View source for Engineering:Space colonization

{{short description|Concept of permanent human habitation outside of Earth}}

[[File:Lunar base concept drawing s99 04195.jpg|thumb|Artist's rendering of an envisioned lunar mining facility]]
[[File:NASA Cloud City on Venus.jpg|thumb|Artist's rendering of a crewed floating outpost on Venus of NASA's High Altitude Venus Operational Concept (HAVOC)]]
'''Space colonization''' (also called '''space settlement''' or '''extraterrestrial colonization''') is the use of [[Astronomy:Outer space|outer space]] or celestial bodies other than Earth for permanent habitation or as extraterrestrial territory.

The inhabitation and territorial use of extraterrestrial space has been proposed, for example, for [[Astronomy:Space habitat|space settlements]] or extraterrestrial mining enterprises. To date, no permanent space settlement other than temporary [[Engineering:Space habitat (facility)|space habitats]] have been set up, nor has any [[Astronomy:Extraterrestrial real estate|extraterrestrial territory or land been legally claimed]]. Making territorial claims in space is prohibited by international [[Astronomy:Space law|space law]], defining space as a [[Social:Common heritage of humanity|common heritage]]. International space law has had the goal to prevent colonial claims and militarization of space,<ref name="Collis 2009 pp. 47–65"/><ref name="Wilson Center 2021"/> and has advocated the installation of international regimes to regulate access to and sharing of space, particularly for specific locations such as the limited space of [[Astronomy:Geostationary orbit#Orbital allocation|geostationary orbit]]<ref name="Collis 2009 pp. 47–65"/> or the Moon.

Many arguments for and against space settlement have been made.<ref>For example, [http://www.thespaceshow.com The Space Show] {{Webarchive|url=https://web.archive.org/web/20200523173938/https://www.thespaceshow.com/ |date=2020-05-23}}, an online radio program, has had on average 16 shows per month going back to 2001, many of which discuss space settlement.</ref> The two most common in favor of colonization are [[Medicine:Space and survival|survival of human civilization]] and life from Earth in the event of a [[Unsolved:Global catastrophic risk|planetary-scale disaster (natural or human-made)]], and the availability of additional resources in space that could enable expansion of human society. The most common objections include concerns that the commodification of the cosmos may be likely to enhance the interests of the already powerful, including major economic and military institutions; enormous [[Finance:Opportunity cost|opportunity cost]] as compared to expending the same resources here on Earth; exacerbation of pre-existing detrimental processes such as [[Social:War|war]]s, [[Social:Economic inequality|economic inequality]], and environmental degradation.<ref>Alan Marshall (1995) [https://www.sciencedirect.com/science/article/abs/pii/026596469593233B Development and Imperialism in Space], ''Space Policy'' Vol. 11, Issue 1, pp41-52.</ref><ref>{{Cite book|last=Deudney|first=Daniel|title=Dark Skies: Space Expansionism, Planetary Geopolitics, and the Ends of Humanity|date=2020|publisher=Oxford University Press|isbn=978-0-19-009024-1|language=en|oclc=1145940182|author-link=Daniel Deudney}}</ref><ref>{{Cite journal|last=Torres|first=Phil|date=June 2018|title=Space colonization and suffering risks: Reassessing the "maxipok rule"|journal=Futures|language=en|volume=100|pages=74–85|doi=10.1016/j.futures.2018.04.008|s2cid=149794325}}</ref><ref name=Dickens-MR-2010-11>{{cite book|last1=Dickens|first1=Peter|last2=Ormrod|first2=James|url=http://monthlyreview.org/2010/11/01/the-humanization-of-the-cosmos-to-what-end/|title=The Humanization of the Cosmos - to What End?|date=Nov 2010|publisher=Monthly Review|access-date=2016-10-03|archive-url=https://web.archive.org/web/20161003183108/http://monthlyreview.org/2010/11/01/the-humanization-of-the-cosmos-to-what-end/|archive-date=2016-10-03|url-status=live}}</ref><ref name=Dickens-MR-2008-02>Dickens, Peter (Feb 2008).  [http://monthlyreview.org/2008/02/01/who-really-won-the-space-race/ Who Really Won the Space Race?] {{Webarchive|url=https://web.archive.org/web/20161003104456/http://monthlyreview.org/2008/02/01/who-really-won-the-space-race/ |date=2016-10-03 }}, ''Monthly Review''</ref><ref name=Dickens-MR-2017-03>Dickens, Peter (March 2017). [https://monthlyreview.org/2017/03/01/astronauts-at-work/ Astronauts at Work: The Social Relations of Space Travel] {{Webarchive|url=https://web.archive.org/web/20170328200150/https://monthlyreview.org/2017/03/01/astronauts-at-work/ |date=2017-03-28 }}, ''Monthly Review''</ref>

A space settlement would set a precedent that would raise numerous socio-political questions. The mere construction of the needed infrastructure presents daunting technological and economic challenges. Space settlements are generally conceived as providing for nearly all (or all) the needs of larger numbers of humans, in an environment out in space that is [[Astronomy:Effect of spaceflight on the human body|very hostile]] to human life and inaccessible for maintenance and supply from Earth. It would involve much development of currently primitive technologies, such as [[Engineering:Controlled ecological life-support system|controlled ecological life-support system]]s. With the high cost of [[Engineering:Orbital spaceflight|orbital spaceflight]] (around $1400 per kg, or $640 per pound, to [[Astronomy:Low Earth orbit|low Earth orbit]] by [[Engineering:Falcon Heavy|Falcon Heavy]]), a space settlement would currently be massively expensive. On the technological front, there is ongoing progress in making access to space cheaper ([[Astronomy:Reusable launch system|reusable launch system]]s could reach $20 per kg to orbit),<ref>{{cite web|url=http://www.popularmechanics.com/space/rockets/a7446/elon-musk-on-spacexs-reusable-rocket-plans-6653023/|title=Elon Musk on SpaceX's Reusable Rocket Plans|date=7 February 2012|access-date=13 June 2015|archive-url=https://web.archive.org/web/20170624061845/http://www.popularmechanics.com/space/rockets/a7446/elon-musk-on-spacexs-reusable-rocket-plans-6653023/|archive-date=24 June 2017|url-status=live}}</ref> and in creating automated manufacturing and construction techniques.

There are yet no plans for building space settlement by any large-scale organization, either government or private. However, many proposals, speculations, and designs for space settlements have been made through the years, and a considerable number of space colonization [[Engineering:Space advocacy|advocates]] and groups are active. Several famous scientists, such as [[Biography:Freeman Dyson|Freeman Dyson]], have come out in favor of space settlement.<ref name=dyson>{{cite web |author=Britt, Robert Roy |date=8 October 2001 |title=Stephen Hawking: Humanity Must Colonize Space to Survive |website=space.com |url=http://www.space.com/missionlaunches/colonize_why_011008-1.html |access-date=2006-07-28 |url-status=dead |archive-url=https://web.archive.org/web/20101125083046/http://www.space.com/missionlaunches/colonize_why_011008-1.html |archive-date=25 November 2010 }}.</ref>

==Definition==

The term has been used very broadly, being applied to any permanent human presence, even robotic,<ref>{{cite web|url=https://www.fastcompany.com/1653562/japan-robots-moon-base-robonaut-nasa-jaxa-lunar-rockets-constellation|title=Japan vs. NASA in the Next Space Race: Lunar Robonauts|work=Fast Company|date=28 May 2010|access-date=12 June 2015}}</ref><ref>{{cite web|url=http://sservi.nasa.gov/articles/japan-plans-2-billion-robot-moon-base-by-2020/|title=SOLAR SYSTEM EXPLORATION RESEARCH|access-date=11 August 2017}}</ref> particularly along with the term "settlement", being imprecisely applied to any human [[Engineering:Space habitat (facility)|space habitat]], from [[Research station|research station]]s to [[Astronomy:Space habitat|self-sustaining communities in space]].

The word colony and colonization are terms rooted in colonial history on Earth, making it a [[Social:Human geography|human geographic]] as well as particularly a political term.
This broad use for any permanent human activity and development in space has been criticized, particularly as [[Social:Colonialism|colonialist]] and undifferentiated<ref>{{cite web|url=https://www.space.com/bill-nye-space-settlement-not-colonization.html|author=Mike Wall|date=25 October 2019|title=Bill Nye: It's Space Settlement, Not Colonization|website=Space.com|access-date=26 November 2020}}</ref> (see below [[Engineering:Space colonization#Objections|Objections]]).

In this sense, a colony is a settlement that claims territory and exploits it for the [[Social:Settler|settler]]s or their metropole. Therefore a human outpost, while possibly a space habitat or even a space settlement, does not automatically constitute a space colony.<ref name="Bartels 2018">{{cite web | last=Bartels | first=Meghan | title=People are calling for a movement to decolonize space-here's why | website=Newsweek | date=May 25, 2018 | url=https://www.newsweek.com/should-we-colonize-space-some-people-argue-we-need-decolonize-it-instead-945130 | access-date=Oct 31, 2021 |quote="[[Biography:Robert Zubrin|Robert Zubrin]], said that the one word he shies away from is colony, preferring settlement because the first "confuses the issue with imperialism.""}}</ref> Though entrepôts like trade ''[[History:Factory (trading post)|factories]]'' did often grow into colonies.

Therefore any basing can be part of colonization, while colonization can be understood as a process that is open to more claims, beyond basing. The [[Astronomy:International Space Station|International Space Station]], the longest-occupied extraterrestrial habitat thus far, does not claim territory and thus is not usually considered a colony.

==History==
When the first space flight programs commenced, they partly used - and have continued to use - colonial spaces on Earth, such as places of indigenous peoples at the RAAF Woomera Range Complex, [[Organization:Guiana Space Centre|Guiana Space Centre]] or contemporarily for astronomy at the [[Religion:Thirty Meter Telescope protests|Mauna Kea telescope]].<ref name="Smiles 2022">{{cite web | last=Smiles | first=Deondre | title=The Settler Logics of (Outer) Space | website=Society & Space | date=2022-05-30 | url=https://www.societyandspace.org/articles/the-settler-logics-of-outer-space | access-date=2022-10-15}}</ref><ref name="Gorman 2005 pp. 85–107">{{cite journal | last=Gorman | first=Alice | title=The cultural landscape of interplanetary space | journal=Journal of Social Archaeology | publisher=SAGE Publications | volume=5 | issue=1 | year=2005 | issn=1469-6053 | doi=10.1177/1469605305050148 | pages=85–107| s2cid=144152006 }}</ref><ref name="nationColonial">{{cite web |url=https://www.thenation.com/article/world/apollo-space-lunar-rockets-colonialism/ |title=Is Spaceflight Colonialism |publisher=The Nation |access-date=15 October 2022 |date=19 July 2019 |author=Haris Durrani}}</ref>
When orbital spaceflight was achieved in the 1950s [[Social:Colonialism|colonialism]] was still a strong international project, e.g. easing the United States to advance its space program and space in general as part of a "New Frontier".<ref>{{cite journal |doi=10.1016/0265-9646(95)93233-B |title=Development and imperialism in space |author=Alan Marshall |date=February 1995 |journal=Space Policy |volume=11 |issue=1 |pages=41–52 |bibcode=1995SpPol..11...41M |access-date=2020-06-28 |url=https://www.researchgate.net/publication/222641231}}</ref> But during the initial decades of the space age, decolonization also gained again in force producing many newly [[Social:Independence|independent]] countries. These newly independent countries confronted spacefaring countries, demanding an anti-colonial stance and regulation of space activity when [[Astronomy:Space law|space law]] was raised and negotiated internationally.
Fears of confrontations because of land grabs and an [[Engineering:Arms race|arms race]] in space between the few countries with spaceflight capabilities grew and were ultimately shared by the spacefaring countries themselves.<ref name="Wilson Center 2021">{{cite web | title=The Global Legal Landscape of Space: Who Writes the Rules on the Final Frontier? | website=Wilson Center | date=2021-10-01 | url=https://www.wilsoncenter.org/article/global-legal-landscape-space-who-writes-rules-final-frontier | access-date=2022-10-14}}</ref> This produced the wording of the agreed on international space law, starting with the [[Engineering:Outer Space Treaty|Outer Space Treaty]] of 1967, calling space a "[[Social:Common heritage of humanity|province of all mankind]]" and securing provisions for international regulation and sharing of outer space.

[[File:Buzz salutes the U.S. Flag.jpg|thumb|A picture of the completed [[Engineering:Lunar Flag Assembly|Lunar Flag Assembly]]. The USSR and the US engaged in dropping pennants<ref name="Capelotti 2014 p. 44">{{cite book | last=Capelotti | first=P.J. | title=The Human Archaeology of Space: Lunar, Planetary and Interstellar Relics of Exploration | publisher=McFarland, Incorporated, Publishers | year=2014 | isbn=978-0-7864-5994-0 | url=https://books.google.com/books?id=98qFL5AYIjQC&pg=PA44 | access-date=2022-10-15 | page=44}}</ref> and raising flags on the Moon while not laying any claims over it, in accordance with the Outer Space Treaty.]]

The advent of geostationary satellites raised the case of limited space in outer space. A group of [[Astronomy:Equator|equator]]ial countries, all of which were countries that were once colonies of colonial empires, but without spaceflight capabilities, signed in 1976 the Bogota Declaration. These countries declared that [[Astronomy:Geostationary orbit|geostationary orbit]] is a limited natural resource and belongs to the equatorial countries directly below, seeing it not as part of outer space, humanity's common. Through this, the declaration challenged the dominance of geostationary orbit by spacefaring countries through identifying their dominance as imperialistic. Furthermore this dominance in space has foreshadowed threats to the Outer Space Treaty guaranteed accessibility to space, as in the case of [[Astronomy:Space debris|space debris]] which is ever increasing because of a lack of access regulation.<ref name="Columbia Journal of Transnational Law 2017">{{cite web | title=The Bogotá Declaration: A Case Study on Sovereignty, Empire, and the Commons in Outer Space | website=Columbia Journal of Transnational Law | date=2017-12-05 | url=http://jtl.columbia.edu/the-bogota-declaration-a-case-study-on-sovereignty-empire-and-the-commons-in-outer-space/ | archive-url=https://web.archive.org/web/20200121062356/http://jtl.columbia.edu/the-bogota-declaration-a-case-study-on-sovereignty-empire-and-the-commons-in-outer-space/ | archive-date=2020-01-21 | url-status=dead | access-date=2022-10-15}}</ref><ref name="Biondi 2018">{{cite web | last=Biondi | first=Charleyne | title=Haris A. Durrani - The Bogotá Declaration: A Global Uprising? – Uprising 13/13 | website=Log In ‹ Blogs @ Columbia Law School | date=2018-01-21 | url=https://blogs.law.columbia.edu/uprising1313/haris-a-durrani-the-bogota-declaration-a-global-uprising/ | access-date=2022-10-15}}</ref><ref name="Collis 2009 pp. 47–65">{{cite journal | last=Collis | first=Christy | title=The Geostationary Orbit: A Critical Legal Geography of Space's Most Valuable Real Estate | journal=The Sociological Review | publisher=SAGE Publications | volume=57 | issue=1_suppl | year=2009 | issn=0038-0261 | doi=10.1111/j.1467-954x.2009.01816.x | pages=47–65| s2cid=127857448 }}</ref>

In 1977, the first sustained space habitat, the [[Engineering:Salyut 6|Salyut 6]] station, was put into Earth's orbit. Eventually the first space stations were succeeded by the ISS, today's largest human outpost in space and closest to a space settlement.
Built and operated under a multilateral regime, it has become a blueprint for future stations, such as [[Astronomy:Lunar Gateway|around]] and possibly [[Astronomy:Moonbase|on the Moon]].<ref name="Foust 2018">{{cite web | last=Foust | first=Jeff | title=Is the Gateway the right way to the moon? | website=SpaceNews | date=2018-12-25 | url=https://spacenews.com/is-the-gateway-the-right-way-to-the-moon/ | access-date=2022-10-15}}</ref><ref name="ESA Blog Navigator – Navigator page for active ESA blogs 2016">{{cite web | title=Moon Village: A vision for global cooperation and Space 4.0 – Jan Wörner's blog | website=ESA Blog Navigator – Navigator page for active ESA blogs | date=2016-11-23 | url=https://blogs.esa.int/janwoerner/2016/11/23/moon-village/ | access-date=2022-10-15}}</ref> An international regime for lunar activity was demanded by the international [[Astronomy:Moon Treaty|Moon Treaty]], but is currently developed multilaterally as with the [[Astronomy:Artemis Accords|Artemis Accords]].<ref name="The Space Review 2020">{{cite web | title=The Space Review: The Artemis Accords: repeating the mistakes of the Age of Exploration | website=The Space Review | date=Jun 29, 2020 | url=https://www.thespacereview.com/article/3975/1 | access-date=Oct 14, 2022}}</ref><ref name="The Space Treaty Institute – Dedicated to Peace and Sustainability in Outer Space. Our Mission">{{cite web | title=The Space Treaty Institute – Dedicated to Peace and Sustainability in Outer Space. Our Mission: To give people Hope and Inspiration by helping the nations of Earth to build a Common Future | website=The Space Treaty Institute – Dedicated to Peace and Sustainability in Outer Space. Our Mission | url=http://www.spacetreaty.org/ | access-date=Oct 14, 2022}}</ref>
The only habitation on a different celestial body so far have been the temporary habitats of the crewed [[Astronomy:Lunar lander|lunar lander]]s.

