board the ISS and diagnosis of medical conditions is a challenge. It is anticipated that remotely guided ultrasound scans will have application on Earth in emergency and rural care situations where access to a trained physician is difficult.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/science/experiments/ADUM.html|date=1 May 2009|accessdate=1 October 2009|author=Brooke Boen|publisher=NASA|title=Advanced Diagnostic Ultrasound in Microgravity (ADUM)}}</ref><ref>{{cite journal|author=Sishir Rao|display-authors=etal|year=2008|title=A Pilot Study of Comprehensive Ultrasound Education at the Wayne State University School of Medicine|journal=Journal of Ultrasound in Medicine|volume=27|pages=745–749|pmid=18424650|issue=5}}</ref><ref>{{cite journal|author=Michael Fincke|display-authors=etal|year=2004|title=Evaluation of Shoulder Integrity in Space: First Report of Musculoskeletal US on the International Space Station|journal=Radiology|issue= 2|pages=319–322|pmid=15533948|doi=10.1148/radiol.2342041680|volume=234}}</ref>

====Microgravity====
[[File:Space Fire.jpg|thumb|A comparison between the combustion of a candle on [[Earth]] (left) and in a microgravity environment, such as that found on the ISS (right)]]
The Earth's gravity is only slightly weaker at the altitude of the ISS than at the surface, but objects in orbit are in a continuous state of [[Free fall|freefall]], resulting in an apparent state of weightlessness. This perceived weightlessness is disturbed by five separate effects:<ref name="gravity">{{cite web|url=http://www.esa.int/Our_Activities/Human_Spaceflight/Human_Spaceflight_Research/European_User_Guide_to_Low-Gravity_Platforms
|title=European Users Guide to Low Gravity Platforms|accessdate=22 March 2013|date=6 December 2005|publisher=European Space Agency}}</ref>
* Drag from the residual atmosphere; when the ISS enters the Earth's shadow, the main solar panels are rotated to minimise this aerodynamic drag, helping reduce [[orbital decay]].
* Vibration from movements of mechanical systems and the crew.
* Actuation of the on-board attitude [[control moment gyroscope]]s.
* [[Rocket engine|Thruster]] firings for attitude or orbital changes.
* [[Gravity-gradient stabilization|Gravity-gradient effects]], also known as [[tidal force|tidal]] effects. Items at different locations within the ISS would, if not attached to the station, follow slightly different orbits. Being mechanically interconnected these items experience small forces that keep the station moving as a [[rigid body]].

[[File:ISS-20 Robert Thirsk at the Minus Eighty Degree Laboratory Freezer.jpg|thumb|left|ISS crew member storing samples]]

Researchers are investigating the effect of the station's near-weightless environment on the evolution, development, growth and internal processes of plants and animals. In response to some of this data, NASA wants to investigate [[microgravity]]'s effects on the growth of three-dimensional, human-like tissues, and the unusual [[protein crystal]]s that can be formed in space.<ref name="NASA Fields of Research" />

The investigation of the physics of fluids in microgravity will allow researchers to model the behaviour of fluids better. Because fluids can be almost completely combined in microgravity, physicists investigate fluids that do not mix well on Earth. In addition, an examination of reactions that are slowed by low gravity and temperatures will give scientists a deeper understanding of [[superconductivity]].<ref name="NASA Fields of Research" />

The study of [[materials science]] is an important ISS research activity, with the objective of reaping economic benefits through the improvement of techniques used on the ground.<ref>{{cite web|url=http://science.nasa.gov/newhome/headlines/msad15sep99_1.htm|title=Materials Science 101|publisher=Science@NASA|accessdate=18 June 2009|date=15 September 1999}}</ref> Other areas of interest include the effect of the low gravity environment on combustion, through the study of the efficiency of burning and control of emissions and pollutants. These findings may improve current knowledge about energy production, and lead to economic and environmental benefits. Future plans are for the researchers aboard the ISS to examine [[aerosol]]s, [[ozone]], [[water vapour]], and [[oxide]]s in Earth's atmosphere, as well as [[cosmic ray]]s, [[cosmic dust]], [[antimatter]], and [[dark matter]] in the universe.<ref name="NASA Fields of Research" />

===Exploration===
[[File:Mars500.jpg|thumb|right|A 3D plan of the Russia-based [[MARS-500]] complex, used for ground-based experiments which complement ISS-based preparations for a [[manned mission to Mars]]]]
The ISS provides a location in the relative safety of Low Earth Orbit to test spacecraft systems that will be required for long-duration missions to [[Moon|the Moon]] and [[Mars]]. This provides experience in operations, maintenance as well as repair and replacement activities on-orbit, which will be essential skills in operating spacecraft farther from Earth, mission risks can be reduced and the capabilities of interplanetary spacecraft advanced.<ref name="ResProg">{{cite web|url=http://spaceflightsystems.grc.nasa.gov/Advanced/ISSResearch/|title=ISS Research Program|publisher=NASA|accessdate=27 February 2009}}{{dead link|date=August 2011}}</ref> Referring to the [[MARS-500]] experiment, ESA states that "Whereas the ISS is essential for answering questions concerning the possible impact of weightlessness, radiation and other space-specific factors, aspects such as the effect of long-term isolation and confinement can be more appropriately addressed via ground-based simulations".<ref name="esa mars500 ">{{cite web|title=Mars500 study overview | publisher = ESA |date= 4 June 2011| url = http://www.esa.int/esaMI/Mars500/SEM7W9XX3RF_0.html }}</ref> Sergey Krasnov, the head of human space flight programmes for Russia's space agency, Roscosmos, in 2011 suggested a "shorter version" of MARS-500 may be carried out on the ISS. <ref name="Mars thing on ISS">{{cite web| title=Space station may be site for next mock Mars mission| url = http://www.newscientist.com/blogs/shortsharpscience/2011/11/space-station-may-be-site-for.html|date=4 November 2011|work=New Scientist}}</ref>

In 2009, noting the value of the partnership framework itself, Sergey Krasnov wrote, "When compared with partners acting separately, partners developing complementary abilities and resources could give us much more assurance of the success and safety of space exploration. The ISS is helping further advance near-Earth space exploration and realisation of prospective programmes of research and exploration of the Solar system, including the Moon and Mars."<ref name=IAF2009>{{cite web|title=The Sustainable Utilisation of the ISS Beyond 2015|url=http://www.iafastro.org/docs/2009/ISS2015.pdf|publisher=International Astronautical Congress|accessdate=15 December 2011}}</ref> [[Manned mission to Mars|A manned mission to Mars]] may be a multinational effort involving space agencies and countries outside the current ISS partnership. In 2010, ESA Director-General Jean-Jacques Dordain stated his agency was ready to propose to the other four partners that China, India and South Korea be invited to join the ISS partnership.<ref name="ESAproposesInvite">{{cite web|title=ESA Chief Lauds Renewed U.S. Commitment to Space Station, Earth Science | publisher =Peter B. de Selding, Space News. |date=2 March 2010 | url =http://www.spacenews.com/civil/100203-esa-chief-lauds-renewed-commitment-space-station-earth-science.html}}</ref> NASA chief [[Charlie Bolden]] stated in February 2011, "Any mission to Mars is likely to be a global effort".<ref name="Mars a global effort">{{cite web|title= Charlie Bolden | publisher = space.com |date=4 June 2011 | url = http://www.space.com/11335-nasa-mars-exploration-space-station.html }}</ref> Currently, American legislation prevents NASA co-operation with China on space projects.<ref name="justice1">{{citation|first=Virginia|last=Seitz|title=Memorandum Opinion for the General Counsel, Office of Science and Technology Policy|url=http://www.justice.gov/olc/2011/conduct-diplomacy.pdf|journal=Office of Legal Counsel|volume=35|date=11 September 2011|accessdate=23 May 2012|archiveurl=https://web.archive.org/web/20120713080223/http://www.justice.gov/olc/2011/conduct-diplomacy.pdf|archivedate=13 July 2012}}</ref>

===Education and cultural outreach===
[[File:ISS-36 HTV-4 berthing 2.jpg|thumb|Japan's Kounotori 4 docking]]
The ISS crew provides opportunities for students on Earth by running student-developed experiments, making educational demonstrations, allowing for student participation in classroom versions of ISS experiments, and directly engaging students using radio, videolink and email.<ref name="ISSRG" /><ref>{{cite journal|author1=Gro Mjeldheim Sandal |author2=Dietrich Manzey|title=Cross-cultural issues in space operations: A survey study among ground personnel of the European Space Agency|journal=Acta Astronautica|volume=65|date=December 2009|pages=1520–1529|doi=10.1016/j.actaastro.2009.03.074|issue=11–12}}</ref> ESA offers a wide range of free teaching materials that can be downloaded for use in classrooms.<ref>[http://www.esa.int/SPECIALS/Education/SEM0LW4KXMF_0.html ESA – Education – Online material]. Esa.int (7 September 2011). Retrieved 8 October 2011.</ref> In one lesson, students can navigate a 3-D model of the interior and exterior of the ISS, and face spontaneous challenges to solve in real time.<ref>[http://www.esa.int/SPECIALS/Education/SEM1LL3Z2OF_0.html ESA – Education – ISS 3-D Teaching Tool: Spaceflight Challenge I]. Esa.int (24 May 2011). Retrieved 8 October 2011.</ref>

JAXA aims both to "Stimulate the curiosity of children, cultivating their spirits, and encouraging their passion to pursue craftsmanship", and to "Heighten the child's awareness of the importance of life and their responsibilities in society."<ref>[http://www.oosa.unvienna.org/pdf/pres/copuos2010/tech-17E.pdf Building Peace in Young Minds through Space Education]. Committee on the Peaceful Uses of Outer Space, 53rd Session. June 2010, Vienna, Austria; Space Education Center, Japan Aerospace Exploration Agency (JAXA)</ref> Through a series of education guides, a deeper understanding of the past and near-term future of manned space flight, as well as that of Earth and life, will be learned.<ref>[http://www.edu.jaxa.jp/education/international/ISS/SSK/en/ JAXA Space Education Center : JAXA Spaceflight Seeds Kids I : Spaceflight Sunflower seeds – Let's make them flower! and learn freshly the Earth environment just by contrast with the Space one]. Edu.jaxa.jp. Retrieved 8 October 2011.</ref><ref>[http://www.edu.jaxa.jp/education/international/ISS/SIS/en/ JAXA Space Education Center : JAXA Seeds in Space I : Let's Cultivate Spaceflight Asagao, Miyako-gusa Seeds and Identify the Mutants!]. Edu.jaxa.jp. Retrieved 8 October 2011.</ref> In the JAXA Seeds in Space experiments, the mutation effects of spaceflight on plant seeds aboard the ISS is explored. Students grow sunflower seeds which flew on the ISS for about nine months as a start to 'touch the Universe'. In the first phase of Kibō utilisation from 2008 to mid-2010, researchers from more than a dozen Japanese universities conducted experiments in diverse fields.<ref>{{cite web |author=Keiji Murakami |url=http://www.spacepolicyonline.com/pages/images/stories/Micro%20Oct%2009%20JEM.pdf |title=JEM Utilization Overview |publisher=JAXA. Steering Committee for the Decadal Survey on Biological and Physical Sciences in Space |date=14 October 2009}}</ref>

[[Image:Crew in ATV with Jules Verne manuscript.jpg|thumb|left|Original Jules Verne manuscripts displayed by crew inside Jules Verne ATV]]
Cultural activities are another major objective. Tetsuo Tanaka, director of JAXA's Space Environment and Utilization Center, says "There is something about space that touches even people who are not interested in science."<ref name="jaxa2">{{cite web |author=Tetsuo Tanaka |url=http://www.jaxa.jp/article/special/kibo/tanaka01_e.html |title=Kibo: Japan's First Human Space Facility |publisher=JAXA |accessdate=8 October 2011}}</ref>

[[ARISS|Amateur Radio on the ISS]] (ARISS) is a volunteer programme which encourages students worldwide to pursue careers in science, technology, engineering and mathematics through [[amateur radio]] communications opportunities with the ISS crew. ARISS is an international working group, consisting of delegations from 9 countries including several countries in Europe as well as Japan, Russia, Canada, and the United States. In areas where radio equipment cannot be used, speakerphones connect students to ground stations which then connect the calls to the station. <ref>{{cite web|url=http://www.rac.ca/ariss/oindex.htm|title=Amateur Radio on the International Space Station|date=6 June 2011|accessdate=10 June 2011}}</ref>

''[[First Orbit]]'' is a feature-length documentary film about [[Vostok 1]], the first manned space flight around the Earth. By matching the orbit of the International Space Station to that of Vostok 1 as closely as possible, in terms of ground path and time of day, documentary filmmaker Christopher Riley and ESA astronaut [[Paolo Nespoli]] were able to film the view that Yuri Gagarin saw on his pioneering orbital space flight. This new footage was cut together with the original Vostok 1 mission audio recordings sourced from the Russian State Archive. Nespoli, during Expedition 26/27, filmed the majority of the footage for this documentary film, and as a result is credited as its [[Cinematographer|director of photography]].<ref>{{cite news|last=Riley|first=Christopher|title=What Yuri Gagarin saw: First Orbit film to reveal the view from Vostok 1|url=http://www.guardian.co.uk/science/blog/2011/apr/11/yuri-gagarin-first-orbit-vostok|newspaper=The Guardian|date=11 April 2011|location=London}}</ref> The film was streamed through the website firstorbit.org in a global YouTube premiere in 2011, under a free license.<ref>{{cite web|url=http://www.firstorbit.org/first-orbit-faqs |title=Yuri Gagarin's First Orbit – FAQs |publisher=Firstorbit.org |accessdate=1 May 2012}}</ref>

In May 2013, commander [[Chris Hadfield]] shot a music video of [[David Bowie]]'s ''[[Space Oddity (song)|Space Oddity]]'' on board the station; the film was released freely on YouTube.<ref>{{cite web|last=Warr |first=Philippa |url=http://www.wired.co.uk/news/archive/2013-05/13/commander-hadfield-space-oddity |title=Commander Hadfield bids farewell to ISS with Reddit-inspired Bowie cover |publisher=Wired.co.uk |date=13 May 2013 |accessdate=22 October 2013}}</ref> It was the first music video ever to be filmed in space<ref>{{Cite web|title = Commander Hadfield bids farewell to ISS with Reddit-inspired Bowie cover (Wired UK)|url = http://www.wired.co.uk/news/archive/2013-05/13/commander-hadfield-space-oddity|accessdate = 2015-08-05}}</ref>

==Assembly==
{{Main|Assembly of the International Space Station|List of ISS spacewalks}}
[[File:ISS-with-S0-S1-P1.jpg|thumb|right|alt=S0, S1 and P1 truss structures installed|Partially constructed ISS in December 2002]]
[[File:S3-S4 Truss Installed 2.jpg|thumb|S3-S4 Truss Installed in 2007]]
[[File:Soyuz TMA-19 spacecraft departs the ISS.jpg|thumb|[[Soyuz TMA-19]] departs in 2010]]
[[File:ISS after STS-117 in June 2007.jpg|thumb|ISS in 2007, with fewer solar arrays]]
The assembly of the International Space Station, a major endeavour in [[space architecture]], began in November 1998.<ref name="OnOrbit">{{cite web|url=http://www.nasa.gov/externalflash/ISSRG/pdfs/on_orbit.pdf|title=On-Orbit Elements|publisher=NASA|author=NASA|date=18 February 2010|accessdate=19 June 2010|format=PDF}}</ref> Russian modules launched and docked robotically, with the exception of ''[[Rassvet (ISS module)|Rassvet]]''. All other modules were delivered by the Space Shuttle, which required installation by ISS and shuttle crewmembers using the [[Mobile Servicing System#Canadarm2|Canadarm2]] (SSRMS) and [[List of ISS spacewalks|EVAs]]; {{as of|2011|06|05|lc=y}}, they had added 159 components during more than 1,000 hours of EVA. 127 of these spacewalks originated from the station, and the remaining 32 were launched from the airlocks of docked Space Shuttles.<ref name="ISStD" /> The [[beta angle]] of the station had to be considered at all times during construction, as the station's beta angle is directly related to the percentage of its orbit that the station (as well as any docked or docking spacecraft) is exposed to the sun; the Space Shuttle would not perform optimally above a limit called the "beta cutoff".<ref name="mcc">{{cite web|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-113/11_23_20_01_179.html|title=MCC Answers|author=Derek Hassman, NASA Flight Director|date=1 December 2002|publisher=NASA|accessdate=14 June 2009}}</ref>

The first module of the ISS, ''[[Zarya]]'', was launched on 20 November 1998 on an autonomous Russian [[Proton (rocket)|Proton rocket]]. It provided propulsion, attitude control, communications, electrical power, but lacked long-term life support functions. Two weeks later a passive NASA module ''[[Unity (ISS module)|Unity]]'' was launched aboard Space Shuttle flight [[STS-88]] and attached to Zarya by astronauts during EVAs. This module has two [[Pressurized Mating Adapter]]s (PMAs), one connects permanently to Zarya, the other allows the Space Shuttle to dock to the space station. At this time, the Russian station Mir was still inhabited. The ISS remained unmanned for two years, during which time Mir was de-orbited. On 12 July 2000 [[Zvezda (ISS module)|Zvezda]] was launched into orbit. Preprogrammed commands on board deployed its solar arrays and communications antenna. It then became the passive vehicle for a rendezvous with the Zarya and Unity. As a passive "target" vehicle, the Zvezda maintained a stationkeeping orbit as the Zarya-Unity vehicle performed the rendezvous and docking via ground control and the Russian automated rendezvous and docking system. Zarya's computer transferred control of the station to Zvezda's computer soon after docking. Zvezda added sleeping quarters, a toilet, kitchen, CO2 scrubbers, dehumidifier, oxygen generators, exercise equipment, plus data, voice and television communications with mission control. This enabled permanent habitation of the station.<ref>[http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/servmod.pdf NASA Facts. The Service Module: A Cornerstone of Russian International Space Station Modules]. NASA. January 1999</ref><ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/missions/sts-88/mission-sts-88.html |title=STS-88 |publisher=Science.ksc.nasa.gov |accessdate=19 April 2011}}</ref>

The first resident crew, [[Expedition 1]], arrived in November 2000 on [[Soyuz TM-31]]. At the end of the first day on the station, astronaut Bill Shepherd requested the use of the radio call sign "''Alpha''", which he and cosmonaut Krikalev preferred to the more cumbersome "''International Space Station''".<ref name=TIME-Nov2>{{cite news|url=http://www.time.com/time/arts/article/0,8599,59500,00.html|title=Upward Bound: Tales of Space Station Alpha|author=Brad Liston|date=2 November 2000|work=Time|accessdate=5 August 2010}}</ref> The name "''Alpha''" had previously been used for the station in the early 1990s,<ref name=GAO>{{cite web|url=http://archive.gao.gov/t2pbat3/151975.pdf|title=Space Station – Impact on the expanded Russian role of funding and research|date=21 June 1994|publisher=[[Government Accountability Office|United State General Accounting Office]]|accessdate=9 August 2010}}</ref> and following the request, its use was authorised for the whole of Expedition 1.<ref name=SPACE-Nov3>{{cite web|url=http://www.space.com/missionlaunches/missions/alpha_male_001103.html|title=Call Bill Shepherd the Alpha Male of the International Space Station|author=Alan Ladwig|date=3 November 2000|publisher=Space.com|accessdate=9 August 2010}}</ref> Shepherd had been advocating the use of a new name to project managers for some time. Referencing a [[Ship naming and launching|naval tradition]] in a pre-launch news conference he had said: "For thousands of years, humans have been going to sea in ships. People have designed and built these vessels, launched them with a good feeling that a name will bring good fortune to the crew and success to their voyage."<ref name=SPACE-Nov2>{{cite web|url=http://www.space.com/missionlaunches/missions/exp1_alpha_001102.html|title=Expedition One Crew Wins Bid To Name Space Station Alpha|date=2 November 2000|author=Todd Halvorson|publisher=Space.com|accessdate=9 August 2010}}</ref> [[Yuri Semenov]], the President of [[S.P. Korolev Rocket and Space Corporation Energia|Russian Space Corporation Energia]] at the time, disapproved of the name "''Alpha''"; he felt that ''Mir'' was the first space station, and so he would have preferred the names "''Beta''" or "''Mir 2''" for the ISS.<ref name=SPACE-Nov3 /><ref>{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=5913|title=Interview with RSC Energia's Yuri Semenov|publisher=Space.com|date=3 September 2001|accessdate=22 August 2010}}</ref><ref>{{cite web|url=http://english.ruvr.ru/2001/03/29/100146.html|title=Interview with Yuri Semenov, general designer of Space Rocket corporation Energy|date=21 March 2001|publisher=[[Voice of Russia]]|accessdate=5 October 2010}}</ref>

[[Expedition 1]] arrived midway between the flights of [[STS-92]] and [[STS-97]]. These two Space Shuttle flights each added segments of the station's [[Integrated Truss Structure]], which provided the station with Ku-band communication for US television, additional attitude support needed for the additional mass of the USOS, and substantial [[solar array]]s supplementing the station's existing 4 solar arrays.<ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/missions/sts-92/mission-sts-92.html |title=STS-92 |publisher=Science.ksc.nasa.gov |accessdate=19 April 2011}}</ref>

Over the next two years the station continued to expand. A [[Soyuz-U]] rocket delivered the [[Pirs (ISS module)|''Pirs'' docking compartment]]. The Space Shuttles ''Discovery'', ''[[Space Shuttle Atlantis|Atlantis]]'', and ''Endeavour'' delivered the [[Destiny (ISS module)|''Destiny'' laboratory]] and [[Quest Joint Airlock|''Quest'' airlock]], in addition to the station's main robot arm, the ''[[Canadarm2]]'', and several more segments of the Integrated Truss Structure.
[[File:Zvezda rear.jpg|thumb|left|Aft view showing a Progress spacecraft docked to Zvezda]]
The expansion schedule was interrupted by the {{OV|102}} [[Space Shuttle Columbia disaster|disaster]] in 2003, with the resulting two year hiatus in the [[Space Shuttle program]]me halting station assembly. The space shuttle was grounded until 2005 with [[STS-114]] flown by ''Discovery''.<ref>{{cite web|url=http://www.nasaspaceflight.com/2005/07/discovery-launches-the-shuttle-is-back/|title=Discovery launches—The Shuttle is back|author=Chris Bergin|publisher=NASASpaceflight.com|accessdate=6 March 2009|date=26 July 2005}}</ref>

Assembly resumed in 2006 with the arrival of [[STS-115]] with ''Atlantis'', which delivered the station's second set of solar arrays. Several more truss segments and a third set of arrays were delivered on [[STS-116]], [[STS-117]], and [[STS-118]]. As a result of the major expansion of the station's power-generating capabilities, more pressurised modules could be accommodated, and the ''[[Harmony (ISS module)|Harmony]]'' node and ''Columbus'' European laboratory were added. These were followed shortly after by the first two components of ''Kibō''. In March 2009, [[STS-119]] completed the Integrated Truss Structure with the installation of the fourth and final set of solar arrays. The final section of ''Kibō'' was delivered in July 2009 on [[STS-127]], followed by the Russian ''[[Poisk (ISS module)|Poisk]]'' module. The third node, ''[[Tranquility (ISS module)|Tranquility]]'', was delivered in February 2010 during [[STS-130]] by the Space Shuttle ''Endeavour'', alongside the [[Cupola (ISS module)|Cupola]], closely followed in May 2010 by the penultimate Russian module, ''[[Rassvet (ISS module)|Rassvet]]''. Rassvet was delivered by Space Shuttle ''Atlantis'' on [[STS-132]] in exchange for the Russian Proton delivery of the Zarya Module in 1998 which had been funded by the United States.<ref>{{cite web|url=http://www.russianspaceweb.com/iss_mim1.html |title=Mini-Research Module 1 (MIM1) Rassvet (MRM-1) |publisher=Russianspaceweb.com |accessdate=12 July 2011}}</ref> The last pressurised module of the USOS, ''Leonardo'', was brought to the station by ''Discovery'' on her final flight, [[STS-133]],<ref name="STS-133">{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/main/index.html |title=STS-133 |publisher=NASA |accessdate=1 September 2014}}</ref> followed by the [[Alpha Magnetic Spectrometer]] on [[STS-134]], delivered by ''Endeavour''.<ref name="STS-134">{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/main/index.html |title=STS-134 |publisher=NASA |accessdate=1 September 2014}}</ref>
[[File:Exterior of Cupola - Exp28.jpg|thumb|The Cupola arrived in 2010]]
{{As of|2011|06}}, the station consisted of fifteen pressurised modules and the [[Integrated Truss Structure]]. Still to be launched are the Russian [[Nauka (ISS module)|Multipurpose Laboratory Module]] ''Nauka'' and a number of external components, including the [[European Robotic Arm]]. Assembly is expected to be completed by April 2014,{{update inline|date=October 2014}} by which point the station will have a mass in excess of 400 [[metric ton|tonnes]] (440 [[short ton]]s).<ref name="OnOrbit" /><ref name="Manifest">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/iss_manifest.html|title=Consolidated Launch Manifest|accessdate=8 July 2008|publisher=NASA|author=NASA|year=2008}}</ref>

The gross mass of the station changes over time. The total launch mass of the modules on orbit is about {{convert|417289|kg|lbs|abbr=on}} (as of 3 September 2011).<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/isstodate.html |title=NASA – The ISS to Date (03/09/2011) |publisher=Nasa.gov |accessdate=12 July 2011}}</ref> The mass of experiments, spare parts, personal effects, crew, foodstuff, clothing, propellants, water supplies, gas supplies, docked spacecraft, and other items add to the total mass of the station. Hydrogen gas is constantly vented overboard by the oxygen generators.

==Station structure==
{{Double image|right|ROS Windows 0114 complete.jpg|130|USOS window identification.png|160|Russian Orbital Segment Windows|USOS International Space Station window locations}}

The ISS is a third generation<ref>{{cite web|url=http://www.dlr.de/iss/en/desktopdefault.aspx/tabid-1945/2746_read-4182/gallery-1/gallery_read-Image.19.2296/ |title=DLR – International Space Station ISS – From Cold War to international cooperation – the story of the ISS |publisher=Dlr.de |accessdate=1 May 2012}}</ref> modular space station.<ref>{{cite web|url=http://www.astronautix.com/articles/thistems.htm |title=Third Generation Soviet Space Systems |publisher=Astronautix.com |accessdate=1 May 2012}}</ref> Modular stations can allow the mission to be changed over time and new modules can be added or removed from the existing structure, allowing greater flexibility.

Below is a diagram of major station components. The blue areas are pressurised sections accessible by the crew without using spacesuits. The station's unpressurised superstructure is indicated in red. Other unpressurised components are yellow. Note that the Unity node joins directly to the Destiny laboratory. For clarity, they are shown apart.

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PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | |AMS|~|ZVEZDA|~|AMS|
AMS = [[Zvezda (ISS module)|Solar array]]
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PIRS = [[Pirs (ISS module)|'''Pirs''' Airlock]]
|SGM2 = [[Poisk (ISS module)|'''Poisk''' (MRM-2) Airlock]]
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{{familytree| | | | | | | | | | | | |!|!|}}
{{familytree| | | | | | | | | | | | |!|`|-|MLM|~|ERA| | |
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| ERA = '''[[European Robotic Arm|European Robotic Arm]]'''
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{{familytree| | | | | | | |SA|~|ZARYA|~|SA| | | |
SA = [[Zarya (ISS module)|Solar array]]
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{{familytree| | | | | | | | | | | | |!|!|}}
{{familytree| | | | | | | | | | | | |!|`|-|SGM1|PORT1|
SGM1 = [[Rassvet (ISS module)|'''Rassvet''' (MRM-1)]]
|PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | | | | | | |!| | |PMM| | |
PMM = [[Leonardo (ISS module)|'''Leonardo''' cargo bay]]
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{{familytree| | | | | | | |QUEST|-|UNITY|-|NOD3|PORT2| |
UNITY = [[Unity (ISS module)|'''Unity''' Node 1]]
|QUEST = [[Quest Joint Airlock|'''Quest''' Airlock]]
|NOD3 = [[Tranquility (ISS module)|'''Tranquility''' Node 3]]
|PORT2 = [[Pressurized Mating Adapter#PMA-3|'''PMA 3''' docking port]]
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{{familytree| |FE0|F|FE| |RADIATOR|!|RADIATOR| |FE|7|FE| | | |
RADIATOR = [[External Active Thermal Control System|Heat Radiator]]
|FE = [[ISS Solar Arrays#Solar arrays|Solar array]]
|FE0 = [[ISS Solar Arrays#Solar arrays|Solar array]]
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{{familytree| |:| | |:| | | | | |:| |!| |:| | | | | |:| | |:|}}
{{familytree| |:| | |:|ELC| | |:|FZ1|:| | |ELC3|:| | |:|
ELC = [[ExPRESS Logistics Carrier#ELC-2|ELC 2]], '''[[Alpha Magnetic Spectrometer|AMS]]'''
|FZ1 = '''[[Z1 truss]]'''
|ELC3 = [[ExPRESS Logistics Carrier#ELC-3|ELC 3]]
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FS56 = '''[[P5 Truss Segment|S5/6 Truss]]'''
|FS34 = '''[[Integrated Truss Structure#P3/P4, S3/S4 truss assemblies|S3/S4 Truss]]'''
|FS1 = '''[[S1 Truss]]'''
|FS0 = '''[[S0 Truss]]'''
|FP1 = '''[[S1 Truss|P1 Truss]]'''
|FP34 = '''[[Integrated Truss Structure#P3/P4, S3/S4 truss assemblies|P3/P4 Truss]]'''
|FP56 = '''[[P5 Truss Segment|P5/6 Truss]]'''
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{{familytree| |:| | |:|ELC4| | | |:|!|:| | | |ELC1|:| | |:|
ELC4 = [[ExPRESS Logistics Carrier#ELC-4|ELC 4]], [[External Stowage Platform#ESP-3|ESP 3]]
|ELC1 = [[ExPRESS Logistics Carrier#ELC-1|ELC 1]]
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CANADARM = '''[[Canadarm2]]'''
|DEXTR = '''[[Dextre]]'''
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|boxstyle_DEXTR = border: 2px solid #fee067; background:#fff4cc;}}
{{familytree| |FE0|L|FE| | | | |!| | | | |FE|J|FE| | | |
FE0 = [[ISS Solar Arrays#Solar arrays|Solar array]]
|FE = [[ISS Solar Arrays#Solar arrays|Solar array]]
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{{familytree| | | | | | | | | | | | |!| | | | |}}
{{familytree| | | | | | | | |ESP1|DESTYNY| | |
DESTYNY = [[Destiny (ISS module)|'''Destiny''' Laboratory]]
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KIBOPS = [[Japanese Experiment Module#Experiment Logistics Module|'''Kibō logistics''' Cargo Bay]]
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{{familytree| | | | | | | | | |HTV|!|HTV| |!|
HTV = '''[[H-II Transfer Vehicle|HTV]]'''/'''[[Dragon (spacecraft)|Dragon]]'''/'''[[Cygnus (spacecraft)|Cygnus]]''' berth ([[Common berthing mechanism|docking port]])
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{{familytree| | | | | | | | | | | |!|!|!| | | |!|KiboRobo|
KiboRobo = [[Japanese Experiment Module|'''Kibō''' Robotic Arm]]
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{{familytree| | | | |COLEXT|COLUMBUS|-|HARMONY|-|KIBO|KiboPlat|
HARMONY = [[Harmony (ISS module)|'''Harmony''' (Node 2)]]
|KiboPlat = [[Japanese Experiment Module|'''Kibō''' External Platform]]
|COLUMBUS = [[Columbus (ISS module)|'''Columbus''' Laboratory]]
|KIBO = [[JEM-PM|'''Kibō''' Laboratory]]
|COLEXT = External Payloads
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PORT2 = [[Pressurized Mating Adapter#PMA-2|'''PMA 2''' docking port]]
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==Pressurised modules==

===Zarya===
[[File:Zarya from STS-88.jpg|thumb|upright|Zarya as seen by [[Space Shuttle Endeavour]] during [[STS-88]]]]
'''''[[Zarya]]''''' (Russian: Заря́; lit. dawn), also known as the [[Functional Cargo Block]] or FGB (from the Russian "Функционально-грузовой блок", Funktsionalno-gruzovoy blok or ФГБ), was the first module of the International Space Station to be launched. The FGB provided electrical power, storage, propulsion, and guidance to the ISS during the initial stage of assembly. With the launch and assembly in orbit of other modules with more specialized functionality, Zarya is now primarily used for storage, both inside the pressurized section and in the externally mounted fuel tanks. The Zarya is a descendant of the [[TKS spacecraft]] designed for the Soviet [[Salyut program]]. The name Zarya was given to the FGB because it signified the dawn of a new era of international cooperation in space. Although it was built by a Russian company, it is owned by the [[United States]]. Zarya weighs {{convert|19300|kg|lb|abbr=on}}, is {{convert|12.55|m|ft|abbr=on}} long and {{convert|4.1|m|ft|abbr=on}} wide, discounting solar arrays.

Built from December 1994 to January 1998 in Russia at the [[Khrunichev State Research and Production Space Center]] (KhSC) in [[Moscow]], Zarya's control system was developed by the Khartron Corp. ([[Kharkiv, Ukraine]]).

Zarya was launched on 20 November 1998, on a Russian [[Proton-K|Proton rocket]] from [[Baikonur Cosmodrome Site 81]] in [[Kazakhstan]] to a {{convert|400|km|mi|abbr=on}} high orbit with a designed lifetime of at least 15 years. After Zarya reached orbit, STS-88 launched on 4 December 1998, to attach the Unity Module.

Although only designed to fly autonomously for six to eight months, Zarya did so for almost two years due to delays with the Russian Service Module, Zvezda, which finally launched on 12 July 2000, and docked with Zarya on 26 July using the Russian [[Kurs (docking system)|Kurs docking system]].

===Unity===
[[File:ISS Unity module.jpg|thumb|Unity as pictured by Space Shuttle Endeavour]]
'''''[[Unity (ISS module)|Unity]]''''', or Node 1, is one of three nodes, or passive connecting modules, in the [[US Orbital Segment]] of the station. It was the first US-built component of the Station to be launched. Cylindrical in shape, with six berthing locations facilitating connections to other modules, Unity was carried into orbit by {{OV|105}} as the primary cargo of [[STS-88]] in 1998. Essential space station resources such as fluids, environmental control and life support systems, electrical and data systems are routed through Unity to supply work and living areas of the station. More than 50,000 mechanical items, 216 lines to carry fluids and gases, and 121 internal and external electrical cables using six miles of wire were installed in the Unity node. Unity is made of aluminum. Prior to its launch aboard Endeavour, conical Pressurized Mating Adapters (PMAs) were attached to the aft and forward berthing mechanisms of Unity. Unity and the two mating adapters together weighed about {{convert|25600|lb|kg|disp=flip|abbr=on}}. The adapters allow the docking systems used by the Space Shuttle and by Russian modules to attach to the node's hatches and berthing mechanisms.

Unity was carried into orbit as the primary cargo of the Space Shuttle Endeavour on STS-88, the first Space Shuttle mission dedicated to assembly of the station. On 6 December 1998, the STS-88 crew mated the aft berthing port of Unity with the forward hatch of the already orbiting Zarya module.

===Zvezda===
'''''[[Zvezda (ISS module)|Zvezda]]''''' ({{lang-ru|link=no|Звезда́}}, meaning "star"), also known as DOS-8, Service Module or SM ({{lang-ru|link=no|СМ}}). It provides all of the station's critical systems,{{clarify|date=August 2013}} its addition rendered the station permanently habitable for the first time, adding life support for up to six crew and living quarters for two. Zvezda's DMS-R computer handles guidance, navigation and control for the entire space station.<ref name="Navigation" /> A second computer which performs the same functions will be installed in the [[Nauka (ISS module)|Nauka]] module, FGB-2.

The hull of Zvezda was completed in February 1985, with major internal equipment installed by October 1986. The module was launched by a Proton-K rocket from Site 81/23 at Baikonur, on 12 July 2000. Zvezda is at the rear of the station according to its normal direction of travel and orientation, its engines are used to boost the station's orbit. Alternatively Russian and European spacecraft can dock to Zvezda's aft port and use their engines to boost the station.

===Destiny===
[[File:Destiny as just installed.jpg|thumb|''Destiny'' interior in 2001]]
'''''[[Destiny (ISS module)|Destiny]]''''' is the primary research facility for United States payloads aboard the ISS. In 2011, NASA solicited proposals for a not-for-profit group to manage all American science on the station which does not relate to manned exploration. The module houses 24 [[International Standard Payload Rack]]s, some of which are used for environmental systems and crew daily living equipment. ''Destiny'' also serves as the mounting point for the station's Truss Structure.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/destiny.html|title=NASA—US Destiny Laboratory|date=26 March 2007|accessdate=26 June 2007|publisher = NASA}}</ref>

===Quest===
'''''[[Quest Joint Airlock|Quest]]''''' is the only USOS airlock, and hosts spacewalks with both United States [[Extravehicular Mobility Unit|EMU]] and Russian [[Orlan space suit|Orlan]] [[Space suit|spacesuits]]. It consists of two segments: the equipment lock, which stores spacesuits and equipment, and the crew lock, from which astronauts can exit into space. This module has a separately controlled atmosphere. Crew sleep in this module, breathing a low nitrogen mixture the night before scheduled EVAs, to avoid [[decompression sickness]] (known as "the bends") in the low-pressure suits.<ref>{{cite web|url=http://spaceflight.nasa.gov/station/eva/outside.html|title=Space Station Extravehicular Activity|accessdate=11 March 2009|publisher=[[NASA]]|date=4 April 2004}}</ref>

===Pirs and Poisk===
'''''[[Pirs (ISS module)|Pirs]]''''' ({{lang-ru|link=no|Пирс}}, meaning "[[pier]]"), ({{lang-ru|link=no|Стыковочный отсек}}), "docking module", SO-1 or DC-1 (docking compartment), and '''''[[Poisk (ISS module)|Poisk]]''''' ({{lang-ru|link=no|По́иск}}; lit. ''Search''), also known as the [[Mini-Research Module]] 2 (MRM 2), {{lang|ru|''Малый исследовательский модуль 2''}}, or МИМ 2. Pirs and Poisk are Russian airlock modules. Each of these modules have 2 identical hatches. An outward opening hatch on the MIR space station failed after it swung open too fast after unlatching, due to a small amount of air pressure remaining in the airlock.<ref>{{cite web|url=http://www.russianspaceweb.com/mir_close_calls.html |title=Mir close calls |publisher=Russianspaceweb.com |accessdate=1 May 2012}}</ref> A different entry was used, and the hatch repaired. All EVA hatches on the ISS open inwards and are pressure sealing. Pirs was used to store, service, and refurbish Russian [[Orlan suits]] and provided contingency entry for crew using the slightly bulkier American suits. The outermost docking ports on both airlocks allow docking of Soyuz and Progress spacecraft, and the automatic transfer of propellants to and from storage on the ROS.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/pirs.html|title=Pirs Docking Compartment|publisher=NASA|accessdate=28 March 2009|date=10 May 2006}}</ref>

{{multiple image |align=right |image1=Node 2 - STS-134.jpg |width1=171 |image2=Node 3 - Isolated view.jpg |width2=190 |caption1=''Harmony'' node in 2011 |caption2=''Tranquility'' node in 2011}}

===Harmony===
'''''[[Harmony (ISS module)|Harmony]]''''' is the second of the station's node modules and the utility hub of the USOS. The module contains four racks that provide electrical power, bus electronic data, and acts as a central connecting point for several other components via its six Common Berthing Mechanisms (CBMs). The European Columbus and Japanese Kibō laboratories are permanently berthed to the starboard and port radial ports respectively. The nadir and zenith ports can be used for docking visiting spacecraft including HTV, Dragon, and Cygnus, with the nadir port serving as the primary docking port. American Shuttle Orbiters docked with the ISS via PMA-2, attached to the forward port.

===Tranquility===
'''''[[Tranquility (ISS module)|Tranquility]]''''' is the third and last of the station's US nodes, it contains an additional life support system to recycle waste water for crew use and supplements oxygen generation. Two of the four berthing locations are not used. One location has the ''[[Cupola (ISS module)|Cupola]]'' installed, one has the docking port adapter, and the third one is occupied by the [[Leonardo (ISS module)|''Leonardo'' PMM]].

[[File:S122e008264.jpg|thumb|left|Columbus module in 2008]]

===Columbus===
'''''[[Columbus (ISS module)|Columbus]]''''', the primary research facility for European payloads aboard the ISS, provides a [[European Drawer Rack|generic laboratory]] as well as facilities specifically designed for [[Biolab|biology]], [[European Physiology Modules|biomedical research]] and [[Fluid Science Laboratory|fluid physics]]. Several mounting locations are affixed to the exterior of the module, which provide power and data to external experiments such as the [[European Technology Exposure Facility]] (EuTEF), [[Solar Monitoring Observatory]], [[Materials International Space Station Experiment]], and [[Atomic Clock Ensemble in Space]]. A number of expansions are planned for the module to study [[quantum physics]] and [[cosmology]].<ref>{{cite news|url=http://www.nasaspaceflight.com/2008/01/prcb-plan-sts-122-for-net-feb-7-three-launches-in-10-11-weeks/|title=PRCB plan STS-122 for NET Feb 7—three launches in 10–11 weeks|accessdate=12 January 2008|author=Chris Bergin|date=10 January 2008|publisher=[[NASASpaceflight.com]]}}</ref><ref>{{cite web|url=http://www.esa.int/esaHS/ESAAYI0VMOC_iss_0.html|title=Columbus laboratory|publisher=[[European Space Agency]] (ESA)|accessdate=6 March 2009|date=10 January 2009}}</ref> ESA's development of technologies on all the main areas of life support has been ongoing for more than 20 years and are/have been used in modules such as Columbus and the ATV. The German Aerospace Center [[German Aerospace Center|DLR]] manages ground control operations for Columbus and the ATV is controlled from the French [[CNES]] [[Toulouse Space Center]].

===Kibō===
[[File:きぼうエアロック Kibo airlock.jpg|thumb|Not large enough for crew using spacesuits, the airlock on Kibō has a sliding drawer for external experiments.]]
'''''[[Kibo (ISS module)|Kibō]]''''' ({{lang-ja|きぼう}}, "[[hope]]") is the largest single ISS module. This laboratory is used to carry out research in space medicine, biology, Earth observations, materials production, biotechnology, communications research, and has facilities for growing plants and fish. During August 2011, an observatory mounted on Kibō, which utilises the ISS's orbital motion to image the whole sky in the X-ray spectrum, detected for the first time the moment a star was swallowed by a black hole.<ref>{{cite web|author=[[JAXA]] |url=http://kibo.jaxa.jp/en/experiment/ef/maxi/ |title=Monitor of All-sky X-ray Image (MAXI):Experiment – Kibo Japanese Experimental Module – JAXA |publisher=Kibo.jaxa.jp |date=30 March 2007 |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://www.jaxa.jp/press/2011/08/20110825_maxi_e.html |title=JAXA | Scientific paper in Nature using the Monitor of All-sky X-ray Image (MAXI) on Kibo and the Swift satellite (USA) observations – First observation of a massive black hole swallowing a star |publisher=Jaxa.jp |accessdate=1 May 2012}}</ref> The laboratory contains a total of 23 racks, including 10 experiment racks and has a dedicated airlock for experiments. In a 'shirt sleeves' environment, crew attach an experiment to the sliding drawer within the airlock, close the inner, and then open the outer hatch. By extending the drawer and removing the experiment using the dedicated robotic arm, payloads are placed on the external platform. The process can be reversed and repeated quickly, allowing access to maintain external experiments without the delays caused by EVAs.

<gallery widths="115px" mode="nolines">
File:Kibo - Pressurized Module.jpg|Pressurized Module
File:Kibo - Experiment Logistics Module (Pressurized Section).jpg|Experiment Logistics Module
File:Kibo - Exposed Facility.jpg|Exposed Facility
File:Kibo - Experiment Logistics Module (Exposed Section).jpg|Experiment Logistics Module
File:Kibo - Remote Manipulator System.jpg|Remote Manipulator System
</gallery>

A smaller pressurised module is attached to the top of Kibō, serving as a cargo bay. The dedicated Interorbital communications system allows large amounts of data to be beamed from Kibō's ICS, first to the Japanese KODAMA satellite in geostationary orbit, then to Japanese ground stations. When a direct communication link is used, contact time between the ISS and a ground station is limited to approximately 10 minutes per visible pass. When KODAMA relays data between a LEO spacecraft and a ground station, real-time communications are possible in 60% of the flight path of the spacecraft. Ground staff use [[telepresence robotics]] to conduct on-orbit research without crew intervention.

===Cupola===
{{multiple image |align=right |image1=STS130 cupola view1.jpg |width1=190 |image2=ISS-27 Dmitri Kondratyev and Paolo Nespoli photograph the Earth through the Cupola.jpg |width2=190 |caption1=The [[Cupola (ISS module)|Cupola]]'s design has been compared to the ''[[Millennium Falcon]]'' from ''[[Star Wars (film)|Star Wars]]''. |caption2=[[Dmitri Kondratyev]] and [[Paolo A. Nespoli|Paolo Nespoli]] in the Cupola. Background left to right, [[Progress M-09M]], [[Soyuz TMA-20]], the [[Leonardo (ISS module)|Leonardo]] module and [[Kounotori 2|HTV-2]].}}
'''[[Cupola (ISS module)|Cupola]]''' is a seven window observatory, used to view Earth and docking spacecraft. Its name derives from the Italian word cupola, which means "dome". The Cupola project was started by NASA and Boeing, but cancelled due to budget cuts. A barter agreement between NASA and the ESA resulted in the Cupola's development being resumed in 1998 by the ESA. It was built by Thales Alenia Space in Torino, Italy. The module comes equipped with robotic workstations for operating the station's main robotic arm and shutters to protect its windows from damage caused by micrometeorites. It features 7 windows, with a {{convert|80|cm|in|adj=on}} round window, the largest window on the station (and the largest flown in space to date). The distinctive design has been compared to the 'turret' of the fictitious ''[[Millennium Falcon]]'' from the motion picture ''[[Star Wars (film)|Star Wars]]'';<ref>{{cite web|url=http://www.space.com/7932-astronauts-bask-spectacular-views-space-windows.html |title=Astronauts Bask in Spectacular Views From New Space Windows |publisher=Space.com |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://news.nationalgeographic.com/news/2010/02/photogalleries/100218-international-space-station-cupola-iss-obama-nasa-pictures/ |title=First Photos: Space Station's Observation Deck Unveiled |work=National Geographic |accessdate=1 May 2012}}</ref> the original prop [[lightsaber]] used by actor [[Mark Hamill]] as [[Luke Skywalker]] in the 1977 film was flown to the station in 2007.<ref>{{cite web|url=http://www.space.com/4283-nasa-shuttle-launch-luke-skywalker-lightsaber.html |title=NASA Shuttle to Launch Luke Skywalker's Lightsaber |publisher=Space.com |date=28 August 2007 |accessdate=1 May 2012}}</ref>

===Rassvet===
'''''[[Rassvet (ISS module)|Rassvet]]''''' ({{lang-ru|link=no|Рассве́т}}; lit. "dawn"), also known as the Mini-Research Module 1 (MRM-1) ({{lang-ru|link=no|Ма́лый иссле́довательский модуль}}, {{lang|ru|МИМ 1}}) and formerly known as the Docking Cargo Module (DCM), is similar in design to the [[Mir Docking Module]] launched on [[STS-74]] in 1995. ''Rassvet'' is primarily used for cargo storage and as a docking port for visiting spacecraft. It was flown to the ISS aboard NASA's {{OV|104}} on the [[STS-132]] mission and connected in May 2010,<ref>{{cite web|url=http://www.nasaspaceflight.com/2009/04/sts-132-prcb-baselines-mission-to-deliver-russias-mrm-1/|title=STS-132: PRCB baselines Atlantis' mission to deliver Russia's MRM-1|author=Chris Gebhardt|publisher=NASAspaceflight.com|date=9 April 2009|accessdate=12 November 2009}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts132/news/STS-132-09.html|author=NASA|date=18 May 2010|accessdate=7 July 2010|title=STS-132 MCC Status Report #09}}</ref> Rassvet is the only Russian owned module launched by NASA, to repay for the launch of Zarya, which is Russian designed and built, but partially paid for by NASA.<ref>[http://www.russianspaceweb.com/iss_mim1.html MIM1]. russianspaceweb.com</ref>  Rassvet was launched with the Russian Nauka Laboratory's Experiments airlock temporarily attached to it, and spare parts for the European Robotic Arm.

===Leonardo===
[[File:STS-133 Installation PMM 3.jpg|thumb|''Leonardo'' installed]]
'''''[[Leonardo (ISS module)|Leonardo]]'' Permanent Multipurpose Module''' (PMM) is a storage module attached to the ''[[Tranquility (ISS module)|Tranquility]]'' node.<ref name="leo-esa20110301">{{cite news |url=http://www.esa.int/Our_Activities/Human_Spaceflight/MagISStra/Leonardo_attached_to_Space_Station |title=Leonardo Attached to Space Station |work=ESA.int |date=1 March 2011 |accessdate=11 June 2013}}</ref><ref>{{cite web |url=http://blogs.nasa.gov/spacestation/2015/05/27/module-relocated-prepping-station-for-commercial-crew/ |title=Module Relocated Prepping Station for Commercial Crew |publisher=NASA |first=Mark |last=Garcia |date=27 May 2015 |accessdate=27 May 2015}}</ref> The three NASA Space Shuttle [[Multi-Purpose Logistics Module|MPLM]] cargo containers—Leonardo, Raffaello and Donatello—were built for NASA in [[Turin]], Italy by Alcatel Alenia Space, now [[Thales Alenia Space]].<ref>[http://www.thalesaleniaspace-issmodules.com/ Thales Alenia Space and ISS modules – Thales Alenia Space and ISS modules]. Thalesaleniaspace-issmodules.com. Retrieved 8 October 2011.</ref> The MPLMs were provided to NASA's ISS programme by Italy (independent of their role as a member state of ESA) and are considered to be US elements. In a bartered exchange for providing these containers, the US gave Italy research time aboard the ISS out of the US allotment in addition to that which Italy receives as a member of ESA.<ref>[http://www.spaceref.com/iss/elements/mplm.html Space Station User's Guide]. SpaceRef (3 April 2001). Retrieved 8 October 2011.</ref> The Permanent Multipurpose Module was created by converting Leonardo into a module that could be permanently attached to the station.<ref name="PLM1">{{cite news|url=http://www.nasaspaceflight.com/2009/08/sts-133-five-crew-one-eva-mission-leave-mpm-on-iss|title=STS-133 refined to a five crew, one EVA mission—will leave MPLM on ISS|publisher=NASASpaceflight.com|author=Chris Gebhardt|date=5 August 2009}}</ref><ref name="PLM2">{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8226309.stm|title=Europe looks to buy Soyuz craft|work=BBC News|last=Amos|first=Jonathan|date=29 August 2009}}</ref><ref>{{cite web|url=http://forum.nasaspaceflight.com/index.php?topic=17437.msg483604#msg483604|publisher=NASASpaceflight.com|accessdate=12 October 2009|title=Shuttle Q&A Part 5|date=27 September 2009}}</ref>

===Scheduled additional modules===

====Nauka====
'''''[[Nauka (ISS module)|Nauka]]''''' ({{lang-ru|link=no|Нау́ка}}; lit. "science"), also known as the Multipurpose Laboratory Module (MLM) or FGB-2 ({{lang-ru|link=no|Многофункциональный лабораторный модуль}}, {{lang|ru|МЛМ}}), is the major Russian laboratory module. It was scheduled to arrive at the station in 2014, docking to the port that was occupied by the Pirs module.<ref>{{cite web|url=http://www.aviationweek.com/Article.aspx?id=/article-xml/asd_05_23_2012_p05-01-460939.xml|title=Russia Sees Moon Base As Logical Next Step| last=Morring| first=Frank| date=23 May 2012| publisher=Aviation Week|accessdate=29 May 2012}}</ref> The date has been postponed to February 2017.<ref>{{cite web|url=http://www.russianspaceweb.com/iss_fgb2.html|title=MLM (FGB-2)|author=Anatoly Zak|publisher=Russian Space Web|date=29 April 2014|accessdate=14 May 2014}}</ref> Prior to the arrival of the Nauka module, a Progress spacecraft was used to remove Pirs from the station, deorbiting it to reenter over the Pacific Ocean. Nauka contains an additional set of life support systems and attitude control. Originally it would have routed power from the single Science-and-Power Platform, but that single module design changed over the first ten years of the ISS mission, and the two science modules, which attach to Nauka via the [[Uzlovoy Module]], or Russian node, each incorporate their own large solar arrays to power Russian science experiments in the ROS.

Nauka's mission has changed over time. During the mid-1990s, it was intended as a backup for the FGB, and later as a universal docking module (UDM); its docking ports will be able to support automatic docking of both spacecraft, additional modules and fuel transfer. Nauka has its own engines. Smaller Russian modules such as Pirs and Poisk were delivered by modified [[Progress (spacecraft)|Progress]] spacecraft, and the larger modules; Zvezda, Zarya, and Nauka, were launched by Proton rockets. Russia plans to separate Nauka, along with the rest of the Russian Orbital Segment, before the ISS is deorbited, to form the [[OPSEK]] space station.

====Uzlovoy Module====
The '''[[Uzlovoy Module]]''' (UM), or Node Module is a 4 metric ton<ref name=Zak>{{cite web|last1=Zak|first1=Anatoly|title=Node Module|url=http://www.russianspaceweb.com/iss_node.html|website=RussianSpaceWeb.com|accessdate=7 January 2015}}</ref> ball shaped module that will support the docking of two scientific and power modules during the final stage of the station assembly and provide the Russian segment additional docking ports to receive Soyuz TMA and Progress M spacecraft. UM is to be incorporated into the ISS in 2016. It will be integrated with a special version of the Progress cargo ship and launched by a standard Soyuz rocket. The Progress would use its own propulsion and flight control system to deliver and dock the Node Module to the nadir (Earth-facing) docking port of the Nauka MLM/FGB-2 module. One port is equipped with an active hybrid docking port, which enables docking with the MLM module. The remaining five ports are passive hybrids, enabling docking of Soyuz and Progress vehicles, as well as heavier modules and future spacecraft with modified docking systems. The node module was conceived to serve as the only permanent element of the future Russian successor to the ISS, [[Orbital Piloted Assembly and Experiment Complex|OPSEK]]. Equipped with six docking ports, the Node Module would serve as a single permanent core of the future station with all other modules coming and going as their life span and mission required.<ref>[http://www.energia.ru/en/news/news-2011/news_01-13.html S.P. Korolev RSC Energia – News]. Energia.ru (13 January 2011). Retrieved 8 October 2011.</ref><ref>[http://www.russianspaceweb.com/iss_node.html Node Module]. Russianspaceweb.com. Retrieved 8 October 2011.</ref> This would be a progression beyond the ISS and Russia's modular MIR space station, which are in turn more advanced than early monolithic first generation stations such as Skylab, and early Salyut and Almaz stations.

'''Science Power Modules 1 & 2''' (NEM-1, NEM-2) ({{lang-ru|link=no|Нау́чно-Энергетический Модуль-1 и -2}})

====Bigelow Expandable Activity Module====
On 16 January 2013, [[Bigelow Aerospace]] was contracted by NASA to provide a [[Bigelow Expandable Activity Module]] (BEAM), scheduled to arrive at the space station in 2015 for a two-year technology demonstration.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/station/news/beam_feature.html |title=NASA to Test Bigelow Expandable Module on Space Station |publisher=NASA |date=16 January 2013 |accessdate=17 January 2013}}</ref> BEAM is an inflatable module that will be attached to the aft hatch of the port-side Tranquility module of the International Space Station. During its two-year test run, instruments will measure its structural integrity and leak rate, along with temperature and radiation levels. The hatch leading into the module will remain mostly closed except for periodic visits by space station crew members for inspections and data collection. Following the test run, the module will be detached and jettisoned from the station.<ref>{{cite web | url=http://www.spaceflightnow.com/news/n1301/16bigelow/ | title=Bigelow inflatable module bound for space station | last=Harwood | first=William | date=16 January 2013 | publisher=Spaceflightnow | accessdate=17 January 2013}}</ref>

[[image:ISS Habitation module.jpg|thumb|left|The cancelled Habitation module under construction in 1997]]

===Cancelled components===
Several modules planned for the station have been cancelled over the course of the ISS programme, whether for budgetary reasons, because the modules became unnecessary, or following a redesign of the station after the 2003 [[Space Shuttle Columbia disaster|''Columbia'' disaster]]. The US [[Centrifuge Accommodations Module]] was intended to host science experiments in varying levels of [[artificial gravity]].<ref>{{cite web|url=http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=12560&mid=269666|title=Where is the Centrifuge Accommodation Module (CAM)?|publisher=NASASpaceflight.com|accessdate=12 October 2009}}</ref> The US [[Habitation Module]] would have served as the station's living quarters. Instead, the sleep stations are now spread throughout the station.<ref>{{cite web|url=http://www.space.com/missionlaunches/060214_iss_module.html|title=NASA Recycles Former ISS Module for Life Support Research|author=Tariq Malik|accessdate=11 March 2009|publisher=Space.com|date=14 February 2006}}</ref> The US [[Interim Control Module]] and [[ISS Propulsion Module]] were intended to replace functions of ''Zvezda'' in case of a launch failure.<ref>{{cite web|title=ICM Interim Control Module|publisher=U.S. Naval Center for Space Technology|url=http://code8200.nrl.navy.mil/icm.html|archiveurl=https://web.archive.org/web/20070208164211/http://code8200.nrl.navy.mil/icm.html|archivedate=8 February 2007}}</ref> The Russian [[Universal Docking Module]], to which the cancelled Russian Research modules and spacecraft would have docked.<ref name="Zak">{{cite web|url=http://www.russianspaceweb.com/iss_russia.html|accessdate=3 October 2009|publisher=russianspaceweb.com|author=Anatoly Zak|title=Russian segment of the ISS}}</ref> The Russian [[Science Power Platform]] would have provided the [[Russian Orbital Segment]] with a power supply independent of the ITS solar arrays,<ref name="Zak" /> and two [[Russian Research Module]]s that were planned to be used for scientific research.<ref>{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/components/russian_laboratory.html|title=Russian Research Modules|publisher=Boeing|accessdate=21 June 2009}}</ref>

==Unpressurised elements==
[[File:Truss breakdown.png|thumb|right|ISS Truss Components breakdown showing Trusses and all ORUs in situ]]
The ISS features a large number of external components that do not require pressurisation. The largest such component is the [[Integrated Truss Structure]] (ITS), to which the station's main solar arrays and thermal radiators are mounted.<ref name="Arrays" /> The ITS consists of ten separate segments forming a structure 108.5 m (356 ft) long.<ref name="OnOrbit" />

The station in its complete form has several smaller external components, such as the six robotic arms, the three [[External Stowage Platform]]s (ESPs) and four [[ExPRESS Logistics Carrier]]s (ELCs).<ref name="Manifest" /><ref>{{cite web|url=http://www.nasa.gov/centers/marshall/news/background/facts/expressrack.html|title=EXPRESS Racks 1 and 2 fact sheet|accessdate=4 October 2009|date=12 April 2008|publisher=NASA}}</ref> Whilst these platforms allow experiments (including [[MISSE]], the STP-H3 and the [[Robotic Refueling Mission]]) to be deployed and conducted in the vacuum of space by providing electricity and processing experimental data locally, the platforms' primary function is to store [[Orbital Replacement Unit]]s (ORUs). ORUs are spare parts that can be replaced when the item either passes its design life or fails. Examples of ORUs include pumps, storage tanks, antennas and battery units. Such units are replaced either by astronauts during EVA or by robotic arms. Spare parts were routinely transported to and from the station via Space Shuttle resupply missions, with a heavy emphasis on ORU transport once the NASA Shuttle approached retirement.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/12/soyuz-tma-03m-docks-iss-returns-station-six-crewmembers-future-ops/ |title=Soyuz TMA-03M docks to ISS, returns station to six crewmembers for future ops |publisher=NASASpaceFlight.com |date=23 December 2011 |accessdate=1 May 2012}}</ref> Several shuttle missions were dedicated to the delivery of ORUs, including [[STS-129]],<ref name="EVA129">{{cite web|url=http://www.nasa.gov/centers/johnson/pdf/404493main_EVA_129_F_E1.pdf|title=EVA Checklist: STS-129 Flight Supplement|author=L. D. Welsch|publisher=NASA|date=30 October 2009}}</ref> [[STS-133]]<ref name="STS-133">{{cite web|url=http://www.nasa.gov/pdf/491387main_STS-133%20Press%20Kit.pdf|title=Space Shuttle Mission: STS-131|date=February 2011|publisher=NASA}}</ref> and [[STS-134]].<ref name="STS-134">{{cite web|url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf|title=Space Shuttle Mission: STS-134|publisher=NASA|date=April 2011}}</ref> {{asof|2011|01}}, only one other mode of transportation of ORUs had been utilised – the Japanese cargo vessel [[H-II Transfer Vehicle|HTV-2]] – which delivered an FHRC and CTC-2 via its Exposed Pallet (EP).<ref name="HTV2">{{cite web|url=http://iss.jaxa.jp/en/htv/mission/htv-2/library/presskit/htv2_presskit_en.pdf|title=HTV2: Mission Press Kit|publisher=Japan Aerospace Exploration Agency|date=20 January 2011}}</ref>{{update after|2013|1|28}}

[[File:STS-116 spacewalk 1.jpg|left|thumb|Construction of the [[Integrated Truss Structure]] over New Zealand.]]
There are also smaller exposure facilities mounted directly to laboratory modules; the JEM [[Japanese Experiment Module#Exposed Facility|Exposed Facility]] serves as an external '[[porch]]' for the Japanese Experiment Module complex,<ref>{{cite web|url=http://kibo.jaxa.jp/en/about/kibo/jef/|title=Exposed Facility:About Kibo|publisher=JAXA|date=29 August 2008|accessdate=9 October 2009}}</ref> and a facility on the European ''Columbus'' laboratory provides power and data connections for experiments such as the [[European Technology Exposure Facility]]<ref name="NASA">{{cite web|url=http://www.nasa.gov/mission_pages/station/science/experiments/EuTEF.html|title=NASA—European Technology Exposure Facility (EuTEF)|publisher=NASA|date=6 October 2008|accessdate=28 February 2009}}</ref><ref name="ESA">{{cite web|url=http://www.esa.int/esaMI/Columbus/SEM7ZTEMKBF_0.html|title=ESA—Columbus—European Technology Exposure Facility (EuTEF)|publisher=ESA|date=13 January 2009|accessdate=28 February 2009}}</ref> and the [[Atomic Clock Ensemble in Space]].<ref>{{cite web|url=http://www.esa.int/SPECIALS/HSF_Research/SEMJSK0YDUF_0.html|publisher=ESA|accessdate=9 October 2009|title=Atomic Clock Ensemble in Space (ACES)}}</ref> A [[remote sensing]] instrument, [[Stratospheric Aerosol and Gas Experiment|SAGE III-ISS]], is due to be delivered to the station in 2014 aboard a [[Dragon (spacecraft)|Dragon capsule]], and the [[Neutron star Interior Composition ExploreR|NICER]] experiment in 2016.<ref>{{cite web |url=http://heasarc.gsfc.nasa.gov/docs/nicer/papers/NICER-SPIE-July2012-v4.pdf | publisher=Goddard Space Flight Center |title=The Neutron star Interior Composition ExploreR (NICER): an Explorer mission of opportunity for soft x-ray timing spectroscopy |accessdate=8 April 2013 |author=NICER Team }}</ref><ref>{{cite web|url=http://www.nasa.gov/topics/earth/features/sage3.html|date=1 March 2011|accessdate=12 March 2011|publisher=NASA|title=Time to Fly: SAGE III — ISS Prepped for Space Station|author=Michael Finneran}}</ref> The largest such scientific payload externally mounted to the ISS is the [[Alpha Magnetic Spectrometer]] (AMS), a particle physics experiment launched on [[STS-134]] in May 2011, and mounted externally on the ITS. The AMS measures [[cosmic ray]]s to look for evidence of [[dark matter]] and [[antimatter]].<ref>{{cite web|url=http://ams.cern.ch/|title=The Alpha Magnetic Spectrometer Experiment|publisher=[[CERN]]|date=21 January 2009|accessdate=6 March 2009}}</ref>

===Robotic arms and cargo cranes===
{{Double image|right|Iss017e011097.jpg|250|Dextrereallyhasnohead.jpg|250|Commander [[Sergey Alexandrovich Volkov|Volkov]] stands on Pirs with his back to the [[Soyuz spacecraft|Soyuz]] whilst operating the manual [[Strela (crane)|Strela crane]] holding photographer [[Oleg Kononenko|Kononenko]]. [[Zarya]] is seen to the left and [[Zvezda (ISS module)|Zvezda]] across the bottom of the image.|[[Dextre]], like many of the station's experiments and robotic arms, can be operated from Earth and perform tasks while the crew sleeps.||}}

The [[Integrated Truss Structure]] serves as a base for the station's primary remote manipulator system, called the [[Mobile Servicing System]] (MSS), which is composed of three main components. [[Canadarm2]], the largest robotic arm on the ISS, has a mass of {{convert|1800|kg|lb}} and is used to dock and manipulate spacecraft and modules on the USOS, hold crew members and equipment in place during EVAs and move Dextre around to perform tasks.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/station/structure/elements/mss.html |title=Canadarm2 and the Mobile Servicing System |publisher=NASA |date=8 January 2013 |accessdate=22 June 2015}}</ref> [[Dextre]] is a {{convert|1560|kg|lb|abbr=on}} robotic manipulator with two arms, a rotating torso and has power tools, lights and video for replacing [[orbital replacement unit]]s (ORUs) and performing other tasks requiring fine control.<ref>{{cite web |url=http://www.asc-csa.gc.ca/eng/iss/dextre/default.asp |title=Dextre, the International Space Station's Robotic Handyman |publisher=Canadian Space Agency |accessdate=22 June 2015}}</ref> The [[Mobile Base System]] (MBS) is 2 platforms which rides on rails along the length of the station's main truss. It serves as a mobile base for Canadarm2 and Dextre, allowing the robotic arms to reach all parts of the USOS.<ref>{{cite web |url=http://www.asc-csa.gc.ca/eng/iss/mobile-base/default.asp |title=Mobile Base System |publisher=Canadian Space Agency |accessdate=22 June 2015}}</ref> To gain access to the Russian Segment a [[Grapple Fixture|grapple fixture]] was added to Zarya on [[STS-134]], so that Canadarm2 can inchworm itself onto the ROS.<ref name="presskit134">{{cite web |url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf |title=Space Shuttle Mission STS-134: Final Flight of ''Endeavour'' - Press Kit |format=PDF |publisher=NASA |pages=51-53 |date=April 2011 |accessdate=22 June 2015}}</ref> Also installed during STS-134 was the {{convert|50|ft|m|abbr=on|order=flip}} [[Orbiter Boom Sensor System]] (OBSS), which had been used to inspect head shield tiles on Space Shuttle missions and can be used on station to increase the reach of the MSS.<ref name="presskit134"/> Staff on Earth or the station can operate the MSS components via remote control, performing work outside the station without space walks.

Japan's [[Kibo (ISS module)#Remote Manipulator System|Remote Manipulator System]], which services the JEM Exposed Facility,<ref>{{cite web |url=http://kibo.jaxa.jp/en/about/kibo/rms/ |title=Remote Manipulator System: About Kibo |publisher=JAXA |date=29 August 2008 |accessdate=4 October 2009}}</ref> was launched on [[STS-124]] and is attached to the JEM Pressurised Module.<ref>{{cite web |url=http://www.nasa.gov/centers/johnson/news/station/2002/iss02-03.txt |title=International Space Station Status Report #02-03 |publisher=NASA |date=14 January 2002 |accessdate=4 October 2009}}</ref> The arm is similar to the Space Shuttle arm as it is permanently attached at one end and has a latching end effector for standard grapple fixtures at the other.

The [[European Robotic Arm]], which will service the Russian Orbital Segment, will be launched alongside the [[Multipurpose Laboratory Module]] in 2017.<ref>{{cite web |url=http://www.russianspaceweb.com/iss_fgb2.html |title=MLM (FGB-2) module of the ISS |publisher=RussianSpaceWeb |accessdate=16 June 2014}}</ref> The ROS does not require spacecraft or modules to be manipulated, as all spacecraft and modules dock automatically and may be discarded the same way. Crew use the two ''[[Strela (crane)|Strela]]'' ({{lang-ru|link=no|Стрела́}}; lit. Arrow) cargo cranes during EVAs for moving crew and equipment around the ROS. Each Strela crane has a mass of {{convert|45|kg|lb|abbr=on}}.

===Comparison===
The ISS follows [[Salyut]] and [[Almaz]] series, [[Cosmos 557]], [[Skylab]], and [[Mir]] as the 11th space station launched, as the [[Genesis II|Genesis]] prototypes were never intended to be manned. Other examples of modular station projects include the Soviet/Russian Mir and the planned Russian OPSEK and [[Chinese space station]]. The first space station, [[Salyut 1]], and other one-piece or 'monolithic' first generation space stations, such as Salyut 2,3,4,5, DOS 2, Kosmos 557, Almaz and NASA's [[Skylab]] stations were not designed for re-supply.<ref>http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/history.pdf</ref> Generally, each crew had to depart the station to free the only docking port for the next crew to arrive, Skylab had more than one docking port but was not designed for resupply. Salyut 6 and 7 had more than one docking port and were designed to be resupplied routinely during crewed operation.<ref>{{cite web|url=http://www.pbs.org/spacestation/station/russian.htm |title=Space Station | Russian Space History |publisher=Pbs.org |accessdate=1 May 2012}}</ref>

==Station systems==

===Life support===
{{Main|ISS ECLSS|Chemical oxygen generator}}
The critical systems are the atmosphere control system, the water supply system, the food supply facilities, the sanitation and hygiene equipment, and fire detection and suppression equipment. The Russian Orbital Segment's life support systems are contained in the Service Module Zvezda. Some of these systems are supplemented by equipment in the USOS. The MLM Nauka laboratory has a complete set of life support systems.