===Conceptual===
Early suggestions for future colonizers like Francis Drake and Christoph Columbus to reach the Moon and people consequently living there were made by John Wilkins in ''A Discourse Concerning a New Planet'' in the first half of the 17th century.<ref>{{cite web|url=https://theoutline.com/post/5809/the-racist-language-of-space-exploration?zd=3&zi=v4x73sgl|title=THE RACIST LANGUAGE OF SPACE EXPLORATION|author=Caroline Haskins|date=14 August 2018|access-date=1 November 2020}}</ref>

The first known work on space colonization was the 1869 novella ''The Brick Moon'' by Edward Everett Hale, about an inhabited artificial satellite.<ref>E. E. Hale. "The Brick Moon". ''Atlantic Monthly'', Vol. 24, 1869.</ref> In 1897 Kurd Lasswitz also wrote about space colonies.

The Russian rocket science pioneer [[Biography:Konstantin Tsiolkovsky|Konstantin Tsiolkovsky]] foresaw elements of the space community in his book ''Beyond Planet Earth'' written about 1900. Tsiolkovsky had his space travelers building greenhouses and raising crops in space.<ref>K. E. Tsiolkovsky. ''Beyond Planet Earth''. Trans. by Kenneth Syers. Oxford, 1960</ref> Tsiolkovsky believed that going into space would help perfect human beings, leading to immortality and peace.<ref name="bio">[http://www.informatics.org/museum/tsiol.html The life of Konstantin Eduardovitch Tsiolkovsky 1857–1935] {{webarchive |url=https://web.archive.org/web/20120615044125/http://www.informatics.org/museum/tsiol.html |date=June 15, 2012 }}</ref>

In the 1920s [[Biography:John Desmond Bernal|John Desmond Bernal]], [[Biography:Hermann Oberth|Hermann Oberth]], Guido von Pirquet and Herman Noordung further developed the idea. [[Biography:Wernher von Braun|Wernher von Braun]] contributed his ideas in a 1952 ''Colliers'' article. In the 1950s and 1960s, Dandridge M. Cole<ref>Dandridge M. Cole and Donald W. Cox ''Islands in Space.'' Chilton, 1964</ref> published his ideas.

Another seminal book on the subject was the book ''The High Frontier: Human Colonies in Space'' by [[Biography:Gerard K. O'Neill|Gerard K. O'Neill]]<ref name=":1">G. K. O'Neill. ''The High Frontier: Human Colonies in Space''. Morrow, 1977.</ref> in 1977 which was followed the same year by ''Colonies in Space'' by T. A. Heppenheimer.<ref>T. A. Heppenheimer. ''Colonies in Space''. Stackpole Books, 1977</ref>

Marianne J. Dyson wrote ''Home on the Moon; Living on a Space Frontier'' in 2003;<ref>Marianne J. Dyson: Living on a Space Frontier. National Geographic, 2003</ref> Peter Eckart wrote ''Lunar Base Handbook'' in 2006<ref>Peter Eckart. ''Lunar Base Handbook''. McGraw-Hill, 2006</ref> and then Harrison Schmitt's ''Return to the Moon'' written in 2007.<ref>Harrison H. Schmitt. '' Return to the Moon''. Springer, 2007.</ref>

==Locations==
[[File:Mars mission.jpg|thumb|Artist Les Bossinas' 1989 concept of [[Astronomy:Human mission to Mars|Mars mission]]]]
Location is a frequent point of contention between space colonization advocates. The location of colonization can be on a physical body [[Astronomy:Planet|planet]], [[Astronomy:Dwarf planet|dwarf planet]], [[Astronomy:Natural satellite|natural satellite]], or [[Astronomy:Asteroid|asteroid]] or orbiting one. Colonization of the Solar System has received the most attention.

For settlements not on a body see also [[Astronomy:Space habitat|space habitat]].

===Near-Earth space===
[[File:Moon colony with rover.jpeg|thumb|Artist's 1986 conception of a lunar base]]

====The Moon====
{{main|Astronomy:Colonization of the Moon}}
The [[Astronomy:Moon|Moon]] is discussed as a target for colonization, due to its proximity to Earth and lower [[Astronomy:Escape velocity|escape velocity]]. Abundant [[Earth:Ice|ice]] is trapped in [[Astronomy:Permanently shadowed crater|permanently shadowed crater]]s near the poles, which could provide support for the water needs of a lunar colony,<ref>{{cite news | url =http://www.hindu.com/2009/09/23/stories/2009092357770100.htm | archive-url =https://web.archive.org/web/20090926073133/http://www.hindu.com/2009/09/23/stories/2009092357770100.htm | url-status =dead | archive-date =26 September 2009 | title =Water discovered on Moon?: "A lot of it actually" | date =23 September 2009 | newspaper =The Hindu | access-date =2009-09-26 }}</ref> though indications that [[Chemistry:Mercury (element)|mercury]] is also similarly trapped there may pose health concerns.<ref>{{cite journal |last1=Reed Jr. |first1=George W. |date=1999 |title=Don't drink the water |url= |journal=Meteoritics & Planetary Science |volume=34 |issue= 5|pages=809–811 |doi=10.1111/j.1945-5100.1999.tb01394.x |bibcode=1999M&PS...34..809R |s2cid=129733422 |access-date=|doi-access=free }}</ref><ref name=prospecting>{{cite journal |last1=Platts |first1=Warren J. |last2=Boucher |first2=Dale |last3=Gladstone |first3=G. Randall |date=12 December 2013 |title=Prospecting for Native Metals in Lunar Polar Craters |url= |journal=7th Symposium on Space Resource Utilization |volume= |issue= |pages= |doi=10.2514/6.2014-0338 |isbn=978-1-62410-315-5 |access-date=}}</ref> Native [[Chemistry:Precious metal|precious metal]]s, such as [[Chemistry:Gold|gold]], [[Chemistry:Silver|silver]], and probably [[Chemistry:Platinum|platinum]], are also concentrated at the lunar poles by electrostatic dust transport.<ref name=prospecting/> However, the Moon's lack of atmosphere provides no protection from space radiation or meteoroids, so [[Astronomy:Lunar lava tube|lunar lava tube]]s have been proposed sites to gain protection.<ref>{{cite news|title=Moon hole might be suitable for colony|url=http://www.cnn.com/2010/TECH/space/01/01/moon.lava.hole/ | work=CNN | date=2010-01-01}}</ref> The Moon's low surface gravity is also a concern, as it is unknown whether 1/6[[Physics:G-force|g]] is enough to maintain human health for long periods.<ref>{{Cite journal|last=Taylor|first=R. L.|date=March 1993|title=The effects of prolonged weightlessness and reduced gravity environments on human survival.|journal=Journal of the British Interplanetary Society|volume=46|issue=3|pages=97–106|pmid=11539500}}</ref> Interest in establishing a [[Astronomy:Moonbase|moonbase]] has increased in the 21st century as an intermediate to Mars colonization, with such proposals as the Moon Village for research, mining, and trade facilities with permanent habitation.<ref>[http://www.bbc.com/future/story/20150712-should-we-build-a-village-on-the-moon Should we build a village on the Moon?] Richard Hollingham, ''BBC News''. 1 July 2015.</ref>

A number of government space agencies such as Russia (2014),{{Citation needed|date=May 2021}} [[Organization:China National Space Administration|China]] (2012)<ref>[https://www.theregister.co.uk/2012/09/21/china_moon_landing_2017_moonbase/ China plots 2017 mission to plan MOON COLONY], 21 September 2012</ref>{{update after|2018|8|21}} and{{when|date=August 2018}} the [[Organization:NASA|US]]<ref>{{Cite web |url=https://www.wsj.com/news/articles/SB10000872396390444017504577648481492479016 |title=NASA Reveals Goal for Eventual Manned Lunar Outpost |access-date=2017-03-13 |archive-url=https://web.archive.org/web/20170112190306/http://www.wsj.com/news/articles/SB10000872396390444017504577648481492479016 |archive-date=2017-01-12 |url-status=dead }}</ref> have periodically floated lunar plans for constructing the first lunar outpost.

The [[Organization:European Space Agency|European Space Agency]] (ESA) head Jan Woerner has proposed{{when|date=August 2018}} cooperation among countries and companies on lunar capabilities, a concept referred to as ''[[Astronomy:Moonbase#Moon Village|Moon Village]]''.<ref name=sn20180529>
{{cite news |last=Foust|first=Jeff |url=https://spacenews.com/bezos-outlines-vision-of-blue-origins-lunar-future/ |title=Bezos outlines vision of Blue Origin's lunar future |work=SpaceNews |date=29 May 2018 |accessdate=21 August 2018 }}</ref>

In a December 2017 directive, the Trump Administration steered [[Organization:NASA|NASA]] to include a lunar mission on the pathway to other beyond Earth orbit (BEO) destinations.<ref name=spo20171217>[https://spacepolicyonline.com/news/text-of-remarks-at-signing-of-trump-space-policy-directive-1-and-list-of-attendees/ "Text of Remarks at Signing of Trump Space Policy Directive 1 and List of Attendees"], Marcia Smith, ''Space Policy Online'', 11 December 2017, accessed 21 August 2018.</ref><ref name=sn20180529/>

In a May 2018 interview, [[Company:Blue Origin|Blue Origin]] CEO [[Biography:Jeff Bezos|Jeff Bezos]] indicated Blue Origin would build and [[Astronomy:New Glenn|fly]] the ''Blue Moon lunar lander'' on its own, with [[Engineering:Private spaceflight|private funding]], but that they would build it a lot faster, and accomplish more, if it were done in a partnership with existing government space agencies. Bezos specifically mentioned the December 2017 NASA direction and the ESA ''Moon Village'' concepts.<ref name=sn20180529/>

====Lagrange points====
[[File:Lagrange points Earth vs Moon.jpg|thumb|A contour plot of the [[Physics:Gravitational potential|gravitational potential]] of the Moon and Earth, showing the five Earth–Moon Lagrange points]]

Another near-Earth possibility are the stable Earth–Moon [[Astronomy:Lagrangian point|Lagrange points]] {{L4}} and {{L5}}, at which point a space colony can float indefinitely. The [[Organization:L5 Society|L5 Society]] was founded to promote settlement by building space stations at these points. [[Biography:Gerard K. O'Neill|Gerard K. O'Neill]] suggested in 1974 that the L<sub>5</sub> point, in particular, could fit several thousands of floating colonies, and would allow easy travel to and from the colonies due to the shallow [[Physics:Effective potential|effective potential]] at this point.<ref name="o'neill">{{cite journal |last1=O'Neill |first1=Gerard K. |title=The colonization of space |journal=Physics Today |date=September 1974 |volume=27 |issue=9 |pages=32–40 |doi=10.1063/1.3128863 |bibcode=1974PhT....27i..32O |doi-access=free }}</ref>

===The inner planets===
Many planets within the [[Astronomy:Solar System|Solar System]] have been considered for colonization and [[Earth:Terraforming|terraforming]]. The main candidates for colonization in the inner Solar System are [[Astronomy:Colonization of Mars|Mars]]<ref>[http://library.thinkquest.org/19455/colonization_of_mars.htm ThinkQuest - Colonization of Mars] {{webarchive|url=https://web.archive.org/web/20110930070651/http://library.thinkquest.org/19455/colonization_of_mars.htm |date=2011-09-30 }}</ref> and [[Astronomy:Colonization of Venus|Venus]].<ref>[https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030022668_2003025525.pdf NASA - Colonization of Venus by Geoffrey A. Landis]</ref> Other possible candidates for colonization include the [[Astronomy:Colonization of the Moon|Moon]]<ref>[https://psmag.com/environment/colonize-moon-much-cost-81543 Should we colonize the Moon? And how much would it cost?]</ref> and even [[Astronomy:Colonization of Mercury|Mercury]].<ref>[https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030062017_2003069386.pdf NASA - Pathways to Colonization by Smitherman Jr.]</ref>

==== Mercury ====
[[File:TerraformedMercuryGlobe.jpg|thumb|An artist's conception of the terraformed Mercury]]
Once thought to be a volatile-depleted body like the Moon, Mercury is now known to be volatile-rich, surprisingly richer in volatiles than any other terrestrial body in the inner Solar System.<ref>{{Cite journal|last1=McCubbin|first1=Francis M.|last2=Riner|first2=Miriam A.|last3=Kaaden|first3=Kathleen E. Vander|last4=Burkemper|first4=Laura K.|date=2012|title=Is Mercury a volatile-rich planet?|journal=Geophysical Research Letters|language=en|volume=39|issue=9|pages=n/a|doi=10.1029/2012GL051711|bibcode=2012GeoRL..39.9202M|issn=1944-8007|doi-access=free}}</ref> The planet also receives six and a half times the solar flux as the Earth/Moon system,<ref name=Bolonkin>{{cite book |last=Bolonkin |first=Alexander A. |date=2015 |editor-last1=Badescu |editor-first1=Viorel |editor-last2=Zacny |editor-first2=Kris |title=Inner Solar System: Prospective Energy and Material Resources |publisher=Springer-Verlag |pages=407–419 |chapter=Chapter 19: Economic Development of Mercury: A Comparison with Mars Colonization |isbn=978-3-319-19568-1}}</ref> making solar energy a very effective energy source; it could be harnessed through orbital solar arrays and beamed to the surface or exported to other planets.<ref name=UTMercury/>

Geologist Stephen Gillett suggested in 1996 that this could make Mercury an ideal place to build and launch [[Physics:Solar sail|solar sail]] spacecraft, which could launch as folded-up "chunks" by [[Physics:Mass driver|mass driver]] from Mercury's surface. Once in space, the solar sails would deploy. Solar energy for the mass driver should be easy to come by, and solar sails near Mercury would have 6.5 times the thrust they do near Earth. This could make Mercury an ideal place to acquire materials useful in building hardware to send to (and terraform) Venus. Vast solar collectors could also be built on or near Mercury to produce power for large-scale engineering activities such as laser-pushed light sails to nearby star systems.<ref>Stanley Schmidt and [[Biography:Robert Zubrin|Robert Zubrin]], eds., "Islands in the Sky: Bold New Ideas for Colonizing Space"; Wiley, 1996, p. 71-84</ref>

As Mercury has essentially no axial tilt, crater floors near its poles lie in [[Astronomy:Crater of eternal darkness|eternal darkness]], never seeing the Sun. They function as [[Astronomy:Cold trap|cold traps]], trapping volatiles for geological periods. It is estimated that the poles of Mercury contain 10<sup>14</sup>–10<sup>15</sup>&nbsp;kg of water, likely covered by about 5.65×10<sup>9</sup> m<sup>3</sup> of hydrocarbons. This would make agriculture possible. It has been suggested that plant varieties could be developed to take advantage of the high light intensity and the long day of Mercury. The poles do not experience the significant day-night variations the rest of Mercury do, making them the best place on the planet to begin a colony.<ref name=Bolonkin/>

Another option is to live underground, where day-night variations would be damped enough that temperatures would stay roughly constant. There are indications that Mercury contains [[Earth:Lava tube|lava tube]]s, like the Moon and Mars, which would be suitable for this purpose.<ref name=UTMercury>{{cite web |url=https://www.universetoday.com/130109/how-do-we-colonize-mercury/ |title=How do we Colonize Mercury? |last=Williams |first=Matt |date=3 August 2016 |website=Universe Today |access-date=22 August 2021}}</ref> Underground temperatures in a ring around Mercury's poles can even reach room temperature on Earth, 22±1&nbsp;°C; and this is achieved at a depths starting from only about 0.7&nbsp;m. This presence of volatiles and abundance of energy has led Alexander Bolonkin and James Shifflett to consider Mercury preferable to Mars for colonization.<ref name=Bolonkin/><ref>{{cite web |url=https://einstein-schrodinger.com/mercury_colony.html |title=A Mercury Colony? |last=Shifflett |first=James |date=n.d. |website=einstein-schrodinger.com |access-date=31 July 2021}}</ref>

Yet a third option could be to continually move to stay on the night side, as Mercury's 176-day-long day-night cycle means that the [[Astronomy:Terminator (solar)|terminator]] travels very slowly.<ref name=UTMercury/>

Because Mercury is very dense, its surface gravity is 0.38g like Mars, even though it is a smaller planet.<ref name=Bolonkin/> This would be easier to adjust to than lunar gravity (0.16g), but still present advantages regarding lower escape velocity from the planet.<ref name=UTMercury/> Mercury's proximity gives it advantages over the asteroids and outer planets, and its low synodic period means that launch windows from Earth to Mercury are more frequent than those from Earth to Venus or Mars.<ref name=UTMercury/>

On the downside, a Mercury colony would require significant shielding from radiation and solar flares, and since Mercury is airless, decompression and temperature extremes would be constant risks.<ref name=UTMercury/>

====Venus====
{{Main|Astronomy:Colonization of Venus}}
[[File:Venusballoonoutpost.png|thumb|An artist's conception of a [[Research station|research station]] in the clouds of Venus]]
Surface conditions on Venus are extremely hostile to human life: average surface temperature is 464&nbsp;°C (hot enough to melt lead), and average surface pressure is 92 times Earth's atmospheric pressure – roughly equivalent to a depth of one kilometre under Earth's oceans.<ref name="fact">{{cite web | url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html | title=Venus Fact Sheet | publisher=NASA Goddard Space Flight Center | last=Williams | first=David R. | date=25 November 2020 | access-date=2021-04-15 | archive-date=11 May 2018 | archive-url=https://web.archive.org/web/20180511140851/https://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html | url-status=live }}</ref> (There is some variation; due to its altitude, the peak of Maxwell Montes is at only 380&nbsp;°C and 45&nbsp;bar, making it the coolest and least pressurised location on Venus' surface.<ref name=Basilevsky_2003>{{cite journal
 |author=Basilevsky A. T., Head J. W.
 |title=The surface of Venus
 |journal=Reports on Progress in Physics
 |date=2003
 |volume=66
 |issue=10
 |pages=1699–1734
 |doi=10.1088/0034-4885/66/10/R04
 |bibcode=2003RPPh...66.1699B
|s2cid=250815558
 }}</ref><ref name=McGill_2010>{{cite book
 |editor=T. R. Watters |editor2=R. A. Schultz
 |title=Planetary Tectonics
 |chapter=Venus tectonics
 |author=McGill G. E. |author2=Stofan E. R. |author3=Smrekar S. E.
 |publisher={{wipe|Cambridge University Press}}
 |date=2010
 |chapter-url=https://books.google.com/books?id=9PD5hxPb6fkC&pg=PA81
 |isbn=978-0-521-76573-2
 |pages=81–120
}}</ref> There are also some hot spots at about 700&nbsp;°C.) Solar energy is not available at the surface due to the constant cloud cover, and the carbon dioxide atmosphere is poisonous.<ref name=landis1/>

However, the upper atmosphere of Venus has much more Earthlike conditions and has been suggested as a plausible colonization location since at least 1971 by Soviet scientists.<ref name="Badescu">{{cite book |author=Badescu, Viorel |editor=Zacny, Kris |title=Inner Solar System: Prospective Energy and Material Resources |url=https://www.springer.com/us/book/9783319195681 |location=Heidelberg |publisher=Springer-Verlag GmbH |page=492 |date=2015 |isbn=978-3319195681}}.<!--Based on ''Technica Molodezhi TM - 9 1971''--></ref> At just over 50&nbsp;km altitude (the cloud tops), atmospheric pressure is roughly equal to that on Earth's surface, and temperatures range from 0–50&nbsp;°C. The volatile elements necessary for life are present (hydrogen, carbon, nitrogen, oxygen, and sulfur), and above the clouds, solar energy is abundant. Pressurization would not be required; humans could even go outside the habitats safely with oxygen provision and clothing to protect against the sulfuric acid droplets. Geoffrey Landis has pointed out that breathable air is a lifting gas in Venus' atmosphere: a cubic meter of air would lift half a kilogram, and an oxygen- and nitrogen-filled aerostat the size of a city on Venus would be able to lift the mass of a city. This suggests floating aerostat cities as a colonization method for Venus. The lack of pressure differences between the outside and inside means that there is ample time to repair habitat breaches. With just over three times the land area of Earth, there would be space even for a billion such cities.<ref name=landis1/> The atmosphere provides enough radiation shielding at this altitude, and Venus' 0.90g gravity is likely sufficient to prevent the negative health effects of microgravity.<ref name=landis1/>

A day on Venus is very long on the surface, but the atmosphere rotates much faster than the planet (a phenomenon called [[Earth:Atmospheric super-rotation|superrotation]]), so a floating habitat would only have a day of about a hundred hours. Landis compares this favorably with polar days and nights on Earth, which are much longer. A floating habitat at higher latitudes on Venus would approach a normal 24-hour cycle. Mining the surface would give access to important industrial metals, and it could be accessed via airplanes, balloons, or fullerene cables meant to withstand high temperatures. To avoid the problem of the habitat being in motion relative to its mining devices, the habitat could descend into the lower atmosphere: this region is hotter, but Landis argues that a large-sized habitat would have enough [[Physics:Heat capacity|heat capacity]] to have no problem with a short stay at higher temperatures.<ref name=landis1/>

The colonization of Venus has been a subject of many works of science fiction since before the dawn of [[Engineering:Spaceflight|spaceflight]] and is still discussed from both a fictional and a scientific standpoint. Proposals for Venus are focused on colonies floating in the upper-middle atmosphere<ref>Daniel Oberhaus and Alex Pasternack, [https://motherboard.vice.com/en_us/article/why-we-should-build-cloud-cities-on-venus "Why We Should Build Cloud Cities on Venus"], ''Motherboard,'' Feb 2 2015 (accessed March 26, 2017).</ref> and on [[Astronomy:Terraforming of Venus|terraforming]].

==== Mars ====
{{Main|Astronomy:Colonization of Mars}}
[[File:Possible exploration of the surface of Mars.jpg|thumb|An artist's conception of a [[Astronomy:Human mission to Mars|human mission to Mars]]]]
The hypothetical colonization of Mars has received interest from public space agencies and private corporations and has received extensive treatment in science fiction writing, film, and art. The most recent{{when|date=May 2021}} commitments to researching permanent settlement include those by public space agencies—[[Organization:NASA|NASA]], [[Organization:European Space Agency|ESA]], [[Company:Roscosmos|Roscosmos]], [[Astronomy:Indian Space Research Organisation|ISRO]], and the [[Organization:China National Space Administration|CNSA]]—and private organizations—[[Company:SpaceX|SpaceX]], [[Company:Lockheed Martin|Lockheed Martin]], and [[Company:Boeing|Boeing]].{{citation needed|date=May 2021}}

===Asteroid belt===
{{Main|Astronomy:Colonization of the asteroid belt}}
The [[Astronomy:Asteroid belt|asteroid belt]] has about 10<sup>18</sup> metric tonnes of overall material available – ten thousand times more than is available in the near-Earth asteroids<ref name=taylor/> – but it is thinly distributed as it covers a vast region of space. The largest asteroid is [[Astronomy:Ceres (dwarf planet)|Ceres]], which at about 940&nbsp;km in diameter is big enough to be a [[Astronomy:Dwarf planet|dwarf planet]]. The next two largest are [[Astronomy:2 Pallas|Pallas]] and [[Astronomy:4 Vesta|Vesta]], both about 520&nbsp;km in diameter. Uncrewed supply craft should be practical with little technological advance, even crossing 500 million kilometers of space. The colonists would have a strong interest in assuring their asteroid did not hit Earth or any other body of significant mass, but would have extreme difficulty in moving an asteroid{{citation needed|date=August 2017}} of any size. The orbits of the Earth and most asteroids are very distant from each other in terms of delta-v and the asteroidal bodies have enormous [[Physics:Momentum|momentum]]. Rockets or mass drivers can perhaps be installed on asteroids to direct their path into a safe course.

Ceres has readily available water, ammonia, and methane, important for survival, fuel, and possibly terraforming of Mars and Venus. The colony could be established on a surface crater or underground.<ref name=UTCeres>{{cite web |url=https://www.universetoday.com/143011/how-do-we-colonize-ceres/ |title=How do we Colonize Ceres? |last=Williams |first=Matt |date=20 November 2019 |website=Universe Today |access-date=22 August 2021}}</ref> However, even Ceres only manages a tiny surface gravity of 0.03g, which is not enough to stave off the negative effects of microgravity (though it does make transportation to and from Ceres easier). Either medical treatments or artificial gravity would thus be required. Additionally, colonizing the main asteroid belt would likely require infrastructure to already be present on the Moon and Mars.<ref name=UTCeres/>

Some have suggested that Ceres could act as a main base or hub for asteroid mining.<ref name=UTCeres/> However, [[Biography:Geoffrey A. Landis|Geoffrey A. Landis]] has pointed out that the asteroid belt is a poor place for an asteroid-mining base if more than one asteroid is to be exploited: the asteroids are not close to each other, and two asteroids chosen at random are quite likely to be on opposite sides from the Sun from each other. He suggests that it would be better to construct such a base on an inner planet, such as Venus: inner planets have higher orbital velocities, making the transfer time to any specific asteroid shorter, and orbit the Sun faster, so that the launch windows to the asteroid are more frequent (a lower synodic period). Thus Venus is closer to the asteroids than Earth or Mars in terms of flight time. Transfer times for the journeys Venus–Ceres and Venus–Vesta are only 1.15 and 0.95&nbsp;years respectively along minimum-energy trajectories, which is shorter even than Earth–Ceres and Earth–Vesta at 1.29 and 1.08&nbsp;years respectively.<ref name="landis1">{{cite book|last=Landis |first=Geoffrey A. |title=AIP Conference Proceedings |chapter=Colonization of Venus | doi = 10.1063/1.1541418| journal=Conference on Human Space Exploration, Space Technology & Applications International Forum, Albuquerque NM |volume=654 |pages=1193–1198 |date=Feb 2–6, 2003|bibcode=2003AIPC..654.1193L }}; draft version of [https://ntrs.nasa.gov/api/citations/20030022668/downloads/20030022668.pdf the full paper] available at NASA Technical Reports Server (accessed 16 May 2012)</ref> Anthony Taylor, Jonathan C. McDowell, and Martin Elvis suggest Mars' moon [[Astronomy:Phobos (moon)|Phobos]] as an asteroid-belt mining hub: the main belt is much more accessible from Martian orbit than from low Earth orbit in terms of [[Astronomy:Delta-v|delta-v]], the moon provides a large platform and a mass for radiation shielding, and it is not far from Mars' surface. Hence, a Phobos base for asteroid mining works hand in hand economically with Mars settlement.<ref name=taylor>{{cite journal |last1=Taylor |first1=Anthony |last2=McDowell |first2=Jonathan C. |last3=Elvis |first3=Martin |date=2022 |title=Phobos and Mars orbit as a base for asteroid exploration and mining |url= |journal=Planetary and Space Science |volume=214 |issue= |pages=105450 |doi=10.1016/j.pss.2022.105450 |access-date=|doi-access=free }}</ref>

===Moons of outer planets===
[[File:Cryobot.jpg|thumb|Artist's impression of a hypothetical ocean cryobot in Europa]]
Human missions to the outer planets would need to arrive quickly due to the effects of space radiation and microgravity along the journey.<ref name=Palaszewski>{{cite conference |url=https://arc.aiaa.org/doi/10.2514/6.2015-1654 |title=Solar System Exploration Augmented by In-Situ Resource Utilization: Human Mercury and Saturn Exploration |last1=Palaszewski |first1=Bryan |date=2015 |publisher= |book-title= |pages= |doi=10.2514/6.2015-1654 |location=Kissimmee, Florida |conference=8th Symposium on Space Resource Utilization |id=|hdl=2060/20150004114 |hdl-access=free }}</ref> In 2012, Thomas B. Kerwick wrote that the distance to the outer planets made their human exploration impractical for now, noting that travel times for round trips to Mars were estimated at two years, and that the closest approach of Jupiter to Earth is over ten times farther than the closest approach of Mars to Earth. However, he noted that this could change with "significant advancement on spacecraft design".<ref name=Kerwick/> [[Engineering:Nuclear thermal rocket|Nuclear-thermal]] or nuclear-electric engines have been suggested as a way to make the journey to Jupiter in a reasonable amount of time.<ref name=UTJupiter/> Another possibility would be plasma [[Physics:Magnetic sail|magnet sails]], a technology already suggested for sending a probe to Jupiter rapidly.<ref>{{Cite journal |last=Freeze |first=Brent |last2=Greason |first2=Jeff |last3=Nader |first3=Ronnie |last4=Febres |first4=Jaime Jaramillo |last5=Chaves-Jiminez |first5=Adolfo |last6=Lamontagne |first6=Michel |last7=Thomas |first7=Stephanie |last8=Cassibry |first8=Jason |last9=Fuller |first9=John |last10=Davis |first10=Eric |last11=Conway |first11=Darrel |date=2022-02-01 |title=Jupiter Observing Velocity Experiment (JOVE): Introduction to Wind Rider Solar Electric Propulsion Demonstrator and Science Objectives |url=https://iopscience.iop.org/article/10.1088/1538-3873/ac4812 |journal=Publications of the Astronomical Society of the Pacific |volume=134 |issue=1032 |pages=023001 |doi=10.1088/1538-3873/ac4812 |issn=0004-6280|doi-access=free }}</ref> The cold would also be a factor, necessitating a robust source of heat energy for spacesuits and bases.<ref name=Kerwick/> Most of the larger moons of the outer planets contain [[Earth:Ice|water ice]], liquid water, and organic compounds that might be useful for sustaining human life.<ref name="icemoons">G.J. Consalmagno, ''Ice-rich moons and the physical properties of ice'', Journal of Physical Chemistry, vol. 87, no. 21, 1983, p. 4204-4208.</ref><ref name="liftveil">Ralph Lorenz and Jacqueline Mitton, ''Lifting Titan's veil: exploring the giant moon of Saturn'', Cambridge University Press, 2002</ref>

[[Biography:Robert Zubrin|Robert Zubrin]] has suggested Saturn, Uranus, and Neptune as advantageous locations for colonization because their atmospheres are good sources of fusion fuels, such as [[Physics:Deuterium|deuterium]] and [[Physics:Helium-3|helium-3]]. Zubrin suggested that Saturn would be the most important and valuable as it is the closest and has an excellent satellite system. Jupiter's high gravity makes it difficult to extract gases from its atmosphere, and its strong radiation belt makes developing its system difficult.<ref name=UTSaturn/> On the other hand, fusion power has yet to be achieved, and fusion power from helium-3 is more difficult to achieve than conventional [[Physics:Deuterium–tritium fusion|deuterium–tritium fusion]].<ref>{{cite news |last1=Day |first1=Dwayne | title=The helium-3 incantation |url=http://www.thespacereview.com/article/2834/1 |access-date=11 January 2019 |work=The Space Review |date=September 28, 2015}}</ref> Jeffrey Van Cleve, Carl Grillmair, and Mark Hanna instead focus on Uranus, because the [[Astronomy:Delta-v|delta-v]] required to get helium-3 from the atmosphere into orbit is half that needed for Jupiter, and because Uranus' atmosphere is five times richer in helium than Saturn's.<ref name="He3U">Jeffrey Van Cleve (Cornell University) et al., [http://www.mines.edu/research/srr/2001abstracts/vancleve.PDF "Helium-3 Mining Aerostats in the Atmosphere of Uranus"] {{webarchive |url=https://web.archive.org/web/20060630164712/http://www.mines.edu/research/srr/2001abstracts/vancleve.PDF |date=June 30, 2006 }}, Abstract for Space Resources Roundtable, accessed May 10, 2006</ref>

Jupiter's [[Astronomy:Galilean moons|Galilean moons]] (Io, Europa, Ganymede, and Callisto) and Saturn's [[Astronomy:Titan (moon)|Titan]] are the only moons that have gravities comparable to Earth's Moon. The Moon has a 0.17g gravity; Io, 0.18g; Europa, 0.13g; Ganymede, 0.15g; Callisto, 0.13g; and Titan, 0.14g. Neptune's [[Astronomy:Triton (moon)|Triton]] has about half the Moon's gravity (0.08g); other [[Astronomy:Planetary-mass moon|round moons]] provide even less (starting from Uranus' [[Astronomy:Titania (moon)|Titania]] and [[Astronomy:Oberon (moon)|Oberon]] at about 0.04g).<ref name=Kerwick/>

====Jovian moons====
[[File:Callisto base.PNG|thumb|right|Artist's impression of a base on Callisto<ref name="CallistoBase">{{cite web|title=Vision for Space Exploration|url=http://www.nasa.gov/pdf/55583main_vision_space_exploration2.pdf|publisher=NASA|year=2004}}</ref>]]
<div style="float:right; margin:2px;">
{| class=wikitable style="text-align:center; font-size:11px"
|+ Jovian radiation
! Moon !! [[Physics:Sievert|Sv]]/day
|-
| Io || 36<ref>{{cite web |url=http://zimmer.csufresno.edu/~fringwal/w08a.jup.txt |title=Archived copy |access-date=2009-09-20 |url-status=dead |archive-url=https://web.archive.org/web/20080725050708/http://zimmer.csufresno.edu/~fringwal/w08a.jup.txt |archive-date=2008-07-25 }}</ref>
|-
| Europa || 5.40<ref name="ringwald"/>
|-
|Ganymede || 0.08<ref name="ringwald">{{cite web
  |date=29 February 2000
  |title=SPS 1020 (Introduction to Space Sciences)
  |publisher=California State University, Fresno
  |author=Frederick A. Ringwald
  |url=http://zimmer.csufresno.edu/~fringwal/w08a.jup.txt
  |access-date=2009-09-20
  |url-status=dead
  |archive-url=https://web.archive.org/web/20080725050708/http://zimmer.csufresno.edu/~fringwal/w08a.jup.txt
  |archive-date=25 July 2008
  }}</ref> 
|-
| Callisto || 0.0001<ref name="ringwald"/>
|}</div>

The [[Astronomy:Jupiter|Jovian]] system in general has particular disadvantages for colonization, including a deep [[Physics:Gravity well|gravity well]]. The [[Astronomy:Magnetosphere of Jupiter|magnetosphere of Jupiter]] bombards the [[Astronomy:Moons of Jupiter|moons of Jupiter]] with intense [[Physics:Ionizing radiation|ionizing radiation]]<ref name="radjup">R. Walker Fillius, Carl E. McIlwain, and Antonio Mogro-Campero, ''Radiation Belts of Jupiter: A Second Look'', Science, Vol. 188. no. 4187, pp. 465–467, 2 May 1975</ref> delivering about 36 [[Physics:Sievert#Dose examples|Sv]] per day to unshielded colonists on [[Astronomy:Io (moon)|Io]] and about 5.40 Sv per day on [[Astronomy:Europa (moon)|Europa]]. Exposure to about 0.75 Sv over a few days is enough to cause [[Physics:Acute radiation syndrome|radiation poisoning]], and about 5&nbsp;Sv over a few days is fatal.<ref name="zoob2jvn">Robert Zubrin, ''Entering Space: Creating a Spacefaring Civilization'', section: Colonizing the Jovian System, pp. 166-170, Tarcher/Putnam, 1999, {{ISBN|1-58542-036-0}}</ref>

Jupiter itself, like the other gas giants, has further disadvantages. There is no accessible surface on which to land, and the light hydrogen atmosphere would not provide good buoyancy for some kind of aerial habitat as has been proposed for Venus.