====Atmospheric control systems====
[[Image:SpaceStationCycle.svg|thumb|The interactions between the components of the ISS Environmental Control and Life Support System (ECLSS)|alt=A flowchart diagram showing the components of the ISS life support system.]]
The atmosphere on board the ISS is similar to the [[Atmosphere of Earth|Earth's]].<ref>{{cite web|url=http://science.howstuffworks.com/space-station2.htm |title=How Space Stations Work|first=Craig|last=Freudenrich|publisher=Howstuffworks|date=20 November 2000|accessdate=23 November 2008}}</ref> Normal air pressure on the ISS is 101.3 [[kilopascal|kPa]] (14.7 [[Pounds per square inch|psi]]);<ref>{{cite web |url=http://nasaexplores.com/show2_5_8a.php?id=04-032&gl=58|archiveurl=https://web.archive.org/web/20061114010931/http://www.nasaexplores.com/show2_5_8a.php?id=04-032&gl=58|archivedate=14 November 2006|work=NASAexplores|title=5–8: The Air Up There|publisher=NASA|accessdate=31 October 2008}}</ref> the same as at sea level on Earth. An Earth-like atmosphere offers benefits for crew comfort, and is much safer than the alternative, a pure oxygen atmosphere, because of the increased risk of a fire such as that responsible for the deaths of the [[Apollo 1]] crew.<ref>{{cite book|author=Clinton Anderson|display-authors=etal|publisher=US Government Printing Office|title=Report of the Committee on Aeronautical and Space Sciences, United States Senate—Apollo 204 Accident|date=30 January 1968|location=Washington, DC|page=8|url=http://klabs.org/richcontent/Reports/Failure_Reports/as-204/senate_956/as204_senate_956.pdf}}</ref> Earth-like atmospheric conditions have been maintained on all Russian and Soviet spacecraft.<ref name=spacemed>{{Citation | last1=Davis | first1=Jeffrey R. | last2=Johnson | first2=Robert | last3=Stepanek | first3=Jan | lastauthoramp=yes | title=Fundamentals of Aerospace Medicine | publisher=Lippincott Williams & Wilkins | place=Philadelphia PA, USA | volume=XII | pages=261–264 | year=2008}}</ref>

The ''[[Elektron (ISS)|Elektron]]'' system aboard ''Zvezda'' and a similar system in ''Destiny'' generate oxygen aboard the station.<ref name="OGS">{{cite web|url=http://www.space.com/businesstechnology/060215_techwed_iss_oxygen.html|title=Air Apparent: New Oxygen Systems for the ISS|author=Tariq Malik|publisher=Space.com|date=15 February 2006|accessdate=21 November 2008}}</ref> The crew has a backup option in the form of bottled oxygen and [[Vika oxygen generator|Solid Fuel Oxygen Generation]] (SFOG) canisters, a [[chemical oxygen generator]] system.<ref name="breath easy">{{cite web|url=http://science.nasa.gov/headlines/y2000/ast13nov_1.htm|title=Breathing Easy on the Space Station|author=Patrick L. Barry|publisher=NASA|date=13 November 2000|accessdate=21 November 2008}}</ref> Carbon dioxide is removed from the air by the [[Vozdukh]] system in ''Zvezda''. Other by-products of human metabolism, such as methane from the intestines and ammonia from sweat, are removed by [[Activated carbon|activated charcoal]] filters.<ref name="breath easy" />

Part of the ROS atmosphere control system is the oxygen supply, triple-redundancy is provided by the Elektron unit, solid fuel generators, and stored oxygen. The Elektron unit is the primary oxygen supply, {{chem|O|2}} and {{chem|H|2}} are produced by [[electrolysis]], with the {{chem|H|2}} being vented overboard. The 1 kW system uses approximately 1 litre of water per crew member per day from stored water from Earth, or water recycled from other systems. MIR was the first spacecraft to use recycled water for oxygen production. The secondary oxygen supply is provided by burning {{chem|O|2}}-producing [[Vika oxygen generator|Vika]] cartridges (see also [[ISS ECLSS]]). Each 'candle' takes 5–20 minutes to decompose at 450–500 °C, producing 600 litres of {{chem|O|2}}. This unit is manually operated.<ref>[http://suzymchale.com/ruspace/issrslss.html RuSpace | ISS Russian Segment Life Support System]. Suzymchale.com. Retrieved 8 October 2011.</ref>

The US Orbital Segment has redundant supplies of oxygen, from a pressurised storage tank on the Quest airlock module delivered in 2001, supplemented ten years later by ESA built Advanced Closed-Loop System (ACLS) in the Tranquility module (Node 3), which produces {{chem|O|2}} by electrolysis.<ref>[http://science.nasa.gov/science-news/science-at-nasa/2000/ast13nov_1/ Breathing Easy on the Space Station – NASA Science]. ''Science''.nasa.gov (13 November 2000). Retrieved 8 October 2011.</ref> Hydrogen produced is combined with carbon dioxide from the cabin atmosphere and converted to water and methane.

===Power and thermal control===
{{Main|Electrical system of the International Space Station|External Active Thermal Control System}}

{{Double image|left|ROSSA.jpg|200|P4 deployed.jpg|200|Russian solar arrays, backlit by sunset.|One of the eight truss mounted pairs of USOS solar arrays}}
Double-sided solar, or [[Photovoltaic]] arrays, provide [[Electric power|electrical power]] for the ISS. These bifacial cells are more efficient and operate at a lower temperature than single-sided cells commonly used on Earth, by collecting sunlight on one side and light [[Albedo|reflected off]] the Earth on the other.<ref>{{cite web |url=http://wenku.baidu.com/view/a815121ffc4ffe473368ab7a.html |title=The early history of bifacial solar cell_百度文库 |publisher=Wenku.baidu.com |date=25 October 2010 |accessdate=14 August 2012}}</ref> 

The Russian segment of the station, like the Space Shuttle and most spacecraft, uses 28 [[volt]] [[direct current|DC]] from four rotating solar arrays mounted on ''Zarya'' and ''Zvezda''. The USOS uses 130–180 V DC from the USOS PV array, power is stabilised and distributed at 160 V DC and converted to the user-required 124 V DC. The [[High voltage|higher distribution voltage]] allows smaller, lighter conductors, at the expense of crew safety. The ROS uses [[Extra-low voltage|low voltage]]. The two station segments share power with converters.<ref name="Arrays" />

The USOS solar arrays are arranged as four wing pairs, with each wing producing nearly 32.8 kW.<ref name="Arrays">{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/truss_segment.html|title=Spread Your Wings, It's Time to Fly|publisher=NASA|date=26 July 2006|accessdate=21 September 2006}}</ref> These arrays normally track the sun to maximise power generation. Each array is about 375 m2 (450 yd2) in area and {{convert|58|m|yd|0}} long. In the complete configuration, the solar arrays track the sun by rotating the ''alpha [[gimbal]]'' once per orbit; the ''beta gimbal'' follows slower changes in the angle of the sun to the orbital plane. The [[Night Glider mode]] aligns the solar arrays parallel to the ground at night to reduce the significant aerodynamic drag at the station's relatively low orbital altitude.<ref>{{cite journal|author=G. Landis and C-Y. Lu|year=1991|title=Solar Array Orientation Options for a Space Station in Low Earth Orbit|journal=Journal of Propulsion and Power|volume=7|issue=1|pages=123–125|doi=10.2514/3.23302}}</ref>

The station uses rechargeable [[Nickel hydrogen battery|nickel-hydrogen batteries]] (NiH2) for continuous power during the 35 minutes of every 90-minute orbit that it is eclipsed by the Earth. The batteries are recharged on the day side of the Earth. They have a 6.5-year lifetime (over 37,000 charge/discharge cycles) and will be regularly replaced over the anticipated 20-year life of the station.<ref>{{cite web|url=http://www.grc.nasa.gov/WWW/RT/RT1999/5000/5420miller.html|title=Nickel-Hydrogen Battery Cell Life Test Program Update for the International Space Station|accessdate=27 November 2009|publisher=NASA|author=Thomas B. Miller|date=24 April 2000}}</ref>

The station's large solar panels generate a high potential voltage difference between the station and the ionosphere. This could cause arcing through insulating surfaces and sputtering of conductive surfaces as ions are accelerated by the spacecraft plasma sheath. To mitigate this, plasma contactor units (PCU)s create current paths between the station and the ambient plasma field.<ref>[http://www.grc.nasa.gov/WWW/RT/RT1998/5000/5430patterson.html Cathodes Delivered for Space Station Plasma Contactor System]. Grc.nasa.gov (18 June 1999). Retrieved 8 October 2011.</ref>

[[File:EATCS.png|thumb|ISS External Active Thermal Control System (EATCS) diagram]]
The large amount of electrical power consumed by the station's systems and experiments is turned almost entirely into heat. The heat which can be dissipated through the walls of the stations modules is insufficient to keep the internal ambient temperature within comfortable, workable limits. [[Ammonia]] is continuously pumped through pipework throughout the station to collect heat, then into external radiators exposed to the cold of space, and back into the station.

The International Space Station (ISS) External Active Thermal Control System (EATCS) maintains an equilibrium when the ISS environment or heat loads exceed the capabilities of the Passive Thermal Control System (PTCS). Note Elements of the PTCS are external surface materials, insulation such as MLI, or Heat Pipes. The EATCS provides heat rejection capabilities for all the US pressurised modules, including the JEM and COF as well as the main power distribution electronics of the S0, S1 and P1 Trusses. The EATCS consists an internal, non-toxic, water coolant loop used to cool and dehumidify the atmosphere, which transfers collected heat into an external liquid ammonia loop capable of withstanding the much lower temperature of space, which is then circulated through radiators to remove the heat. The EATCS is capable of rejecting up to 70 kW, and provides a substantial upgrade in heat rejection capacity from the 14 kW capability of the Early External Active Thermal Control System (EEATCS) via the Early Ammonia Servicer (EAS), which was launched on [[STS-105]] and installed onto the P6 Truss.<ref>[http://www.nasa.gov/pdf/473486main_iss_atcs_overview.pdf ATCS Team Overview]. (PDF). Retrieved 8 October 2011.</ref>

===Communications and computers===
{{Main|Tracking and Data Relay Satellite|Luch (satellite)}}
{{See also2|[[ThinkPad#Use in space|ThinkPad use in space]]}}
[[File:ISS Communication Systems.png|thumb|The communications systems used by the ISS * Luch satellite not currently in use|alt=Diagram showing communications links between the ISS and other elements.]]
Radio communications provide [[telemetry]] and scientific data links between the station and [[Mission Control Center|Mission Control Centres]]. Radio links are also used during [[Space rendezvous|rendezvous and docking procedures]] and for audio and video communication between crewmembers, flight controllers and family members. As a result, the ISS is equipped with internal and external communication systems used for different purposes.<ref name="BoeingComm" />


The Russian Orbital Segment communicates directly with the ground via the ''[[Lira (ISS)|Lira]]'' [[Antenna (radio)|antenna]] mounted to ''Zvezda''.<ref name="ISSRG" /><ref>{{cite web|url=http://www.nasa.gov/home/hqnews/2005/mar/HQ_ss05015_ISS_status_report.html|title=International Space Station Status Report: SS05-015|last=Mathews|first=Melissa|author2=James Hartsfield|date=25 March 2005|work=NASA News|publisher=NASA|accessdate=11 January 2010}}</ref> The ''Lira'' antenna also has the capability to use the ''[[Luch (satellite)|Luch]]'' data relay satellite system.<ref name="ISSRG" /> This system, used for communications with ''Mir'', fell into disrepair during the 1990s, and as a result is no longer in use,<ref name="ISSRG" /><ref name="SSSM">{{cite book|first=David|last=Harland|title=The Story of Space Station Mir|publisher=Springer-Verlag New York Inc|date=30 November 2004|location=New York|isbn=978-0-387-23011-5}}</ref><ref name="Harvey">{{cite book|last=Harvey|first=Brian|title=The rebirth of the Russian space program: 50 years after Sputnik, new frontiers|publisher=Springer Praxis Books|year=2007|page=263|isbn=0-387-71354-9}}</ref> although two new ''Luch'' satellites—''Luch''-5A and ''Luch''-5B—were launched in 2011 and 2012 respectively to restore the operational capability of the system.<ref>{{cite web|publisher=RussianSpaceWeb|url=http://www.russianspaceweb.com/2011.html|accessdate=12 January 2010|title=Space exploration in 2011|date=4 January 2010|author=Anatoly Zak}}</ref> Another Russian communications system is the [[Voskhod-M]], which enables internal telephone communications between ''Zvezda'', ''Zarya'', ''Pirs'', ''Poisk'' and the USOS, and also provides a VHF radio link to ground control centres via antennas on ''Zvezda''{{'s}} exterior.<ref>{{cite web|url=http://www.nasa.gov/directorates/somd/reports/iss_reports/2010/05022010.html|date=2 May 2010|accessdate=7 July 2010|publisher=NASA|title=ISS On-Orbit Status 05/02/10}}</ref>

The [[US Orbital Segment]] (USOS) makes use of two separate radio links mounted in the [[Z1 truss]] structure: the [[S band]] (used for audio) and [[Ku band|Ku band]] (used for audio, video and data) systems. These transmissions are routed via the United States [[Tracking and Data Relay Satellite]] System (TDRSS) in [[geostationary orbit]], which allows for almost continuous real-time communications with [[Christopher C. Kraft Jr. Mission Control Center|NASA's Mission Control Center]] (MCC-H) in [[Houston]].<ref name="ISSBook" /><ref name="ISSRG" /><ref name="BoeingComm">{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/systems/communications_tracking.html|publisher=Boeing|accessdate=30 November 2009|title=Communications and Tracking|archiveurl = https://web.archive.org/web/20080611115319/http://www.boeing.com/defense-space/space/spacestation/systems/communications_tracking.html |archivedate = 11 June 2008}}</ref> Data channels for the Canadarm2, European ''Columbus'' laboratory and Japanese ''Kibō'' modules are routed via the S band and Ku band systems, although the [[European Data Relay System]] and a similar Japanese system will eventually complement the TDRSS in this role.<ref name="ISSBook" /><ref name="JAXA-MOU">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/nasa_japan.html|title=Memorandum of Understanding Between the National Aeronautics and Space Administration of the United States of America and the Government of Japan Concerning Cooperation on the Civil International Space Station|publisher=NASA|accessdate=19 April 2009|date=24 February 1998}}</ref> Communications between modules are carried on an internal digital [[wireless network]].<ref>{{cite web|title=Operations Local Area Network (OPS LAN) Interface Control Document|format=PDF|publisher=NASA|url=http://www.spaceref.com/iss/computer/iss.ops.lan.icd.pdf|accessdate=30 November 2009|date=February 2000}}</ref>

[[File:STS-128 ISS-20 Destiny Canadarm2.jpg|thumb|left|Laptop computers surround the Canadarm2 console.]]
[[Ultra high frequency|UHF radio]] is used by astronauts and cosmonauts conducting [[Extra-vehicular activity|EVAs]]. UHF is employed by other spacecraft that dock to or undock from the station, such as Soyuz, Progress, HTV, ATV and the Space Shuttle (except the shuttle also makes use of the S band and Ku band systems via TDRSS), to receive commands from Mission Control and ISS crewmembers.<ref name="ISSRG" /> Automated spacecraft are fitted with their own communications equipment; the ATV uses a [[laser]] attached to the spacecraft and equipment attached to ''Zvezda'', known as the Proximity Communications Equipment, to accurately dock to the station.<ref>{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=16247|title=ISS/ATV communication system flight on Soyuz|accessdate=30 November 2009|publisher=[[EADS Astrium]]|date=28 February 2005}}</ref><ref>{{cite web|publisher=NASASpaceflight.com|author=Chris Bergin|url=http://www.nasaspaceflight.com/2009/11/sts-129-support-dragon-communication-demo-iss/|date=10 November 2009|accessdate=30 November 2009|title=STS-129 ready to support Dragon communication demo with ISS}}</ref>

The ISS is equipped with approximately 100 [[IBM]] and [[Lenovo]] [[ThinkPad#Use in space|ThinkPad]] model A31 and T61P laptop computers. Each computer is a [[commercial off-the-shelf]] purchase which is then modified for safety and operation including updates to connectors, cooling and power to accommodate the station's 28V DC power system and weightless environment. Heat generated by the laptops does not rise, but stagnates surrounding the laptop, so additional forced ventilation is required. Laptops aboard the ISS are connected to the station's [[wireless LAN]] via [[Wi-Fi]] and to the ground via Ku band. This provides speeds of 10 [[Megabit per second|Mbit/s]] to and 3 Mbit/s from the station, comparable to home [[digital subscriber line|DSL]] connection speeds.<ref name="issit">{{cite news |url=http://bits.blogs.nytimes.com/2010/01/22/first-tweet-from-space/ |title=First Tweet From Space |work=[[The New York Times]] |first=Nick |last=Bilton |date=22 January 2010 |accessdate=29 April 2014}}</ref><ref name="tested20121019">{{cite news |url=http://www.tested.com/science/space/449539-how-fast-isss-internet-and-other-space-questions-answered/ |title=How Fast is the ISS's Internet? (and Other Space Questions Answered) |work=Tested.com |first=Will |last=Smith |date=19 October 2012 |accessdate=29 April 2014}}</ref>

The operating system used for key station functions is the [[Debian]] [[GNU/Linux distribution]].<ref>{{cite news|last=Thomson|first=Iain|title=Penguins in spa-a-a-ce! ISS dumps Windows for Linux on laptops|url=http://www.theregister.co.uk/2013/05/10/iss_linux_debian_deployment/|accessdate=15 May 2013|newspaper=The Register|date=10 May 2013}}</ref> The migration from [[Microsoft Windows]] was made in May 2013 for reasons of reliability, stability and flexibility.<ref>{{cite news|last=Gunter|first=Joel|title=International Space Station to boldly go with Linux over Windows|url=http://www.telegraph.co.uk/technology/news/10049444/International-Space-Station-to-boldly-go-with-Linux-over-Windows.html|accessdate=15 May 2013|newspaper=The Daily Telegraph|date=10 May 2013}}</ref>

==Station operations==

===Expeditions and private flights===
[[File:Sts088-703-019e.jpg|thumb|Zarya and Unity were entered for the first time on 10 December 1998.]]
[[File:Soyuz tm-31 transported to launch pad.jpg|right|thumb|Soyuz TM-31 being prepared to bring the first resident crew to the station in October 2000]]
[[File:STS-115 ISS after undocking.jpg|thumb|right|ISS was slowly assembled over a decade of spaceflights and crews]]
[[File:Tracy Caldwell Dyson in Cupola ISS.jpg|thumb|Expeditions have included male and female crew-members from many nations]]
''See also the [[list of International Space Station expeditions]] (professional crew), [[space tourism]] (private travellers), and the [[list of human spaceflights to the ISS]] (both).''

Each permanent crew is given an expedition number. Expeditions run up to six months, from launch until undocking, an 'increment' covers the same time period, but includes cargo ships and all activities. Expeditions 1 to 6 consisted of 3 person crews, Expeditions 7 to 12 were reduced to the safe minimum of two following the destruction of the NASA Shuttle Columbia. From Expedition 13 the crew gradually increased to 6 around 2010.<ref name="ISSEx">{{cite web|title=International Space Station Expeditions|publisher=NASA|url=http://www.nasa.gov/mission_pages/station/expeditions/index.html|date=10 April 2009|accessdate=13 April 2009}}</ref><ref name="current">{{cite web|url=http://www.nasa.gov/mission_pages/station/main/index.html|title=International Space Station|accessdate=22 October 2008|publisher=NASA|year=2008|author=NASA}}</ref> With the arrival of the American [[Commercial Crew Development|Commercial Crew]] vehicles in the middle of the 2010s, expedition size may be increased to seven crew members, the number ISS is designed for.<ref>{{cite web|url=http://www.aviationweek.com/article.aspx?id=/article-xml/asd_07_26_2012_p01-02-480253.xml|title=ISS Research Hampered By Crew Availability|last=Morring|first=Frank|date=27 July 2012|quote=A commercial capability would allow the station's crew to grow from six to seven by providing a four-seat vehicle for emergency departures in addition to the three-seat Russian Soyuz capsules in use today.|publisher=Aviation Week|accessdate=30 July 2012}}</ref><ref>{{cite web|url=http://www.airspacemag.com/space-exploration/AS-Interview-Mike-Suffredini.html|title=Assembly (Nearly) Complete |last=Hoversten|first=Paul|date=1 May 2011|publisher=Air & Space Magazine|quote=In fact, we're designed on the U.S. side to take four crew. The ISS design is actually for seven. We operate with six because first, we can get all our work done with six, and second, we don't have a vehicle that allows us to fly a seventh crew member. Our requirement for the new vehicles being designed is for four seats. So I don't expect us to go down in crew size. I would expect us to increase it.|accessdate=8 May 2011}}</ref>

[[Sergei Krikalev]], member of [[Expedition 1]] and Commander of [[Expedition 11]] has spent more time in space than anyone else, a total of 803 days and 9 hours and 39 minutes. His awards include the [[Order of Lenin]], [[Hero of the Soviet Union]], [[Hero of the Russian Federation]], and 4 NASA medals. On 16 August 2005 at 1:44 am EDT he passed the record of 748 days held by [[Sergei Avdeyev]], who had 'time travelled' 1/50th of a second into the future on board MIR.<ref>{{cite web|url=http://www.popsci.com/scitech/article/2002-02/lets-do-time-warp-again?page=2 |archiveurl=https://web.archive.org/web/20100628190931/http://www.popsci.com/scitech/article/2002-02/lets-do-time-warp-again?page=2 |archivedate=28 June 2010 |title=Let's Do the Time Warp Again |publisher=Web.archive.org |date=28 June 2010 |accessdate=1 May 2012}}</ref> He participated in psychosocial experiment SFINCSS-99 (Simulation of Flight of International Crew on Space Station), which examined inter-cultural and other stress factors affecting integration of crew in preparation for the ISS spaceflights. Commander [[Michael Fincke]] has spent a total of 382 days in space – more than any other American astronaut.

Travellers who pay for their own passage into space are termed spaceflight participants by Roscosmos and NASA, and are sometimes informally referred to as space tourists, a term they generally dislike.{{refn|Privately funded travellers who have objected to the term include Dennis Tito, the first such traveller (''Associated Press'', 8 May 2001), [[Mark Shuttleworth]], founder of [[Ubuntu (operating system)|Ubuntu]] (''Associated Press, The Spokesman Review, 6 January 2002, p. A4''), Gregory Olsen and Richard Garriott.<ref>{{cite news|last=Schwartz|first=John|title=Russia Leads Way in Space Tourism With Paid Trips into Orbit|url=http://www.nytimes.com/2008/10/11/science/space/11space.html|newspaper=The New York Times|date=10 October 2008}}</ref><ref>{{cite web|last=Boyle|first=Alan|title=Space passenger Olsen to pull his own weight|url=http://msnbc.msn.com/id/9323509/#.Tz5lcFE-qr4|publisher=MSNBC}}</ref> Canadian astronaut Bob Thirsk said the term does not seem appropriate, referring to his crewmate, [[Guy Laliberté]], founder of [[Cirque du Soleil]].<ref>{{cite web|url=http://www.stcatharinesstandard.ca/ArticleDisplay.aspx?e=1975186&archive=true |title=Flight to space ignited dreams | St. Catharines Standard |publisher=Stcatharinesstandard.ca |accessdate=1 May 2012}}</ref> Anousheh Ansari denied being a tourist<ref>{{cite web|url=http://www.esa.int/esaHS/SEMD58BE8YE_business_0.html |title=ESA – Human Spaceflight and Exploration – Business – "I am NOT a tourist" |publisher=Esa.int |date=18 September 2006 |accessdate=1 May 2012}}</ref> and took offence at the term.<ref>{{cite web|url=http://www.space.com/2889-interview-anousheh-ansari-female-space-tourist.html |title=Interview with Anousheh Ansari, the First Female Space Tourist |publisher=Space.com |date=15 September 2006 |accessdate=1 May 2012}}</ref>|group=note|name}} All seven were transported to the ISS on Russian Soyuz spacecraft. When professional crews change over in numbers not divisible by the three seats in a Soyuz, and a short-stay crewmember is not sent, the spare seat is sold by MirCorp through Space Adventures. When the space shuttle retired in 2011, and the station's crew size was reduced to 6, space tourism was halted, as the partners relied on Russian transport seats for access to the station. Soyuz flight schedules increase after 2013, allowing 5 Soyuz flights (15 seats) with only two expeditions (12 seats) required.<ref>{{cite web|url=http://www.spaceflightnow.com/news/n1101/12soyuz/ |title=Breaking News | Resumption of Soyuz tourist flights announced |publisher=Spaceflight Now |accessdate=1 May 2012}}</ref> The remaining seats are sold for around {{US$|40 million}} to members of the public who can pass a medical. ESA and NASA criticised private spaceflight at the beginning of the ISS, and NASA initially resisted training [[Dennis Tito]], the first man to pay for his own passage to the ISS.{{refn|ESA director Jörg Feustel-Büechl said in 2001 that Russia had no right to send 'amateurs' to the ISS. A 'stand-off' occurred at the Johnson Space Centre between Commander Talgat Musabayev and NASA manager Robert Cabana. Cabana refused to train Dennis Tito, a member of Musabayev's crew along with Yuri Baturin. The commander argued that Tito had trained 700 hours in the last year and was as qualified as any NASA astronaut, and refused to allow his crew to be trained on the American portions of the station without Tito. Cabana stated training could not begin, and the commander returned with his crew to their hotel.|group=note|name}}  [[Toyohiro Akiyama]] was flown to Mir for a week, he was classed as a business traveller, as his employer, [[Tokyo Broadcasting System]], paid for his ticket, and he gave a daily TV broadcast from orbit.

[[Anousheh Ansari]] ({{lang-fa|انوشه انصاری}}) became the first Iranian in space and the first self-funded woman to fly to the station. Officials reported that her education and experience make her much more than a tourist, and her performance in training had been "excellent."<ref>{{cite web|last=Maher |first=Heather |url=http://www.rferl.org/content/article/1071358.html |title=U.S.: Iranian-American To Be First Female Civilian in Space |publisher=Radio Free Europe/Radio Liberty |date=15 September 2006 |accessdate=1 May 2012}}</ref> Ansari herself dismisses the idea that she is a tourist. She did Russian and European studies involving medicine and microbiology during her 10-day stay. The documentary ''[[Space Tourists]]'' follows her journey to the station, where she fulfilled "an age-old dream of man: to leave our planet as a «normal person» and travel into outer space."<ref>{{cite web|url=http://www.space-tourists-film.com/en/film_synopsis.php |title=Space Tourists | A Film By Christian Frei |publisher=Space-tourists-film.com |accessdate=1 May 2012}}</ref> In the film, some Kazakhs are shown waiting in the middle of the steppes for four rocket stages to literally fall from the sky. Film-maker Christian Frei states "Filming the work of the Kazakh scrap metal collectors was anything but easy. The Russian authorities finally gave us a film permit in principle, but they imposed crippling preconditions on our activities. The real daily routine of the scrap metal collectors could definitely not be shown. Secret service agents and military personnel dressed in overalls and helmets were willing to ''re-enact'' their work for the cameras – in an idealised way that officials in Moscow deemed to be presentable, but not at all how it takes place in reality."

Spaceflight participant [[Richard Garriott]] placed a [[Geocaching|geocache]] aboard the ISS during his flight.<ref>{{cite web|url=http://www.geocaching.com/seek/cache_details.aspx?wp=GC1BE91|title=International Space Station Traditional Geocache}}</ref> This is currently the only non-terrestrial geocache in existence.<ref>{{cite web |url=http://www.geekwire.com/2011/outer-space-ocean-floor-15m-geocaches-counting/|accessdate=27 February 2013|last=Cook|first=John|title=From outer space to the ocean floor, Geocaching.com now boasts more than 1.5 million hidden treasures|date=29 August 2011}}</ref>

===Orbit===
{{Double image|right|Internationale Raumstation Bahnhöhe (dumb version).png|300|Iss.ogg|235|Graph showing the changing altitude of the ISS from November 1998 until January 2009|Animation of ISS orbit from a North American geostationary point of view (sped up 1800 times)}}
The ISS is maintained in a nearly circular orbit with a minimum mean altitude of 330 km (205 mi) and a maximum of 410 km (255 mi), in the centre of the [[thermosphere]], at an [[inclination]] of 51.6 degrees to Earth's equator, necessary to ensure that Russian [[Soyuz (spacecraft)|Soyuz]] and [[Progress (spacecraft)|Progress]] spacecraft launched from the [[Baikonur Cosmodrome]] may be safely launched to reach the station. Spent rocket stages must be dropped into uninhabited areas and this limits the directions rockets can be launched from the spaceport.<ref name="MCC Answer">{{cite web|last=Cooney|first=Jim|title=Mission Control Answers Your Questions|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-112/09_04_12_54_17.html|location=Houston, TX|quote=Jim Cooney ISS Trajectory Operations Officer}}</ref><ref>{{cite book|last=Pelt|first=Michel van|title=Into the Solar System on a String : Space Tethers and Space Elevators|year=2009|publisher=Springer New York|location=New York, NY|isbn=0-387-76555-7|page=133|edition=1.}}</ref> The orbital inclination chosen was also low enough to allow American space shuttles launched from Florida to reach the ISS.

It travels at an average speed of 27,724 kilometres (17,227 mi) per hour, and completes {{Orbit|daily orbits|15.54}} orbits per day (93 minutes per orbit).{{Orbit|ref|<ref name="heavens-above"/>}}<ref name="tracking">{{cite web|url=http://spaceflight.nasa.gov/realdata/tracking/index.html|title=Current ISS Tracking data|accessdate=28 January 2009|publisher=NASA|date=15 December 2008|author=NASA}}</ref> The station's altitude was allowed to fall around the time of each NASA shuttle mission. Orbital boost burns would generally be delayed until after the shuttle's departure. This allowed shuttle payloads to be lifted with the station's engines during the routine firings, rather than have the shuttle lift itself and the payload together to a higher orbit. This trade-off allowed heavier loads to be transferred to the station. After the retirement of the NASA shuttle, the nominal orbit of the space station was raised in altitude.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/06/europes-atv-2-depart-iss-make-way-russias-progress-m-11m/ |title=Europe's ATV-2 departs ISS to make way for Russia's Progress M-11M |publisher=NASASpaceFlight.com |date=20 June 2011 |accessdate=1 May 2012}}</ref><ref name="Popular Mechanics">{{cite web|url=http://www.popularmechanics.com/science/air_space/4275571.html|title=The Uncertain Future of the International Space Station: Analysis|author=Rand Simberg|date=29 July 2008|accessdate=6 March 2009|publisher=[[Popular Mechanics]]}}</ref> Other, more frequent supply ships do not require this adjustment as they are substantially lighter vehicles.<ref name="Worldbook at NASA">{{cite web|url=http://www.nasa.gov/worldbook/intspacestation_worldbook.html|title = International Space Station|year=2005|accessdate=14 June 2008|publisher=World Book, Inc|author=James Oberg|work=World Book Online Reference Center}}{{dead link|date=May 2012}}</ref><ref name="nasa.gov-iss-environment">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archiveurl=https://web.archive.org/web/20080213164432/http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archivedate=13 February 2008|title=ISS Environment|accessdate=15 October 2007|publisher=[[Johnson Space Center]]}}</ref>
[[File:ISS orbits 04132013.jpg|thumbnail|Orbits of the ISS, shown in April 2013]]
Orbital boosting can be performed by the station's two main engines on the ''[[Zvezda (ISS module)|Zvezda]]'' service module, or Russian or European spacecraft docked to Zvezda's aft port. The ATV has been designed with the possibility of adding a [[Automated Transfer Vehicle#ATV evolution proposals|second docking port]] to its other end, allowing it to remain at the ISS and still allow other craft to dock and boost the station. It takes approximately two orbits (three hours) for the boost to a higher altitude to be completed.<ref name="nasa.gov-iss-environment" /> In December 2008 NASA signed an agreement with the [[Ad Astra Rocket Company]] which may result in the testing on the ISS of a [[VASIMR]] plasma propulsion engine.<ref name="vasimr">{{cite web|url=http://www.adastrarocket.com/AdAstra-NASA_PR12Dec08.pdf|publisher=AdAstra Rocket Company|title=Press Release 121208|accessdate=7 December 2009|date=12 December 2008|format=PDF}}</ref> This technology could allow [[Orbital station-keeping|station-keeping]] to be done more economically than at present.<ref name="future-prop">{{cite web|url=http://www.nasa.gov/vision/space/travelinginspace/future_propulsion.html|title=Propulsion Systems of the Future|accessdate=29 May 2009|publisher=NASA}}</ref><ref>{{cite web|work=New Scientist|accessdate=7 October 2009|url=http://www.newscientist.com/article/dn17918-rocket-company-tests-worlds-most-powerful-ion-engine.html|title=Rocket company tests world's most powerful ion engine|author=David Shiga|date=5 October 2009}}</ref>

The Russian Orbital Segment contains the station's engines and control [[Bridge (nautical)|bridge]], which handles Guidance, Navigation and Control (ROS GNC) for the entire station.<ref name="Navigation">{{cite web|url=http://www.esa.int/export/esaHS/ESAOXX0VMOC_iss_0.html|title=DMS-R: ESA's Data Management System for the Russian Segment of the ISS}}</ref> Initially, Zarya, the first module of the station, controlled the station until a short time after the Russian service module Zvezda docked and was transferred control. Zvezda contains the ESA built DMS-R Data Management System.<ref name="EsaComputer">{{cite web|url=http://www.esa.int/esapub/onstation/onstation17/os17_chapter6.pdf|title=Exercising Control 49 months of DMS-R Operations}}</ref> Using two fault-tolerant computers (FTC), Zvezda computes the station's position and orbital trajectory using redundant Earth horizon sensors, Solar horizon sensors as well as Sun and star trackers. The FTCs each contain three identical processing units working in parallel and provide advanced fault-masking by majority voting. Zvezda uses gyroscopes and thrusters to turn itself around. Gyroscopes do not require propellant, rather they use electricity to 'store' momentum in flywheels by turning in the opposite direction to the station's movement. The USOS has its own computer controlled gyroscopes to handle the extra mass of that section. When gyroscopes 'saturate', reaching their maximum speed, thrusters are used to cancel out the stored momentum. During [[Expedition 10]], an incorrect command was sent to the station's computer, using about 14 kilograms of propellant before the fault was noticed and fixed. When attitude control computers in the ROS and USOS fail to communicate properly, it can result in a rare 'force fight' where the ROS GNC computer must ignore the USOS counterpart, which has no thrusters.<ref>{{cite web|url=http://pims.grc.nasa.gov/pimsdocs/public/ISS%20Handbook/hb_qs_vehicle_RussianUSGNCForceFight.pdf |title=Microsoft Word – hb_qs_vehicle_RussianUSGNCForceFight_pg1.doc |format=PDF |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://spaceflight.nasa.gov/spacenews/reports/issreports/2005/iss05-7.html|title = International Space Station Status Report #05-7|date=11 February 2005|publisher=NASA|accessdate=23 November 2008}}</ref><ref>{{cite book|title=Dynamics and Control of Attitude, Power, and Momentum for a Spacecraft Using Flywheels and Control Moment Gyroscopes|author=Carlos Roithmayr|format=PDF|year=2003|publisher=NASA|location=Langley Research Center|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030038806_2003038772.pdf|accessdate=12 July 2011}}</ref> When an ATV, NASA Shuttle, or Soyuz is docked to the station, it can also be used to maintain station attitude such as for troubleshooting. Shuttle control was used exclusively during [[STS-117|installation]] of the S3/S4 truss, which provides electrical power and data interfaces for the station's electronics.<ref>{{cite web|url=http://www.nasaspaceflight.com/2007/06/atlantis-ready-to-support-iss-troubleshooting/|title=Atlantis ready to support ISS troubleshooting|publisher=NASASPaceflight.com|author=Chris Bergin|accessdate=6 March 2009|date=14 June 2007}}</ref>

==Mission controls==
The components of the ISS are operated and monitored by their respective space agencies at [[Mission Control Center|mission control centres]] across the globe, including:
* Roscosmos's [[Mission Control Center#RKA Mission Control Center|Mission Control Center]] at [[Korolyov (city)|Korolyov]], Moscow Oblast, controls the [[Russian Orbital Segment]] which handles Guidance, Navigation & Control for the entire Station.,<ref name="Navigation" /><ref name="EsaComputer" /> in addition to individual Soyuz and Progress missions.<ref name="ISSRG" />
* ESA's [[ATV Control Centre]], at the [[Toulouse Space Centre]] (CST) in [[Toulouse]], France, controls flights of the unmanned European [[Automated Transfer Vehicle]].<ref name="ISSRG" />
* JAXA's [[JEM Control Center]] and [[HTV Control Center]] at [[Tsukuba Space Center]] (TKSC) in [[Tsukuba]], Japan, are responsible for operating the Japanese Experiment Module complex and all flights of the 'White Stork' HTV Cargo spacecraft, respectively.<ref name="ISSRG" />
* NASA's [[Christopher C. Kraft Jr. Mission Control Center|Mission Control Center]] at [[Lyndon B. Johnson Space Center]] in Houston, Texas, serves as the primary control facility for the United States segment of the ISS and also controlled the Space Shuttle missions that visited the station.<ref name="ISSRG">{{cite book|author=Gary Kitmacher|title=Reference Guide to the International Space Station| publisher =[[Apogee Books]]|location=Canada|year=2006|isbn=978-1-894959-34-6|issn=1496-6921|pages=71–80}}</ref>
* NASA's [[Payload Operations and Integration Center]] at [[Marshall Space Flight Center]] in [[Huntsville, Alabama]], coordinates payload operations in the USOS.<ref name="ISSRG" />
* ESA's [[Columbus Control Center|Columbus Control Centre]] at the [[German Aerospace Center|German Aerospace Centre]] (DLR) in [[Oberpfaffenhofen]], Germany, manages the European ''Columbus'' research laboratory.<ref name="ISSRG" />
* CSA's [[MSS Control]] at [[Saint-Hubert, Quebec]], Canada, controls and monitors the [[Mobile Servicing System]], or Canadarm2.<ref name="ISSRG" />
{{wide image|ISS Centers.svg|880px|Space centres involved with the ISS programme|alt=A world map highlighting the locations of space centres. See adjacent text for details.}}

===Repairs===
{{Main|Orbital Replacement Units|International Space Station maintenance}}
'''[[Orbital Replacement Units]]''' ('''ORUs''') are spare parts that can be readily replaced when a unit either passes its design life or fails. Examples of ORUs are pumps, storage tanks, controller boxes, antennas, and battery units. Some units can be replaced using robotic arms. Many are stored outside the station, either on small pallets called [[ExPRESS Logistics Carrier]]s (ELCs) or share larger platforms called [[External Stowage Platform]]s which also hold science experiments. Both kinds of pallets have electricity as many parts which could be damaged by the cold of space require heating. The larger logistics carriers also have computer local area network connections (LAN) and telemetry to connect experiments. A heavy emphasis on stocking the USOS with ORU's occurred around 2011, before the end of the NASA shuttle programme, as its commercial replacements, [[Cygnus (spacecraft)|Cygnus]] and [[Dragon (spacecraft)|Dragon]], carry one tenth to one quarter the payload.

[[File:ISS Unpressurized Platforms.png|thumb|Spare parts are called [[Orbit Replaceable Unit|ORU]]s; some are externally stored on pallets called [[ExPRESS Logistics Carrier|ELC]]s and [[External stowage platform|ESP]]s.]]

Unexpected problems and failures have impacted the station's assembly time-line and work schedules leading to periods of reduced capabilities and, in some cases, could have forced abandonment of the station for safety reasons, had these problems not been resolved. During [[STS-120]] in 2007, following the relocation of the P6 truss and solar arrays, it was noted during the redeployment of the array that it had become torn and was not deploying properly.<ref name="Astronauts notice tear in solar panel">{{cite news|url=http://www.redorbit.com/news/space/1123767/astronauts_notice_tear_in_solar_panel/index.html |title=Astronauts notice tear in solar panel|accessdate=30 October 2007|agency=Associated Press|date=30 October 2007|author=Liz Austin Peterson}}</ref> An EVA was carried out by [[Scott E. Parazynski|Scott Parazynski]], assisted by [[Douglas H. Wheelock|Douglas Wheelock]]. The men took extra precautions to reduce the risk of electric shock, as the repairs were carried out with the solar array exposed to sunlight.<ref name="Space Station's Damaged Panel Is Fixed">{{cite news|url=http://www.washingtonpost.com/wp-dyn/content/article/2007/11/03/AR2007110300227.html|title=Space Station's Damaged Panel Is Fixed|accessdate=4 November 2007|work=The Washington Post|date=4 November 2007|first=Rob|last=Stein}}</ref> The issues with the array were followed in the same year by problems with the starboard Solar Alpha Rotary Joint (SARJ), which rotates the arrays on the starboard side of the station. Excessive vibration and high-current spikes in the array drive motor were noted, resulting in a decision to substantially curtail motion of the starboard SARJ until the cause was understood. Inspections during EVAs on STS-120 and [[STS-123]] showed extensive contamination from metallic shavings and debris in the large drive gear and confirmed damage to the large metallic race ring at the heart of the joint, and so the joint was locked to prevent further damage.<ref name="joint-update">{{cite news|url=http://spaceflightnow.com/shuttle/sts123/080325sarj/index.html|title=Station chief gives detailed update on joint problem|accessdate=5 November 2008|author=William Harwood|publisher=CBS News & SpaceflightNow.com|date=25 March 2008}}</ref> Repairs to the joint were carried out during [[STS-126]] with lubrication of both joints and the replacement of 11 out of 12 trundle bearings on the joint.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts126/126_overview.html|title=Crew Expansion Prep, SARJ Repair Focus of STS-126|accessdate=5 November 2008|publisher=NASA|date=30 October 2008}}</ref><ref>{{cite news|url=http://www.spaceflightnow.com/shuttle/sts126/081118fd5/index.html|title=Astronauts prepare for first spacewalk of shuttle flight|date=18 November 2008|author=William Harwood|publisher=CBS News & SpaceflightNow.com|accessdate=22 November 2008}}</ref>

[[File:STS-120 EVA Scott Parazynski.jpg|thumb|While anchored on the end of the [[Orbiter Boom Sensor System|OBSS]], astronaut [[Scott Parazynski]] performs makeshift repairs to a US Solar array which damaged itself when unfolding, during [[STS-120]].|alt=Two black and orange solar arrays, shown uneven and with a large tear visible. A crew member in a spacesuit, attached to the end of a robotic arm, holds a latticework between two solar sails.]]
2009 saw damage to the S1 radiator, one of the components of the station's cooling system. The problem was first noticed in [[Soyuz spacecraft|Soyuz]] imagery in September 2008, but was not thought to be serious.<ref name="Radiator">{{cite web|url=http://www.nasaspaceflight.com/2009/04/iss-concern-s1-radiator-may-require-replacement-shuttle-mission/|author=Chris Bergin|date=1 April 2009|publisher=NASASpaceflight.com|title=ISS concern over S1 Radiator – may require replacement via shuttle mission|accessdate=3 April 2009}}</ref> The imagery showed that the surface of one sub-panel has peeled back from the underlying central structure, possibly due to micro-meteoroid or debris impact. It is also known that a Service Module thruster cover, jettisoned during an EVA in 2008, had struck the S1 radiator, but its effect, if any, has not been determined. On 15 May 2009 the damaged radiator panel's ammonia tubing was mechanically shut off from the rest of the cooling system by the computer-controlled closure of a valve. The same valve was used immediately afterwards to vent the ammonia from the damaged panel, eliminating the possibility of an ammonia leak from the cooling system via the damaged panel.<ref name="Radiator" />

Early on 1 August 2010, a failure in cooling Loop A (starboard side), one of two external cooling loops, left the station with only half of its normal cooling capacity and zero redundancy in some systems.<ref>{{cite web|url=http://spaceflightnow.com/news/n1007/31station/ |title=Problem forces partial powerdown aboard station |publisher=Spaceflightnow.com |date=31 July 2010 |accessdate=16 November 2010}}</ref><ref>{{cite web|url=http://www.spaceref.com/news/viewsr.html?pid=34622 |title=NASA ISS On-Orbit Status 1 August 2010 (early edition) |publisher=Spaceref.com |date=31 July 2010 |accessdate=16 November 2010}}</ref><ref>{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/systems/atcs.html |title=ISS Active Control System |publisher=Boeing |date=21 November 2006 |accessdate=16 November 2010}}</ref> The problem appeared to be in the ammonia pump module that circulates the ammonia cooling fluid. Several subsystems, including two of the four CMGs, were shut down.

Planned operations on the ISS were interrupted through a series of EVAs to address the cooling system issue. A first EVA on 7 August 2010, to replace the failed pump module, was not fully completed due to an ammonia leak in one of four quick-disconnects. A second EVA on 11 August successfully removed the failed pump module.<ref>[http://spaceflightnow.com/station/exp24/100810evapre/index.html Spaceflight Now] "Wednesday spacewalk to remove failed coolant pump"</ref><ref>[http://www.nasaspaceflight.com/2010/08/live-second-eva-with-pump-module-changeout/ NASA spaceflight 11 August] "Large success for second EVA as failed Pump Module is removed"</ref> A third EVA was required to restore Loop A to normal functionality.<ref>[http://spaceflightnow.com/station/exp24/100811eva2/index5.html Spaceflight Now 12 August] "Station's bad pump removed; more spacewalking ahead"</ref><ref>[http://www.nasaspaceflight.com/2010/08/iss-cooling-returning-normal-confirming-etcs-pm-success/ Spaceflight Now, 18 August] ISS cooling configuration returning to normal confirming ETCS PM success</ref>

The USOS's cooling system is largely built by the American company [[Boeing]],<ref>{{cite web|url=http://www.space.com/businesstechnology/international-space-station-complexities-100802.html|title=Cooling System Malfunction Highlights Space Station's Complexity|publisher=Space.com|date=2 August 2010}}</ref> which is also the manufacturer of the failed pump.<ref>{{cite web|url=http://spaceflightnow.com/news/n1007/31station/|title=Spacewalks needed to fix station cooling problem|publisher=Spaceflightnow|date=31 July 2010}}</ref>

An air leak from the USOS in 2004,<ref>{{cite news|url=http://www.msnbc.msn.com/id/3882962/|title=Crew finds 'culprit' in space station leak|publisher=MSNBC|date=11 January 2004|author=James Oberg|accessdate=22 August 2010}}</ref> the venting of fumes from an ''[[Elektron (ISS)|Elektron]]'' oxygen generator in 2006,<ref>{{cite news|url=http://spaceflightnow.com/station/exp13/060918elektron.html|title=Oxygen Generator Problem Triggers Station Alarm|publisher = CBS News through Spaceflight Now|date=18 September 2006|author=William Harwood|accessdate=24 November 2008}}</ref> and the failure of the computers in the ROS in 2007 during [[STS-117]] left the station without thruster, ''Elektron'', ''[[Vozdukh]]'' and other environmental control system operations, the root cause of which was found to be condensation inside the electrical connectors leading to a short-circuit.{{Citation needed|date=June 2011}}
[[File:STS-134 EVA4 view to the Russian Orbital Segment.jpg|thumb|right|In the foreground, a set of heat radiators]]
The four Main Bus Switching Units (MBSUs, located in the S0 truss), control the routing of power from the four solar array wings to the rest of the ISS. In late 2011 MBSU-1, while still routing power correctly, ceased responding to commands or sending data confirming its health, and was scheduled to be swapped out at the next available EVA. In each MBSU, two power channels feed 160V DC from the arrays to two DC-to-DC power converters (DDCUs) that supply the 124V power used in the station. A spare MBSU was already on board, but 30 August 2012 EVA failed to be completed when a bolt being tightened to finish installation of the spare unit jammed before electrical connection was secured.<ref>{{cite web|author=30 August 2012 by Pete Harding |url=http://www.nasaspaceflight.com/2012/08/astronaut-perform-first-post-shuttle-spacewalk-iss |title=Astronaut duo complete challenging first post-Shuttle US spacewalk on ISS |publisher=Nasaspaceflight.com |date=30 August 2012 |accessdate=22 October 2013}}</ref> The loss of MBSU-1 limits the station to 75% of its normal power capacity, requiring minor limitations in normal operations until the problem can be addressed.

On 5 September 2012, in a second, 6 hr, EVA to replace MBSU-1, astronauts Sunita Williams and Akihiko Hoshide successfully restored the ISS to 100% power.<ref>[http://spaceref.com/international-space-station/critical-space-station-spacewalk-a-success.html Spaceref.com Sept 5, 2012] Marc Boucher "Critical Space Station spacewalk a Success".</ref>
[[File:Astronaut Mike Hopkins on Dec. 24 Spacewalk.jpg|thumb|Mike Hopkins on his Christmas Eve spacewalk]]
On 24 December 2013, astronauts made a rare Christmas Eve space walk, installing a new ammonia pump for the station's cooling system. The faulty cooling system had failed earlier in the month, halting many of the station's science experiments. Astronauts had to brave a "mini blizzard" of ammonia while installing the new pump. It was only the second Christmas Eve spacewalk in NASA history.<ref>{{cite web|last=AP|title=Astronauts Complete Rare Christmas Eve Spacewalk|url=http://www.leaker.com/astronauts-complete-rare-christmas-eve-spacewalk/|publisher=Leaker|accessdate=24 December 2013|date=24 December 2013}}</ref>

[[File:Iss orbit and expeditions.png|thumb|Iss orbit with calendar of expeditions and modules]]

==Fleet operations==
:{{See also|List of human spaceflights to the International Space Station|List of unmanned spaceflights to the International Space Station}}
A wide variety of manned and unmanned spacecraft have supported the station's activities. 
[[Progress M-28M]] (ISS-60P) was the 62nd Progress spacecraft planned to arrive at the ISS, including [[Progress M-MIM2|M-MIM2]] and [[Progress M-SO1|M-SO1]] which installed modules. 35 flights of the retired NASA Space Shuttle were made to the station.<ref name="ISStD">{{cite web|url=http://spaceflight.nasa.gov/station/isstodate.html|title=The ISS to Date|accessdate=21 March 2011|publisher=NASA|date=9 March 2011|author=NASA}}</ref> [[Soyuz TMA-16M|TMA-16M]] is the 42nd Soyuz flight, and there have been 5 [[Automated Transfer Vehicle|European ATV]], 4 Japanese [[H-II Transfer Vehicle|Kounotori]] 'White Stork', 8 [[SpaceX]] [[Dragon (spacecraft)|Dragon]] and 4 OSC [[Cygnus (spacecraft)|Cygnus]] planned arrivals.

===Currently docked/berthed===
''See also the list of [[List of International Space Station expeditions|professional]] crew, [[Space tourism|private]] travellers, [[List of human spaceflights to the ISS|both]] or just [[List of unmanned spaceflights to the ISS|unmanned spaceflights]].''

;Key
{{legend|lightblue|Uncrewed cargoships are in light blue}}
{{legend|#cfc|Crewed spacecraft are in light green}}

{| class="wikitable" style="margin: 1em auto 1em auto;text-align: left; font-size: 95%;"
|-Currently Docked
|style="text-align:center; background:#BBB" colspan="3" | '''Spacecraft and mission'''
|style="text-align:center; background:#BBB"|'''Location'''
|style="text-align:center; background:#BBB"|'''Arrived''' ([[UTC]])
|style="text-align:center; background:#BBB"|'''Departure date'''
|- style="background:lightblue;"
| {{flagicon|RUS}}
| [[Progress M-26M]]
| Progress 58 Cargo
| [[Zvezda (ISS module)|Zvezda]] aft
| 17 February 2015
| 14 August 2015
|- style="background:#cfc;"
| {{flagicon|RUS}}
| [[Soyuz TMA-16M]]
| [[Expedition 43]]/[[Expedition 44|44]]
| [[Poisk (ISS module)|Poisk]] zenith
| 28 March 2015
| 11 September 2015
|- style="background:lightblue;"
| {{flagicon|RUS}}
| [[Progress M-28M]]
| Progress 60 Cargo
| [[Pirs (ISS module)|Pirs]] nadir
| 5 July 2015
| 19 November 2015
|- style="background:#cfc;"
| {{flagicon|RUS}}
| [[Soyuz TMA-17M]]
| [[Expedition 44]]/[[Expedition 45|45]]
| [[Rassvet (ISS module)|Rassvet]] nadir
| 23 July 2015
| 22 December 2015
|}

===Scheduled launches and dockings/berthings===
* All dates are [[UTC]]. Dates are the earliest possible dates and may change.
* Forward ports are at the front of the station according to its normal direction of travel and orientation ([[Yaw, pitch and roll#Aircraft attitudes|attitude]]). Aft is at the rear of the station, used by spacecraft boosting the station's orbit. [[Nadir]] is closest the Earth, [[Zenith]] is on top.
* Spacecraft operated by government agencies are indicated with 'Gov' and under commercial arrangements are indicated with 'Com'.

;Key
{{legend|lightblue|Uncrewed cargoships are in light blue colour}}
{{legend|#cfc|Crewed spacecraft are in light green colour}}
{{legend|wheat|Modules are in wheat colour}}

{| class="wikitable" style="margin: 1em auto 1em auto;text-align: left; font-size: 95%;"
|+Planned Missions
|style="text-align:center; background:#BBB"|'''Launch''' ({{abbr|NET|Not Earlier Than}})
|style="text-align:center; background:#BBB"|'''Launch Vehicle'''
|style="text-align:center; background:#BBB"|'''Launch Site'''
|style="text-align:center; background:#BBB" colspan="3"| '''Launch Service Provider'''
|style="text-align:center; background:#BBB"|'''Payload'''
|style="text-align:center; background:#BBB"|'''Spacecraft'''
|style="text-align:center; background:#BBB"|'''Mission'''
|style="text-align:center; background:#BBB"|'''Docking / Berthing Port'''
|style="text-align:center; background:#BBB"|'''Ref.'''
|-
| nowrap| 16 August 2015
| nowrap| [[H-IIB]]
| nowrap| {{flagicon|JPN}} [[Tanegashima Space Center|Tanegashima]] [[Yoshinobu Launch Complex|LA-Y2]]
| nowrap| {{flagicon|JPN}}
| nowrap| Gov
| nowrap| [[JAXA]]
| style="background:lightblue;" nowrap| [[Kounotori 5|HTV-5]]
| nowrap| [[H-II Transfer Vehicle|HTV]]
| ISS Resupply
| nowrap| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule">{{cite web |url=http://spaceflightnow.com/launch-schedule/ |title=Launch Calendar |work=Spaceflight Now |date=28 March 2015 |accessdate=28 March 2015}}</ref><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 2 September 2015
| nowrap| [[Soyuz-FG]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:#cfc;" nowrap| [[Soyuz TMA-18M]]
| nowrap| [[Soyuz (spacecraft)|Soyuz]]
| [[Expedition 45]]/[[Expedition 46|46]] including [[European Space Agency|ESA]] [[Denmark|Danish]] Astronaut [[Andreas Mogensen]] and [[Kazakhstan]] cosmonaut [[Aydyn Aimbetov]].
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 21 September 2015
| nowrap| [[Soyuz-U]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:lightblue;" nowrap| [[Progress M-29M]]
| nowrap| [[Progress (spacecraft)|Progress]]
| ISS Resupply
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| NET September 2015 (TBD)
| nowrap|[[Falcon 9 v1.1]]
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 40|SLC-40]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[SpaceX]]
| style="background:lightblue;" nowrap| [[SpaceX CRS-8]]
| nowrap| [[Dragon (spacecraft)|Dragon]]
| ISS resupply. Will deliver [[Bigelow Expandable Activity Module|Bigelow Expandable Activity Module (BEAM)]] to the ISS.
| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| 21 November 2015
| nowrap| [[Soyuz-2 (rocket)|Soyuz-2.1a]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:lightblue;" nowrap| [[Progress MS-1]]
| nowrap| [[Progress (spacecraft)|Progress]]
| ISS Resupply. First launch of the new [[Progress (spacecraft)#Progress MS|Progress-MS]] variant.
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 3 December 2015
| nowrap| [[Atlas V]] 401
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 41|SLC-41]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[United Launch Alliance|ULA]]
| style="background:lightblue;" nowrap| [[Cygnus CRS Orb-4]]
| nowrap| [[Cygnus (spacecraft)|Cygnus]]
| ISS Resupply
| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/><ref>{{cite web|url=http://www.space.com/27962-cygnus-cargo-spacecraft-new-rocket.html |title=Private Cargo Spacecraft Gets New Rocket Ride After Accident |publisher=Space.com |date= |accessdate=2015-04-04}}</ref>
|-
| nowrap| 15 December 2015
| nowrap| [[Soyuz-FG]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:#cfc;" nowrap| [[Soyuz TMA-19M]]
| nowrap| [[Soyuz (spacecraft)|Soyuz]]
| [[Expedition 46]]/[[Expedition 47|47]]
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| NET December 2015 (TBD)
| nowrap|[[Falcon 9 v1.1]]
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[SpaceX]]
| style="background:lightblue;" nowrap| [[SpaceX CRS-9]]
| nowrap| [[Dragon (spacecraft)|Dragon]]
| ISS resupply. Will deliver the IDA-2 segment of the [[NASA Docking System]] to the ISS.
| nowrap| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |
url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|}

===Docking===
{{See also|Docking and berthing of spacecraft}}
[[File:Progress M-14M.jpg|thumb|The [[Progress M-14M]] resupply vehicle as it approaches the ISS in 2012. Over 50 unpiloted [[Progress (spacecraft)|Progress]] spacecraft have been sent with supplies during the lifetime of the station.]]
All Russian spacecraft and self-propelled modules are able to rendezvous and dock to the space station without human intervention using the [[Kurs (docking system)|Kurs]] docking system. Radar allows these vehicles to detect and intercept ISS from over 200 kilometres away. The European ATV uses star sensors and GPS to determine its intercept course. When it catches up it then uses laser equipment to [[Computer vision|optically]] recognise Zvezda, along with the Kurs system for redundancy.  Crew supervise these craft, but do not intervene except to send abort commands in emergencies. The Japanese [[H-II Transfer Vehicle]] parks itself in progressively closer orbits to the station, and then awaits 'approach' commands from the crew, until it is close enough for a robotic arm to grapple and berth the vehicle to the USOS. The American Space Shuttle was manually docked, and on missions with a [[Multi-Purpose Logistics Module|cargo container]], the container would be berthed to the Station with the use of manual robotic arms. Berthed craft can transfer [[International Standard Payload Rack]]s. Japanese spacecraft berth for one to two months. Russian and European Supply craft can remain at the ISS for six months,<ref>{{cite web|url=http://www.esa.int/esaMI/ATV/SEMBW0PR4CF_0.html |title=ESA — ATV — Crew role in mission control |publisher=Esa.int |date=2 March 2011 |accessdate=23 May 2011}}</ref><ref>{{cite web|url=http://www.esa.int/esaHS/ESA4ZJ0VMOC_iss_0.html |title=ESA — Human Spaceflight and Exploration — International Space Station — Automated Transfer Vehicle (ATV) |publisher=Esa.int |date=16 January 2009 |accessdate=23 May 2011}}</ref> allowing great flexibility in crew time for loading and unloading of supplies and trash. NASA Shuttles could remain docked for 11–12 days.<ref>{{cite web|url=http://www.boeing.com/news/frontiers/archive/2005/july/i_ids4.html|title=Space Shuttle upgrade lets astronauts at ISS stay in space longer|last=Memi|first=Ed|publisher=Boeing|accessdate=17 September 2011}}</ref>

The American manual approach to docking allows greater initial flexibility and less complexity. The downside to this mode of operation is that each mission becomes unique and requires specialised training and planning, making the process more labour-intensive and expensive. The Russians pursued an automated methodology that used the crew in override or monitoring roles. Although the initial development costs were high, the system has become very reliable with standardisations that provide significant cost benefits in repetitive routine operations.<ref>David C. Wo±nden and David K. Geller [http://www.usu.edu/mae/aerospace/publications/JDSC_RoadToAutonomy.pdf The Road to Autonomous Orbital Rendezvous]. Utah State University, Logan, Utah</ref> An automated approach could allow assembly of modules orbiting other worlds prior to crew arrival.

[[File:ISS and Endeavour seen from the Soyuz TMA-20 spacecraft 27.jpg|thumb|left|{{OV|105}}, [[ATV-2]], [[Soyuz TMA-21]] and [[Progress M-10M]] docked to the ISS during [[STS-134]], as seen from the departing [[Soyuz TMA-20]]|alt=A side-on view of the ISS showing a Space Shuttle docked to the forward end, an ATV to the aft end and Soyuz & Progress spacecraft projecting from the Russian segment.]]
Soyuz spacecraft used for crew rotation also serve as lifeboats for emergency evacuation; they are replaced every six months and have been used once to remove excess crew after the [[Space Shuttle Columbia disaster|Columbia disaster]].<ref>{{cite web|url=http://www.astronautix.com/flights/isseo6.htm |title=ISS EO-6 |publisher=Astronautix.com |accessdate=1 May 2012}}</ref> Expeditions require, on average, {{nowrap|2 722 kg}} of supplies, and {{As of|2011|03|09|lc=yes}}, crews had consumed a total of around {{nowrap|22 000 meals}}.<ref name="ISStD" /> Soyuz crew rotation flights and Progress resupply flights visit the station on average two and three times respectively each year,<ref name="Livelist">{{cite web|url=http://www.nasa.gov/mission_pages/station/resupply/index.html|archiveurl=https://web.archive.org/web/20080803015945/http://www.nasa.gov/mission_pages/station/resupply/index.html|archivedate=3 August 2008|title=Live listing of spacecraft operations|publisher=NASA|date=1 December 2009|accessdate=8 December 2009}}</ref> with the ATV and HTV planned to visit annually from 2010 onwards.{{Citation needed|date=January 2012}} Following retirement of the NASA Shuttle [[Cygnus spacecraft|Cygnus]] and [[SpaceX Dragon|Dragon]] were contracted to fly cargo to the station.<ref>{{cite web|author=Space Operations Mission Directorate|title=Human Space Flight Transition Plan|publisher=NASA|date=30 August 2006|url=http://www.nasa.gov/pdf/315546main_space_flight_transition_plan.pdf}}</ref><ref>{{cite press release|publisher=NASA|date=18 January 2006|title=NASA Seeks Proposals for Crew and Cargo Transportation to Orbit|url=http://www.spaceref.com/news/viewpr.html?pid=18791|accessdate=21 November 2006}}</ref>

From 26 February 2011 to 7 March 2011 four of the governmental partners (United States, ESA, Japan and Russia) had their spacecraft (NASA Shuttle, ATV, HTV, Progress and Soyuz) docked at the ISS, the only time this has happened to date.<ref>{{cite news|title=NASA proposes Soyuz photo op; shuttle launch readiness reviewed (UPDATED)|url=http://www.cbsnews.com/network/news/space/home/spacenews/files/b0e194a8338c336e823c03601f046707-157.html|publisher=CBS|accessdate=11 February 2011}}</ref> On 25 May 2012, [[SpaceX]] became the world's first privately held company to send cargo, via the [[Dragon (spacecraft)|Dragon spacecraft]], to the International Space Station.<ref name="NYT-20120525">{{cite news |last=Chang |first=Kenneth |title=Space X Capsule Docks at Space Station |url=http://www.nytimes.com/2012/05/26/science/space/space-x-capsule-docks-at-space-station.html |date=25 May 2012 |work=[[The New York Times]] |accessdate=25 May 2012 }}</ref>

===Launch and docking windows===
Prior to a ship's docking to the ISS, navigation and attitude control (GNC) is handed over to the ground control of the ships' country of origin. GNC is set to allow the station to drift in space, rather than fire its thrusters or turn using gyroscopes. The solar panels of the station are turned edge-on to the incoming ships, so residue from its thrusters does not damage the cells. When a NASA shuttle docked to the station, other ships were grounded, as the carbon wingtips, cameras, windows, and instruments aboard the shuttle were at too much risk from damage from thruster residue from other ships movements.

Approximately 30% of NASA shuttle launch delays were caused by poor weather. Occasional priority was given to the Soyuz arrivals at the station where the Soyuz carried crew with time-critical cargoes such as biological experiment materials, also causing shuttle delays. Departure of the NASA shuttle was often delayed or prioritised according to weather over its two landing sites.<ref>{{cite web |url=http://www.nasa.gov/home/hqnews/2009/may/HQ_09-118_Shuttle_Landing_Delayed.html |title=NASA's Space Shuttle Landing Delayed by Weather |publisher=NASA |first1=Katherine |last1=Trinidad |first2=Candrea |last2=Thomas |date=22 May 2009 |accessdate=26 June 2015}}</ref> Whilst the Soyuz is capable of landing anywhere, anytime, its planned landing time and place is chosen to give consideration to helicopter pilots and ground recovery crew, to give acceptable flying weather and lighting conditions. Soyuz launches occur in adverse weather conditions, but the cosmodrome has been shut down on occasions when buried by snow drifts up to 6 metres in depth, hampering ground operations.

==Life aboard==

===Crew activities===
[[File:Exp18home nasa big.jpg|thumb|Crewmember peers out of a window]]

A typical day for the crew begins with a wake-up at 06:00, followed by post-sleep activities and a morning inspection of the station. The crew then eats breakfast and takes part in a daily planning conference with Mission Control before starting work at around 08:10. The first scheduled exercise of the day follows, after which the crew continues work until 13:05. Following a one-hour lunch break, the afternoon consists of more exercise and work before the crew carries out its pre-sleep activities beginning at 19:30, including dinner and a crew conference. The scheduled sleep period begins at 21:30. In general, the crew works ten hours per day on a weekday, and five hours on Saturdays, with the rest of the time their own for relaxation or work catch-up.<ref>{{cite web|url=http://www.nasa.gov/pdf/287386main_110508_tl.pdf|title=ISS Crew Timeline|date=5 November 2008|accessdate=5 November 2008|publisher=NASA|format=PDF}}</ref>

The time zone used on board the ISS is [[Coordinated Universal Time]] (UTC). The windows are covered at night hours to give the impression of darkness because the station experiences 16 sunrises and sunsets a day. During visiting space shuttle missions, the ISS crew will mostly follow the shuttle's [[Mission Elapsed Time]] (MET), which is a flexible time zone based on the launch time of the shuttle mission.<ref>{{Cite web|title = NASA - Time in Space, A Space in Time|url = https://www.nasa.gov/mission_pages/station/research/news/time_in_space.html|website = www.nasa.gov|accessdate = 2015-05-05}}</ref><ref>{{Cite web|title = A Slice of Time Pie|url = https://web.archive.org/web/20130317075600/http://blogs.nasa.gov/cm/blog/ISS%20Science%20Blog/posts/post_1340820317951.html|date = 2013-03-17|accessdate = 2015-05-05}}</ref><ref>{{Cite web|title = Human Space Flight (HSF) - Crew Answers|url = http://spaceflight.nasa.gov/feedback/expert/answer/crew/sts-113/index_2.html|website = spaceflight.nasa.gov|accessdate = 2015-05-05}}</ref>

The station provides crew quarters for each member of the expedition's crew, with two 'sleep stations' in the ''Zvezda'' and four more installed in ''Harmony''.<ref>{{cite web|url=https://www.youtube.com/watch?v=Q4dG9vSyUFQ|title=At Home with Commander Scott Kelly (Video)|date=6 December 2010|publisher=NASA|accessdate=8 May 2011|location=International Space Station}}</ref><ref>{{cite web|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080013462_2008012884.pdf|title=International Space Station USOS Crew Quarters Development|first1=James Lee |last1=Broyan |first2=Melissa Ann |last2=Borrego |first3=Juergen F. |last3=Bahr|year=2008|publisher=SAE International|accessdate=8 May 2011}}</ref> The American quarters are private, approximately person-sized soundproof booths. The Russian crew quarters include a small window, but do not provide the same amount of ventilation or block the same amount of noise as their American counterparts. A crewmember can sleep in a crew quarter in a tethered sleeping bag, listen to music, use a laptop, and store personal items in a large drawer or in nets attached to the module's walls. The module also provides a reading lamp, a shelf and a desktop.<ref name="ESALife">{{cite web|url=http://www.esa.int/esaHS/ESAH1V0VMOC_astronauts_0.html|publisher=ESA|accessdate=28 October 2009|date=19 July 2004|title=Daily life}}</ref><ref name="NASACrewEquip">{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/126_payload.html|title=Station Prepares for Expanding Crew|publisher=NASA|first=Cheryl L. |last=Mansfield|date=7 November 2008|accessdate=17 September 2009}}</ref><ref name="CSALife">{{cite web|url=http://www.asc-csa.gc.ca/pdf/educator-liv_wor_iss.pdf|title=Living and Working on the International Space Station|accessdate=28 October 2009|publisher=CSA}}</ref> Visiting crews have no allocated sleep module, and attach a sleeping bag to an available space on a wall—it is possible to sleep floating freely through the station, but this is generally avoided because of the possibility of bumping into sensitive equipment.<ref name="SRLife">{{cite web|url=http://www.space.com/missionlaunches/090827-sts127-space-sleeping.html|title=Sleeping in Space is Easy, But There's No Shower|first=Tariq|last=Malik|accessdate=29 October 2009|date=27 July 2009|publisher=Space.com}}</ref> It is important that crew accommodations be well ventilated; otherwise, astronauts can wake up oxygen-deprived and gasping for air, because a bubble of their own exhaled carbon dioxide has formed around their heads.<ref name="ESALife" />
{{See also|Christmas on the International Space Station}}

===Food===
[[File:Meal STS127.jpg|thumb|alt=Nine astronauts seated around a table covered in open cans of food strapped down to the table. In the background a selection of equipment is visible, as well as the salmon-coloured walls of the Unity node.|The crews of [[STS-127]] and [[Expedition 20]] enjoy a meal inside ''Unity''.]]
{{See also|Space food}}

Most of the food on board is vacuum sealed in plastic bags. Cans are heavy and expensive to transport, so there are not as many. The preserved food is generally not held in high regard by the crew, and when combined with the reduced sense of taste in a microgravity environment,<ref name="ESALife" /> a great deal of effort is made to make the food more palatable. More spices are used than in regular cooking, and the crew looks forward to the arrival of any ships from Earth, as they bring fresh fruit and vegetables with them. Care is taken that foods do not create crumbs. Sauces are often used to ensure station equipment is not contaminated. Each crew member has individual food packages and cooks them using the on-board galley. The galley features two food warmers, a refrigerator added in November 2008, and a water dispenser that provides both heated and unheated water.<ref name="NASACrewEquip" /> Drinks are provided in dehydrated powder form and are mixed with water before consumption.<ref name="NASACrewEquip" /><ref name="CSALife" /> Drinks and soups are sipped from plastic bags with straws; solid food is eaten with a knife and fork, which are attached to a tray with magnets to prevent them from floating away. Any food that floats away, including crumbs, must be collected to prevent it from clogging up the station's air filters and other equipment.<ref name="CSALife" />

===Hygiene===
[[File:Zvezda toilet.jpg|thumb|right|upright|Space toilet in the [[Zvezda (ISS module)|Zvezda Service Module]]]]

Showers on space stations were introduced in the early 1970s on Skylab and Salyut 3.<ref name="livingandworking">Benson, Charles Dunlap and William David Compton. ''[http://history.nasa.gov/SP-4208/contents.htm Living and Working in Space: A History of Skylab]''. NASA publication SP-4208.</ref>{{rp|139}} By Salyut 6, in the early 1980s, the crew complained of the complexity of showering in space, which was a monthly activity.<ref name="Portree1995-86">{{cite book |url=http://history.nasa.gov/SP-4225/documentation/mhh/mirheritage.pdf |title=Mir Hardware Heritage |publisher=NASA |first=David S. F. |last=Portree |page=86 |date=March 1995 |id=Reference Publication 1357 |oclc=755272548}}</ref> The ISS does not feature a shower; instead, crewmembers wash using a water jet and wet wipes, with soap dispensed from a toothpaste tube-like container. Crews are also provided with rinseless shampoo and edible toothpaste to save water.<ref name="SRLife" /><ref>{{cite AV media |url=https://www.youtube.com/watch?v=uIjNfZbUYu8 |title=Karen Nyberg Shows How You Wash Hair in Space |publisher=NASA |work=YouTube.com |first=Karen |last=Nyberg |date=12 July 2013 |accessdate=6 June 2015}}</ref>

There are two [[space toilet]]s on the ISS, both of Russian design, located in ''[[Zvezda (ISS module)|Zvezda]]'' and ''[[Tranquility (ISS module)|Tranquility]]''.<ref name="NASACrewEquip" /> These Waste and Hygiene Compartments use a fan-driven suction system similar to the Space Shuttle Waste Collection System. Astronauts first fasten themselves to the toilet seat, which is equipped with spring-loaded restraining bars to ensure a good seal.<ref name="ESALife" /> A lever operates a powerful fan and a suction hole slides open: the air stream carries the waste away. Solid waste is collected in individual bags which are stored in an aluminium container. Full containers are transferred to Progress spacecraft for disposal.<ref name="NASACrewEquip" /><ref>{{cite web |first=Ed |last=Lu |title=Greetings Earthling |url=http://spaceflight.nasa.gov/station/crew/exp7/luletters/lu_letter9.html |date=8 September 2003 |accessdate=1 November 2009 |publisher=NASA}}</ref> Liquid waste is evacuated by a hose connected to the front of the toilet, with anatomically correct "urine funnel adapters" attached to the tube so both men and women can use the same toilet. Waste is collected and transferred to the Water Recovery System, where it is recycled back into drinking water.<ref name="CSALife" />

==Crew health and safety==
{{Main|Effect of spaceflight on the human body}}

===Radiation===
The ISS is partially protected from the space environment by the Earth's magnetic field. From an average distance of about {{convert|70,000|km|abbr=on}}, depending on Solar activity, the [[magnetosphere]] begins to deflect solar wind around the Earth and ISS. [[coronal mass ejection|Solar flares]] are still a hazard to the crew, who may receive only a few minutes warning. The crew of [[Expedition 10]] took shelter as a precaution in 2005 in a more heavily shielded part of the ROS designed for this purpose during the initial 'proton storm' of an X-3 class solar flare,<ref>{{cite web|title=Solar Flare Hits Earth and Mars|author=Ker Than|publisher=Space.com|date=23 February 2006|url=http://www.space.com/2080-solar-flare-hits-earth-mars.html}}</ref><ref>{{cite web|title=A new kind of solar storm|publisher=NASA|date=10 June 2005|url=http://science.nasa.gov/science-news/science-at-nasa/2005/10jun_newstorm/}}</ref> but without the limited protection of the Earth's [[magnetosphere]], interplanetary manned missions are especially vulnerable.

[[File:Aurora Australis.ogv|thumb|left|Video of the [[Aurora Australis]] taken by the crew of [[Expedition 28]] on an ascending pass from south of [[Madagascar]] to just north of Australia over the Indian Ocean.]]