Radiation levels on [[Astronomy:Io (moon)|Io]] and [[Astronomy:Europa (moon)|Europa]] are extreme, enough to kill unshielded humans within an Earth day.<ref name="zoob2ttn"/> Therefore, only [[Astronomy:Callisto (moon)|Callisto]] and perhaps [[Astronomy:Ganymede (moon)|Ganymede]] could reasonably support a human colony. Callisto orbits outside Jupiter's radiation belt.<ref name=Kerwick/> Ganymede's low latitudes are partially shielded by the moon's magnetic field, though not enough to completely remove the need for radiation shielding. Both of them have available water, silicate rock, and metals that could be mined and used for construction.<ref name=Kerwick/>

Although Io's volcanism and tidal heating constitute valuable resources, exploiting them is probably impractical.<ref name=Kerwick>{{cite journal |last1=Kerwick |first1=Thomas B. |date=2012 |title=Colonizing Jupiter's Moons: An Assessment of Our Options and Alternatives |url=https://www.jstor.org/stable/24536505 |journal=Journal of the Washington Academy of Sciences |volume=98 |issue=4 |pages=15–26 |jstor=24536505 |access-date=1 August 2021}}</ref> Europa is rich in water (its subsurface ocean is expected to contain over twice as much water as all Earth's oceans together)<ref name=UTJupiter/> and likely oxygen, but metals and minerals would have to be imported. If alien microbial life exists on Europa, human immune systems may not protect against it. Sufficient radiation shielding might, however, make Europa an interesting location for a research base.<ref name=Kerwick/> The private ''[[Astronomy:Artemis Project|Artemis Project]]'' drafted a plan in 1997 to colonize Europa, involving surface igloos as bases to drill down into the ice and explore the ocean underneath, and suggesting that humans could live in "air pockets" in the ice layer.<ref name=UTJupiter>{{cite web |url=https://www.universetoday.com/130637/colonize-jupiters-moons/ |title=How do we Colonize Jupiter's Moons? |last=Williams |first=Matt |date=23 November 2016 |website=Universe Today |access-date=10 January 2022}}</ref> Ganymede<ref name=UTJupiter/> and Callisto are also expected to have internal oceans.<ref name='OW Roadmap 2019'>{{cite journal | last1 = Hendrix | first1 = Amanda R. | last2 = Hurford | first2 = Terry A. | last3 = Barge | first3 = Laura M. | last4 = Bland | first4 = Michael T. | last5 = Bowman | first5 = Jeff S. | last6 = Brinckerhoff | first6 = William | last7 = Buratti | first7 = Bonnie J. | last8 = Cable | first8 = Morgan L. | last9 = Castillo-Rogez | first9 = Julie | last10 = Collins | first10 = Geoffrey C. | display-authors = etal | year = 2019| title = The NASA Roadmap to Ocean Worlds | journal = Astrobiology | volume =  19| issue = 1 | pages =  1–27| doi = 10.1089/ast.2018.1955 | pmid = 30346215 | pmc = 6338575 | bibcode = 2019AsBio..19....1H | doi-access = free }}</ref> It might be possible to build a surface base that would produce fuel for further exploration of the Solar System.

In 2003, NASA performed a study called ''HOPE'' (Revolutionary Concepts for Human Outer Planet Exploration) regarding the future exploration of the Solar System.<ref>Patrick A. Troutman (NASA Langley Research Center) et al., [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030063128.pdf Revolutionary Concepts for Human Outer Planet Exploration (HOPE)] {{Webarchive|url=https://web.archive.org/web/20170815051016/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030063128.pdf |date=2017-08-15 }}, accessed May 10, 2006 (.doc format)</ref> The target chosen was [[Astronomy:Callisto (moon)|Callisto]] due to its distance from Jupiter, and thus the planet's harmful radiation. It could be possible to build a surface base that would produce fuel for further exploration of the Solar System. HOPE estimated a round trip time for a crewed mission of about 2–5 years, assuming significant progress in propulsion technologies.<ref name=Kerwick/>

[[Astronomy:Io (moon)|Io]] is not ideal for colonization, due to its hostile environment. The moon is under influence of high tidal forces, causing high volcanic activity. Jupiter's strong radiation belt overshadows Io, delivering 36 Sv a day to the moon. The moon is also extremely dry. Io is the least ideal place for the colonization of the four Galilean moons.
Despite this, its volcanoes could be energy resources for the other moons, which are better suited to colonization.

[[File:Currents in Jovian Magnetosphere.png|thumb|right|300px|The magnetic field of Jupiter and co-rotation rotation enforcing currents]]
The [[Astronomy:Artemis Project|Artemis Project]] proposed a plan to colonize [[Astronomy:Europa (moon)|Europa]].<ref>[http://www.asi.org/ Artemis Society International] {{Webarchive|url=https://web.archive.org/web/20110820180833/http://asi.org/ |date=2011-08-20 }} official website</ref><ref>Peter Kokh et al., "[http://asi.org/adb/06/09/03/02/110/europa2-wkshp.html Europa II Workshop Report] {{Webarchive|url=https://web.archive.org/web/20190607102248/http://asi.org/adb/06/09/03/02/110/europa2-wkshp.html |date=2019-06-07 }}", ''Moon Miner's Manifesto'' #110, Nov. 1997</ref> Scientists would inhabit igloos and drill down into the Europan ice crust, exploring any subsurface ocean. The report also discusses the use of air pockets for human habitation.

[[Astronomy:Ganymede (moon)|Ganymede]] is the largest moon in the Solar System. Ganymede is the only moon with a [[Astronomy:Magnetosphere|magnetosphere]], albeit overshadowed by [[Astronomy:Magnetosphere of Jupiter|Jupiter's magnetic field]]. Because of this magnetic field, Ganymede is one of only two Jovian moons where surface settlements would be feasible because it receives about 0.08 [[Physics:Sievert|Sv]] of radiation per day. Ganymede could be terraformed.<ref name="ringwald"/>

The Keck Observatory announced in 2006 that the binary [[Astronomy:Jupiter trojan|Jupiter trojan]] [[Astronomy:617 Patroclus|617 Patroclus]], and possibly many other Jupiter trojans, are likely composed of water ice, with a layer of dust. This suggests that mining water and other volatiles in this region and transporting them elsewhere in the Solar System, perhaps via the proposed [[Interplanetary Transport Network]], may be feasible in the not-so-distant future. This could make [[Astronomy:Colonization of the Moon|colonization of the Moon]], [[Astronomy:Colonization of Mercury|Mercury]] and main-belt [[Astronomy:Colonization of the asteroids|asteroids]] more practical.

====Saturnian moons====
[[File:PIA09184 -Titan Sea and Lake Superior.jpg|thumb|Ligeia Mare, a sea on Titan (left) compared at scale to Lake Superior on Earth (right)]]
Saturn has seven moons [[Astronomy:Planetary-mass moon|large enough to be round]]: in order of increasing distance from Saturn, they are Mimas, [[Astronomy:Enceladus|Enceladus]], Tethys, Dione, [[Astronomy:Rhea (moon)|Rhea]], [[Astronomy:Titan (moon)|Titan]], and Iapetus. Titan is the largest and the only one with a Moon-like gravity: it is the only moon in the Solar System to have a dense atmosphere and is rich in carbon-bearing compounds, suggesting it as a colonization target.<ref name="zoob2ttn">Robert Zubrin, ''Entering Space: Creating a Spacefaring Civilization'', section: Titan, pp. 163–170, Tarcher/Putnam, 1999, {{ISBN|978-1-58542-036-0}}</ref> Titan has water ice and large methane oceans.<ref name=NasaNews>{{Cite web |url=https://saturn.jpl.nasa.gov/science/titan/ |date=2016-12-24 |archive-url=https://web.archive.org/web/20161224232352/https://saturn.jpl.nasa.gov/science/titan/ |archive-date=2016-12-24 |title=Titan}}</ref> [[Biography:Robert Zubrin|Robert Zubrin]] identified Titan as possessing an abundance of all the elements necessary to support life, making Titan perhaps the most advantageous locale in the outer Solar System for colonization.<ref name="zoob2ttn"/>

The small moon Enceladus is also of interest, having a subsurface ocean that is separated from the surface by only tens of meters of ice at the south pole, compared to kilometers of ice separating the ocean from the surface on Europa. Volatile and organic compounds are present there, and the moon's high density for an ice world (1.6&nbsp;g/cm<sup>3</sup>) indicates that its core is rich in silicates.<ref name=UTSaturn>{{cite web |url=https://www.universetoday.com/132413/colonize-saturns-moons/ |title=How do we Colonize Saturns' Moons |last=Williams |first=Matt |date=22 December 2016 |website=Universe Today |access-date=22 August 2021}}</ref>

Saturn's radiation belt is much weaker than Jupiter's, so radiation is less of an issue here. Dione, Rhea, Titan, and Iapetus all orbit outside the radiation belt, and Titan's thick atmosphere would adequately shield against cosmic radiation.<ref name=UTSaturn/>

[[Biography:Robert Zubrin|Robert Zubrin]] identified [[Astronomy:Saturn|Saturn]], [[Astronomy:Uranus|Uranus]] and [[Astronomy:Neptune|Neptune]] as "the Persian Gulf of the Solar System", as the largest sources of [[Physics:Deuterium|deuterium]] and helium-3 to drive a [[Physics:Nuclear fusion|fusion]] economy, with Saturn the most important and most valuable of the three, because of its relative proximity, low radiation, and large system of moons.<ref name="zoob2pgs">Robert Zubrin, ''Entering Space: Creating a Spacefaring Civilization'', section: The Persian Gulf of the Solar System, pp. 161-163, Tarcher/Putnam, 1999, {{ISBN|1-58542-036-0}}</ref> On the other hand, planetary scientist [[Biography:John S. Lewis|John Lewis]] in his 1997 book ''[[Astronomy:Mining the Sky|Mining the Sky]]'', insists that Uranus is the likeliest place to mine helium-3 because of its significantly shallower gravity well, which makes it easier for a laden tanker spacecraft to thrust itself out. Furthermore, Uranus is an [[Astronomy:Ice giant|ice giant]], which would likely make it easier to separate the helium out of the atmosphere.

Zubrin identified [[Astronomy:Titan (moon)|Titan]] as possessing an abundance of all the elements necessary to support life, making Titan perhaps the most advantageous locale in the outer Solar System for colonization. He said, "In certain ways, Titan is the most hospitable extraterrestrial world within the Solar System for human colonization."<ref name="zoob2ttn"/> A widely published expert on [[Earth:Terraforming|terraforming]], Christopher McKay, is also a co-investigator on the ''Huygens'' probe that landed on Titan in January 2005.

The surface of Titan is mostly uncratered and thus inferred to be very young and active, and probably composed of mostly water ice, and lakes of liquid hydrocarbons (methane/ethane) in its polar regions. While the temperature is cryogenic (95 K) it should be able to support a base, but more information regarding Titan's surface and the activities on it is necessary. The thick atmosphere and the weather, such as potential flash floods, are also factors to consider.

On 9 March 2006, [[Organization:NASA|NASA]]'s ''[[Astronomy:Cassini–Huygens|Cassini]]'' space probe found possible evidence of liquid water on [[Astronomy:Enceladus|Enceladus]].<ref>{{cite web|url=http://www.nasa.gov/mission_pages/cassini/media/cassini-20060309.html |title=NASA's Cassini Discovers Potential Liquid Water on Enceladus |publisher=Nasa.gov |date=2007-11-22 |access-date=2011-08-20}}</ref> According to that article, "pockets of liquid water may be no more than tens of meters below the surface." These findings were confirmed in 2014 by NASA. This means liquid water could be collected much more easily and safely on Enceladus than, for instance, on Europa (see above). Discovery of water, especially liquid water, generally makes a celestial body a much more likely candidate for colonization. An alternative model of Enceladus's activity is the decomposition of methane/water clathrates – a process requiring lower temperatures than liquid water eruptions. The higher density of Enceladus indicates a larger than Saturnian average silicate core that could provide materials for base operations.

===Trans-Neptunian region===
{{main|Astronomy:Colonization of trans-Neptunian objects}}

[[Biography:Freeman Dyson|Freeman Dyson]] suggested that within a few centuries human civilization will have relocated to the [[Astronomy:Kuiper belt|Kuiper belt]].<ref>Freeman Dyson, ''The Sun, The Genome, and The Internet'' (1999) Oxford University Press. {{ISBN|0-19-513922-4}}</ref><ref>Freeman Dyson, "The World, the Flesh, and the Devil", Third J.D. Bernal Lecture, May 1972, reprinted in ''Communication with Extraterrestrial Intelligence'', [[Biography:Carl Sagan|Carl Sagan]], ed., MIT Press, 1973, {{ISBN|0-262-69037-3}}</ref> Several hundred billion to trillion comet-like ice-rich bodies exist outside the orbit of Neptune, in the Kuiper belt and Inner and Outer Oort cloud. These may contain all the ingredients for life (water ice, ammonia, and carbon-rich compounds), including significant amounts of deuterium and helium-3. Since Dyson's proposal, the number of trans-Neptunian objects known has increased greatly.

Colonists could live in the dwarf planet's icy crust or mantle, using fusion or geothermal heat{{Citation needed|date=December 2023}} and mining the soft-ice or liquid inner ocean for volatiles and minerals. Given the light gravity and resulting lower pressure in the ice mantle or inner ocean, colonizing the rocky core's outer surface might give colonists the largest number of mineral and volatile resources as well as insulating them from cold.{{Citation needed|date=December 2023}} Surface habitats or domes are another possibility, as background radiation levels are likely to be low.{{citation needed|date=February 2023}}

===Orbit around gas giants===
There have also been proposals to place robotic [[Engineering:Aerostat|aerostat]]s in the upper atmospheres of the Solar System's [[Astronomy:Gas giant|gas giant]] planets for exploration and possibly mining of [[Physics:Helium-3|helium-3]], which could have a very high value per unit mass as a thermonuclear fuel.<ref name="zoob2sop">Robert Zubrin, ''Entering Space: Creating a Spacefaring Civilization'', section: Settling the Outer Solar System: The Sources of Power, pp. 158-160, Tarcher/Putnam, 1999, {{ISBN|1-58542-036-0}}</ref><ref name="He3U"/>

Because [[Astronomy:Uranus|Uranus]] has the lowest [[Astronomy:Escape velocity|escape velocity]] of the four gas giants, it has been proposed as a mining site for [[Physics:Helium-3|helium-3]].<ref name="He3U"/> If human supervision of the robotic activity proved necessary, one of Uranus's natural satellites might serve as a base.

It is hypothesized that one of [[Astronomy:Neptune|Neptune]]'s satellites could be used for colonization. [[Astronomy:Triton (moon)|Triton]]'s surface shows signs of extensive geological activity that implies a subsurface ocean, perhaps composed of ammonia/water.<ref>{{cite journal| last=Ruiz| first=Javier| year=2003| title=Heat flow and depth to a possible internal ocean on Triton| journal=Icarus| volume=166| doi=10.1016/j.icarus.2003.09.009| page=436| bibcode=2003Icar..166..436R| issue=2| url=http://eprints.ucm.es/10454/1/11-Trit%C3%B3n_1.pdf| access-date=2023-04-10| archive-date=2019-12-12| archive-url=https://web.archive.org/web/20191212145428/http://eprints.ucm.es/10454/1/11-Trit%C3%B3n_1.pdf| url-status=dead}}</ref> If technology advanced to the point that tapping such geothermal energy was possible, it could make colonizing a cryogenic world like Triton feasible, supplemented by [[Physics:Nuclear fusion|nuclear fusion]] power.

===Beyond the Solar System===
[[File:LH 95.jpg|thumb|right|A [[Astronomy:Star|star]] forming region in the Large Magellanic Cloud]]
Looking beyond the Solar System, there are up to several hundred billion potential stars with possible colonization targets. The main difficulty is the vast distances to other stars: roughly a hundred thousand times farther away than the planets in the Solar System. This means that some combination of very high speed (some more-than-fractional percentage of the [[Physics:Speed of light|speed of light]]), or travel times lasting centuries or millennia, would be required. These speeds are far beyond what current [[Astronomy:Spacecraft propulsion|spacecraft propulsion]] systems can provide.

Space colonization technology could in principle allow human expansion at high, but sub-relativistic speeds, substantially less than the speed of light, ''c''.&nbsp; An interstellar colony ship would be similar to a space habitat, with the addition of major propulsion capabilities and independent energy generation.

Hypothetical [[Engineering:Starship|starship]] concepts proposed both by scientists and in hard science fiction include:
* A [[Engineering:Generation ship|generation ship]] would travel much slower than light, with consequent interstellar trip times of many decades or centuries. The crew would go through generations before the journey was complete, so none of the initial crew would be expected to survive to arrive at the destination, assuming current human lifespans.
* A [[Engineering:Sleeper ship|sleeper ship]], where most or all of the crew spend the journey in some form of [[Biology:Hibernation|hibernation]] or [[Biology:Suspended animation|suspended animation]], allowing some or all to reach the destination.
* An [[Unsolved:Embryo space colonization|embryo-carrying interstellar starship]] (EIS), much smaller than a generation ship or sleeper ship, transporting human [[Biology:Embryo|embryo]]s or DNA in a frozen or dormant state to the destination. (Obvious biological and psychological problems in birthing, raising, and educating such voyagers, neglected here, may not be fundamental.)
* A [[Physics:Nuclear fusion|nuclear fusion]] or [[Physics:Nuclear fission|fission]] powered ship (e.g. ion drive) of some kind, achieving velocities of up to perhaps 10% ''c''&nbsp; permitting one-way trips to nearby stars with durations comparable to a human lifetime.
* A [[Astronomy:Project Orion (nuclear propulsion)|Project Orion]]-ship, a nuclear-powered concept proposed by [[Biography:Freeman Dyson|Freeman Dyson]] which would use nuclear explosions to propel a starship. A special case of the preceding nuclear rocket concepts, with similar potential velocity capability, but possibly easier technology.
* [[Physics:Solar sail|Laser propulsion]] concepts, using some form of beaming of power from the Solar System might allow a [[Physics:Solar sail|light-sail]] or other ship to reach high speeds, comparable to those theoretically attainable by the fusion-powered electric rocket, above. These methods would need some means, such as supplementary nuclear propulsion, to stop at the destination, but a hybrid (light-sail for acceleration, fusion-electric for deceleration) system might be possible.
* [[Philosophy:Mind uploading|Uploaded human minds]] or [[Artificial intelligence|artificial intelligence]] may be transmitted via radio or laser at light speed to interstellar destinations where [[Self-replicating spacecraft|self-replicating spacecraft]] have traveled subluminally and set up infrastructure and possibly also brought some minds. [[Philosophy:Extraterrestrial intelligence|Extraterrestrial intelligence]] might be another viable destination.