Subatomic charged particles, primarily protons from [[cosmic ray]]s and [[solar wind]], are normally absorbed by the Earth's atmosphere. When they interact in sufficient quantity, their effect becomes visible to the naked eye in a phenomenon called an aurora. Without the protection of the Earth's atmosphere, which absorbs this radiation, crews are exposed to about 1 [[millisievert]] each day, which is about the same as someone would get in a year on Earth from natural sources. This results in a higher risk of astronauts developing cancer. Radiation can penetrate living tissue, damage DNA, and cause damage to the [[chromosome]]s of [[lymphocytes]]. These cells are central to the [[immune system]], and so any damage to them could contribute to the lowered [[immunity (medical)|immunity]] experienced by astronauts. Radiation has also been linked to a higher incidence of [[cataracts]] in astronauts. Protective shielding and protective drugs may lower the risks to an acceptable level.<ref name="JCB"/>

The radiation levels experienced on the ISS are about five times greater than those experienced by airline passengers and crew. The Earth's electromagnetic field provides almost the same level of protection against solar and other radiation in low Earth orbit as in the stratosphere. Airline passengers experience this level of radiation for no more than 15 hours for the longest intercontinental flights. For example, on a 12-hour flight an airline passenger would experience 0.1 millisieverts of radiation, or a rate of 0.2 millisieverts per day; only 1/5 the rate experienced by an astronaut in LEO.<ref>{{cite web|url=http://jag.cami.jccbi.gov./cariprofile.asp|title=Galactic Radiation Received in Flight|accessdate=20 May 2010|publisher=FAA Civil Aeromedical Institute}}</ref>
{{See also|Coronal mass ejection|Aurora (astronomy)}}

===Stress===
[[File:Nikolai Budarin in a sleep station in Zvezda.jpg|thumb|Cosmonaut [[Nikolai Budarin]] at work inside [[Zvezda (ISS module)|Zvezda]] service module crew quarters]]
There has been considerable evidence that psychosocial stressors are among the most important impediments to optimal crew morale and performance.<ref>{{cite book| author1 =Peter Suedfeld1| author2 = Kasia E. Wilk| author3 = Lindi Cassel| title = Flying with Strangers: Postmission Reflections of Multinational Space Crews}}</ref> Cosmonaut [[Valery Ryumin]], wrote in his journal during a particularly difficult period on board the [[Salyut 6]] space station: "All the conditions necessary for murder are met if you shut two men in a cabin measuring 18 feet by 20 and leave them together for two months."

NASA's interest in psychological stress caused by space travel, initially studied when their manned missions began, was rekindled when astronauts joined cosmonauts on the Russian space station Mir. Common sources of stress in early American missions included maintaining high performance under public scrutiny, as well as isolation from peers and family. The latter is still often a cause of stress on the ISS, such as when the mother of NASA Astronaut [[Daniel M. Tani|Daniel Tani]] died in a car accident, and when Michael Fincke was forced to miss the birth of his second child.


A study of the longest spaceflight concluded that the first three weeks represent a critical period where attention is adversely affected because of the demand to adjust to the extreme change of environment.<ref>{{cite doi|10.1080/001401398186991}}</ref> Skylab's 3 crews remained one, two, and three months respectively, long term crews on Salyut 6, [[Salyut 7]], and the ISS last about five to six months and Mir's expeditions often lasted longer. The ISS working environment includes further stress caused by living and working in cramped conditions with people from very different cultures who speak a different language. First generation space stations had crews who spoke a single language; second and third-generation stations have crew from many cultures who speak many languages. The ISS is unique because visitors are not classed automatically into 'host' or 'guest' categories as with previous stations and spacecraft, and may not suffer from feelings of isolation in the same way. Crew members with a military pilot background and those with an academic science background or teachers and politicians may have problems understanding each other's jargon and worldview.

===Medical===
[[File:Frank De Winne on treadmill cropped.jpg|thumb|Astronaut [[Frank De Winne]] is attached to the [[Treadmill with Vibration Isolation System|TVIS treadmill]] with bungee cords aboard the International Space Station|alt=Astronaut Frank De Winne is attached to the TVIS treadmill with bungee cords aboard the International Space Station]]
Medical effects of long-term weightlessness include [[muscle atrophy]], deterioration of the skeleton [[spaceflight osteopenia|(osteopenia)]], fluid redistribution, a slowing of the cardiovascular system, decreased production of red blood cells, balance disorders, and a weakening of the immune system. Lesser symptoms include loss of body mass, and puffiness of the face.<ref name="JCB" />

Sleep is disturbed on the ISS regularly due to mission demands, such as incoming or departing ships. Sound levels in the station are unavoidably high; because the atmosphere is unable to [[thermosiphon]], fans are required at all times to allow processing of the atmosphere which would stagnate in the freefall (zero-g) environment.

To prevent some of these adverse [[physiological]] effects, the station is equipped with two treadmills (including the [[Treadmill with Vibration Isolation System|COLBERT]]), and the aRED (advanced Resistive Exercise Device) which enables various weightlifting exercises which add muscle but do nothing for bone density,<ref>{{cite pmid|14600562}}</ref> and a stationary bicycle; each astronaut spends at least two hours per day exercising on the equipment.<ref name="ESALife" /><ref name="NASACrewEquip" /> Astronauts use bungee cords to strap themselves to the treadmill.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/bungee_running.html|accessdate=23 August 2009|title=Bungee Cords Keep Astronauts Grounded While Running|date=16 June 2009|publisher=NASA}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/colbert_feature.html|accessdate=23 August 2009|title=Do Tread on Me|date=19 August 2009|author=Amiko Kauderer|publisher=NASA}}</ref>

===Microbiological environmental hazards===
{{see also|Mir#Microbiological environmental hazards}}
Hazardous moulds which can foul air and water filters may develop aboard space stations. They can produce acids which degrade metal, glass, and rubber. They can also be harmful for the crew health. Microbiological hazards have lead into a development of the [[LOCAD#Portable Test System|LOCAD-PTS]] that can identify common bacteria and moulds faster than standard methods of [[Cell culture|culturing]], which may require a sample to be sent back to Earth.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2007/11may_locad3/|author=Trudy E. Bell|year=2007|title=Preventing "Sick" Spaceships|access-date=March 29, 2015}}</ref> {{As of|2012}}, 76 types of unregulated micro-organisms have been detected on the ISS.<ref>{{cite web|url=http://rt.com/news/iss-bacteria-mir-mutation-765/|title=Mutant space microbes attack ISS: 'Munch' metal, may crack glass |author= |date=April 23, 2012|website=[[RT (TV network)|RT]]|access-date=March 29, 2015}}</ref>

Reduced humidity, paint with mould killing chemical and antiseptic solutions can be used to prevent contamination in space stations. All materials used in the ISS are tested for resistance against fungi.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2000/ast26nov_1/|author=Patrick L. Barry|year=2000|title=Microscopic Stowaways on the ISS|access-date=March 29, 2015}}</ref>

==Threat of orbital debris==
{{Main|Space debris}}
{{Double image|right|SDIO KEW Lexan projectile.jpg|225|Debris-GEO1280.jpg|225|A 7 gram object (shown in centre) shot at 7 km/s (23,000 ft/sec) (the orbital velocity of the ISS) made this 15 cm (5 7/8 in) crater in a solid block of aluminium.|[[Radar]]-trackable objects including debris, with distinct ring of [[Geostationary orbit|geostationary]] satellites||}}
At the low altitudes at which the ISS orbits there is a variety of space debris,<ref>{{cite web|url=http://defensenews.com/blogs/space-symposium/2009/04/03/its-getting-crowded-up-there/#more-155|publisher=Defense News|accessdate=7 October 2009|author=Michael Hoffman|title=National Space Symposium 2009: It's getting crowded up there|date=3 April 2009}}</ref> consisting of many different objects including entire spent rocket stages, defunct satellites, explosion fragments—including materials from [[anti-satellite weapon]] tests, paint flakes, slag from solid rocket motors, and coolant released by [[US-A]] nuclear-powered satellites. These objects, in addition to natural [[micrometeoroid]]s,<ref>{{cite journal|author=F. L. Whipple|year=1949|title=The Theory of Micrometeoroids|journal=Popular Astronomy|volume=57|page=517|bibcode=1949PA.....57..517W}}</ref> are a significant threat. Large objects could destroy the station, but are less of a threat as their orbits can be predicted.<ref name="NSFdebris">{{cite web|publisher=NASASpaceflight.com|accessdate=28 June 2011|date=28 June 2011|author=Chris Bergin|url=http://www.nasaspaceflight.com/2011/06/sts-135-frr-july-8-atlantis-debris-misses-iss/|title=STS-135: FRR sets 8 July Launch Date for Atlantis – Debris misses ISS}}</ref><ref>{{cite web|author=Henry Nahra|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19890016664_1989016664.pdf|title=Effect of Micrometeoroid and Space Debris Impacts on the Space Station Freedom Solar Array Surfaces|date=24–29 April 1989|publisher=NASA|accessdate=7 October 2009}}</ref> Objects too small to be detected by optical and radar instruments, from approximately 1 cm down to microscopic size, number in the trillions. Despite their small size, some of these objects are still a threat because of their [[kinetic energy]] and direction in relation to the station. Spacesuits of spacewalking crew could puncture, causing [[Space exposure|exposure to vacuum]].<ref name=debrisdecomp>{{cite web|title=Space Suit Punctures and Decompression|url=http://www.asi.org/adb/04/03/08/suit-punctures.html|publisher=The Artemis Project|accessdate=20 July 2011}}</ref>

The station's shields and structure are divided between the ROS and the USOS, with completely different designs. On the USOS, a thin aluminium sheet is held apart from the hull, the sheet causes objects to shatter into a cloud before hitting the hull thereby spreading the energy of the impact. On the ROS, a carbon plastic honeycomb screen is spaced from the hull, an aluminium honeycomb screen is spaced from that, with a screen-vacuum thermal insulation covering, and glass cloth over the top. It is about 50% less likely to be punctured,  and crew move to the ROS when the station is under threat. Punctures on the ROS would be contained within the panels which are 70 cm square.

[[File:ISS impact risk.jpg|thumb|left|Example of [[risk management]]: A NASA model showing areas at high risk from impact for the International Space Station.]]

Space debris objects are tracked remotely from the ground, and the station crew can be notified.<ref>{{cite web|url=http://www.orbitaldebris.jsc.nasa.gov/library/EducationPackage.pdf |title=Microsoft PowerPoint – EducationPackage SMALL.ppt |format=PDF |accessdate=1 May 2012}}</ref> This allows for a [[Debris Avoidance Manoeuvre]] (DAM) to be conducted, which uses thrusters on the Russian Orbital Segment to alter the station's orbital altitude, avoiding the debris. DAMs are not uncommon, taking place if computational models show the debris will approach within a certain threat distance. Eight DAMs had been performed prior to March 2009,<ref>{{cite web|url=http://www.newscientist.com/article/dn16777-space-station-may-move-to-dodge-debris.html|title=Space station may move to dodge debris|work=New Scientist|date=16 March 2009|accessdate=20 April 2010|author=Rachel Courtland}}</ref> the first seven between October 1999 and May 2003.<ref name=ODOct08>{{cite journal|url=http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv12i4.pdf|title=ISS Maneuvers to Avoid Russian Fragmentation Debris|publisher=NASA|pages=1&2|journal=Orbital Debris Quarterly News|date=October 2008|accessdate=20 April 2010|volume=12|issue=4}}</ref> Usually the orbit is raised by one or two kilometres by means of an increase in orbital velocity of the order of 1 m/s. Unusually there was a lowering of 1.7 km on 27 August 2008, the first such lowering for 8 years.<ref name=ODOct08 /><ref>{{cite web|url=http://www.esa.int/esaMI/ATV/SEM64X0SAKF_0.html|title=ATV carries out first debris avoidance manoeuvre for the ISS|publisher=ESA|date=28 August 2008|accessdate=26 February 2010}}</ref> There were two DAMs in 2009, on 22 March and 17 July.<ref>{{cite journal|url=http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv14i1.pdf|title=Avoiding satellite collisions in 2009|page=2|journal=Orbital Debris Quarterly News|publisher=NASA|volume=14|date=January 2010|issue=1|accessdate=20 April 2010}}</ref> If a threat from orbital debris is identified too late for a DAM to be safely conducted, the station crew close all the hatches aboard the station and retreat into their [[Soyuz spacecraft]], so that they would be able to evacuate in the event the station was seriously damaged by the debris. This partial station evacuation has occurred on 13 March 2009, 28 June 2011, 24 March 2012 and 16 June 2015.<ref>{{cite news| url=http://www.bbc.co.uk/news/science-environment-17497766| title=ISS crew take to escape capsules in space junk alert| accessdate=24 March 2012 |work=BBC News |date=24 March 2012}}</ref><ref>{{cite news| url=https://blogs.nasa.gov/spacestation/2015/07/16/station-crew-takes-precautions-for-close-pass-of-space-debris/| title=Station Crew Takes Precautions for Close Pass of Space Debris| accessdate=16 June 2015 |work=NASA Blog |date=16 June 2015}}</ref>
Ballistic panels, also called micrometeorite shielding, are incorporated into the station to protect pressurised sections and critical systems. The type and thickness of these panels varies depending upon their predicted exposure to damage.

==End of mission==
[[File:Jules Verne Automated Transfer Vehicle re-enters Earth's atmosphere.jpg|thumb|right|Many ISS resupply spacecraft have already undergone [[Atmospheric entry|atmospheric re-entry]], such as [[Jules Verne ATV]]]]
According to a 2009 report, [[S.P. Korolev Rocket and Space Corporation Energia|Space Corporation Energia]] is considering methods to remove from the station some modules of the Russian Orbital Segment when the end of mission is reached and use them as a basis for a new station, known as the [[Orbital Piloted Assembly and Experiment Complex]] (OPSEK). The modules under consideration for removal from the current ISS include the [[Multipurpose Laboratory Module]] (MLM), currently scheduled to be launched in 2017, with other Russian modules which are currently planned to be attached to the MLM afterwards. Neither the MLM nor any additional modules attached to it would have reached the end of their useful lives in 2016 or 2020. The report presents a statement from an unnamed Russian engineer who believes that, based on the experience from ''Mir'', a thirty-year life should be possible, except for micrometeorite damage, because the Russian modules have been built with on-orbit refurbishment in mind.<ref name="RussiaSave">{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8064060.stm|title=Russia 'to save its ISS modules'|work=BBC News|date=22 May 2009|accessdate=23 May 2009|author=Anatoly Zak}}</ref>

According to the [[Outer Space Treaty]] the United States and Russia are legally responsible for all modules they have launched.<ref>[http://www.unoosa.org/pdf/publications/STSPACE11E.pdf United Nations Treaties and Principles on Outer Space]. (PDF). United Nations. New York. 2002. ISBN 92-1-100900-6. Retrieved 8 October 2011.</ref> In ISS planning, NASA examined options including returning the station to Earth via shuttle missions (deemed too expensive, as the station (USOS) is not designed for disassembly and this would require at least 27 shuttle missions<ref>{{cite book|url=http://search.nap.edu/openbook.php?record_id=9794&page=28|isbn=0-309-06938-6|publisher=National Academies Press|year=2000|pages=28–30|author=Thomas Kelly|title=Engineering Challenges to the Long-Term Operation of the International Space Station|accessdate=12 July 2011}}</ref>), natural orbital decay with random reentry similar to [[Skylab]], boosting the station to a higher altitude (which would delay reentry) and a controlled targeted de-orbit to a remote ocean area.<ref name=ISSEIS>{{cite web|title = Tier 2 EIS for ISS|publisher = NASA|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960053133_1996092350.pdf|accessdate=12 July 2011 }}</ref>

The technical feasibility of a controlled targeted deorbit into a remote ocean was found to be possible only with Russia's assistance.<ref name=ISSEIS /> The Russian Space Agency has experience from de-orbiting the [[Salyut 4]], [[Salyut 5|5]], [[Salyut 6|6]], [[Salyut 7|7]] and [[Mir]] space stations; NASA's first intentional controlled de-orbit of a satellite (the [[Compton Gamma Ray Observatory]]) occurred in 2000.<ref>{{cite web|title=Entry Debris Field estimation methods and application to Compton Gamma Ray Observatory|publisher=Mission Operations Directorate, NASA Johnson Space Center|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010084992_2001127597.pdf|accessdate=12 July 2011}}</ref> As of late 2010, the preferred plan is to use a slightly modified Progress spacecraft to de-orbit the ISS.<ref name=deo>{{cite web|url=http://www.nasa.gov/pdf/578543main_asap_eol_plan_2010_101020.pdf|title=ISS End-of-Life Disposal Plan|last=Suffredini|first=Michael|date=October 2010|publisher=NASA|accessdate=7 March 2012}}</ref> This plan was seen as the simplest, most cost efficient one with the highest margin.<ref name=deo /> [[Skylab]], the only space station built and launched entirely by the US, decayed from orbit slowly over 5 years, and no attempt was made to de-orbit the station using a [[Atmospheric entry|deorbital burn]]. Remains of Skylab hit populated areas of [[Esperance, Western Australia]]<ref name="debris">{{cite web|url=http://www.eclipsetours.com/sat/debris.html|accessdate=28 May 2011|title=Paul Maley's (Skylab spaceflight controller) Space Debris Page}}</ref> without injuries or loss of life.

The [[Exploration Gateway Platform]], a discussion by NASA and Boeing at the end of 2011, suggested using leftover USOS hardware and '[[Zvezda (ISS module)|Zvezda]] 2' {{sic}} as a refuelling depot and servicing station located at one of the Earth Moon [[Lagrange points]], L1 or L2. The entire USOS cannot be reused and will be discarded, but some other Russian modules are planned to be reused. [[Nauka (ISS module)|Nauka]], the [[Uzlovoy Module|Node module]], two science power platforms and Rassvet, launched between 2010 and 2015 and joined to the ROS may be separated to form [[OPSEK]].<ref>{{cite web|url=http://www.russianspaceweb.com/iss_dc.html|title=DC-1 and MIM-2|publisher=Russianspaceweb.com|accessdate=12 July 2011}}</ref> The [[Nauka (ISS module)|Nauka module]] of the ISS will be used in the station, whose main goal is supporting manned deep space exploration. OPSEK will orbit at a higher inclination of 71 degrees, allowing observation to and from all of the Russian Federation.

In February 2015, Roscosmos announced that it would remain a part of the international space station program until 2024.<ref name=sn20150225>{{cite news |last1=de Selding|first1=Peter B. |title=Russia — and Its Modules — To Part Ways with ISS in 2024 |url=http://spacenews.com/russia-and-its-modules-to-part-ways-with-iss-in-2024/ |accessdate=26 February 2015 |work=Space News |date=25 February 2015}}</ref> Nine months earlier—in response to US sanctions against Russia over the [[2014 Crimean crisis|conflict in the Crimea]]—Russian Deputy Prime Minister [[Dmitry Rogozin]] had stated that Russia would reject a US request to prolong the orbiting station's use beyond 2020, and would only supply rocket engines to the US for non-military satellite launches.<ref>{{cite web|url=http://www.telegraph.co.uk/news/worldnews/europe/russia/10828964/Russia-to-ban-US-from-using-Space-Station-over-Ukraine-sanctions.html|title=Russia to ban US from using Space Station over Ukraine sanctions|agency=Reuters|work=The Telegraph|date=13 May 2014|accessdate=14 May 2014}}</ref>

A proposed modification that would allow some of the ISS American and European segments to be reused would be to attach a [[VASIMR]] drive module to the vacated Node with its own onboard power source. It would allow long term reliability testing of the concept for less cost than building a dedicated space station from scratch.<ref name="nbcnews">{{cite web|url=http://www.nbcnews.com/id/48260759/ns/technology_and_science-space/#.U4LaQCjFBdg|title=From the earth to the moon, and then beyond - Technology & science - Space | NBC News|publisher=nbcnews.com|accessdate=27 May 2014}}</ref>

On March 28, 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS.<ref name=":0"/><ref name=":1"/> [[Igor Komarov]], the head of Russia's Roscosmos, made the announcement with NASA administrator Charles Bolden at his side. Komarov said "Roscosmos together with NASA will work on the programme of a future orbital station," "We agreed that the group of countries taking part in the ISS project will work on the future project of a new orbital station," "The first step is that the ISS will operate until 2024," and that Roscosmos and NASA "do not rule out that the station's flight could be extended,"<ref>{{cite web|url=http://www.spacedaily.com/reports/Russia_announces_plan_to_build_new_space_station_with_NASA_999.html|title=Russia announces plan to build new space station with NASA|work=spacedaily.com}}</ref> In a statement provided to SpaceNews March 28, NASA spokesman David Weaver said the agency appreciated the Russian commitment to extending the ISS, but did not confirm any plans for a future space station.<ref name="no plans" />

==Cost==
The ISS is arguably the most expensive single item ever constructed.<ref>{{cite web|author=Zidbits |url=http://zidbits.com/?p=19 |title=What Is The Most Expensive Object Ever Built? |publisher=Zidbits.com |date=6 November 2010 |accessdate=22 October 2013}}</ref> In 2010 the cost was expected to be $150 billion. It includes NASA's budget of $58.7 billion (inflation unadjusted) for the station from 1985 to 2015 ($72.4 billion in 2010 dollars), Russia's $12 billion, Europe's $5 billion, Japan's $5 billion, Canada's $2 billion, and the cost of 36 shuttle flights to build the station; estimated at $1.4 billion each, or $50.4 billion total. Assuming 20,000 person-days of use from 2000 to 2015 by two to six-person crews, each person-day would cost $7.5 million, less than half the inflation adjusted $19.6 million ($5.5 million before inflation) per person-day of Skylab.<ref name="lafleur20100308">{{cite news | url=http://www.thespacereview.com/article/1579/1 | title=Costs of US piloted programs | work=The Space Review | date=8 March 2010 | accessdate=18 February 2012 | author=Lafleur, Claude}} See author correction in comments.</ref>

==International co-operation==
[[File:ISS Agreements.jpg|thumb|right|upright|Dated 29 January 1998]]
{{Main|Politics of the International Space Station|International Space Station program}}
;Participating countries
{{columns-list|colwidth=20em|

* '''{{flagcountry|Canada}}'''
* '''{{flagcountry|Japan}}'''
* '''{{flagcountry|Russia}}'''
* '''{{flagcountry|United States}}'''
* [[File:ESA logo simple.svg|15x15px]] '''[[European Space Agency]]'''
** {{flagcountry|Austria}}
** {{flagcountry|Belgium}}
** {{flagcountry|Czech Republic}}
** {{flagcountry|Denmark}}
** {{flagcountry|Estonia}}
** {{flagcountry|Finland}}
** {{flagcountry|France}}
** {{flagcountry|Germany}}
** {{flagcountry|Greece}}
** {{flagcountry|Hungary}}
** {{flagcountry|Ireland}}
** {{flagcountry|Italy}}
** {{flagcountry|Luxembourg}}
** {{flagcountry|Netherlands}}
** {{flagcountry|Norway}}
** {{flagcountry|Poland}}
** {{flagcountry|Portugal}}
** {{flagcountry|Romania}}
** {{flagcountry|Spain}}
** {{flagcountry|Sweden}}
** {{flagcountry|Switzerland}}
** {{flagcountry|United Kingdom}}
}}

==Sightings from Earth==

===Naked eye===
The ISS is visible to the [[naked eye]] as a slow-moving, bright white dot due to reflected sunlight, and can be seen in the hours after sunset and before sunrise when the station remains sunlit but the ground and sky are dark.<ref name="Price2005">{{cite book |title=The Backyard Stargazer: An Absolute Beginner's Guide to Skywatching With and Without a Telescope |publisher=Quarry Books |location=Gloucester, MA |first=Pat |last=Price |page=140 |year=2005 |isbn=1-59253-148-2}}</ref> The ISS takes about ten minutes to move from one horizon to another, and will only be visible part of that time due to moving into or out of the Earth's shadow. Because of the size of its reflective surface area, the ISS is the brightest man-made object in the sky excluding [[Satellite flare|flares]], with an approximate maximum [[Apparent magnitude|magnitude of −4]] when overhead, similar to Venus. The ISS, like many satellites including the [[Iridium constellation]], can also produce flares of up to 8 or 16 times the brightness of Venus as sunlight glints off reflective surfaces.<ref>{{cite web|url=http://www.calsky.com/cs.cgi/Satellites/8 |title=Artificial Satellites > (Iridium) Flares |publisher=Calsky.com |accessdate=1 May 2012}}</ref><ref name="haydenplanetarium">{{cite web|url=http://www.amnh.org/our-research/hayden-planetarium/blog/how-to-spot-the-international-space-station-and-other-satellites |title=How to Spot the International Space Station (and other satellites) |publisher=Hayden Planetarium |accessdate=12 July 2011}}</ref> The ISS is also visible during broad daylight conditions, albeit with a great deal more effort.

Tools are provided by a number of websites such as [[Heavens-Above]] (see [[#Live viewing|''Live viewing'']] below) as well as [[smartphone]] applications that use the known [[ephemeris|orbital data]] and the observer's longitude and latitude to predict when the ISS will be visible (weather permitting), where the station will appear to rise to the observer, the altitude above the horizon it will reach and the duration of the pass before the station disappears to the observer either by setting below the horizon or entering into Earth's shadow.<ref name="see">{{cite web|url=http://spaceflight.nasa.gov/realdata/sightings/index.html|title=International Space Station Sighting Opportunities|accessdate=28 January 2009|publisher=NASA|date=2 July 2008|author=NASA}}</ref><ref>{{cite web|url=http://www.heavens-above.com/satinfo.aspx?satid=25544&lat=0&lng=0&loc=Unspecified&alt=0&tz=CET|title=ISS – Information|publisher=Heavens-Above.com|accessdate=8 July 2010}}</ref><ref>{{cite journal|author=Harold F. Weaver|title=The Visibility of Stars Without Optical Aid|journal=Publications of the Astronomical Society of the Pacific|volume=59|issue=350|year=1947|doi=10.1086/125956 }}</ref><ref name="daytime visibility">{{cite web|url=http://spaceweather.com/archive.php?view=1&day=05&month=06&year=2009|title=ISS visible during the daytime|accessdate=5 June 2009|work=Spaceweather.com|date=5 June 2009}}</ref>

{{Double image|right|Isshtv120090917200858nm.jpg|223|ISS 2008-01-10.jpg|230|The ISS and HTV photographed using a telescope-mounted camera by [[Ralf Vandebergh]]|A time exposure of a station pass|A fuzzy image of the ISS set against a black background, with a smaller, cylindrical object visible to the left of the station.|A view of a dark blue, starry sky with a white line visible from the bottom-left to the top-right of the image. A tree is visible to the bottom right.}}

In November 2012 NASA launched its 'Spot the Station' service, which sends people text and email alerts when the station is due to fly above their town.<ref>{{cite news| url= http://www.3news.co.nz/Get-notified-when-the-International-Space-Station-is-in-your-area/tabid/1160/articleID/275612/Default.aspx|work=3 News NZ |title= Get notified when the International Space Station is in your area| date=6 November 2012}}</ref>

The station is visible from 95% of the inhabited land on Earth, but is not visible from extreme northern or southern latitudes.<ref name="MCC Answer" />

===Astrophotography=== 
Using a telescope mounted camera to photograph the station is a popular hobby for astronomers, <ref>{{cite web|url=http://www.hobbyspace.com/SatWatching/ |title=Satellite Watching |publisher=HobbySpace |accessdate=1 May 2012}}</ref> whilst using a mounted camera to photograph the Earth and stars is a popular hobby for crew.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2003/24mar_noseprints/ |title=Space StationAstrophotography – NASA Science |publisher=Science.nasa.gov |date=24 March 2003 |accessdate=1 May 2012}}</ref> The use of a telescope or binoculars allows viewing of the ISS during daylight hours.<ref>{{cite web|url=http://www.zmescience.com/space/video-the-iss-and-atlantis-shuttle-as-seen-in-broad-daylight/ |title=[VIDEO] The ISS and Atlantis shuttle as seen in broad daylight |publisher=Zmescience.com |date=20 July 2011 |accessdate=1 May 2012}}</ref>

Parisian engineer and astrophotographer Thierry Legault, known for his photos of spaceships crossing the Sun (called [[occultation]]), travelled to Oman in 2011, to photograph the Sun, moon and space station all lined up.<ref>{{cite news| url=http://www.wired.com/2011/01/double-eclipse/ | work=Wired | first=Lisa | last=Grossman | title=Moon and Space Station Eclipse the Sun}}</ref> Legault, who received the Marius Jacquemetton award from the [[Société astronomique de France]] in 1999, and other hobbyists, use websites that predict when the ISS will pass in front of the Sun or Moon and from what location those passes will be visible.

==See also==
{{Wikipedia books|International Space Station}}
{{Portal|Spaceflight|Space}}
* [[Center for the Advancement of Science in Space]] - operates the US National Laboratory on the ISS
* [[List of space stations]]
* [[Origins of the International Space Station]]
* [[Space architecture]]

==Gallery==
[[File:ISS and Endeavour seen from the Soyuz TMA-20 spacecraft 14.jpg|thumb|left|550px|<center>International Space Station docked with ''Endeavour'' and ''Johannes Kepler'' ]]
{{-}}

==Notes==
{{Reflist|group="note"}}

==References==
{{Reflist|colwidth=25em}}

==External links==
{{Sister project links|wikt=no|n=Category:International Space Station|voy=Space}}

===Agency ISS websites===
{{divcol|20em}}
* {{flagicon|Canada}} [http://www.asc-csa.gc.ca/eng/iss/default.asp Canadian Space Agency]
* [[File:Not the esa logo.png]] [http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station European Space Agency]
* {{flagicon|France}} [http://www.cnes.fr/web/CNES-en/1422-iss-the-international-space-station.php Centre national d'études spatiales (National Centre for Space Studies)]
* {{flagicon|Germany}} [http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10300 German Aerospace Centre]
* {{flagicon|Italy}} [http://www.asi.it/en/flash_en/living Italian Space Agency]
* {{flagicon|Japan}} [http://www.jaxa.jp/projects/iss_human/index_e.html Japan Aerospace Exploration Agency]
* {{flagicon|Russia}} [http://www.energia.ru/eng/iss/iss.html S.P. Korolev Rocket and Space Corporation Energia]
* {{flagicon|Russia}} [http://www.roscosmos.ru/ Russian Federal Space Agency]
* {{flagicon|USA}} [http://www.nasa.gov/mission_pages/station/main/ National Aeronautics and Space Administration]
{{Div col end}}

===Research===
* [https://blogs.nasa.gov/spacestation/ NASA: Daily ISS Reports]
* [http://www.nasa.gov/mission_pages/station/science/index.html NASA: Station Science]
* [http://www.esa.int/Our_Activities/Human_Spaceflight/Columbus ESA: Columbus]
* [http://www.energia.ru/en/iss/researches/iss-researches.html RSC Energia: Science Research on ISS Russian Segment]

===Live viewing===
{{See also|List of satellite pass predictors}}
* [http://www.ustream.tv/channel/live-iss-stream Live ISS webcam] by NASA at uStream.tv
* [http://heavens-above.com/orbit.aspx?satid=25544 Real-time position] at Heavens-above.com
* [http://www.n2yo.com/?s=25544 Real-time position] at N2YO.com
* [http://wheretheiss.at/ Real-time position] at WheretheISS.at

===Multimedia===
* [http://www.nasa.gov/externalflash/ISSRG/index.html Interactive reference guide] at NASA.gov
* [http://spaceflight.nasa.gov/gallery/images/station/ Image gallery search page] at NASA.gov
* [http://i.usatoday.net/tech/graphics/iss_timeline/flash.htm Assembly sequence animation] by ''USA Today'' and NASA
* [https://www.youtube.com/watch?v=doN4t5NKW-k ISS tour with Sunita Williams] by NASA at YouTube.com
* [https://www.youtube.com/watch?v=QF2w2Dx_QMs ISS tour with André Kuipers] by ESA at YouTube.com
* [http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station/Highlights/International_Space_Station_panoramic_tour ISS photo tour with Samantha Cristoforetti] by ESA
* [https://www.youtube.com/watch?v=vMmcLmu3V1k ''The Future of Hope'', Kibo module documentary] by JAXA at YouTube.com
* [https://www.youtube.com/playlist?list=PLbyvawxScNbsoD_tGlw8kWCw3S5htiVKZ Journey to the ISS] by ESA at YouTube.com

{{ISS modules}}
{{International Space Station}}
{{Manned ISS flight}}
{{Unmanned ISS resupply flights}}
{{People currently in space}}
{{Space stations}}
{{US manned space programs}}
{{Russian manned space programs}}
{{Spaceflight}}
{{Orbital launches in 1998}}

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{{Authority control}}
[[Category:International Space Station| ]]
[[Category:Artificial satellites orbiting Earth]]
[[Category:Populated places established in 1998]]
[[Category:United States Department of Energy national laboratories]]
[[Category:Spacecraft launched in 1998]]
[[Category:1998 in spaceflight]]
[[Category:Articles containing video clips]]

User:WikipediaTutorials/sandbox

2015-08-05T03:23:04Z

WikipediaTutorials: /* Education and cultural outreach */ added citation

{{User sandbox}}

{{redirect|ISS}}
{{Use British English|date=December 2013}}
{{Use dmy dates|date=February 2015}}
{{Infobox space station
| station = International Space Station
| station_image =International Space Station after undocking of STS-132.jpg
| station_image_alt = A rearward view of the International Space Station backdropped by the limb of the Earth. In view are the station's four large, gold-coloured solar array wings, two on either side of the station, mounted to a central truss structure. Further along the truss are six large, white radiators, three next to each pair of arrays. In between the solar arrays and radiators is a cluster of pressurised modules arranged in an elongated T shape, also attached to the truss. A set of blue solar arrays are mounted to the module at the aft end of the cluster.
| station_image_size = 300px
| extra_image_size = 300px
| extra_image_caption = The International Space Station on 23 May 2010 as seen from the departing {{OV|104}} during [[STS-132]].
| sign = ''Alpha'', ''Station''
| crew = Fully crewed: 6 Currently aboard: 6 ([[Expedition 44]])
| launch = 20 November 1998
| launch_pad = {{nowrap|[[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|1/5]] and [[Baikonur Cosmodrome Site 81|81/23]] [[Kennedy Space Center|Kennedy]] [[Kennedy Space Center Launch Complex 39|LC-39]]}}
| mass = Approximately {{convert|450000|kg|lbs|abbr=on}}
| length = {{convert|72.8|m|ft|abbr=on}}
| width = {{convert|108.5|m|ft|abbr=on}}
| height = c. 20 m (c. 66 ft) nadir–zenith, arrays forward–aft (27 November 2009){{Update after|2010|05|23|reason=MRM-1 & MRM-2}}
| volume = {{convert|916|m3|abbr=on}} (3 November 2014)
| pressure = 101.3 [[pascal (unit)|kPa]] (29.91 [[inch of mercury|inHg]], 1 [[Atmosphere (unit)|atm]])
| apogee = {{convert|{{Orbit|apogee|416}}|km|abbr=on}} [[Above mean sea level|AMSL]]{{Orbit|ref|<ref name="heavens-above">{{cite web|url=http://www.heavens-above.com/orbit.aspx?satid=25544|title=ISS - Orbit|last=Peat|first=Chris|publisher=Heavens-Above|date=25 January 2015|accessdate=25 January 2015}}</ref>}}
| perigee = {{convert|{{Orbit|perigee|409}}|km|abbr=on}} [[Above mean sea level|AMSL]]{{Orbit|ref|<ref name="heavens-above"/>}}
| inclination = {{Orbit|inclination|51.65}} [[degree (angle)|degrees]]{{Orbit|ref|<ref name="heavens-above"/>}}
| speed = {{convert|{{Orbit|speed at epoch|7.66}}|km/s|km/h mph}}{{Orbit|ref|<ref name="heavens-above"/>}}
| period = {{Orbit|period|92.69}} minutes{{Orbit|ref|<ref name="heavens-above"/>}}
| in_orbit = {{age in days|1998|11|20}} ({{date||dmy}})
| occupied = {{age in days|2000|11|02}} ({{date||dmy}})
| orbits = {{Orbit|orbits|92579}}{{Orbit|ref|<ref name="heavens-above"/>}}
| orbit_epoch = {{Orbit|epoch|25 January 2015}}{{Orbit|ref|<ref name="heavens-above"/>}}
| decay = 2 km/month
| NSSDC_ID = 1998-067A
| as_of = 9 March 2011 (unless noted otherwise)
| stats_ref =<ref name="heavens-above" /><ref name="ISStD" /><ref name="OnOrbit" /><ref>{{cite web|format=PDF|url=http://www.nasa.gov/pdf/451029main_sts132_press_kit.pdf|publisher=NASA|accessdate=19 June 2010|title=STS-132 Press Kit|date=7 May 2010}}</ref><ref>{{cite web|url=http://www.nasa.gov/pdf/521138main_fd04_ep.pdf|publisher=NASA|date=27 February 2011|accessdate=27 February 2011|title=STS-133 FD 04 Execute Package}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html|publisher=NASA|date=3 November 2014|accessdate=5 December 2014|title=NASA — Facts and Figures — International Space Station}}</ref>
| configuration_image = ISS configuration 2011-05 en.svg
| configuration_alt = The components of the ISS in an exploded diagram, with modules on-orbit highlighted in orange, and those still awaiting launch in blue or pink
| configuration_caption = Station elements {{As of|2011|12|lc=on}}, but missing ''Pirs'' ([[exploded view]])
| configuration_size = 300px
}}

The '''International Space Station''' ('''ISS''') is a [[space station]], or a habitable [[satellite|artificial satellite]], in [[low Earth orbit]]. Its first component launched into orbit in 1998, and the ISS is now the largest artificial body in orbit and can often be seen with the [[naked eye]] from Earth.<ref>{{cite web|title= Central Research Institute for Machine Building (FGUP TSNIIMASH) Control of manned and unmanned space vehicles from Mission Control Centre Moscow |publisher= Russian Federal Space Agency |url=ftp://130.206.92.88/Espacio/Mesa%20Redonda%205%20-%20R3%20-%20TSNIIMASH%20-%20V%20M%20IVANOV.pdf| accessdate=26 September 2011}}</ref><ref>{{cite web|url=http://spaceflight.nasa.gov/realdata/sightings/help.html |title=NASA Sightings Help Page |publisher=Spaceflight.nasa.gov |date=30 November 2011 |accessdate=1 May 2012}}</ref> The ISS consists of pressurised modules, external trusses, [[solar arrays]] and other components. ISS components have been launched by Russian [[Proton (rocket)|Proton]] and [[Soyuz (rocket family)|Soyuz]] rockets as well as American [[Space Shuttle]]s.<ref name="ISSBook">{{cite book|isbn=978-0-387-78144-0|date=17 June 2008|publisher=Springer-Praxis|author=John E. Catchpole|title=The International Space Station: Building for the Future}}</ref>

The ISS serves as a [[microgravity]] and [[space environment]] research laboratory in which crew members conduct experiments in [[biology]], [[human biology]], [[physics]], [[astronomy]], [[meteorology]] and [[Scientific research on the ISS|other fields]].<ref name="ISS overview">{{cite web|url=http://www.shuttlepresskit.com/ISS_OVR/index.htm|title=International Space Station Overview|publisher=ShuttlePressKit.com|date=3 June 1999|accessdate=17 February 2009}}</ref><ref name="NASA Fields of Research">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/A-fieldsresearch/index.html|archiveurl=https://web.archive.org/web/20080123150641/http://pdlprod3.hosc.msfc.nasa.gov/A-fieldsresearch/index.html|archivedate=25 March 2008|title=Fields of Research|date=26 June 2007|publisher = NASA}}</ref><ref name="NASA ISS Goals">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/B-gettingonboard/index.html|archiveurl=https://web.archive.org/web/20071208091537/http://pdlprod3.hosc.msfc.nasa.gov/B-gettingonboard/index.html|archivedate=8 December 2007| title = Getting on Board|date = 26 June 2007| publisher=NASA}}</ref> The station is suited for the testing of spacecraft systems and equipment required for missions to the Moon and Mars.<ref name="ResProg">{{cite web|url=http://spaceflightsystems.grc.nasa.gov/Advanced/ISSResearch/|title=ISS Research Program|publisher=NASA|accessdate=27 February 2009}}{{dead link|date=August 2011}}</ref> The ISS [[Orbital station-keeping|maintains an orbit with an altitude]] of between {{convert|330|and|435|km|mi|0|abbr=on}} by means of reboost manoeuvres using the engines of the [[Zvezda (ISS module)|Zvezda module]] or visiting spacecraft. It completes {{Orbit|daily orbits|15.54}} orbits per day.<ref name="tracking" />

ISS is the ninth space station to be inhabited by crews, following the Soviet and later Russian [[Salyut]], [[Almaz]], and [[Mir]] stations as well as [[Skylab]] from the US. The station has been continuously occupied for {{age in years and days|2 Nov 2000|sep=and}} since the arrival of [[Expedition 1]] on 2 November 2000. This is the longest continuous human presence in space, having surpassed the previous record of {{age in years and days|5 Sep 1989|28 Aug 1999|sep=and}} held by Mir. The station is serviced by a variety of visiting spacecraft: [[Soyuz (spacecraft)|Soyuz]], [[Progress (spacecraft)|Progress]], the [[Automated Transfer Vehicle]], the [[H-II Transfer Vehicle]],<ref name="ISSRG" /> [[Dragon (spacecraft)|Dragon]], and [[Cygnus (spacecraft)|Cygnus]]. It has been visited by astronauts, cosmonauts and space tourists from [[List of International Space Station visitors|15 different nations]].<ref name="10th">{{cite web|url=http://www.nasa.gov/mission_pages/station/main/10th_anniversary.html|title=Nations Around the World Mark 10th Anniversary of International Space Station|publisher=NASA|date=17 November 2008|accessdate=6 March 2009}}</ref>

After the US Space Shuttle program ended in 2011, Soyuz rockets became the only provider of transport for astronauts at the International Space Station, and Dragon became the only provider of bulk [[downmass|cargo-return-to-Earth]] services (downmass capability of Soyuz capsules is very limited).

The [[International Space Station program|ISS programme]] is a joint project among five participating space agencies: [[NASA]], [[Russian Federal Space Agency|Roscosmos]], [[Japan Aerospace Exploration Agency|JAXA]], [[European Space Agency|ESA]], and [[Canadian Space Agency|CSA]].<ref name="ISSRG" /><ref name="PartStates">{{cite web|url=http://www.esa.int/esaHS/partstates.html|title=Human Spaceflight and Exploration—European Participating States|accessdate=17 January 2009|publisher=European Space Agency (ESA)|year=2009}}</ref> The ownership and use of the space station is established by intergovernmental treaties and agreements.<ref name="ESA-IGA">{{cite web|url=http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station/International_Space_Station_legal_framework|title=International Space Station legal framework|publisher=European Space Agency (ESA)|accessdate=21 February 2015|date=19 November 2013}}</ref> The station is divided into two sections, the [[Russian Orbital Segment]] (ROS) and the [[US Orbital Segment|United States Orbital Segment]] (USOS), which is shared by many nations. {{asof|2014|January}}, the American portion of ISS was funded until 2024.<ref>{{cite web|url=http://www.washingtonpost.com/national/health-science/nasa-space-station-operation-extended-by-obama-until-2024-at-least/2014/01/08/9819d5c8-788e-11e3-8963-b4b654bcc9b2_story.html|title=NASA: International space station operation extended by Obama until at least 2024|last=Achenbach|first=Joel|publisher=washingtonpost.com|date=8 January 2014|accessdate=8 January 2014}}</ref><ref>{{cite web|url=http://spaceflightnow.com/news/n1003/11station/|title=Space station partners set 2028 as certification goal|last=Clark|first=Stephen|date=11 March 2010|publisher=Spaceflight Now|accessdate=1 June 2011}}</ref><ref>{{cite news| url=http://www.cbc.ca/news/technology/story/2012/02/29/science-international-space-station.html | work=CBC News | title=Canada's space station commitment renewed | date=29 February 2012}}</ref> Roscosmos has endorsed the continued operation of ISS through 2024,<ref name="sn20150225"/> but have proposed using elements of the Russian Orbital Segment to construct a new Russian space station called [[Orbital Piloted Assembly and Experiment Complex|OPSEK]].<ref name="moscow20141117">{{cite news |url=http://www.themoscowtimes.com/business/article/russia-may-be-planning-national-space-station-to-replace-iss/511299.html |title=Russia May Be Planning National Space Station to Replace ISS |work=The Moscow Times |first=Matthew |last=Bodner |date=17 November 2014 |accessdate=3 March 2015}}</ref>

On March 28, 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS.<ref name=":0">{{cite web|url= http://www.independent.co.uk/news/science/russia-and-the-us-will-build-a-new-space-station-together-10140890.html|title=Russia and the US will build a new space station together |publisher=The Independent|date=28 March 2015}}</ref><ref name=":1">{{Cite news|url = http://rt.com/news/244797-russia-us-new-space-station/|title = Russia & US agree to build new space station after ISS, work on joint Mars project|last = |first = |date = March 28, 2015|work = RT|access-date = March 28, 2015}}</ref> NASA later issued a guarded statement expressing thanks for Russia's interest in future cooperation in space exploration, but fell short of confirming the Russian announcement.<ref>{{Cite news|url = http://www.engadget.com/2015/03/28/nasa-is-working-with-russia-on-a-new-space-station/|title = NASA is working with Russia on a new space station (update: not quite) |last = Moon|first = Mariella|date = 28 March 2015|work = Engadget|access-date = 29 March 2015}}</ref><ref name="no plans">{{cite web|url=http://spacenews.com/nasa-says-no-plans-for-iss-replacement-with-russia/|title=NASA Says No Plans for ISS Replacement with Russia|date=March 28, 2015|author=Jeff Foust|publisher=SpaceNews}}</ref>

{{TOC limit|limit=3}}

==Purpose==
[[File:STS-129 Zvezda sunrise.jpg|thumb|Sunrise at ''Zvezda'']]
[[File:STS-134 EVA4 view to the Space Shuttle Endeavour.jpg|thumb|right|Fisheye view of several labs]]
According to the original Memorandum of Understanding between NASA and Rosaviakosmos, the International Space Station was intended to be a laboratory, observatory and factory in [[low Earth orbit]]. It was also planned to provide transportation, maintenance, and act as a staging base for possible future missions to the Moon, Mars and asteroids.<ref name="RSA-MOU">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/nasa_rsa.html|title=Memorandum of Understanding Between the National Aeronautics and Space Administration of the United States of America and the Russian Space Agency Concerning Cooperation on the Civil International Space Station|publisher=NASA|accessdate=19 April 2009|date=29 January 1998}}</ref> In the 2010 United States National Space Policy, the ISS was given additional roles of serving commercial, diplomatic<ref>{{cite journal|last=Payette|first=Julie|title=Research and Diplomacy 350 Kilometers above the Earth: Lessons from the International Space Station|journal=Science & Diplomacy|date=10 December 2012|volume=1|issue=4|url=http://www.sciencediplomacy.org/article/2012/research-and-diplomacy-350-kilometers-above-earth}}</ref> and educational purposes.<ref name=USNSP>{{cite web|title=National Space Policy of the United States of America|url=http://www.whitehouse.gov/sites/default/files/national_space_policy_6-28-10.pdf|publisher=White House; USA Federal government|accessdate=20 July 2011}}</ref>

===Scientific research===
{{Main|Scientific research on the ISS|l1=Scientific research on the ISS}}
The ISS provides a platform to conduct scientific research. Small unmanned spacecraft can provide platforms for zero gravity and exposure to space, but space stations offer a long term environment where studies can be performed potentially for decades, combined with ready access by human researchers over periods that exceed the capabilities of manned spacecraft.<ref name="10th" /><ref name="Worldbook at NASA" />

The Station simplifies individual experiments by eliminating the need for separate rocket launches and research staff. The wide variety of research fields include [[astrobiology]], [[astronomy]], [[Zero g#Health effects of weightlessness|human research]] including [[space medicine]] and [[life science]]s, [[physical science]]s, [[materials science]], [[space weather]], and weather on Earth ([[meteorology]]).<ref name="ISS overview" /><ref name="NASA Fields of Research" /><ref name="NASA ISS Goals" /><ref>{{cite web|url=http://www.isas.jaxa.jp/e/forefront/2009/ueno/index.shtml|title=Monitor of All-sky X-ray Image (MAXI)|year=2008|publisher=JAXA|accessdate=12 March 2011}}</ref><ref>[http://www.spaceref.com/news/viewpr.html?pid=33007 ESA via SPACEREF] "SOLAR: three years observing and ready for solar maximum", 14 March 2011</ref> Scientists on Earth have access to the crew's data and can modify experiments or launch new ones, which are benefits generally unavailable on unmanned spacecraft.<ref name="Worldbook at NASA" /> Crews fly [[List of International Space Station expeditions|expeditions]] of several months duration, providing approximately 160-man-hours per week of labour with a crew of 6.<ref name="ISS overview"/><ref name="Science in School">{{cite web|url=http://www.scienceinschool.org/2008/issue10/iss|title=The International Space Station: life in space|publisher=Science in School|date=10 December 2008|accessdate=17 February 2009}}</ref>

To detect dark matter and answer other fundamental questions about our universe, engineers and scientists from all over the world built the [[Alpha Magnetic Spectrometer]] (AMS), which NASA compares to the [[Hubble space telescope]], and says could not be accommodated on a free flying satellite platform due in part to its power requirements and data bandwidth needs.<ref>[http://www.nasa.gov/mission_pages/shuttle/main/amsprocessing.html NASA – AMS to Focus on Invisible Universe]. Nasa.gov (18 March 2011). Retrieved 8 October 2011.</ref><ref>[http://science.nasa.gov/science-news/science-at-nasa/2009/14aug_ams/ In Search of Antimatter Galaxies – NASA Science]. ''Science''.nasa.gov (16 May 2011). Retrieved 8 October 2011.</ref> On 3 April 2013, [[NASA]] scientists reported that hints of [[dark matter]] may have been detected by the Alpha Magnetic Spectrometer.<ref name="APS-20130403">{{cite journal |authors=Aguilar, M. et al. (AMS Collaboration) |title=First Result from the Alpha Magnetic Spectrometer on the International Space Station: Precision Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–350 GeV|url=http://prl.aps.org/abstract/PRL/v110/i14/e141102 |date=3 April 2013 |journal=[[Physical Review Letters]]|accessdate=3 April 2013 |doi=10.1103/PhysRevLett.110.141102 }}</ref><ref name="AMS-20130403">{{cite web |author=Staff |title=First Result from the Alpha Magnetic Spectrometer Experiment|url=http://www.ams02.org/2013/04/first-results-from-the-alpha-magnetic-spectrometer-ams-experiment/ |date=3 April 2013 |work=AMS Collaboration |accessdate=3 April 2013 }}</ref><ref name="AP-20130403">{{cite news |last1=Heilprin|first1=John |last2=Borenstein |first2=Seth |title=Scientists find hint of dark matter from cosmos|url=http://apnews.excite.com/article/20130403/DA5E6JAG3.html |date=3 April 2013 |agency=Associated Press |accessdate=3 April 2013 }}</ref><ref name="BBC-20130403">{{cite news |last=Amos |first=Jonathan |title=Alpha Magnetic Spectrometer zeroes in on dark matter |url=http://www.bbc.co.uk/news/science-environment-22016504 |date=3 April 2013 |work=[[BBC News]] |accessdate=3 April 2013 }}</ref><ref name="NASA-20130403">{{cite web |last1=Perrotto|first1=Trent J. |last2=Byerly |first2=Josh |title=NASA TV Briefing Discusses Alpha Magnetic Spectrometer Results|url=http://www.nasa.gov/home/hqnews/2013/apr/HQ_M13-054_AMS_Findings_Briefing.html |date=2 April 2013|work=[[NASA]] |accessdate=3 April 2013 }}</ref><ref name="NYT-20130403">{{cite news |last=Overbye |first=Dennis |title=New Clues to the Mystery of Dark Matter |url=http://www.nytimes.com/2013/04/04/science/space/new-clues-to-the-mystery-of-dark-matter.html |date=3 April 2013 |work=[[The New York Times]] |accessdate=3 April 2013 }}</ref> According to the scientists, "[[Alpha Magnetic Spectrometer#First results|The first results]] from the space-borne Alpha Magnetic Spectrometer confirm an unexplained excess of high-energy positrons in Earth-bound cosmic rays."

{{Double image|right|Iss030e015472 Edit.jpg|117|ISS-08 Michael Foale conducts an inspection of the Microgravity Science Glovebox.jpg|241|[[C/2011 W3 (Lovejoy)|Comet Lovejoy]] photographed by [[Expedition 30]] commander [[Dan Burbank]]|[[Expedition 8]] Commander and Science Officer [[Michael Foale]] conducts an inspection of the [[Microgravity Science Glovebox]]}}
The space environment is hostile to life. Unprotected presence in space is characterised by an intense radiation field (consisting primarily of protons and other subatomic charged particles from the [[solar wind]], in addition to [[cosmic ray]]s), high vacuum, extreme temperatures, and microgravity.<ref name="Space Microbiology">{{cite web|url=http://syntheticbiology.arc.nasa.gov/files/SpaceMicrobiology%20MMBR%201.pdf|title=Space Microbiology, section Space Environment (p. 122)|publisher=Microbiology and Molecular Biology Reviews|date=March 2010|accessdate=4 June 2011|author=G Horneck, DM Klaus & RL Mancinelli}}</ref> Some simple forms of life called [[extremophile]]s,<ref name="Beer microbes">{{cite news|url=http://www.bbc.co.uk/news/science-environment-11039206|title=Beer microbes live 553 days outside ISS|work=[[BBC News]]|date=23 August 2010|accessdate=4 June 2011|author=Jonathan Amos}}</ref> including small invertebrates called [[tardigrade]]s<ref name="Waterbears">{{cite web|url=http://www.nature.com/news/2008/080908/full/news.2008.1087.html|title=Spacesuits optional for 'water bears'|work=Nature|date=8 September 2008|accessdate=4 June 2011}}</ref> can survive in this environment in an extremely dry state called [[Desiccation#Biology and ecology|desiccation]].

Medical research improves knowledge about the effects of long-term space exposure on the human body, including [[muscle atrophy]], [[Osteoporosis|bone loss]], and fluid shift. This data will be used to determine whether lengthy [[human spaceflight]] and [[space colonisation]] are feasible. As of 2006, data on bone loss and muscular atrophy suggest that there would be a significant risk of fractures and movement problems if astronauts landed on a planet after a lengthy interplanetary cruise, such as the six-month interval required to [[Manned mission to Mars|travel to Mars]].<ref name="JCB">{{cite book|author=Jay Buckey|title=Space Physiology|publisher=Oxford University Press USA|date=23 February 2006|isbn=978-0-19-513725-5}}</ref><ref>{{cite web|url=http://www.newscientist.com/article/dn17476-ion-engine-could-one-day-power-39day-trips-to-mars.html?full=true|work=New Scientist|accessdate=8 January 2010|date=24 July 2009|author=List Grossman|title=Ion engine could one day power 39-day trips to Mars}}</ref>
Medical studies are conducted aboard the ISS on behalf of the [[National Space Biomedical Research Institute]] (NSBRI). Prominent among these is the [[Advanced Diagnostic Ultrasound in Microgravity]] study in which astronauts perform ultrasound scans under the guidance of remote experts. The study considers the diagnosis and treatment of medical conditions in space. Usually, there is no physician on board the ISS and diagnosis of medical conditions is a challenge. It is anticipated that remotely guided ultrasound scans will have application on Earth in emergency and rural care situations where access to a trained physician is difficult.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/science/experiments/ADUM.html|date=1 May 2009|accessdate=1 October 2009|author=Brooke Boen|publisher=NASA|title=Advanced Diagnostic Ultrasound in Microgravity (ADUM)}}</ref><ref>{{cite journal|author=Sishir Rao|display-authors=etal|year=2008|title=A Pilot Study of Comprehensive Ultrasound Education at the Wayne State University School of Medicine|journal=Journal of Ultrasound in Medicine|volume=27|pages=745–749|pmid=18424650|issue=5}}</ref><ref>{{cite journal|author=Michael Fincke|display-authors=etal|year=2004|title=Evaluation of Shoulder Integrity in Space: First Report of Musculoskeletal US on the International Space Station|journal=Radiology|issue= 2|pages=319–322|pmid=15533948|doi=10.1148/radiol.2342041680|volume=234}}</ref>

====Microgravity====
[[File:Space Fire.jpg|thumb|A comparison between the combustion of a candle on [[Earth]] (left) and in a microgravity environment, such as that found on the ISS (right)]]
The Earth's gravity is only slightly weaker at the altitude of the ISS than at the surface, but objects in orbit are in a continuous state of [[Free fall|freefall]], resulting in an apparent state of weightlessness. This perceived weightlessness is disturbed by five separate effects:<ref name="gravity">{{cite web|url=http://www.esa.int/Our_Activities/Human_Spaceflight/Human_Spaceflight_Research/European_User_Guide_to_Low-Gravity_Platforms
|title=European Users Guide to Low Gravity Platforms|accessdate=22 March 2013|date=6 December 2005|publisher=European Space Agency}}</ref>
* Drag from the residual atmosphere; when the ISS enters the Earth's shadow, the main solar panels are rotated to minimise this aerodynamic drag, helping reduce [[orbital decay]].
* Vibration from movements of mechanical systems and the crew.
* Actuation of the on-board attitude [[control moment gyroscope]]s.
* [[Rocket engine|Thruster]] firings for attitude or orbital changes.
* [[Gravity-gradient stabilization|Gravity-gradient effects]], also known as [[tidal force|tidal]] effects. Items at different locations within the ISS would, if not attached to the station, follow slightly different orbits. Being mechanically interconnected these items experience small forces that keep the station moving as a [[rigid body]].

[[File:ISS-20 Robert Thirsk at the Minus Eighty Degree Laboratory Freezer.jpg|thumb|left|ISS crew member storing samples]]

Researchers are investigating the effect of the station's near-weightless environment on the evolution, development, growth and internal processes of plants and animals. In response to some of this data, NASA wants to investigate [[microgravity]]'s effects on the growth of three-dimensional, human-like tissues, and the unusual [[protein crystal]]s that can be formed in space.<ref name="NASA Fields of Research" />

The investigation of the physics of fluids in microgravity will allow researchers to model the behaviour of fluids better. Because fluids can be almost completely combined in microgravity, physicists investigate fluids that do not mix well on Earth. In addition, an examination of reactions that are slowed by low gravity and temperatures will give scientists a deeper understanding of [[superconductivity]].<ref name="NASA Fields of Research" />

The study of [[materials science]] is an important ISS research activity, with the objective of reaping economic benefits through the improvement of techniques used on the ground.<ref>{{cite web|url=http://science.nasa.gov/newhome/headlines/msad15sep99_1.htm|title=Materials Science 101|publisher=Science@NASA|accessdate=18 June 2009|date=15 September 1999}}</ref> Other areas of interest include the effect of the low gravity environment on combustion, through the study of the efficiency of burning and control of emissions and pollutants. These findings may improve current knowledge about energy production, and lead to economic and environmental benefits. Future plans are for the researchers aboard the ISS to examine [[aerosol]]s, [[ozone]], [[water vapour]], and [[oxide]]s in Earth's atmosphere, as well as [[cosmic ray]]s, [[cosmic dust]], [[antimatter]], and [[dark matter]] in the universe.<ref name="NASA Fields of Research" />

===Exploration===
[[File:Mars500.jpg|thumb|right|A 3D plan of the Russia-based [[MARS-500]] complex, used for ground-based experiments which complement ISS-based preparations for a [[manned mission to Mars]]]]
The ISS provides a location in the relative safety of Low Earth Orbit to test spacecraft systems that will be required for long-duration missions to [[the Moon]] and [[Mars]]. This provides experience in operations, maintenance as well as repair and replacement activities on-orbit, which will be essential skills in operating spacecraft farther from Earth, mission risks can be reduced and the capabilities of interplanetary spacecraft advanced.<ref name="ResProg">{{cite web|url=http://spaceflightsystems.grc.nasa.gov/Advanced/ISSResearch/|title=ISS Research Program|publisher=NASA|accessdate=27 February 2009}}{{dead link|date=August 2011}}</ref> Referring to the [[MARS-500]] experiment, ESA states that "Whereas the ISS is essential for answering questions concerning the possible impact of weightlessness, radiation and other space-specific factors, aspects such as the effect of long-term isolation and confinement can be more appropriately addressed via ground-based simulations".<ref name="esa mars500 ">{{cite web|title=Mars500 study overview | publisher = ESA |date= 4 June 2011| url = http://www.esa.int/esaMI/Mars500/SEM7W9XX3RF_0.html }}</ref> Sergey Krasnov, the head of human space flight programmes for Russia's space agency, Roscosmos, in 2011 suggested a "shorter version" of MARS-500 may be carried out on the ISS. <ref name="Mars thing on ISS">{{cite web| title=Space station may be site for next mock Mars mission| url = http://www.newscientist.com/blogs/shortsharpscience/2011/11/space-station-may-be-site-for.html|date=4 November 2011|work=New Scientist}}</ref>

In 2009, noting the value of the partnership framework itself, Sergey Krasnov wrote, "When compared with partners acting separately, partners developing complementary abilities and resources could give us much more assurance of the success and safety of space exploration. The ISS is helping further advance near-Earth space exploration and realisation of prospective programmes of research and exploration of the Solar system, including the Moon and Mars."<ref name=IAF2009>{{cite web|title=The Sustainable Utilisation of the ISS Beyond 2015|url=http://www.iafastro.org/docs/2009/ISS2015.pdf|publisher=International Astronautical Congress|accessdate=15 December 2011}}</ref> [[Manned mission to Mars|A manned mission to Mars]] may be a multinational effort involving space agencies and countries outside the current ISS partnership. In 2010, ESA Director-General Jean-Jacques Dordain stated his agency was ready to propose to the other four partners that China, India and South Korea be invited to join the ISS partnership.<ref name="ESAproposesInvite">{{cite web|title=ESA Chief Lauds Renewed U.S. Commitment to Space Station, Earth Science | publisher =Peter B. de Selding, Space News. |date=2 March 2010 | url =http://www.spacenews.com/civil/100203-esa-chief-lauds-renewed-commitment-space-station-earth-science.html}}</ref> NASA chief [[Charlie Bolden]] stated in February 2011, "Any mission to Mars is likely to be a global effort".<ref name="Mars a global effort">{{cite web|title= Charlie Bolden | publisher = space.com |date=4 June 2011 | url = http://www.space.com/11335-nasa-mars-exploration-space-station.html }}</ref> Currently, American legislation prevents NASA co-operation with China on space projects.<ref name="justice1">{{citation|first=Virginia|last=Seitz|title=Memorandum Opinion for the General Counsel, Office of Science and Technology Policy|url=http://www.justice.gov/olc/2011/conduct-diplomacy.pdf|journal=Office of Legal Counsel|volume=35|date=11 September 2011|accessdate=23 May 2012|archiveurl=https://web.archive.org/web/20120713080223/http://www.justice.gov/olc/2011/conduct-diplomacy.pdf|archivedate=13 July 2012}}</ref>

===Education and cultural outreach===
[[File:ISS-36 HTV-4 berthing 2.jpg|thumb|Japan's Kounotori 4 docking]]
The ISS crew provides opportunities for students on Earth by running student-developed experiments, making educational demonstrations, allowing for student participation in classroom versions of ISS experiments, and directly engaging students using radio, videolink and email.<ref name="ISSRG" /><ref>{{cite journal|author1=Gro Mjeldheim Sandal |author2=Dietrich Manzey|title=Cross-cultural issues in space operations: A survey study among ground personnel of the European Space Agency|journal=Acta Astronautica|volume=65|date=December 2009|pages=1520–1529|doi=10.1016/j.actaastro.2009.03.074|issue=11–12}}</ref> ESA offers a wide range of free teaching materials that can be downloaded for use in classrooms.<ref>[http://www.esa.int/SPECIALS/Education/SEM0LW4KXMF_0.html ESA – Education – Online material]. Esa.int (7 September 2011). Retrieved 8 October 2011.</ref> In one lesson, students can navigate a 3-D model of the interior and exterior of the ISS, and face spontaneous challenges to solve in real time.<ref>[http://www.esa.int/SPECIALS/Education/SEM1LL3Z2OF_0.html ESA – Education – ISS 3-D Teaching Tool: Spaceflight Challenge I]. Esa.int (24 May 2011). Retrieved 8 October 2011.</ref>

JAXA aims both to "Stimulate the curiosity of children, cultivating their spirits, and encouraging their passion to pursue craftsmanship", and to "Heighten the child's awareness of the importance of life and their responsibilities in society."<ref>[http://www.oosa.unvienna.org/pdf/pres/copuos2010/tech-17E.pdf Building Peace in Young Minds through Space Education]. Committee on the Peaceful Uses of Outer Space, 53rd Session. June 2010, Vienna, Austria; Space Education Center, Japan Aerospace Exploration Agency (JAXA)</ref> Through a series of education guides, a deeper understanding of the past and near-term future of manned space flight, as well as that of Earth and life, will be learned.<ref>[http://www.edu.jaxa.jp/education/international/ISS/SSK/en/ JAXA Space Education Center : JAXA Spaceflight Seeds Kids I : Spaceflight Sunflower seeds – Let's make them flower! and learn freshly the Earth environment just by contrast with the Space one]. Edu.jaxa.jp. Retrieved 8 October 2011.</ref><ref>[http://www.edu.jaxa.jp/education/international/ISS/SIS/en/ JAXA Space Education Center : JAXA Seeds in Space I : Let's Cultivate Spaceflight Asagao, Miyako-gusa Seeds and Identify the Mutants!]. Edu.jaxa.jp. Retrieved 8 October 2011.</ref> In the JAXA Seeds in Space experiments, the mutation effects of spaceflight on plant seeds aboard the ISS is explored. Students grow sunflower seeds which flew on the ISS for about nine months as a start to 'touch the Universe'. In the first phase of Kibō utilisation from 2008 to mid-2010, researchers from more than a dozen Japanese universities conducted experiments in diverse fields.<ref>{{cite web |author=Keiji Murakami |url=http://www.spacepolicyonline.com/pages/images/stories/Micro%20Oct%2009%20JEM.pdf |title=JEM Utilization Overview |publisher=JAXA. Steering Committee for the Decadal Survey on Biological and Physical Sciences in Space |date=14 October 2009}}</ref>

[[Image:Crew in ATV with Jules Verne manuscript.jpg|thumb|left|Original Jules Verne manuscripts displayed by crew inside Jules Verne ATV]]
Cultural activities are another major objective. Tetsuo Tanaka, director of JAXA's Space Environment and Utilization Center, says "There is something about space that touches even people who are not interested in science."<ref name="jaxa2">{{cite web |author=Tetsuo Tanaka |url=http://www.jaxa.jp/article/special/kibo/tanaka01_e.html |title=Kibo: Japan's First Human Space Facility |publisher=JAXA |accessdate=8 October 2011}}</ref>

[[ARISS|Amateur Radio on the ISS]] (ARISS) is a volunteer programme which encourages students worldwide to pursue careers in science, technology, engineering and mathematics through [[amateur radio]] communications opportunities with the ISS crew. ARISS is an international working group, consisting of delegations from 9 countries including several countries in Europe as well as Japan, Russia, Canada, and the United States. In areas where radio equipment cannot be used, speakerphones connect students to ground stations which then connect the calls to the station. <ref>{{cite web|url=http://www.rac.ca/ariss/oindex.htm|title=Amateur Radio on the International Space Station|date=6 June 2011|accessdate=10 June 2011}}</ref>

''[[First Orbit]]'' is a feature-length documentary film about [[Vostok 1]], the first manned space flight around the Earth. By matching the orbit of the International Space Station to that of Vostok 1 as closely as possible, in terms of ground path and time of day, documentary filmmaker Christopher Riley and ESA astronaut [[Paolo Nespoli]] were able to film the view that Yuri Gagarin saw on his pioneering orbital space flight. This new footage was cut together with the original Vostok 1 mission audio recordings sourced from the Russian State Archive. Nespoli, during Expedition 26/27, filmed the majority of the footage for this documentary film, and as a result is credited as its [[Cinematographer|director of photography]].<ref>{{cite news|last=Riley|first=Christopher|title=What Yuri Gagarin saw: First Orbit film to reveal the view from Vostok 1|url=http://www.guardian.co.uk/science/blog/2011/apr/11/yuri-gagarin-first-orbit-vostok|newspaper=The Guardian|date=11 April 2011|location=London}}</ref> The film was streamed through the website firstorbit.org in a global YouTube premiere in 2011, under a free license.<ref>{{cite web|url=http://www.firstorbit.org/first-orbit-faqs |title=Yuri Gagarin's First Orbit – FAQs |publisher=Firstorbit.org |accessdate=1 May 2012}}</ref>

In May 2013, commander [[Chris Hadfield]] shot a music video of [[David Bowie]]'s ''[[Space Oddity (song)|Space Oddity]]'' on board the station; the film was released freely on YouTube.<ref>{{cite web|last=Warr |first=Philippa |url=http://www.wired.co.uk/news/archive/2013-05/13/commander-hadfield-space-oddity |title=Commander Hadfield bids farewell to ISS with Reddit-inspired Bowie cover |publisher=Wired.co.uk |date=13 May 2013 |accessdate=22 October 2013}}</ref> It was the first music video ever to be filmed in space<ref>{{Cite web|title = Commander Hadfield bids farewell to ISS with Reddit-inspired Bowie cover (Wired UK)|url = http://www.wired.co.uk/news/archive/2013-05/13/commander-hadfield-space-oddity|accessdate = 2015-08-05}}</ref>

==Assembly==
{{Main|Assembly of the International Space Station|List of ISS spacewalks}}
[[File:ISS-with-S0-S1-P1.jpg|thumb|right|alt=S0, S1 and P1 truss structures installed|Partially constructed ISS in December 2002]]
[[File:S3-S4 Truss Installed 2.jpg|thumb|S3-S4 Truss Installed in 2007]]
[[File:Soyuz TMA-19 spacecraft departs the ISS.jpg|thumb|[[Soyuz TMA-19]] departs in 2010]]
[[File:ISS after STS-117 in June 2007.jpg|thumb|ISS in 2007, with fewer solar arrays]]
The assembly of the International Space Station, a major endeavour in [[space architecture]], began in November 1998.<ref name="OnOrbit">{{cite web|url=http://www.nasa.gov/externalflash/ISSRG/pdfs/on_orbit.pdf|title=On-Orbit Elements|publisher=NASA|author=NASA|date=18 February 2010|accessdate=19 June 2010|format=PDF}}</ref> Russian modules launched and docked robotically, with the exception of ''[[Rassvet (ISS module)|Rassvet]]''. All other modules were delivered by the Space Shuttle, which required installation by ISS and shuttle crewmembers using the [[Mobile Servicing System#Canadarm2|Canadarm2]] (SSRMS) and [[List of ISS spacewalks|EVAs]]; {{as of|2011|06|05|lc=y}}, they had added 159 components during more than 1,000 hours of EVA. 127 of these spacewalks originated from the station, and the remaining 32 were launched from the airlocks of docked Space Shuttles.<ref name="ISStD" /> The [[beta angle]] of the station had to be considered at all times during construction, as the station's beta angle is directly related to the percentage of its orbit that the station (as well as any docked or docking spacecraft) is exposed to the sun; the Space Shuttle would not perform optimally above a limit called the "beta cutoff".<ref name="mcc">{{cite web|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-113/11_23_20_01_179.html|title=MCC Answers|author=Derek Hassman, NASA Flight Director|date=1 December 2002|publisher=NASA|accessdate=14 June 2009}}</ref>

The first module of the ISS, ''[[Zarya]]'', was launched on 20 November 1998 on an autonomous Russian [[Proton (rocket)|Proton rocket]]. It provided propulsion, attitude control, communications, electrical power, but lacked long-term life support functions. Two weeks later a passive NASA module ''[[Unity (ISS module)|Unity]]'' was launched aboard Space Shuttle flight [[STS-88]] and attached to Zarya by astronauts during EVAs. This module has two [[Pressurized Mating Adapter]]s (PMAs), one connects permanently to Zarya, the other allows the Space Shuttle to dock to the space station. At this time, the Russian station Mir was still inhabited. The ISS remained unmanned for two years, during which time Mir was de-orbited. On 12 July 2000 [[Zvezda (ISS module)|Zvezda]] was launched into orbit. Preprogrammed commands on board deployed its solar arrays and communications antenna. It then became the passive vehicle for a rendezvous with the Zarya and Unity. As a passive "target" vehicle, the Zvezda maintained a stationkeeping orbit as the Zarya-Unity vehicle performed the rendezvous and docking via ground control and the Russian automated rendezvous and docking system. Zarya's computer transferred control of the station to Zvezda's computer soon after docking. Zvezda added sleeping quarters, a toilet, kitchen, CO2 scrubbers, dehumidifier, oxygen generators, exercise equipment, plus data, voice and television communications with mission control. This enabled permanent habitation of the station.<ref>[http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/servmod.pdf NASA Facts. The Service Module: A Cornerstone of Russian International Space Station Modules]. NASA. January 1999</ref><ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/missions/sts-88/mission-sts-88.html |title=STS-88 |publisher=Science.ksc.nasa.gov |accessdate=19 April 2011}}</ref>

The first resident crew, [[Expedition 1]], arrived in November 2000 on [[Soyuz TM-31]]. At the end of the first day on the station, astronaut Bill Shepherd requested the use of the radio call sign "''Alpha''", which he and cosmonaut Krikalev preferred to the more cumbersome "''International Space Station''".<ref name=TIME-Nov2>{{cite news|url=http://www.time.com/time/arts/article/0,8599,59500,00.html|title=Upward Bound: Tales of Space Station Alpha|author=Brad Liston|date=2 November 2000|work=Time|accessdate=5 August 2010}}</ref> The name "''Alpha''" had previously been used for the station in the early 1990s,<ref name=GAO>{{cite web|url=http://archive.gao.gov/t2pbat3/151975.pdf|title=Space Station – Impact on the expanded Russian role of funding and research|date=21 June 1994|publisher=[[Government Accountability Office|United State General Accounting Office]]|accessdate=9 August 2010}}</ref> and following the request, its use was authorised for the whole of Expedition 1.<ref name=SPACE-Nov3>{{cite web|url=http://www.space.com/missionlaunches/missions/alpha_male_001103.html|title=Call Bill Shepherd the Alpha Male of the International Space Station|author=Alan Ladwig|date=3 November 2000|publisher=Space.com|accessdate=9 August 2010}}</ref> Shepherd had been advocating the use of a new name to project managers for some time. Referencing a [[Ship naming and launching|naval tradition]] in a pre-launch news conference he had said: "For thousands of years, humans have been going to sea in ships. People have designed and built these vessels, launched them with a good feeling that a name will bring good fortune to the crew and success to their voyage."<ref name=SPACE-Nov2>{{cite web|url=http://www.space.com/missionlaunches/missions/exp1_alpha_001102.html|title=Expedition One Crew Wins Bid To Name Space Station Alpha|date=2 November 2000|author=Todd Halvorson|publisher=Space.com|accessdate=9 August 2010}}</ref> [[Yuri Semenov]], the President of [[S.P. Korolev Rocket and Space Corporation Energia|Russian Space Corporation Energia]] at the time, disapproved of the name "''Alpha''"; he felt that ''Mir'' was the first space station, and so he would have preferred the names "''Beta''" or "''Mir 2''" for the ISS.<ref name=SPACE-Nov3 /><ref>{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=5913|title=Interview with RSC Energia's Yuri Semenov|publisher=Space.com|date=3 September 2001|accessdate=22 August 2010}}</ref><ref>{{cite web|url=http://english.ruvr.ru/2001/03/29/100146.html|title=Interview with Yuri Semenov, general designer of Space Rocket corporation Energy|date=21 March 2001|publisher=[[Voice of Russia]]|accessdate=5 October 2010}}</ref>

[[Expedition 1]] arrived midway between the flights of [[STS-92]] and [[STS-97]]. These two Space Shuttle flights each added segments of the station's [[Integrated Truss Structure]], which provided the station with Ku-band communication for US television, additional attitude support needed for the additional mass of the USOS, and substantial [[solar array]]s supplementing the station's existing 4 solar arrays.<ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/missions/sts-92/mission-sts-92.html |title=STS-92 |publisher=Science.ksc.nasa.gov |accessdate=19 April 2011}}</ref>

Over the next two years the station continued to expand. A [[Soyuz-U]] rocket delivered the [[Pirs (ISS module)|''Pirs'' docking compartment]]. The Space Shuttles ''Discovery'', ''[[Space Shuttle Atlantis|Atlantis]]'', and ''Endeavour'' delivered the [[Destiny (ISS module)|''Destiny'' laboratory]] and [[Quest Joint Airlock|''Quest'' airlock]], in addition to the station's main robot arm, the ''[[Canadarm2]]'', and several more segments of the Integrated Truss Structure.
[[File:Zvezda rear.jpg|thumb|left|Aft view showing a Progress spacecraft docked to Zvezda]]
The expansion schedule was interrupted by the {{OV|102}} [[Space Shuttle Columbia disaster|disaster]] in 2003, with the resulting two year hiatus in the [[Space Shuttle program]]me halting station assembly. The space shuttle was grounded until 2005 with [[STS-114]] flown by ''Discovery''.<ref>{{cite web|url=http://www.nasaspaceflight.com/2005/07/discovery-launches-the-shuttle-is-back/|title=Discovery launches—The Shuttle is back|author=Chris Bergin|publisher=NASASpaceflight.com|accessdate=6 March 2009|date=26 July 2005}}</ref>

Assembly resumed in 2006 with the arrival of [[STS-115]] with ''Atlantis'', which delivered the station's second set of solar arrays. Several more truss segments and a third set of arrays were delivered on [[STS-116]], [[STS-117]], and [[STS-118]]. As a result of the major expansion of the station's power-generating capabilities, more pressurised modules could be accommodated, and the ''[[Harmony (ISS module)|Harmony]]'' node and ''Columbus'' European laboratory were added. These were followed shortly after by the first two components of ''Kibō''. In March 2009, [[STS-119]] completed the Integrated Truss Structure with the installation of the fourth and final set of solar arrays. The final section of ''Kibō'' was delivered in July 2009 on [[STS-127]], followed by the Russian ''[[Poisk (ISS module)|Poisk]]'' module. The third node, ''[[Tranquility (ISS module)|Tranquility]]'', was delivered in February 2010 during [[STS-130]] by the Space Shuttle ''Endeavour'', alongside the [[Cupola (ISS module)|Cupola]], closely followed in May 2010 by the penultimate Russian module, ''[[Rassvet (ISS module)|Rassvet]]''. Rassvet was delivered by Space Shuttle ''Atlantis'' on [[STS-132]] in exchange for the Russian Proton delivery of the Zarya Module in 1998 which had been funded by the United States.<ref>{{cite web|url=http://www.russianspaceweb.com/iss_mim1.html |title=Mini-Research Module 1 (MIM1) Rassvet (MRM-1) |publisher=Russianspaceweb.com |accessdate=12 July 2011}}</ref> The last pressurised module of the USOS, ''Leonardo'', was brought to the station by ''Discovery'' on her final flight, [[STS-133]],<ref name="STS-133">{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/main/index.html |title=STS-133 |publisher=NASA |accessdate=1 September 2014}}</ref> followed by the [[Alpha Magnetic Spectrometer]] on [[STS-134]], delivered by ''Endeavour''.<ref name="STS-134">{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/main/index.html |title=STS-134 |publisher=NASA |accessdate=1 September 2014}}</ref>
[[File:Exterior of Cupola - Exp28.jpg|thumb|The Cupola arrived in 2010]]
{{As of|2011|06}}, the station consisted of fifteen pressurised modules and the [[Integrated Truss Structure]]. Still to be launched are the Russian [[Nauka (ISS module)|Multipurpose Laboratory Module]] ''Nauka'' and a number of external components, including the [[European Robotic Arm]]. Assembly is expected to be completed by April 2014,{{update inline|date=October 2014}} by which point the station will have a mass in excess of 400 [[metric ton|tonnes]] (440 [[short ton]]s).<ref name="OnOrbit" /><ref name="Manifest">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/iss_manifest.html|title=Consolidated Launch Manifest|accessdate=8 July 2008|publisher=NASA|author=NASA|year=2008}}</ref>

The gross mass of the station changes over time. The total launch mass of the modules on orbit is about {{convert|417289|kg|lbs|abbr=on}} (as of 3 September 2011).<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/isstodate.html |title=NASA – The ISS to Date (03/09/2011) |publisher=Nasa.gov |accessdate=12 July 2011}}</ref> The mass of experiments, spare parts, personal effects, crew, foodstuff, clothing, propellants, water supplies, gas supplies, docked spacecraft, and other items add to the total mass of the station. Hydrogen gas is constantly vented overboard by the oxygen generators.