The above concepts appear limited to high, but still sub-relativistic speeds, due to fundamental energy and reaction mass considerations, and all would entail trip times which might be enabled by space colonization technology, permitting self-contained habitats with lifetimes of decades to centuries. Yet human interstellar expansion at average speeds of even 0.1% of ''c''&nbsp; would permit settlement of the entire Galaxy in less than one-half of the Sun's galactic orbital period of ~240,000,000 years, which is comparable to the timescale of other galactic processes. Thus, even if interstellar travel at near relativistic speeds is never feasible (which cannot be determined at this time), the development of space colonization could allow human expansion beyond the Solar System without requiring technological advances that cannot yet be reasonably foreseen. This could greatly improve the chances for the survival of intelligent life over cosmic timescales, given the many natural and human-related hazards that have been widely noted.

If humanity does gain access to a large amount of energy, on the order of the mass-energy of entire planets, it may eventually become feasible to construct [[Alcubierre drive]]s. These are one of the few methods of superluminal travel which may be possible under current physics. However, it is probable that such a device could never exist, due to the fundamental challenges posed. For more on this see [[Alcubierre drive#Difficulties|Difficulties of making and using an Alcubierre Drive]].

====Intergalactic travel====
{{Main|Astronomy:Intergalactic travel}} 
The distances between galaxies are on the order of a million times farther than those between the stars, and thus intergalactic colonization would involve voyages of millions of years via special self-sustaining methods.<ref name="burruss">{{cite journal | first1 = Robert Page | last1 = Burruss | first2= J. | last2= Colwell | title = Intergalactic Travel: The Long Voyage From Home | journal = The Futurist | date=September–October 1987 | volume= 21 | issue= 5 | pages = 29–33}}</ref><ref>{{cite journal | author= Fogg, Martyn | title= The Feasibility of Intergalactic Colonisation and its Relevance to SETI | journal= Journal of the British Interplanetary Society | volume= 41 | number= 11 | date= November 1988 | pages= 491–496 | url= https://www.academia.edu/4166742 | bibcode= 1988JBIS...41..491F }}</ref><ref>{{cite journal | author= Armstrong, Stuart | author2= Sandberg, Anders | url= http://www.fhi.ox.ac.uk/intergalactic-spreading.pdf | title=Eternity in six hours: intergalactic spreading of intelligent life and sharpening the Fermi paradox | journal= Acta Astronautica | year= 2013 | volume= 89 | pages= 1–13 | publisher= Future of Humanity Institute, Philosophy Department, Oxford University| doi= 10.1016/j.actaastro.2013.04.002 | bibcode= 2013AcAau..89....1A }}</ref>

==Law, governance, and sovereignty==
{{Main|Astronomy:Space law|Social:Space policy|Social:Common heritage of humanity|Astronomy:Extraterrestrial real estate}}
Space activity is legally based on the [[Engineering:Outer Space Treaty|Outer Space Treaty]], the main international treaty. But [[Astronomy:Space law|space law]] has become a larger legal field, which includes other international agreements such as the significantly less ratified [[Astronomy:Moon Treaty|Moon Treaty]] and diverse national laws.

The Outer Space Treaty established the basic ramifications for space activity in article one:"The exploration and use of outer space, including the Moon and other celestial bodies, shall be carried out for the benefit and in the interests of all countries, irrespective of their degree of economic or scientific development, and shall be the province of all mankind."

And continued in article two by stating:"Outer space, including the Moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means."<ref name=unoda>{{cite web  | url=http://disarmament.un.org/treaties/t/outer_space  | title = Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies | access-date = 7 November 2020 | publisher= United Nations Office for Disarmament Affairs}}</ref>

The development of international space law has revolved much around outer space being defined as [[Social:Common heritage of mankind|common heritage of mankind]]. The ''Magna Carta of Space'' presented by William A. Hyman in 1966 framed outer space explicitly not as ''[[Social:Terra nullius|terra nullius]]'' but as ''res communis'', which subsequently influenced the work of the United Nations Committee on the Peaceful Uses of Outer Space.<ref name="Durrani 2019"/><ref>{{cite web|url=https://blogs.bl.uk/digitisedmanuscripts/2015/06/space-the-final-frontier.html|author=Alexander Lock|website=The British Library - Medieval manuscripts blog|title=Space: The Final Frontier|date=6 June 2015|access-date=2 November 2020}}</ref>

[[File:Buzz salutes the U.S. Flag.jpg|thumb|right|The deploying of the United States flag during the first crewed Moon landing (Apollo 11) on the lunar surface does not constitute a territorial claim, unlike historically practiced on Earth, since the US reinforced the Outer Space Treaty by adhering to it and making no such territorial claim.<ref name="Smith 2019">{{cite web | last=Smith | first=Kiona N. | title=How Apollo 11 Raised The Flag on the Moon, And What It Means Today | website=Forbes | date=Jul 20, 2019 | url=https://www.forbes.com/sites/kionasmith/2019/07/20/how-apollo-11-raised-the-flag-on-the-moon-and-what-it-means-today/ | access-date=Sep 16, 2021}}</ref>]]

==Reasons==

===Survival of human civilization===
{{Main|Medicine:Space and survival}}

A primary argument calling for space colonization is the long-term survival of human civilization and terrestrial life.<ref>{{Cite web|last=Piper|first=Kelsey|date=2018-10-22|title=Jeff Bezos and Elon Musk want to colonize space to save humanity|url=https://www.vox.com/future-perfect/2018/10/22/17991736/jeff-bezos-elon-musk-colonizing-mars-moon-space-blue-origin-spacex|access-date=2021-04-02|website=Vox|language=en}}</ref> By developing alternative locations off Earth, the planet's species, including humans, could live on in the event of [[Unsolved:Global catastrophic risk|natural or human-made disasters on our own planet]].<ref>{{cite book | last = Kaku | first = Michio |  title = The Future of Humanity: Terraforming Mars, Interstellar Travel, Immortality, and Our Destiny Beyond Earth | publisher = Doubleday | year = 2018 | pages = 3–6 | isbn = 978-0385542760 | quote = It is as inescapable as the laws of physics that humanity will one day confront some type of [[Biology:Extinction|extinction]]-level [[Biology:Extinction event|event]]. . . . [W]e face threats [that include] [[Earth:Global warming|global warming]] . . . [[Biology:Biological warfare|weaponized microbes]] . . . [[Earth:Quaternary glaciation|the onset of another ice age]] . . . the possibility that [[Earth:Yellowstone Caldera|the supervolcano under Yellowstone National Park]] may awaken from its long slumber . . . [and] another [[Astronomy:Impact event|meteor or cometary impact]] . . . . [from one of the] several thousand [[Astronomy:Near-Earth object|NEOs (near-Earth objects)]] that cross the orbit of the Earth. . . . . Life is too precious to be placed on a single planet . . . . Perhaps our fate is to become a multiplanet species that lives [[Engineering:Interstellar travel|among the stars]].}}</ref>

On two occasions, theoretical physicist and cosmologist [[Biography:Stephen Hawking|Stephen Hawking]] argued for space colonization as a means of saving humanity. In 2001, Hawking predicted that the human race would become extinct within the next thousand years unless colonies could be established in space.<ref>{{cite news |last=Highfield |first=Roger |url=https://www.telegraph.co.uk/news/uknews/1359562/Colonies-in-space-may-be-only-hope-says-Hawking.html |title=Colonies in space may be only hope, says Hawking |work=The Telegraph |date=16 October 2001 |access-date=5 August 2012 |archive-url=https://web.archive.org/web/20090426232042/http://www.telegraph.co.uk/news/uknews/1359562/Colonies-in-space-may-be-only-hope-says-Hawking.html |archive-date=26 April 2009 |url-status=live}}</ref> In 2010, he stated that humanity faces two options: either we colonize space within the next two hundred years, or we will face the long-term prospect of [[Unsolved:Human extinction|extinction]].<ref>{{cite news|agency=Press Association|date=2010-08-09|title=Stephen Hawking: mankind must colonise space or die out|language=en-GB|work=The Guardian|url=https://www.theguardian.com/science/2010/aug/09/stephen-hawking-human-race-colonise-space|access-date=2020-06-20|issn=0261-3077}}</ref>

In 2005, then [[Organization:NASA|NASA]] Administrator Michael Griffin identified space colonization as the ultimate goal of current spaceflight programs, saying:
{{blockquote|...&nbsp;the goal isn't just scientific exploration&nbsp;... it's also about extending the range of human habitat out from Earth into the solar system as we go forward in time&nbsp;... In the long run, a single-planet species will not survive&nbsp;... If we humans want to survive for hundreds of thousands of millions of years, we must ultimately populate other planets. Now, today the technology is such that this is barely conceivable. We're in the infancy of it.&nbsp;... I'm talking about that one day, I don't know when that day is, but there will be more human beings who live off the Earth than on it. We may well have people living on the Moon. We may have people living on the moons of Jupiter and other planets. We may have people making habitats on asteroids&nbsp;... I know that humans will colonize the solar system and one day go beyond.<ref>{{cite news| url=https://www.washingtonpost.com/wp-dyn/content/article/2005/09/23/AR2005092301691.html| title=NASA's Griffin: 'Humans Will Colonize the Solar System'| date=September 25, 2005| newspaper=Washington Post| page=B07| access-date=September 14, 2017| archive-url=https://web.archive.org/web/20110604141654/http://www.washingtonpost.com/wp-dyn/content/article/2005/09/23/AR2005092301691.html| archive-date=June 4, 2011| url-status=live}}</ref>|sign=|source=}}

Louis J. Halle, formerly of the United States Department of State, wrote in ''Foreign Affairs'' (Summer 1980) that the colonization of space will protect humanity in the event of global nuclear warfare.<ref>{{cite journal |url=http://www.foreignaffairs.org/19800601faessay8146/louis-j-halle/a-hopeful-future-for-mankind.html |title=A Hopeful Future for Mankind |first=Louis J. |last=Halle |journal=Foreign Affairs |date=Summer 1980 |doi=10.2307/20040585 |volume=58 |issue=5 |pages=1129–36 |url-status=dead |archive-url=https://web.archive.org/web/20041013051342/http://www.foreignaffairs.org/19800601faessay8146/louis-j-halle/a-hopeful-future-for-mankind.html |archive-date=2004-10-13 |jstor=20040585}}</ref> The physicist [[Biography:Paul Davies|Paul Davies]] also supports the view that if a planetary catastrophe threatens the survival of the human species on Earth, a self-sufficient colony could "reverse-colonize" Earth and restore [[Social:Civilization|human civilization]]. The author and journalist William E. Burrows and the biochemist Robert Shapiro proposed a private project, the [[Astronomy:Alliance to Rescue Civilization|Alliance to Rescue Civilization]], with the goal of establishing an off-Earth "[[Backup|backup]]" of human civilization.<ref>{{cite news |url=https://www.nytimes.com/2006/08/01/science/01arc.html |title=Life After Earth: Imagining Survival Beyond This Terra Firma |newspaper=The New York Times |first=Richard |last=Morgan |date=2006-08-01 |access-date=2010-05-23 |archive-url=https://web.archive.org/web/20090417023904/http://www.nytimes.com/2006/08/01/science/01arc.html |archive-date=2009-04-17 |url-status=live}}</ref>

Based on his [[Astronomy:Copernican principle|Copernican principle]], [[Biography:J. Richard Gott|J. Richard Gott]] has estimated that the human race could survive for another 7.8&nbsp;million years, but it is not likely to ever colonize other planets. However, he expressed a hope to be proven wrong, because "colonizing other worlds is our best chance to hedge our bets and improve the survival prospects of our species".<ref>{{cite news |last=Tierney |first=John |url=https://www.nytimes.com/2007/07/17/science/17tier.html?ex=1342324800&en=ccf375ae9f268470&ei=5090&partner=rssuserland&emc=rss |title=A Survival Imperative for Space Colonization |date=July 17, 2007 |work=The New York Times |access-date=February 23, 2017 |archive-url=https://web.archive.org/web/20170629081936/http://www.nytimes.com/2007/07/17/science/17tier.html?ex=1342324800&en=ccf375ae9f268470&ei=5090&partner=rssuserland&emc=rss |archive-date=June 29, 2017 |url-status=live}}</ref>

In a theoretical study from 2019, a group of researchers have pondered the long-term trajectory of human civilization.<ref name=sb01>{{cite journal |last=Baum |first=Seth D. |display-authors=0 |date=2019 |title=Long-Term Trajectories of Human Civilization |url=http://gcrinstitute.org/papers/trajectories.pdf |journal=Foresight |volume=21 |issue=1 |location=Bingley |publisher=Emerald Group Publishing |doi=10.1108/FS-04-2018-0037 |pages=53–83 |s2cid=52042667 |access-date=2019-09-23 |archive-url=https://web.archive.org/web/20200102042937/http://gcrinstitute.org/papers/trajectories.pdf |archive-date=2020-01-02 |url-status=live}}</ref> It is argued that due to Earth's finitude as well as the [[Astronomy:Formation and evolution of the Solar System#The Sun and planetary environments|limited duration of the Solar System]], mankind's survival into the far future will very likely require extensive space colonization.<ref name=sb01/>{{rp|8, 22f}} This 'astronomical trajectory' of mankind, as it is termed, could come about in four steps: First step, plenty of space colonies could be established at various habitable locations — be it in outer space or on [[Astronomy:Astronomical object|celestial bodies]] away from Earth – and allowed to remain dependent on support from Earth for a start. In the second step, these colonies could gradually become self-sufficient, enabling them to survive if or when the mother civilization on Earth fails or dies. Third step, the colonies could develop and expand their habitation by themselves on their space stations or celestial bodies, for example via [[Earth:Terraforming|terraforming]]. In the fourth step, the colonies could self-replicate and establish new colonies further into space, a process that could then repeat itself and continue at an [[Exponential growth|exponential rate]] throughout the cosmos. However, this astronomical trajectory may not be a lasting one, as it will most likely be interrupted and eventually decline due to resource depletion or straining competition between various human factions, bringing about some 'star wars' scenario.<ref name=sb01/>{{rp|23–25}}

===Vast resources in space===
Resources in space, both in materials and energy, are enormous. The [[Astronomy:Solar System|Solar System]] alone has, according to different estimates, enough material and energy to support anywhere from several thousand to over a billion times that of the current Earth-based human population, mostly from the Sun itself.<ref>Estimated 3000 times the land area of Earth. O'Neill, Gerard K. (1976, 2000). ''The High Frontier''. Apogee Books {{ISBN|1-896522-67-X}}</ref><ref>Estimated 10 quadrillion (10<sup>16</sup>) people. Lewis, John S. (1997). ''[[Astronomy:Mining the Sky|Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets]].'' Helix Books/Addison-Wesley. {{ISBN|0-201-32819-4}} version 3</ref><ref>Estimated 5 quintillion (5 x 10<sup>18</sup>) people. Savage, Marshall (1992, 1994). ''The Millennial Project: Colonizing the Galaxy in Eight Easy Steps.'' Little, Brown. {{ISBN|0-316-77163-5}}</ref>

Asteroid mining will also be a key player in space colonization. Water and materials to make structures and shielding can be easily found in asteroids. Instead of resupplying on Earth, mining and fuel stations need to be established on asteroids to facilitate better space travel.<ref>[https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_I_Phase_II/Sustainable_Human_Exploration Optical Mining of Asteroids, Moons, and Planets to Enable Sustainable Human Exploration and Space Industrialization] {{Webarchive|url=https://web.archive.org/web/20200304024010/https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_I_Phase_II/Sustainable_Human_Exploration/ |date=2020-03-04 }}; April 6, 2017; NASA</ref> Optical mining is the term NASA uses to describe extracting materials from asteroids. NASA believes by using propellant derived from asteroids for exploration to the moon, Mars, and beyond will save $100&nbsp;billion. If funding and technology come sooner than estimated, asteroid mining might be possible within a decade.<ref>[https://www.forbes.com/sites/brucedorminey/2016/05/24/how-to-optically-mine-water-from-an-asteroid/#37f0e05c389f Turning Near-Earth Asteroids Into Strategically-Placed Fuel Dumps] {{Webarchive|url=https://web.archive.org/web/20170918065620/https://www.forbes.com/sites/brucedorminey/2016/05/24/how-to-optically-mine-water-from-an-asteroid/#37f0e05c389f |date=2017-09-18 }}; May 24, 2016; Forbe</ref>