==Station structure==
{{Double image|right|ROS Windows 0114 complete.jpg|130|USOS window identification.png|160|Russian Orbital Segment Windows|USOS International Space Station window locations}}

The ISS is a third generation<ref>{{cite web|url=http://www.dlr.de/iss/en/desktopdefault.aspx/tabid-1945/2746_read-4182/gallery-1/gallery_read-Image.19.2296/ |title=DLR – International Space Station ISS – From Cold War to international cooperation – the story of the ISS |publisher=Dlr.de |accessdate=1 May 2012}}</ref> modular space station.<ref>{{cite web|url=http://www.astronautix.com/articles/thistems.htm |title=Third Generation Soviet Space Systems |publisher=Astronautix.com |accessdate=1 May 2012}}</ref> Modular stations can allow the mission to be changed over time and new modules can be added or removed from the existing structure, allowing greater flexibility.

Below is a diagram of major station components. The blue areas are pressurised sections accessible by the crew without using spacesuits. The station's unpressurised superstructure is indicated in red. Other unpressurised components are yellow. Note that the Unity node joins directly to the Destiny laboratory. For clarity, they are shown apart.

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{{familytree| | | | | | | |AMS|~|ZVEZDA|~|AMS|
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{{familytree| |:| | |:|ELC| | |:|FZ1|:| | |ELC3|:| | |:|
ELC = [[ExPRESS Logistics Carrier#ELC-2|ELC 2]], '''[[Alpha Magnetic Spectrometer|AMS]]'''
|FZ1 = '''[[Z1 truss]]'''
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|FS1 = '''[[S1 Truss]]'''
|FS0 = '''[[S0 Truss]]'''
|FP1 = '''[[S1 Truss|P1 Truss]]'''
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{{familytree| | | | | | | | |ESP1|DESTYNY| | |
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{{familytree| | | | | | | | | |HTV|!|HTV| |!|
HTV = '''[[H-II Transfer Vehicle|HTV]]'''/'''[[Dragon (spacecraft)|Dragon]]'''/'''[[Cygnus (spacecraft)|Cygnus]]''' berth ([[Common berthing mechanism|docking port]])
|boxstyle_HTV = border: 1px solid #a3ff66; background:#ccddff;}}
{{familytree| | | | | | | | | | | |!|!|!| | | |!|KiboRobo|
KiboRobo = [[Japanese Experiment Module|'''Kibō''' Robotic Arm]]
|boxstyle_KiboRobo = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| | | | |COLEXT|COLUMBUS|-|HARMONY|-|KIBO|KiboPlat|
HARMONY = [[Harmony (ISS module)|'''Harmony''' (Node 2)]]
|KiboPlat = [[Japanese Experiment Module|'''Kibō''' External Platform]]
|COLUMBUS = [[Columbus (ISS module)|'''Columbus''' Laboratory]]
|KIBO = [[JEM-PM|'''Kibō''' Laboratory]]
|COLEXT = External Payloads
|boxstyle_HARMONY = border: 2px solid #6699ff; background:#ccddff;
|boxstyle_COLUMBUS = border: 2px solid #6699ff; background:#ccddff;
|boxstyle_COLEXT = border: 1px solid #fee067; background:#fff4cc;
|boxstyle_KIBO = border: 2px solid #6699ff; background:#ccddff;
|boxstyle_KiboPlat = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| | | | | | | | | | | |PORT2| |
PORT2 = [[Pressurized Mating Adapter#PMA-2|'''PMA 2''' docking port]]
|boxstyle_PORT2 = border: 1px solid #a3ff66; background:#ccddff;}}
{{familytree| | | | | | | | | | | | | | | |}}
{{familytree/end|nocat=1}}

==Pressurised modules==

===Zarya===
[[File:Zarya from STS-88.jpg|thumb|upright|Zarya as seen by [[Space Shuttle Endeavour]] during [[STS-88]]]]
'''''[[Zarya]]''''' (Russian: Заря́; lit. dawn), also known as the [[Functional Cargo Block]] or FGB (from the Russian "Функционально-грузовой блок", Funktsionalno-gruzovoy blok or ФГБ), was the first module of the International Space Station to be launched. The FGB provided electrical power, storage, propulsion, and guidance to the ISS during the initial stage of assembly. With the launch and assembly in orbit of other modules with more specialized functionality, Zarya is now primarily used for storage, both inside the pressurized section and in the externally mounted fuel tanks. The Zarya is a descendant of the [[TKS spacecraft]] designed for the Soviet [[Salyut program]]. The name Zarya was given to the FGB because it signified the dawn of a new era of international cooperation in space. Although it was built by a Russian company, it is owned by the [[United States]]. Zarya weighs {{convert|19300|kg|lb|abbr=on}}, is {{convert|12.55|m|ft|abbr=on}} long and {{convert|4.1|m|ft|abbr=on}} wide, discounting solar arrays.

Built from December 1994 to January 1998 in Russia at the [[Khrunichev State Research and Production Space Center]] (KhSC) in [[Moscow]], Zarya's control system was developed by the Khartron Corp. ([[Kharkiv, Ukraine]]).

Zarya was launched on 20 November 1998, on a Russian [[Proton-K|Proton rocket]] from [[Baikonur Cosmodrome Site 81]] in [[Kazakhstan]] to a {{convert|400|km|mi|abbr=on}} high orbit with a designed lifetime of at least 15 years. After Zarya reached orbit, STS-88 launched on 4 December 1998, to attach the Unity Module.

Although only designed to fly autonomously for six to eight months, Zarya did so for almost two years due to delays with the Russian Service Module, Zvezda, which finally launched on 12 July 2000, and docked with Zarya on 26 July using the Russian [[Kurs (docking system)|Kurs docking system]].

===Unity===
[[File:ISS Unity module.jpg|thumb|Unity as pictured by Space Shuttle Endeavour]]
'''''[[Unity (ISS module)|Unity]]''''', or Node 1, is one of three nodes, or passive connecting modules, in the [[US Orbital Segment]] of the station. It was the first US-built component of the Station to be launched. Cylindrical in shape, with six berthing locations facilitating connections to other modules, Unity was carried into orbit by {{OV|105}} as the primary cargo of [[STS-88]] in 1998. Essential space station resources such as fluids, environmental control and life support systems, electrical and data systems are routed through Unity to supply work and living areas of the station. More than 50,000 mechanical items, 216 lines to carry fluids and gases, and 121 internal and external electrical cables using six miles of wire were installed in the Unity node. Unity is made of aluminum. Prior to its launch aboard Endeavour, conical Pressurized Mating Adapters (PMAs) were attached to the aft and forward berthing mechanisms of Unity. Unity and the two mating adapters together weighed about {{convert|25600|lb|kg|disp=flip|abbr=on}}. The adapters allow the docking systems used by the Space Shuttle and by Russian modules to attach to the node's hatches and berthing mechanisms.

Unity was carried into orbit as the primary cargo of the Space Shuttle Endeavour on STS-88, the first Space Shuttle mission dedicated to assembly of the station. On 6 December 1998, the STS-88 crew mated the aft berthing port of Unity with the forward hatch of the already orbiting Zarya module.

===Zvezda===
'''''[[Zvezda (ISS module)|Zvezda]]''''' ({{lang-ru|link=no|Звезда́}}, meaning "star"), also known as DOS-8, Service Module or SM ({{lang-ru|link=no|СМ}}). It provides all of the station's critical systems,{{clarify|date=August 2013}} its addition rendered the station permanently habitable for the first time, adding life support for up to six crew and living quarters for two. Zvezda's DMS-R computer handles guidance, navigation and control for the entire space station.<ref name="Navigation" /> A second computer which performs the same functions will be installed in the [[Nauka (ISS module)|Nauka]] module, FGB-2.

The hull of Zvezda was completed in February 1985, with major internal equipment installed by October 1986. The module was launched by a Proton-K rocket from Site 81/23 at Baikonur, on 12 July 2000. Zvezda is at the rear of the station according to its normal direction of travel and orientation, its engines are used to boost the station's orbit. Alternatively Russian and European spacecraft can dock to Zvezda's aft port and use their engines to boost the station.

===Destiny===
[[File:Destiny as just installed.jpg|thumb|''Destiny'' interior in 2001]]
'''''[[Destiny (ISS module)|Destiny]]''''' is the primary research facility for United States payloads aboard the ISS. In 2011, NASA solicited proposals for a not-for-profit group to manage all American science on the station which does not relate to manned exploration. The module houses 24 [[International Standard Payload Rack]]s, some of which are used for environmental systems and crew daily living equipment. ''Destiny'' also serves as the mounting point for the station's Truss Structure.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/destiny.html|title=NASA—US Destiny Laboratory|date=26 March 2007|accessdate=26 June 2007|publisher = NASA}}</ref>

===Quest===
'''''[[Quest Joint Airlock|Quest]]''''' is the only USOS airlock, and hosts spacewalks with both United States [[Extravehicular Mobility Unit|EMU]] and Russian [[Orlan space suit|Orlan]] [[Space suit|spacesuits]]. It consists of two segments: the equipment lock, which stores spacesuits and equipment, and the crew lock, from which astronauts can exit into space. This module has a separately controlled atmosphere. Crew sleep in this module, breathing a low nitrogen mixture the night before scheduled EVAs, to avoid [[decompression sickness]] (known as "the bends") in the low-pressure suits.<ref>{{cite web|url=http://spaceflight.nasa.gov/station/eva/outside.html|title=Space Station Extravehicular Activity|accessdate=11 March 2009|publisher=[[NASA]]|date=4 April 2004}}</ref>

===Pirs and Poisk===
'''''[[Pirs (ISS module)|Pirs]]''''' ({{lang-ru|link=no|Пирс}}, meaning "[[pier]]"), ({{lang-ru|link=no|Стыковочный отсек}}), "docking module", SO-1 or DC-1 (docking compartment), and '''''[[Poisk (ISS module)|Poisk]]''''' ({{lang-ru|link=no|По́иск}}; lit. ''Search''), also known as the [[Mini-Research Module]] 2 (MRM 2), {{lang|ru|''Малый исследовательский модуль 2''}}, or МИМ 2. Pirs and Poisk are Russian airlock modules. Each of these modules have 2 identical hatches. An outward opening hatch on the MIR space station failed after it swung open too fast after unlatching, due to a small amount of air pressure remaining in the airlock.<ref>{{cite web|url=http://www.russianspaceweb.com/mir_close_calls.html |title=Mir close calls |publisher=Russianspaceweb.com |accessdate=1 May 2012}}</ref> A different entry was used, and the hatch repaired. All EVA hatches on the ISS open inwards and are pressure sealing. Pirs was used to store, service, and refurbish Russian [[Orlan suits]] and provided contingency entry for crew using the slightly bulkier American suits. The outermost docking ports on both airlocks allow docking of Soyuz and Progress spacecraft, and the automatic transfer of propellants to and from storage on the ROS.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/pirs.html|title=Pirs Docking Compartment|publisher=NASA|accessdate=28 March 2009|date=10 May 2006}}</ref>

{{multiple image |align=right |image1=Node 2 - STS-134.jpg |width1=171 |image2=Node 3 - Isolated view.jpg |width2=190 |caption1=''Harmony'' node in 2011 |caption2=''Tranquility'' node in 2011}}

===Harmony===
'''''[[Harmony (ISS module)|Harmony]]''''' is the second of the station's node modules and the utility hub of the USOS. The module contains four racks that provide electrical power, bus electronic data, and acts as a central connecting point for several other components via its six Common Berthing Mechanisms (CBMs). The European Columbus and Japanese Kibō laboratories are permanently berthed to the starboard and port radial ports respectively. The nadir and zenith ports can be used for docking visiting spacecraft including HTV, Dragon, and Cygnus, with the nadir port serving as the primary docking port. American Shuttle Orbiters docked with the ISS via PMA-2, attached to the forward port.

===Tranquility===
'''''[[Tranquility (ISS module)|Tranquility]]''''' is the third and last of the station's US nodes, it contains an additional life support system to recycle waste water for crew use and supplements oxygen generation. Two of the four berthing locations are not used. One location has the ''[[Cupola (ISS module)|Cupola]]'' installed, one has the docking port adapter, and the third one is occupied by the [[Leonardo (ISS module)|''Leonardo'' PMM]].

[[File:S122e008264.jpg|thumb|left|Columbus module in 2008]]

===Columbus===
'''''[[Columbus (ISS module)|Columbus]]''''', the primary research facility for European payloads aboard the ISS, provides a [[European Drawer Rack|generic laboratory]] as well as facilities specifically designed for [[Biolab|biology]], [[European Physiology Modules|biomedical research]] and [[Fluid Science Laboratory|fluid physics]]. Several mounting locations are affixed to the exterior of the module, which provide power and data to external experiments such as the [[European Technology Exposure Facility]] (EuTEF), [[Solar Monitoring Observatory]], [[Materials International Space Station Experiment]], and [[Atomic Clock Ensemble in Space]]. A number of expansions are planned for the module to study [[quantum physics]] and [[cosmology]].<ref>{{cite news|url=http://www.nasaspaceflight.com/2008/01/prcb-plan-sts-122-for-net-feb-7-three-launches-in-10-11-weeks/|title=PRCB plan STS-122 for NET Feb 7—three launches in 10–11 weeks|accessdate=12 January 2008|author=Chris Bergin|date=10 January 2008|publisher=[[NASASpaceflight.com]]}}</ref><ref>{{cite web|url=http://www.esa.int/esaHS/ESAAYI0VMOC_iss_0.html|title=Columbus laboratory|publisher=[[European Space Agency]] (ESA)|accessdate=6 March 2009|date=10 January 2009}}</ref> ESA's development of technologies on all the main areas of life support has been ongoing for more than 20 years and are/have been used in modules such as Columbus and the ATV. The German Aerospace Center [[German Aerospace Center|DLR]] manages ground control operations for Columbus and the ATV is controlled from the French [[CNES]] [[Toulouse Space Center]].

===Kibō===
[[File:きぼうエアロック Kibo airlock.jpg|thumb|Not large enough for crew using spacesuits, the airlock on Kibō has a sliding drawer for external experiments.]]
'''''[[Kibo (ISS module)|Kibō]]''''' ({{lang-ja|きぼう}}, "[[hope]]") is the largest single ISS module. This laboratory is used to carry out research in space medicine, biology, Earth observations, materials production, biotechnology, communications research, and has facilities for growing plants and fish. During August 2011, an observatory mounted on Kibō, which utilises the ISS's orbital motion to image the whole sky in the X-ray spectrum, detected for the first time the moment a star was swallowed by a black hole.<ref>{{cite web|author=[[JAXA]] |url=http://kibo.jaxa.jp/en/experiment/ef/maxi/ |title=Monitor of All-sky X-ray Image (MAXI):Experiment – Kibo Japanese Experimental Module – JAXA |publisher=Kibo.jaxa.jp |date=30 March 2007 |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://www.jaxa.jp/press/2011/08/20110825_maxi_e.html |title=JAXA | Scientific paper in Nature using the Monitor of All-sky X-ray Image (MAXI) on Kibo and the Swift satellite (USA) observations – First observation of a massive black hole swallowing a star |publisher=Jaxa.jp |accessdate=1 May 2012}}</ref> The laboratory contains a total of 23 racks, including 10 experiment racks and has a dedicated airlock for experiments. In a 'shirt sleeves' environment, crew attach an experiment to the sliding drawer within the airlock, close the inner, and then open the outer hatch. By extending the drawer and removing the experiment using the dedicated robotic arm, payloads are placed on the external platform. The process can be reversed and repeated quickly, allowing access to maintain external experiments without the delays caused by EVAs.

<gallery widths="115px" mode="nolines">
File:Kibo - Pressurized Module.jpg|Pressurized Module
File:Kibo - Experiment Logistics Module (Pressurized Section).jpg|Experiment Logistics Module
File:Kibo - Exposed Facility.jpg|Exposed Facility
File:Kibo - Experiment Logistics Module (Exposed Section).jpg|Experiment Logistics Module
File:Kibo - Remote Manipulator System.jpg|Remote Manipulator System
</gallery>

A smaller pressurised module is attached to the top of Kibō, serving as a cargo bay. The dedicated Interorbital communications system allows large amounts of data to be beamed from Kibō's ICS, first to the Japanese KODAMA satellite in geostationary orbit, then to Japanese ground stations. When a direct communication link is used, contact time between the ISS and a ground station is limited to approximately 10 minutes per visible pass. When KODAMA relays data between a LEO spacecraft and a ground station, real-time communications are possible in 60% of the flight path of the spacecraft. Ground staff use [[telepresence robotics]] to conduct on-orbit research without crew intervention.

===Cupola===
{{multiple image |align=right |image1=STS130 cupola view1.jpg |width1=190 |image2=ISS-27 Dmitri Kondratyev and Paolo Nespoli photograph the Earth through the Cupola.jpg |width2=190 |caption1=The [[Cupola (ISS module)|Cupola]]'s design has been compared to the ''[[Millennium Falcon]]'' from ''[[Star Wars (film)|Star Wars]]''. |caption2=[[Dmitri Kondratyev]] and [[Paolo A. Nespoli|Paolo Nespoli]] in the Cupola. Background left to right, [[Progress M-09M]], [[Soyuz TMA-20]], the [[Leonardo (ISS module)|Leonardo]] module and [[Kounotori 2|HTV-2]].}}
'''[[Cupola (ISS module)|Cupola]]''' is a seven window observatory, used to view Earth and docking spacecraft. Its name derives from the Italian word cupola, which means "dome". The Cupola project was started by NASA and Boeing, but cancelled due to budget cuts. A barter agreement between NASA and the ESA resulted in the Cupola's development being resumed in 1998 by the ESA. It was built by Thales Alenia Space in Torino, Italy. The module comes equipped with robotic workstations for operating the station's main robotic arm and shutters to protect its windows from damage caused by micrometeorites. It features 7 windows, with a {{convert|80|cm|in|adj=on}} round window, the largest window on the station (and the largest flown in space to date). The distinctive design has been compared to the 'turret' of the fictitious ''[[Millennium Falcon]]'' from the motion picture ''[[Star Wars (film)|Star Wars]]'';<ref>{{cite web|url=http://www.space.com/7932-astronauts-bask-spectacular-views-space-windows.html |title=Astronauts Bask in Spectacular Views From New Space Windows |publisher=Space.com |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://news.nationalgeographic.com/news/2010/02/photogalleries/100218-international-space-station-cupola-iss-obama-nasa-pictures/ |title=First Photos: Space Station's Observation Deck Unveiled |work=National Geographic |accessdate=1 May 2012}}</ref> the original prop [[lightsaber]] used by actor [[Mark Hamill]] as [[Luke Skywalker]] in the 1977 film was flown to the station in 2007.<ref>{{cite web|url=http://www.space.com/4283-nasa-shuttle-launch-luke-skywalker-lightsaber.html |title=NASA Shuttle to Launch Luke Skywalker's Lightsaber |publisher=Space.com |date=28 August 2007 |accessdate=1 May 2012}}</ref>

===Rassvet===
'''''[[Rassvet (ISS module)|Rassvet]]''''' ({{lang-ru|link=no|Рассве́т}}; lit. "dawn"), also known as the Mini-Research Module 1 (MRM-1) ({{lang-ru|link=no|Ма́лый иссле́довательский модуль}}, {{lang|ru|МИМ 1}}) and formerly known as the Docking Cargo Module (DCM), is similar in design to the [[Mir Docking Module]] launched on [[STS-74]] in 1995. ''Rassvet'' is primarily used for cargo storage and as a docking port for visiting spacecraft. It was flown to the ISS aboard NASA's {{OV|104}} on the [[STS-132]] mission and connected in May 2010,<ref>{{cite web|url=http://www.nasaspaceflight.com/2009/04/sts-132-prcb-baselines-mission-to-deliver-russias-mrm-1/|title=STS-132: PRCB baselines Atlantis' mission to deliver Russia's MRM-1|author=Chris Gebhardt|publisher=NASAspaceflight.com|date=9 April 2009|accessdate=12 November 2009}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts132/news/STS-132-09.html|author=NASA|date=18 May 2010|accessdate=7 July 2010|title=STS-132 MCC Status Report #09}}</ref> Rassvet is the only Russian owned module launched by NASA, to repay for the launch of Zarya, which is Russian designed and built, but partially paid for by NASA.<ref>[http://www.russianspaceweb.com/iss_mim1.html MIM1]. russianspaceweb.com</ref>  Rassvet was launched with the Russian Nauka Laboratory's Experiments airlock temporarily attached to it, and spare parts for the European Robotic Arm.

===Leonardo===
[[File:STS-133 Installation PMM 3.jpg|thumb|''Leonardo'' installed]]
'''''[[Leonardo (ISS module)|Leonardo]]'' Permanent Multipurpose Module''' (PMM) is a storage module attached to the ''[[Tranquility (ISS module)|Tranquility]]'' node.<ref name="leo-esa20110301">{{cite news |url=http://www.esa.int/Our_Activities/Human_Spaceflight/MagISStra/Leonardo_attached_to_Space_Station |title=Leonardo Attached to Space Station |work=ESA.int |date=1 March 2011 |accessdate=11 June 2013}}</ref><ref>{{cite web |url=http://blogs.nasa.gov/spacestation/2015/05/27/module-relocated-prepping-station-for-commercial-crew/ |title=Module Relocated Prepping Station for Commercial Crew |publisher=NASA |first=Mark |last=Garcia |date=27 May 2015 |accessdate=27 May 2015}}</ref> The three NASA Space Shuttle [[Multi-Purpose Logistics Module|MPLM]] cargo containers—Leonardo, Raffaello and Donatello—were built for NASA in [[Turin]], Italy by Alcatel Alenia Space, now [[Thales Alenia Space]].<ref>[http://www.thalesaleniaspace-issmodules.com/ Thales Alenia Space and ISS modules – Thales Alenia Space and ISS modules]. Thalesaleniaspace-issmodules.com. Retrieved 8 October 2011.</ref> The MPLMs were provided to NASA's ISS programme by Italy (independent of their role as a member state of ESA) and are considered to be US elements. In a bartered exchange for providing these containers, the US gave Italy research time aboard the ISS out of the US allotment in addition to that which Italy receives as a member of ESA.<ref>[http://www.spaceref.com/iss/elements/mplm.html Space Station User's Guide]. SpaceRef (3 April 2001). Retrieved 8 October 2011.</ref> The Permanent Multipurpose Module was created by converting Leonardo into a module that could be permanently attached to the station.<ref name="PLM1">{{cite news|url=http://www.nasaspaceflight.com/2009/08/sts-133-five-crew-one-eva-mission-leave-mpm-on-iss|title=STS-133 refined to a five crew, one EVA mission—will leave MPLM on ISS|publisher=NASASpaceflight.com|author=Chris Gebhardt|date=5 August 2009}}</ref><ref name="PLM2">{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8226309.stm|title=Europe looks to buy Soyuz craft|work=BBC News|last=Amos|first=Jonathan|date=29 August 2009}}</ref><ref>{{cite web|url=http://forum.nasaspaceflight.com/index.php?topic=17437.msg483604#msg483604|publisher=NASASpaceflight.com|accessdate=12 October 2009|title=Shuttle Q&A Part 5|date=27 September 2009}}</ref>

===Scheduled additional modules===

====Nauka====
'''''[[Nauka (ISS module)|Nauka]]''''' ({{lang-ru|link=no|Нау́ка}}; lit. "science"), also known as the Multipurpose Laboratory Module (MLM) or FGB-2 ({{lang-ru|link=no|Многофункциональный лабораторный модуль}}, {{lang|ru|МЛМ}}), is the major Russian laboratory module. It was scheduled to arrive at the station in 2014, docking to the port that was occupied by the Pirs module.<ref>{{cite web|url=http://www.aviationweek.com/Article.aspx?id=/article-xml/asd_05_23_2012_p05-01-460939.xml|title=Russia Sees Moon Base As Logical Next Step| last=Morring| first=Frank| date=23 May 2012| publisher=Aviation Week|accessdate=29 May 2012}}</ref> The date has been postponed to February 2017.<ref>{{cite web|url=http://www.russianspaceweb.com/iss_fgb2.html|title=MLM (FGB-2)|author=Anatoly Zak|publisher=Russian Space Web|date=29 April 2014|accessdate=14 May 2014}}</ref> Prior to the arrival of the Nauka module, a Progress spacecraft was used to remove Pirs from the station, deorbiting it to reenter over the Pacific Ocean. Nauka contains an additional set of life support systems and attitude control. Originally it would have routed power from the single Science-and-Power Platform, but that single module design changed over the first ten years of the ISS mission, and the two science modules, which attach to Nauka via the [[Uzlovoy Module]], or Russian node, each incorporate their own large solar arrays to power Russian science experiments in the ROS.

Nauka's mission has changed over time. During the mid-1990s, it was intended as a backup for the FGB, and later as a universal docking module (UDM); its docking ports will be able to support automatic docking of both spacecraft, additional modules and fuel transfer. Nauka has its own engines. Smaller Russian modules such as Pirs and Poisk were delivered by modified [[Progress (spacecraft)|Progress]] spacecraft, and the larger modules; Zvezda, Zarya, and Nauka, were launched by Proton rockets. Russia plans to separate Nauka, along with the rest of the Russian Orbital Segment, before the ISS is deorbited, to form the [[OPSEK]] space station.

====Uzlovoy Module====
The '''[[Uzlovoy Module]]''' (UM), or Node Module is a 4 metric ton<ref name=Zak>{{cite web|last1=Zak|first1=Anatoly|title=Node Module|url=http://www.russianspaceweb.com/iss_node.html|website=RussianSpaceWeb.com|accessdate=7 January 2015}}</ref> ball shaped module that will support the docking of two scientific and power modules during the final stage of the station assembly and provide the Russian segment additional docking ports to receive Soyuz TMA and Progress M spacecraft. UM is to be incorporated into the ISS in 2016. It will be integrated with a special version of the Progress cargo ship and launched by a standard Soyuz rocket. The Progress would use its own propulsion and flight control system to deliver and dock the Node Module to the nadir (Earth-facing) docking port of the Nauka MLM/FGB-2 module. One port is equipped with an active hybrid docking port, which enables docking with the MLM module. The remaining five ports are passive hybrids, enabling docking of Soyuz and Progress vehicles, as well as heavier modules and future spacecraft with modified docking systems. The node module was conceived to serve as the only permanent element of the future Russian successor to the ISS, [[Orbital Piloted Assembly and Experiment Complex|OPSEK]]. Equipped with six docking ports, the Node Module would serve as a single permanent core of the future station with all other modules coming and going as their life span and mission required.<ref>[http://www.energia.ru/en/news/news-2011/news_01-13.html S.P. Korolev RSC Energia – News]. Energia.ru (13 January 2011). Retrieved 8 October 2011.</ref><ref>[http://www.russianspaceweb.com/iss_node.html Node Module]. Russianspaceweb.com. Retrieved 8 October 2011.</ref> This would be a progression beyond the ISS and Russia's modular MIR space station, which are in turn more advanced than early monolithic first generation stations such as Skylab, and early Salyut and Almaz stations.

'''Science Power Modules 1 & 2''' (NEM-1, NEM-2) ({{lang-ru|link=no|Нау́чно-Энергетический Модуль-1 и -2}})

====Bigelow Expandable Activity Module====
On 16 January 2013, [[Bigelow Aerospace]] was contracted by NASA to provide a [[Bigelow Expandable Activity Module]] (BEAM), scheduled to arrive at the space station in 2015 for a two-year technology demonstration.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/station/news/beam_feature.html |title=NASA to Test Bigelow Expandable Module on Space Station |publisher=NASA |date=16 January 2013 |accessdate=17 January 2013}}</ref> BEAM is an inflatable module that will be attached to the aft hatch of the port-side Tranquility module of the International Space Station. During its two-year test run, instruments will measure its structural integrity and leak rate, along with temperature and radiation levels. The hatch leading into the module will remain mostly closed except for periodic visits by space station crew members for inspections and data collection. Following the test run, the module will be detached and jettisoned from the station.<ref>{{cite web | url=http://www.spaceflightnow.com/news/n1301/16bigelow/ | title=Bigelow inflatable module bound for space station | last=Harwood | first=William | date=16 January 2013 | publisher=Spaceflightnow | accessdate=17 January 2013}}</ref>

[[image:ISS Habitation module.jpg|thumb|left|The cancelled Habitation module under construction in 1997]]

===Cancelled components===
Several modules planned for the station have been cancelled over the course of the ISS programme, whether for budgetary reasons, because the modules became unnecessary, or following a redesign of the station after the 2003 [[Space Shuttle Columbia disaster|''Columbia'' disaster]]. The US [[Centrifuge Accommodations Module]] was intended to host science experiments in varying levels of [[artificial gravity]].<ref>{{cite web|url=http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=12560&mid=269666|title=Where is the Centrifuge Accommodation Module (CAM)?|publisher=NASASpaceflight.com|accessdate=12 October 2009}}</ref> The US [[Habitation Module]] would have served as the station's living quarters. Instead, the sleep stations are now spread throughout the station.<ref>{{cite web|url=http://www.space.com/missionlaunches/060214_iss_module.html|title=NASA Recycles Former ISS Module for Life Support Research|author=Tariq Malik|accessdate=11 March 2009|publisher=Space.com|date=14 February 2006}}</ref> The US [[Interim Control Module]] and [[ISS Propulsion Module]] were intended to replace functions of ''Zvezda'' in case of a launch failure.<ref>{{cite web|title=ICM Interim Control Module|publisher=U.S. Naval Center for Space Technology|url=http://code8200.nrl.navy.mil/icm.html|archiveurl=https://web.archive.org/web/20070208164211/http://code8200.nrl.navy.mil/icm.html|archivedate=8 February 2007}}</ref> The Russian [[Universal Docking Module]], to which the cancelled Russian Research modules and spacecraft would have docked.<ref name="Zak">{{cite web|url=http://www.russianspaceweb.com/iss_russia.html|accessdate=3 October 2009|publisher=russianspaceweb.com|author=Anatoly Zak|title=Russian segment of the ISS}}</ref> The Russian [[Science Power Platform]] would have provided the [[Russian Orbital Segment]] with a power supply independent of the ITS solar arrays,<ref name="Zak" /> and two [[Russian Research Module]]s that were planned to be used for scientific research.<ref>{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/components/russian_laboratory.html|title=Russian Research Modules|publisher=Boeing|accessdate=21 June 2009}}</ref>

==Unpressurised elements==
[[File:Truss breakdown.png|thumb|right|ISS Truss Components breakdown showing Trusses and all ORUs in situ]]
The ISS features a large number of external components that do not require pressurisation. The largest such component is the [[Integrated Truss Structure]] (ITS), to which the station's main solar arrays and thermal radiators are mounted.<ref name="Arrays" /> The ITS consists of ten separate segments forming a structure 108.5 m (356 ft) long.<ref name="OnOrbit" />

The station in its complete form has several smaller external components, such as the six robotic arms, the three [[External Stowage Platform]]s (ESPs) and four [[ExPRESS Logistics Carrier]]s (ELCs).<ref name="Manifest" /><ref>{{cite web|url=http://www.nasa.gov/centers/marshall/news/background/facts/expressrack.html|title=EXPRESS Racks 1 and 2 fact sheet|accessdate=4 October 2009|date=12 April 2008|publisher=NASA}}</ref> Whilst these platforms allow experiments (including [[MISSE]], the STP-H3 and the [[Robotic Refueling Mission]]) to be deployed and conducted in the vacuum of space by providing electricity and processing experimental data locally, the platforms' primary function is to store [[Orbital Replacement Unit]]s (ORUs). ORUs are spare parts that can be replaced when the item either passes its design life or fails. Examples of ORUs include pumps, storage tanks, antennas and battery units. Such units are replaced either by astronauts during EVA or by robotic arms. Spare parts were routinely transported to and from the station via Space Shuttle resupply missions, with a heavy emphasis on ORU transport once the NASA Shuttle approached retirement.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/12/soyuz-tma-03m-docks-iss-returns-station-six-crewmembers-future-ops/ |title=Soyuz TMA-03M docks to ISS, returns station to six crewmembers for future ops |publisher=NASASpaceFlight.com |date=23 December 2011 |accessdate=1 May 2012}}</ref> Several shuttle missions were dedicated to the delivery of ORUs, including [[STS-129]],<ref name="EVA129">{{cite web|url=http://www.nasa.gov/centers/johnson/pdf/404493main_EVA_129_F_E1.pdf|title=EVA Checklist: STS-129 Flight Supplement|author=L. D. Welsch|publisher=NASA|date=30 October 2009}}</ref> [[STS-133]]<ref name="STS-133">{{cite web|url=http://www.nasa.gov/pdf/491387main_STS-133%20Press%20Kit.pdf|title=Space Shuttle Mission: STS-131|date=February 2011|publisher=NASA}}</ref> and [[STS-134]].<ref name="STS-134">{{cite web|url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf|title=Space Shuttle Mission: STS-134|publisher=NASA|date=April 2011}}</ref> {{asof|2011|01}}, only one other mode of transportation of ORUs had been utilised – the Japanese cargo vessel [[H-II Transfer Vehicle|HTV-2]] – which delivered an FHRC and CTC-2 via its Exposed Pallet (EP).<ref name="HTV2">{{cite web|url=http://iss.jaxa.jp/en/htv/mission/htv-2/library/presskit/htv2_presskit_en.pdf|title=HTV2: Mission Press Kit|publisher=Japan Aerospace Exploration Agency|date=20 January 2011}}</ref>{{update after|2013|1|28}}

[[File:STS-116 spacewalk 1.jpg|left|thumb|Construction of the [[Integrated Truss Structure]] over New Zealand.]]
There are also smaller exposure facilities mounted directly to laboratory modules; the JEM [[Japanese Experiment Module#Exposed Facility|Exposed Facility]] serves as an external '[[porch]]' for the Japanese Experiment Module complex,<ref>{{cite web|url=http://kibo.jaxa.jp/en/about/kibo/jef/|title=Exposed Facility:About Kibo|publisher=JAXA|date=29 August 2008|accessdate=9 October 2009}}</ref> and a facility on the European ''Columbus'' laboratory provides power and data connections for experiments such as the [[European Technology Exposure Facility]]<ref name="NASA">{{cite web|url=http://www.nasa.gov/mission_pages/station/science/experiments/EuTEF.html|title=NASA—European Technology Exposure Facility (EuTEF)|publisher=NASA|date=6 October 2008|accessdate=28 February 2009}}</ref><ref name="ESA">{{cite web|url=http://www.esa.int/esaMI/Columbus/SEM7ZTEMKBF_0.html|title=ESA—Columbus—European Technology Exposure Facility (EuTEF)|publisher=ESA|date=13 January 2009|accessdate=28 February 2009}}</ref> and the [[Atomic Clock Ensemble in Space]].<ref>{{cite web|url=http://www.esa.int/SPECIALS/HSF_Research/SEMJSK0YDUF_0.html|publisher=ESA|accessdate=9 October 2009|title=Atomic Clock Ensemble in Space (ACES)}}</ref> A [[remote sensing]] instrument, [[Stratospheric Aerosol and Gas Experiment|SAGE III-ISS]], is due to be delivered to the station in 2014 aboard a [[Dragon (spacecraft)|Dragon capsule]], and the [[Neutron star Interior Composition ExploreR|NICER]] experiment in 2016.<ref>{{cite web |url=http://heasarc.gsfc.nasa.gov/docs/nicer/papers/NICER-SPIE-July2012-v4.pdf | publisher=Goddard Space Flight Center |title=The Neutron star Interior Composition ExploreR (NICER): an Explorer mission of opportunity for soft x-ray timing spectroscopy |accessdate=8 April 2013 |author=NICER Team }}</ref><ref>{{cite web|url=http://www.nasa.gov/topics/earth/features/sage3.html|date=1 March 2011|accessdate=12 March 2011|publisher=NASA|title=Time to Fly: SAGE III — ISS Prepped for Space Station|author=Michael Finneran}}</ref> The largest such scientific payload externally mounted to the ISS is the [[Alpha Magnetic Spectrometer]] (AMS), a particle physics experiment launched on [[STS-134]] in May 2011, and mounted externally on the ITS. The AMS measures [[cosmic ray]]s to look for evidence of [[dark matter]] and [[antimatter]].<ref>{{cite web|url=http://ams.cern.ch/|title=The Alpha Magnetic Spectrometer Experiment|publisher=[[CERN]]|date=21 January 2009|accessdate=6 March 2009}}</ref>

===Robotic arms and cargo cranes===
{{Double image|right|Iss017e011097.jpg|250|Dextrereallyhasnohead.jpg|250|Commander [[Sergey Alexandrovich Volkov|Volkov]] stands on Pirs with his back to the [[Soyuz spacecraft|Soyuz]] whilst operating the manual [[Strela (crane)|Strela crane]] holding photographer [[Oleg Kononenko|Kononenko]]. [[Zarya]] is seen to the left and [[Zvezda (ISS module)|Zvezda]] across the bottom of the image.|[[Dextre]], like many of the station's experiments and robotic arms, can be operated from Earth and perform tasks while the crew sleeps.||}}

The [[Integrated Truss Structure]] serves as a base for the station's primary remote manipulator system, called the [[Mobile Servicing System]] (MSS), which is composed of three main components. [[Canadarm2]], the largest robotic arm on the ISS, has a mass of {{convert|1800|kg|lb}} and is used to dock and manipulate spacecraft and modules on the USOS, hold crew members and equipment in place during EVAs and move Dextre around to perform tasks.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/station/structure/elements/mss.html |title=Canadarm2 and the Mobile Servicing System |publisher=NASA |date=8 January 2013 |accessdate=22 June 2015}}</ref> [[Dextre]] is a {{convert|1560|kg|lb|abbr=on}} robotic manipulator with two arms, a rotating torso and has power tools, lights and video for replacing [[orbital replacement unit]]s (ORUs) and performing other tasks requiring fine control.<ref>{{cite web |url=http://www.asc-csa.gc.ca/eng/iss/dextre/default.asp |title=Dextre, the International Space Station's Robotic Handyman |publisher=Canadian Space Agency |accessdate=22 June 2015}}</ref> The [[Mobile Base System]] (MBS) is 2 platforms which rides on rails along the length of the station's main truss. It serves as a mobile base for Canadarm2 and Dextre, allowing the robotic arms to reach all parts of the USOS.<ref>{{cite web |url=http://www.asc-csa.gc.ca/eng/iss/mobile-base/default.asp |title=Mobile Base System |publisher=Canadian Space Agency |accessdate=22 June 2015}}</ref> To gain access to the Russian Segment a [[Grapple Fixture|grapple fixture]] was added to Zarya on [[STS-134]], so that Canadarm2 can inchworm itself onto the ROS.<ref name="presskit134">{{cite web |url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf |title=Space Shuttle Mission STS-134: Final Flight of ''Endeavour'' - Press Kit |format=PDF |publisher=NASA |pages=51-53 |date=April 2011 |accessdate=22 June 2015}}</ref> Also installed during STS-134 was the {{convert|50|ft|m|abbr=on|order=flip}} [[Orbiter Boom Sensor System]] (OBSS), which had been used to inspect head shield tiles on Space Shuttle missions and can be used on station to increase the reach of the MSS.<ref name="presskit134"/> Staff on Earth or the station can operate the MSS components via remote control, performing work outside the station without space walks.

Japan's [[Kibo (ISS module)#Remote Manipulator System|Remote Manipulator System]], which services the JEM Exposed Facility,<ref>{{cite web |url=http://kibo.jaxa.jp/en/about/kibo/rms/ |title=Remote Manipulator System: About Kibo |publisher=JAXA |date=29 August 2008 |accessdate=4 October 2009}}</ref> was launched on [[STS-124]] and is attached to the JEM Pressurised Module.<ref>{{cite web |url=http://www.nasa.gov/centers/johnson/news/station/2002/iss02-03.txt |title=International Space Station Status Report #02-03 |publisher=NASA |date=14 January 2002 |accessdate=4 October 2009}}</ref> The arm is similar to the Space Shuttle arm as it is permanently attached at one end and has a latching end effector for standard grapple fixtures at the other.

The [[European Robotic Arm]], which will service the Russian Orbital Segment, will be launched alongside the [[Multipurpose Laboratory Module]] in 2017.<ref>{{cite web |url=http://www.russianspaceweb.com/iss_fgb2.html |title=MLM (FGB-2) module of the ISS |publisher=RussianSpaceWeb |accessdate=16 June 2014}}</ref> The ROS does not require spacecraft or modules to be manipulated, as all spacecraft and modules dock automatically and may be discarded the same way. Crew use the two ''[[Strela (crane)|Strela]]'' ({{lang-ru|link=no|Стрела́}}; lit. Arrow) cargo cranes during EVAs for moving crew and equipment around the ROS. Each Strela crane has a mass of {{convert|45|kg|lb|abbr=on}}.

===Comparison===
The ISS follows [[Salyut]] and [[Almaz]] series, [[Cosmos 557]], [[Skylab]], and [[Mir]] as the 11th space station launched, as the [[Genesis II|Genesis]] prototypes were never intended to be manned. Other examples of modular station projects include the Soviet/Russian Mir and the planned Russian OPSEK and [[Chinese space station]]. The first space station, [[Salyut 1]], and other one-piece or 'monolithic' first generation space stations, such as Salyut 2,3,4,5, DOS 2, Kosmos 557, Almaz and NASA's [[Skylab]] stations were not designed for re-supply.<ref>http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/history.pdf</ref> Generally, each crew had to depart the station to free the only docking port for the next crew to arrive, Skylab had more than one docking port but was not designed for resupply. Salyut 6 and 7 had more than one docking port and were designed to be resupplied routinely during crewed operation.<ref>{{cite web|url=http://www.pbs.org/spacestation/station/russian.htm |title=Space Station | Russian Space History |publisher=Pbs.org |accessdate=1 May 2012}}</ref>

==Station systems==

===Life support===
{{Main|ISS ECLSS|Chemical oxygen generator}}
The critical systems are the atmosphere control system, the water supply system, the food supply facilities, the sanitation and hygiene equipment, and fire detection and suppression equipment. The Russian Orbital Segment's life support systems are contained in the Service Module Zvezda. Some of these systems are supplemented by equipment in the USOS. The MLM Nauka laboratory has a complete set of life support systems.

====Atmospheric control systems====
[[Image:SpaceStationCycle.svg|thumb|The interactions between the components of the ISS Environmental Control and Life Support System (ECLSS)|alt=A flowchart diagram showing the components of the ISS life support system.]]
The atmosphere on board the ISS is similar to the [[Atmosphere of Earth|Earth's]].<ref>{{cite web|url=http://science.howstuffworks.com/space-station2.htm |title=How Space Stations Work|first=Craig|last=Freudenrich|publisher=Howstuffworks|date=20 November 2000|accessdate=23 November 2008}}</ref> Normal air pressure on the ISS is 101.3 [[kilopascal|kPa]] (14.7 [[Pounds per square inch|psi]]);<ref>{{cite web |url=http://nasaexplores.com/show2_5_8a.php?id=04-032&gl=58|archiveurl=https://web.archive.org/web/20061114010931/http://www.nasaexplores.com/show2_5_8a.php?id=04-032&gl=58|archivedate=14 November 2006|work=NASAexplores|title=5–8: The Air Up There|publisher=NASA|accessdate=31 October 2008}}</ref> the same as at sea level on Earth. An Earth-like atmosphere offers benefits for crew comfort, and is much safer than the alternative, a pure oxygen atmosphere, because of the increased risk of a fire such as that responsible for the deaths of the [[Apollo 1]] crew.<ref>{{cite book|author=Clinton Anderson|display-authors=etal|publisher=US Government Printing Office|title=Report of the Committee on Aeronautical and Space Sciences, United States Senate—Apollo 204 Accident|date=30 January 1968|location=Washington, DC|page=8|url=http://klabs.org/richcontent/Reports/Failure_Reports/as-204/senate_956/as204_senate_956.pdf}}</ref> Earth-like atmospheric conditions have been maintained on all Russian and Soviet spacecraft.<ref name=spacemed>{{Citation | last1=Davis | first1=Jeffrey R. | last2=Johnson | first2=Robert | last3=Stepanek | first3=Jan | lastauthoramp=yes | title=Fundamentals of Aerospace Medicine | publisher=Lippincott Williams & Wilkins | place=Philadelphia PA, USA | volume=XII | pages=261–264 | year=2008}}</ref>

The ''[[Elektron (ISS)|Elektron]]'' system aboard ''Zvezda'' and a similar system in ''Destiny'' generate oxygen aboard the station.<ref name="OGS">{{cite web|url=http://www.space.com/businesstechnology/060215_techwed_iss_oxygen.html|title=Air Apparent: New Oxygen Systems for the ISS|author=Tariq Malik|publisher=Space.com|date=15 February 2006|accessdate=21 November 2008}}</ref> The crew has a backup option in the form of bottled oxygen and [[Vika oxygen generator|Solid Fuel Oxygen Generation]] (SFOG) canisters, a [[chemical oxygen generator]] system.<ref name="breath easy">{{cite web|url=http://science.nasa.gov/headlines/y2000/ast13nov_1.htm|title=Breathing Easy on the Space Station|author=Patrick L. Barry|publisher=NASA|date=13 November 2000|accessdate=21 November 2008}}</ref> Carbon dioxide is removed from the air by the [[Vozdukh]] system in ''Zvezda''. Other by-products of human metabolism, such as methane from the intestines and ammonia from sweat, are removed by [[Activated carbon|activated charcoal]] filters.<ref name="breath easy" />

Part of the ROS atmosphere control system is the oxygen supply, triple-redundancy is provided by the Elektron unit, solid fuel generators, and stored oxygen. The Elektron unit is the primary oxygen supply, {{chem|O|2}} and {{chem|H|2}} are produced by [[electrolysis]], with the {{chem|H|2}} being vented overboard. The 1 kW system uses approximately 1 litre of water per crew member per day from stored water from Earth, or water recycled from other systems. MIR was the first spacecraft to use recycled water for oxygen production. The secondary oxygen supply is provided by burning {{chem|O|2}}-producing [[Vika oxygen generator|Vika]] cartridges (see also [[ISS ECLSS]]). Each 'candle' takes 5–20 minutes to decompose at 450–500 °C, producing 600 litres of {{chem|O|2}}. This unit is manually operated.<ref>[http://suzymchale.com/ruspace/issrslss.html RuSpace | ISS Russian Segment Life Support System]. Suzymchale.com. Retrieved 8 October 2011.</ref>

The US Orbital Segment has redundant supplies of oxygen, from a pressurised storage tank on the Quest airlock module delivered in 2001, supplemented ten years later by ESA built Advanced Closed-Loop System (ACLS) in the Tranquility module (Node 3), which produces {{chem|O|2}} by electrolysis.<ref>[http://science.nasa.gov/science-news/science-at-nasa/2000/ast13nov_1/ Breathing Easy on the Space Station – NASA Science]. ''Science''.nasa.gov (13 November 2000). Retrieved 8 October 2011.</ref> Hydrogen produced is combined with carbon dioxide from the cabin atmosphere and converted to water and methane.

===Power and thermal control===
{{Main|Electrical system of the International Space Station|External Active Thermal Control System}}

{{Double image|left|ROSSA.jpg|200|P4 deployed.jpg|200|Russian solar arrays, backlit by sunset.|One of the eight truss mounted pairs of USOS solar arrays}}
Double-sided solar, or [[Photovoltaic]] arrays, provide [[Electric power|electrical power]] for the ISS. These bifacial cells are more efficient and operate at a lower temperature than single-sided cells commonly used on Earth, by collecting sunlight on one side and light [[Albedo|reflected off]] the Earth on the other.<ref>{{cite web |url=http://wenku.baidu.com/view/a815121ffc4ffe473368ab7a.html |title=The early history of bifacial solar cell_百度文库 |publisher=Wenku.baidu.com |date=25 October 2010 |accessdate=14 August 2012}}</ref> 

The Russian segment of the station, like the Space Shuttle and most spacecraft, uses 28 [[volt]] [[direct current|DC]] from four rotating solar arrays mounted on ''Zarya'' and ''Zvezda''. The USOS uses 130–180 V DC from the USOS PV array, power is stabilised and distributed at 160 V DC and converted to the user-required 124 V DC. The [[High voltage|higher distribution voltage]] allows smaller, lighter conductors, at the expense of crew safety. The ROS uses [[Extra-low voltage|low voltage]]. The two station segments share power with converters.<ref name="Arrays" />

The USOS solar arrays are arranged as four wing pairs, with each wing producing nearly 32.8 kW.<ref name="Arrays">{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/truss_segment.html|title=Spread Your Wings, It's Time to Fly|publisher=NASA|date=26 July 2006|accessdate=21 September 2006}}</ref> These arrays normally track the sun to maximise power generation. Each array is about 375 m2 (450 yd2) in area and {{convert|58|m|yd|0}} long. In the complete configuration, the solar arrays track the sun by rotating the ''alpha [[gimbal]]'' once per orbit; the ''beta gimbal'' follows slower changes in the angle of the sun to the orbital plane. The [[Night Glider mode]] aligns the solar arrays parallel to the ground at night to reduce the significant aerodynamic drag at the station's relatively low orbital altitude.<ref>{{cite journal|author=G. Landis and C-Y. Lu|year=1991|title=Solar Array Orientation Options for a Space Station in Low Earth Orbit|journal=Journal of Propulsion and Power|volume=7|issue=1|pages=123–125|doi=10.2514/3.23302}}</ref>

The station uses rechargeable [[Nickel hydrogen battery|nickel-hydrogen batteries]] (NiH2) for continuous power during the 35 minutes of every 90-minute orbit that it is eclipsed by the Earth. The batteries are recharged on the day side of the Earth. They have a 6.5-year lifetime (over 37,000 charge/discharge cycles) and will be regularly replaced over the anticipated 20-year life of the station.<ref>{{cite web|url=http://www.grc.nasa.gov/WWW/RT/RT1999/5000/5420miller.html|title=Nickel-Hydrogen Battery Cell Life Test Program Update for the International Space Station|accessdate=27 November 2009|publisher=NASA|author=Thomas B. Miller|date=24 April 2000}}</ref>

The station's large solar panels generate a high potential voltage difference between the station and the ionosphere. This could cause arcing through insulating surfaces and sputtering of conductive surfaces as ions are accelerated by the spacecraft plasma sheath. To mitigate this, plasma contactor units (PCU)s create current paths between the station and the ambient plasma field.<ref>[http://www.grc.nasa.gov/WWW/RT/RT1998/5000/5430patterson.html Cathodes Delivered for Space Station Plasma Contactor System]. Grc.nasa.gov (18 June 1999). Retrieved 8 October 2011.</ref>

[[File:EATCS.png|thumb|ISS External Active Thermal Control System (EATCS) diagram]]
The large amount of electrical power consumed by the station's systems and experiments is turned almost entirely into heat. The heat which can be dissipated through the walls of the stations modules is insufficient to keep the internal ambient temperature within comfortable, workable limits. [[Ammonia]] is continuously pumped through pipework throughout the station to collect heat, then into external radiators exposed to the cold of space, and back into the station.

The International Space Station (ISS) External Active Thermal Control System (EATCS) maintains an equilibrium when the ISS environment or heat loads exceed the capabilities of the Passive Thermal Control System (PTCS). Note Elements of the PTCS are external surface materials, insulation such as MLI, or Heat Pipes. The EATCS provides heat rejection capabilities for all the US pressurised modules, including the JEM and COF as well as the main power distribution electronics of the S0, S1 and P1 Trusses. The EATCS consists an internal, non-toxic, water coolant loop used to cool and dehumidify the atmosphere, which transfers collected heat into an external liquid ammonia loop capable of withstanding the much lower temperature of space, which is then circulated through radiators to remove the heat. The EATCS is capable of rejecting up to 70 kW, and provides a substantial upgrade in heat rejection capacity from the 14 kW capability of the Early External Active Thermal Control System (EEATCS) via the Early Ammonia Servicer (EAS), which was launched on [[STS-105]] and installed onto the P6 Truss.<ref>[http://www.nasa.gov/pdf/473486main_iss_atcs_overview.pdf ATCS Team Overview]. (PDF). Retrieved 8 October 2011.</ref>

===Communications and computers===
{{Main|Tracking and Data Relay Satellite|Luch (satellite)}}
{{See also2|[[ThinkPad#Use in space|ThinkPad use in space]]}}
[[File:ISS Communication Systems.png|thumb|The communications systems used by the ISS * Luch satellite not currently in use|alt=Diagram showing communications links between the ISS and other elements.]]
Radio communications provide [[telemetry]] and scientific data links between the station and [[Mission Control Center|Mission Control Centres]]. Radio links are also used during [[Space rendezvous|rendezvous and docking procedures]] and for audio and video communication between crewmembers, flight controllers and family members. As a result, the ISS is equipped with internal and external communication systems used for different purposes.<ref name="BoeingComm" />


The Russian Orbital Segment communicates directly with the ground via the ''[[Lira (ISS)|Lira]]'' [[Antenna (radio)|antenna]] mounted to ''Zvezda''.<ref name="ISSRG" /><ref>{{cite web|url=http://www.nasa.gov/home/hqnews/2005/mar/HQ_ss05015_ISS_status_report.html|title=International Space Station Status Report: SS05-015|last=Mathews|first=Melissa|author2=James Hartsfield|date=25 March 2005|work=NASA News|publisher=NASA|accessdate=11 January 2010}}</ref> The ''Lira'' antenna also has the capability to use the ''[[Luch (satellite)|Luch]]'' data relay satellite system.<ref name="ISSRG" /> This system, used for communications with ''Mir'', fell into disrepair during the 1990s, and as a result is no longer in use,<ref name="ISSRG" /><ref name="SSSM">{{cite book|first=David|last=Harland|title=The Story of Space Station Mir|publisher=Springer-Verlag New York Inc|date=30 November 2004|location=New York|isbn=978-0-387-23011-5}}</ref><ref name="Harvey">{{cite book|last=Harvey|first=Brian|title=The rebirth of the Russian space program: 50 years after Sputnik, new frontiers|publisher=Springer Praxis Books|year=2007|page=263|isbn=0-387-71354-9}}</ref> although two new ''Luch'' satellites—''Luch''-5A and ''Luch''-5B—were launched in 2011 and 2012 respectively to restore the operational capability of the system.<ref>{{cite web|publisher=RussianSpaceWeb|url=http://www.russianspaceweb.com/2011.html|accessdate=12 January 2010|title=Space exploration in 2011|date=4 January 2010|author=Anatoly Zak}}</ref> Another Russian communications system is the [[Voskhod-M]], which enables internal telephone communications between ''Zvezda'', ''Zarya'', ''Pirs'', ''Poisk'' and the USOS, and also provides a VHF radio link to ground control centres via antennas on ''Zvezda''{{'s}} exterior.<ref>{{cite web|url=http://www.nasa.gov/directorates/somd/reports/iss_reports/2010/05022010.html|date=2 May 2010|accessdate=7 July 2010|publisher=NASA|title=ISS On-Orbit Status 05/02/10}}</ref>

The [[US Orbital Segment]] (USOS) makes use of two separate radio links mounted in the [[Z1 truss]] structure: the [[S band]] (used for audio) and [[Ku band|Ku band]] (used for audio, video and data) systems. These transmissions are routed via the United States [[Tracking and Data Relay Satellite]] System (TDRSS) in [[geostationary orbit]], which allows for almost continuous real-time communications with [[Christopher C. Kraft Jr. Mission Control Center|NASA's Mission Control Center]] (MCC-H) in [[Houston]].<ref name="ISSBook" /><ref name="ISSRG" /><ref name="BoeingComm">{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/systems/communications_tracking.html|publisher=Boeing|accessdate=30 November 2009|title=Communications and Tracking|archiveurl = https://web.archive.org/web/20080611115319/http://www.boeing.com/defense-space/space/spacestation/systems/communications_tracking.html |archivedate = 11 June 2008}}</ref> Data channels for the Canadarm2, European ''Columbus'' laboratory and Japanese ''Kibō'' modules are routed via the S band and Ku band systems, although the [[European Data Relay System]] and a similar Japanese system will eventually complement the TDRSS in this role.<ref name="ISSBook" /><ref name="JAXA-MOU">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/nasa_japan.html|title=Memorandum of Understanding Between the National Aeronautics and Space Administration of the United States of America and the Government of Japan Concerning Cooperation on the Civil International Space Station|publisher=NASA|accessdate=19 April 2009|date=24 February 1998}}</ref> Communications between modules are carried on an internal digital [[wireless network]].<ref>{{cite web|title=Operations Local Area Network (OPS LAN) Interface Control Document|format=PDF|publisher=NASA|url=http://www.spaceref.com/iss/computer/iss.ops.lan.icd.pdf|accessdate=30 November 2009|date=February 2000}}</ref>

[[File:STS-128 ISS-20 Destiny Canadarm2.jpg|thumb|left|Laptop computers surround the Canadarm2 console.]]
[[Ultra high frequency|UHF radio]] is used by astronauts and cosmonauts conducting [[Extra-vehicular activity|EVAs]]. UHF is employed by other spacecraft that dock to or undock from the station, such as Soyuz, Progress, HTV, ATV and the Space Shuttle (except the shuttle also makes use of the S band and Ku band systems via TDRSS), to receive commands from Mission Control and ISS crewmembers.<ref name="ISSRG" /> Automated spacecraft are fitted with their own communications equipment; the ATV uses a [[laser]] attached to the spacecraft and equipment attached to ''Zvezda'', known as the Proximity Communications Equipment, to accurately dock to the station.<ref>{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=16247|title=ISS/ATV communication system flight on Soyuz|accessdate=30 November 2009|publisher=[[EADS Astrium]]|date=28 February 2005}}</ref><ref>{{cite web|publisher=NASASpaceflight.com|author=Chris Bergin|url=http://www.nasaspaceflight.com/2009/11/sts-129-support-dragon-communication-demo-iss/|date=10 November 2009|accessdate=30 November 2009|title=STS-129 ready to support Dragon communication demo with ISS}}</ref>

The ISS is equipped with approximately 100 [[IBM]] and [[Lenovo]] [[ThinkPad#Use in space|ThinkPad]] model A31 and T61P laptop computers. Each computer is a [[commercial off-the-shelf]] purchase which is then modified for safety and operation including updates to connectors, cooling and power to accommodate the station's 28V DC power system and weightless environment. Heat generated by the laptops does not rise, but stagnates surrounding the laptop, so additional forced ventilation is required. Laptops aboard the ISS are connected to the station's [[wireless LAN]] via [[Wi-Fi]] and to the ground via Ku band. This provides speeds of 10 [[Megabit per second|Mbit/s]] to and 3 Mbit/s from the station, comparable to home [[digital subscriber line|DSL]] connection speeds.<ref name="issit">{{cite news |url=http://bits.blogs.nytimes.com/2010/01/22/first-tweet-from-space/ |title=First Tweet From Space |work=[[The New York Times]] |first=Nick |last=Bilton |date=22 January 2010 |accessdate=29 April 2014}}</ref><ref name="tested20121019">{{cite news |url=http://www.tested.com/science/space/449539-how-fast-isss-internet-and-other-space-questions-answered/ |title=How Fast is the ISS's Internet? (and Other Space Questions Answered) |work=Tested.com |first=Will |last=Smith |date=19 October 2012 |accessdate=29 April 2014}}</ref>

The operating system used for key station functions is the [[Debian]] [[GNU/Linux distribution]].<ref>{{cite news|last=Thomson|first=Iain|title=Penguins in spa-a-a-ce! ISS dumps Windows for Linux on laptops|url=http://www.theregister.co.uk/2013/05/10/iss_linux_debian_deployment/|accessdate=15 May 2013|newspaper=The Register|date=10 May 2013}}</ref> The migration from [[Microsoft Windows]] was made in May 2013 for reasons of reliability, stability and flexibility.<ref>{{cite news|last=Gunter|first=Joel|title=International Space Station to boldly go with Linux over Windows|url=http://www.telegraph.co.uk/technology/news/10049444/International-Space-Station-to-boldly-go-with-Linux-over-Windows.html|accessdate=15 May 2013|newspaper=The Daily Telegraph|date=10 May 2013}}</ref>

==Station operations==

===Expeditions and private flights===
[[File:Sts088-703-019e.jpg|thumb|Zarya and Unity were entered for the first time on 10 December 1998.]]
[[File:Soyuz tm-31 transported to launch pad.jpg|right|thumb|Soyuz TM-31 being prepared to bring the first resident crew to the station in October 2000]]
[[File:STS-115 ISS after undocking.jpg|thumb|right|ISS was slowly assembled over a decade of spaceflights and crews]]
[[File:Tracy Caldwell Dyson in Cupola ISS.jpg|thumb|Expeditions have included male and female crew-members from many nations]]
''See also the [[list of International Space Station expeditions]] (professional crew), [[space tourism]] (private travellers), and the [[list of human spaceflights to the ISS]] (both).''

Each permanent crew is given an expedition number. Expeditions run up to six months, from launch until undocking, an 'increment' covers the same time period, but includes cargo ships and all activities. Expeditions 1 to 6 consisted of 3 person crews, Expeditions 7 to 12 were reduced to the safe minimum of two following the destruction of the NASA Shuttle Columbia. From Expedition 13 the crew gradually increased to 6 around 2010.<ref name="ISSEx">{{cite web|title=International Space Station Expeditions|publisher=NASA|url=http://www.nasa.gov/mission_pages/station/expeditions/index.html|date=10 April 2009|accessdate=13 April 2009}}</ref><ref name="current">{{cite web|url=http://www.nasa.gov/mission_pages/station/main/index.html|title=International Space Station|accessdate=22 October 2008|publisher=NASA|year=2008|author=NASA}}</ref> With the arrival of the American [[Commercial Crew Development|Commercial Crew]] vehicles in the middle of the 2010s, expedition size may be increased to seven crew members, the number ISS is designed for.<ref>{{cite web|url=http://www.aviationweek.com/article.aspx?id=/article-xml/asd_07_26_2012_p01-02-480253.xml|title=ISS Research Hampered By Crew Availability|last=Morring|first=Frank|date=27 July 2012|quote=A commercial capability would allow the station's crew to grow from six to seven by providing a four-seat vehicle for emergency departures in addition to the three-seat Russian Soyuz capsules in use today.|publisher=Aviation Week|accessdate=30 July 2012}}</ref><ref>{{cite web|url=http://www.airspacemag.com/space-exploration/AS-Interview-Mike-Suffredini.html|title=Assembly (Nearly) Complete |last=Hoversten|first=Paul|date=1 May 2011|publisher=Air & Space Magazine|quote=In fact, we're designed on the U.S. side to take four crew. The ISS design is actually for seven. We operate with six because first, we can get all our work done with six, and second, we don't have a vehicle that allows us to fly a seventh crew member. Our requirement for the new vehicles being designed is for four seats. So I don't expect us to go down in crew size. I would expect us to increase it.|accessdate=8 May 2011}}</ref>

[[Sergei Krikalev]], member of [[Expedition 1]] and Commander of [[Expedition 11]] has spent more time in space than anyone else, a total of 803 days and 9 hours and 39 minutes. His awards include the [[Order of Lenin]], [[Hero of the Soviet Union]], [[Hero of the Russian Federation]], and 4 NASA medals. On 16 August 2005 at 1:44 am EDT he passed the record of 748 days held by [[Sergei Avdeyev]], who had 'time travelled' 1/50th of a second into the future on board MIR.<ref>{{cite web|url=http://www.popsci.com/scitech/article/2002-02/lets-do-time-warp-again?page=2 |archiveurl=https://web.archive.org/web/20100628190931/http://www.popsci.com/scitech/article/2002-02/lets-do-time-warp-again?page=2 |archivedate=28 June 2010 |title=Let's Do the Time Warp Again |publisher=Web.archive.org |date=28 June 2010 |accessdate=1 May 2012}}</ref> He participated in psychosocial experiment SFINCSS-99 (Simulation of Flight of International Crew on Space Station), which examined inter-cultural and other stress factors affecting integration of crew in preparation for the ISS spaceflights. Commander [[Michael Fincke]] has spent a total of 382 days in space – more than any other American astronaut.

Travellers who pay for their own passage into space are termed spaceflight participants by Roscosmos and NASA, and are sometimes informally referred to as space tourists, a term they generally dislike.{{refn|Privately funded travellers who have objected to the term include Dennis Tito, the first such traveller (''Associated Press'', 8 May 2001), [[Mark Shuttleworth]], founder of [[Ubuntu (operating system)|Ubuntu]] (''Associated Press, The Spokesman Review, 6 January 2002, p. A4''), Gregory Olsen and Richard Garriott.<ref>{{cite news|last=Schwartz|first=John|title=Russia Leads Way in Space Tourism With Paid Trips into Orbit|url=http://www.nytimes.com/2008/10/11/science/space/11space.html|newspaper=The New York Times|date=10 October 2008}}</ref><ref>{{cite web|last=Boyle|first=Alan|title=Space passenger Olsen to pull his own weight|url=http://msnbc.msn.com/id/9323509/#.Tz5lcFE-qr4|publisher=MSNBC}}</ref> Canadian astronaut Bob Thirsk said the term does not seem appropriate, referring to his crewmate, [[Guy Laliberté]], founder of [[Cirque du Soleil]].<ref>{{cite web|url=http://www.stcatharinesstandard.ca/ArticleDisplay.aspx?e=1975186&archive=true |title=Flight to space ignited dreams | St. Catharines Standard |publisher=Stcatharinesstandard.ca |accessdate=1 May 2012}}</ref> Anousheh Ansari denied being a tourist<ref>{{cite web|url=http://www.esa.int/esaHS/SEMD58BE8YE_business_0.html |title=ESA – Human Spaceflight and Exploration – Business – "I am NOT a tourist" |publisher=Esa.int |date=18 September 2006 |accessdate=1 May 2012}}</ref> and took offence at the term.<ref>{{cite web|url=http://www.space.com/2889-interview-anousheh-ansari-female-space-tourist.html |title=Interview with Anousheh Ansari, the First Female Space Tourist |publisher=Space.com |date=15 September 2006 |accessdate=1 May 2012}}</ref>|group=note|name}} All seven were transported to the ISS on Russian Soyuz spacecraft. When professional crews change over in numbers not divisible by the three seats in a Soyuz, and a short-stay crewmember is not sent, the spare seat is sold by MirCorp through Space Adventures. When the space shuttle retired in 2011, and the station's crew size was reduced to 6, space tourism was halted, as the partners relied on Russian transport seats for access to the station. Soyuz flight schedules increase after 2013, allowing 5 Soyuz flights (15 seats) with only two expeditions (12 seats) required.<ref>{{cite web|url=http://www.spaceflightnow.com/news/n1101/12soyuz/ |title=Breaking News | Resumption of Soyuz tourist flights announced |publisher=Spaceflight Now |accessdate=1 May 2012}}</ref> The remaining seats are sold for around {{US$|40 million}} to members of the public who can pass a medical. ESA and NASA criticised private spaceflight at the beginning of the ISS, and NASA initially resisted training [[Dennis Tito]], the first man to pay for his own passage to the ISS.{{refn|ESA director Jörg Feustel-Büechl said in 2001 that Russia had no right to send 'amateurs' to the ISS. A 'stand-off' occurred at the Johnson Space Centre between Commander Talgat Musabayev and NASA manager Robert Cabana. Cabana refused to train Dennis Tito, a member of Musabayev's crew along with Yuri Baturin. The commander argued that Tito had trained 700 hours in the last year and was as qualified as any NASA astronaut, and refused to allow his crew to be trained on the American portions of the station without Tito. Cabana stated training could not begin, and the commander returned with his crew to their hotel.|group=note|name}}  [[Toyohiro Akiyama]] was flown to Mir for a week, he was classed as a business traveller, as his employer, [[Tokyo Broadcasting System]], paid for his ticket, and he gave a daily TV broadcast from orbit.

[[Anousheh Ansari]] ({{lang-fa|انوشه انصاری}}) became the first Iranian in space and the first self-funded woman to fly to the station. Officials reported that her education and experience make her much more than a tourist, and her performance in training had been "excellent."<ref>{{cite web|last=Maher |first=Heather |url=http://www.rferl.org/content/article/1071358.html |title=U.S.: Iranian-American To Be First Female Civilian in Space |publisher=Radio Free Europe/Radio Liberty |date=15 September 2006 |accessdate=1 May 2012}}</ref> Ansari herself dismisses the idea that she is a tourist. She did Russian and European studies involving medicine and microbiology during her 10-day stay. The documentary ''[[Space Tourists]]'' follows her journey to the station, where she fulfilled "an age-old dream of man: to leave our planet as a «normal person» and travel into outer space."<ref>{{cite web|url=http://www.space-tourists-film.com/en/film_synopsis.php |title=Space Tourists | A Film By Christian Frei |publisher=Space-tourists-film.com |accessdate=1 May 2012}}</ref> In the film, some Kazakhs are shown waiting in the middle of the steppes for four rocket stages to literally fall from the sky. Film-maker Christian Frei states "Filming the work of the Kazakh scrap metal collectors was anything but easy. The Russian authorities finally gave us a film permit in principle, but they imposed crippling preconditions on our activities. The real daily routine of the scrap metal collectors could definitely not be shown. Secret service agents and military personnel dressed in overalls and helmets were willing to ''re-enact'' their work for the cameras – in an idealised way that officials in Moscow deemed to be presentable, but not at all how it takes place in reality."

Spaceflight participant [[Richard Garriott]] placed a [[Geocaching|geocache]] aboard the ISS during his flight.<ref>{{cite web|url=http://www.geocaching.com/seek/cache_details.aspx?wp=GC1BE91|title=International Space Station Traditional Geocache}}</ref> This is currently the only non-terrestrial geocache in existence.<ref>{{cite web |url=http://www.geekwire.com/2011/outer-space-ocean-floor-15m-geocaches-counting/|accessdate=27 February 2013|last=Cook|first=John|title=From outer space to the ocean floor, Geocaching.com now boasts more than 1.5 million hidden treasures|date=29 August 2011}}</ref>

===Orbit===
{{Double image|right|Internationale Raumstation Bahnhöhe (dumb version).png|300|Iss.ogg|235|Graph showing the changing altitude of the ISS from November 1998 until January 2009|Animation of ISS orbit from a North American geostationary point of view (sped up 1800 times)}}
The ISS is maintained in a nearly circular orbit with a minimum mean altitude of 330 km (205 mi) and a maximum of 410 km (255 mi), in the centre of the [[thermosphere]], at an [[inclination]] of 51.6 degrees to Earth's equator, necessary to ensure that Russian [[Soyuz (spacecraft)|Soyuz]] and [[Progress (spacecraft)|Progress]] spacecraft launched from the [[Baikonur Cosmodrome]] may be safely launched to reach the station. Spent rocket stages must be dropped into uninhabited areas and this limits the directions rockets can be launched from the spaceport.<ref name="MCC Answer">{{cite web|last=Cooney|first=Jim|title=Mission Control Answers Your Questions|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-112/09_04_12_54_17.html|location=Houston, TX|quote=Jim Cooney ISS Trajectory Operations Officer}}</ref><ref>{{cite book|last=Pelt|first=Michel van|title=Into the Solar System on a String : Space Tethers and Space Elevators|year=2009|publisher=Springer New York|location=New York, NY|isbn=0-387-76555-7|page=133|edition=1.}}</ref> The orbital inclination chosen was also low enough to allow American space shuttles launched from Florida to reach the ISS.

It travels at an average speed of 27,724 kilometres (17,227 mi) per hour, and completes {{Orbit|daily orbits|15.54}} orbits per day (93 minutes per orbit).{{Orbit|ref|<ref name="heavens-above"/>}}<ref name="tracking">{{cite web|url=http://spaceflight.nasa.gov/realdata/tracking/index.html|title=Current ISS Tracking data|accessdate=28 January 2009|publisher=NASA|date=15 December 2008|author=NASA}}</ref> The station's altitude was allowed to fall around the time of each NASA shuttle mission. Orbital boost burns would generally be delayed until after the shuttle's departure. This allowed shuttle payloads to be lifted with the station's engines during the routine firings, rather than have the shuttle lift itself and the payload together to a higher orbit. This trade-off allowed heavier loads to be transferred to the station. After the retirement of the NASA shuttle, the nominal orbit of the space station was raised in altitude.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/06/europes-atv-2-depart-iss-make-way-russias-progress-m-11m/ |title=Europe's ATV-2 departs ISS to make way for Russia's Progress M-11M |publisher=NASASpaceFlight.com |date=20 June 2011 |accessdate=1 May 2012}}</ref><ref name="Popular Mechanics">{{cite web|url=http://www.popularmechanics.com/science/air_space/4275571.html|title=The Uncertain Future of the International Space Station: Analysis|author=Rand Simberg|date=29 July 2008|accessdate=6 March 2009|publisher=[[Popular Mechanics]]}}</ref> Other, more frequent supply ships do not require this adjustment as they are substantially lighter vehicles.<ref name="Worldbook at NASA">{{cite web|url=http://www.nasa.gov/worldbook/intspacestation_worldbook.html|title = International Space Station|year=2005|accessdate=14 June 2008|publisher=World Book, Inc|author=James Oberg|work=World Book Online Reference Center}}{{dead link|date=May 2012}}</ref><ref name="nasa.gov-iss-environment">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archiveurl=https://web.archive.org/web/20080213164432/http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archivedate=13 February 2008|title=ISS Environment|accessdate=15 October 2007|publisher=[[Johnson Space Center]]}}</ref>
[[File:ISS orbits 04132013.jpg|thumbnail|Orbits of the ISS, shown in April 2013]]
Orbital boosting can be performed by the station's two main engines on the ''[[Zvezda (ISS module)|Zvezda]]'' service module, or Russian or European spacecraft docked to Zvezda's aft port. The ATV has been designed with the possibility of adding a [[Automated Transfer Vehicle#ATV evolution proposals|second docking port]] to its other end, allowing it to remain at the ISS and still allow other craft to dock and boost the station. It takes approximately two orbits (three hours) for the boost to a higher altitude to be completed.<ref name="nasa.gov-iss-environment" /> In December 2008 NASA signed an agreement with the [[Ad Astra Rocket Company]] which may result in the testing on the ISS of a [[VASIMR]] plasma propulsion engine.<ref name="vasimr">{{cite web|url=http://www.adastrarocket.com/AdAstra-NASA_PR12Dec08.pdf|publisher=AdAstra Rocket Company|title=Press Release 121208|accessdate=7 December 2009|date=12 December 2008|format=PDF}}</ref> This technology could allow [[Orbital station-keeping|station-keeping]] to be done more economically than at present.<ref name="future-prop">{{cite web|url=http://www.nasa.gov/vision/space/travelinginspace/future_propulsion.html|title=Propulsion Systems of the Future|accessdate=29 May 2009|publisher=NASA}}</ref><ref>{{cite web|work=New Scientist|accessdate=7 October 2009|url=http://www.newscientist.com/article/dn17918-rocket-company-tests-worlds-most-powerful-ion-engine.html|title=Rocket company tests world's most powerful ion engine|author=David Shiga|date=5 October 2009}}</ref>

The Russian Orbital Segment contains the station's engines and control [[Bridge (nautical)|bridge]], which handles Guidance, Navigation and Control (ROS GNC) for the entire station.<ref name="Navigation">{{cite web|url=http://www.esa.int/export/esaHS/ESAOXX0VMOC_iss_0.html|title=DMS-R: ESA's Data Management System for the Russian Segment of the ISS}}</ref> Initially, Zarya, the first module of the station, controlled the station until a short time after the Russian service module Zvezda docked and was transferred control. Zvezda contains the ESA built DMS-R Data Management System.<ref name="EsaComputer">{{cite web|url=http://www.esa.int/esapub/onstation/onstation17/os17_chapter6.pdf|title=Exercising Control 49 months of DMS-R Operations}}</ref> Using two fault-tolerant computers (FTC), Zvezda computes the station's position and orbital trajectory using redundant Earth horizon sensors, Solar horizon sensors as well as Sun and star trackers. The FTCs each contain three identical processing units working in parallel and provide advanced fault-masking by majority voting. Zvezda uses gyroscopes and thrusters to turn itself around. Gyroscopes do not require propellant, rather they use electricity to 'store' momentum in flywheels by turning in the opposite direction to the station's movement. The USOS has its own computer controlled gyroscopes to handle the extra mass of that section. When gyroscopes 'saturate', reaching their maximum speed, thrusters are used to cancel out the stored momentum. During [[Expedition 10]], an incorrect command was sent to the station's computer, using about 14 kilograms of propellant before the fault was noticed and fixed. When attitude control computers in the ROS and USOS fail to communicate properly, it can result in a rare 'force fight' where the ROS GNC computer must ignore the USOS counterpart, which has no thrusters.<ref>{{cite web|url=http://pims.grc.nasa.gov/pimsdocs/public/ISS%20Handbook/hb_qs_vehicle_RussianUSGNCForceFight.pdf |title=Microsoft Word – hb_qs_vehicle_RussianUSGNCForceFight_pg1.doc |format=PDF |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://spaceflight.nasa.gov/spacenews/reports/issreports/2005/iss05-7.html|title = International Space Station Status Report #05-7|date=11 February 2005|publisher=NASA|accessdate=23 November 2008}}</ref><ref>{{cite book|title=Dynamics and Control of Attitude, Power, and Momentum for a Spacecraft Using Flywheels and Control Moment Gyroscopes|author=Carlos Roithmayr|format=PDF|year=2003|publisher=NASA|location=Langley Research Center|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030038806_2003038772.pdf|accessdate=12 July 2011}}</ref> When an ATV, NASA Shuttle, or Soyuz is docked to the station, it can also be used to maintain station attitude such as for troubleshooting. Shuttle control was used exclusively during [[STS-117|installation]] of the S3/S4 truss, which provides electrical power and data interfaces for the station's electronics.<ref>{{cite web|url=http://www.nasaspaceflight.com/2007/06/atlantis-ready-to-support-iss-troubleshooting/|title=Atlantis ready to support ISS troubleshooting|publisher=NASASPaceflight.com|author=Chris Bergin|accessdate=6 March 2009|date=14 June 2007}}</ref>

==Mission controls==
The components of the ISS are operated and monitored by their respective space agencies at [[Mission Control Center|mission control centres]] across the globe, including:
* Roscosmos's [[Mission Control Center#RKA Mission Control Center|Mission Control Center]] at [[Korolyov (city)|Korolyov]], Moscow Oblast, controls the [[Russian Orbital Segment]] which handles Guidance, Navigation & Control for the entire Station.,<ref name="Navigation" /><ref name="EsaComputer" /> in addition to individual Soyuz and Progress missions.<ref name="ISSRG" />
* ESA's [[ATV Control Centre]], at the [[Toulouse Space Centre]] (CST) in [[Toulouse]], France, controls flights of the unmanned European [[Automated Transfer Vehicle]].<ref name="ISSRG" />
* JAXA's [[JEM Control Center]] and [[HTV Control Center]] at [[Tsukuba Space Center]] (TKSC) in [[Tsukuba]], Japan, are responsible for operating the Japanese Experiment Module complex and all flights of the 'White Stork' HTV Cargo spacecraft, respectively.<ref name="ISSRG" />
* NASA's [[Christopher C. Kraft Jr. Mission Control Center|Mission Control Center]] at [[Lyndon B. Johnson Space Center]] in Houston, Texas, serves as the primary control facility for the United States segment of the ISS and also controlled the Space Shuttle missions that visited the station.<ref name="ISSRG">{{cite book|author=Gary Kitmacher|title=Reference Guide to the International Space Station| publisher =[[Apogee Books]]|location=Canada|year=2006|isbn=978-1-894959-34-6|issn=1496-6921|pages=71–80}}</ref>
* NASA's [[Payload Operations and Integration Center]] at [[Marshall Space Flight Center]] in [[Huntsville, Alabama]], coordinates payload operations in the USOS.<ref name="ISSRG" />
* ESA's [[Columbus Control Center|Columbus Control Centre]] at the [[German Aerospace Center|German Aerospace Centre]] (DLR) in [[Oberpfaffenhofen]], Germany, manages the European ''Columbus'' research laboratory.<ref name="ISSRG" />
* CSA's [[MSS Control]] at [[Saint-Hubert, Quebec]], Canada, controls and monitors the [[Mobile Servicing System]], or Canadarm2.<ref name="ISSRG" />
{{wide image|ISS Centers.svg|880px|Space centres involved with the ISS programme|alt=A world map highlighting the locations of space centres. See adjacent text for details.}}

===Repairs===
{{Main|Orbital Replacement Units|International Space Station maintenance}}
'''[[Orbital Replacement Units]]''' ('''ORUs''') are spare parts that can be readily replaced when a unit either passes its design life or fails. Examples of ORUs are pumps, storage tanks, controller boxes, antennas, and battery units. Some units can be replaced using robotic arms. Many are stored outside the station, either on small pallets called [[ExPRESS Logistics Carrier]]s (ELCs) or share larger platforms called [[External Stowage Platform]]s which also hold science experiments. Both kinds of pallets have electricity as many parts which could be damaged by the cold of space require heating. The larger logistics carriers also have computer local area network connections (LAN) and telemetry to connect experiments. A heavy emphasis on stocking the USOS with ORU's occurred around 2011, before the end of the NASA shuttle programme, as its commercial replacements, [[Cygnus (spacecraft)|Cygnus]] and [[Dragon (spacecraft)|Dragon]], carry one tenth to one quarter the payload.

[[File:ISS Unpressurized Platforms.png|thumb|Spare parts are called [[Orbit Replaceable Unit|ORU]]s; some are externally stored on pallets called [[ExPRESS Logistics Carrier|ELC]]s and [[External stowage platform|ESP]]s.]]

Unexpected problems and failures have impacted the station's assembly time-line and work schedules leading to periods of reduced capabilities and, in some cases, could have forced abandonment of the station for safety reasons, had these problems not been resolved. During [[STS-120]] in 2007, following the relocation of the P6 truss and solar arrays, it was noted during the redeployment of the array that it had become torn and was not deploying properly.<ref name="Astronauts notice tear in solar panel">{{cite news|url=http://www.redorbit.com/news/space/1123767/astronauts_notice_tear_in_solar_panel/index.html |title=Astronauts notice tear in solar panel|accessdate=30 October 2007|agency=Associated Press|date=30 October 2007|author=Liz Austin Peterson}}</ref> An EVA was carried out by [[Scott E. Parazynski|Scott Parazynski]], assisted by [[Douglas H. Wheelock|Douglas Wheelock]]. The men took extra precautions to reduce the risk of electric shock, as the repairs were carried out with the solar array exposed to sunlight.<ref name="Space Station's Damaged Panel Is Fixed">{{cite news|url=http://www.washingtonpost.com/wp-dyn/content/article/2007/11/03/AR2007110300227.html|title=Space Station's Damaged Panel Is Fixed|accessdate=4 November 2007|work=The Washington Post|date=4 November 2007|first=Rob|last=Stein}}</ref> The issues with the array were followed in the same year by problems with the starboard Solar Alpha Rotary Joint (SARJ), which rotates the arrays on the starboard side of the station. Excessive vibration and high-current spikes in the array drive motor were noted, resulting in a decision to substantially curtail motion of the starboard SARJ until the cause was understood. Inspections during EVAs on STS-120 and [[STS-123]] showed extensive contamination from metallic shavings and debris in the large drive gear and confirmed damage to the large metallic race ring at the heart of the joint, and so the joint was locked to prevent further damage.<ref name="joint-update">{{cite news|url=http://spaceflightnow.com/shuttle/sts123/080325sarj/index.html|title=Station chief gives detailed update on joint problem|accessdate=5 November 2008|author=William Harwood|publisher=CBS News & SpaceflightNow.com|date=25 March 2008}}</ref> Repairs to the joint were carried out during [[STS-126]] with lubrication of both joints and the replacement of 11 out of 12 trundle bearings on the joint.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts126/126_overview.html|title=Crew Expansion Prep, SARJ Repair Focus of STS-126|accessdate=5 November 2008|publisher=NASA|date=30 October 2008}}</ref><ref>{{cite news|url=http://www.spaceflightnow.com/shuttle/sts126/081118fd5/index.html|title=Astronauts prepare for first spacewalk of shuttle flight|date=18 November 2008|author=William Harwood|publisher=CBS News & SpaceflightNow.com|accessdate=22 November 2008}}</ref>

[[File:STS-120 EVA Scott Parazynski.jpg|thumb|While anchored on the end of the [[Orbiter Boom Sensor System|OBSS]], astronaut [[Scott Parazynski]] performs makeshift repairs to a US Solar array which damaged itself when unfolding, during [[STS-120]].|alt=Two black and orange solar arrays, shown uneven and with a large tear visible. A crew member in a spacesuit, attached to the end of a robotic arm, holds a latticework between two solar sails.]]
2009 saw damage to the S1 radiator, one of the components of the station's cooling system. The problem was first noticed in [[Soyuz spacecraft|Soyuz]] imagery in September 2008, but was not thought to be serious.<ref name="Radiator">{{cite web|url=http://www.nasaspaceflight.com/2009/04/iss-concern-s1-radiator-may-require-replacement-shuttle-mission/|author=Chris Bergin|date=1 April 2009|publisher=NASASpaceflight.com|title=ISS concern over S1 Radiator – may require replacement via shuttle mission|accessdate=3 April 2009}}</ref> The imagery showed that the surface of one sub-panel has peeled back from the underlying central structure, possibly due to micro-meteoroid or debris impact. It is also known that a Service Module thruster cover, jettisoned during an EVA in 2008, had struck the S1 radiator, but its effect, if any, has not been determined. On 15 May 2009 the damaged radiator panel's ammonia tubing was mechanically shut off from the rest of the cooling system by the computer-controlled closure of a valve. The same valve was used immediately afterwards to vent the ammonia from the damaged panel, eliminating the possibility of an ammonia leak from the cooling system via the damaged panel.<ref name="Radiator" />

Early on 1 August 2010, a failure in cooling Loop A (starboard side), one of two external cooling loops, left the station with only half of its normal cooling capacity and zero redundancy in some systems.<ref>{{cite web|url=http://spaceflightnow.com/news/n1007/31station/ |title=Problem forces partial powerdown aboard station |publisher=Spaceflightnow.com |date=31 July 2010 |accessdate=16 November 2010}}</ref><ref>{{cite web|url=http://www.spaceref.com/news/viewsr.html?pid=34622 |title=NASA ISS On-Orbit Status 1 August 2010 (early edition) |publisher=Spaceref.com |date=31 July 2010 |accessdate=16 November 2010}}</ref><ref>{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/systems/atcs.html |title=ISS Active Control System |publisher=Boeing |date=21 November 2006 |accessdate=16 November 2010}}</ref> The problem appeared to be in the ammonia pump module that circulates the ammonia cooling fluid. Several subsystems, including two of the four CMGs, were shut down.

Planned operations on the ISS were interrupted through a series of EVAs to address the cooling system issue. A first EVA on 7 August 2010, to replace the failed pump module, was not fully completed due to an ammonia leak in one of four quick-disconnects. A second EVA on 11 August successfully removed the failed pump module.<ref>[http://spaceflightnow.com/station/exp24/100810evapre/index.html Spaceflight Now] "Wednesday spacewalk to remove failed coolant pump"</ref><ref>[http://www.nasaspaceflight.com/2010/08/live-second-eva-with-pump-module-changeout/ NASA spaceflight 11 August] "Large success for second EVA as failed Pump Module is removed"</ref> A third EVA was required to restore Loop A to normal functionality.<ref>[http://spaceflightnow.com/station/exp24/100811eva2/index5.html Spaceflight Now 12 August] "Station's bad pump removed; more spacewalking ahead"</ref><ref>[http://www.nasaspaceflight.com/2010/08/iss-cooling-returning-normal-confirming-etcs-pm-success/ Spaceflight Now, 18 August] ISS cooling configuration returning to normal confirming ETCS PM success</ref>

The USOS's cooling system is largely built by the American company [[Boeing]],<ref>{{cite web|url=http://www.space.com/businesstechnology/international-space-station-complexities-100802.html|title=Cooling System Malfunction Highlights Space Station's Complexity|publisher=Space.com|date=2 August 2010}}</ref> which is also the manufacturer of the failed pump.<ref>{{cite web|url=http://spaceflightnow.com/news/n1007/31station/|title=Spacewalks needed to fix station cooling problem|publisher=Spaceflightnow|date=31 July 2010}}</ref>

An air leak from the USOS in 2004,<ref>{{cite news|url=http://www.msnbc.msn.com/id/3882962/|title=Crew finds 'culprit' in space station leak|publisher=MSNBC|date=11 January 2004|author=James Oberg|accessdate=22 August 2010}}</ref> the venting of fumes from an ''[[Elektron (ISS)|Elektron]]'' oxygen generator in 2006,<ref>{{cite news|url=http://spaceflightnow.com/station/exp13/060918elektron.html|title=Oxygen Generator Problem Triggers Station Alarm|publisher = CBS News through Spaceflight Now|date=18 September 2006|author=William Harwood|accessdate=24 November 2008}}</ref> and the failure of the computers in the ROS in 2007 during [[STS-117]] left the station without thruster, ''Elektron'', ''[[Vozdukh]]'' and other environmental control system operations, the root cause of which was found to be condensation inside the electrical connectors leading to a short-circuit.{{Citation needed|date=June 2011}}
[[File:STS-134 EVA4 view to the Russian Orbital Segment.jpg|thumb|right|In the foreground, a set of heat radiators]]
The four Main Bus Switching Units (MBSUs, located in the S0 truss), control the routing of power from the four solar array wings to the rest of the ISS. In late 2011 MBSU-1, while still routing power correctly, ceased responding to commands or sending data confirming its health, and was scheduled to be swapped out at the next available EVA. In each MBSU, two power channels feed 160V DC from the arrays to two DC-to-DC power converters (DDCUs) that supply the 124V power used in the station. A spare MBSU was already on board, but 30 August 2012 EVA failed to be completed when a bolt being tightened to finish installation of the spare unit jammed before electrical connection was secured.<ref>{{cite web|author=30 August 2012 by Pete Harding |url=http://www.nasaspaceflight.com/2012/08/astronaut-perform-first-post-shuttle-spacewalk-iss |title=Astronaut duo complete challenging first post-Shuttle US spacewalk on ISS |publisher=Nasaspaceflight.com |date=30 August 2012 |accessdate=22 October 2013}}</ref> The loss of MBSU-1 limits the station to 75% of its normal power capacity, requiring minor limitations in normal operations until the problem can be addressed.

On 5 September 2012, in a second, 6 hr, EVA to replace MBSU-1, astronauts Sunita Williams and Akihiko Hoshide successfully restored the ISS to 100% power.<ref>[http://spaceref.com/international-space-station/critical-space-station-spacewalk-a-success.html Spaceref.com Sept 5, 2012] Marc Boucher "Critical Space Station spacewalk a Success".</ref>
[[File:Astronaut Mike Hopkins on Dec. 24 Spacewalk.jpg|thumb|Mike Hopkins on his Christmas Eve spacewalk]]
On 24 December 2013, astronauts made a rare Christmas Eve space walk, installing a new ammonia pump for the station's cooling system. The faulty cooling system had failed earlier in the month, halting many of the station's science experiments. Astronauts had to brave a "mini blizzard" of ammonia while installing the new pump. It was only the second Christmas Eve spacewalk in NASA history.<ref>{{cite web|last=AP|title=Astronauts Complete Rare Christmas Eve Spacewalk|url=http://www.leaker.com/astronauts-complete-rare-christmas-eve-spacewalk/|publisher=Leaker|accessdate=24 December 2013|date=24 December 2013}}</ref>

[[File:Iss orbit and expeditions.png|thumb|Iss orbit with calendar of expeditions and modules]]

==Fleet operations==
:{{See also|List of human spaceflights to the International Space Station|List of unmanned spaceflights to the International Space Station}}
A wide variety of manned and unmanned spacecraft have supported the station's activities. 
[[Progress M-28M]] (ISS-60P) was the 62nd Progress spacecraft planned to arrive at the ISS, including [[Progress M-MIM2|M-MIM2]] and [[Progress M-SO1|M-SO1]] which installed modules. 35 flights of the retired NASA Space Shuttle were made to the station.<ref name="ISStD">{{cite web|url=http://spaceflight.nasa.gov/station/isstodate.html|title=The ISS to Date|accessdate=21 March 2011|publisher=NASA|date=9 March 2011|author=NASA}}</ref> [[Soyuz TMA-16M|TMA-16M]] is the 42nd Soyuz flight, and there have been 5 [[Automated Transfer Vehicle|European ATV]], 4 Japanese [[H-II Transfer Vehicle|Kounotori]] 'White Stork', 8 [[SpaceX]] [[Dragon (spacecraft)|Dragon]] and 4 OSC [[Cygnus (spacecraft)|Cygnus]] planned arrivals.

===Currently docked/berthed===
''See also the list of [[List of International Space Station expeditions|professional]] crew, [[Space tourism|private]] travellers, [[List of human spaceflights to the ISS|both]] or just [[List of unmanned spaceflights to the ISS|unmanned spaceflights]].''

;Key
{{legend|lightblue|Uncrewed cargoships are in light blue}}
{{legend|#cfc|Crewed spacecraft are in light green}}

{| class="wikitable" style="margin: 1em auto 1em auto;text-align: left; font-size: 95%;"
|-Currently Docked
|style="text-align:center; background:#BBB" colspan="3" | '''Spacecraft and mission'''
|style="text-align:center; background:#BBB"|'''Location'''
|style="text-align:center; background:#BBB"|'''Arrived''' ([[UTC]])
|style="text-align:center; background:#BBB"|'''Departure date'''
|- style="background:lightblue;"
| {{flagicon|RUS}}
| [[Progress M-26M]]
| Progress 58 Cargo
| [[Zvezda (ISS module)|Zvezda]] aft
| 17 February 2015
| 14 August 2015
|- style="background:#cfc;"
| {{flagicon|RUS}}
| [[Soyuz TMA-16M]]
| [[Expedition 43]]/[[Expedition 44|44]]
| [[Poisk (ISS module)|Poisk]] zenith
| 28 March 2015
| 11 September 2015
|- style="background:lightblue;"
| {{flagicon|RUS}}
| [[Progress M-28M]]
| Progress 60 Cargo
| [[Pirs (ISS module)|Pirs]] nadir
| 5 July 2015
| 19 November 2015
|- style="background:#cfc;"
| {{flagicon|RUS}}
| [[Soyuz TMA-17M]]
| [[Expedition 44]]/[[Expedition 45|45]]
| [[Rassvet (ISS module)|Rassvet]] nadir
| 23 July 2015
| 22 December 2015
|}

===Scheduled launches and dockings/berthings===
* All dates are [[UTC]]. Dates are the earliest possible dates and may change.
* Forward ports are at the front of the station according to its normal direction of travel and orientation ([[Yaw, pitch and roll#Aircraft attitudes|attitude]]). Aft is at the rear of the station, used by spacecraft boosting the station's orbit. [[Nadir]] is closest the Earth, [[Zenith]] is on top.
* Spacecraft operated by government agencies are indicated with 'Gov' and under commercial arrangements are indicated with 'Com'.

;Key
{{legend|lightblue|Uncrewed cargoships are in light blue colour}}
{{legend|#cfc|Crewed spacecraft are in light green colour}}
{{legend|wheat|Modules are in wheat colour}}

{| class="wikitable" style="margin: 1em auto 1em auto;text-align: left; font-size: 95%;"
|+Planned Missions
|style="text-align:center; background:#BBB"|'''Launch''' ({{abbr|NET|Not Earlier Than}})
|style="text-align:center; background:#BBB"|'''Launch Vehicle'''
|style="text-align:center; background:#BBB"|'''Launch Site'''
|style="text-align:center; background:#BBB" colspan="3"| '''Launch Service Provider'''
|style="text-align:center; background:#BBB"|'''Payload'''
|style="text-align:center; background:#BBB"|'''Spacecraft'''
|style="text-align:center; background:#BBB"|'''Mission'''
|style="text-align:center; background:#BBB"|'''Docking / Berthing Port'''
|style="text-align:center; background:#BBB"|'''Ref.'''
|-
| nowrap| 16 August 2015
| nowrap| [[H-IIB]]
| nowrap| {{flagicon|JPN}} [[Tanegashima Space Center|Tanegashima]] [[Yoshinobu Launch Complex|LA-Y2]]
| nowrap| {{flagicon|JPN}}
| nowrap| Gov
| nowrap| [[JAXA]]
| style="background:lightblue;" nowrap| [[Kounotori 5|HTV-5]]
| nowrap| [[H-II Transfer Vehicle|HTV]]
| ISS Resupply
| nowrap| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule">{{cite web |url=http://spaceflightnow.com/launch-schedule/ |title=Launch Calendar |work=Spaceflight Now |date=28 March 2015 |accessdate=28 March 2015}}</ref><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 2 September 2015
| nowrap| [[Soyuz-FG]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:#cfc;" nowrap| [[Soyuz TMA-18M]]
| nowrap| [[Soyuz (spacecraft)|Soyuz]]
| [[Expedition 45]]/[[Expedition 46|46]] including [[European Space Agency|ESA]] [[Denmark|Danish]] Astronaut [[Andreas Mogensen]] and [[Kazakhstan]] cosmonaut [[Aydyn Aimbetov]].
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 21 September 2015
| nowrap| [[Soyuz-U]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:lightblue;" nowrap| [[Progress M-29M]]
| nowrap| [[Progress (spacecraft)|Progress]]
| ISS Resupply
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| NET September 2015 (TBD)
| nowrap|[[Falcon 9 v1.1]]
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 40|SLC-40]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[SpaceX]]
| style="background:lightblue;" nowrap| [[SpaceX CRS-8]]
| nowrap| [[Dragon (spacecraft)|Dragon]]
| ISS resupply. Will deliver [[Bigelow Expandable Activity Module|Bigelow Expandable Activity Module (BEAM)]] to the ISS.
| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| 21 November 2015
| nowrap| [[Soyuz-2 (rocket)|Soyuz-2.1a]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:lightblue;" nowrap| [[Progress MS-1]]
| nowrap| [[Progress (spacecraft)|Progress]]
| ISS Resupply. First launch of the new [[Progress (spacecraft)#Progress MS|Progress-MS]] variant.
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 3 December 2015
| nowrap| [[Atlas V]] 401
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 41|SLC-41]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[United Launch Alliance|ULA]]
| style="background:lightblue;" nowrap| [[Cygnus CRS Orb-4]]
| nowrap| [[Cygnus (spacecraft)|Cygnus]]
| ISS Resupply
| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/><ref>{{cite web|url=http://www.space.com/27962-cygnus-cargo-spacecraft-new-rocket.html |title=Private Cargo Spacecraft Gets New Rocket Ride After Accident |publisher=Space.com |date= |accessdate=2015-04-04}}</ref>
|-
| nowrap| 15 December 2015
| nowrap| [[Soyuz-FG]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:#cfc;" nowrap| [[Soyuz TMA-19M]]
| nowrap| [[Soyuz (spacecraft)|Soyuz]]
| [[Expedition 46]]/[[Expedition 47|47]]
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| NET December 2015 (TBD)
| nowrap|[[Falcon 9 v1.1]]
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[SpaceX]]
| style="background:lightblue;" nowrap| [[SpaceX CRS-9]]
| nowrap| [[Dragon (spacecraft)|Dragon]]
| ISS resupply. Will deliver the IDA-2 segment of the [[NASA Docking System]] to the ISS.
| nowrap| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |
url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|}

===Docking===
{{See also|Docking and berthing of spacecraft}}
[[File:Progress M-14M.jpg|thumb|The [[Progress M-14M]] resupply vehicle as it approaches the ISS in 2012. Over 50 unpiloted [[Progress (spacecraft)|Progress]] spacecraft have been sent with supplies during the lifetime of the station.]]
All Russian spacecraft and self-propelled modules are able to rendezvous and dock to the space station without human intervention using the [[Kurs (docking system)|Kurs]] docking system. Radar allows these vehicles to detect and intercept ISS from over 200 kilometres away. The European ATV uses star sensors and GPS to determine its intercept course. When it catches up it then uses laser equipment to [[Computer vision|optically]] recognise Zvezda, along with the Kurs system for redundancy.  Crew supervise these craft, but do not intervene except to send abort commands in emergencies. The Japanese [[H-II Transfer Vehicle]] parks itself in progressively closer orbits to the station, and then awaits 'approach' commands from the crew, until it is close enough for a robotic arm to grapple and berth the vehicle to the USOS. The American Space Shuttle was manually docked, and on missions with a [[Multi-Purpose Logistics Module|cargo container]], the container would be berthed to the Station with the use of manual robotic arms. Berthed craft can transfer [[International Standard Payload Rack]]s. Japanese spacecraft berth for one to two months. Russian and European Supply craft can remain at the ISS for six months,<ref>{{cite web|url=http://www.esa.int/esaMI/ATV/SEMBW0PR4CF_0.html |title=ESA — ATV — Crew role in mission control |publisher=Esa.int |date=2 March 2011 |accessdate=23 May 2011}}</ref><ref>{{cite web|url=http://www.esa.int/esaHS/ESA4ZJ0VMOC_iss_0.html |title=ESA — Human Spaceflight and Exploration — International Space Station — Automated Transfer Vehicle (ATV) |publisher=Esa.int |date=16 January 2009 |accessdate=23 May 2011}}</ref> allowing great flexibility in crew time for loading and unloading of supplies and trash. NASA Shuttles could remain docked for 11–12 days.<ref>{{cite web|url=http://www.boeing.com/news/frontiers/archive/2005/july/i_ids4.html|title=Space Shuttle upgrade lets astronauts at ISS stay in space longer|last=Memi|first=Ed|publisher=Boeing|accessdate=17 September 2011}}</ref>

The American manual approach to docking allows greater initial flexibility and less complexity. The downside to this mode of operation is that each mission becomes unique and requires specialised training and planning, making the process more labour-intensive and expensive. The Russians pursued an automated methodology that used the crew in override or monitoring roles. Although the initial development costs were high, the system has become very reliable with standardisations that provide significant cost benefits in repetitive routine operations.<ref>David C. Wo±nden and David K. Geller [http://www.usu.edu/mae/aerospace/publications/JDSC_RoadToAutonomy.pdf The Road to Autonomous Orbital Rendezvous]. Utah State University, Logan, Utah</ref> An automated approach could allow assembly of modules orbiting other worlds prior to crew arrival.

[[File:ISS and Endeavour seen from the Soyuz TMA-20 spacecraft 27.jpg|thumb|left|{{OV|105}}, [[ATV-2]], [[Soyuz TMA-21]] and [[Progress M-10M]] docked to the ISS during [[STS-134]], as seen from the departing [[Soyuz TMA-20]]|alt=A side-on view of the ISS showing a Space Shuttle docked to the forward end, an ATV to the aft end and Soyuz & Progress spacecraft projecting from the Russian segment.]]
Soyuz spacecraft used for crew rotation also serve as lifeboats for emergency evacuation; they are replaced every six months and have been used once to remove excess crew after the [[Space Shuttle Columbia disaster|Columbia disaster]].<ref>{{cite web|url=http://www.astronautix.com/flights/isseo6.htm |title=ISS EO-6 |publisher=Astronautix.com |accessdate=1 May 2012}}</ref> Expeditions require, on average, {{nowrap|2 722 kg}} of supplies, and {{As of|2011|03|09|lc=yes}}, crews had consumed a total of around {{nowrap|22 000 meals}}.<ref name="ISStD" /> Soyuz crew rotation flights and Progress resupply flights visit the station on average two and three times respectively each year,<ref name="Livelist">{{cite web|url=http://www.nasa.gov/mission_pages/station/resupply/index.html|archiveurl=https://web.archive.org/web/20080803015945/http://www.nasa.gov/mission_pages/station/resupply/index.html|archivedate=3 August 2008|title=Live listing of spacecraft operations|publisher=NASA|date=1 December 2009|accessdate=8 December 2009}}</ref> with the ATV and HTV planned to visit annually from 2010 onwards.{{Citation needed|date=January 2012}} Following retirement of the NASA Shuttle [[Cygnus spacecraft|Cygnus]] and [[SpaceX Dragon|Dragon]] were contracted to fly cargo to the station.<ref>{{cite web|author=Space Operations Mission Directorate|title=Human Space Flight Transition Plan|publisher=NASA|date=30 August 2006|url=http://www.nasa.gov/pdf/315546main_space_flight_transition_plan.pdf}}</ref><ref>{{cite press release|publisher=NASA|date=18 January 2006|title=NASA Seeks Proposals for Crew and Cargo Transportation to Orbit|url=http://www.spaceref.com/news/viewpr.html?pid=18791|accessdate=21 November 2006}}</ref>

From 26 February 2011 to 7 March 2011 four of the governmental partners (United States, ESA, Japan and Russia) had their spacecraft (NASA Shuttle, ATV, HTV, Progress and Soyuz) docked at the ISS, the only time this has happened to date.<ref>{{cite news|title=NASA proposes Soyuz photo op; shuttle launch readiness reviewed (UPDATED)|url=http://www.cbsnews.com/network/news/space/home/spacenews/files/b0e194a8338c336e823c03601f046707-157.html|publisher=CBS|accessdate=11 February 2011}}</ref> On 25 May 2012, [[SpaceX]] became the world's first privately held company to send cargo, via the [[Dragon (spacecraft)|Dragon spacecraft]], to the International Space Station.<ref name="NYT-20120525">{{cite news |last=Chang |first=Kenneth |title=Space X Capsule Docks at Space Station |url=http://www.nytimes.com/2012/05/26/science/space/space-x-capsule-docks-at-space-station.html |date=25 May 2012 |work=[[The New York Times]] |accessdate=25 May 2012 }}</ref>

===Launch and docking windows===
Prior to a ship's docking to the ISS, navigation and attitude control (GNC) is handed over to the ground control of the ships' country of origin. GNC is set to allow the station to drift in space, rather than fire its thrusters or turn using gyroscopes. The solar panels of the station are turned edge-on to the incoming ships, so residue from its thrusters does not damage the cells. When a NASA shuttle docked to the station, other ships were grounded, as the carbon wingtips, cameras, windows, and instruments aboard the shuttle were at too much risk from damage from thruster residue from other ships movements.

Approximately 30% of NASA shuttle launch delays were caused by poor weather. Occasional priority was given to the Soyuz arrivals at the station where the Soyuz carried crew with time-critical cargoes such as biological experiment materials, also causing shuttle delays. Departure of the NASA shuttle was often delayed or prioritised according to weather over its two landing sites.<ref>{{cite web |url=http://www.nasa.gov/home/hqnews/2009/may/HQ_09-118_Shuttle_Landing_Delayed.html |title=NASA's Space Shuttle Landing Delayed by Weather |publisher=NASA |first1=Katherine |last1=Trinidad |first2=Candrea |last2=Thomas |date=22 May 2009 |accessdate=26 June 2015}}</ref> Whilst the Soyuz is capable of landing anywhere, anytime, its planned landing time and place is chosen to give consideration to helicopter pilots and ground recovery crew, to give acceptable flying weather and lighting conditions. Soyuz launches occur in adverse weather conditions, but the cosmodrome has been shut down on occasions when buried by snow drifts up to 6 metres in depth, hampering ground operations.

==Life aboard==

===Crew activities===
[[File:Exp18home nasa big.jpg|thumb|Crewmember peers out of a window]]

A typical day for the crew begins with a wake-up at 06:00, followed by post-sleep activities and a morning inspection of the station. The crew then eats breakfast and takes part in a daily planning conference with Mission Control before starting work at around 08:10. The first scheduled exercise of the day follows, after which the crew continues work until 13:05. Following a one-hour lunch break, the afternoon consists of more exercise and work before the crew carries out its pre-sleep activities beginning at 19:30, including dinner and a crew conference. The scheduled sleep period begins at 21:30. In general, the crew works ten hours per day on a weekday, and five hours on Saturdays, with the rest of the time their own for relaxation or work catch-up.<ref>{{cite web|url=http://www.nasa.gov/pdf/287386main_110508_tl.pdf|title=ISS Crew Timeline|date=5 November 2008|accessdate=5 November 2008|publisher=NASA|format=PDF}}</ref>

The time zone used on board the ISS is [[Coordinated Universal Time]] (UTC). The windows are covered at night hours to give the impression of darkness because the station experiences 16 sunrises and sunsets a day. During visiting space shuttle missions, the ISS crew will mostly follow the shuttle's [[Mission Elapsed Time]] (MET), which is a flexible time zone based on the launch time of the shuttle mission.<ref>{{Cite web|title = NASA - Time in Space, A Space in Time|url = https://www.nasa.gov/mission_pages/station/research/news/time_in_space.html|website = www.nasa.gov|accessdate = 2015-05-05}}</ref><ref>{{Cite web|title = A Slice of Time Pie|url = https://web.archive.org/web/20130317075600/http://blogs.nasa.gov/cm/blog/ISS%20Science%20Blog/posts/post_1340820317951.html|date = 2013-03-17|accessdate = 2015-05-05}}</ref><ref>{{Cite web|title = Human Space Flight (HSF) - Crew Answers|url = http://spaceflight.nasa.gov/feedback/expert/answer/crew/sts-113/index_2.html|website = spaceflight.nasa.gov|accessdate = 2015-05-05}}</ref>

The station provides crew quarters for each member of the expedition's crew, with two 'sleep stations' in the ''Zvezda'' and four more installed in ''Harmony''.<ref>{{cite web|url=https://www.youtube.com/watch?v=Q4dG9vSyUFQ|title=At Home with Commander Scott Kelly (Video)|date=6 December 2010|publisher=NASA|accessdate=8 May 2011|location=International Space Station}}</ref><ref>{{cite web|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080013462_2008012884.pdf|title=International Space Station USOS Crew Quarters Development|first1=James Lee |last1=Broyan |first2=Melissa Ann |last2=Borrego |first3=Juergen F. |last3=Bahr|year=2008|publisher=SAE International|accessdate=8 May 2011}}</ref> The American quarters are private, approximately person-sized soundproof booths. The Russian crew quarters include a small window, but do not provide the same amount of ventilation or block the same amount of noise as their American counterparts. A crewmember can sleep in a crew quarter in a tethered sleeping bag, listen to music, use a laptop, and store personal items in a large drawer or in nets attached to the module's walls. The module also provides a reading lamp, a shelf and a desktop.<ref name="ESALife">{{cite web|url=http://www.esa.int/esaHS/ESAH1V0VMOC_astronauts_0.html|publisher=ESA|accessdate=28 October 2009|date=19 July 2004|title=Daily life}}</ref><ref name="NASACrewEquip">{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/126_payload.html|title=Station Prepares for Expanding Crew|publisher=NASA|first=Cheryl L. |last=Mansfield|date=7 November 2008|accessdate=17 September 2009}}</ref><ref name="CSALife">{{cite web|url=http://www.asc-csa.gc.ca/pdf/educator-liv_wor_iss.pdf|title=Living and Working on the International Space Station|accessdate=28 October 2009|publisher=CSA}}</ref> Visiting crews have no allocated sleep module, and attach a sleeping bag to an available space on a wall—it is possible to sleep floating freely through the station, but this is generally avoided because of the possibility of bumping into sensitive equipment.<ref name="SRLife">{{cite web|url=http://www.space.com/missionlaunches/090827-sts127-space-sleeping.html|title=Sleeping in Space is Easy, But There's No Shower|first=Tariq|last=Malik|accessdate=29 October 2009|date=27 July 2009|publisher=Space.com}}</ref> It is important that crew accommodations be well ventilated; otherwise, astronauts can wake up oxygen-deprived and gasping for air, because a bubble of their own exhaled carbon dioxide has formed around their heads.<ref name="ESALife" />
{{See also|Christmas on the International Space Station}}

===Food===
[[File:Meal STS127.jpg|thumb|alt=Nine astronauts seated around a table covered in open cans of food strapped down to the table. In the background a selection of equipment is visible, as well as the salmon-coloured walls of the Unity node.|The crews of [[STS-127]] and [[Expedition 20]] enjoy a meal inside ''Unity''.]]
{{See also|Space food}}

Most of the food on board is vacuum sealed in plastic bags. Cans are heavy and expensive to transport, so there are not as many. The preserved food is generally not held in high regard by the crew, and when combined with the reduced sense of taste in a microgravity environment,<ref name="ESALife" /> a great deal of effort is made to make the food more palatable. More spices are used than in regular cooking, and the crew looks forward to the arrival of any ships from Earth, as they bring fresh fruit and vegetables with them. Care is taken that foods do not create crumbs. Sauces are often used to ensure station equipment is not contaminated. Each crew member has individual food packages and cooks them using the on-board galley. The galley features two food warmers, a refrigerator added in November 2008, and a water dispenser that provides both heated and unheated water.<ref name="NASACrewEquip" /> Drinks are provided in dehydrated powder form and are mixed with water before consumption.<ref name="NASACrewEquip" /><ref name="CSALife" /> Drinks and soups are sipped from plastic bags with straws; solid food is eaten with a knife and fork, which are attached to a tray with magnets to prevent them from floating away. Any food that floats away, including crumbs, must be collected to prevent it from clogging up the station's air filters and other equipment.<ref name="CSALife" />

===Hygiene===
[[File:Zvezda toilet.jpg|thumb|right|upright|Space toilet in the [[Zvezda (ISS module)|Zvezda Service Module]]]]

Showers on space stations were introduced in the early 1970s on Skylab and Salyut 3.<ref name="livingandworking">Benson, Charles Dunlap and William David Compton. ''[http://history.nasa.gov/SP-4208/contents.htm Living and Working in Space: A History of Skylab]''. NASA publication SP-4208.</ref>{{rp|139}} By Salyut 6, in the early 1980s, the crew complained of the complexity of showering in space, which was a monthly activity.<ref name="Portree1995-86">{{cite book |url=http://history.nasa.gov/SP-4225/documentation/mhh/mirheritage.pdf |title=Mir Hardware Heritage |publisher=NASA |first=David S. F. |last=Portree |page=86 |date=March 1995 |id=Reference Publication 1357 |oclc=755272548}}</ref> The ISS does not feature a shower; instead, crewmembers wash using a water jet and wet wipes, with soap dispensed from a toothpaste tube-like container. Crews are also provided with rinseless shampoo and edible toothpaste to save water.<ref name="SRLife" /><ref>{{cite AV media |url=https://www.youtube.com/watch?v=uIjNfZbUYu8 |title=Karen Nyberg Shows How You Wash Hair in Space |publisher=NASA |work=YouTube.com |first=Karen |last=Nyberg |date=12 July 2013 |accessdate=6 June 2015}}</ref>

There are two [[space toilet]]s on the ISS, both of Russian design, located in ''[[Zvezda (ISS module)|Zvezda]]'' and ''[[Tranquility (ISS module)|Tranquility]]''.<ref name="NASACrewEquip" /> These Waste and Hygiene Compartments use a fan-driven suction system similar to the Space Shuttle Waste Collection System. Astronauts first fasten themselves to the toilet seat, which is equipped with spring-loaded restraining bars to ensure a good seal.<ref name="ESALife" /> A lever operates a powerful fan and a suction hole slides open: the air stream carries the waste away. Solid waste is collected in individual bags which are stored in an aluminium container. Full containers are transferred to Progress spacecraft for disposal.<ref name="NASACrewEquip" /><ref>{{cite web |first=Ed |last=Lu |title=Greetings Earthling |url=http://spaceflight.nasa.gov/station/crew/exp7/luletters/lu_letter9.html |date=8 September 2003 |accessdate=1 November 2009 |publisher=NASA}}</ref> Liquid waste is evacuated by a hose connected to the front of the toilet, with anatomically correct "urine funnel adapters" attached to the tube so both men and women can use the same toilet. Waste is collected and transferred to the Water Recovery System, where it is recycled back into drinking water.<ref name="CSALife" />

==Crew health and safety==
{{Main|Effect of spaceflight on the human body}}

===Radiation===
The ISS is partially protected from the space environment by the Earth's magnetic field. From an average distance of about {{convert|70,000|km|abbr=on}}, depending on Solar activity, the [[magnetosphere]] begins to deflect solar wind around the Earth and ISS. [[coronal mass ejection|Solar flares]] are still a hazard to the crew, who may receive only a few minutes warning. The crew of [[Expedition 10]] took shelter as a precaution in 2005 in a more heavily shielded part of the ROS designed for this purpose during the initial 'proton storm' of an X-3 class solar flare,<ref>{{cite web|title=Solar Flare Hits Earth and Mars|author=Ker Than|publisher=Space.com|date=23 February 2006|url=http://www.space.com/2080-solar-flare-hits-earth-mars.html}}</ref><ref>{{cite web|title=A new kind of solar storm|publisher=NASA|date=10 June 2005|url=http://science.nasa.gov/science-news/science-at-nasa/2005/10jun_newstorm/}}</ref> but without the limited protection of the Earth's [[magnetosphere]], interplanetary manned missions are especially vulnerable.

[[File:Aurora Australis.ogv|thumb|left|Video of the [[Aurora Australis]] taken by the crew of [[Expedition 28]] on an ascending pass from south of [[Madagascar]] to just north of Australia over the Indian Ocean.]]

Subatomic charged particles, primarily protons from [[cosmic ray]]s and [[solar wind]], are normally absorbed by the Earth's atmosphere. When they interact in sufficient quantity, their effect becomes visible to the naked eye in a phenomenon called an aurora. Without the protection of the Earth's atmosphere, which absorbs this radiation, crews are exposed to about 1 [[millisievert]] each day, which is about the same as someone would get in a year on Earth from natural sources. This results in a higher risk of astronauts developing cancer. Radiation can penetrate living tissue, damage DNA, and cause damage to the [[chromosome]]s of [[lymphocytes]]. These cells are central to the [[immune system]], and so any damage to them could contribute to the lowered [[immunity (medical)|immunity]] experienced by astronauts. Radiation has also been linked to a higher incidence of [[cataracts]] in astronauts. Protective shielding and protective drugs may lower the risks to an acceptable level.<ref name="JCB"/>

The radiation levels experienced on the ISS are about five times greater than those experienced by airline passengers and crew. The Earth's electromagnetic field provides almost the same level of protection against solar and other radiation in low Earth orbit as in the stratosphere. Airline passengers experience this level of radiation for no more than 15 hours for the longest intercontinental flights. For example, on a 12-hour flight an airline passenger would experience 0.1 millisieverts of radiation, or a rate of 0.2 millisieverts per day; only 1/5 the rate experienced by an astronaut in LEO.<ref>{{cite web|url=http://jag.cami.jccbi.gov./cariprofile.asp|title=Galactic Radiation Received in Flight|accessdate=20 May 2010|publisher=FAA Civil Aeromedical Institute}}</ref>
{{See also|Coronal mass ejection|Aurora (astronomy)}}

===Stress===
[[File:Nikolai Budarin in a sleep station in Zvezda.jpg|thumb|Cosmonaut [[Nikolai Budarin]] at work inside [[Zvezda (ISS module)|Zvezda]] service module crew quarters]]
There has been considerable evidence that psychosocial stressors are among the most important impediments to optimal crew morale and performance.<ref>{{cite book| author1 =Peter Suedfeld1| author2 = Kasia E. Wilk| author3 = Lindi Cassel| title = Flying with Strangers: Postmission Reflections of Multinational Space Crews}}</ref> Cosmonaut [[Valery Ryumin]], wrote in his journal during a particularly difficult period on board the [[Salyut 6]] space station: "All the conditions necessary for murder are met if you shut two men in a cabin measuring 18 feet by 20 and leave them together for two months."

NASA's interest in psychological stress caused by space travel, initially studied when their manned missions began, was rekindled when astronauts joined cosmonauts on the Russian space station Mir. Common sources of stress in early American missions included maintaining high performance under public scrutiny, as well as isolation from peers and family. The latter is still often a cause of stress on the ISS, such as when the mother of NASA Astronaut [[Daniel M. Tani|Daniel Tani]] died in a car accident, and when Michael Fincke was forced to miss the birth of his second child.


A study of the longest spaceflight concluded that the first three weeks represent a critical period where attention is adversely affected because of the demand to adjust to the extreme change of environment.<ref>{{cite doi|10.1080/001401398186991}}</ref> Skylab's 3 crews remained one, two, and three months respectively, long term crews on Salyut 6, [[Salyut 7]], and the ISS last about five to six months and Mir's expeditions often lasted longer. The ISS working environment includes further stress caused by living and working in cramped conditions with people from very different cultures who speak a different language. First generation space stations had crews who spoke a single language; second and third-generation stations have crew from many cultures who speak many languages. The ISS is unique because visitors are not classed automatically into 'host' or 'guest' categories as with previous stations and spacecraft, and may not suffer from feelings of isolation in the same way. Crew members with a military pilot background and those with an academic science background or teachers and politicians may have problems understanding each other's jargon and worldview.

===Medical===
[[File:Frank De Winne on treadmill cropped.jpg|thumb|Astronaut [[Frank De Winne]] is attached to the [[Treadmill with Vibration Isolation System|TVIS treadmill]] with bungee cords aboard the International Space Station|alt=Astronaut Frank De Winne is attached to the TVIS treadmill with bungee cords aboard the International Space Station]]
Medical effects of long-term weightlessness include [[muscle atrophy]], deterioration of the skeleton [[spaceflight osteopenia|(osteopenia)]], fluid redistribution, a slowing of the cardiovascular system, decreased production of red blood cells, balance disorders, and a weakening of the immune system. Lesser symptoms include loss of body mass, and puffiness of the face.<ref name="JCB" />

Sleep is disturbed on the ISS regularly due to mission demands, such as incoming or departing ships. Sound levels in the station are unavoidably high; because the atmosphere is unable to [[thermosiphon]], fans are required at all times to allow processing of the atmosphere which would stagnate in the freefall (zero-g) environment.

To prevent some of these adverse [[physiological]] effects, the station is equipped with two treadmills (including the [[Treadmill with Vibration Isolation System|COLBERT]]), and the aRED (advanced Resistive Exercise Device) which enables various weightlifting exercises which add muscle but do nothing for bone density,<ref>{{cite pmid|14600562}}</ref> and a stationary bicycle; each astronaut spends at least two hours per day exercising on the equipment.<ref name="ESALife" /><ref name="NASACrewEquip" /> Astronauts use bungee cords to strap themselves to the treadmill.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/bungee_running.html|accessdate=23 August 2009|title=Bungee Cords Keep Astronauts Grounded While Running|date=16 June 2009|publisher=NASA}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/colbert_feature.html|accessdate=23 August 2009|title=Do Tread on Me|date=19 August 2009|author=Amiko Kauderer|publisher=NASA}}</ref>

===Microbiological environmental hazards===
{{see also|Mir#Microbiological environmental hazards}}
Hazardous moulds which can foul air and water filters may develop aboard space stations. They can produce acids which degrade metal, glass, and rubber. They can also be harmful for the crew health. Microbiological hazards have lead into a development of the [[LOCAD#Portable Test System|LOCAD-PTS]] that can identify common bacteria and moulds faster than standard methods of [[Cell culture|culturing]], which may require a sample to be sent back to Earth.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2007/11may_locad3/|author=Trudy E. Bell|year=2007|title=Preventing "Sick" Spaceships|access-date=March 29, 2015}}</ref> {{As of|2012}}, 76 types of unregulated micro-organisms have been detected on the ISS.<ref>{{cite web|url=http://rt.com/news/iss-bacteria-mir-mutation-765/|title=Mutant space microbes attack ISS: 'Munch' metal, may crack glass |author= |date=April 23, 2012|website=[[RT (TV network)|RT]]|access-date=March 29, 2015}}</ref>

Reduced humidity, paint with mould killing chemical and antiseptic solutions can be used to prevent contamination in space stations. All materials used in the ISS are tested for resistance against fungi.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2000/ast26nov_1/|author=Patrick L. Barry|year=2000|title=Microscopic Stowaways on the ISS|access-date=March 29, 2015}}</ref>

==Threat of orbital debris==
{{Main|Space debris}}
{{Double image|right|SDIO KEW Lexan projectile.jpg|225|Debris-GEO1280.jpg|225|A 7 gram object (shown in centre) shot at 7 km/s (23,000 ft/sec) (the orbital velocity of the ISS) made this 15 cm (5 7/8 in) crater in a solid block of aluminium.|[[Radar]]-trackable objects including debris, with distinct ring of [[Geostationary orbit|geostationary]] satellites||}}
At the low altitudes at which the ISS orbits there is a variety of space debris,<ref>{{cite web|url=http://defensenews.com/blogs/space-symposium/2009/04/03/its-getting-crowded-up-there/#more-155|publisher=Defense News|accessdate=7 October 2009|author=Michael Hoffman|title=National Space Symposium 2009: It's getting crowded up there|date=3 April 2009}}</ref> consisting of many different objects including entire spent rocket stages, defunct satellites, explosion fragments—including materials from [[anti-satellite weapon]] tests, paint flakes, slag from solid rocket motors, and coolant released by [[US-A]] nuclear-powered satellites. These objects, in addition to natural [[micrometeoroid]]s,<ref>{{cite journal|author=F. L. Whipple|year=1949|title=The Theory of Micrometeoroids|journal=Popular Astronomy|volume=57|page=517|bibcode=1949PA.....57..517W}}</ref> are a significant threat. Large objects could destroy the station, but are less of a threat as their orbits can be predicted.<ref name="NSFdebris">{{cite web|publisher=NASASpaceflight.com|accessdate=28 June 2011|date=28 June 2011|author=Chris Bergin|url=http://www.nasaspaceflight.com/2011/06/sts-135-frr-july-8-atlantis-debris-misses-iss/|title=STS-135: FRR sets 8 July Launch Date for Atlantis – Debris misses ISS}}</ref><ref>{{cite web|author=Henry Nahra|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19890016664_1989016664.pdf|title=Effect of Micrometeoroid and Space Debris Impacts on the Space Station Freedom Solar Array Surfaces|date=24–29 April 1989|publisher=NASA|accessdate=7 October 2009}}</ref> Objects too small to be detected by optical and radar instruments, from approximately 1 cm down to microscopic size, number in the trillions. Despite their small size, some of these objects are still a threat because of their [[kinetic energy]] and direction in relation to the station. Spacesuits of spacewalking crew could puncture, causing [[Space exposure|exposure to vacuum]].<ref name=debrisdecomp>{{cite web|title=Space Suit Punctures and Decompression|url=http://www.asi.org/adb/04/03/08/suit-punctures.html|publisher=The Artemis Project|accessdate=20 July 2011}}</ref>

The station's shields and structure are divided between the ROS and the USOS, with completely different designs. On the USOS, a thin aluminium sheet is held apart from the hull, the sheet causes objects to shatter into a cloud before hitting the hull thereby spreading the energy of the impact. On the ROS, a carbon plastic honeycomb screen is spaced from the hull, an aluminium honeycomb screen is spaced from that, with a screen-vacuum thermal insulation covering, and glass cloth over the top. It is about 50% less likely to be punctured,  and crew move to the ROS when the station is under threat. Punctures on the ROS would be contained within the panels which are 70 cm square.

[[File:ISS impact risk.jpg|thumb|left|Example of [[risk management]]: A NASA model showing areas at high risk from impact for the International Space Station.]]

Space debris objects are tracked remotely from the ground, and the station crew can be notified.<ref>{{cite web|url=http://www.orbitaldebris.jsc.nasa.gov/library/EducationPackage.pdf |title=Microsoft PowerPoint – EducationPackage SMALL.ppt |format=PDF |accessdate=1 May 2012}}</ref> This allows for a [[Debris Avoidance Manoeuvre]] (DAM) to be conducted, which uses thrusters on the Russian Orbital Segment to alter the station's orbital altitude, avoiding the debris. DAMs are not uncommon, taking place if computational models show the debris will approach within a certain threat distance. Eight DAMs had been performed prior to March 2009,<ref>{{cite web|url=http://www.newscientist.com/article/dn16777-space-station-may-move-to-dodge-debris.html|title=Space station may move to dodge debris|work=New Scientist|date=16 March 2009|accessdate=20 April 2010|author=Rachel Courtland}}</ref> the first seven between October 1999 and May 2003.<ref name=ODOct08>{{cite journal|url=http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv12i4.pdf|title=ISS Maneuvers to Avoid Russian Fragmentation Debris|publisher=NASA|pages=1&2|journal=Orbital Debris Quarterly News|date=October 2008|accessdate=20 April 2010|volume=12|issue=4}}</ref> Usually the orbit is raised by one or two kilometres by means of an increase in orbital velocity of the order of 1 m/s. Unusually there was a lowering of 1.7 km on 27 August 2008, the first such lowering for 8 years.<ref name=ODOct08 /><ref>{{cite web|url=http://www.esa.int/esaMI/ATV/SEM64X0SAKF_0.html|title=ATV carries out first debris avoidance manoeuvre for the ISS|publisher=ESA|date=28 August 2008|accessdate=26 February 2010}}</ref> There were two DAMs in 2009, on 22 March and 17 July.<ref>{{cite journal|url=http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv14i1.pdf|title=Avoiding satellite collisions in 2009|page=2|journal=Orbital Debris Quarterly News|publisher=NASA|volume=14|date=January 2010|issue=1|accessdate=20 April 2010}}</ref> If a threat from orbital debris is identified too late for a DAM to be safely conducted, the station crew close all the hatches aboard the station and retreat into their [[Soyuz spacecraft]], so that they would be able to evacuate in the event the station was seriously damaged by the debris. This partial station evacuation has occurred on 13 March 2009, 28 June 2011, 24 March 2012 and 16 June 2015.<ref>{{cite news| url=http://www.bbc.co.uk/news/science-environment-17497766| title=ISS crew take to escape capsules in space junk alert| accessdate=24 March 2012 |work=BBC News |date=24 March 2012}}</ref><ref>{{cite news| url=https://blogs.nasa.gov/spacestation/2015/07/16/station-crew-takes-precautions-for-close-pass-of-space-debris/| title=Station Crew Takes Precautions for Close Pass of Space Debris| accessdate=16 June 2015 |work=NASA Blog |date=16 June 2015}}</ref>
Ballistic panels, also called micrometeorite shielding, are incorporated into the station to protect pressurised sections and critical systems. The type and thickness of these panels varies depending upon their predicted exposure to damage.

==End of mission==
[[File:Jules Verne Automated Transfer Vehicle re-enters Earth's atmosphere.jpg|thumb|right|Many ISS resupply spacecraft have already undergone [[Atmospheric entry|atmospheric re-entry]], such as [[Jules Verne ATV]]]]
According to a 2009 report, [[S.P. Korolev Rocket and Space Corporation Energia|Space Corporation Energia]] is considering methods to remove from the station some modules of the Russian Orbital Segment when the end of mission is reached and use them as a basis for a new station, known as the [[Orbital Piloted Assembly and Experiment Complex]] (OPSEK). The modules under consideration for removal from the current ISS include the [[Multipurpose Laboratory Module]] (MLM), currently scheduled to be launched in 2017, with other Russian modules which are currently planned to be attached to the MLM afterwards. Neither the MLM nor any additional modules attached to it would have reached the end of their useful lives in 2016 or 2020. The report presents a statement from an unnamed Russian engineer who believes that, based on the experience from ''Mir'', a thirty-year life should be possible, except for micrometeorite damage, because the Russian modules have been built with on-orbit refurbishment in mind.<ref name="RussiaSave">{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8064060.stm|title=Russia 'to save its ISS modules'|work=BBC News|date=22 May 2009|accessdate=23 May 2009|author=Anatoly Zak}}</ref>

According to the [[Outer Space Treaty]] the United States and Russia are legally responsible for all modules they have launched.<ref>[http://www.unoosa.org/pdf/publications/STSPACE11E.pdf United Nations Treaties and Principles on Outer Space]. (PDF). United Nations. New York. 2002. ISBN 92-1-100900-6. Retrieved 8 October 2011.</ref> In ISS planning, NASA examined options including returning the station to Earth via shuttle missions (deemed too expensive, as the station (USOS) is not designed for disassembly and this would require at least 27 shuttle missions<ref>{{cite book|url=http://search.nap.edu/openbook.php?record_id=9794&page=28|isbn=0-309-06938-6|publisher=National Academies Press|year=2000|pages=28–30|author=Thomas Kelly|title=Engineering Challenges to the Long-Term Operation of the International Space Station|accessdate=12 July 2011}}</ref>), natural orbital decay with random reentry similar to [[Skylab]], boosting the station to a higher altitude (which would delay reentry) and a controlled targeted de-orbit to a remote ocean area.<ref name=ISSEIS>{{cite web|title = Tier 2 EIS for ISS|publisher = NASA|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960053133_1996092350.pdf|accessdate=12 July 2011 }}</ref>

The technical feasibility of a controlled targeted deorbit into a remote ocean was found to be possible only with Russia's assistance.<ref name=ISSEIS /> The Russian Space Agency has experience from de-orbiting the [[Salyut 4]], [[Salyut 5|5]], [[Salyut 6|6]], [[Salyut 7|7]] and [[Mir]] space stations; NASA's first intentional controlled de-orbit of a satellite (the [[Compton Gamma Ray Observatory]]) occurred in 2000.<ref>{{cite web|title=Entry Debris Field estimation methods and application to Compton Gamma Ray Observatory|publisher=Mission Operations Directorate, NASA Johnson Space Center|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010084992_2001127597.pdf|accessdate=12 July 2011}}</ref> As of late 2010, the preferred plan is to use a slightly modified Progress spacecraft to de-orbit the ISS.<ref name=deo>{{cite web|url=http://www.nasa.gov/pdf/578543main_asap_eol_plan_2010_101020.pdf|title=ISS End-of-Life Disposal Plan|last=Suffredini|first=Michael|date=October 2010|publisher=NASA|accessdate=7 March 2012}}</ref> This plan was seen as the simplest, most cost efficient one with the highest margin.<ref name=deo /> [[Skylab]], the only space station built and launched entirely by the US, decayed from orbit slowly over 5 years, and no attempt was made to de-orbit the station using a [[Atmospheric entry|deorbital burn]]. Remains of Skylab hit populated areas of [[Esperance, Western Australia]]<ref name="debris">{{cite web|url=http://www.eclipsetours.com/sat/debris.html|accessdate=28 May 2011|title=Paul Maley's (Skylab spaceflight controller) Space Debris Page}}</ref> without injuries or loss of life.

The [[Exploration Gateway Platform]], a discussion by NASA and Boeing at the end of 2011, suggested using leftover USOS hardware and '[[Zvezda (ISS module)|Zvezda]] 2' {{sic}} as a refuelling depot and servicing station located at one of the Earth Moon [[Lagrange points]], L1 or L2. The entire USOS cannot be reused and will be discarded, but some other Russian modules are planned to be reused. [[Nauka (ISS module)|Nauka]], the [[Uzlovoy Module|Node module]], two science power platforms and Rassvet, launched between 2010 and 2015 and joined to the ROS may be separated to form [[OPSEK]].<ref>{{cite web|url=http://www.russianspaceweb.com/iss_dc.html|title=DC-1 and MIM-2|publisher=Russianspaceweb.com|accessdate=12 July 2011}}</ref> The [[Nauka (ISS module)|Nauka module]] of the ISS will be used in the station, whose main goal is supporting manned deep space exploration. OPSEK will orbit at a higher inclination of 71 degrees, allowing observation to and from all of the Russian Federation.