Although some items of the infrastructure requirements above can already be easily produced on Earth and would therefore not be very valuable as trade items (oxygen, water, base metal ores, silicates, etc.), other high-value items are more abundant, more easily produced, of higher quality, or can only be produced in space. These would provide (over the long-term) a very high return on the initial investment in space infrastructure.<ref>[http://www.spacefuture.com/archive/the_technical_and_economic_feasibility_of_mining_the_near_earth_asteriods.shtml The Technical and Economic Feasibility of Mining the Near-Earth Asteroids] {{Webarchive|url=https://web.archive.org/web/20080815034645/http://www.spacefuture.com/archive/the_technical_and_economic_feasibility_of_mining_the_near_earth_asteriods.shtml |date=2008-08-15 }} Presented at 49th IAF Congress, Sept 28 – Oct 2, 1998, Melbourne, Australia by Mark J Sonter&nbsp;
– Space Future</ref>

Some of these high-value trade goods include precious metals,<ref name="members.nova.org">[http://members.nova.org/~sol/station/ast-mine.htm Asteroid Mining] {{Webarchive|url=https://web.archive.org/web/20080512000822/http://members.nova.org/~sol/station/ast-mine.htm |date=2008-05-12 }} - Sol Station</ref><ref>{{Cite news|last=Whitehouse|first=David|title=Gold rush in space?|publisher=BBC|date=22 July 1999|url=http://news.bbc.co.uk/1/hi/sci/tech/401227.stm|access-date=2009-05-25|archive-url=https://web.archive.org/web/20080307111033/http://news.bbc.co.uk/1/hi/sci/tech/401227.stm|archive-date=7 March 2008|url-status=live}}</ref> gemstones,<ref name="tricitiesnet.com">{{cite web |url=http://www.tricitiesnet.com/donsastronomy/mining.html |title=Asteroid Mining for Profit |website=Don's Astronomy Pages |access-date=7 August 2008 |archive-url=https://web.archive.org/web/20080706123345/http://www.tricitiesnet.com/donsastronomy/mining.html |archive-date=6 July 2008}}{{self-published source|date=August 2015}}</ref> power,<ref>[http://www.spacefuture.com/archive/conceptual_study_of_a_solar_power_satellite_sps_2000.shtml Conceptual Study of A Solar Power Satellite, SPS 2000] {{Webarchive|url=https://web.archive.org/web/20080725171510/http://spacefuture.com/archive/conceptual_study_of_a_solar_power_satellite_sps_2000.shtml |date=2008-07-25 }} By Makoto Nagatomo, Susumu Sasaki and Yoshihiro Naruo&nbsp;– Proceedings of the 19th International Symposium on Space Technology and Science, Yokohama, Japan, May 1994, pp.&nbsp;469–76 Paper No. ISTS-94-e-04 – Space Future</ref> solar cells,<ref name="panix.com">[http://www.panix.com/~kingdon/space/manuf.html Space Manufacturing] {{Webarchive|url=https://web.archive.org/web/20080904234210/http://www.panix.com/~kingdon/space/manuf.html |date=2008-09-04 }} – Jim Kingdon's space markets page.</ref> ball bearings,<ref name="panix.com"/> semi-conductors,<ref name="panix.com"/> and pharmaceuticals.<ref name="panix.com"/>

The mining and extraction of metals from a small asteroid the size of [[Astronomy:3554 Amun|3554 Amun]] or [[Astronomy:(6178) 1986 DA|(6178) 1986 DA]], both small near-Earth asteroids, would be 30 times as much metal as humans have mined throughout history. A metal asteroid this size would be worth approximately US$20&nbsp;trillion at 2001 market prices<ref>{{Cite web|url=https://space.nss.org/asteroids/|title=Asteroids{{!}}National Space Society|date=2 February 2017|language=en-US|access-date=2019-02-26|archive-url=https://web.archive.org/web/20190226111255/https://space.nss.org/asteroids/|archive-date=2019-02-26|url-status=live}}</ref>

The main impediments to commercial exploitation of these resources are the very high cost of initial investment,<ref>{{Cite journal|last=Lee|first=Ricky J.|title=Costing and financing a commercial asteroid mining venture|journal=54th International Astronautical Congress|location=Bremen, Germany|year=2003|id=IAC-03-IAA.3.1.06|url=http://www.aiaa.org/content.cfm?pageid=406&gTable=Paper&gID=16257|access-date=2009-05-25|url-status=dead|archive-url=https://web.archive.org/web/20090809183150/http://www.aiaa.org/content.cfm?pageid=406&gTable=Paper&gID=16257|archive-date=2009-08-09}}</ref> the very long period required for the expected return on those investments (''The Eros Project'' plans a 50-year development),<ref>[http://www.orbdev.com/erosproj.html The Eros Project] {{Webarchive|url=https://web.archive.org/web/20080705103530/http://www.orbdev.com/erosproj.html |date=2008-07-05 }} – Orbital Development</ref> and the fact that the venture has never been carried out before—the high-risk nature of the investment.

===Expansion with fewer negative consequences===
{{Further|Earth:Holocene extinction}}

Expansion of humans and technological progress has usually resulted in some form of environmental devastation, and destruction of [[Earth:Ecosystem|ecosystem]]s and their accompanying wildlife. In the past, expansion has often come at the expense of displacing many indigenous peoples, the resulting treatment of these peoples ranging anywhere from encroachment to genocide. Because space has no known life, this need not be a consequence, as some space settlement advocates have pointed out.<ref>{{Cite news| url=http://www.space-settlement-institute.org/meaning.html| title=The Meaning of Space Settlement| publisher=Space Settlement Institute| access-date=5 September 2014| archive-url=https://web.archive.org/web/20141003151529/http://www.space-settlement-institute.org/meaning.html| archive-date=3 October 2014| url-status=live}}</ref><ref>Savage, Marshall (1992, 1994). ''The Millennial Project: Colonizing the Galaxy in Eight Easy Steps''. Little, Brown. {{ISBN|0-316-77163-5}}</ref> However, on some bodies of the Solar System, there is the potential for extant native lifeforms and so the negative consequences of space colonization cannot be dismissed.<ref>See for example, the work of Dr. Alan Marshall in Alan Marshall (1993) '[https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1468-5930.1993.tb00078.x Ethics and the Extraterrestrial Environment]', ''Journal of Applied Philosophy'', Vol. 10, No 2, pp227-237; Alan Marshall (1994) 'Martians Beware', ''New Zealand Science Monthly'', December 1994 issue; Alan Marshall (1997) 'Extraterrestrial Environmentalism', ''Australian Science'', Vol. 18, No. 2, Winter issue, pp25-27. July 1997; and "Cosmic Preservationist", The Word: ''[https://www.newscientist.com/article/mg17723765-100-the-word-cosmic-preservationist/ New Scientist],'' January 4th, 2003 issue.</ref>

Counterarguments state that changing only the location but not the logic of exploitation will not create a more sustainable future.<ref name="Yun">{{cite web |author=Joon Yun |website=Worth.com |title=The Problem With Today's Ideas About Space Exploration. |date=January 2, 2020 
|url=https://www.worth.com/is-space-the-next-frontier-for-the-same-old-story-of-imperialism/ |access-date=2020-06-28}}</ref>

===Alleviating overpopulation and resource demand===
An argument for space colonization is to mitigate proposed impacts of [[Unsolved:Human overpopulation|overpopulation of Earth]], such as resource depletion.<ref>{{Cite journal|date=1976-01-01|title=The impact of space colonization on world dynamics|journal=Technological Forecasting and Social Change|language=en|volume=9|issue=4|pages=361–99|doi=10.1016/0040-1625(76)90019-6|issn=0040-1625|last1=Vajk|first1=J.Peter}}</ref> If the resources of space were opened to use and viable life-supporting habitats were built, Earth would no longer define the limitations of growth. Although many of Earth's resources are non-renewable, off-planet colonies could satisfy the majority of the planet's resource requirements. With the availability of extraterrestrial resources, demand on terrestrial ones would decline.<ref>O'Neill, ''Colonies in Space''; Pournelle, ''A Step Farther Out''.</ref> Proponents of this idea include [[Biography:Stephen Hawking|Stephen Hawking]]<ref>{{Cite web|date=2014-08-17|title=Stephen Hawking: mankind must move to outer space within a century - Telegraph|url=http://www.telegraph.co.uk/science/space/7935505/Stephen-Hawking-mankind-must-move-to-outer-space-within-a-century.html|access-date=2021-08-09|archive-url=https://web.archive.org/web/20140817025438/http://www.telegraph.co.uk/science/space/7935505/Stephen-Hawking-mankind-must-move-to-outer-space-within-a-century.html|archive-date=2014-08-17}}</ref> and [[Biography:Gerard K. O'Neill|Gerard K. O'Neill]].<ref name=":1" />

Others including cosmologist [[Biography:Carl Sagan|Carl Sagan]] and science fiction writers [[Biography:Arthur C. Clarke|Arthur C. Clarke]],<ref name = clarkebipeds>''Greetings, Carbon-Based Bipeds!'' (1999) [[Biography:Arthur C. Clarke|Arthur C. Clarke]], Voyager {{ISBN|0-00-224698-8}}</ref> and [[Biography:Isaac Asimov|Isaac Asimov]],<ref>''The Good Earth Is Dying'' (1971) [[Biography:Isaac Asimov|Isaac Asimov]] (published in ''Der Spiegel'')</ref> have argued that shipping any excess population into space is not a viable solution to human overpopulation. According to Clarke, "the population battle must be fought or won here on Earth".<ref name = clarkebipeds/> The problem for these authors is not the lack of resources in space (as shown in books such as ''Mining the Sky''<ref>Mining the Sky (1996) John&nbsp;S. Lewis. Addison Wesley. {{ISBN|0-201-47959-1}}</ref>), but the physical impracticality of shipping vast numbers of people into space to "solve" overpopulation on Earth.

===Other arguments===
Advocates for space colonization cite a presumed innate human drive to explore and discover, and call it a quality at the core of progress and thriving civilizations.<ref>{{cite book |author= Clarke, Arthur C. |title= Profiles of the Future: An Inquiry Into the Limits of the Possible |chapter-url= https://archive.org/details/profilesoffuture00clar |chapter-url-access= registration |year= 1962 |chapter= Rocket to the Renaissance}}</ref><ref>{{cite web | url= http://www.spacedaily.com/news/oped-03y.html | title= The Space Settlement Summit | author= McKnight, John Carter | publisher= Space Daily | date= 20 March 2003 | access-date= 12 March 2013 | archive-url= https://web.archive.org/web/20130514103953/http://www.spacedaily.com/news/oped-03y.html | archive-date= 14 May 2013 | url-status= live }}</ref>

[[Biography:Nick Bostrom|Nick Bostrom]] has argued that from a [[Philosophy:Utilitarianism|utilitarian]] perspective, space colonization should be a chief goal as it would enable a very large population to live for a very long period of time (possibly billions of years), which would produce an enormous amount of utility (or happiness).<ref>{{cite journal |url= http://www.nickbostrom.com/astronomical/waste.html |title= Astronomical Waste: The Opportunity Cost of Delayed Technological Development |journal= Utilitas |volume= 15 |number= 3 |date= November 2003 |pages= 308–14 |doi= 10.1017/S0953820800004076 |last1= Bostrom |first1= Nick |citeseerx= 10.1.1.429.2849 |s2cid= 15860897 |access-date= 2009-10-20 |archive-url= https://web.archive.org/web/20140409031022/http://www.nickbostrom.com/astronomical/waste.html |archive-date= 2014-04-09 |url-status= live }}</ref> He claims that it is more important to reduce existential risks to increase the probability of eventual colonization than to accelerate technological development so that space colonization could happen sooner. In his paper, he assumes that the created lives will have positive ethical value despite the problem of [[Social:Suffering|suffering]].

In a 2001 interview with Freeman Dyson, J.&nbsp;Richard Gott and Sid Goldstein, they were asked for reasons why some humans should live in space.<ref name=dyson /> Their answers were:
* Spread life and beauty throughout the universe
* Ensure the survival of our species
* Make money through new forms of space commercialization such as [[Physics:Space-based solar power|solar-power satellites]], [[Astronomy:Asteroid mining|asteroid mining]], and space manufacturing
* Save the environment of Earth by moving people and industry into space
[[Biology:Biotic ethics|Biotic ethics]] is a branch of ethics that values life itself. For biotic ethics, and their extension to space as panbiotic ethics, it is a human purpose to secure and propagate life and to use space to maximize life.

==Difficulties==
There would be many problems in colonizing the outer Solar System. These include:
*Distance from [[Astronomy:Earth|Earth]]: The outer planets are much farther from Earth than the inner planets, and would therefore be harder and more time-consuming to reach. In addition, return voyages may well be prohibitive considering the time and distance.
*Extreme cold: temperatures are near [[Physics:Absolute zero|absolute zero]] in many parts of the outer Solar System.
*Power: [[Engineering:Solar power|Solar power]] is many times less concentrated in the outer Solar System than in the inner Solar System. It is unclear as to whether it would be usable there, using some form of concentration mirrors, or whether [[Physics:Nuclear power|nuclear power]] would be necessary. There have also been proposals to use the [[Physics:Gravitational energy|gravitational potential energy]] of planets or dwarf planets with moons.
*[[Astronomy:Effect of spaceflight on the human body#Weightlessness|Effects of low gravity on the human body]]: All moons of the gas giants and all outer dwarf planets have a very low gravity, the highest being [[Astronomy:Io (moon)|Io's]] gravity (0.183 g) which is less than 1/5 of the Earth's gravity. Since the [[Astronomy:Apollo program|Apollo program]] all crewed spaceflight has been constrained to [[Astronomy:Low Earth orbit|Low Earth orbit]] and there has been no opportunity to test the effects of such low gravitational accelerations on the human body. It is speculated (but not confirmed) that the low gravity environments might have very similar effects to long-term exposure in [[Physics:Weightlessness|weightlessness]]. Such effects can be avoided by [[Physics:Artificial gravity#Centripetal force|rotating spacecraft creating artificial gravity]].

== Criticisms ==
Space colonization has been seen as a relief to the problem of [[Unsolved:Human overpopulation|human overpopulation]] as early as 1758,<ref name = tsr2009>[http://www.thespacereview.com/article/1296/1 Planetary demographics and space colonization] {{Webarchive|url=https://web.archive.org/web/20160513062857/http://www.thespacereview.com/article/1296/1 |date=2016-05-13 }}; Nader Elhefnawy, The Space Review, February 2, 2009.</ref><!--would be best if the original article that Otto Diederich Lutken published were put here--> and listed as one of Stephen Hawking's reasons for pursuing space exploration.<ref>{{cite news|url=https://www.telegraph.co.uk/news/science/space/7935505/Stephen-Hawking-mankind-must-move-to-outer-space-within-a-century.html|title=Stephen Hawking: mankind must move to outer space within a century|date=2010-08-09|last1=Alleyne|first1=Richard|access-date=2018-04-05|archive-url=https://web.archive.org/web/20180423144633/https://www.telegraph.co.uk/news/science/space/7935505/Stephen-Hawking-mankind-must-move-to-outer-space-within-a-century.html|archive-date=2018-04-23|url-status=live}}</ref> Critics note, however, that a slowdown in population growth rates since the 1980s has alleviated the risk of overpopulation.<ref name = tsr2009/>

Critics also argue that the costs of commercial activity in space are too high to be profitable against Earth-based industries, and hence that it is unlikely to see significant exploitation of space resources in the foreseeable future.<ref name=Marshall>
{{cite journal
|last=Marshall |first=P
|year=1981
|title=Nicole Oresme on the Nature, Reflection, and Speed of Light
|journal=Isis
|volume=72 |issue=3 |pages=357–74 [367–74]
|doi=10.1086/352787
|s2cid=144035661
}}</ref>

Other objections include concerns that the forthcoming colonization and commodification of the cosmos is likely to enhance the interests of the already powerful, including major economic and military institutions e.g. the large financial institutions, the major aerospace companies and the military–industrial complex, to lead to new [[Social:War|war]]s, and to exacerbate pre-existing exploitation of [[Finance:Exploitation of labour|workers]] and resources, [[Social:Economic inequality|economic inequality]], poverty, social division and [[Philosophy:Social exclusion|marginalization]], environmental degradation, and other detrimental processes or institutions.<ref name=Dickens-MR-2010-11/><ref name=Dickens-MR-2008-02/><ref name=Dickens-MR-2017-03/>

Additional concerns include creating a culture in which humans are no longer seen as human, but rather as material assets. The issues of human dignity, [[Philosophy:Morality|morality]], [[Philosophy:Philosophy|philosophy]], [[Social:Culture|culture]], [[Philosophy:Bioethics|bioethics]], and the threat of megalomaniac leaders in these new "societies" would all have to be addressed in order for space colonization to meet the psychological and social needs of people living in isolated colonies.<ref>[http://er.jsc.nasa.gov/seh/sociology.html Sociology and Space Development] {{Webarchive|url=https://web.archive.org/web/20080628172018/http://er.jsc.nasa.gov/seh/sociology.html |date=2008-06-28 }} B.J. Bluth, Sociology Department, California State University, Northridge, SPACE SOCIAL SCIENCE</ref>

As an alternative or addendum for the future of the human race, many science fiction writers have focused on the realm of the 'inner-space', that is the computer-aided exploration of the human mind and human [[Philosophy:Consciousness|consciousness]]—possibly en route developmentally to a Matrioshka Brain.<ref>{{Cite web|url=https://curiosity.com/topics/a-matrioshka-brain-is-a-computer-the-size-of-a-solar-system-curiosity/|title=A Matrioshka Brain Is A Computer The Size of a Solar System|website=curiosity.com|access-date=2018-08-14|archive-url=https://web.archive.org/web/20180814040151/https://curiosity.com/topics/a-matrioshka-brain-is-a-computer-the-size-of-a-solar-system-curiosity/|archive-date=2018-08-14|url-status=live}}</ref>

[[Engineering:Robotic spacecraft|Robotic spacecraft]] are proposed as an alternative to gain many of the same scientific advantages without the limited mission duration and high cost of life support and return transportation involved in human missions.<ref>{{Cite news|url=https://www.scientificamerican.com/report/robotic-planetary-exploration/|title=Robotic Exploration of the Solar System|work=Scientific American|access-date=2018-08-14|language=en|archive-url=https://web.archive.org/web/20180814040634/https://www.scientificamerican.com/report/robotic-planetary-exploration/|archive-date=2018-08-14|url-status=live}}</ref>

A corollary to the [[Astronomy:Fermi paradox|Fermi paradox]]—"nobody else is doing it"<ref>{{Cite news|url=https://www.forbes.com/sites/startswithabang/2018/06/26/no-we-cannot-know-whether-humans-are-alone-in-the-universe/|title=No, We Haven't Solved The Drake Equation, The Fermi Paradox, Or Whether Humans Are Alone|last=Siegel|first=Ethan|work=Forbes|access-date=2018-08-14|language=en|archive-url=https://web.archive.org/web/20180814041251/https://www.forbes.com/sites/startswithabang/2018/06/26/no-we-cannot-know-whether-humans-are-alone-in-the-universe/|archive-date=2018-08-14|url-status=live}}</ref>—is the argument that, because no evidence of [[Astronomy:Fermi paradox#Alien constructs|alien colonization technology]] exists, it is statistically unlikely to even be possible to use that same level of technology ourselves.<ref>{{Cite news|url=https://www.businessinsider.com/why-aliens-have-not-contacted-humans-2015-9|title=The likeliest reasons why we haven't contacted aliens are deeply unsettling|work=Business Insider|access-date=2018-08-14|archive-url=https://web.archive.org/web/20180814040227/https://www.businessinsider.com/why-aliens-have-not-contacted-humans-2015-9|archive-date=2018-08-14|url-status=live}}</ref>

===Colonialism===
[[File:Gemini5insignia.png|200px|thumb|[[Astronomy:Gemini 5|Gemini 5]] mission badge (1965) connecting spaceflight to colonial endeavours<ref name="Roger Launiuss Blog 2011">{{cite web | author=Roger Launius| title=Reconsidering the Foundations of Human Spaceflight in the 1950s | website=Roger Launius's Blog | date=Jun 8, 2011 | url=https://launiusr.wordpress.com/2011/06/08/reconsidering-the-foundations-of-human-spaceflight-in-the-1950s/ | access-date=Sep 6, 2021}}</ref>]]

[[Image:NASA Artemis Gateway logo.png|200px|The logo and name of the [[Astronomy:Lunar Gateway|Lunar Gateway]] references the St. Louis Gateway Arch,<ref>{{cite web|url=https://www.space.com/nasa-lunar-gateway-moon-station-logo.html|title=NASA Reveals New Gateway Logo for Artemis Lunar Orbit Way Station|website=Space.com|date=September 18, 2019|access-date=2020-06-28|author=Robert Z. Pearlman}}</ref> which some see as associating Mars with the American frontier and the ''manifest destiny'' mentality of American settler colonialism.<ref name="NPR.org 2015">{{cite web | title=As Gateway Arch Turns 50, Its Message Gets Reframed | website=NPR.org | date=2015-10-28 | url=https://www.npr.org/2015/10/28/452299164/as-gateway-arch-turns-50-its-message-gets-reframed | access-date=2022-06-27}}</ref>|thumb]]

Space colonization has been discussed as [[Philosophy:Postcolonialism|postcolonial]]<ref name="Durrani 2019">{{cite magazine | last=Durrani | first=Haris | title=Is Spaceflight Colonialism? | website=The Nation | date=19 July 2019 | url=https://www.thenation.com/article/world/apollo-space-lunar-rockets-colonialism/ | access-date=2 October 2020}}</ref> continuation of [[Social:Imperialism|imperialism]] and [[Social:Colonialism|colonialism]],<ref>{{cite news|title=How imperialism shaped the race to the moon|url=https://www.washingtonpost.com/outlook/2019/07/22/how-imperialism-shaped-race-moon/|newspaper={{wipe|The Washington Post}}|access-date=19 September 2019|date=22 July 2019|author=Gabrielle Cornish|language=en|archive-url=https://web.archive.org/web/20190723032005/https://www.washingtonpost.com/outlook/2019/07/22/how-imperialism-shaped-race-moon/|archive-date=23 July 2019|url-status=live}}</ref><ref name="Haskins"/><ref name="Drake"/><ref name="marshall"/> calling for decolonization instead of colonization.<ref name="Bartels 2018h"/><ref name="NatGeo 2018">{{cite web | title=We need to change the way we talk about space exploration | website=Science | date=2018-11-09 | url=https://www.nationalgeographic.com/science/article/we-need-to-change-way-we-talk-about-space-exploration-mars | access-date=2021-11-09}}</ref> Critics argue that the present politico-legal regimes and their philosophic grounding advantage imperialist development of space<ref name="marshall">{{cite journal |doi=10.1016/0265-9646(95)93233-B |title=Development and imperialism in space |author=Alan Marshall |date=February 1995 |journal=Space Policy |pages=41–52 |access-date=2020-06-28 |url=https://www.sciencedirect.com/science/article/abs/pii/026596469593233B |volume=11|issue=1 |bibcode=1995SpPol..11...41M}}</ref> and that key decisionmakers in space colonization are often wealthy elites affiliated with private corporations, and that space colonization would primarily appeal to their peers rather than ordinary citizens.<ref name="DNLee"/><ref>{{cite web|title=Against Mars-a-Lago: Why SpaceX's Mars colonization plan should terrify you|url=https://www.salon.com/2017/10/08/against-mars-a-lago-why-spacexs-mars-colonization-plan-should-terrify-you/|website=Salon.com|access-date=20 September 2019|date=8 October 2017|author=Keith A. Spencer|language=en|archive-url=https://web.archive.org/web/20190919201220/https://www.salon.com/2017/10/08/against-mars-a-lago-why-spacexs-mars-colonization-plan-should-terrify-you/|archive-date=19 September 2019|url-status=live}}</ref> Furthermore, it is argued that there is a need for inclusive<ref>{{cite web|title=Rethinking the Narrative of Mars Colonisation|url=https://othersociologist.com/2015/03/26/rethinking-the-narrative-of-mars-colonisation/|website=Other Sociologist|access-date=20 September 2019|date=26 March 2015|author=Zuleyka Zevallos|language=en|archive-url=https://web.archive.org/web/20191211122431/https://othersociologist.com/2015/03/26/rethinking-the-narrative-of-mars-colonisation/|archive-date=11 December 2019|url-status=live}}</ref> and democratic participation and implementation of any space exploration, infrastructure or habitation.<ref name="Tavares Buckner Burton McKaig 2020">{{cite arXiv | last1=Tavares | first1=Frank | last2=Buckner | first2=Denise | last3=Burton | first3=Dana | last4=McKaig | first4=Jordan | last5=Prem | first5=Parvathy | last6=Ravanis | first6=Eleni | last7=Trevino | first7=Natalie | last8=Venkatesan | first8=Aparna | last9=Vance | first9=Steven D. | last10=Vidaurri | first10=Monica | last11=Walkowicz | first11=Lucianne | last12=Wilhelm | first12=Mary Beth | title=Ethical Exploration and the Role of Planetary Protection in Disrupting Colonial Practices | date=Oct 15, 2020 | class=astro-ph.IM | eprint =2010.08344v2}}</ref><ref>{{cite web|title=Keep the Red Planet Red|url=https://www.jacobinmag.com/2017/02/mars-elon-musk-space-exploration-nasa-colonization|website=Jacobin|access-date=20 September 2019|date=2 May 2017|author=Keith A. Spencer|language=en|archive-url=https://web.archive.org/web/20191103165331/https://jacobinmag.com/2017/02/mars-elon-musk-space-exploration-nasa-colonization|archive-date=3 November 2019|url-status=live}}</ref> According to space law expert Michael Dodge, existing [[Astronomy:Space law|space law]], such as the [[Engineering:Outer Space Treaty|Outer Space Treaty]], guarantees access to space, but does not enforce social inclusiveness or regulate non-state actors.<ref name="Bartels 2018h">{{cite web | last=Bartels | first=Meghan | title=People are calling for a movement to decolonize space—here's why | website=Newsweek | date=May 25, 2018 | url=https://www.newsweek.com/should-we-colonize-space-some-people-argue-we-need-decolonize-it-instead-945130 | access-date=Nov 9, 2021}}</ref>

Particularly the narrative of the "New Frontier" has been criticized as unreflected continuation of [[Social:Settler colonialism|settler colonialism]] and manifest destiny, continuing the narrative of exploration as fundamental to the assumed [[Philosophy:Human nature|human nature]].<ref name="Schaberg 2021">{{cite web | last=Schaberg | first=Christopher | title=We're Already Colonizing Mars | website=Slate Magazine | date=Mar 30, 2021 | url=https://slate.com/technology/2021/03/mars-colonization-is-already-happening.html | access-date=Sep 8, 2021}}</ref><ref name="Renstrom 2021">{{cite web | last=Renstrom | first=Joelle | title=The Troubling Rhetoric of Space Exploration | website=Undark Magazine | date=2021-03-18 | url=https://undark.org/2021/03/18/rhetoric-of-space-exploration/ | access-date=2021-08-15}}</ref><ref name="Haskins">{{cite web|title=The racist language of space exploration|url=https://theoutline.com/post/5809/the-racist-language-of-space-exploration|website=The Outline|access-date=20 September 2019|date=14 August 2018|author=Caroline Haskins|language=en|archive-url=https://web.archive.org/web/20191016235916/https://theoutline.com/post/5809/the-racist-language-of-space-exploration|archive-date=16 October 2019|url-status=live}}</ref><ref name="DNLee">{{cite web|title=When discussing Humanity's next move to space, the language we use matters.|url=https://blogs.scientificamerican.com/urban-scientist/when-discussing-humanity-8217-s-next-move-to-space-the-language-we-use-matters/|website=Scientific American|access-date=20 September 2019|date=26 March 2015|author=DNLee|language=en|archive-url=https://web.archive.org/web/20190914011756/https://blogs.scientificamerican.com/urban-scientist/when-discussing-humanity-8217-s-next-move-to-space-the-language-we-use-matters/|archive-date=14 September 2019|url-status=live}}</ref><ref name="Drake">{{cite web|date=2018-11-09|title=We need to change the way we talk about space exploration|first=Nadia|last=Drake|publisher=National Geographic|access-date=2019-10-19|url=https://www.nationalgeographic.com/science/article/we-need-to-change-way-we-talk-about-space-exploration-mars|archive-url=https://web.archive.org/web/20191016235826/https://www.nationalgeographic.com/science/2018/11/we-need-to-change-way-we-talk-about-space-exploration-mars/|archive-date=2019-10-16|url-status=live}}</ref> Joon Yun considers [[Medicine:Space and survival|space colonization as a solution to human survival]] and global problems like pollution to be imperialist;<ref>{{cite web |author=Joon Yun |website=Worth.com |title=The Problem With Today's Ideas About Space Exploration. |date=January 2, 2020 |url=https://www.worth.com/is-space-the-next-frontier-for-the-same-old-story-of-imperialism/ |access-date=2020-06-28}}</ref> others have identified space as a new [[Finance:Sacrifice zone|sacrifice zone]] of colonialism.<ref name="Calma 2021">{{cite web | last=Calma | first=Justine | title=Jeff Bezos eyes space as a new 'sacrifice zone' | website=The Verge | date=Jul 21, 2021 | url=https://www.theverge.com/2021/7/21/22587249/jeff-bezos-space-pollution-industry-sacrifice-zone-amazon-environmental-justice | access-date=Nov 9, 2021}}</ref>

Natalie B. Trevino argues that not colonialism but [[Philosophy:Decoloniality|coloniality]] will be carried into space if not reflected on.<ref name="Filling Space 2021">{{cite web | title=What is the legacy of colonialism on space exploration? | website=Filling Space | date=Feb 18, 2021 | url=https://filling-space.com/2021/02/19/what-is-the-legacy-of-colonialism-on-space-exploration/ | access-date=Sep 9, 2021 | archive-date=September 9, 2021 | archive-url=https://web.archive.org/web/20210909113549/https://filling-space.com/2021/02/19/what-is-the-legacy-of-colonialism-on-space-exploration/ | url-status=dead }}</ref><ref name="Trevino 2021">{{cite thesis | last=Trevino | first=Natalie B | title=The Cosmos is Not Finished  |type=PhD dissertation |publisher=University of Western Ontario | date=Oct 30, 2020 | url=https://ir.lib.uwo.ca/etd/7567 | access-date=Sep 9, 2021}}</ref>

More specifically the advocacy for territorial colonization of Mars opposed to habitation in the atmospheric space of Venus has been called ''surfacism'',<ref name="Tickle 2015">{{cite web | last=Tickle | first=Glen | title=A Look into Whether Humans Should Try to Colonize Venus Instead of Mars | website=Laughing Squid | date=2015-03-05 | url=https://laughingsquid.com/a-look-into-whether-humans-should-try-to-colonize-venus-instead-of-mars/ | access-date=2021-09-01}}</ref><ref>{{cite web|title=Colonization of the Venusian Clouds: Is 'Surfacism' Clouding Our Judgement?|url=https://www.visionlearning.com/blog/2017/03/14/colonization-venusian-clouds-surfacism-clouding-judgement/|website=Vision Learning|access-date=20 September 2019|date=14 March 2017|author=David Warmflash|language=en|archive-date=11 December 2019|archive-url=https://web.archive.org/web/20191211122431/https://www.visionlearning.com/blog/2017/03/14/colonization-venusian-clouds-surfacism-clouding-judgement/|url-status=dead}}</ref> a concept similar to [[Biography:Thomas Gold|Thomas Gold]]s ''surface chauvinism''.

More generally space infrastructure such as the [[Organization:Mauna Kea Observatories|Mauna Kea Observatories]] have also been [[Religion:Opposition to the Mauna Kea Observatories|criticized and protested against]] as being colonialist.<ref name="Matson Nunn 2021">{{cite web | last1=Matson | first1=Zannah Mae | last2=Nunn | first2=Neil | title=Space Infrastructure, Empire, And The Final Frontier: What The Mauna Kea Land Defenders Teach Us About Colonial Totality | website=Society & Space | date=Sep 6, 2021 | url=https://www.societyandspace.org/articles/space-infrastructure-empire-and-the-final-frontier-what-the-mauna-kea-land-defenders-teach-us-about-colonial-totality | access-date=Sep 7, 2021}}</ref> [[Organization:Guiana Space Centre|Guiana Space Centre]] has also been the site of anti-colonial protests, connecting colonization as an issue on Earth and in space.<ref name="Durrani 2019"/>

In regard to the scenario of extraterrestrial [[Social:First contact (anthropology)|first contact]] it has been argued that being used to employ colonial language would endanger such first impressions and encounters.<ref name="Bartels 2018h"/>

Furthermore spaceflight as a whole and space law more particularly has been criticized as a postcolonial project by being built on a colonial legacy and by not facilitating the sharing of access to space and its benefits, too often allowing spaceflight to be used to sustain colonialism and imperialism, most of all on Earth instead.<ref name="Durrani 2019"/>

===Planetary protection===

Robotic spacecraft to Mars are required to be sterilized, to have at most 300,000 spores on the exterior of the craft—and more thoroughly sterilized if they contact "special regions" containing water, or it could contaminate life-detection experiments or the planet itself.<ref name=groundwatercontamination>[https://www.bbc.co.uk/news/uk-northern-ireland-27526981 Queens University Belfast scientist helps NASA Mars project] {{Webarchive|url=https://web.archive.org/web/20181119091228/https://www.bbc.co.uk/news/uk-northern-ireland-27526981 |date=2018-11-19}} "No-one has yet proved that there is deep groundwater on Mars, but it is plausible as there is certainly surface ice and atmospheric water vapour, so we wouldn't want to contaminate it and make it unusable by the introduction of micro-organisms."</ref><ref name="COSPAR PLANETARY PROTECTION POLICY">[https://science.nasa.gov/media/medialibrary/2012/05/04/COSPAR_Planetary_Protection_Policy_v3-24-11.pdf COSPAR PLANETARY PROTECTION POLICY] {{webarchive|url=https://web.archive.org/web/20130306111646/https://science.nasa.gov/media/medialibrary/2012/05/04/COSPAR_Planetary_Protection_Policy_v3-24-11.pdf |date=2013-03-06 }} (20 October 2002; As Amended to 24 March 2011)</ref>