In February 2015, Roscosmos announced that it would remain a part of the international space station program until 2024.<ref name=sn20150225>{{cite news |last1=de Selding|first1=Peter B. |title=Russia — and Its Modules — To Part Ways with ISS in 2024 |url=http://spacenews.com/russia-and-its-modules-to-part-ways-with-iss-in-2024/ |accessdate=26 February 2015 |work=Space News |date=25 February 2015}}</ref> Nine months earlier—in response to US sanctions against Russia over the [[2014 Crimean crisis|conflict in the Crimea]]—Russian Deputy Prime Minister [[Dmitry Rogozin]] had stated that Russia would reject a US request to prolong the orbiting station's use beyond 2020, and would only supply rocket engines to the US for non-military satellite launches.<ref>{{cite web|url=http://www.telegraph.co.uk/news/worldnews/europe/russia/10828964/Russia-to-ban-US-from-using-Space-Station-over-Ukraine-sanctions.html|title=Russia to ban US from using Space Station over Ukraine sanctions|agency=Reuters|work=The Telegraph|date=13 May 2014|accessdate=14 May 2014}}</ref>

A proposed modification that would allow some of the ISS American and European segments to be reused would be to attach a [[VASIMR]] drive module to the vacated Node with its own onboard power source. It would allow long term reliability testing of the concept for less cost than building a dedicated space station from scratch.<ref name="nbcnews">{{cite web|url=http://www.nbcnews.com/id/48260759/ns/technology_and_science-space/#.U4LaQCjFBdg|title=From the earth to the moon, and then beyond - Technology & science - Space | NBC News|publisher=nbcnews.com|accessdate=27 May 2014}}</ref>

On March 28, 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS.<ref name=":0"/><ref name=":1"/> [[Igor Komarov]], the head of Russia's Roscosmos, made the announcement with NASA administrator Charles Bolden at his side. Komarov said "Roscosmos together with NASA will work on the programme of a future orbital station," "We agreed that the group of countries taking part in the ISS project will work on the future project of a new orbital station," "The first step is that the ISS will operate until 2024," and that Roscosmos and NASA "do not rule out that the station's flight could be extended,"<ref>{{cite web|url=http://www.spacedaily.com/reports/Russia_announces_plan_to_build_new_space_station_with_NASA_999.html|title=Russia announces plan to build new space station with NASA|work=spacedaily.com}}</ref> In a statement provided to SpaceNews March 28, NASA spokesman David Weaver said the agency appreciated the Russian commitment to extending the ISS, but did not confirm any plans for a future space station.<ref name="no plans" />

==Cost==
The ISS is arguably the most expensive single item ever constructed.<ref>{{cite web|author=Zidbits |url=http://zidbits.com/?p=19 |title=What Is The Most Expensive Object Ever Built? |publisher=Zidbits.com |date=6 November 2010 |accessdate=22 October 2013}}</ref> In 2010 the cost was expected to be $150 billion. It includes NASA's budget of $58.7 billion (inflation unadjusted) for the station from 1985 to 2015 ($72.4 billion in 2010 dollars), Russia's $12 billion, Europe's $5 billion, Japan's $5 billion, Canada's $2 billion, and the cost of 36 shuttle flights to build the station; estimated at $1.4 billion each, or $50.4 billion total. Assuming 20,000 person-days of use from 2000 to 2015 by two to six-person crews, each person-day would cost $7.5 million, less than half the inflation adjusted $19.6 million ($5.5 million before inflation) per person-day of Skylab.<ref name="lafleur20100308">{{cite news | url=http://www.thespacereview.com/article/1579/1 | title=Costs of US piloted programs | work=The Space Review | date=8 March 2010 | accessdate=18 February 2012 | author=Lafleur, Claude}} See author correction in comments.</ref>

==International co-operation==
[[File:ISS Agreements.jpg|thumb|right|upright|Dated 29 January 1998]]
{{Main|Politics of the International Space Station|International Space Station program}}
;Participating countries
{{columns-list|colwidth=20em|

* '''{{flagcountry|Canada}}'''
* '''{{flagcountry|Japan}}'''
* '''{{flagcountry|Russia}}'''
* '''{{flagcountry|United States}}'''
* [[File:ESA logo simple.svg|15x15px]] '''[[European Space Agency]]'''
** {{flagcountry|Austria}}
** {{flagcountry|Belgium}}
** {{flagcountry|Czech Republic}}
** {{flagcountry|Denmark}}
** {{flagcountry|Estonia}}
** {{flagcountry|Finland}}
** {{flagcountry|France}}
** {{flagcountry|Germany}}
** {{flagcountry|Greece}}
** {{flagcountry|Hungary}}
** {{flagcountry|Ireland}}
** {{flagcountry|Italy}}
** {{flagcountry|Luxembourg}}
** {{flagcountry|Netherlands}}
** {{flagcountry|Norway}}
** {{flagcountry|Poland}}
** {{flagcountry|Portugal}}
** {{flagcountry|Romania}}
** {{flagcountry|Spain}}
** {{flagcountry|Sweden}}
** {{flagcountry|Switzerland}}
** {{flagcountry|United Kingdom}}
}}

==Sightings from Earth==

===Naked eye===
The ISS is visible to the [[naked eye]] as a slow-moving, bright white dot due to reflected sunlight, and can be seen in the hours after sunset and before sunrise when the station remains sunlit but the ground and sky are dark.<ref name="Price2005">{{cite book |title=The Backyard Stargazer: An Absolute Beginner's Guide to Skywatching With and Without a Telescope |publisher=Quarry Books |location=Gloucester, MA |first=Pat |last=Price |page=140 |year=2005 |isbn=1-59253-148-2}}</ref> The ISS takes about ten minutes to move from one horizon to another, and will only be visible part of that time due to moving into or out of the Earth's shadow. Because of the size of its reflective surface area, the ISS is the brightest man-made object in the sky excluding [[Satellite flare|flares]], with an approximate maximum [[Apparent magnitude|magnitude of −4]] when overhead, similar to Venus. The ISS, like many satellites including the [[Iridium constellation]], can also produce flares of up to 8 or 16 times the brightness of Venus as sunlight glints off reflective surfaces.<ref>{{cite web|url=http://www.calsky.com/cs.cgi/Satellites/8 |title=Artificial Satellites > (Iridium) Flares |publisher=Calsky.com |accessdate=1 May 2012}}</ref><ref name="haydenplanetarium">{{cite web|url=http://www.amnh.org/our-research/hayden-planetarium/blog/how-to-spot-the-international-space-station-and-other-satellites |title=How to Spot the International Space Station (and other satellites) |publisher=Hayden Planetarium |accessdate=12 July 2011}}</ref> The ISS is also visible during broad daylight conditions, albeit with a great deal more effort.

Tools are provided by a number of websites such as [[Heavens-Above]] (see [[#Live viewing|''Live viewing'']] below) as well as [[smartphone]] applications that use the known [[ephemeris|orbital data]] and the observer's longitude and latitude to predict when the ISS will be visible (weather permitting), where the station will appear to rise to the observer, the altitude above the horizon it will reach and the duration of the pass before the station disappears to the observer either by setting below the horizon or entering into Earth's shadow.<ref name="see">{{cite web|url=http://spaceflight.nasa.gov/realdata/sightings/index.html|title=International Space Station Sighting Opportunities|accessdate=28 January 2009|publisher=NASA|date=2 July 2008|author=NASA}}</ref><ref>{{cite web|url=http://www.heavens-above.com/satinfo.aspx?satid=25544&lat=0&lng=0&loc=Unspecified&alt=0&tz=CET|title=ISS – Information|publisher=Heavens-Above.com|accessdate=8 July 2010}}</ref><ref>{{cite journal|author=Harold F. Weaver|title=The Visibility of Stars Without Optical Aid|journal=Publications of the Astronomical Society of the Pacific|volume=59|issue=350|year=1947|doi=10.1086/125956 }}</ref><ref name="daytime visibility">{{cite web|url=http://spaceweather.com/archive.php?view=1&day=05&month=06&year=2009|title=ISS visible during the daytime|accessdate=5 June 2009|work=Spaceweather.com|date=5 June 2009}}</ref>

{{Double image|right|Isshtv120090917200858nm.jpg|223|ISS 2008-01-10.jpg|230|The ISS and HTV photographed using a telescope-mounted camera by [[Ralf Vandebergh]]|A time exposure of a station pass|A fuzzy image of the ISS set against a black background, with a smaller, cylindrical object visible to the left of the station.|A view of a dark blue, starry sky with a white line visible from the bottom-left to the top-right of the image. A tree is visible to the bottom right.}}

In November 2012 NASA launched its 'Spot the Station' service, which sends people text and email alerts when the station is due to fly above their town.<ref>{{cite news| url= http://www.3news.co.nz/Get-notified-when-the-International-Space-Station-is-in-your-area/tabid/1160/articleID/275612/Default.aspx|work=3 News NZ |title= Get notified when the International Space Station is in your area| date=6 November 2012}}</ref>

The station is visible from 95% of the inhabited land on Earth, but is not visible from extreme northern or southern latitudes.<ref name="MCC Answer" />

===Astrophotography=== 
Using a telescope mounted camera to photograph the station is a popular hobby for astronomers, <ref>{{cite web|url=http://www.hobbyspace.com/SatWatching/ |title=Satellite Watching |publisher=HobbySpace |accessdate=1 May 2012}}</ref> whilst using a mounted camera to photograph the Earth and stars is a popular hobby for crew.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2003/24mar_noseprints/ |title=Space StationAstrophotography – NASA Science |publisher=Science.nasa.gov |date=24 March 2003 |accessdate=1 May 2012}}</ref> The use of a telescope or binoculars allows viewing of the ISS during daylight hours.<ref>{{cite web|url=http://www.zmescience.com/space/video-the-iss-and-atlantis-shuttle-as-seen-in-broad-daylight/ |title=[VIDEO] The ISS and Atlantis shuttle as seen in broad daylight |publisher=Zmescience.com |date=20 July 2011 |accessdate=1 May 2012}}</ref>

Parisian engineer and astrophotographer Thierry Legault, known for his photos of spaceships crossing the Sun (called [[occultation]]), travelled to Oman in 2011, to photograph the Sun, moon and space station all lined up.<ref>{{cite news| url=http://www.wired.com/2011/01/double-eclipse/ | work=Wired | first=Lisa | last=Grossman | title=Moon and Space Station Eclipse the Sun}}</ref> Legault, who received the Marius Jacquemetton award from the [[Société astronomique de France]] in 1999, and other hobbyists, use websites that predict when the ISS will pass in front of the Sun or Moon and from what location those passes will be visible.

==See also==
{{Wikipedia books|International Space Station}}
{{Portal|Spaceflight|Space}}
* [[Center for the Advancement of Science in Space]] - operates the US National Laboratory on the ISS
* [[List of space stations]]
* [[Origins of the International Space Station]]
* [[Space architecture]]

==Gallery==
[[File:ISS and Endeavour seen from the Soyuz TMA-20 spacecraft 14.jpg|thumb|left|550px|<center>International Space Station docked with ''Endeavour'' and ''Johannes Kepler'' ]]
{{-}}

==Notes==
{{Reflist|group="note"}}

==References==
{{Reflist|colwidth=25em}}

==External links==
{{Sister project links|wikt=no|n=Category:International Space Station|voy=Space}}

===Agency ISS websites===
{{divcol|20em}}
* {{flagicon|Canada}} [http://www.asc-csa.gc.ca/eng/iss/default.asp Canadian Space Agency]
* [[File:Not the esa logo.png]] [http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station European Space Agency]
* {{flagicon|France}} [http://www.cnes.fr/web/CNES-en/1422-iss-the-international-space-station.php Centre national d'études spatiales (National Centre for Space Studies)]
* {{flagicon|Germany}} [http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10300 German Aerospace Centre]
* {{flagicon|Italy}} [http://www.asi.it/en/flash_en/living Italian Space Agency]
* {{flagicon|Japan}} [http://www.jaxa.jp/projects/iss_human/index_e.html Japan Aerospace Exploration Agency]
* {{flagicon|Russia}} [http://www.energia.ru/eng/iss/iss.html S.P. Korolev Rocket and Space Corporation Energia]
* {{flagicon|Russia}} [http://www.roscosmos.ru/ Russian Federal Space Agency]
* {{flagicon|USA}} [http://www.nasa.gov/mission_pages/station/main/ National Aeronautics and Space Administration]
{{Div col end}}

===Research===
* [https://blogs.nasa.gov/spacestation/ NASA: Daily ISS Reports]
* [http://www.nasa.gov/mission_pages/station/science/index.html NASA: Station Science]
* [http://www.esa.int/Our_Activities/Human_Spaceflight/Columbus ESA: Columbus]
* [http://www.energia.ru/en/iss/researches/iss-researches.html RSC Energia: Science Research on ISS Russian Segment]

===Live viewing===
{{See also|List of satellite pass predictors}}
* [http://www.ustream.tv/channel/live-iss-stream Live ISS webcam] by NASA at uStream.tv
* [http://heavens-above.com/orbit.aspx?satid=25544 Real-time position] at Heavens-above.com
* [http://www.n2yo.com/?s=25544 Real-time position] at N2YO.com
* [http://wheretheiss.at/ Real-time position] at WheretheISS.at

===Multimedia===
* [http://www.nasa.gov/externalflash/ISSRG/index.html Interactive reference guide] at NASA.gov
* [http://spaceflight.nasa.gov/gallery/images/station/ Image gallery search page] at NASA.gov
* [http://i.usatoday.net/tech/graphics/iss_timeline/flash.htm Assembly sequence animation] by ''USA Today'' and NASA
* [https://www.youtube.com/watch?v=doN4t5NKW-k ISS tour with Sunita Williams] by NASA at YouTube.com
* [https://www.youtube.com/watch?v=QF2w2Dx_QMs ISS tour with André Kuipers] by ESA at YouTube.com
* [http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station/Highlights/International_Space_Station_panoramic_tour ISS photo tour with Samantha Cristoforetti] by ESA
* [https://www.youtube.com/watch?v=vMmcLmu3V1k ''The Future of Hope'', Kibo module documentary] by JAXA at YouTube.com
* [https://www.youtube.com/playlist?list=PLbyvawxScNbsoD_tGlw8kWCw3S5htiVKZ Journey to the ISS] by ESA at YouTube.com

{{ISS modules}}
{{International Space Station}}
{{Manned ISS flight}}
{{Unmanned ISS resupply flights}}
{{People currently in space}}
{{Space stations}}
{{US manned space programs}}
{{Russian manned space programs}}
{{Spaceflight}}
{{Orbital launches in 1998}}

{{Orbit|satcat|25544|hide}}{{Orbit|datasource|HN}}
{{active editnotice}}

{{Authority control}}
[[Category:International Space Station| ]]
[[Category:Artificial satellites orbiting Earth]]
[[Category:Populated places established in 1998]]
[[Category:United States Department of Energy national laboratories]]
[[Category:Spacecraft launched in 1998]]
[[Category:1998 in spaceflight]]
[[Category:Articles containing video clips]]

User:WikipediaTutorials/sandbox

2015-08-05T03:14:55Z

WikipediaTutorials: added citation

{{User sandbox}}

{{redirect|ISS}}
{{Use British English|date=December 2013}}
{{Use dmy dates|date=February 2015}}
{{Infobox space station
| station = International Space Station
| station_image =International Space Station after undocking of STS-132.jpg
| station_image_alt = A rearward view of the International Space Station backdropped by the limb of the Earth. In view are the station's four large, gold-coloured solar array wings, two on either side of the station, mounted to a central truss structure. Further along the truss are six large, white radiators, three next to each pair of arrays. In between the solar arrays and radiators is a cluster of pressurised modules arranged in an elongated T shape, also attached to the truss. A set of blue solar arrays are mounted to the module at the aft end of the cluster.
| station_image_size = 300px
| extra_image_size = 300px
| extra_image_caption = The International Space Station on 23 May 2010 as seen from the departing {{OV|104}} during [[STS-132]].
| sign = ''Alpha'', ''Station''
| crew = Fully crewed: 6 Currently aboard: 6 ([[Expedition 44]])
| launch = 20 November 1998
| launch_pad = {{nowrap|[[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|1/5]] and [[Baikonur Cosmodrome Site 81|81/23]] [[Kennedy Space Center|Kennedy]] [[Kennedy Space Center Launch Complex 39|LC-39]]}}
| mass = Approximately {{convert|450000|kg|lbs|abbr=on}}
| length = {{convert|72.8|m|ft|abbr=on}}
| width = {{convert|108.5|m|ft|abbr=on}}
| height = c. 20 m (c. 66 ft) nadir–zenith, arrays forward–aft (27 November 2009){{Update after|2010|05|23|reason=MRM-1 & MRM-2}}
| volume = {{convert|916|m3|abbr=on}} (3 November 2014)
| pressure = 101.3 [[pascal (unit)|kPa]] (29.91 [[inch of mercury|inHg]], 1 [[Atmosphere (unit)|atm]])
| apogee = {{convert|{{Orbit|apogee|416}}|km|abbr=on}} [[Above mean sea level|AMSL]]{{Orbit|ref|<ref name="heavens-above">{{cite web|url=http://www.heavens-above.com/orbit.aspx?satid=25544|title=ISS - Orbit|last=Peat|first=Chris|publisher=Heavens-Above|date=25 January 2015|accessdate=25 January 2015}}</ref>}}
| perigee = {{convert|{{Orbit|perigee|409}}|km|abbr=on}} [[Above mean sea level|AMSL]]{{Orbit|ref|<ref name="heavens-above"/>}}
| inclination = {{Orbit|inclination|51.65}} [[degree (angle)|degrees]]{{Orbit|ref|<ref name="heavens-above"/>}}
| speed = {{convert|{{Orbit|speed at epoch|7.66}}|km/s|km/h mph}}{{Orbit|ref|<ref name="heavens-above"/>}}
| period = {{Orbit|period|92.69}} minutes{{Orbit|ref|<ref name="heavens-above"/>}}
| in_orbit = {{age in days|1998|11|20}} ({{date||dmy}})
| occupied = {{age in days|2000|11|02}} ({{date||dmy}})
| orbits = {{Orbit|orbits|92579}}{{Orbit|ref|<ref name="heavens-above"/>}}
| orbit_epoch = {{Orbit|epoch|25 January 2015}}{{Orbit|ref|<ref name="heavens-above"/>}}
| decay = 2 km/month
| NSSDC_ID = 1998-067A
| as_of = 9 March 2011 (unless noted otherwise)
| stats_ref =<ref name="heavens-above" /><ref name="ISStD" /><ref name="OnOrbit" /><ref>{{cite web|format=PDF|url=http://www.nasa.gov/pdf/451029main_sts132_press_kit.pdf|publisher=NASA|accessdate=19 June 2010|title=STS-132 Press Kit|date=7 May 2010}}</ref><ref>{{cite web|url=http://www.nasa.gov/pdf/521138main_fd04_ep.pdf|publisher=NASA|date=27 February 2011|accessdate=27 February 2011|title=STS-133 FD 04 Execute Package}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html|publisher=NASA|date=3 November 2014|accessdate=5 December 2014|title=NASA — Facts and Figures — International Space Station}}</ref>
| configuration_image = ISS configuration 2011-05 en.svg
| configuration_alt = The components of the ISS in an exploded diagram, with modules on-orbit highlighted in orange, and those still awaiting launch in blue or pink
| configuration_caption = Station elements {{As of|2011|12|lc=on}}, but missing ''Pirs'' ([[exploded view]])
| configuration_size = 300px
}}

The '''International Space Station''' ('''ISS''') is a [[space station]], or a habitable [[satellite|artificial satellite]], in [[low Earth orbit]]. Its first component launched into orbit in 1998, and the ISS is now the largest artificial body in orbit and can often be seen with the [[naked eye]] from Earth.<ref>{{cite web|title= Central Research Institute for Machine Building (FGUP TSNIIMASH) Control of manned and unmanned space vehicles from Mission Control Centre Moscow |publisher= Russian Federal Space Agency |url=ftp://130.206.92.88/Espacio/Mesa%20Redonda%205%20-%20R3%20-%20TSNIIMASH%20-%20V%20M%20IVANOV.pdf| accessdate=26 September 2011}}</ref><ref>{{cite web|url=http://spaceflight.nasa.gov/realdata/sightings/help.html |title=NASA Sightings Help Page |publisher=Spaceflight.nasa.gov |date=30 November 2011 |accessdate=1 May 2012}}</ref> The ISS consists of pressurised modules, external trusses, [[solar arrays]] and other components. ISS components have been launched by Russian [[Proton (rocket)|Proton]] and [[Soyuz (rocket family)|Soyuz]] rockets as well as American [[Space Shuttle]]s.<ref name="ISSBook">{{cite book|isbn=978-0-387-78144-0|date=17 June 2008|publisher=Springer-Praxis|author=John E. Catchpole|title=The International Space Station: Building for the Future}}</ref>

The ISS serves as a [[microgravity]] and [[space environment]] research laboratory in which crew members conduct experiments in [[biology]], [[human biology]], [[physics]], [[astronomy]], [[meteorology]] and [[Scientific research on the ISS|other fields]].<ref name="ISS overview">{{cite web|url=http://www.shuttlepresskit.com/ISS_OVR/index.htm|title=International Space Station Overview|publisher=ShuttlePressKit.com|date=3 June 1999|accessdate=17 February 2009}}</ref><ref name="NASA Fields of Research">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/A-fieldsresearch/index.html|archiveurl=https://web.archive.org/web/20080123150641/http://pdlprod3.hosc.msfc.nasa.gov/A-fieldsresearch/index.html|archivedate=25 March 2008|title=Fields of Research|date=26 June 2007|publisher = NASA}}</ref><ref name="NASA ISS Goals">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/B-gettingonboard/index.html|archiveurl=https://web.archive.org/web/20071208091537/http://pdlprod3.hosc.msfc.nasa.gov/B-gettingonboard/index.html|archivedate=8 December 2007| title = Getting on Board|date = 26 June 2007| publisher=NASA}}</ref> The station is suited for the testing of spacecraft systems and equipment required for missions to the Moon and Mars.<ref name="ResProg">{{cite web|url=http://spaceflightsystems.grc.nasa.gov/Advanced/ISSResearch/|title=ISS Research Program|publisher=NASA|accessdate=27 February 2009}}{{dead link|date=August 2011}}</ref> The ISS [[Orbital station-keeping|maintains an orbit with an altitude]] of between {{convert|330|and|435|km|mi|0|abbr=on}} by means of reboost manoeuvres using the engines of the [[Zvezda (ISS module)|Zvezda module]] or visiting spacecraft. It completes {{Orbit|daily orbits|15.54}} orbits per day.<ref name="tracking" />

ISS is the ninth space station to be inhabited by crews, following the Soviet and later Russian [[Salyut]], [[Almaz]], and [[Mir]] stations as well as [[Skylab]] from the US. The station has been continuously occupied for {{age in years and days|2 Nov 2000|sep=and}} since the arrival of [[Expedition 1]] on 2 November 2000. This is the longest continuous human presence in space, having surpassed the previous record of {{age in years and days|5 Sep 1989|28 Aug 1999|sep=and}} held by Mir. The station is serviced by a variety of visiting spacecraft: [[Soyuz (spacecraft)|Soyuz]], [[Progress (spacecraft)|Progress]], the [[Automated Transfer Vehicle]], the [[H-II Transfer Vehicle]],<ref name="ISSRG" /> [[Dragon (spacecraft)|Dragon]], and [[Cygnus (spacecraft)|Cygnus]]. It has been visited by astronauts, cosmonauts and space tourists from [[List of International Space Station visitors|15 different nations]].<ref name="10th">{{cite web|url=http://www.nasa.gov/mission_pages/station/main/10th_anniversary.html|title=Nations Around the World Mark 10th Anniversary of International Space Station|publisher=NASA|date=17 November 2008|accessdate=6 March 2009}}</ref>

After the US Space Shuttle program ended in 2011, Soyuz rockets became the only provider of transport for astronauts at the International Space Station, and Dragon became the only provider of bulk [[downmass|cargo-return-to-Earth]] services (downmass capability of Soyuz capsules is very limited).

The [[International Space Station program|ISS programme]] is a joint project among five participating space agencies: [[NASA]], [[Russian Federal Space Agency|Roscosmos]], [[Japan Aerospace Exploration Agency|JAXA]], [[European Space Agency|ESA]], and [[Canadian Space Agency|CSA]].<ref name="ISSRG" /><ref name="PartStates">{{cite web|url=http://www.esa.int/esaHS/partstates.html|title=Human Spaceflight and Exploration—European Participating States|accessdate=17 January 2009|publisher=European Space Agency (ESA)|year=2009}}</ref> The ownership and use of the space station is established by intergovernmental treaties and agreements.<ref name="ESA-IGA">{{cite web|url=http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station/International_Space_Station_legal_framework|title=International Space Station legal framework|publisher=European Space Agency (ESA)|accessdate=21 February 2015|date=19 November 2013}}</ref> The station is divided into two sections, the [[Russian Orbital Segment]] (ROS) and the [[US Orbital Segment|United States Orbital Segment]] (USOS), which is shared by many nations. {{asof|2014|January}}, the American portion of ISS was funded until 2024.<ref>{{cite web|url=http://www.washingtonpost.com/national/health-science/nasa-space-station-operation-extended-by-obama-until-2024-at-least/2014/01/08/9819d5c8-788e-11e3-8963-b4b654bcc9b2_story.html|title=NASA: International space station operation extended by Obama until at least 2024|last=Achenbach|first=Joel|publisher=washingtonpost.com|date=8 January 2014|accessdate=8 January 2014}}</ref><ref>{{cite web|url=http://spaceflightnow.com/news/n1003/11station/|title=Space station partners set 2028 as certification goal|last=Clark|first=Stephen|date=11 March 2010|publisher=Spaceflight Now|accessdate=1 June 2011}}</ref><ref>{{cite news| url=http://www.cbc.ca/news/technology/story/2012/02/29/science-international-space-station.html | work=CBC News | title=Canada's space station commitment renewed | date=29 February 2012}}</ref> Roscosmos has endorsed the continued operation of ISS through 2024,<ref name="sn20150225"/> but have proposed using elements of the Russian Orbital Segment to construct a new Russian space station called [[Orbital Piloted Assembly and Experiment Complex|OPSEK]].<ref name="moscow20141117">{{cite news |url=http://www.themoscowtimes.com/business/article/russia-may-be-planning-national-space-station-to-replace-iss/511299.html |title=Russia May Be Planning National Space Station to Replace ISS |work=The Moscow Times |first=Matthew |last=Bodner |date=17 November 2014 |accessdate=3 March 2015}}</ref>

On March 28, 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS.<ref name=":0">{{cite web|url= http://www.independent.co.uk/news/science/russia-and-the-us-will-build-a-new-space-station-together-10140890.html|title=Russia and the US will build a new space station together |publisher=The Independent|date=28 March 2015}}</ref><ref name=":1">{{Cite news|url = http://rt.com/news/244797-russia-us-new-space-station/|title = Russia & US agree to build new space station after ISS, work on joint Mars project|last = |first = |date = March 28, 2015|work = RT|access-date = March 28, 2015}}</ref> NASA later issued a guarded statement expressing thanks for Russia's interest in future cooperation in space exploration, but fell short of confirming the Russian announcement.<ref>{{Cite news|url = http://www.engadget.com/2015/03/28/nasa-is-working-with-russia-on-a-new-space-station/|title = NASA is working with Russia on a new space station (update: not quite) |last = Moon|first = Mariella|date = 28 March 2015|work = Engadget|access-date = 29 March 2015}}</ref><ref name="no plans">{{cite web|url=http://spacenews.com/nasa-says-no-plans-for-iss-replacement-with-russia/|title=NASA Says No Plans for ISS Replacement with Russia|date=March 28, 2015|author=Jeff Foust|publisher=SpaceNews}}</ref>

{{TOC limit|limit=3}}

==Purpose==
[[File:STS-129 Zvezda sunrise.jpg|thumb|Sunrise at ''Zvezda'']]
[[File:STS-134 EVA4 view to the Space Shuttle Endeavour.jpg|thumb|right|Fisheye view of several labs]]
According to the original Memorandum of Understanding between NASA and Rosaviakosmos, the International Space Station was intended to be a laboratory, observatory and factory in [[low Earth orbit]]. It was also planned to provide transportation, maintenance, and act as a staging base for possible future missions to the Moon, Mars and asteroids.<ref name="RSA-MOU">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/nasa_rsa.html|title=Memorandum of Understanding Between the National Aeronautics and Space Administration of the United States of America and the Russian Space Agency Concerning Cooperation on the Civil International Space Station|publisher=NASA|accessdate=19 April 2009|date=29 January 1998}}</ref> In the 2010 United States National Space Policy, the ISS was given additional roles of serving commercial, diplomatic<ref>{{cite journal|last=Payette|first=Julie|title=Research and Diplomacy 350 Kilometers above the Earth: Lessons from the International Space Station|journal=Science & Diplomacy|date=10 December 2012|volume=1|issue=4|url=http://www.sciencediplomacy.org/article/2012/research-and-diplomacy-350-kilometers-above-earth}}</ref> and educational purposes.<ref name=USNSP>{{cite web|title=National Space Policy of the United States of America|url=http://www.whitehouse.gov/sites/default/files/national_space_policy_6-28-10.pdf|publisher=White House; USA Federal government|accessdate=20 July 2011}}</ref>

===Scientific research===
{{Main|Scientific research on the ISS|l1=Scientific research on the ISS}}
The ISS provides a platform to conduct scientific research. Small unmanned spacecraft can provide platforms for zero gravity and exposure to space, but space stations offer a long term environment where studies can be performed potentially for decades, combined with ready access by human researchers over periods that exceed the capabilities of manned spacecraft.<ref name="10th" /><ref name="Worldbook at NASA" />

The Station simplifies individual experiments by eliminating the need for separate rocket launches and research staff. The wide variety of research fields include [[astrobiology]], [[astronomy]], [[Zero g#Health effects of weightlessness|human research]] including [[space medicine]] and [[life science]]s, [[physical science]]s, [[materials science]], [[space weather]], and weather on Earth ([[meteorology]]).<ref name="ISS overview" /><ref name="NASA Fields of Research" /><ref name="NASA ISS Goals" /><ref>{{cite web|url=http://www.isas.jaxa.jp/e/forefront/2009/ueno/index.shtml|title=Monitor of All-sky X-ray Image (MAXI)|year=2008|publisher=JAXA|accessdate=12 March 2011}}</ref><ref>[http://www.spaceref.com/news/viewpr.html?pid=33007 ESA via SPACEREF] "SOLAR: three years observing and ready for solar maximum", 14 March 2011</ref> Scientists on Earth have access to the crew's data and can modify experiments or launch new ones, which are benefits generally unavailable on unmanned spacecraft.<ref name="Worldbook at NASA" /> Crews fly [[List of International Space Station expeditions|expeditions]] of several months duration, providing approximately 160-man-hours per week of labour with a crew of 6.<ref name="ISS overview"/><ref name="Science in School">{{cite web|url=http://www.scienceinschool.org/2008/issue10/iss|title=The International Space Station: life in space|publisher=Science in School|date=10 December 2008|accessdate=17 February 2009}}</ref>

To detect dark matter and answer other fundamental questions about our universe, engineers and scientists from all over the world built the [[Alpha Magnetic Spectrometer]] (AMS), which NASA compares to the [[Hubble space telescope]], and says could not be accommodated on a free flying satellite platform due in part to its power requirements and data bandwidth needs.<ref>[http://www.nasa.gov/mission_pages/shuttle/main/amsprocessing.html NASA – AMS to Focus on Invisible Universe]. Nasa.gov (18 March 2011). Retrieved 8 October 2011.</ref><ref>[http://science.nasa.gov/science-news/science-at-nasa/2009/14aug_ams/ In Search of Antimatter Galaxies – NASA Science]. ''Science''.nasa.gov (16 May 2011). Retrieved 8 October 2011.</ref> On 3 April 2013, [[NASA]] scientists reported that hints of [[dark matter]] may have been detected by the Alpha Magnetic Spectrometer.<ref name="APS-20130403">{{cite journal |authors=Aguilar, M. et al. (AMS Collaboration) |title=First Result from the Alpha Magnetic Spectrometer on the International Space Station: Precision Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–350 GeV|url=http://prl.aps.org/abstract/PRL/v110/i14/e141102 |date=3 April 2013 |journal=[[Physical Review Letters]]|accessdate=3 April 2013 |doi=10.1103/PhysRevLett.110.141102 }}</ref><ref name="AMS-20130403">{{cite web |author=Staff |title=First Result from the Alpha Magnetic Spectrometer Experiment|url=http://www.ams02.org/2013/04/first-results-from-the-alpha-magnetic-spectrometer-ams-experiment/ |date=3 April 2013 |work=AMS Collaboration |accessdate=3 April 2013 }}</ref><ref name="AP-20130403">{{cite news |last1=Heilprin|first1=John |last2=Borenstein |first2=Seth |title=Scientists find hint of dark matter from cosmos|url=http://apnews.excite.com/article/20130403/DA5E6JAG3.html |date=3 April 2013 |agency=Associated Press |accessdate=3 April 2013 }}</ref><ref name="BBC-20130403">{{cite news |last=Amos |first=Jonathan |title=Alpha Magnetic Spectrometer zeroes in on dark matter |url=http://www.bbc.co.uk/news/science-environment-22016504 |date=3 April 2013 |work=[[BBC News]] |accessdate=3 April 2013 }}</ref><ref name="NASA-20130403">{{cite web |last1=Perrotto|first1=Trent J. |last2=Byerly |first2=Josh |title=NASA TV Briefing Discusses Alpha Magnetic Spectrometer Results|url=http://www.nasa.gov/home/hqnews/2013/apr/HQ_M13-054_AMS_Findings_Briefing.html |date=2 April 2013|work=[[NASA]] |accessdate=3 April 2013 }}</ref><ref name="NYT-20130403">{{cite news |last=Overbye |first=Dennis |title=New Clues to the Mystery of Dark Matter |url=http://www.nytimes.com/2013/04/04/science/space/new-clues-to-the-mystery-of-dark-matter.html |date=3 April 2013 |work=[[The New York Times]] |accessdate=3 April 2013 }}</ref> According to the scientists, "[[Alpha Magnetic Spectrometer#First results|The first results]] from the space-borne Alpha Magnetic Spectrometer confirm an unexplained excess of high-energy positrons in Earth-bound cosmic rays."

{{Double image|right|Iss030e015472 Edit.jpg|117|ISS-08 Michael Foale conducts an inspection of the Microgravity Science Glovebox.jpg|241|[[C/2011 W3 (Lovejoy)|Comet Lovejoy]] photographed by [[Expedition 30]] commander [[Dan Burbank]]|[[Expedition 8]] Commander and Science Officer [[Michael Foale]] conducts an inspection of the [[Microgravity Science Glovebox]]}}
The space environment is hostile to life. Unprotected presence in space is characterised by an intense radiation field (consisting primarily of protons and other subatomic charged particles from the [[solar wind]], in addition to [[cosmic ray]]s), high vacuum, extreme temperatures, and microgravity.<ref name="Space Microbiology">{{cite web|url=http://syntheticbiology.arc.nasa.gov/files/SpaceMicrobiology%20MMBR%201.pdf|title=Space Microbiology, section Space Environment (p. 122)|publisher=Microbiology and Molecular Biology Reviews|date=March 2010|accessdate=4 June 2011|author=G Horneck, DM Klaus & RL Mancinelli}}</ref> Some simple forms of life called [[extremophile]]s,<ref name="Beer microbes">{{cite news|url=http://www.bbc.co.uk/news/science-environment-11039206|title=Beer microbes live 553 days outside ISS|work=[[BBC News]]|date=23 August 2010|accessdate=4 June 2011|author=Jonathan Amos}}</ref> including small invertebrates called [[tardigrade]]s<ref name="Waterbears">{{cite web|url=http://www.nature.com/news/2008/080908/full/news.2008.1087.html|title=Spacesuits optional for 'water bears'|work=Nature|date=8 September 2008|accessdate=4 June 2011}}</ref> can survive in this environment in an extremely dry state called [[Desiccation#Biology and ecology|desiccation]].

Medical research improves knowledge about the effects of long-term space exposure on the human body, including [[muscle atrophy]], [[Osteoporosis|bone loss]], and fluid shift. This data will be used to determine whether lengthy [[human spaceflight]] and [[space colonisation]] are feasible. As of 2006, data on bone loss and muscular atrophy suggest that there would be a significant risk of fractures and movement problems if astronauts landed on a planet after a lengthy interplanetary cruise, such as the six-month interval required to [[Manned mission to Mars|travel to Mars]].<ref name="JCB">{{cite book|author=Jay Buckey|title=Space Physiology|publisher=Oxford University Press USA|date=23 February 2006|isbn=978-0-19-513725-5}}</ref><ref>{{cite web|url=http://www.newscientist.com/article/dn17476-ion-engine-could-one-day-power-39day-trips-to-mars.html?full=true|work=New Scientist|accessdate=8 January 2010|date=24 July 2009|author=List Grossman|title=Ion engine could one day power 39-day trips to Mars}}</ref>
Medical studies are conducted aboard the ISS on behalf of the [[National Space Biomedical Research Institute]] (NSBRI). Prominent among these is the [[Advanced Diagnostic Ultrasound in Microgravity]] study in which astronauts perform ultrasound scans under the guidance of remote experts. The study considers the diagnosis and treatment of medical conditions in space. Usually, there is no physician on board the ISS and diagnosis of medical conditions is a challenge. It is anticipated that remotely guided ultrasound scans will have application on Earth in emergency and rural care situations where access to a trained physician is difficult.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/science/experiments/ADUM.html|date=1 May 2009|accessdate=1 October 2009|author=Brooke Boen|publisher=NASA|title=Advanced Diagnostic Ultrasound in Microgravity (ADUM)}}</ref><ref>{{cite journal|author=Sishir Rao|display-authors=etal|year=2008|title=A Pilot Study of Comprehensive Ultrasound Education at the Wayne State University School of Medicine|journal=Journal of Ultrasound in Medicine|volume=27|pages=745–749|pmid=18424650|issue=5}}</ref><ref>{{cite journal|author=Michael Fincke|display-authors=etal|year=2004|title=Evaluation of Shoulder Integrity in Space: First Report of Musculoskeletal US on the International Space Station|journal=Radiology|issue= 2|pages=319–322|pmid=15533948|doi=10.1148/radiol.2342041680|volume=234}}</ref>

====Microgravity====
[[File:Space Fire.jpg|thumb|A comparison between the combustion of a candle on [[Earth]] (left) and in a microgravity environment, such as that found on the ISS (right)]]
The Earth's gravity is only slightly weaker at the altitude of the ISS than at the surface, but objects in orbit are in a continuous state of [[Free fall|freefall]], resulting in an apparent state of weightlessness. This perceived weightlessness is disturbed by five separate effects:<ref name="gravity">{{cite web|url=http://www.esa.int/Our_Activities/Human_Spaceflight/Human_Spaceflight_Research/European_User_Guide_to_Low-Gravity_Platforms
|title=European Users Guide to Low Gravity Platforms|accessdate=22 March 2013|date=6 December 2005|publisher=European Space Agency}}</ref>
* Drag from the residual atmosphere; when the ISS enters the Earth's shadow, the main solar panels are rotated to minimise this aerodynamic drag, helping reduce [[orbital decay]].
* Vibration from movements of mechanical systems and the crew.
* Actuation of the on-board attitude [[control moment gyroscope]]s.
* [[Rocket engine|Thruster]] firings for attitude or orbital changes.
* [[Gravity-gradient stabilization|Gravity-gradient effects]], also known as [[tidal force|tidal]] effects. Items at different locations within the ISS would, if not attached to the station, follow slightly different orbits. Being mechanically interconnected these items experience small forces that keep the station moving as a [[rigid body]].

[[File:ISS-20 Robert Thirsk at the Minus Eighty Degree Laboratory Freezer.jpg|thumb|left|ISS crew member storing samples]]

Researchers are investigating the effect of the station's near-weightless environment on the evolution, development, growth and internal processes of plants and animals. In response to some of this data, NASA wants to investigate [[microgravity]]'s effects on the growth of three-dimensional, human-like tissues, and the unusual [[protein crystal]]s that can be formed in space.<ref name="NASA Fields of Research" />

The investigation of the physics of fluids in microgravity will allow researchers to model the behaviour of fluids better. Because fluids can be almost completely combined in microgravity, physicists investigate fluids that do not mix well on Earth. In addition, an examination of reactions that are slowed by low gravity and temperatures will give scientists a deeper understanding of [[superconductivity]].<ref name="NASA Fields of Research" />

The study of [[materials science]] is an important ISS research activity, with the objective of reaping economic benefits through the improvement of techniques used on the ground.<ref>{{cite web|url=http://science.nasa.gov/newhome/headlines/msad15sep99_1.htm|title=Materials Science 101|publisher=Science@NASA|accessdate=18 June 2009|date=15 September 1999}}</ref> Other areas of interest include the effect of the low gravity environment on combustion, through the study of the efficiency of burning and control of emissions and pollutants. These findings may improve current knowledge about energy production, and lead to economic and environmental benefits. Future plans are for the researchers aboard the ISS to examine [[aerosol]]s, [[ozone]], [[water vapour]], and [[oxide]]s in Earth's atmosphere, as well as [[cosmic ray]]s, [[cosmic dust]], [[antimatter]], and [[dark matter]] in the universe.<ref name="NASA Fields of Research" />

===Exploration===
[[File:Mars500.jpg|thumb|right|A 3D plan of the Russia-based [[MARS-500]] complex, used for ground-based experiments which complement ISS-based preparations for a [[manned mission to Mars]]]]
The ISS provides a location in the relative safety of Low Earth Orbit to test spacecraft systems that will be required for long-duration missions to [[the Moon]] and [[Mars]]. This provides experience in operations, maintenance as well as repair and replacement activities on-orbit, which will be essential skills in operating spacecraft farther from Earth, mission risks can be reduced and the capabilities of interplanetary spacecraft advanced.<ref name="ResProg">{{cite web|url=http://spaceflightsystems.grc.nasa.gov/Advanced/ISSResearch/|title=ISS Research Program|publisher=NASA|accessdate=27 February 2009}}{{dead link|date=August 2011}}</ref> Referring to the [[MARS-500]] experiment, ESA states that "Whereas the ISS is essential for answering questions concerning the possible impact of weightlessness, radiation and other space-specific factors, aspects such as the effect of long-term isolation and confinement can be more appropriately addressed via ground-based simulations".<ref name="esa mars500 ">{{cite web|title=Mars500 study overview | publisher = ESA |date= 4 June 2011| url = http://www.esa.int/esaMI/Mars500/SEM7W9XX3RF_0.html }}</ref> Sergey Krasnov, the head of human space flight programmes for Russia's space agency, Roscosmos, in 2011 suggested a "shorter version" of MARS-500 may be carried out on the ISS. <ref name="Mars thing on ISS">{{cite web| title=Space station may be site for next mock Mars mission| url = http://www.newscientist.com/blogs/shortsharpscience/2011/11/space-station-may-be-site-for.html|date=4 November 2011|work=New Scientist}}</ref>

In 2009, noting the value of the partnership framework itself, Sergey Krasnov wrote, "When compared with partners acting separately, partners developing complementary abilities and resources could give us much more assurance of the success and safety of space exploration. The ISS is helping further advance near-Earth space exploration and realisation of prospective programmes of research and exploration of the Solar system, including the Moon and Mars."<ref name=IAF2009>{{cite web|title=The Sustainable Utilisation of the ISS Beyond 2015|url=http://www.iafastro.org/docs/2009/ISS2015.pdf|publisher=International Astronautical Congress|accessdate=15 December 2011}}</ref> [[Manned mission to Mars|A manned mission to Mars]] may be a multinational effort involving space agencies and countries outside the current ISS partnership. In 2010, ESA Director-General Jean-Jacques Dordain stated his agency was ready to propose to the other four partners that China, India and South Korea be invited to join the ISS partnership.<ref name="ESAproposesInvite">{{cite web|title=ESA Chief Lauds Renewed U.S. Commitment to Space Station, Earth Science | publisher =Peter B. de Selding, Space News. |date=2 March 2010 | url =http://www.spacenews.com/civil/100203-esa-chief-lauds-renewed-commitment-space-station-earth-science.html}}</ref> NASA chief [[Charlie Bolden]] stated in February 2011, "Any mission to Mars is likely to be a global effort".<ref name="Mars a global effort">{{cite web|title= Charlie Bolden | publisher = space.com |date=4 June 2011 | url = http://www.space.com/11335-nasa-mars-exploration-space-station.html }}</ref> Currently, American legislation prevents NASA co-operation with China on space projects.<ref name="justice1">{{citation|first=Virginia|last=Seitz|title=Memorandum Opinion for the General Counsel, Office of Science and Technology Policy|url=http://www.justice.gov/olc/2011/conduct-diplomacy.pdf|journal=Office of Legal Counsel|volume=35|date=11 September 2011|accessdate=23 May 2012|archiveurl=https://web.archive.org/web/20120713080223/http://www.justice.gov/olc/2011/conduct-diplomacy.pdf|archivedate=13 July 2012}}</ref>

===Education and cultural outreach===
[[File:ISS-36 HTV-4 berthing 2.jpg|thumb|Japan's Kounotori 4 docking]]
The ISS crew provides opportunities for students on Earth by running student-developed experiments, making educational demonstrations, allowing for student participation in classroom versions of ISS experiments, and directly engaging students using radio, videolink and email.<ref name="ISSRG" /><ref>{{cite journal|author1=Gro Mjeldheim Sandal |author2=Dietrich Manzey|title=Cross-cultural issues in space operations: A survey study among ground personnel of the European Space Agency|journal=Acta Astronautica|volume=65|date=December 2009|pages=1520–1529|doi=10.1016/j.actaastro.2009.03.074|issue=11–12}}</ref> ESA offers a wide range of free teaching materials that can be downloaded for use in classrooms.<ref>[http://www.esa.int/SPECIALS/Education/SEM0LW4KXMF_0.html ESA – Education – Online material]. Esa.int (7 September 2011). Retrieved 8 October 2011.</ref> In one lesson, students can navigate a 3-D model of the interior and exterior of the ISS, and face spontaneous challenges to solve in real time.<ref>[http://www.esa.int/SPECIALS/Education/SEM1LL3Z2OF_0.html ESA – Education – ISS 3-D Teaching Tool: Spaceflight Challenge I]. Esa.int (24 May 2011). Retrieved 8 October 2011.</ref>

JAXA aims both to "Stimulate the curiosity of children, cultivating their spirits, and encouraging their passion to pursue craftsmanship", and to "Heighten the child's awareness of the importance of life and their responsibilities in society."<ref>[http://www.oosa.unvienna.org/pdf/pres/copuos2010/tech-17E.pdf Building Peace in Young Minds through Space Education]. Committee on the Peaceful Uses of Outer Space, 53rd Session. June 2010, Vienna, Austria; Space Education Center, Japan Aerospace Exploration Agency (JAXA)</ref> Through a series of education guides, a deeper understanding of the past and near-term future of manned space flight, as well as that of Earth and life, will be learned.<ref>[http://www.edu.jaxa.jp/education/international/ISS/SSK/en/ JAXA Space Education Center : JAXA Spaceflight Seeds Kids I : Spaceflight Sunflower seeds – Let's make them flower! and learn freshly the Earth environment just by contrast with the Space one]. Edu.jaxa.jp. Retrieved 8 October 2011.</ref><ref>[http://www.edu.jaxa.jp/education/international/ISS/SIS/en/ JAXA Space Education Center : JAXA Seeds in Space I : Let's Cultivate Spaceflight Asagao, Miyako-gusa Seeds and Identify the Mutants!]. Edu.jaxa.jp. Retrieved 8 October 2011.</ref> In the JAXA Seeds in Space experiments, the mutation effects of spaceflight on plant seeds aboard the ISS is explored. Students grow sunflower seeds which flew on the ISS for about nine months as a start to 'touch the Universe'. In the first phase of Kibō utilisation from 2008 to mid-2010, researchers from more than a dozen Japanese universities conducted experiments in diverse fields.<ref>{{cite web |author=Keiji Murakami |url=http://www.spacepolicyonline.com/pages/images/stories/Micro%20Oct%2009%20JEM.pdf |title=JEM Utilization Overview |publisher=JAXA. Steering Committee for the Decadal Survey on Biological and Physical Sciences in Space |date=14 October 2009}}</ref>

[[Image:Crew in ATV with Jules Verne manuscript.jpg|thumb|left|Original Jules Verne manuscripts displayed by crew inside Jules Verne ATV]]
Cultural activities are another major objective. Tetsuo Tanaka, director of JAXA's Space Environment and Utilization Center, says "There is something about space that touches even people who are not interested in science."<ref name="jaxa2">{{cite web |author=Tetsuo Tanaka |url=http://www.jaxa.jp/article/special/kibo/tanaka01_e.html |title=Kibo: Japan's First Human Space Facility |publisher=JAXA |accessdate=8 October 2011}}</ref>

[[ARISS|Amateur Radio on the ISS]] (ARISS) is a volunteer programme which encourages students worldwide to pursue careers in science, technology, engineering and mathematics through [[amateur radio]] communications opportunities with the ISS crew. ARISS is an international working group, consisting of delegations from 9 countries including several countries in Europe as well as Japan, Russia, Canada, and the United States. In areas where radio equipment cannot be used, speakerphones connect students to ground stations which then connect the calls to the station. <ref>{{cite web|url=http://www.rac.ca/ariss/oindex.htm|title=Amateur Radio on the International Space Station|date=6 June 2011|accessdate=10 June 2011}}</ref>

''[[First Orbit]]'' is a feature-length documentary film about [[Vostok 1]], the first manned space flight around the Earth. By matching the orbit of the International Space Station to that of Vostok 1 as closely as possible, in terms of ground path and time of day, documentary filmmaker Christopher Riley and ESA astronaut [[Paolo Nespoli]] were able to film the view that Yuri Gagarin saw on his pioneering orbital space flight. This new footage was cut together with the original Vostok 1 mission audio recordings sourced from the Russian State Archive. Nespoli, during Expedition 26/27, filmed the majority of the footage for this documentary film, and as a result is credited as its [[Cinematographer|director of photography]].<ref>{{cite news|last=Riley|first=Christopher|title=What Yuri Gagarin saw: First Orbit film to reveal the view from Vostok 1|url=http://www.guardian.co.uk/science/blog/2011/apr/11/yuri-gagarin-first-orbit-vostok|newspaper=The Guardian|date=11 April 2011|location=London}}</ref> The film was streamed through the website firstorbit.org in a global YouTube premiere in 2011, under a free license.<ref>{{cite web|url=http://www.firstorbit.org/first-orbit-faqs |title=Yuri Gagarin's First Orbit – FAQs |publisher=Firstorbit.org |accessdate=1 May 2012}}</ref>

In May 2013, commander [[Chris Hadfield]] shot a music video of [[David Bowie]]'s ''[[Space Oddity (song)|Space Oddity]]'' on board the station; the film was released freely on YouTube.<ref>{{cite web|last=Warr |first=Philippa |url=http://www.wired.co.uk/news/archive/2013-05/13/commander-hadfield-space-oddity |title=Commander Hadfield bids farewell to ISS with Reddit-inspired Bowie cover |publisher=Wired.co.uk |date=13 May 2013 |accessdate=22 October 2013}}</ref> It was the first music video ever to be filmed in space.<ref>{{Cite web|title = Commander Hadfield bids farewell to ISS with Reddit-inspired Bowie cover (Wired UK)|url = http://www.wired.co.uk/news/archive/2013-05/13/commander-hadfield-space-oddity|accessdate = 2015-08-05}}</ref>

==Assembly==
{{Main|Assembly of the International Space Station|List of ISS spacewalks}}
[[File:ISS-with-S0-S1-P1.jpg|thumb|right|alt=S0, S1 and P1 truss structures installed|Partially constructed ISS in December 2002]]
[[File:S3-S4 Truss Installed 2.jpg|thumb|S3-S4 Truss Installed in 2007]]
[[File:Soyuz TMA-19 spacecraft departs the ISS.jpg|thumb|[[Soyuz TMA-19]] departs in 2010]]
[[File:ISS after STS-117 in June 2007.jpg|thumb|ISS in 2007, with fewer solar arrays]]
The assembly of the International Space Station, a major endeavour in [[space architecture]], began in November 1998.<ref name="OnOrbit">{{cite web|url=http://www.nasa.gov/externalflash/ISSRG/pdfs/on_orbit.pdf|title=On-Orbit Elements|publisher=NASA|author=NASA|date=18 February 2010|accessdate=19 June 2010|format=PDF}}</ref> Russian modules launched and docked robotically, with the exception of ''[[Rassvet (ISS module)|Rassvet]]''. All other modules were delivered by the Space Shuttle, which required installation by ISS and shuttle crewmembers using the [[Mobile Servicing System#Canadarm2|Canadarm2]] (SSRMS) and [[List of ISS spacewalks|EVAs]]; {{as of|2011|06|05|lc=y}}, they had added 159 components during more than 1,000 hours of EVA. 127 of these spacewalks originated from the station, and the remaining 32 were launched from the airlocks of docked Space Shuttles.<ref name="ISStD" /> The [[beta angle]] of the station had to be considered at all times during construction, as the station's beta angle is directly related to the percentage of its orbit that the station (as well as any docked or docking spacecraft) is exposed to the sun; the Space Shuttle would not perform optimally above a limit called the "beta cutoff".<ref name="mcc">{{cite web|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-113/11_23_20_01_179.html|title=MCC Answers|author=Derek Hassman, NASA Flight Director|date=1 December 2002|publisher=NASA|accessdate=14 June 2009}}</ref>

The first module of the ISS, ''[[Zarya]]'', was launched on 20 November 1998 on an autonomous Russian [[Proton (rocket)|Proton rocket]]. It provided propulsion, attitude control, communications, electrical power, but lacked long-term life support functions. Two weeks later a passive NASA module ''[[Unity (ISS module)|Unity]]'' was launched aboard Space Shuttle flight [[STS-88]] and attached to Zarya by astronauts during EVAs. This module has two [[Pressurized Mating Adapter]]s (PMAs), one connects permanently to Zarya, the other allows the Space Shuttle to dock to the space station. At this time, the Russian station Mir was still inhabited. The ISS remained unmanned for two years, during which time Mir was de-orbited. On 12 July 2000 [[Zvezda (ISS module)|Zvezda]] was launched into orbit. Preprogrammed commands on board deployed its solar arrays and communications antenna. It then became the passive vehicle for a rendezvous with the Zarya and Unity. As a passive "target" vehicle, the Zvezda maintained a stationkeeping orbit as the Zarya-Unity vehicle performed the rendezvous and docking via ground control and the Russian automated rendezvous and docking system. Zarya's computer transferred control of the station to Zvezda's computer soon after docking. Zvezda added sleeping quarters, a toilet, kitchen, CO2 scrubbers, dehumidifier, oxygen generators, exercise equipment, plus data, voice and television communications with mission control. This enabled permanent habitation of the station.<ref>[http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/servmod.pdf NASA Facts. The Service Module: A Cornerstone of Russian International Space Station Modules]. NASA. January 1999</ref><ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/missions/sts-88/mission-sts-88.html |title=STS-88 |publisher=Science.ksc.nasa.gov |accessdate=19 April 2011}}</ref>

The first resident crew, [[Expedition 1]], arrived in November 2000 on [[Soyuz TM-31]]. At the end of the first day on the station, astronaut Bill Shepherd requested the use of the radio call sign "''Alpha''", which he and cosmonaut Krikalev preferred to the more cumbersome "''International Space Station''".<ref name=TIME-Nov2>{{cite news|url=http://www.time.com/time/arts/article/0,8599,59500,00.html|title=Upward Bound: Tales of Space Station Alpha|author=Brad Liston|date=2 November 2000|work=Time|accessdate=5 August 2010}}</ref> The name "''Alpha''" had previously been used for the station in the early 1990s,<ref name=GAO>{{cite web|url=http://archive.gao.gov/t2pbat3/151975.pdf|title=Space Station – Impact on the expanded Russian role of funding and research|date=21 June 1994|publisher=[[Government Accountability Office|United State General Accounting Office]]|accessdate=9 August 2010}}</ref> and following the request, its use was authorised for the whole of Expedition 1.<ref name=SPACE-Nov3>{{cite web|url=http://www.space.com/missionlaunches/missions/alpha_male_001103.html|title=Call Bill Shepherd the Alpha Male of the International Space Station|author=Alan Ladwig|date=3 November 2000|publisher=Space.com|accessdate=9 August 2010}}</ref> Shepherd had been advocating the use of a new name to project managers for some time. Referencing a [[Ship naming and launching|naval tradition]] in a pre-launch news conference he had said: "For thousands of years, humans have been going to sea in ships. People have designed and built these vessels, launched them with a good feeling that a name will bring good fortune to the crew and success to their voyage."<ref name=SPACE-Nov2>{{cite web|url=http://www.space.com/missionlaunches/missions/exp1_alpha_001102.html|title=Expedition One Crew Wins Bid To Name Space Station Alpha|date=2 November 2000|author=Todd Halvorson|publisher=Space.com|accessdate=9 August 2010}}</ref> [[Yuri Semenov]], the President of [[S.P. Korolev Rocket and Space Corporation Energia|Russian Space Corporation Energia]] at the time, disapproved of the name "''Alpha''"; he felt that ''Mir'' was the first space station, and so he would have preferred the names "''Beta''" or "''Mir 2''" for the ISS.<ref name=SPACE-Nov3 /><ref>{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=5913|title=Interview with RSC Energia's Yuri Semenov|publisher=Space.com|date=3 September 2001|accessdate=22 August 2010}}</ref><ref>{{cite web|url=http://english.ruvr.ru/2001/03/29/100146.html|title=Interview with Yuri Semenov, general designer of Space Rocket corporation Energy|date=21 March 2001|publisher=[[Voice of Russia]]|accessdate=5 October 2010}}</ref>

[[Expedition 1]] arrived midway between the flights of [[STS-92]] and [[STS-97]]. These two Space Shuttle flights each added segments of the station's [[Integrated Truss Structure]], which provided the station with Ku-band communication for US television, additional attitude support needed for the additional mass of the USOS, and substantial [[solar array]]s supplementing the station's existing 4 solar arrays.<ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/missions/sts-92/mission-sts-92.html |title=STS-92 |publisher=Science.ksc.nasa.gov |accessdate=19 April 2011}}</ref>

Over the next two years the station continued to expand. A [[Soyuz-U]] rocket delivered the [[Pirs (ISS module)|''Pirs'' docking compartment]]. The Space Shuttles ''Discovery'', ''[[Space Shuttle Atlantis|Atlantis]]'', and ''Endeavour'' delivered the [[Destiny (ISS module)|''Destiny'' laboratory]] and [[Quest Joint Airlock|''Quest'' airlock]], in addition to the station's main robot arm, the ''[[Canadarm2]]'', and several more segments of the Integrated Truss Structure.
[[File:Zvezda rear.jpg|thumb|left|Aft view showing a Progress spacecraft docked to Zvezda]]
The expansion schedule was interrupted by the {{OV|102}} [[Space Shuttle Columbia disaster|disaster]] in 2003, with the resulting two year hiatus in the [[Space Shuttle program]]me halting station assembly. The space shuttle was grounded until 2005 with [[STS-114]] flown by ''Discovery''.<ref>{{cite web|url=http://www.nasaspaceflight.com/2005/07/discovery-launches-the-shuttle-is-back/|title=Discovery launches—The Shuttle is back|author=Chris Bergin|publisher=NASASpaceflight.com|accessdate=6 March 2009|date=26 July 2005}}</ref>

Assembly resumed in 2006 with the arrival of [[STS-115]] with ''Atlantis'', which delivered the station's second set of solar arrays. Several more truss segments and a third set of arrays were delivered on [[STS-116]], [[STS-117]], and [[STS-118]]. As a result of the major expansion of the station's power-generating capabilities, more pressurised modules could be accommodated, and the ''[[Harmony (ISS module)|Harmony]]'' node and ''Columbus'' European laboratory were added. These were followed shortly after by the first two components of ''Kibō''. In March 2009, [[STS-119]] completed the Integrated Truss Structure with the installation of the fourth and final set of solar arrays. The final section of ''Kibō'' was delivered in July 2009 on [[STS-127]], followed by the Russian ''[[Poisk (ISS module)|Poisk]]'' module. The third node, ''[[Tranquility (ISS module)|Tranquility]]'', was delivered in February 2010 during [[STS-130]] by the Space Shuttle ''Endeavour'', alongside the [[Cupola (ISS module)|Cupola]], closely followed in May 2010 by the penultimate Russian module, ''[[Rassvet (ISS module)|Rassvet]]''. Rassvet was delivered by Space Shuttle ''Atlantis'' on [[STS-132]] in exchange for the Russian Proton delivery of the Zarya Module in 1998 which had been funded by the United States.<ref>{{cite web|url=http://www.russianspaceweb.com/iss_mim1.html |title=Mini-Research Module 1 (MIM1) Rassvet (MRM-1) |publisher=Russianspaceweb.com |accessdate=12 July 2011}}</ref> The last pressurised module of the USOS, ''Leonardo'', was brought to the station by ''Discovery'' on her final flight, [[STS-133]],<ref name="STS-133">{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/main/index.html |title=STS-133 |publisher=NASA |accessdate=1 September 2014}}</ref> followed by the [[Alpha Magnetic Spectrometer]] on [[STS-134]], delivered by ''Endeavour''.<ref name="STS-134">{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/main/index.html |title=STS-134 |publisher=NASA |accessdate=1 September 2014}}</ref>
[[File:Exterior of Cupola - Exp28.jpg|thumb|The Cupola arrived in 2010]]
{{As of|2011|06}}, the station consisted of fifteen pressurised modules and the [[Integrated Truss Structure]]. Still to be launched are the Russian [[Nauka (ISS module)|Multipurpose Laboratory Module]] ''Nauka'' and a number of external components, including the [[European Robotic Arm]]. Assembly is expected to be completed by April 2014,{{update inline|date=October 2014}} by which point the station will have a mass in excess of 400 [[metric ton|tonnes]] (440 [[short ton]]s).<ref name="OnOrbit" /><ref name="Manifest">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/iss_manifest.html|title=Consolidated Launch Manifest|accessdate=8 July 2008|publisher=NASA|author=NASA|year=2008}}</ref>

The gross mass of the station changes over time. The total launch mass of the modules on orbit is about {{convert|417289|kg|lbs|abbr=on}} (as of 3 September 2011).<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/isstodate.html |title=NASA – The ISS to Date (03/09/2011) |publisher=Nasa.gov |accessdate=12 July 2011}}</ref> The mass of experiments, spare parts, personal effects, crew, foodstuff, clothing, propellants, water supplies, gas supplies, docked spacecraft, and other items add to the total mass of the station. Hydrogen gas is constantly vented overboard by the oxygen generators.

==Station structure==
{{Double image|right|ROS Windows 0114 complete.jpg|130|USOS window identification.png|160|Russian Orbital Segment Windows|USOS International Space Station window locations}}

The ISS is a third generation<ref>{{cite web|url=http://www.dlr.de/iss/en/desktopdefault.aspx/tabid-1945/2746_read-4182/gallery-1/gallery_read-Image.19.2296/ |title=DLR – International Space Station ISS – From Cold War to international cooperation – the story of the ISS |publisher=Dlr.de |accessdate=1 May 2012}}</ref> modular space station.<ref>{{cite web|url=http://www.astronautix.com/articles/thistems.htm |title=Third Generation Soviet Space Systems |publisher=Astronautix.com |accessdate=1 May 2012}}</ref> Modular stations can allow the mission to be changed over time and new modules can be added or removed from the existing structure, allowing greater flexibility.

Below is a diagram of major station components. The blue areas are pressurised sections accessible by the crew without using spacesuits. The station's unpressurised superstructure is indicated in red. Other unpressurised components are yellow. Note that the Unity node joins directly to the Destiny laboratory. For clarity, they are shown apart.

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{{familytree| | | | | | | | | | | | | | | |}}
{{familytree| | | | | | | | | | | |PORT1| | |
PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | |AMS|~|ZVEZDA|~|AMS|
AMS = [[Zvezda (ISS module)|Solar array]]
|ZVEZDA = [[Zvezda (ISS module)|'''Zvezda DOS-8''' Service Module]]
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{{familytree| | | | | | | | | | | |!|!|!| |}}
{{familytree| | | | |PORT1|SGM2|-|'|!|)|-|PIRS|PORT1|
PIRS = [[Pirs (ISS module)|'''Pirs''' Airlock]]
|SGM2 = [[Poisk (ISS module)|'''Poisk''' (MRM-2) Airlock]]
|PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | | | | | | |!|!|}}
{{familytree| | | | | | | | | | | | |!|`|-|MLM|~|ERA| | |
MLM = [[Nauka (ISS module)|'''Nauka lab''' to Replace Pirs]]
| ERA = '''[[European Robotic Arm|European Robotic Arm]]'''
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{{familytree| | | | | | | | | | | | |!| | | | | | | | |}}
{{familytree| | | | | | | |SA|~|ZARYA|~|SA| | | |
SA = [[Zarya (ISS module)|Solar array]]
| ZARYA = [[Zarya (ISS module)|'''Zarya FGB''' (first module)]]
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{{familytree| | | | | | | | | | | | |!|!|}}
{{familytree| | | | | | | | | | | | |!|`|-|SGM1|PORT1|
SGM1 = [[Rassvet (ISS module)|'''Rassvet''' (MRM-1)]]
|PORT1 = [[Soyuz "probe and drogue"|Russian docking port]]
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{{familytree| | | | | | | | | | | | |!| | | | | | | | |}}
{{familytree| | | | | | | | | | | | |!| | |PMM| | |
PMM = [[Leonardo (ISS module)|'''Leonardo''' cargo bay]]
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{{familytree| | | | | | | | | | | |PMA| | |!|
PMA = [[Pressurized Mating Adapter#PMA-1|PMA 1]]
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{{familytree| | | | | | | |QUEST|-|UNITY|-|NOD3|PORT2| |
UNITY = [[Unity (ISS module)|'''Unity''' Node 1]]
|QUEST = [[Quest Joint Airlock|'''Quest''' Airlock]]
|NOD3 = [[Tranquility (ISS module)|'''Tranquility''' Node 3]]
|PORT2 = [[Pressurized Mating Adapter#PMA-3|'''PMA 3''' docking port]]
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{{familytree| | | | | | | |ESP2| | |!| | |CUPOLA|
ESP2 = '''[[External Stowage Platform#ESP-2|ESP-2]]'''
|CUPOLA = '''[[Cupola (ISS module)|Cupola]]'''
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{{familytree| | | | | | | | | | | | |!|}}
{{familytree| |FE0|F|FE| |RADIATOR|!|RADIATOR| |FE|7|FE| | | |
RADIATOR = [[External Active Thermal Control System|Heat Radiator]]
|FE = [[ISS Solar Arrays#Solar arrays|Solar array]]
|FE0 = [[ISS Solar Arrays#Solar arrays|Solar array]]
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|boxstyle_FE = border: 1px solid #fee067; background:#fff4cc;
|boxstyle_FE0 = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| |:| | |:| | | | | |:| |!| |:| | | | | |:| | |:|}}
{{familytree| |:| | |:|ELC| | |:|FZ1|:| | |ELC3|:| | |:|
ELC = [[ExPRESS Logistics Carrier#ELC-2|ELC 2]], '''[[Alpha Magnetic Spectrometer|AMS]]'''
|FZ1 = '''[[Z1 truss]]'''
|ELC3 = [[ExPRESS Logistics Carrier#ELC-3|ELC 3]]
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|boxstyle_FZ1 = border: 2px solid #ff6666; background:#ffcccc;
|boxstyle_ELC = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| |D|FS56|FS34|FS1|FS0|FP1|FP34|FP56|C|
FS56 = '''[[P5 Truss Segment|S5/6 Truss]]'''
|FS34 = '''[[Integrated Truss Structure#P3/P4, S3/S4 truss assemblies|S3/S4 Truss]]'''
|FS1 = '''[[S1 Truss]]'''
|FS0 = '''[[S0 Truss]]'''
|FP1 = '''[[S1 Truss|P1 Truss]]'''
|FP34 = '''[[Integrated Truss Structure#P3/P4, S3/S4 truss assemblies|P3/P4 Truss]]'''
|FP56 = '''[[P5 Truss Segment|P5/6 Truss]]'''
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|boxstyle_FS34 = border: 2px solid #ff6666; background:#ffcccc;
|boxstyle_FS1 = border: 2px solid #ff6666; background:#ffcccc;
|boxstyle_FS0 = border: 2px solid #ff6666; background:#ffcccc;
|boxstyle_FP1 = border: 2px solid #ff6666; background:#ffcccc;
|boxstyle_FP34 = border: 2px solid #ff6666; background:#ffcccc;
|boxstyle_FP56 = border: 2px solid #ff6666; background:#ffcccc;}}
{{familytree| |:| | |:|ELC4| | | |:|!|:| | | |ELC1|:| | |:|
ELC4 = [[ExPRESS Logistics Carrier#ELC-4|ELC 4]], [[External Stowage Platform#ESP-3|ESP 3]]
|ELC1 = [[ExPRESS Logistics Carrier#ELC-1|ELC 1]]
|boxstyle_ELC1 = border: 1px solid #fee067; background:#fff4cc;
|boxstyle_ELC4 = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| |:| | |:| | | | |DEXTR|!|CANADARM| | | | |:| | |:|
CANADARM = '''[[Canadarm2]]'''
|DEXTR = '''[[Dextre]]'''
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|boxstyle_DEXTR = border: 2px solid #fee067; background:#fff4cc;}}
{{familytree| |FE0|L|FE| | | | |!| | | | |FE|J|FE| | | |
FE0 = [[ISS Solar Arrays#Solar arrays|Solar array]]
|FE = [[ISS Solar Arrays#Solar arrays|Solar array]]
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|boxstyle_FE = border: 1px solid #fee067; background:#fff4cc;
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{{familytree| | | | | | | | | | | | |!| | | | |}}
{{familytree| | | | | | | | |ESP1|DESTYNY| | |
DESTYNY = [[Destiny (ISS module)|'''Destiny''' Laboratory]]
|ESP1 = [[External Stowage Platform#ESP-1|External stowage]]
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|boxstyle_ESP1 = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| | | | | | | | | | | | |!| | | | |KIBOPS| | |
KIBOPS = [[Japanese Experiment Module#Experiment Logistics Module|'''Kibō logistics''' Cargo Bay]]
|boxstyle_KIBOPS = border: 2px solid #6699ff; background:#ccddff;}}
{{familytree| | | | | | | | | |HTV|!|HTV| |!|
HTV = '''[[H-II Transfer Vehicle|HTV]]'''/'''[[Dragon (spacecraft)|Dragon]]'''/'''[[Cygnus (spacecraft)|Cygnus]]''' berth ([[Common berthing mechanism|docking port]])
|boxstyle_HTV = border: 1px solid #a3ff66; background:#ccddff;}}
{{familytree| | | | | | | | | | | |!|!|!| | | |!|KiboRobo|
KiboRobo = [[Japanese Experiment Module|'''Kibō''' Robotic Arm]]
|boxstyle_KiboRobo = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| | | | |COLEXT|COLUMBUS|-|HARMONY|-|KIBO|KiboPlat|
HARMONY = [[Harmony (ISS module)|'''Harmony''' (Node 2)]]
|KiboPlat = [[Japanese Experiment Module|'''Kibō''' External Platform]]
|COLUMBUS = [[Columbus (ISS module)|'''Columbus''' Laboratory]]
|KIBO = [[JEM-PM|'''Kibō''' Laboratory]]
|COLEXT = External Payloads
|boxstyle_HARMONY = border: 2px solid #6699ff; background:#ccddff;
|boxstyle_COLUMBUS = border: 2px solid #6699ff; background:#ccddff;
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|boxstyle_KIBO = border: 2px solid #6699ff; background:#ccddff;
|boxstyle_KiboPlat = border: 1px solid #fee067; background:#fff4cc;}}
{{familytree| | | | | | | | | | | |PORT2| |
PORT2 = [[Pressurized Mating Adapter#PMA-2|'''PMA 2''' docking port]]
|boxstyle_PORT2 = border: 1px solid #a3ff66; background:#ccddff;}}
{{familytree| | | | | | | | | | | | | | | |}}
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==Pressurised modules==

===Zarya===
[[File:Zarya from STS-88.jpg|thumb|upright|Zarya as seen by [[Space Shuttle Endeavour]] during [[STS-88]]]]
'''''[[Zarya]]''''' (Russian: Заря́; lit. dawn), also known as the [[Functional Cargo Block]] or FGB (from the Russian "Функционально-грузовой блок", Funktsionalno-gruzovoy blok or ФГБ), was the first module of the International Space Station to be launched. The FGB provided electrical power, storage, propulsion, and guidance to the ISS during the initial stage of assembly. With the launch and assembly in orbit of other modules with more specialized functionality, Zarya is now primarily used for storage, both inside the pressurized section and in the externally mounted fuel tanks. The Zarya is a descendant of the [[TKS spacecraft]] designed for the Soviet [[Salyut program]]. The name Zarya was given to the FGB because it signified the dawn of a new era of international cooperation in space. Although it was built by a Russian company, it is owned by the [[United States]]. Zarya weighs {{convert|19300|kg|lb|abbr=on}}, is {{convert|12.55|m|ft|abbr=on}} long and {{convert|4.1|m|ft|abbr=on}} wide, discounting solar arrays.

Built from December 1994 to January 1998 in Russia at the [[Khrunichev State Research and Production Space Center]] (KhSC) in [[Moscow]], Zarya's control system was developed by the Khartron Corp. ([[Kharkiv, Ukraine]]).

Zarya was launched on 20 November 1998, on a Russian [[Proton-K|Proton rocket]] from [[Baikonur Cosmodrome Site 81]] in [[Kazakhstan]] to a {{convert|400|km|mi|abbr=on}} high orbit with a designed lifetime of at least 15 years. After Zarya reached orbit, STS-88 launched on 4 December 1998, to attach the Unity Module.

Although only designed to fly autonomously for six to eight months, Zarya did so for almost two years due to delays with the Russian Service Module, Zvezda, which finally launched on 12 July 2000, and docked with Zarya on 26 July using the Russian [[Kurs (docking system)|Kurs docking system]].

===Unity===
[[File:ISS Unity module.jpg|thumb|Unity as pictured by Space Shuttle Endeavour]]
'''''[[Unity (ISS module)|Unity]]''''', or Node 1, is one of three nodes, or passive connecting modules, in the [[US Orbital Segment]] of the station. It was the first US-built component of the Station to be launched. Cylindrical in shape, with six berthing locations facilitating connections to other modules, Unity was carried into orbit by {{OV|105}} as the primary cargo of [[STS-88]] in 1998. Essential space station resources such as fluids, environmental control and life support systems, electrical and data systems are routed through Unity to supply work and living areas of the station. More than 50,000 mechanical items, 216 lines to carry fluids and gases, and 121 internal and external electrical cables using six miles of wire were installed in the Unity node. Unity is made of aluminum. Prior to its launch aboard Endeavour, conical Pressurized Mating Adapters (PMAs) were attached to the aft and forward berthing mechanisms of Unity. Unity and the two mating adapters together weighed about {{convert|25600|lb|kg|disp=flip|abbr=on}}. The adapters allow the docking systems used by the Space Shuttle and by Russian modules to attach to the node's hatches and berthing mechanisms.

Unity was carried into orbit as the primary cargo of the Space Shuttle Endeavour on STS-88, the first Space Shuttle mission dedicated to assembly of the station. On 6 December 1998, the STS-88 crew mated the aft berthing port of Unity with the forward hatch of the already orbiting Zarya module.

===Zvezda===
'''''[[Zvezda (ISS module)|Zvezda]]''''' ({{lang-ru|link=no|Звезда́}}, meaning "star"), also known as DOS-8, Service Module or SM ({{lang-ru|link=no|СМ}}). It provides all of the station's critical systems,{{clarify|date=August 2013}} its addition rendered the station permanently habitable for the first time, adding life support for up to six crew and living quarters for two. Zvezda's DMS-R computer handles guidance, navigation and control for the entire space station.<ref name="Navigation" /> A second computer which performs the same functions will be installed in the [[Nauka (ISS module)|Nauka]] module, FGB-2.

The hull of Zvezda was completed in February 1985, with major internal equipment installed by October 1986. The module was launched by a Proton-K rocket from Site 81/23 at Baikonur, on 12 July 2000. Zvezda is at the rear of the station according to its normal direction of travel and orientation, its engines are used to boost the station's orbit. Alternatively Russian and European spacecraft can dock to Zvezda's aft port and use their engines to boost the station.

===Destiny===
[[File:Destiny as just installed.jpg|thumb|''Destiny'' interior in 2001]]
'''''[[Destiny (ISS module)|Destiny]]''''' is the primary research facility for United States payloads aboard the ISS. In 2011, NASA solicited proposals for a not-for-profit group to manage all American science on the station which does not relate to manned exploration. The module houses 24 [[International Standard Payload Rack]]s, some of which are used for environmental systems and crew daily living equipment. ''Destiny'' also serves as the mounting point for the station's Truss Structure.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/destiny.html|title=NASA—US Destiny Laboratory|date=26 March 2007|accessdate=26 June 2007|publisher = NASA}}</ref>

===Quest===
'''''[[Quest Joint Airlock|Quest]]''''' is the only USOS airlock, and hosts spacewalks with both United States [[Extravehicular Mobility Unit|EMU]] and Russian [[Orlan space suit|Orlan]] [[Space suit|spacesuits]]. It consists of two segments: the equipment lock, which stores spacesuits and equipment, and the crew lock, from which astronauts can exit into space. This module has a separately controlled atmosphere. Crew sleep in this module, breathing a low nitrogen mixture the night before scheduled EVAs, to avoid [[decompression sickness]] (known as "the bends") in the low-pressure suits.<ref>{{cite web|url=http://spaceflight.nasa.gov/station/eva/outside.html|title=Space Station Extravehicular Activity|accessdate=11 March 2009|publisher=[[NASA]]|date=4 April 2004}}</ref>

===Pirs and Poisk===
'''''[[Pirs (ISS module)|Pirs]]''''' ({{lang-ru|link=no|Пирс}}, meaning "[[pier]]"), ({{lang-ru|link=no|Стыковочный отсек}}), "docking module", SO-1 or DC-1 (docking compartment), and '''''[[Poisk (ISS module)|Poisk]]''''' ({{lang-ru|link=no|По́иск}}; lit. ''Search''), also known as the [[Mini-Research Module]] 2 (MRM 2), {{lang|ru|''Малый исследовательский модуль 2''}}, or МИМ 2. Pirs and Poisk are Russian airlock modules. Each of these modules have 2 identical hatches. An outward opening hatch on the MIR space station failed after it swung open too fast after unlatching, due to a small amount of air pressure remaining in the airlock.<ref>{{cite web|url=http://www.russianspaceweb.com/mir_close_calls.html |title=Mir close calls |publisher=Russianspaceweb.com |accessdate=1 May 2012}}</ref> A different entry was used, and the hatch repaired. All EVA hatches on the ISS open inwards and are pressure sealing. Pirs was used to store, service, and refurbish Russian [[Orlan suits]] and provided contingency entry for crew using the slightly bulkier American suits. The outermost docking ports on both airlocks allow docking of Soyuz and Progress spacecraft, and the automatic transfer of propellants to and from storage on the ROS.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/pirs.html|title=Pirs Docking Compartment|publisher=NASA|accessdate=28 March 2009|date=10 May 2006}}</ref>

{{multiple image |align=right |image1=Node 2 - STS-134.jpg |width1=171 |image2=Node 3 - Isolated view.jpg |width2=190 |caption1=''Harmony'' node in 2011 |caption2=''Tranquility'' node in 2011}}

===Harmony===
'''''[[Harmony (ISS module)|Harmony]]''''' is the second of the station's node modules and the utility hub of the USOS. The module contains four racks that provide electrical power, bus electronic data, and acts as a central connecting point for several other components via its six Common Berthing Mechanisms (CBMs). The European Columbus and Japanese Kibō laboratories are permanently berthed to the starboard and port radial ports respectively. The nadir and zenith ports can be used for docking visiting spacecraft including HTV, Dragon, and Cygnus, with the nadir port serving as the primary docking port. American Shuttle Orbiters docked with the ISS via PMA-2, attached to the forward port.

===Tranquility===
'''''[[Tranquility (ISS module)|Tranquility]]''''' is the third and last of the station's US nodes, it contains an additional life support system to recycle waste water for crew use and supplements oxygen generation. Two of the four berthing locations are not used. One location has the ''[[Cupola (ISS module)|Cupola]]'' installed, one has the docking port adapter, and the third one is occupied by the [[Leonardo (ISS module)|''Leonardo'' PMM]].

[[File:S122e008264.jpg|thumb|left|Columbus module in 2008]]

===Columbus===
'''''[[Columbus (ISS module)|Columbus]]''''', the primary research facility for European payloads aboard the ISS, provides a [[European Drawer Rack|generic laboratory]] as well as facilities specifically designed for [[Biolab|biology]], [[European Physiology Modules|biomedical research]] and [[Fluid Science Laboratory|fluid physics]]. Several mounting locations are affixed to the exterior of the module, which provide power and data to external experiments such as the [[European Technology Exposure Facility]] (EuTEF), [[Solar Monitoring Observatory]], [[Materials International Space Station Experiment]], and [[Atomic Clock Ensemble in Space]]. A number of expansions are planned for the module to study [[quantum physics]] and [[cosmology]].<ref>{{cite news|url=http://www.nasaspaceflight.com/2008/01/prcb-plan-sts-122-for-net-feb-7-three-launches-in-10-11-weeks/|title=PRCB plan STS-122 for NET Feb 7—three launches in 10–11 weeks|accessdate=12 January 2008|author=Chris Bergin|date=10 January 2008|publisher=[[NASASpaceflight.com]]}}</ref><ref>{{cite web|url=http://www.esa.int/esaHS/ESAAYI0VMOC_iss_0.html|title=Columbus laboratory|publisher=[[European Space Agency]] (ESA)|accessdate=6 March 2009|date=10 January 2009}}</ref> ESA's development of technologies on all the main areas of life support has been ongoing for more than 20 years and are/have been used in modules such as Columbus and the ATV. The German Aerospace Center [[German Aerospace Center|DLR]] manages ground control operations for Columbus and the ATV is controlled from the French [[CNES]] [[Toulouse Space Center]].

===Kibō===
[[File:きぼうエアロック Kibo airlock.jpg|thumb|Not large enough for crew using spacesuits, the airlock on Kibō has a sliding drawer for external experiments.]]
'''''[[Kibo (ISS module)|Kibō]]''''' ({{lang-ja|きぼう}}, "[[hope]]") is the largest single ISS module. This laboratory is used to carry out research in space medicine, biology, Earth observations, materials production, biotechnology, communications research, and has facilities for growing plants and fish. During August 2011, an observatory mounted on Kibō, which utilises the ISS's orbital motion to image the whole sky in the X-ray spectrum, detected for the first time the moment a star was swallowed by a black hole.<ref>{{cite web|author=[[JAXA]] |url=http://kibo.jaxa.jp/en/experiment/ef/maxi/ |title=Monitor of All-sky X-ray Image (MAXI):Experiment – Kibo Japanese Experimental Module – JAXA |publisher=Kibo.jaxa.jp |date=30 March 2007 |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://www.jaxa.jp/press/2011/08/20110825_maxi_e.html |title=JAXA | Scientific paper in Nature using the Monitor of All-sky X-ray Image (MAXI) on Kibo and the Swift satellite (USA) observations – First observation of a massive black hole swallowing a star |publisher=Jaxa.jp |accessdate=1 May 2012}}</ref> The laboratory contains a total of 23 racks, including 10 experiment racks and has a dedicated airlock for experiments. In a 'shirt sleeves' environment, crew attach an experiment to the sliding drawer within the airlock, close the inner, and then open the outer hatch. By extending the drawer and removing the experiment using the dedicated robotic arm, payloads are placed on the external platform. The process can be reversed and repeated quickly, allowing access to maintain external experiments without the delays caused by EVAs.

<gallery widths="115px" mode="nolines">
File:Kibo - Pressurized Module.jpg|Pressurized Module
File:Kibo - Experiment Logistics Module (Pressurized Section).jpg|Experiment Logistics Module
File:Kibo - Exposed Facility.jpg|Exposed Facility
File:Kibo - Experiment Logistics Module (Exposed Section).jpg|Experiment Logistics Module
File:Kibo - Remote Manipulator System.jpg|Remote Manipulator System
</gallery>

A smaller pressurised module is attached to the top of Kibō, serving as a cargo bay. The dedicated Interorbital communications system allows large amounts of data to be beamed from Kibō's ICS, first to the Japanese KODAMA satellite in geostationary orbit, then to Japanese ground stations. When a direct communication link is used, contact time between the ISS and a ground station is limited to approximately 10 minutes per visible pass. When KODAMA relays data between a LEO spacecraft and a ground station, real-time communications are possible in 60% of the flight path of the spacecraft. Ground staff use [[telepresence robotics]] to conduct on-orbit research without crew intervention.

===Cupola===
{{multiple image |align=right |image1=STS130 cupola view1.jpg |width1=190 |image2=ISS-27 Dmitri Kondratyev and Paolo Nespoli photograph the Earth through the Cupola.jpg |width2=190 |caption1=The [[Cupola (ISS module)|Cupola]]'s design has been compared to the ''[[Millennium Falcon]]'' from ''[[Star Wars (film)|Star Wars]]''. |caption2=[[Dmitri Kondratyev]] and [[Paolo A. Nespoli|Paolo Nespoli]] in the Cupola. Background left to right, [[Progress M-09M]], [[Soyuz TMA-20]], the [[Leonardo (ISS module)|Leonardo]] module and [[Kounotori 2|HTV-2]].}}
'''[[Cupola (ISS module)|Cupola]]''' is a seven window observatory, used to view Earth and docking spacecraft. Its name derives from the Italian word cupola, which means "dome". The Cupola project was started by NASA and Boeing, but cancelled due to budget cuts. A barter agreement between NASA and the ESA resulted in the Cupola's development being resumed in 1998 by the ESA. It was built by Thales Alenia Space in Torino, Italy. The module comes equipped with robotic workstations for operating the station's main robotic arm and shutters to protect its windows from damage caused by micrometeorites. It features 7 windows, with a {{convert|80|cm|in|adj=on}} round window, the largest window on the station (and the largest flown in space to date). The distinctive design has been compared to the 'turret' of the fictitious ''[[Millennium Falcon]]'' from the motion picture ''[[Star Wars (film)|Star Wars]]'';<ref>{{cite web|url=http://www.space.com/7932-astronauts-bask-spectacular-views-space-windows.html |title=Astronauts Bask in Spectacular Views From New Space Windows |publisher=Space.com |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://news.nationalgeographic.com/news/2010/02/photogalleries/100218-international-space-station-cupola-iss-obama-nasa-pictures/ |title=First Photos: Space Station's Observation Deck Unveiled |work=National Geographic |accessdate=1 May 2012}}</ref> the original prop [[lightsaber]] used by actor [[Mark Hamill]] as [[Luke Skywalker]] in the 1977 film was flown to the station in 2007.<ref>{{cite web|url=http://www.space.com/4283-nasa-shuttle-launch-luke-skywalker-lightsaber.html |title=NASA Shuttle to Launch Luke Skywalker's Lightsaber |publisher=Space.com |date=28 August 2007 |accessdate=1 May 2012}}</ref>

===Rassvet===
'''''[[Rassvet (ISS module)|Rassvet]]''''' ({{lang-ru|link=no|Рассве́т}}; lit. "dawn"), also known as the Mini-Research Module 1 (MRM-1) ({{lang-ru|link=no|Ма́лый иссле́довательский модуль}}, {{lang|ru|МИМ 1}}) and formerly known as the Docking Cargo Module (DCM), is similar in design to the [[Mir Docking Module]] launched on [[STS-74]] in 1995. ''Rassvet'' is primarily used for cargo storage and as a docking port for visiting spacecraft. It was flown to the ISS aboard NASA's {{OV|104}} on the [[STS-132]] mission and connected in May 2010,<ref>{{cite web|url=http://www.nasaspaceflight.com/2009/04/sts-132-prcb-baselines-mission-to-deliver-russias-mrm-1/|title=STS-132: PRCB baselines Atlantis' mission to deliver Russia's MRM-1|author=Chris Gebhardt|publisher=NASAspaceflight.com|date=9 April 2009|accessdate=12 November 2009}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts132/news/STS-132-09.html|author=NASA|date=18 May 2010|accessdate=7 July 2010|title=STS-132 MCC Status Report #09}}</ref> Rassvet is the only Russian owned module launched by NASA, to repay for the launch of Zarya, which is Russian designed and built, but partially paid for by NASA.<ref>[http://www.russianspaceweb.com/iss_mim1.html MIM1]. russianspaceweb.com</ref>  Rassvet was launched with the Russian Nauka Laboratory's Experiments airlock temporarily attached to it, and spare parts for the European Robotic Arm.

===Leonardo===
[[File:STS-133 Installation PMM 3.jpg|thumb|''Leonardo'' installed]]
'''''[[Leonardo (ISS module)|Leonardo]]'' Permanent Multipurpose Module''' (PMM) is a storage module attached to the ''[[Tranquility (ISS module)|Tranquility]]'' node.<ref name="leo-esa20110301">{{cite news |url=http://www.esa.int/Our_Activities/Human_Spaceflight/MagISStra/Leonardo_attached_to_Space_Station |title=Leonardo Attached to Space Station |work=ESA.int |date=1 March 2011 |accessdate=11 June 2013}}</ref><ref>{{cite web |url=http://blogs.nasa.gov/spacestation/2015/05/27/module-relocated-prepping-station-for-commercial-crew/ |title=Module Relocated Prepping Station for Commercial Crew |publisher=NASA |first=Mark |last=Garcia |date=27 May 2015 |accessdate=27 May 2015}}</ref> The three NASA Space Shuttle [[Multi-Purpose Logistics Module|MPLM]] cargo containers—Leonardo, Raffaello and Donatello—were built for NASA in [[Turin]], Italy by Alcatel Alenia Space, now [[Thales Alenia Space]].<ref>[http://www.thalesaleniaspace-issmodules.com/ Thales Alenia Space and ISS modules – Thales Alenia Space and ISS modules]. Thalesaleniaspace-issmodules.com. Retrieved 8 October 2011.</ref> The MPLMs were provided to NASA's ISS programme by Italy (independent of their role as a member state of ESA) and are considered to be US elements. In a bartered exchange for providing these containers, the US gave Italy research time aboard the ISS out of the US allotment in addition to that which Italy receives as a member of ESA.<ref>[http://www.spaceref.com/iss/elements/mplm.html Space Station User's Guide]. SpaceRef (3 April 2001). Retrieved 8 October 2011.</ref> The Permanent Multipurpose Module was created by converting Leonardo into a module that could be permanently attached to the station.<ref name="PLM1">{{cite news|url=http://www.nasaspaceflight.com/2009/08/sts-133-five-crew-one-eva-mission-leave-mpm-on-iss|title=STS-133 refined to a five crew, one EVA mission—will leave MPLM on ISS|publisher=NASASpaceflight.com|author=Chris Gebhardt|date=5 August 2009}}</ref><ref name="PLM2">{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8226309.stm|title=Europe looks to buy Soyuz craft|work=BBC News|last=Amos|first=Jonathan|date=29 August 2009}}</ref><ref>{{cite web|url=http://forum.nasaspaceflight.com/index.php?topic=17437.msg483604#msg483604|publisher=NASASpaceflight.com|accessdate=12 October 2009|title=Shuttle Q&A Part 5|date=27 September 2009}}</ref>

===Scheduled additional modules===

====Nauka====
'''''[[Nauka (ISS module)|Nauka]]''''' ({{lang-ru|link=no|Нау́ка}}; lit. "science"), also known as the Multipurpose Laboratory Module (MLM) or FGB-2 ({{lang-ru|link=no|Многофункциональный лабораторный модуль}}, {{lang|ru|МЛМ}}), is the major Russian laboratory module. It was scheduled to arrive at the station in 2014, docking to the port that was occupied by the Pirs module.<ref>{{cite web|url=http://www.aviationweek.com/Article.aspx?id=/article-xml/asd_05_23_2012_p05-01-460939.xml|title=Russia Sees Moon Base As Logical Next Step| last=Morring| first=Frank| date=23 May 2012| publisher=Aviation Week|accessdate=29 May 2012}}</ref> The date has been postponed to February 2017.<ref>{{cite web|url=http://www.russianspaceweb.com/iss_fgb2.html|title=MLM (FGB-2)|author=Anatoly Zak|publisher=Russian Space Web|date=29 April 2014|accessdate=14 May 2014}}</ref> Prior to the arrival of the Nauka module, a Progress spacecraft was used to remove Pirs from the station, deorbiting it to reenter over the Pacific Ocean. Nauka contains an additional set of life support systems and attitude control. Originally it would have routed power from the single Science-and-Power Platform, but that single module design changed over the first ten years of the ISS mission, and the two science modules, which attach to Nauka via the [[Uzlovoy Module]], or Russian node, each incorporate their own large solar arrays to power Russian science experiments in the ROS.

Nauka's mission has changed over time. During the mid-1990s, it was intended as a backup for the FGB, and later as a universal docking module (UDM); its docking ports will be able to support automatic docking of both spacecraft, additional modules and fuel transfer. Nauka has its own engines. Smaller Russian modules such as Pirs and Poisk were delivered by modified [[Progress (spacecraft)|Progress]] spacecraft, and the larger modules; Zvezda, Zarya, and Nauka, were launched by Proton rockets. Russia plans to separate Nauka, along with the rest of the Russian Orbital Segment, before the ISS is deorbited, to form the [[OPSEK]] space station.

====Uzlovoy Module====
The '''[[Uzlovoy Module]]''' (UM), or Node Module is a 4 metric ton<ref name=Zak>{{cite web|last1=Zak|first1=Anatoly|title=Node Module|url=http://www.russianspaceweb.com/iss_node.html|website=RussianSpaceWeb.com|accessdate=7 January 2015}}</ref> ball shaped module that will support the docking of two scientific and power modules during the final stage of the station assembly and provide the Russian segment additional docking ports to receive Soyuz TMA and Progress M spacecraft. UM is to be incorporated into the ISS in 2016. It will be integrated with a special version of the Progress cargo ship and launched by a standard Soyuz rocket. The Progress would use its own propulsion and flight control system to deliver and dock the Node Module to the nadir (Earth-facing) docking port of the Nauka MLM/FGB-2 module. One port is equipped with an active hybrid docking port, which enables docking with the MLM module. The remaining five ports are passive hybrids, enabling docking of Soyuz and Progress vehicles, as well as heavier modules and future spacecraft with modified docking systems. The node module was conceived to serve as the only permanent element of the future Russian successor to the ISS, [[Orbital Piloted Assembly and Experiment Complex|OPSEK]]. Equipped with six docking ports, the Node Module would serve as a single permanent core of the future station with all other modules coming and going as their life span and mission required.<ref>[http://www.energia.ru/en/news/news-2011/news_01-13.html S.P. Korolev RSC Energia – News]. Energia.ru (13 January 2011). Retrieved 8 October 2011.</ref><ref>[http://www.russianspaceweb.com/iss_node.html Node Module]. Russianspaceweb.com. Retrieved 8 October 2011.</ref> This would be a progression beyond the ISS and Russia's modular MIR space station, which are in turn more advanced than early monolithic first generation stations such as Skylab, and early Salyut and Almaz stations.

'''Science Power Modules 1 & 2''' (NEM-1, NEM-2) ({{lang-ru|link=no|Нау́чно-Энергетический Модуль-1 и -2}})

====Bigelow Expandable Activity Module====
On 16 January 2013, [[Bigelow Aerospace]] was contracted by NASA to provide a [[Bigelow Expandable Activity Module]] (BEAM), scheduled to arrive at the space station in 2015 for a two-year technology demonstration.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/station/news/beam_feature.html |title=NASA to Test Bigelow Expandable Module on Space Station |publisher=NASA |date=16 January 2013 |accessdate=17 January 2013}}</ref> BEAM is an inflatable module that will be attached to the aft hatch of the port-side Tranquility module of the International Space Station. During its two-year test run, instruments will measure its structural integrity and leak rate, along with temperature and radiation levels. The hatch leading into the module will remain mostly closed except for periodic visits by space station crew members for inspections and data collection. Following the test run, the module will be detached and jettisoned from the station.<ref>{{cite web | url=http://www.spaceflightnow.com/news/n1301/16bigelow/ | title=Bigelow inflatable module bound for space station | last=Harwood | first=William | date=16 January 2013 | publisher=Spaceflightnow | accessdate=17 January 2013}}</ref>

[[image:ISS Habitation module.jpg|thumb|left|The cancelled Habitation module under construction in 1997]]

===Cancelled components===
Several modules planned for the station have been cancelled over the course of the ISS programme, whether for budgetary reasons, because the modules became unnecessary, or following a redesign of the station after the 2003 [[Space Shuttle Columbia disaster|''Columbia'' disaster]]. The US [[Centrifuge Accommodations Module]] was intended to host science experiments in varying levels of [[artificial gravity]].<ref>{{cite web|url=http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=12560&mid=269666|title=Where is the Centrifuge Accommodation Module (CAM)?|publisher=NASASpaceflight.com|accessdate=12 October 2009}}</ref> The US [[Habitation Module]] would have served as the station's living quarters. Instead, the sleep stations are now spread throughout the station.<ref>{{cite web|url=http://www.space.com/missionlaunches/060214_iss_module.html|title=NASA Recycles Former ISS Module for Life Support Research|author=Tariq Malik|accessdate=11 March 2009|publisher=Space.com|date=14 February 2006}}</ref> The US [[Interim Control Module]] and [[ISS Propulsion Module]] were intended to replace functions of ''Zvezda'' in case of a launch failure.<ref>{{cite web|title=ICM Interim Control Module|publisher=U.S. Naval Center for Space Technology|url=http://code8200.nrl.navy.mil/icm.html|archiveurl=https://web.archive.org/web/20070208164211/http://code8200.nrl.navy.mil/icm.html|archivedate=8 February 2007}}</ref> The Russian [[Universal Docking Module]], to which the cancelled Russian Research modules and spacecraft would have docked.<ref name="Zak">{{cite web|url=http://www.russianspaceweb.com/iss_russia.html|accessdate=3 October 2009|publisher=russianspaceweb.com|author=Anatoly Zak|title=Russian segment of the ISS}}</ref> The Russian [[Science Power Platform]] would have provided the [[Russian Orbital Segment]] with a power supply independent of the ITS solar arrays,<ref name="Zak" /> and two [[Russian Research Module]]s that were planned to be used for scientific research.<ref>{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/components/russian_laboratory.html|title=Russian Research Modules|publisher=Boeing|accessdate=21 June 2009}}</ref>

==Unpressurised elements==
[[File:Truss breakdown.png|thumb|right|ISS Truss Components breakdown showing Trusses and all ORUs in situ]]
The ISS features a large number of external components that do not require pressurisation. The largest such component is the [[Integrated Truss Structure]] (ITS), to which the station's main solar arrays and thermal radiators are mounted.<ref name="Arrays" /> The ITS consists of ten separate segments forming a structure 108.5 m (356 ft) long.<ref name="OnOrbit" />

The station in its complete form has several smaller external components, such as the six robotic arms, the three [[External Stowage Platform]]s (ESPs) and four [[ExPRESS Logistics Carrier]]s (ELCs).<ref name="Manifest" /><ref>{{cite web|url=http://www.nasa.gov/centers/marshall/news/background/facts/expressrack.html|title=EXPRESS Racks 1 and 2 fact sheet|accessdate=4 October 2009|date=12 April 2008|publisher=NASA}}</ref> Whilst these platforms allow experiments (including [[MISSE]], the STP-H3 and the [[Robotic Refueling Mission]]) to be deployed and conducted in the vacuum of space by providing electricity and processing experimental data locally, the platforms' primary function is to store [[Orbital Replacement Unit]]s (ORUs). ORUs are spare parts that can be replaced when the item either passes its design life or fails. Examples of ORUs include pumps, storage tanks, antennas and battery units. Such units are replaced either by astronauts during EVA or by robotic arms. Spare parts were routinely transported to and from the station via Space Shuttle resupply missions, with a heavy emphasis on ORU transport once the NASA Shuttle approached retirement.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/12/soyuz-tma-03m-docks-iss-returns-station-six-crewmembers-future-ops/ |title=Soyuz TMA-03M docks to ISS, returns station to six crewmembers for future ops |publisher=NASASpaceFlight.com |date=23 December 2011 |accessdate=1 May 2012}}</ref> Several shuttle missions were dedicated to the delivery of ORUs, including [[STS-129]],<ref name="EVA129">{{cite web|url=http://www.nasa.gov/centers/johnson/pdf/404493main_EVA_129_F_E1.pdf|title=EVA Checklist: STS-129 Flight Supplement|author=L. D. Welsch|publisher=NASA|date=30 October 2009}}</ref> [[STS-133]]<ref name="STS-133">{{cite web|url=http://www.nasa.gov/pdf/491387main_STS-133%20Press%20Kit.pdf|title=Space Shuttle Mission: STS-131|date=February 2011|publisher=NASA}}</ref> and [[STS-134]].<ref name="STS-134">{{cite web|url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf|title=Space Shuttle Mission: STS-134|publisher=NASA|date=April 2011}}</ref> {{asof|2011|01}}, only one other mode of transportation of ORUs had been utilised – the Japanese cargo vessel [[H-II Transfer Vehicle|HTV-2]] – which delivered an FHRC and CTC-2 via its Exposed Pallet (EP).<ref name="HTV2">{{cite web|url=http://iss.jaxa.jp/en/htv/mission/htv-2/library/presskit/htv2_presskit_en.pdf|title=HTV2: Mission Press Kit|publisher=Japan Aerospace Exploration Agency|date=20 January 2011}}</ref>{{update after|2013|1|28}}

[[File:STS-116 spacewalk 1.jpg|left|thumb|Construction of the [[Integrated Truss Structure]] over New Zealand.]]
There are also smaller exposure facilities mounted directly to laboratory modules; the JEM [[Japanese Experiment Module#Exposed Facility|Exposed Facility]] serves as an external '[[porch]]' for the Japanese Experiment Module complex,<ref>{{cite web|url=http://kibo.jaxa.jp/en/about/kibo/jef/|title=Exposed Facility:About Kibo|publisher=JAXA|date=29 August 2008|accessdate=9 October 2009}}</ref> and a facility on the European ''Columbus'' laboratory provides power and data connections for experiments such as the [[European Technology Exposure Facility]]<ref name="NASA">{{cite web|url=http://www.nasa.gov/mission_pages/station/science/experiments/EuTEF.html|title=NASA—European Technology Exposure Facility (EuTEF)|publisher=NASA|date=6 October 2008|accessdate=28 February 2009}}</ref><ref name="ESA">{{cite web|url=http://www.esa.int/esaMI/Columbus/SEM7ZTEMKBF_0.html|title=ESA—Columbus—European Technology Exposure Facility (EuTEF)|publisher=ESA|date=13 January 2009|accessdate=28 February 2009}}</ref> and the [[Atomic Clock Ensemble in Space]].<ref>{{cite web|url=http://www.esa.int/SPECIALS/HSF_Research/SEMJSK0YDUF_0.html|publisher=ESA|accessdate=9 October 2009|title=Atomic Clock Ensemble in Space (ACES)}}</ref> A [[remote sensing]] instrument, [[Stratospheric Aerosol and Gas Experiment|SAGE III-ISS]], is due to be delivered to the station in 2014 aboard a [[Dragon (spacecraft)|Dragon capsule]], and the [[Neutron star Interior Composition ExploreR|NICER]] experiment in 2016.<ref>{{cite web |url=http://heasarc.gsfc.nasa.gov/docs/nicer/papers/NICER-SPIE-July2012-v4.pdf | publisher=Goddard Space Flight Center |title=The Neutron star Interior Composition ExploreR (NICER): an Explorer mission of opportunity for soft x-ray timing spectroscopy |accessdate=8 April 2013 |author=NICER Team }}</ref><ref>{{cite web|url=http://www.nasa.gov/topics/earth/features/sage3.html|date=1 March 2011|accessdate=12 March 2011|publisher=NASA|title=Time to Fly: SAGE III — ISS Prepped for Space Station|author=Michael Finneran}}</ref> The largest such scientific payload externally mounted to the ISS is the [[Alpha Magnetic Spectrometer]] (AMS), a particle physics experiment launched on [[STS-134]] in May 2011, and mounted externally on the ITS. The AMS measures [[cosmic ray]]s to look for evidence of [[dark matter]] and [[antimatter]].<ref>{{cite web|url=http://ams.cern.ch/|title=The Alpha Magnetic Spectrometer Experiment|publisher=[[CERN]]|date=21 January 2009|accessdate=6 March 2009}}</ref>

===Robotic arms and cargo cranes===
{{Double image|right|Iss017e011097.jpg|250|Dextrereallyhasnohead.jpg|250|Commander [[Sergey Alexandrovich Volkov|Volkov]] stands on Pirs with his back to the [[Soyuz spacecraft|Soyuz]] whilst operating the manual [[Strela (crane)|Strela crane]] holding photographer [[Oleg Kononenko|Kononenko]]. [[Zarya]] is seen to the left and [[Zvezda (ISS module)|Zvezda]] across the bottom of the image.|[[Dextre]], like many of the station's experiments and robotic arms, can be operated from Earth and perform tasks while the crew sleeps.||}}

The [[Integrated Truss Structure]] serves as a base for the station's primary remote manipulator system, called the [[Mobile Servicing System]] (MSS), which is composed of three main components. [[Canadarm2]], the largest robotic arm on the ISS, has a mass of {{convert|1800|kg|lb}} and is used to dock and manipulate spacecraft and modules on the USOS, hold crew members and equipment in place during EVAs and move Dextre around to perform tasks.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/station/structure/elements/mss.html |title=Canadarm2 and the Mobile Servicing System |publisher=NASA |date=8 January 2013 |accessdate=22 June 2015}}</ref> [[Dextre]] is a {{convert|1560|kg|lb|abbr=on}} robotic manipulator with two arms, a rotating torso and has power tools, lights and video for replacing [[orbital replacement unit]]s (ORUs) and performing other tasks requiring fine control.<ref>{{cite web |url=http://www.asc-csa.gc.ca/eng/iss/dextre/default.asp |title=Dextre, the International Space Station's Robotic Handyman |publisher=Canadian Space Agency |accessdate=22 June 2015}}</ref> The [[Mobile Base System]] (MBS) is 2 platforms which rides on rails along the length of the station's main truss. It serves as a mobile base for Canadarm2 and Dextre, allowing the robotic arms to reach all parts of the USOS.<ref>{{cite web |url=http://www.asc-csa.gc.ca/eng/iss/mobile-base/default.asp |title=Mobile Base System |publisher=Canadian Space Agency |accessdate=22 June 2015}}</ref> To gain access to the Russian Segment a [[Grapple Fixture|grapple fixture]] was added to Zarya on [[STS-134]], so that Canadarm2 can inchworm itself onto the ROS.<ref name="presskit134">{{cite web |url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf |title=Space Shuttle Mission STS-134: Final Flight of ''Endeavour'' - Press Kit |format=PDF |publisher=NASA |pages=51-53 |date=April 2011 |accessdate=22 June 2015}}</ref> Also installed during STS-134 was the {{convert|50|ft|m|abbr=on|order=flip}} [[Orbiter Boom Sensor System]] (OBSS), which had been used to inspect head shield tiles on Space Shuttle missions and can be used on station to increase the reach of the MSS.<ref name="presskit134"/> Staff on Earth or the station can operate the MSS components via remote control, performing work outside the station without space walks.

Japan's [[Kibo (ISS module)#Remote Manipulator System|Remote Manipulator System]], which services the JEM Exposed Facility,<ref>{{cite web |url=http://kibo.jaxa.jp/en/about/kibo/rms/ |title=Remote Manipulator System: About Kibo |publisher=JAXA |date=29 August 2008 |accessdate=4 October 2009}}</ref> was launched on [[STS-124]] and is attached to the JEM Pressurised Module.<ref>{{cite web |url=http://www.nasa.gov/centers/johnson/news/station/2002/iss02-03.txt |title=International Space Station Status Report #02-03 |publisher=NASA |date=14 January 2002 |accessdate=4 October 2009}}</ref> The arm is similar to the Space Shuttle arm as it is permanently attached at one end and has a latching end effector for standard grapple fixtures at the other.

The [[European Robotic Arm]], which will service the Russian Orbital Segment, will be launched alongside the [[Multipurpose Laboratory Module]] in 2017.<ref>{{cite web |url=http://www.russianspaceweb.com/iss_fgb2.html |title=MLM (FGB-2) module of the ISS |publisher=RussianSpaceWeb |accessdate=16 June 2014}}</ref> The ROS does not require spacecraft or modules to be manipulated, as all spacecraft and modules dock automatically and may be discarded the same way. Crew use the two ''[[Strela (crane)|Strela]]'' ({{lang-ru|link=no|Стрела́}}; lit. Arrow) cargo cranes during EVAs for moving crew and equipment around the ROS. Each Strela crane has a mass of {{convert|45|kg|lb|abbr=on}}.

===Comparison===
The ISS follows [[Salyut]] and [[Almaz]] series, [[Cosmos 557]], [[Skylab]], and [[Mir]] as the 11th space station launched, as the [[Genesis II|Genesis]] prototypes were never intended to be manned. Other examples of modular station projects include the Soviet/Russian Mir and the planned Russian OPSEK and [[Chinese space station]]. The first space station, [[Salyut 1]], and other one-piece or 'monolithic' first generation space stations, such as Salyut 2,3,4,5, DOS 2, Kosmos 557, Almaz and NASA's [[Skylab]] stations were not designed for re-supply.<ref>http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/history.pdf</ref> Generally, each crew had to depart the station to free the only docking port for the next crew to arrive, Skylab had more than one docking port but was not designed for resupply. Salyut 6 and 7 had more than one docking port and were designed to be resupplied routinely during crewed operation.<ref>{{cite web|url=http://www.pbs.org/spacestation/station/russian.htm |title=Space Station | Russian Space History |publisher=Pbs.org |accessdate=1 May 2012}}</ref>

==Station systems==

===Life support===
{{Main|ISS ECLSS|Chemical oxygen generator}}
The critical systems are the atmosphere control system, the water supply system, the food supply facilities, the sanitation and hygiene equipment, and fire detection and suppression equipment. The Russian Orbital Segment's life support systems are contained in the Service Module Zvezda. Some of these systems are supplemented by equipment in the USOS. The MLM Nauka laboratory has a complete set of life support systems.

====Atmospheric control systems====
[[Image:SpaceStationCycle.svg|thumb|The interactions between the components of the ISS Environmental Control and Life Support System (ECLSS)|alt=A flowchart diagram showing the components of the ISS life support system.]]
The atmosphere on board the ISS is similar to the [[Atmosphere of Earth|Earth's]].<ref>{{cite web|url=http://science.howstuffworks.com/space-station2.htm |title=How Space Stations Work|first=Craig|last=Freudenrich|publisher=Howstuffworks|date=20 November 2000|accessdate=23 November 2008}}</ref> Normal air pressure on the ISS is 101.3 [[kilopascal|kPa]] (14.7 [[Pounds per square inch|psi]]);<ref>{{cite web |url=http://nasaexplores.com/show2_5_8a.php?id=04-032&gl=58|archiveurl=https://web.archive.org/web/20061114010931/http://www.nasaexplores.com/show2_5_8a.php?id=04-032&gl=58|archivedate=14 November 2006|work=NASAexplores|title=5–8: The Air Up There|publisher=NASA|accessdate=31 October 2008}}</ref> the same as at sea level on Earth. An Earth-like atmosphere offers benefits for crew comfort, and is much safer than the alternative, a pure oxygen atmosphere, because of the increased risk of a fire such as that responsible for the deaths of the [[Apollo 1]] crew.<ref>{{cite book|author=Clinton Anderson|display-authors=etal|publisher=US Government Printing Office|title=Report of the Committee on Aeronautical and Space Sciences, United States Senate—Apollo 204 Accident|date=30 January 1968|location=Washington, DC|page=8|url=http://klabs.org/richcontent/Reports/Failure_Reports/as-204/senate_956/as204_senate_956.pdf}}</ref> Earth-like atmospheric conditions have been maintained on all Russian and Soviet spacecraft.<ref name=spacemed>{{Citation | last1=Davis | first1=Jeffrey R. | last2=Johnson | first2=Robert | last3=Stepanek | first3=Jan | lastauthoramp=yes | title=Fundamentals of Aerospace Medicine | publisher=Lippincott Williams & Wilkins | place=Philadelphia PA, USA | volume=XII | pages=261–264 | year=2008}}</ref>

The ''[[Elektron (ISS)|Elektron]]'' system aboard ''Zvezda'' and a similar system in ''Destiny'' generate oxygen aboard the station.<ref name="OGS">{{cite web|url=http://www.space.com/businesstechnology/060215_techwed_iss_oxygen.html|title=Air Apparent: New Oxygen Systems for the ISS|author=Tariq Malik|publisher=Space.com|date=15 February 2006|accessdate=21 November 2008}}</ref> The crew has a backup option in the form of bottled oxygen and [[Vika oxygen generator|Solid Fuel Oxygen Generation]] (SFOG) canisters, a [[chemical oxygen generator]] system.<ref name="breath easy">{{cite web|url=http://science.nasa.gov/headlines/y2000/ast13nov_1.htm|title=Breathing Easy on the Space Station|author=Patrick L. Barry|publisher=NASA|date=13 November 2000|accessdate=21 November 2008}}</ref> Carbon dioxide is removed from the air by the [[Vozdukh]] system in ''Zvezda''. Other by-products of human metabolism, such as methane from the intestines and ammonia from sweat, are removed by [[Activated carbon|activated charcoal]] filters.<ref name="breath easy" />

Part of the ROS atmosphere control system is the oxygen supply, triple-redundancy is provided by the Elektron unit, solid fuel generators, and stored oxygen. The Elektron unit is the primary oxygen supply, {{chem|O|2}} and {{chem|H|2}} are produced by [[electrolysis]], with the {{chem|H|2}} being vented overboard. The 1 kW system uses approximately 1 litre of water per crew member per day from stored water from Earth, or water recycled from other systems. MIR was the first spacecraft to use recycled water for oxygen production. The secondary oxygen supply is provided by burning {{chem|O|2}}-producing [[Vika oxygen generator|Vika]] cartridges (see also [[ISS ECLSS]]). Each 'candle' takes 5–20 minutes to decompose at 450–500 °C, producing 600 litres of {{chem|O|2}}. This unit is manually operated.<ref>[http://suzymchale.com/ruspace/issrslss.html RuSpace | ISS Russian Segment Life Support System]. Suzymchale.com. Retrieved 8 October 2011.</ref>

The US Orbital Segment has redundant supplies of oxygen, from a pressurised storage tank on the Quest airlock module delivered in 2001, supplemented ten years later by ESA built Advanced Closed-Loop System (ACLS) in the Tranquility module (Node 3), which produces {{chem|O|2}} by electrolysis.<ref>[http://science.nasa.gov/science-news/science-at-nasa/2000/ast13nov_1/ Breathing Easy on the Space Station – NASA Science]. ''Science''.nasa.gov (13 November 2000). Retrieved 8 October 2011.</ref> Hydrogen produced is combined with carbon dioxide from the cabin atmosphere and converted to water and methane.

===Power and thermal control===
{{Main|Electrical system of the International Space Station|External Active Thermal Control System}}

{{Double image|left|ROSSA.jpg|200|P4 deployed.jpg|200|Russian solar arrays, backlit by sunset.|One of the eight truss mounted pairs of USOS solar arrays}}
Double-sided solar, or [[Photovoltaic]] arrays, provide [[Electric power|electrical power]] for the ISS. These bifacial cells are more efficient and operate at a lower temperature than single-sided cells commonly used on Earth, by collecting sunlight on one side and light [[Albedo|reflected off]] the Earth on the other.<ref>{{cite web |url=http://wenku.baidu.com/view/a815121ffc4ffe473368ab7a.html |title=The early history of bifacial solar cell_百度文库 |publisher=Wenku.baidu.com |date=25 October 2010 |accessdate=14 August 2012}}</ref> 

The Russian segment of the station, like the Space Shuttle and most spacecraft, uses 28 [[volt]] [[direct current|DC]] from four rotating solar arrays mounted on ''Zarya'' and ''Zvezda''. The USOS uses 130–180 V DC from the USOS PV array, power is stabilised and distributed at 160 V DC and converted to the user-required 124 V DC. The [[High voltage|higher distribution voltage]] allows smaller, lighter conductors, at the expense of crew safety. The ROS uses [[Extra-low voltage|low voltage]]. The two station segments share power with converters.<ref name="Arrays" />

The USOS solar arrays are arranged as four wing pairs, with each wing producing nearly 32.8 kW.<ref name="Arrays">{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/truss_segment.html|title=Spread Your Wings, It's Time to Fly|publisher=NASA|date=26 July 2006|accessdate=21 September 2006}}</ref> These arrays normally track the sun to maximise power generation. Each array is about 375 m2 (450 yd2) in area and {{convert|58|m|yd|0}} long. In the complete configuration, the solar arrays track the sun by rotating the ''alpha [[gimbal]]'' once per orbit; the ''beta gimbal'' follows slower changes in the angle of the sun to the orbital plane. The [[Night Glider mode]] aligns the solar arrays parallel to the ground at night to reduce the significant aerodynamic drag at the station's relatively low orbital altitude.<ref>{{cite journal|author=G. Landis and C-Y. Lu|year=1991|title=Solar Array Orientation Options for a Space Station in Low Earth Orbit|journal=Journal of Propulsion and Power|volume=7|issue=1|pages=123–125|doi=10.2514/3.23302}}</ref>

The station uses rechargeable [[Nickel hydrogen battery|nickel-hydrogen batteries]] (NiH2) for continuous power during the 35 minutes of every 90-minute orbit that it is eclipsed by the Earth. The batteries are recharged on the day side of the Earth. They have a 6.5-year lifetime (over 37,000 charge/discharge cycles) and will be regularly replaced over the anticipated 20-year life of the station.<ref>{{cite web|url=http://www.grc.nasa.gov/WWW/RT/RT1999/5000/5420miller.html|title=Nickel-Hydrogen Battery Cell Life Test Program Update for the International Space Station|accessdate=27 November 2009|publisher=NASA|author=Thomas B. Miller|date=24 April 2000}}</ref>

The station's large solar panels generate a high potential voltage difference between the station and the ionosphere. This could cause arcing through insulating surfaces and sputtering of conductive surfaces as ions are accelerated by the spacecraft plasma sheath. To mitigate this, plasma contactor units (PCU)s create current paths between the station and the ambient plasma field.<ref>[http://www.grc.nasa.gov/WWW/RT/RT1998/5000/5430patterson.html Cathodes Delivered for Space Station Plasma Contactor System]. Grc.nasa.gov (18 June 1999). Retrieved 8 October 2011.</ref>

[[File:EATCS.png|thumb|ISS External Active Thermal Control System (EATCS) diagram]]
The large amount of electrical power consumed by the station's systems and experiments is turned almost entirely into heat. The heat which can be dissipated through the walls of the stations modules is insufficient to keep the internal ambient temperature within comfortable, workable limits. [[Ammonia]] is continuously pumped through pipework throughout the station to collect heat, then into external radiators exposed to the cold of space, and back into the station.

The International Space Station (ISS) External Active Thermal Control System (EATCS) maintains an equilibrium when the ISS environment or heat loads exceed the capabilities of the Passive Thermal Control System (PTCS). Note Elements of the PTCS are external surface materials, insulation such as MLI, or Heat Pipes. The EATCS provides heat rejection capabilities for all the US pressurised modules, including the JEM and COF as well as the main power distribution electronics of the S0, S1 and P1 Trusses. The EATCS consists an internal, non-toxic, water coolant loop used to cool and dehumidify the atmosphere, which transfers collected heat into an external liquid ammonia loop capable of withstanding the much lower temperature of space, which is then circulated through radiators to remove the heat. The EATCS is capable of rejecting up to 70 kW, and provides a substantial upgrade in heat rejection capacity from the 14 kW capability of the Early External Active Thermal Control System (EEATCS) via the Early Ammonia Servicer (EAS), which was launched on [[STS-105]] and installed onto the P6 Truss.<ref>[http://www.nasa.gov/pdf/473486main_iss_atcs_overview.pdf ATCS Team Overview]. (PDF). Retrieved 8 October 2011.</ref>

===Communications and computers===
{{Main|Tracking and Data Relay Satellite|Luch (satellite)}}
{{See also2|[[ThinkPad#Use in space|ThinkPad use in space]]}}
[[File:ISS Communication Systems.png|thumb|The communications systems used by the ISS * Luch satellite not currently in use|alt=Diagram showing communications links between the ISS and other elements.]]
Radio communications provide [[telemetry]] and scientific data links between the station and [[Mission Control Center|Mission Control Centres]]. Radio links are also used during [[Space rendezvous|rendezvous and docking procedures]] and for audio and video communication between crewmembers, flight controllers and family members. As a result, the ISS is equipped with internal and external communication systems used for different purposes.<ref name="BoeingComm" />


The Russian Orbital Segment communicates directly with the ground via the ''[[Lira (ISS)|Lira]]'' [[Antenna (radio)|antenna]] mounted to ''Zvezda''.<ref name="ISSRG" /><ref>{{cite web|url=http://www.nasa.gov/home/hqnews/2005/mar/HQ_ss05015_ISS_status_report.html|title=International Space Station Status Report: SS05-015|last=Mathews|first=Melissa|author2=James Hartsfield|date=25 March 2005|work=NASA News|publisher=NASA|accessdate=11 January 2010}}</ref> The ''Lira'' antenna also has the capability to use the ''[[Luch (satellite)|Luch]]'' data relay satellite system.<ref name="ISSRG" /> This system, used for communications with ''Mir'', fell into disrepair during the 1990s, and as a result is no longer in use,<ref name="ISSRG" /><ref name="SSSM">{{cite book|first=David|last=Harland|title=The Story of Space Station Mir|publisher=Springer-Verlag New York Inc|date=30 November 2004|location=New York|isbn=978-0-387-23011-5}}</ref><ref name="Harvey">{{cite book|last=Harvey|first=Brian|title=The rebirth of the Russian space program: 50 years after Sputnik, new frontiers|publisher=Springer Praxis Books|year=2007|page=263|isbn=0-387-71354-9}}</ref> although two new ''Luch'' satellites—''Luch''-5A and ''Luch''-5B—were launched in 2011 and 2012 respectively to restore the operational capability of the system.<ref>{{cite web|publisher=RussianSpaceWeb|url=http://www.russianspaceweb.com/2011.html|accessdate=12 January 2010|title=Space exploration in 2011|date=4 January 2010|author=Anatoly Zak}}</ref> Another Russian communications system is the [[Voskhod-M]], which enables internal telephone communications between ''Zvezda'', ''Zarya'', ''Pirs'', ''Poisk'' and the USOS, and also provides a VHF radio link to ground control centres via antennas on ''Zvezda''{{'s}} exterior.<ref>{{cite web|url=http://www.nasa.gov/directorates/somd/reports/iss_reports/2010/05022010.html|date=2 May 2010|accessdate=7 July 2010|publisher=NASA|title=ISS On-Orbit Status 05/02/10}}</ref>

The [[US Orbital Segment]] (USOS) makes use of two separate radio links mounted in the [[Z1 truss]] structure: the [[S band]] (used for audio) and [[Ku band|Ku band]] (used for audio, video and data) systems. These transmissions are routed via the United States [[Tracking and Data Relay Satellite]] System (TDRSS) in [[geostationary orbit]], which allows for almost continuous real-time communications with [[Christopher C. Kraft Jr. Mission Control Center|NASA's Mission Control Center]] (MCC-H) in [[Houston]].<ref name="ISSBook" /><ref name="ISSRG" /><ref name="BoeingComm">{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/systems/communications_tracking.html|publisher=Boeing|accessdate=30 November 2009|title=Communications and Tracking|archiveurl = https://web.archive.org/web/20080611115319/http://www.boeing.com/defense-space/space/spacestation/systems/communications_tracking.html |archivedate = 11 June 2008}}</ref> Data channels for the Canadarm2, European ''Columbus'' laboratory and Japanese ''Kibō'' modules are routed via the S band and Ku band systems, although the [[European Data Relay System]] and a similar Japanese system will eventually complement the TDRSS in this role.<ref name="ISSBook" /><ref name="JAXA-MOU">{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/nasa_japan.html|title=Memorandum of Understanding Between the National Aeronautics and Space Administration of the United States of America and the Government of Japan Concerning Cooperation on the Civil International Space Station|publisher=NASA|accessdate=19 April 2009|date=24 February 1998}}</ref> Communications between modules are carried on an internal digital [[wireless network]].<ref>{{cite web|title=Operations Local Area Network (OPS LAN) Interface Control Document|format=PDF|publisher=NASA|url=http://www.spaceref.com/iss/computer/iss.ops.lan.icd.pdf|accessdate=30 November 2009|date=February 2000}}</ref>

[[File:STS-128 ISS-20 Destiny Canadarm2.jpg|thumb|left|Laptop computers surround the Canadarm2 console.]]
[[Ultra high frequency|UHF radio]] is used by astronauts and cosmonauts conducting [[Extra-vehicular activity|EVAs]]. UHF is employed by other spacecraft that dock to or undock from the station, such as Soyuz, Progress, HTV, ATV and the Space Shuttle (except the shuttle also makes use of the S band and Ku band systems via TDRSS), to receive commands from Mission Control and ISS crewmembers.<ref name="ISSRG" /> Automated spacecraft are fitted with their own communications equipment; the ATV uses a [[laser]] attached to the spacecraft and equipment attached to ''Zvezda'', known as the Proximity Communications Equipment, to accurately dock to the station.<ref>{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=16247|title=ISS/ATV communication system flight on Soyuz|accessdate=30 November 2009|publisher=[[EADS Astrium]]|date=28 February 2005}}</ref><ref>{{cite web|publisher=NASASpaceflight.com|author=Chris Bergin|url=http://www.nasaspaceflight.com/2009/11/sts-129-support-dragon-communication-demo-iss/|date=10 November 2009|accessdate=30 November 2009|title=STS-129 ready to support Dragon communication demo with ISS}}</ref>

The ISS is equipped with approximately 100 [[IBM]] and [[Lenovo]] [[ThinkPad#Use in space|ThinkPad]] model A31 and T61P laptop computers. Each computer is a [[commercial off-the-shelf]] purchase which is then modified for safety and operation including updates to connectors, cooling and power to accommodate the station's 28V DC power system and weightless environment. Heat generated by the laptops does not rise, but stagnates surrounding the laptop, so additional forced ventilation is required. Laptops aboard the ISS are connected to the station's [[wireless LAN]] via [[Wi-Fi]] and to the ground via Ku band. This provides speeds of 10 [[Megabit per second|Mbit/s]] to and 3 Mbit/s from the station, comparable to home [[digital subscriber line|DSL]] connection speeds.<ref name="issit">{{cite news |url=http://bits.blogs.nytimes.com/2010/01/22/first-tweet-from-space/ |title=First Tweet From Space |work=[[The New York Times]] |first=Nick |last=Bilton |date=22 January 2010 |accessdate=29 April 2014}}</ref><ref name="tested20121019">{{cite news |url=http://www.tested.com/science/space/449539-how-fast-isss-internet-and-other-space-questions-answered/ |title=How Fast is the ISS's Internet? (and Other Space Questions Answered) |work=Tested.com |first=Will |last=Smith |date=19 October 2012 |accessdate=29 April 2014}}</ref>

The operating system used for key station functions is the [[Debian]] [[GNU/Linux distribution]].<ref>{{cite news|last=Thomson|first=Iain|title=Penguins in spa-a-a-ce! ISS dumps Windows for Linux on laptops|url=http://www.theregister.co.uk/2013/05/10/iss_linux_debian_deployment/|accessdate=15 May 2013|newspaper=The Register|date=10 May 2013}}</ref> The migration from [[Microsoft Windows]] was made in May 2013 for reasons of reliability, stability and flexibility.<ref>{{cite news|last=Gunter|first=Joel|title=International Space Station to boldly go with Linux over Windows|url=http://www.telegraph.co.uk/technology/news/10049444/International-Space-Station-to-boldly-go-with-Linux-over-Windows.html|accessdate=15 May 2013|newspaper=The Daily Telegraph|date=10 May 2013}}</ref>

==Station operations==

===Expeditions and private flights===
[[File:Sts088-703-019e.jpg|thumb|Zarya and Unity were entered for the first time on 10 December 1998.]]
[[File:Soyuz tm-31 transported to launch pad.jpg|right|thumb|Soyuz TM-31 being prepared to bring the first resident crew to the station in October 2000]]
[[File:STS-115 ISS after undocking.jpg|thumb|right|ISS was slowly assembled over a decade of spaceflights and crews]]
[[File:Tracy Caldwell Dyson in Cupola ISS.jpg|thumb|Expeditions have included male and female crew-members from many nations]]
''See also the [[list of International Space Station expeditions]] (professional crew), [[space tourism]] (private travellers), and the [[list of human spaceflights to the ISS]] (both).''

Each permanent crew is given an expedition number. Expeditions run up to six months, from launch until undocking, an 'increment' covers the same time period, but includes cargo ships and all activities. Expeditions 1 to 6 consisted of 3 person crews, Expeditions 7 to 12 were reduced to the safe minimum of two following the destruction of the NASA Shuttle Columbia. From Expedition 13 the crew gradually increased to 6 around 2010.<ref name="ISSEx">{{cite web|title=International Space Station Expeditions|publisher=NASA|url=http://www.nasa.gov/mission_pages/station/expeditions/index.html|date=10 April 2009|accessdate=13 April 2009}}</ref><ref name="current">{{cite web|url=http://www.nasa.gov/mission_pages/station/main/index.html|title=International Space Station|accessdate=22 October 2008|publisher=NASA|year=2008|author=NASA}}</ref> With the arrival of the American [[Commercial Crew Development|Commercial Crew]] vehicles in the middle of the 2010s, expedition size may be increased to seven crew members, the number ISS is designed for.<ref>{{cite web|url=http://www.aviationweek.com/article.aspx?id=/article-xml/asd_07_26_2012_p01-02-480253.xml|title=ISS Research Hampered By Crew Availability|last=Morring|first=Frank|date=27 July 2012|quote=A commercial capability would allow the station's crew to grow from six to seven by providing a four-seat vehicle for emergency departures in addition to the three-seat Russian Soyuz capsules in use today.|publisher=Aviation Week|accessdate=30 July 2012}}</ref><ref>{{cite web|url=http://www.airspacemag.com/space-exploration/AS-Interview-Mike-Suffredini.html|title=Assembly (Nearly) Complete |last=Hoversten|first=Paul|date=1 May 2011|publisher=Air & Space Magazine|quote=In fact, we're designed on the U.S. side to take four crew. The ISS design is actually for seven. We operate with six because first, we can get all our work done with six, and second, we don't have a vehicle that allows us to fly a seventh crew member. Our requirement for the new vehicles being designed is for four seats. So I don't expect us to go down in crew size. I would expect us to increase it.|accessdate=8 May 2011}}</ref>

[[Sergei Krikalev]], member of [[Expedition 1]] and Commander of [[Expedition 11]] has spent more time in space than anyone else, a total of 803 days and 9 hours and 39 minutes. His awards include the [[Order of Lenin]], [[Hero of the Soviet Union]], [[Hero of the Russian Federation]], and 4 NASA medals. On 16 August 2005 at 1:44 am EDT he passed the record of 748 days held by [[Sergei Avdeyev]], who had 'time travelled' 1/50th of a second into the future on board MIR.<ref>{{cite web|url=http://www.popsci.com/scitech/article/2002-02/lets-do-time-warp-again?page=2 |archiveurl=https://web.archive.org/web/20100628190931/http://www.popsci.com/scitech/article/2002-02/lets-do-time-warp-again?page=2 |archivedate=28 June 2010 |title=Let's Do the Time Warp Again |publisher=Web.archive.org |date=28 June 2010 |accessdate=1 May 2012}}</ref> He participated in psychosocial experiment SFINCSS-99 (Simulation of Flight of International Crew on Space Station), which examined inter-cultural and other stress factors affecting integration of crew in preparation for the ISS spaceflights. Commander [[Michael Fincke]] has spent a total of 382 days in space – more than any other American astronaut.

Travellers who pay for their own passage into space are termed spaceflight participants by Roscosmos and NASA, and are sometimes informally referred to as space tourists, a term they generally dislike.{{refn|Privately funded travellers who have objected to the term include Dennis Tito, the first such traveller (''Associated Press'', 8 May 2001), [[Mark Shuttleworth]], founder of [[Ubuntu (operating system)|Ubuntu]] (''Associated Press, The Spokesman Review, 6 January 2002, p. A4''), Gregory Olsen and Richard Garriott.<ref>{{cite news|last=Schwartz|first=John|title=Russia Leads Way in Space Tourism With Paid Trips into Orbit|url=http://www.nytimes.com/2008/10/11/science/space/11space.html|newspaper=The New York Times|date=10 October 2008}}</ref><ref>{{cite web|last=Boyle|first=Alan|title=Space passenger Olsen to pull his own weight|url=http://msnbc.msn.com/id/9323509/#.Tz5lcFE-qr4|publisher=MSNBC}}</ref> Canadian astronaut Bob Thirsk said the term does not seem appropriate, referring to his crewmate, [[Guy Laliberté]], founder of [[Cirque du Soleil]].<ref>{{cite web|url=http://www.stcatharinesstandard.ca/ArticleDisplay.aspx?e=1975186&archive=true |title=Flight to space ignited dreams | St. Catharines Standard |publisher=Stcatharinesstandard.ca |accessdate=1 May 2012}}</ref> Anousheh Ansari denied being a tourist<ref>{{cite web|url=http://www.esa.int/esaHS/SEMD58BE8YE_business_0.html |title=ESA – Human Spaceflight and Exploration – Business – "I am NOT a tourist" |publisher=Esa.int |date=18 September 2006 |accessdate=1 May 2012}}</ref> and took offence at the term.<ref>{{cite web|url=http://www.space.com/2889-interview-anousheh-ansari-female-space-tourist.html |title=Interview with Anousheh Ansari, the First Female Space Tourist |publisher=Space.com |date=15 September 2006 |accessdate=1 May 2012}}</ref>|group=note|name}} All seven were transported to the ISS on Russian Soyuz spacecraft. When professional crews change over in numbers not divisible by the three seats in a Soyuz, and a short-stay crewmember is not sent, the spare seat is sold by MirCorp through Space Adventures. When the space shuttle retired in 2011, and the station's crew size was reduced to 6, space tourism was halted, as the partners relied on Russian transport seats for access to the station. Soyuz flight schedules increase after 2013, allowing 5 Soyuz flights (15 seats) with only two expeditions (12 seats) required.<ref>{{cite web|url=http://www.spaceflightnow.com/news/n1101/12soyuz/ |title=Breaking News | Resumption of Soyuz tourist flights announced |publisher=Spaceflight Now |accessdate=1 May 2012}}</ref> The remaining seats are sold for around {{US$|40 million}} to members of the public who can pass a medical. ESA and NASA criticised private spaceflight at the beginning of the ISS, and NASA initially resisted training [[Dennis Tito]], the first man to pay for his own passage to the ISS.{{refn|ESA director Jörg Feustel-Büechl said in 2001 that Russia had no right to send 'amateurs' to the ISS. A 'stand-off' occurred at the Johnson Space Centre between Commander Talgat Musabayev and NASA manager Robert Cabana. Cabana refused to train Dennis Tito, a member of Musabayev's crew along with Yuri Baturin. The commander argued that Tito had trained 700 hours in the last year and was as qualified as any NASA astronaut, and refused to allow his crew to be trained on the American portions of the station without Tito. Cabana stated training could not begin, and the commander returned with his crew to their hotel.|group=note|name}}  [[Toyohiro Akiyama]] was flown to Mir for a week, he was classed as a business traveller, as his employer, [[Tokyo Broadcasting System]], paid for his ticket, and he gave a daily TV broadcast from orbit.

[[Anousheh Ansari]] ({{lang-fa|انوشه انصاری}}) became the first Iranian in space and the first self-funded woman to fly to the station. Officials reported that her education and experience make her much more than a tourist, and her performance in training had been "excellent."<ref>{{cite web|last=Maher |first=Heather |url=http://www.rferl.org/content/article/1071358.html |title=U.S.: Iranian-American To Be First Female Civilian in Space |publisher=Radio Free Europe/Radio Liberty |date=15 September 2006 |accessdate=1 May 2012}}</ref> Ansari herself dismisses the idea that she is a tourist. She did Russian and European studies involving medicine and microbiology during her 10-day stay. The documentary ''[[Space Tourists]]'' follows her journey to the station, where she fulfilled "an age-old dream of man: to leave our planet as a «normal person» and travel into outer space."<ref>{{cite web|url=http://www.space-tourists-film.com/en/film_synopsis.php |title=Space Tourists | A Film By Christian Frei |publisher=Space-tourists-film.com |accessdate=1 May 2012}}</ref> In the film, some Kazakhs are shown waiting in the middle of the steppes for four rocket stages to literally fall from the sky. Film-maker Christian Frei states "Filming the work of the Kazakh scrap metal collectors was anything but easy. The Russian authorities finally gave us a film permit in principle, but they imposed crippling preconditions on our activities. The real daily routine of the scrap metal collectors could definitely not be shown. Secret service agents and military personnel dressed in overalls and helmets were willing to ''re-enact'' their work for the cameras – in an idealised way that officials in Moscow deemed to be presentable, but not at all how it takes place in reality."

Spaceflight participant [[Richard Garriott]] placed a [[Geocaching|geocache]] aboard the ISS during his flight.<ref>{{cite web|url=http://www.geocaching.com/seek/cache_details.aspx?wp=GC1BE91|title=International Space Station Traditional Geocache}}</ref> This is currently the only non-terrestrial geocache in existence.<ref>{{cite web |url=http://www.geekwire.com/2011/outer-space-ocean-floor-15m-geocaches-counting/|accessdate=27 February 2013|last=Cook|first=John|title=From outer space to the ocean floor, Geocaching.com now boasts more than 1.5 million hidden treasures|date=29 August 2011}}</ref>

===Orbit===
{{Double image|right|Internationale Raumstation Bahnhöhe (dumb version).png|300|Iss.ogg|235|Graph showing the changing altitude of the ISS from November 1998 until January 2009|Animation of ISS orbit from a North American geostationary point of view (sped up 1800 times)}}
The ISS is maintained in a nearly circular orbit with a minimum mean altitude of 330 km (205 mi) and a maximum of 410 km (255 mi), in the centre of the [[thermosphere]], at an [[inclination]] of 51.6 degrees to Earth's equator, necessary to ensure that Russian [[Soyuz (spacecraft)|Soyuz]] and [[Progress (spacecraft)|Progress]] spacecraft launched from the [[Baikonur Cosmodrome]] may be safely launched to reach the station. Spent rocket stages must be dropped into uninhabited areas and this limits the directions rockets can be launched from the spaceport.<ref name="MCC Answer">{{cite web|last=Cooney|first=Jim|title=Mission Control Answers Your Questions|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-112/09_04_12_54_17.html|location=Houston, TX|quote=Jim Cooney ISS Trajectory Operations Officer}}</ref><ref>{{cite book|last=Pelt|first=Michel van|title=Into the Solar System on a String : Space Tethers and Space Elevators|year=2009|publisher=Springer New York|location=New York, NY|isbn=0-387-76555-7|page=133|edition=1.}}</ref> The orbital inclination chosen was also low enough to allow American space shuttles launched from Florida to reach the ISS.

It travels at an average speed of 27,724 kilometres (17,227 mi) per hour, and completes {{Orbit|daily orbits|15.54}} orbits per day (93 minutes per orbit).{{Orbit|ref|<ref name="heavens-above"/>}}<ref name="tracking">{{cite web|url=http://spaceflight.nasa.gov/realdata/tracking/index.html|title=Current ISS Tracking data|accessdate=28 January 2009|publisher=NASA|date=15 December 2008|author=NASA}}</ref> The station's altitude was allowed to fall around the time of each NASA shuttle mission. Orbital boost burns would generally be delayed until after the shuttle's departure. This allowed shuttle payloads to be lifted with the station's engines during the routine firings, rather than have the shuttle lift itself and the payload together to a higher orbit. This trade-off allowed heavier loads to be transferred to the station. After the retirement of the NASA shuttle, the nominal orbit of the space station was raised in altitude.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/06/europes-atv-2-depart-iss-make-way-russias-progress-m-11m/ |title=Europe's ATV-2 departs ISS to make way for Russia's Progress M-11M |publisher=NASASpaceFlight.com |date=20 June 2011 |accessdate=1 May 2012}}</ref><ref name="Popular Mechanics">{{cite web|url=http://www.popularmechanics.com/science/air_space/4275571.html|title=The Uncertain Future of the International Space Station: Analysis|author=Rand Simberg|date=29 July 2008|accessdate=6 March 2009|publisher=[[Popular Mechanics]]}}</ref> Other, more frequent supply ships do not require this adjustment as they are substantially lighter vehicles.<ref name="Worldbook at NASA">{{cite web|url=http://www.nasa.gov/worldbook/intspacestation_worldbook.html|title = International Space Station|year=2005|accessdate=14 June 2008|publisher=World Book, Inc|author=James Oberg|work=World Book Online Reference Center}}{{dead link|date=May 2012}}</ref><ref name="nasa.gov-iss-environment">{{cite web|url=http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archiveurl=https://web.archive.org/web/20080213164432/http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archivedate=13 February 2008|title=ISS Environment|accessdate=15 October 2007|publisher=[[Johnson Space Center]]}}</ref>
[[File:ISS orbits 04132013.jpg|thumbnail|Orbits of the ISS, shown in April 2013]]
Orbital boosting can be performed by the station's two main engines on the ''[[Zvezda (ISS module)|Zvezda]]'' service module, or Russian or European spacecraft docked to Zvezda's aft port. The ATV has been designed with the possibility of adding a [[Automated Transfer Vehicle#ATV evolution proposals|second docking port]] to its other end, allowing it to remain at the ISS and still allow other craft to dock and boost the station. It takes approximately two orbits (three hours) for the boost to a higher altitude to be completed.<ref name="nasa.gov-iss-environment" /> In December 2008 NASA signed an agreement with the [[Ad Astra Rocket Company]] which may result in the testing on the ISS of a [[VASIMR]] plasma propulsion engine.<ref name="vasimr">{{cite web|url=http://www.adastrarocket.com/AdAstra-NASA_PR12Dec08.pdf|publisher=AdAstra Rocket Company|title=Press Release 121208|accessdate=7 December 2009|date=12 December 2008|format=PDF}}</ref> This technology could allow [[Orbital station-keeping|station-keeping]] to be done more economically than at present.<ref name="future-prop">{{cite web|url=http://www.nasa.gov/vision/space/travelinginspace/future_propulsion.html|title=Propulsion Systems of the Future|accessdate=29 May 2009|publisher=NASA}}</ref><ref>{{cite web|work=New Scientist|accessdate=7 October 2009|url=http://www.newscientist.com/article/dn17918-rocket-company-tests-worlds-most-powerful-ion-engine.html|title=Rocket company tests world's most powerful ion engine|author=David Shiga|date=5 October 2009}}</ref>

The Russian Orbital Segment contains the station's engines and control [[Bridge (nautical)|bridge]], which handles Guidance, Navigation and Control (ROS GNC) for the entire station.<ref name="Navigation">{{cite web|url=http://www.esa.int/export/esaHS/ESAOXX0VMOC_iss_0.html|title=DMS-R: ESA's Data Management System for the Russian Segment of the ISS}}</ref> Initially, Zarya, the first module of the station, controlled the station until a short time after the Russian service module Zvezda docked and was transferred control. Zvezda contains the ESA built DMS-R Data Management System.<ref name="EsaComputer">{{cite web|url=http://www.esa.int/esapub/onstation/onstation17/os17_chapter6.pdf|title=Exercising Control 49 months of DMS-R Operations}}</ref> Using two fault-tolerant computers (FTC), Zvezda computes the station's position and orbital trajectory using redundant Earth horizon sensors, Solar horizon sensors as well as Sun and star trackers. The FTCs each contain three identical processing units working in parallel and provide advanced fault-masking by majority voting. Zvezda uses gyroscopes and thrusters to turn itself around. Gyroscopes do not require propellant, rather they use electricity to 'store' momentum in flywheels by turning in the opposite direction to the station's movement. The USOS has its own computer controlled gyroscopes to handle the extra mass of that section. When gyroscopes 'saturate', reaching their maximum speed, thrusters are used to cancel out the stored momentum. During [[Expedition 10]], an incorrect command was sent to the station's computer, using about 14 kilograms of propellant before the fault was noticed and fixed. When attitude control computers in the ROS and USOS fail to communicate properly, it can result in a rare 'force fight' where the ROS GNC computer must ignore the USOS counterpart, which has no thrusters.<ref>{{cite web|url=http://pims.grc.nasa.gov/pimsdocs/public/ISS%20Handbook/hb_qs_vehicle_RussianUSGNCForceFight.pdf |title=Microsoft Word – hb_qs_vehicle_RussianUSGNCForceFight_pg1.doc |format=PDF |accessdate=1 May 2012}}</ref><ref>{{cite web|url=http://spaceflight.nasa.gov/spacenews/reports/issreports/2005/iss05-7.html|title = International Space Station Status Report #05-7|date=11 February 2005|publisher=NASA|accessdate=23 November 2008}}</ref><ref>{{cite book|title=Dynamics and Control of Attitude, Power, and Momentum for a Spacecraft Using Flywheels and Control Moment Gyroscopes|author=Carlos Roithmayr|format=PDF|year=2003|publisher=NASA|location=Langley Research Center|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030038806_2003038772.pdf|accessdate=12 July 2011}}</ref> When an ATV, NASA Shuttle, or Soyuz is docked to the station, it can also be used to maintain station attitude such as for troubleshooting. Shuttle control was used exclusively during [[STS-117|installation]] of the S3/S4 truss, which provides electrical power and data interfaces for the station's electronics.<ref>{{cite web|url=http://www.nasaspaceflight.com/2007/06/atlantis-ready-to-support-iss-troubleshooting/|title=Atlantis ready to support ISS troubleshooting|publisher=NASASPaceflight.com|author=Chris Bergin|accessdate=6 March 2009|date=14 June 2007}}</ref>

==Mission controls==
The components of the ISS are operated and monitored by their respective space agencies at [[Mission Control Center|mission control centres]] across the globe, including:
* Roscosmos's [[Mission Control Center#RKA Mission Control Center|Mission Control Center]] at [[Korolyov (city)|Korolyov]], Moscow Oblast, controls the [[Russian Orbital Segment]] which handles Guidance, Navigation & Control for the entire Station.,<ref name="Navigation" /><ref name="EsaComputer" /> in addition to individual Soyuz and Progress missions.<ref name="ISSRG" />
* ESA's [[ATV Control Centre]], at the [[Toulouse Space Centre]] (CST) in [[Toulouse]], France, controls flights of the unmanned European [[Automated Transfer Vehicle]].<ref name="ISSRG" />
* JAXA's [[JEM Control Center]] and [[HTV Control Center]] at [[Tsukuba Space Center]] (TKSC) in [[Tsukuba]], Japan, are responsible for operating the Japanese Experiment Module complex and all flights of the 'White Stork' HTV Cargo spacecraft, respectively.<ref name="ISSRG" />
* NASA's [[Christopher C. Kraft Jr. Mission Control Center|Mission Control Center]] at [[Lyndon B. Johnson Space Center]] in Houston, Texas, serves as the primary control facility for the United States segment of the ISS and also controlled the Space Shuttle missions that visited the station.<ref name="ISSRG">{{cite book|author=Gary Kitmacher|title=Reference Guide to the International Space Station| publisher =[[Apogee Books]]|location=Canada|year=2006|isbn=978-1-894959-34-6|issn=1496-6921|pages=71–80}}</ref>
* NASA's [[Payload Operations and Integration Center]] at [[Marshall Space Flight Center]] in [[Huntsville, Alabama]], coordinates payload operations in the USOS.<ref name="ISSRG" />
* ESA's [[Columbus Control Center|Columbus Control Centre]] at the [[German Aerospace Center|German Aerospace Centre]] (DLR) in [[Oberpfaffenhofen]], Germany, manages the European ''Columbus'' research laboratory.<ref name="ISSRG" />
* CSA's [[MSS Control]] at [[Saint-Hubert, Quebec]], Canada, controls and monitors the [[Mobile Servicing System]], or Canadarm2.<ref name="ISSRG" />
{{wide image|ISS Centers.svg|880px|Space centres involved with the ISS programme|alt=A world map highlighting the locations of space centres. See adjacent text for details.}}

===Repairs===
{{Main|Orbital Replacement Units|International Space Station maintenance}}
'''[[Orbital Replacement Units]]''' ('''ORUs''') are spare parts that can be readily replaced when a unit either passes its design life or fails. Examples of ORUs are pumps, storage tanks, controller boxes, antennas, and battery units. Some units can be replaced using robotic arms. Many are stored outside the station, either on small pallets called [[ExPRESS Logistics Carrier]]s (ELCs) or share larger platforms called [[External Stowage Platform]]s which also hold science experiments. Both kinds of pallets have electricity as many parts which could be damaged by the cold of space require heating. The larger logistics carriers also have computer local area network connections (LAN) and telemetry to connect experiments. A heavy emphasis on stocking the USOS with ORU's occurred around 2011, before the end of the NASA shuttle programme, as its commercial replacements, [[Cygnus (spacecraft)|Cygnus]] and [[Dragon (spacecraft)|Dragon]], carry one tenth to one quarter the payload.

[[File:ISS Unpressurized Platforms.png|thumb|Spare parts are called [[Orbit Replaceable Unit|ORU]]s; some are externally stored on pallets called [[ExPRESS Logistics Carrier|ELC]]s and [[External stowage platform|ESP]]s.]]

Unexpected problems and failures have impacted the station's assembly time-line and work schedules leading to periods of reduced capabilities and, in some cases, could have forced abandonment of the station for safety reasons, had these problems not been resolved. During [[STS-120]] in 2007, following the relocation of the P6 truss and solar arrays, it was noted during the redeployment of the array that it had become torn and was not deploying properly.<ref name="Astronauts notice tear in solar panel">{{cite news|url=http://www.redorbit.com/news/space/1123767/astronauts_notice_tear_in_solar_panel/index.html |title=Astronauts notice tear in solar panel|accessdate=30 October 2007|agency=Associated Press|date=30 October 2007|author=Liz Austin Peterson}}</ref> An EVA was carried out by [[Scott E. Parazynski|Scott Parazynski]], assisted by [[Douglas H. Wheelock|Douglas Wheelock]]. The men took extra precautions to reduce the risk of electric shock, as the repairs were carried out with the solar array exposed to sunlight.<ref name="Space Station's Damaged Panel Is Fixed">{{cite news|url=http://www.washingtonpost.com/wp-dyn/content/article/2007/11/03/AR2007110300227.html|title=Space Station's Damaged Panel Is Fixed|accessdate=4 November 2007|work=The Washington Post|date=4 November 2007|first=Rob|last=Stein}}</ref> The issues with the array were followed in the same year by problems with the starboard Solar Alpha Rotary Joint (SARJ), which rotates the arrays on the starboard side of the station. Excessive vibration and high-current spikes in the array drive motor were noted, resulting in a decision to substantially curtail motion of the starboard SARJ until the cause was understood. Inspections during EVAs on STS-120 and [[STS-123]] showed extensive contamination from metallic shavings and debris in the large drive gear and confirmed damage to the large metallic race ring at the heart of the joint, and so the joint was locked to prevent further damage.<ref name="joint-update">{{cite news|url=http://spaceflightnow.com/shuttle/sts123/080325sarj/index.html|title=Station chief gives detailed update on joint problem|accessdate=5 November 2008|author=William Harwood|publisher=CBS News & SpaceflightNow.com|date=25 March 2008}}</ref> Repairs to the joint were carried out during [[STS-126]] with lubrication of both joints and the replacement of 11 out of 12 trundle bearings on the joint.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts126/126_overview.html|title=Crew Expansion Prep, SARJ Repair Focus of STS-126|accessdate=5 November 2008|publisher=NASA|date=30 October 2008}}</ref><ref>{{cite news|url=http://www.spaceflightnow.com/shuttle/sts126/081118fd5/index.html|title=Astronauts prepare for first spacewalk of shuttle flight|date=18 November 2008|author=William Harwood|publisher=CBS News & SpaceflightNow.com|accessdate=22 November 2008}}</ref>

[[File:STS-120 EVA Scott Parazynski.jpg|thumb|While anchored on the end of the [[Orbiter Boom Sensor System|OBSS]], astronaut [[Scott Parazynski]] performs makeshift repairs to a US Solar array which damaged itself when unfolding, during [[STS-120]].|alt=Two black and orange solar arrays, shown uneven and with a large tear visible. A crew member in a spacesuit, attached to the end of a robotic arm, holds a latticework between two solar sails.]]
2009 saw damage to the S1 radiator, one of the components of the station's cooling system. The problem was first noticed in [[Soyuz spacecraft|Soyuz]] imagery in September 2008, but was not thought to be serious.<ref name="Radiator">{{cite web|url=http://www.nasaspaceflight.com/2009/04/iss-concern-s1-radiator-may-require-replacement-shuttle-mission/|author=Chris Bergin|date=1 April 2009|publisher=NASASpaceflight.com|title=ISS concern over S1 Radiator – may require replacement via shuttle mission|accessdate=3 April 2009}}</ref> The imagery showed that the surface of one sub-panel has peeled back from the underlying central structure, possibly due to micro-meteoroid or debris impact. It is also known that a Service Module thruster cover, jettisoned during an EVA in 2008, had struck the S1 radiator, but its effect, if any, has not been determined. On 15 May 2009 the damaged radiator panel's ammonia tubing was mechanically shut off from the rest of the cooling system by the computer-controlled closure of a valve. The same valve was used immediately afterwards to vent the ammonia from the damaged panel, eliminating the possibility of an ammonia leak from the cooling system via the damaged panel.<ref name="Radiator" />

Early on 1 August 2010, a failure in cooling Loop A (starboard side), one of two external cooling loops, left the station with only half of its normal cooling capacity and zero redundancy in some systems.<ref>{{cite web|url=http://spaceflightnow.com/news/n1007/31station/ |title=Problem forces partial powerdown aboard station |publisher=Spaceflightnow.com |date=31 July 2010 |accessdate=16 November 2010}}</ref><ref>{{cite web|url=http://www.spaceref.com/news/viewsr.html?pid=34622 |title=NASA ISS On-Orbit Status 1 August 2010 (early edition) |publisher=Spaceref.com |date=31 July 2010 |accessdate=16 November 2010}}</ref><ref>{{cite web|url=http://www.boeing.com/defense-space/space/spacestation/systems/atcs.html |title=ISS Active Control System |publisher=Boeing |date=21 November 2006 |accessdate=16 November 2010}}</ref> The problem appeared to be in the ammonia pump module that circulates the ammonia cooling fluid. Several subsystems, including two of the four CMGs, were shut down.

Planned operations on the ISS were interrupted through a series of EVAs to address the cooling system issue. A first EVA on 7 August 2010, to replace the failed pump module, was not fully completed due to an ammonia leak in one of four quick-disconnects. A second EVA on 11 August successfully removed the failed pump module.<ref>[http://spaceflightnow.com/station/exp24/100810evapre/index.html Spaceflight Now] "Wednesday spacewalk to remove failed coolant pump"</ref><ref>[http://www.nasaspaceflight.com/2010/08/live-second-eva-with-pump-module-changeout/ NASA spaceflight 11 August] "Large success for second EVA as failed Pump Module is removed"</ref> A third EVA was required to restore Loop A to normal functionality.<ref>[http://spaceflightnow.com/station/exp24/100811eva2/index5.html Spaceflight Now 12 August] "Station's bad pump removed; more spacewalking ahead"</ref><ref>[http://www.nasaspaceflight.com/2010/08/iss-cooling-returning-normal-confirming-etcs-pm-success/ Spaceflight Now, 18 August] ISS cooling configuration returning to normal confirming ETCS PM success</ref>

The USOS's cooling system is largely built by the American company [[Boeing]],<ref>{{cite web|url=http://www.space.com/businesstechnology/international-space-station-complexities-100802.html|title=Cooling System Malfunction Highlights Space Station's Complexity|publisher=Space.com|date=2 August 2010}}</ref> which is also the manufacturer of the failed pump.<ref>{{cite web|url=http://spaceflightnow.com/news/n1007/31station/|title=Spacewalks needed to fix station cooling problem|publisher=Spaceflightnow|date=31 July 2010}}</ref>

An air leak from the USOS in 2004,<ref>{{cite news|url=http://www.msnbc.msn.com/id/3882962/|title=Crew finds 'culprit' in space station leak|publisher=MSNBC|date=11 January 2004|author=James Oberg|accessdate=22 August 2010}}</ref> the venting of fumes from an ''[[Elektron (ISS)|Elektron]]'' oxygen generator in 2006,<ref>{{cite news|url=http://spaceflightnow.com/station/exp13/060918elektron.html|title=Oxygen Generator Problem Triggers Station Alarm|publisher = CBS News through Spaceflight Now|date=18 September 2006|author=William Harwood|accessdate=24 November 2008}}</ref> and the failure of the computers in the ROS in 2007 during [[STS-117]] left the station without thruster, ''Elektron'', ''[[Vozdukh]]'' and other environmental control system operations, the root cause of which was found to be condensation inside the electrical connectors leading to a short-circuit.{{Citation needed|date=June 2011}}
[[File:STS-134 EVA4 view to the Russian Orbital Segment.jpg|thumb|right|In the foreground, a set of heat radiators]]
The four Main Bus Switching Units (MBSUs, located in the S0 truss), control the routing of power from the four solar array wings to the rest of the ISS. In late 2011 MBSU-1, while still routing power correctly, ceased responding to commands or sending data confirming its health, and was scheduled to be swapped out at the next available EVA. In each MBSU, two power channels feed 160V DC from the arrays to two DC-to-DC power converters (DDCUs) that supply the 124V power used in the station. A spare MBSU was already on board, but 30 August 2012 EVA failed to be completed when a bolt being tightened to finish installation of the spare unit jammed before electrical connection was secured.<ref>{{cite web|author=30 August 2012 by Pete Harding |url=http://www.nasaspaceflight.com/2012/08/astronaut-perform-first-post-shuttle-spacewalk-iss |title=Astronaut duo complete challenging first post-Shuttle US spacewalk on ISS |publisher=Nasaspaceflight.com |date=30 August 2012 |accessdate=22 October 2013}}</ref> The loss of MBSU-1 limits the station to 75% of its normal power capacity, requiring minor limitations in normal operations until the problem can be addressed.

On 5 September 2012, in a second, 6 hr, EVA to replace MBSU-1, astronauts Sunita Williams and Akihiko Hoshide successfully restored the ISS to 100% power.<ref>[http://spaceref.com/international-space-station/critical-space-station-spacewalk-a-success.html Spaceref.com Sept 5, 2012] Marc Boucher "Critical Space Station spacewalk a Success".</ref>
[[File:Astronaut Mike Hopkins on Dec. 24 Spacewalk.jpg|thumb|Mike Hopkins on his Christmas Eve spacewalk]]
On 24 December 2013, astronauts made a rare Christmas Eve space walk, installing a new ammonia pump for the station's cooling system. The faulty cooling system had failed earlier in the month, halting many of the station's science experiments. Astronauts had to brave a "mini blizzard" of ammonia while installing the new pump. It was only the second Christmas Eve spacewalk in NASA history.<ref>{{cite web|last=AP|title=Astronauts Complete Rare Christmas Eve Spacewalk|url=http://www.leaker.com/astronauts-complete-rare-christmas-eve-spacewalk/|publisher=Leaker|accessdate=24 December 2013|date=24 December 2013}}</ref>

[[File:Iss orbit and expeditions.png|thumb|Iss orbit with calendar of expeditions and modules]]

==Fleet operations==
:{{See also|List of human spaceflights to the International Space Station|List of unmanned spaceflights to the International Space Station}}
A wide variety of manned and unmanned spacecraft have supported the station's activities. 
[[Progress M-28M]] (ISS-60P) was the 62nd Progress spacecraft planned to arrive at the ISS, including [[Progress M-MIM2|M-MIM2]] and [[Progress M-SO1|M-SO1]] which installed modules. 35 flights of the retired NASA Space Shuttle were made to the station.<ref name="ISStD">{{cite web|url=http://spaceflight.nasa.gov/station/isstodate.html|title=The ISS to Date|accessdate=21 March 2011|publisher=NASA|date=9 March 2011|author=NASA}}</ref> [[Soyuz TMA-16M|TMA-16M]] is the 42nd Soyuz flight, and there have been 5 [[Automated Transfer Vehicle|European ATV]], 4 Japanese [[H-II Transfer Vehicle|Kounotori]] 'White Stork', 8 [[SpaceX]] [[Dragon (spacecraft)|Dragon]] and 4 OSC [[Cygnus (spacecraft)|Cygnus]] planned arrivals.

===Currently docked/berthed===
''See also the list of [[List of International Space Station expeditions|professional]] crew, [[Space tourism|private]] travellers, [[List of human spaceflights to the ISS|both]] or just [[List of unmanned spaceflights to the ISS|unmanned spaceflights]].''

;Key
{{legend|lightblue|Uncrewed cargoships are in light blue}}
{{legend|#cfc|Crewed spacecraft are in light green}}

{| class="wikitable" style="margin: 1em auto 1em auto;text-align: left; font-size: 95%;"
|-Currently Docked
|style="text-align:center; background:#BBB" colspan="3" | '''Spacecraft and mission'''
|style="text-align:center; background:#BBB"|'''Location'''
|style="text-align:center; background:#BBB"|'''Arrived''' ([[UTC]])
|style="text-align:center; background:#BBB"|'''Departure date'''
|- style="background:lightblue;"
| {{flagicon|RUS}}
| [[Progress M-26M]]
| Progress 58 Cargo
| [[Zvezda (ISS module)|Zvezda]] aft
| 17 February 2015
| 14 August 2015
|- style="background:#cfc;"
| {{flagicon|RUS}}
| [[Soyuz TMA-16M]]
| [[Expedition 43]]/[[Expedition 44|44]]
| [[Poisk (ISS module)|Poisk]] zenith
| 28 March 2015
| 11 September 2015
|- style="background:lightblue;"
| {{flagicon|RUS}}
| [[Progress M-28M]]
| Progress 60 Cargo
| [[Pirs (ISS module)|Pirs]] nadir
| 5 July 2015
| 19 November 2015
|- style="background:#cfc;"
| {{flagicon|RUS}}
| [[Soyuz TMA-17M]]
| [[Expedition 44]]/[[Expedition 45|45]]
| [[Rassvet (ISS module)|Rassvet]] nadir
| 23 July 2015
| 22 December 2015
|}

===Scheduled launches and dockings/berthings===
* All dates are [[UTC]]. Dates are the earliest possible dates and may change.
* Forward ports are at the front of the station according to its normal direction of travel and orientation ([[Yaw, pitch and roll#Aircraft attitudes|attitude]]). Aft is at the rear of the station, used by spacecraft boosting the station's orbit. [[Nadir]] is closest the Earth, [[Zenith]] is on top.
* Spacecraft operated by government agencies are indicated with 'Gov' and under commercial arrangements are indicated with 'Com'.

;Key
{{legend|lightblue|Uncrewed cargoships are in light blue colour}}
{{legend|#cfc|Crewed spacecraft are in light green colour}}
{{legend|wheat|Modules are in wheat colour}}

{| class="wikitable" style="margin: 1em auto 1em auto;text-align: left; font-size: 95%;"
|+Planned Missions
|style="text-align:center; background:#BBB"|'''Launch''' ({{abbr|NET|Not Earlier Than}})
|style="text-align:center; background:#BBB"|'''Launch Vehicle'''
|style="text-align:center; background:#BBB"|'''Launch Site'''
|style="text-align:center; background:#BBB" colspan="3"| '''Launch Service Provider'''
|style="text-align:center; background:#BBB"|'''Payload'''
|style="text-align:center; background:#BBB"|'''Spacecraft'''
|style="text-align:center; background:#BBB"|'''Mission'''
|style="text-align:center; background:#BBB"|'''Docking / Berthing Port'''
|style="text-align:center; background:#BBB"|'''Ref.'''
|-
| nowrap| 16 August 2015
| nowrap| [[H-IIB]]
| nowrap| {{flagicon|JPN}} [[Tanegashima Space Center|Tanegashima]] [[Yoshinobu Launch Complex|LA-Y2]]
| nowrap| {{flagicon|JPN}}
| nowrap| Gov
| nowrap| [[JAXA]]
| style="background:lightblue;" nowrap| [[Kounotori 5|HTV-5]]
| nowrap| [[H-II Transfer Vehicle|HTV]]
| ISS Resupply
| nowrap| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule">{{cite web |url=http://spaceflightnow.com/launch-schedule/ |title=Launch Calendar |work=Spaceflight Now |date=28 March 2015 |accessdate=28 March 2015}}</ref><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 2 September 2015
| nowrap| [[Soyuz-FG]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:#cfc;" nowrap| [[Soyuz TMA-18M]]
| nowrap| [[Soyuz (spacecraft)|Soyuz]]
| [[Expedition 45]]/[[Expedition 46|46]] including [[European Space Agency|ESA]] [[Denmark|Danish]] Astronaut [[Andreas Mogensen]] and [[Kazakhstan]] cosmonaut [[Aydyn Aimbetov]].
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 21 September 2015
| nowrap| [[Soyuz-U]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:lightblue;" nowrap| [[Progress M-29M]]
| nowrap| [[Progress (spacecraft)|Progress]]
| ISS Resupply
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| NET September 2015 (TBD)
| nowrap|[[Falcon 9 v1.1]]
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 40|SLC-40]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[SpaceX]]
| style="background:lightblue;" nowrap| [[SpaceX CRS-8]]
| nowrap| [[Dragon (spacecraft)|Dragon]]
| ISS resupply. Will deliver [[Bigelow Expandable Activity Module|Bigelow Expandable Activity Module (BEAM)]] to the ISS.
| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| 21 November 2015
| nowrap| [[Soyuz-2 (rocket)|Soyuz-2.1a]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:lightblue;" nowrap| [[Progress MS-1]]
| nowrap| [[Progress (spacecraft)|Progress]]
| ISS Resupply. First launch of the new [[Progress (spacecraft)#Progress MS|Progress-MS]] variant.
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |

url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|-
| nowrap| 3 December 2015
| nowrap| [[Atlas V]] 401
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 41|SLC-41]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[United Launch Alliance|ULA]]
| style="background:lightblue;" nowrap| [[Cygnus CRS Orb-4]]
| nowrap| [[Cygnus (spacecraft)|Cygnus]]
| ISS Resupply
| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/><ref>{{cite web|url=http://www.space.com/27962-cygnus-cargo-spacecraft-new-rocket.html |title=Private Cargo Spacecraft Gets New Rocket Ride After Accident |publisher=Space.com |date= |accessdate=2015-04-04}}</ref>
|-
| nowrap| 15 December 2015
| nowrap| [[Soyuz-FG]]
| nowrap| {{flagicon|KAZ}} [[Baikonur Cosmodrome|Baikonur]] [[Gagarin's Start|Site 1/5]]
| nowrap| {{flagicon|RUS}}
| nowrap| Gov
| nowrap| [[Russian Federal Space Agency|Roscosmos]]
| style="background:#cfc;" nowrap| [[Soyuz TMA-19M]]
| nowrap| [[Soyuz (spacecraft)|Soyuz]]
| [[Expedition 46]]/[[Expedition 47|47]]
| nowrap|
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule"/>
|-
| nowrap| NET December 2015 (TBD)
| nowrap|[[Falcon 9 v1.1]]
| nowrap| {{flagicon|USA}} [[Cape Canaveral Air Force Station|Cape Canaveral]]
| nowrap| {{flagicon|USA}}
| nowrap| Com
| nowrap| [[SpaceX]]
| style="background:lightblue;" nowrap| [[SpaceX CRS-9]]
| nowrap| [[Dragon (spacecraft)|Dragon]]
| ISS resupply. Will deliver the IDA-2 segment of the [[NASA Docking System]] to the ISS.
| nowrap| [[Harmony (ISS module)|Harmony]] nadir
| nowrap| <ref name="sfnow-schedule"/><ref name="NASA-schedule">{{cite web |
url=http://www.nasa.gov/launchschedule/ |title=NASA Launch Schedule |work=NASA |accessdate=13 May 2015}}</ref>
|}

===Docking===
{{See also|Docking and berthing of spacecraft}}
[[File:Progress M-14M.jpg|thumb|The [[Progress M-14M]] resupply vehicle as it approaches the ISS in 2012. Over 50 unpiloted [[Progress (spacecraft)|Progress]] spacecraft have been sent with supplies during the lifetime of the station.]]
All Russian spacecraft and self-propelled modules are able to rendezvous and dock to the space station without human intervention using the [[Kurs (docking system)|Kurs]] docking system. Radar allows these vehicles to detect and intercept ISS from over 200 kilometres away. The European ATV uses star sensors and GPS to determine its intercept course. When it catches up it then uses laser equipment to [[Computer vision|optically]] recognise Zvezda, along with the Kurs system for redundancy.  Crew supervise these craft, but do not intervene except to send abort commands in emergencies. The Japanese [[H-II Transfer Vehicle]] parks itself in progressively closer orbits to the station, and then awaits 'approach' commands from the crew, until it is close enough for a robotic arm to grapple and berth the vehicle to the USOS. The American Space Shuttle was manually docked, and on missions with a [[Multi-Purpose Logistics Module|cargo container]], the container would be berthed to the Station with the use of manual robotic arms. Berthed craft can transfer [[International Standard Payload Rack]]s. Japanese spacecraft berth for one to two months. Russian and European Supply craft can remain at the ISS for six months,<ref>{{cite web|url=http://www.esa.int/esaMI/ATV/SEMBW0PR4CF_0.html |title=ESA — ATV — Crew role in mission control |publisher=Esa.int |date=2 March 2011 |accessdate=23 May 2011}}</ref><ref>{{cite web|url=http://www.esa.int/esaHS/ESA4ZJ0VMOC_iss_0.html |title=ESA — Human Spaceflight and Exploration — International Space Station — Automated Transfer Vehicle (ATV) |publisher=Esa.int |date=16 January 2009 |accessdate=23 May 2011}}</ref> allowing great flexibility in crew time for loading and unloading of supplies and trash. NASA Shuttles could remain docked for 11–12 days.<ref>{{cite web|url=http://www.boeing.com/news/frontiers/archive/2005/july/i_ids4.html|title=Space Shuttle upgrade lets astronauts at ISS stay in space longer|last=Memi|first=Ed|publisher=Boeing|accessdate=17 September 2011}}</ref>

The American manual approach to docking allows greater initial flexibility and less complexity. The downside to this mode of operation is that each mission becomes unique and requires specialised training and planning, making the process more labour-intensive and expensive. The Russians pursued an automated methodology that used the crew in override or monitoring roles. Although the initial development costs were high, the system has become very reliable with standardisations that provide significant cost benefits in repetitive routine operations.<ref>David C. Wo±nden and David K. Geller [http://www.usu.edu/mae/aerospace/publications/JDSC_RoadToAutonomy.pdf The Road to Autonomous Orbital Rendezvous]. Utah State University, Logan, Utah</ref> An automated approach could allow assembly of modules orbiting other worlds prior to crew arrival.

[[File:ISS and Endeavour seen from the Soyuz TMA-20 spacecraft 27.jpg|thumb|left|{{OV|105}}, [[ATV-2]], [[Soyuz TMA-21]] and [[Progress M-10M]] docked to the ISS during [[STS-134]], as seen from the departing [[Soyuz TMA-20]]|alt=A side-on view of the ISS showing a Space Shuttle docked to the forward end, an ATV to the aft end and Soyuz & Progress spacecraft projecting from the Russian segment.]]
Soyuz spacecraft used for crew rotation also serve as lifeboats for emergency evacuation; they are replaced every six months and have been used once to remove excess crew after the [[Space Shuttle Columbia disaster|Columbia disaster]].<ref>{{cite web|url=http://www.astronautix.com/flights/isseo6.htm |title=ISS EO-6 |publisher=Astronautix.com |accessdate=1 May 2012}}</ref> Expeditions require, on average, {{nowrap|2 722 kg}} of supplies, and {{As of|2011|03|09|lc=yes}}, crews had consumed a total of around {{nowrap|22 000 meals}}.<ref name="ISStD" /> Soyuz crew rotation flights and Progress resupply flights visit the station on average two and three times respectively each year,<ref name="Livelist">{{cite web|url=http://www.nasa.gov/mission_pages/station/resupply/index.html|archiveurl=https://web.archive.org/web/20080803015945/http://www.nasa.gov/mission_pages/station/resupply/index.html|archivedate=3 August 2008|title=Live listing of spacecraft operations|publisher=NASA|date=1 December 2009|accessdate=8 December 2009}}</ref> with the ATV and HTV planned to visit annually from 2010 onwards.{{Citation needed|date=January 2012}} Following retirement of the NASA Shuttle [[Cygnus spacecraft|Cygnus]] and [[SpaceX Dragon|Dragon]] were contracted to fly cargo to the station.<ref>{{cite web|author=Space Operations Mission Directorate|title=Human Space Flight Transition Plan|publisher=NASA|date=30 August 2006|url=http://www.nasa.gov/pdf/315546main_space_flight_transition_plan.pdf}}</ref><ref>{{cite press release|publisher=NASA|date=18 January 2006|title=NASA Seeks Proposals for Crew and Cargo Transportation to Orbit|url=http://www.spaceref.com/news/viewpr.html?pid=18791|accessdate=21 November 2006}}</ref>

From 26 February 2011 to 7 March 2011 four of the governmental partners (United States, ESA, Japan and Russia) had their spacecraft (NASA Shuttle, ATV, HTV, Progress and Soyuz) docked at the ISS, the only time this has happened to date.<ref>{{cite news|title=NASA proposes Soyuz photo op; shuttle launch readiness reviewed (UPDATED)|url=http://www.cbsnews.com/network/news/space/home/spacenews/files/b0e194a8338c336e823c03601f046707-157.html|publisher=CBS|accessdate=11 February 2011}}</ref> On 25 May 2012, [[SpaceX]] became the world's first privately held company to send cargo, via the [[Dragon (spacecraft)|Dragon spacecraft]], to the International Space Station.<ref name="NYT-20120525">{{cite news |last=Chang |first=Kenneth |title=Space X Capsule Docks at Space Station |url=http://www.nytimes.com/2012/05/26/science/space/space-x-capsule-docks-at-space-station.html |date=25 May 2012 |work=[[The New York Times]] |accessdate=25 May 2012 }}</ref>

===Launch and docking windows===
Prior to a ship's docking to the ISS, navigation and attitude control (GNC) is handed over to the ground control of the ships' country of origin. GNC is set to allow the station to drift in space, rather than fire its thrusters or turn using gyroscopes. The solar panels of the station are turned edge-on to the incoming ships, so residue from its thrusters does not damage the cells. When a NASA shuttle docked to the station, other ships were grounded, as the carbon wingtips, cameras, windows, and instruments aboard the shuttle were at too much risk from damage from thruster residue from other ships movements.

Approximately 30% of NASA shuttle launch delays were caused by poor weather. Occasional priority was given to the Soyuz arrivals at the station where the Soyuz carried crew with time-critical cargoes such as biological experiment materials, also causing shuttle delays. Departure of the NASA shuttle was often delayed or prioritised according to weather over its two landing sites.<ref>{{cite web |url=http://www.nasa.gov/home/hqnews/2009/may/HQ_09-118_Shuttle_Landing_Delayed.html |title=NASA's Space Shuttle Landing Delayed by Weather |publisher=NASA |first1=Katherine |last1=Trinidad |first2=Candrea |last2=Thomas |date=22 May 2009 |accessdate=26 June 2015}}</ref> Whilst the Soyuz is capable of landing anywhere, anytime, its planned landing time and place is chosen to give consideration to helicopter pilots and ground recovery crew, to give acceptable flying weather and lighting conditions. Soyuz launches occur in adverse weather conditions, but the cosmodrome has been shut down on occasions when buried by snow drifts up to 6 metres in depth, hampering ground operations.

==Life aboard==

===Crew activities===
[[File:Exp18home nasa big.jpg|thumb|Crewmember peers out of a window]]

A typical day for the crew begins with a wake-up at 06:00, followed by post-sleep activities and a morning inspection of the station. The crew then eats breakfast and takes part in a daily planning conference with Mission Control before starting work at around 08:10. The first scheduled exercise of the day follows, after which the crew continues work until 13:05. Following a one-hour lunch break, the afternoon consists of more exercise and work before the crew carries out its pre-sleep activities beginning at 19:30, including dinner and a crew conference. The scheduled sleep period begins at 21:30. In general, the crew works ten hours per day on a weekday, and five hours on Saturdays, with the rest of the time their own for relaxation or work catch-up.<ref>{{cite web|url=http://www.nasa.gov/pdf/287386main_110508_tl.pdf|title=ISS Crew Timeline|date=5 November 2008|accessdate=5 November 2008|publisher=NASA|format=PDF}}</ref>

The time zone used on board the ISS is [[Coordinated Universal Time]] (UTC). The windows are covered at night hours to give the impression of darkness because the station experiences 16 sunrises and sunsets a day. During visiting space shuttle missions, the ISS crew will mostly follow the shuttle's [[Mission Elapsed Time]] (MET), which is a flexible time zone based on the launch time of the shuttle mission.<ref>{{Cite web|title = NASA - Time in Space, A Space in Time|url = https://www.nasa.gov/mission_pages/station/research/news/time_in_space.html|website = www.nasa.gov|accessdate = 2015-05-05}}</ref><ref>{{Cite web|title = A Slice of Time Pie|url = https://web.archive.org/web/20130317075600/http://blogs.nasa.gov/cm/blog/ISS%20Science%20Blog/posts/post_1340820317951.html|date = 2013-03-17|accessdate = 2015-05-05}}</ref><ref>{{Cite web|title = Human Space Flight (HSF) - Crew Answers|url = http://spaceflight.nasa.gov/feedback/expert/answer/crew/sts-113/index_2.html|website = spaceflight.nasa.gov|accessdate = 2015-05-05}}</ref>

The station provides crew quarters for each member of the expedition's crew, with two 'sleep stations' in the ''Zvezda'' and four more installed in ''Harmony''.<ref>{{cite web|url=https://www.youtube.com/watch?v=Q4dG9vSyUFQ|title=At Home with Commander Scott Kelly (Video)|date=6 December 2010|publisher=NASA|accessdate=8 May 2011|location=International Space Station}}</ref><ref>{{cite web|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080013462_2008012884.pdf|title=International Space Station USOS Crew Quarters Development|first1=James Lee |last1=Broyan |first2=Melissa Ann |last2=Borrego |first3=Juergen F. |last3=Bahr|year=2008|publisher=SAE International|accessdate=8 May 2011}}</ref> The American quarters are private, approximately person-sized soundproof booths. The Russian crew quarters include a small window, but do not provide the same amount of ventilation or block the same amount of noise as their American counterparts. A crewmember can sleep in a crew quarter in a tethered sleeping bag, listen to music, use a laptop, and store personal items in a large drawer or in nets attached to the module's walls. The module also provides a reading lamp, a shelf and a desktop.<ref name="ESALife">{{cite web|url=http://www.esa.int/esaHS/ESAH1V0VMOC_astronauts_0.html|publisher=ESA|accessdate=28 October 2009|date=19 July 2004|title=Daily life}}</ref><ref name="NASACrewEquip">{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/126_payload.html|title=Station Prepares for Expanding Crew|publisher=NASA|first=Cheryl L. |last=Mansfield|date=7 November 2008|accessdate=17 September 2009}}</ref><ref name="CSALife">{{cite web|url=http://www.asc-csa.gc.ca/pdf/educator-liv_wor_iss.pdf|title=Living and Working on the International Space Station|accessdate=28 October 2009|publisher=CSA}}</ref> Visiting crews have no allocated sleep module, and attach a sleeping bag to an available space on a wall—it is possible to sleep floating freely through the station, but this is generally avoided because of the possibility of bumping into sensitive equipment.<ref name="SRLife">{{cite web|url=http://www.space.com/missionlaunches/090827-sts127-space-sleeping.html|title=Sleeping in Space is Easy, But There's No Shower|first=Tariq|last=Malik|accessdate=29 October 2009|date=27 July 2009|publisher=Space.com}}</ref> It is important that crew accommodations be well ventilated; otherwise, astronauts can wake up oxygen-deprived and gasping for air, because a bubble of their own exhaled carbon dioxide has formed around their heads.<ref name="ESALife" />
{{See also|Christmas on the International Space Station}}

===Food===
[[File:Meal STS127.jpg|thumb|alt=Nine astronauts seated around a table covered in open cans of food strapped down to the table. In the background a selection of equipment is visible, as well as the salmon-coloured walls of the Unity node.|The crews of [[STS-127]] and [[Expedition 20]] enjoy a meal inside ''Unity''.]]
{{See also|Space food}}

Most of the food on board is vacuum sealed in plastic bags. Cans are heavy and expensive to transport, so there are not as many. The preserved food is generally not held in high regard by the crew, and when combined with the reduced sense of taste in a microgravity environment,<ref name="ESALife" /> a great deal of effort is made to make the food more palatable. More spices are used than in regular cooking, and the crew looks forward to the arrival of any ships from Earth, as they bring fresh fruit and vegetables with them. Care is taken that foods do not create crumbs. Sauces are often used to ensure station equipment is not contaminated. Each crew member has individual food packages and cooks them using the on-board galley. The galley features two food warmers, a refrigerator added in November 2008, and a water dispenser that provides both heated and unheated water.<ref name="NASACrewEquip" /> Drinks are provided in dehydrated powder form and are mixed with water before consumption.<ref name="NASACrewEquip" /><ref name="CSALife" /> Drinks and soups are sipped from plastic bags with straws; solid food is eaten with a knife and fork, which are attached to a tray with magnets to prevent them from floating away. Any food that floats away, including crumbs, must be collected to prevent it from clogging up the station's air filters and other equipment.<ref name="CSALife" />

===Hygiene===
[[File:Zvezda toilet.jpg|thumb|right|upright|Space toilet in the [[Zvezda (ISS module)|Zvezda Service Module]]]]

Showers on space stations were introduced in the early 1970s on Skylab and Salyut 3.<ref name="livingandworking">Benson, Charles Dunlap and William David Compton. ''[http://history.nasa.gov/SP-4208/contents.htm Living and Working in Space: A History of Skylab]''. NASA publication SP-4208.</ref>{{rp|139}} By Salyut 6, in the early 1980s, the crew complained of the complexity of showering in space, which was a monthly activity.<ref name="Portree1995-86">{{cite book |url=http://history.nasa.gov/SP-4225/documentation/mhh/mirheritage.pdf |title=Mir Hardware Heritage |publisher=NASA |first=David S. F. |last=Portree |page=86 |date=March 1995 |id=Reference Publication 1357 |oclc=755272548}}</ref> The ISS does not feature a shower; instead, crewmembers wash using a water jet and wet wipes, with soap dispensed from a toothpaste tube-like container. Crews are also provided with rinseless shampoo and edible toothpaste to save water.<ref name="SRLife" /><ref>{{cite AV media |url=https://www.youtube.com/watch?v=uIjNfZbUYu8 |title=Karen Nyberg Shows How You Wash Hair in Space |publisher=NASA |work=YouTube.com |first=Karen |last=Nyberg |date=12 July 2013 |accessdate=6 June 2015}}</ref>

There are two [[space toilet]]s on the ISS, both of Russian design, located in ''[[Zvezda (ISS module)|Zvezda]]'' and ''[[Tranquility (ISS module)|Tranquility]]''.<ref name="NASACrewEquip" /> These Waste and Hygiene Compartments use a fan-driven suction system similar to the Space Shuttle Waste Collection System. Astronauts first fasten themselves to the toilet seat, which is equipped with spring-loaded restraining bars to ensure a good seal.<ref name="ESALife" /> A lever operates a powerful fan and a suction hole slides open: the air stream carries the waste away. Solid waste is collected in individual bags which are stored in an aluminium container. Full containers are transferred to Progress spacecraft for disposal.<ref name="NASACrewEquip" /><ref>{{cite web |first=Ed |last=Lu |title=Greetings Earthling |url=http://spaceflight.nasa.gov/station/crew/exp7/luletters/lu_letter9.html |date=8 September 2003 |accessdate=1 November 2009 |publisher=NASA}}</ref> Liquid waste is evacuated by a hose connected to the front of the toilet, with anatomically correct "urine funnel adapters" attached to the tube so both men and women can use the same toilet. Waste is collected and transferred to the Water Recovery System, where it is recycled back into drinking water.<ref name="CSALife" />

==Crew health and safety==
{{Main|Effect of spaceflight on the human body}}

===Radiation===
The ISS is partially protected from the space environment by the Earth's magnetic field. From an average distance of about {{convert|70,000|km|abbr=on}}, depending on Solar activity, the [[magnetosphere]] begins to deflect solar wind around the Earth and ISS. [[coronal mass ejection|Solar flares]] are still a hazard to the crew, who may receive only a few minutes warning. The crew of [[Expedition 10]] took shelter as a precaution in 2005 in a more heavily shielded part of the ROS designed for this purpose during the initial 'proton storm' of an X-3 class solar flare,<ref>{{cite web|title=Solar Flare Hits Earth and Mars|author=Ker Than|publisher=Space.com|date=23 February 2006|url=http://www.space.com/2080-solar-flare-hits-earth-mars.html}}</ref><ref>{{cite web|title=A new kind of solar storm|publisher=NASA|date=10 June 2005|url=http://science.nasa.gov/science-news/science-at-nasa/2005/10jun_newstorm/}}</ref> but without the limited protection of the Earth's [[magnetosphere]], interplanetary manned missions are especially vulnerable.

[[File:Aurora Australis.ogv|thumb|left|Video of the [[Aurora Australis]] taken by the crew of [[Expedition 28]] on an ascending pass from south of [[Madagascar]] to just north of Australia over the Indian Ocean.]]

Subatomic charged particles, primarily protons from [[cosmic ray]]s and [[solar wind]], are normally absorbed by the Earth's atmosphere. When they interact in sufficient quantity, their effect becomes visible to the naked eye in a phenomenon called an aurora. Without the protection of the Earth's atmosphere, which absorbs this radiation, crews are exposed to about 1 [[millisievert]] each day, which is about the same as someone would get in a year on Earth from natural sources. This results in a higher risk of astronauts developing cancer. Radiation can penetrate living tissue, damage DNA, and cause damage to the [[chromosome]]s of [[lymphocytes]]. These cells are central to the [[immune system]], and so any damage to them could contribute to the lowered [[immunity (medical)|immunity]] experienced by astronauts. Radiation has also been linked to a higher incidence of [[cataracts]] in astronauts. Protective shielding and protective drugs may lower the risks to an acceptable level.<ref name="JCB"/>

The radiation levels experienced on the ISS are about five times greater than those experienced by airline passengers and crew. The Earth's electromagnetic field provides almost the same level of protection against solar and other radiation in low Earth orbit as in the stratosphere. Airline passengers experience this level of radiation for no more than 15 hours for the longest intercontinental flights. For example, on a 12-hour flight an airline passenger would experience 0.1 millisieverts of radiation, or a rate of 0.2 millisieverts per day; only 1/5 the rate experienced by an astronaut in LEO.<ref>{{cite web|url=http://jag.cami.jccbi.gov./cariprofile.asp|title=Galactic Radiation Received in Flight|accessdate=20 May 2010|publisher=FAA Civil Aeromedical Institute}}</ref>
{{See also|Coronal mass ejection|Aurora (astronomy)}}

===Stress===
[[File:Nikolai Budarin in a sleep station in Zvezda.jpg|thumb|Cosmonaut [[Nikolai Budarin]] at work inside [[Zvezda (ISS module)|Zvezda]] service module crew quarters]]
There has been considerable evidence that psychosocial stressors are among the most important impediments to optimal crew morale and performance.<ref>{{cite book| author1 =Peter Suedfeld1| author2 = Kasia E. Wilk| author3 = Lindi Cassel| title = Flying with Strangers: Postmission Reflections of Multinational Space Crews}}</ref> Cosmonaut [[Valery Ryumin]], wrote in his journal during a particularly difficult period on board the [[Salyut 6]] space station: "All the conditions necessary for murder are met if you shut two men in a cabin measuring 18 feet by 20 and leave them together for two months."

NASA's interest in psychological stress caused by space travel, initially studied when their manned missions began, was rekindled when astronauts joined cosmonauts on the Russian space station Mir. Common sources of stress in early American missions included maintaining high performance under public scrutiny, as well as isolation from peers and family. The latter is still often a cause of stress on the ISS, such as when the mother of NASA Astronaut [[Daniel M. Tani|Daniel Tani]] died in a car accident, and when Michael Fincke was forced to miss the birth of his second child.


A study of the longest spaceflight concluded that the first three weeks represent a critical period where attention is adversely affected because of the demand to adjust to the extreme change of environment.<ref>{{cite doi|10.1080/001401398186991}}</ref> Skylab's 3 crews remained one, two, and three months respectively, long term crews on Salyut 6, [[Salyut 7]], and the ISS last about five to six months and Mir's expeditions often lasted longer. The ISS working environment includes further stress caused by living and working in cramped conditions with people from very different cultures who speak a different language. First generation space stations had crews who spoke a single language; second and third-generation stations have crew from many cultures who speak many languages. The ISS is unique because visitors are not classed automatically into 'host' or 'guest' categories as with previous stations and spacecraft, and may not suffer from feelings of isolation in the same way. Crew members with a military pilot background and those with an academic science background or teachers and politicians may have problems understanding each other's jargon and worldview.

===Medical===
[[File:Frank De Winne on treadmill cropped.jpg|thumb|Astronaut [[Frank De Winne]] is attached to the [[Treadmill with Vibration Isolation System|TVIS treadmill]] with bungee cords aboard the International Space Station|alt=Astronaut Frank De Winne is attached to the TVIS treadmill with bungee cords aboard the International Space Station]]
Medical effects of long-term weightlessness include [[muscle atrophy]], deterioration of the skeleton [[spaceflight osteopenia|(osteopenia)]], fluid redistribution, a slowing of the cardiovascular system, decreased production of red blood cells, balance disorders, and a weakening of the immune system. Lesser symptoms include loss of body mass, and puffiness of the face.<ref name="JCB" />

Sleep is disturbed on the ISS regularly due to mission demands, such as incoming or departing ships. Sound levels in the station are unavoidably high; because the atmosphere is unable to [[thermosiphon]], fans are required at all times to allow processing of the atmosphere which would stagnate in the freefall (zero-g) environment.

To prevent some of these adverse [[physiological]] effects, the station is equipped with two treadmills (including the [[Treadmill with Vibration Isolation System|COLBERT]]), and the aRED (advanced Resistive Exercise Device) which enables various weightlifting exercises which add muscle but do nothing for bone density,<ref>{{cite pmid|14600562}}</ref> and a stationary bicycle; each astronaut spends at least two hours per day exercising on the equipment.<ref name="ESALife" /><ref name="NASACrewEquip" /> Astronauts use bungee cords to strap themselves to the treadmill.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/bungee_running.html|accessdate=23 August 2009|title=Bungee Cords Keep Astronauts Grounded While Running|date=16 June 2009|publisher=NASA}}</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/station/behindscenes/colbert_feature.html|accessdate=23 August 2009|title=Do Tread on Me|date=19 August 2009|author=Amiko Kauderer|publisher=NASA}}</ref>

===Microbiological environmental hazards===
{{see also|Mir#Microbiological environmental hazards}}
Hazardous moulds which can foul air and water filters may develop aboard space stations. They can produce acids which degrade metal, glass, and rubber. They can also be harmful for the crew health. Microbiological hazards have lead into a development of the [[LOCAD#Portable Test System|LOCAD-PTS]] that can identify common bacteria and moulds faster than standard methods of [[Cell culture|culturing]], which may require a sample to be sent back to Earth.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2007/11may_locad3/|author=Trudy E. Bell|year=2007|title=Preventing "Sick" Spaceships|access-date=March 29, 2015}}</ref> {{As of|2012}}, 76 types of unregulated micro-organisms have been detected on the ISS.<ref>{{cite web|url=http://rt.com/news/iss-bacteria-mir-mutation-765/|title=Mutant space microbes attack ISS: 'Munch' metal, may crack glass |author= |date=April 23, 2012|website=[[RT (TV network)|RT]]|access-date=March 29, 2015}}</ref>

Reduced humidity, paint with mould killing chemical and antiseptic solutions can be used to prevent contamination in space stations. All materials used in the ISS are tested for resistance against fungi.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2000/ast26nov_1/|author=Patrick L. Barry|year=2000|title=Microscopic Stowaways on the ISS|access-date=March 29, 2015}}</ref>

==Threat of orbital debris==
{{Main|Space debris}}
{{Double image|right|SDIO KEW Lexan projectile.jpg|225|Debris-GEO1280.jpg|225|A 7 gram object (shown in centre) shot at 7 km/s (23,000 ft/sec) (the orbital velocity of the ISS) made this 15 cm (5 7/8 in) crater in a solid block of aluminium.|[[Radar]]-trackable objects including debris, with distinct ring of [[Geostationary orbit|geostationary]] satellites||}}
At the low altitudes at which the ISS orbits there is a variety of space debris,<ref>{{cite web|url=http://defensenews.com/blogs/space-symposium/2009/04/03/its-getting-crowded-up-there/#more-155|publisher=Defense News|accessdate=7 October 2009|author=Michael Hoffman|title=National Space Symposium 2009: It's getting crowded up there|date=3 April 2009}}</ref> consisting of many different objects including entire spent rocket stages, defunct satellites, explosion fragments—including materials from [[anti-satellite weapon]] tests, paint flakes, slag from solid rocket motors, and coolant released by [[US-A]] nuclear-powered satellites. These objects, in addition to natural [[micrometeoroid]]s,<ref>{{cite journal|author=F. L. Whipple|year=1949|title=The Theory of Micrometeoroids|journal=Popular Astronomy|volume=57|page=517|bibcode=1949PA.....57..517W}}</ref> are a significant threat. Large objects could destroy the station, but are less of a threat as their orbits can be predicted.<ref name="NSFdebris">{{cite web|publisher=NASASpaceflight.com|accessdate=28 June 2011|date=28 June 2011|author=Chris Bergin|url=http://www.nasaspaceflight.com/2011/06/sts-135-frr-july-8-atlantis-debris-misses-iss/|title=STS-135: FRR sets 8 July Launch Date for Atlantis – Debris misses ISS}}</ref><ref>{{cite web|author=Henry Nahra|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19890016664_1989016664.pdf|title=Effect of Micrometeoroid and Space Debris Impacts on the Space Station Freedom Solar Array Surfaces|date=24–29 April 1989|publisher=NASA|accessdate=7 October 2009}}</ref> Objects too small to be detected by optical and radar instruments, from approximately 1 cm down to microscopic size, number in the trillions. Despite their small size, some of these objects are still a threat because of their [[kinetic energy]] and direction in relation to the station. Spacesuits of spacewalking crew could puncture, causing [[Space exposure|exposure to vacuum]].<ref name=debrisdecomp>{{cite web|title=Space Suit Punctures and Decompression|url=http://www.asi.org/adb/04/03/08/suit-punctures.html|publisher=The Artemis Project|accessdate=20 July 2011}}</ref>

The station's shields and structure are divided between the ROS and the USOS, with completely different designs. On the USOS, a thin aluminium sheet is held apart from the hull, the sheet causes objects to shatter into a cloud before hitting the hull thereby spreading the energy of the impact. On the ROS, a carbon plastic honeycomb screen is spaced from the hull, an aluminium honeycomb screen is spaced from that, with a screen-vacuum thermal insulation covering, and glass cloth over the top. It is about 50% less likely to be punctured,  and crew move to the ROS when the station is under threat. Punctures on the ROS would be contained within the panels which are 70 cm square.

[[File:ISS impact risk.jpg|thumb|left|Example of [[risk management]]: A NASA model showing areas at high risk from impact for the International Space Station.]]

Space debris objects are tracked remotely from the ground, and the station crew can be notified.<ref>{{cite web|url=http://www.orbitaldebris.jsc.nasa.gov/library/EducationPackage.pdf |title=Microsoft PowerPoint – EducationPackage SMALL.ppt |format=PDF |accessdate=1 May 2012}}</ref> This allows for a [[Debris Avoidance Manoeuvre]] (DAM) to be conducted, which uses thrusters on the Russian Orbital Segment to alter the station's orbital altitude, avoiding the debris. DAMs are not uncommon, taking place if computational models show the debris will approach within a certain threat distance. Eight DAMs had been performed prior to March 2009,<ref>{{cite web|url=http://www.newscientist.com/article/dn16777-space-station-may-move-to-dodge-debris.html|title=Space station may move to dodge debris|work=New Scientist|date=16 March 2009|accessdate=20 April 2010|author=Rachel Courtland}}</ref> the first seven between October 1999 and May 2003.<ref name=ODOct08>{{cite journal|url=http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv12i4.pdf|title=ISS Maneuvers to Avoid Russian Fragmentation Debris|publisher=NASA|pages=1&2|journal=Orbital Debris Quarterly News|date=October 2008|accessdate=20 April 2010|volume=12|issue=4}}</ref> Usually the orbit is raised by one or two kilometres by means of an increase in orbital velocity of the order of 1 m/s. Unusually there was a lowering of 1.7 km on 27 August 2008, the first such lowering for 8 years.<ref name=ODOct08 /><ref>{{cite web|url=http://www.esa.int/esaMI/ATV/SEM64X0SAKF_0.html|title=ATV carries out first debris avoidance manoeuvre for the ISS|publisher=ESA|date=28 August 2008|accessdate=26 February 2010}}</ref> There were two DAMs in 2009, on 22 March and 17 July.<ref>{{cite journal|url=http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv14i1.pdf|title=Avoiding satellite collisions in 2009|page=2|journal=Orbital Debris Quarterly News|publisher=NASA|volume=14|date=January 2010|issue=1|accessdate=20 April 2010}}</ref> If a threat from orbital debris is identified too late for a DAM to be safely conducted, the station crew close all the hatches aboard the station and retreat into their [[Soyuz spacecraft]], so that they would be able to evacuate in the event the station was seriously damaged by the debris. This partial station evacuation has occurred on 13 March 2009, 28 June 2011, 24 March 2012 and 16 June 2015.<ref>{{cite news| url=http://www.bbc.co.uk/news/science-environment-17497766| title=ISS crew take to escape capsules in space junk alert| accessdate=24 March 2012 |work=BBC News |date=24 March 2012}}</ref><ref>{{cite news| url=https://blogs.nasa.gov/spacestation/2015/07/16/station-crew-takes-precautions-for-close-pass-of-space-debris/| title=Station Crew Takes Precautions for Close Pass of Space Debris| accessdate=16 June 2015 |work=NASA Blog |date=16 June 2015}}</ref>
Ballistic panels, also called micrometeorite shielding, are incorporated into the station to protect pressurised sections and critical systems. The type and thickness of these panels varies depending upon their predicted exposure to damage.

==End of mission==
[[File:Jules Verne Automated Transfer Vehicle re-enters Earth's atmosphere.jpg|thumb|right|Many ISS resupply spacecraft have already undergone [[Atmospheric entry|atmospheric re-entry]], such as [[Jules Verne ATV]]]]
According to a 2009 report, [[S.P. Korolev Rocket and Space Corporation Energia|Space Corporation Energia]] is considering methods to remove from the station some modules of the Russian Orbital Segment when the end of mission is reached and use them as a basis for a new station, known as the [[Orbital Piloted Assembly and Experiment Complex]] (OPSEK). The modules under consideration for removal from the current ISS include the [[Multipurpose Laboratory Module]] (MLM), currently scheduled to be launched in 2017, with other Russian modules which are currently planned to be attached to the MLM afterwards. Neither the MLM nor any additional modules attached to it would have reached the end of their useful lives in 2016 or 2020. The report presents a statement from an unnamed Russian engineer who believes that, based on the experience from ''Mir'', a thirty-year life should be possible, except for micrometeorite damage, because the Russian modules have been built with on-orbit refurbishment in mind.<ref name="RussiaSave">{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8064060.stm|title=Russia 'to save its ISS modules'|work=BBC News|date=22 May 2009|accessdate=23 May 2009|author=Anatoly Zak}}</ref>

According to the [[Outer Space Treaty]] the United States and Russia are legally responsible for all modules they have launched.<ref>[http://www.unoosa.org/pdf/publications/STSPACE11E.pdf United Nations Treaties and Principles on Outer Space]. (PDF). United Nations. New York. 2002. ISBN 92-1-100900-6. Retrieved 8 October 2011.</ref> In ISS planning, NASA examined options including returning the station to Earth via shuttle missions (deemed too expensive, as the station (USOS) is not designed for disassembly and this would require at least 27 shuttle missions<ref>{{cite book|url=http://search.nap.edu/openbook.php?record_id=9794&page=28|isbn=0-309-06938-6|publisher=National Academies Press|year=2000|pages=28–30|author=Thomas Kelly|title=Engineering Challenges to the Long-Term Operation of the International Space Station|accessdate=12 July 2011}}</ref>), natural orbital decay with random reentry similar to [[Skylab]], boosting the station to a higher altitude (which would delay reentry) and a controlled targeted de-orbit to a remote ocean area.<ref name=ISSEIS>{{cite web|title = Tier 2 EIS for ISS|publisher = NASA|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960053133_1996092350.pdf|accessdate=12 July 2011 }}</ref>

The technical feasibility of a controlled targeted deorbit into a remote ocean was found to be possible only with Russia's assistance.<ref name=ISSEIS /> The Russian Space Agency has experience from de-orbiting the [[Salyut 4]], [[Salyut 5|5]], [[Salyut 6|6]], [[Salyut 7|7]] and [[Mir]] space stations; NASA's first intentional controlled de-orbit of a satellite (the [[Compton Gamma Ray Observatory]]) occurred in 2000.<ref>{{cite web|title=Entry Debris Field estimation methods and application to Compton Gamma Ray Observatory|publisher=Mission Operations Directorate, NASA Johnson Space Center|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010084992_2001127597.pdf|accessdate=12 July 2011}}</ref> As of late 2010, the preferred plan is to use a slightly modified Progress spacecraft to de-orbit the ISS.<ref name=deo>{{cite web|url=http://www.nasa.gov/pdf/578543main_asap_eol_plan_2010_101020.pdf|title=ISS End-of-Life Disposal Plan|last=Suffredini|first=Michael|date=October 2010|publisher=NASA|accessdate=7 March 2012}}</ref> This plan was seen as the simplest, most cost efficient one with the highest margin.<ref name=deo /> [[Skylab]], the only space station built and launched entirely by the US, decayed from orbit slowly over 5 years, and no attempt was made to de-orbit the station using a [[Atmospheric entry|deorbital burn]]. Remains of Skylab hit populated areas of [[Esperance, Western Australia]]<ref name="debris">{{cite web|url=http://www.eclipsetours.com/sat/debris.html|accessdate=28 May 2011|title=Paul Maley's (Skylab spaceflight controller) Space Debris Page}}</ref> without injuries or loss of life.

The [[Exploration Gateway Platform]], a discussion by NASA and Boeing at the end of 2011, suggested using leftover USOS hardware and '[[Zvezda (ISS module)|Zvezda]] 2' {{sic}} as a refuelling depot and servicing station located at one of the Earth Moon [[Lagrange points]], L1 or L2. The entire USOS cannot be reused and will be discarded, but some other Russian modules are planned to be reused. [[Nauka (ISS module)|Nauka]], the [[Uzlovoy Module|Node module]], two science power platforms and Rassvet, launched between 2010 and 2015 and joined to the ROS may be separated to form [[OPSEK]].<ref>{{cite web|url=http://www.russianspaceweb.com/iss_dc.html|title=DC-1 and MIM-2|publisher=Russianspaceweb.com|accessdate=12 July 2011}}</ref> The [[Nauka (ISS module)|Nauka module]] of the ISS will be used in the station, whose main goal is supporting manned deep space exploration. OPSEK will orbit at a higher inclination of 71 degrees, allowing observation to and from all of the Russian Federation.

In February 2015, Roscosmos announced that it would remain a part of the international space station program until 2024.<ref name=sn20150225>{{cite news |last1=de Selding|first1=Peter B. |title=Russia — and Its Modules — To Part Ways with ISS in 2024 |url=http://spacenews.com/russia-and-its-modules-to-part-ways-with-iss-in-2024/ |accessdate=26 February 2015 |work=Space News |date=25 February 2015}}</ref> Nine months earlier—in response to US sanctions against Russia over the [[2014 Crimean crisis|conflict in the Crimea]]—Russian Deputy Prime Minister [[Dmitry Rogozin]] had stated that Russia would reject a US request to prolong the orbiting station's use beyond 2020, and would only supply rocket engines to the US for non-military satellite launches.<ref>{{cite web|url=http://www.telegraph.co.uk/news/worldnews/europe/russia/10828964/Russia-to-ban-US-from-using-Space-Station-over-Ukraine-sanctions.html|title=Russia to ban US from using Space Station over Ukraine sanctions|agency=Reuters|work=The Telegraph|date=13 May 2014|accessdate=14 May 2014}}</ref>

A proposed modification that would allow some of the ISS American and European segments to be reused would be to attach a [[VASIMR]] drive module to the vacated Node with its own onboard power source. It would allow long term reliability testing of the concept for less cost than building a dedicated space station from scratch.<ref name="nbcnews">{{cite web|url=http://www.nbcnews.com/id/48260759/ns/technology_and_science-space/#.U4LaQCjFBdg|title=From the earth to the moon, and then beyond - Technology & science - Space | NBC News|publisher=nbcnews.com|accessdate=27 May 2014}}</ref>

On March 28, 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS.<ref name=":0"/><ref name=":1"/> [[Igor Komarov]], the head of Russia's Roscosmos, made the announcement with NASA administrator Charles Bolden at his side. Komarov said "Roscosmos together with NASA will work on the programme of a future orbital station," "We agreed that the group of countries taking part in the ISS project will work on the future project of a new orbital station," "The first step is that the ISS will operate until 2024," and that Roscosmos and NASA "do not rule out that the station's flight could be extended,"<ref>{{cite web|url=http://www.spacedaily.com/reports/Russia_announces_plan_to_build_new_space_station_with_NASA_999.html|title=Russia announces plan to build new space station with NASA|work=spacedaily.com}}</ref> In a statement provided to SpaceNews March 28, NASA spokesman David Weaver said the agency appreciated the Russian commitment to extending the ISS, but did not confirm any plans for a future space station.<ref name="no plans" />

==Cost==
The ISS is arguably the most expensive single item ever constructed.<ref>{{cite web|author=Zidbits |url=http://zidbits.com/?p=19 |title=What Is The Most Expensive Object Ever Built? |publisher=Zidbits.com |date=6 November 2010 |accessdate=22 October 2013}}</ref> In 2010 the cost was expected to be $150 billion. It includes NASA's budget of $58.7 billion (inflation unadjusted) for the station from 1985 to 2015 ($72.4 billion in 2010 dollars), Russia's $12 billion, Europe's $5 billion, Japan's $5 billion, Canada's $2 billion, and the cost of 36 shuttle flights to build the station; estimated at $1.4 billion each, or $50.4 billion total. Assuming 20,000 person-days of use from 2000 to 2015 by two to six-person crews, each person-day would cost $7.5 million, less than half the inflation adjusted $19.6 million ($5.5 million before inflation) per person-day of Skylab.<ref name="lafleur20100308">{{cite news | url=http://www.thespacereview.com/article/1579/1 | title=Costs of US piloted programs | work=The Space Review | date=8 March 2010 | accessdate=18 February 2012 | author=Lafleur, Claude}} See author correction in comments.</ref>

==International co-operation==
[[File:ISS Agreements.jpg|thumb|right|upright|Dated 29 January 1998]]
{{Main|Politics of the International Space Station|International Space Station program}}
;Participating countries
{{columns-list|colwidth=20em|

* '''{{flagcountry|Canada}}'''
* '''{{flagcountry|Japan}}'''
* '''{{flagcountry|Russia}}'''
* '''{{flagcountry|United States}}'''
* [[File:ESA logo simple.svg|15x15px]] '''[[European Space Agency]]'''
** {{flagcountry|Austria}}
** {{flagcountry|Belgium}}
** {{flagcountry|Czech Republic}}
** {{flagcountry|Denmark}}
** {{flagcountry|Estonia}}
** {{flagcountry|Finland}}
** {{flagcountry|France}}
** {{flagcountry|Germany}}
** {{flagcountry|Greece}}
** {{flagcountry|Hungary}}
** {{flagcountry|Ireland}}
** {{flagcountry|Italy}}
** {{flagcountry|Luxembourg}}
** {{flagcountry|Netherlands}}
** {{flagcountry|Norway}}
** {{flagcountry|Poland}}
** {{flagcountry|Portugal}}
** {{flagcountry|Romania}}
** {{flagcountry|Spain}}
** {{flagcountry|Sweden}}
** {{flagcountry|Switzerland}}
** {{flagcountry|United Kingdom}}
}}

==Sightings from Earth==

===Naked eye===
The ISS is visible to the [[naked eye]] as a slow-moving, bright white dot due to reflected sunlight, and can be seen in the hours after sunset and before sunrise when the station remains sunlit but the ground and sky are dark.<ref name="Price2005">{{cite book |title=The Backyard Stargazer: An Absolute Beginner's Guide to Skywatching With and Without a Telescope |publisher=Quarry Books |location=Gloucester, MA |first=Pat |last=Price |page=140 |year=2005 |isbn=1-59253-148-2}}</ref> The ISS takes about ten minutes to move from one horizon to another, and will only be visible part of that time due to moving into or out of the Earth's shadow. Because of the size of its reflective surface area, the ISS is the brightest man-made object in the sky excluding [[Satellite flare|flares]], with an approximate maximum [[Apparent magnitude|magnitude of −4]] when overhead, similar to Venus. The ISS, like many satellites including the [[Iridium constellation]], can also produce flares of up to 8 or 16 times the brightness of Venus as sunlight glints off reflective surfaces.<ref>{{cite web|url=http://www.calsky.com/cs.cgi/Satellites/8 |title=Artificial Satellites > (Iridium) Flares |publisher=Calsky.com |accessdate=1 May 2012}}</ref><ref name="haydenplanetarium">{{cite web|url=http://www.amnh.org/our-research/hayden-planetarium/blog/how-to-spot-the-international-space-station-and-other-satellites |title=How to Spot the International Space Station (and other satellites) |publisher=Hayden Planetarium |accessdate=12 July 2011}}</ref> The ISS is also visible during broad daylight conditions, albeit with a great deal more effort.

Tools are provided by a number of websites such as [[Heavens-Above]] (see [[#Live viewing|''Live viewing'']] below) as well as [[smartphone]] applications that use the known [[ephemeris|orbital data]] and the observer's longitude and latitude to predict when the ISS will be visible (weather permitting), where the station will appear to rise to the observer, the altitude above the horizon it will reach and the duration of the pass before the station disappears to the observer either by setting below the horizon or entering into Earth's shadow.<ref name="see">{{cite web|url=http://spaceflight.nasa.gov/realdata/sightings/index.html|title=International Space Station Sighting Opportunities|accessdate=28 January 2009|publisher=NASA|date=2 July 2008|author=NASA}}</ref><ref>{{cite web|url=http://www.heavens-above.com/satinfo.aspx?satid=25544&lat=0&lng=0&loc=Unspecified&alt=0&tz=CET|title=ISS – Information|publisher=Heavens-Above.com|accessdate=8 July 2010}}</ref><ref>{{cite journal|author=Harold F. Weaver|title=The Visibility of Stars Without Optical Aid|journal=Publications of the Astronomical Society of the Pacific|volume=59|issue=350|year=1947|doi=10.1086/125956 }}</ref><ref name="daytime visibility">{{cite web|url=http://spaceweather.com/archive.php?view=1&day=05&month=06&year=2009|title=ISS visible during the daytime|accessdate=5 June 2009|work=Spaceweather.com|date=5 June 2009}}</ref>

{{Double image|right|Isshtv120090917200858nm.jpg|223|ISS 2008-01-10.jpg|230|The ISS and HTV photographed using a telescope-mounted camera by [[Ralf Vandebergh]]|A time exposure of a station pass|A fuzzy image of the ISS set against a black background, with a smaller, cylindrical object visible to the left of the station.|A view of a dark blue, starry sky with a white line visible from the bottom-left to the top-right of the image. A tree is visible to the bottom right.}}

In November 2012 NASA launched its 'Spot the Station' service, which sends people text and email alerts when the station is due to fly above their town.<ref>{{cite news| url= http://www.3news.co.nz/Get-notified-when-the-International-Space-Station-is-in-your-area/tabid/1160/articleID/275612/Default.aspx|work=3 News NZ |title= Get notified when the International Space Station is in your area| date=6 November 2012}}</ref>

The station is visible from 95% of the inhabited land on Earth, but is not visible from extreme northern or southern latitudes.<ref name="MCC Answer" />

===Astrophotography=== 
Using a telescope mounted camera to photograph the station is a popular hobby for astronomers, <ref>{{cite web|url=http://www.hobbyspace.com/SatWatching/ |title=Satellite Watching |publisher=HobbySpace |accessdate=1 May 2012}}</ref> whilst using a mounted camera to photograph the Earth and stars is a popular hobby for crew.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2003/24mar_noseprints/ |title=Space StationAstrophotography – NASA Science |publisher=Science.nasa.gov |date=24 March 2003 |accessdate=1 May 2012}}</ref> The use of a telescope or binoculars allows viewing of the ISS during daylight hours.<ref>{{cite web|url=http://www.zmescience.com/space/video-the-iss-and-atlantis-shuttle-as-seen-in-broad-daylight/ |title=[VIDEO] The ISS and Atlantis shuttle as seen in broad daylight |publisher=Zmescience.com |date=20 July 2011 |accessdate=1 May 2012}}</ref>

Parisian engineer and astrophotographer Thierry Legault, known for his photos of spaceships crossing the Sun (called [[occultation]]), travelled to Oman in 2011, to photograph the Sun, moon and space station all lined up.<ref>{{cite news| url=http://www.wired.com/2011/01/double-eclipse/ | work=Wired | first=Lisa | last=Grossman | title=Moon and Space Station Eclipse the Sun}}</ref> Legault, who received the Marius Jacquemetton award from the [[Société astronomique de France]] in 1999, and other hobbyists, use websites that predict when the ISS will pass in front of the Sun or Moon and from what location those passes will be visible.

==See also==
{{Wikipedia books|International Space Station}}
{{Portal|Spaceflight|Space}}
* [[Center for the Advancement of Science in Space]] - operates the US National Laboratory on the ISS
* [[List of space stations]]
* [[Origins of the International Space Station]]
* [[Space architecture]]

==Gallery==
[[File:ISS and Endeavour seen from the Soyuz TMA-20 spacecraft 14.jpg|thumb|left|550px|<center>International Space Station docked with ''Endeavour'' and ''Johannes Kepler'' ]]
{{-}}

==Notes==
{{Reflist|group="note"}}

==References==
{{Reflist|colwidth=25em}}

==External links==
{{Sister project links|wikt=no|n=Category:International Space Station|voy=Space}}

===Agency ISS websites===
{{divcol|20em}}
* {{flagicon|Canada}} [http://www.asc-csa.gc.ca/eng/iss/default.asp Canadian Space Agency]
* [[File:Not the esa logo.png]] [http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station European Space Agency]
* {{flagicon|France}} [http://www.cnes.fr/web/CNES-en/1422-iss-the-international-space-station.php Centre national d'études spatiales (National Centre for Space Studies)]
* {{flagicon|Germany}} [http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10300 German Aerospace Centre]
* {{flagicon|Italy}} [http://www.asi.it/en/flash_en/living Italian Space Agency]
* {{flagicon|Japan}} [http://www.jaxa.jp/projects/iss_human/index_e.html Japan Aerospace Exploration Agency]
* {{flagicon|Russia}} [http://www.energia.ru/eng/iss/iss.html S.P. Korolev Rocket and Space Corporation Energia]
* {{flagicon|Russia}} [http://www.roscosmos.ru/ Russian Federal Space Agency]
* {{flagicon|USA}} [http://www.nasa.gov/mission_pages/station/main/ National Aeronautics and Space Administration]
{{Div col end}}

===Research===
* [https://blogs.nasa.gov/spacestation/ NASA: Daily ISS Reports]
* [http://www.nasa.gov/mission_pages/station/science/index.html NASA: Station Science]
* [http://www.esa.int/Our_Activities/Human_Spaceflight/Columbus ESA: Columbus]
* [http://www.energia.ru/en/iss/researches/iss-researches.html RSC Energia: Science Research on ISS Russian Segment]

===Live viewing===
{{See also|List of satellite pass predictors}}
* [http://www.ustream.tv/channel/live-iss-stream Live ISS webcam] by NASA at uStream.tv
* [http://heavens-above.com/orbit.aspx?satid=25544 Real-time position] at Heavens-above.com
* [http://www.n2yo.com/?s=25544 Real-time position] at N2YO.com
* [http://wheretheiss.at/ Real-time position] at WheretheISS.at

===Multimedia===
* [http://www.nasa.gov/externalflash/ISSRG/index.html Interactive reference guide] at NASA.gov
* [http://spaceflight.nasa.gov/gallery/images/station/ Image gallery search page] at NASA.gov
* [http://i.usatoday.net/tech/graphics/iss_timeline/flash.htm Assembly sequence animation] by ''USA Today'' and NASA
* [https://www.youtube.com/watch?v=doN4t5NKW-k ISS tour with Sunita Williams] by NASA at YouTube.com
* [https://www.youtube.com/watch?v=QF2w2Dx_QMs ISS tour with André Kuipers] by ESA at YouTube.com
* [http://www.esa.int/Our_Activities/Human_Spaceflight/International_Space_Station/Highlights/International_Space_Station_panoramic_tour ISS photo tour with Samantha Cristoforetti] by ESA
* [https://www.youtube.com/watch?v=vMmcLmu3V1k ''The Future of Hope'', Kibo module documentary] by JAXA at YouTube.com
* [https://www.youtube.com/playlist?list=PLbyvawxScNbsoD_tGlw8kWCw3S5htiVKZ Journey to the ISS] by ESA at YouTube.com

{{ISS modules}}
{{International Space Station}}
{{Manned ISS flight}}
{{Unmanned ISS resupply flights}}
{{People currently in space}}
{{Space stations}}
{{US manned space programs}}
{{Russian manned space programs}}
{{Spaceflight}}
{{Orbital launches in 1998}}

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{{Authority control}}
[[Category:International Space Station| ]]
[[Category:Artificial satellites orbiting Earth]]
[[Category:Populated places established in 1998]]
[[Category:United States Department of Energy national laboratories]]
[[Category:Spacecraft launched in 1998]]
[[Category:1998 in spaceflight]]
[[Category:Articles containing video clips]]