It is impossible to sterilize human missions to this level, as humans are host to typically a hundred trillion [[Biology:Microorganism|microorganism]]s of thousands of species of the [[Biology:Human microbiome|human microbiome]], and these cannot be removed while preserving the life of the human. Containment seems the only option, but it is a major challenge in the event of a hard landing (i.e. crash).<ref name=biospherescollide>[http://www.nasa.gov/connect/ebooks/when_biospheres_collide_detail.html#.U_uVh_mwJcQ When Biospheres Collide – a history of NASA's Planetary Protection Programs] {{Webarchive|url=https://web.archive.org/web/20190714112103/https://www.nasa.gov/connect/ebooks/when_biospheres_collide_detail.html#.U_uVh_mwJcQ |date=2019-07-14 }}, Michael Meltzer, May 31, 2012, see Chapter 7, Return to Mars – final section: "Should we do away with human missions to sensitive targets"</ref> There have been several planetary workshops on this issue, but with no final guidelines for a way forward yet.<ref>Johnson, James E. [http://www.hou.usra.edu/meetings/ppw2015/pdf/1010.pdf "Planetary Protection Knowledge Gaps for Human Extraterrestrial Missions: Goals and Scope." (2015)] {{Webarchive|url=https://web.archive.org/web/20191026125720/https://www.hou.usra.edu/meetings/ppw2015/pdf/1010.pdf |date=2019-10-26 }}</ref> Human explorers could also inadvertently contaminate Earth if they return to the planet while carrying extraterrestrial microorganisms.<ref>[http://www.nap.edu/openbook.php?record_id=10360&page=37 Safe on Mars page 37] {{Webarchive|url=https://web.archive.org/web/20150906050040/http://www.nap.edu/openbook.php?record_id=10360&page=37 |date=2015-09-06 }} "Martian biological contamination may occur if astronauts breathe contaminated dust or if they contact material that is introduced into their habitat. If an astronaut becomes contaminated or infected, it is conceivable that he or she could transmit Martian biological entities or even disease to fellow astronauts, or introduce such entities into the biosphere upon returning to Earth. A contaminated vehicle or item of equipment returned to Earth could also be a source of contamination."</ref>

===Physical, mental and emotional health risks to colonizers===
{{main|Astronomy:Effect of spaceflight on the human body}}
The health of the humans who may participate in a colonization venture would be subject to increased physical, mental and emotional risks. [[Organization:NASA|NASA]] learned that &ndash; without gravity &ndash; bones lose [[Chemistry:Mineral (nutrient)|mineral]]s, causing [[Medicine:Osteoporosis|osteoporosis]].<ref>{{Cite news|url=https://www.bbc.com/news/world-42627341|title=Here's what happens to your body in space|newspaper=BBC News|date=10 January 2018|access-date=2019-04-09|language=en-GB|archive-url=https://web.archive.org/web/20190411152723/https://www.bbc.com/news/world-42627341|archive-date=11 April 2019|url-status=live}}</ref> [[Physics:Bone density|Bone density]] may decrease by 1% per month,<ref name="nasa-body">{{Cite web|url=http://www.nasa.gov/hrp/bodyinspace|title=The Human Body in Space|vauthors=Abadie LJ, Lloyd CW, Shelhamer MJ|date=11 June 2018|publisher=NASA|access-date=2019-03-04|archive-url=https://web.archive.org/web/20190726081140/https://www.nasa.gov/hrp/bodyinspace/|archive-date=26 July 2019|url-status=live}}</ref> which may lead to a greater risk of osteoporosis-related fractures later in life. Fluid shifts towards to the head may cause vision problems.<ref>{{Cite news|url=https://www.npr.org/sections/health-shots/2017/03/04/518214299/doctor-launches-vision-quest-to-help-astronauts-eyeballs|title=Doctor Launches Vision Quest To Help Astronauts' Eyeballs|author=Lauren Silverman|date=4 March 2017|website=NPR.org|access-date=2019-03-07|archive-url=https://web.archive.org/web/20190305165258/https://www.npr.org/sections/health-shots/2017/03/04/518214299/doctor-launches-vision-quest-to-help-astronauts-eyeballs|archive-date=5 March 2019|url-status=live}}</ref> NASA found that isolation in closed environments aboard the [[Astronomy:International Space Station|International Space Station]] led to [[Medicine:Depression (mood)|depression]], [[Medicine:Sleep disorder|sleep disorder]]s, and diminished personal interactions, likely due to confined spaces and the monotony and boredom of long space flight.<ref name=nasa-body/><ref>{{Cite web|url=https://www.nasa.gov/mission_pages/station/research/experiments/991.html|title=NASA - Behavioral Issues Associated with isolation and Confinement: Review and Analysis of Astronaut Journals|author=Jack W. Stuster|publisher=NASA|access-date=2019-04-09|archive-url=https://web.archive.org/web/20190411152721/https://www.nasa.gov/mission_pages/station/research/experiments/991.html|archive-date=2019-04-11|url-status=live}}</ref> [[Biology:Circadian rhythm|Circadian rhythm]] may also be susceptible to the effects of space life due to the effects on sleep of disrupted timing of sunset and sunrise.<ref name="weir">{{Cite web|url=https://www.apa.org/monitor/2018/06/mission-mars|title=Mission to Mars|publisher=American Psychological Association|author=Kirsten Weir|date=1 June 2018|access-date=2019-03-04|quote=We are a circadian species, and if you don't have the proper lighting to maintain that [[Biology:Chronobiology|chronobiology]], it can create significant problems for crew members|archive-url=https://web.archive.org/web/20191212130533/https://www.apa.org/monitor/2018/06/mission-mars|archive-date=12 December 2019|url-status=live}}</ref> This can lead to exhaustion, as well as other sleep problems such as [[Medicine:Insomnia|insomnia]], which can reduce their productivity and lead to mental health disorders.<ref name=weir/> High-energy radiation is a health risk that colonizers would face, as radiation in deep space is deadlier than what astronauts face now in low Earth orbit. Metal shielding on space vehicles protects against only 25-30% of space radiation, possibly leaving colonizers exposed to the other 70% of radiation and its short and long-term health complications.<ref name=":0"/>

==Implementation==
Building colonies in space would require access to water, food, space, people, construction materials, energy, transportation, [[Biology:Communication|communication]]s, [[Engineering:Life support system|life support]], simulated gravity, [[Physics:Radiation|radiation]] protection and capital investment. It is likely the colonies would be located near the necessary physical resources. The practice of [[Engineering:Space architecture|space architecture]] seeks to transform spaceflight from a heroic test of human endurance to a normality within the bounds of comfortable experience. As is true of other frontier-opening endeavors, the capital investment necessary for space colonization would probably come from governments,<ref>{{cite journal |url=http://www.jetpress.org/volume4/space.htm |title=The Political Economy of Very Large Space Projects |author=John Hickman |journal=Journal of Evolution and Technology |volume=4 |date=November 1999 |access-date=2013-12-14 |issn=1541-0099 |archive-url=https://web.archive.org/web/20131204190958/http://www.jetpress.org/volume4/space.htm |archive-date=2013-12-04 |url-status=live }}</ref> an argument made by John Hickman<ref>John Hickman (2010). Reopening the Space Frontier. Common Ground. {{ISBN|978-1-86335-800-2}}.</ref> and [[Biography:Neil deGrasse Tyson|Neil deGrasse Tyson]].<ref>Neil deGrasse Tyson (2012). Space Chronicles: Facing the Ultimate Frontier. W.W. Norton & Company. {{ISBN|978-0-393-08210-4}}.</ref>

===Life support===
{{Further|Astronomy:Effect of spaceflight on the human body|Medicine:Space medicine|Astronomy:Space food}}

[[File:Mars Food Production - Bisected.jpg|alt=|thumb|Depiction of NASA's plans to grow food on Mars]]

In space settlements, a life support system must recycle or import all the nutrients without "crashing." The closest terrestrial analogue to space life support is possibly that of a [[Engineering:Nuclear submarine|nuclear submarine]]. Nuclear submarines use mechanical life support systems to support humans for months without surfacing, and this same basic technology could presumably be employed for space use. However, nuclear submarines run "open loop"—extracting oxygen from seawater, and typically dumping [[Chemistry:Carbon dioxide|carbon dioxide]] overboard, although they recycle existing oxygen.<ref>{{Cite web|url=https://www.airitilibrary.com/Publication/alDetailedMesh?DocID=P20100106003-200911-201004190023-201004190023-1642-1650|title=A Novel Application of the SAWD-Sabatier-SPE Integrated System for CO2 Removal and O2 Regeneration in Submarine Cabins during Prolonged Voyages|last=Huang|first=Zhi|website=Airiti Library|access-date=10 September 2018}}</ref> Another commonly proposed life-support system is a [[Engineering:Closed ecological system|closed ecological system]] such as Biosphere 2.<ref>{{cite book | title=Manmade Closed Ecological Systems | author= I. I. Gitelson | author2= G. M. Lisovsky | author3= R. D. MacElroy | name-list-style= amp | publisher= Taylor & Francis |date=2003 | isbn = 0-415-29998-5}}</ref>

==== Solutions to health risks ====
Although there are many physical, mental, and emotional health risks for future colonizers and pioneers, solutions have been proposed to correct these problems. Mars500, HI-SEAS, and SMART-OP represent efforts to help reduce the effects of loneliness and confinement for long periods of time. Keeping contact with family members, celebrating holidays, and maintaining cultural identities all had an impact on minimizing the deterioration of mental health.<ref>{{Cite web|url=https://anxiety.psych.ucla.edu/nasa-study-stress-management-and-resilience-training-for-optimal-performance-smart-op|title=NASA Study: Stress Management and Resilience Training for Optimal Performance (SMART-OP) – Anxiety and Depression Research Center at UCLA|language=en-US|access-date=2019-03-04|archive-url=https://web.archive.org/web/20190404154812/https://anxiety.psych.ucla.edu/nasa-study-stress-management-and-resilience-training-for-optimal-performance-smart-op|archive-date=2019-04-04|url-status=live}}</ref> There are also health tools in development to help astronauts reduce anxiety, as well as helpful tips to reduce the spread of germs and bacteria in a closed environment.<ref>{{Cite web|url=https://phys.org/news/2017-09-e-mental-health-tool-key-astronauts.html|title=E-mental health tool may be key for astronauts to cope with anxiety, depression in space|website=Phys.org|language=en-us|access-date=2019-03-04|archive-url=https://web.archive.org/web/20190404154812/https://phys.org/news/2017-09-e-mental-health-tool-key-astronauts.html|archive-date=2019-04-04|url-status=live}}</ref> Radiation risk may be reduced for astronauts by frequent monitoring and focusing work away from the shielding on the shuttle.<ref name=":0">{{Cite web|url=https://www.nasa.gov/vision/space/travelinginspace/30sept_spacemedicine.html|title=NASA - Keeping Astronauts Healthy in Space|publisher=NASA|language=en|access-date=2019-03-05|archive-url=https://web.archive.org/web/20190202103324/https://www.nasa.gov/vision/space/travelinginspace/30sept_spacemedicine.html|archive-date=2019-02-02|url-status=live}}</ref> Future space agencies can also ensure that every colonizer would have a mandatory amount of daily exercise to prevent degradation of muscle.<ref name=":0" />

====Radiation protection====

Cosmic rays and [[Astronomy:Solar flare|solar flare]]s create a lethal radiation environment in space. In orbit around certain planets with magnetospheres (including Earth), the Van Allen belts make living above the atmosphere difficult. To protect life, settlements must be surrounded by sufficient mass to absorb most incoming radiation, unless magnetic or plasma radiation shields were developed.<ref name = spacecraftshielding>[http://engineering.dartmouth.edu/~simon_g_shepherd/research/Shielding/ Spacecraft Shielding] {{Webarchive|url=https://web.archive.org/web/20110928223044/http://engineering.dartmouth.edu/~simon_g_shepherd/research/Shielding/ |date=2011-09-28 }} engineering.dartmouth.edu. Retrieved 3 May 2011.</ref> In the case of Van Allen belts, these could be drained using orbiting tethers<ref name="mirnov1996">{{cite journal |last1=Mirnov |first1=Vladimir |last2=Üçer |first2=Defne |last3=Danilov |first3=Valentin |date=November 10–15, 1996 |title=High-Voltage Tethers For Enhanced Particle Scattering In Van Allen Belts |journal=APS Division of Plasma Physics Meeting Abstracts |volume=38 |pages=7 |bibcode=1996APS..DPP..7E06M |oclc=205379064 |id=Abstract #7E.06}}</ref> or radio waves.<ref>{{Cite web |title=NASA Finds Lightning Clears Safe Zone in Earth's Radiation Belt - NASA |url=https://www.nasa.gov/news-release/nasa-finds-lightning-clears-safe-zone-in-earths-radiation-belt/ |access-date=2023-12-11 |language=en-US}}</ref>

Passive mass shielding of four metric tons per square meter of surface area will reduce radiation dosage to several [[Physics:Sievert#Yearly dose examples|mSv]] or less annually, well below the rate of some populated [[Physics:Background radiation#Natural background radiation|high natural background areas]] on Earth.<ref>NASA SP-413 [http://settlement.arc.nasa.gov/75SummerStudy/5appendE.html Space Settlements: A Design Study. Appendix E Mass Shielding] {{Webarchive|url=https://web.archive.org/web/20130227031349/http://settlement.arc.nasa.gov//75SummerStudy/5appendE.html |date=2013-02-27 }} Retrieved 3 May 2011.</ref> This can be leftover material (slag) from processing lunar soil and asteroids into oxygen, metals, and other useful materials. However, it represents a significant obstacle to manoeuvring vessels with such massive bulk (mobile spacecraft being particularly likely to use less massive active shielding).<ref name = spacecraftshielding/> Inertia would necessitate powerful thrusters to start or stop rotation, or electric motors to spin two massive portions of a vessel in opposite senses. Shielding material can be stationary around a rotating interior.

====Psychological adjustment====
The monotony and loneliness that comes from a prolonged space mission can leave astronauts susceptible to cabin fever or having a psychotic break. Moreover, lack of sleep, fatigue, and work overload can affect an astronaut's ability to perform well in an environment such as space where every action is critical.<ref>Clynes, Manfred E. and Nathan S. Kline, (1960) "Cyborgs and Space," Astronautics, September, pp.&nbsp;26–27 and 74–76;</ref>

===Economics===
Space colonization can roughly be said to be possible when the necessary methods of space colonization become cheap enough (such as space access by cheaper launch systems) to meet the cumulative funds that have been gathered for the purpose, in addition to estimated profits from [[Astronomy:Commercial use of space|commercial use of space]].{{citation needed|date=September 2021}}

Although there are no immediate prospects for the large amounts of money required for space colonization to be available given traditional launch costs,<ref>[http://settlement.arc.nasa.gov/Basics/wwwwh.html Space Settlement Basics] {{Webarchive|url=https://web.archive.org/web/20120706031203/http://settlement.arc.nasa.gov/basics/wwwwh.html |date=2012-07-06 }} by Al Globus, NASA Ames Research Center. Last Updated: February 02, 2012</ref> there is some prospect of a radical reduction to launch costs in the 2010s, which would consequently lessen the cost of any efforts in that direction. With a published price of {{USD|56.5 million}} per launch of up to {{convert|13150|kg|abbr=on}} payload<ref name=sxCapabilitiesSvcs20131211>{{cite web |title=SpaceX Capabilities and Services |url=http://www.spacex.com/about/capabilities |year=2013<!-- copyright date; no other date provided --> |publisher=SpaceX |access-date=2013-12-11 |archive-url=https://web.archive.org/web/20131007205105/http://www.spacex.com/about/capabilities |archive-date=2013-10-07 |url-status=dead }} <!-- SpaceX refers to these prices as the "PAID IN FULL STANDARD LAUNCH PRICES (2013)" --></ref> to [[Astronomy:Low Earth orbit|low Earth orbit]], [[Company:SpaceX|SpaceX]] [[Engineering:Falcon 9|Falcon 9]] rockets are already the "cheapest in the industry".<ref name=fp20131209/> Advancements currently being developed as part of the [[Engineering:SpaceX reusable launch system development program|SpaceX reusable launch system development program]] to enable reusable Falcon 9s "could drop the price by an order of magnitude, sparking more space-based enterprise, which in turn would drop the cost of access to space still further through economies of scale."<ref name=fp20131209>{{cite news |last=Belfiore |first=Michael |title=The Rocketeer |url=https://foreignpolicy.com/articles/2013/12/02/the_rocketeer_elon_musk |access-date=2013-12-11 |newspaper=Foreign Policy |date=2013-12-09 |archive-url=https://web.archive.org/web/20131210233009/http://www.foreignpolicy.com/articles/2013/12/02/the_rocketeer_elon_musk |archive-date=2013-12-10 |url-status=live }}</ref> If SpaceX is successful in developing the reusable technology, it would be expected to "have a major impact on the cost of access to space", and change the increasingly [[Finance:Competition (economics)|competitive market]] in space launch services.<ref name="bbc20130930">{{cite news |url=https://www.bbc.co.uk/news/science-environment-24331860 |title=Recycled rockets: SpaceX calls time on expendable launch vehicles |work=BBC News |last=Amos |first=Jonathan |date=September 30, 2013 |access-date=October 2, 2013 |archive-url=https://web.archive.org/web/20131003085420/http://www.bbc.co.uk/news/science-environment-24331860 |archive-date=October 3, 2013 |url-status=live }}</ref>

The President's Commission on Implementation of United States Space Exploration Policy suggested that an inducement prize should be established, perhaps by government, for the achievement of space colonization, for example by offering the prize to the first organization to place humans on the Moon and sustain them for a fixed period before they return to Earth.<ref>[http://www.nasa.gov/pdf/60736main_M2M_report_small.pdf A Journey to Inspire, Innovate, and Discover] {{Webarchive|url=https://web.archive.org/web/20121010151959/http://www.nasa.gov/pdf/60736main_M2M_report_small.pdf |date=2012-10-10 }} - Report of the President's Commission on Implementation of United States Space Exploration Policy, June 2004</ref>

==== Money and currency ====
Experts have debated on the possible usage of money and currencies in societies that will be established in space. The Quasi Universal Intergalactic Denomination, or QUID, is a physical currency made from a space-qualified polymer [[Chemistry:Polytetrafluoroethylene|PTFE]] for inter-planetary travelers. QUID was designed for the foreign exchange company Travelex by scientists from Britain's National Space Centre and the University of Leicester.<ref>{{Cite web|url=https://www.space.com/4454-scientists-design-space-currency.html|title=Scientists Design New Space Currency|last=Christensen|first=Bill|date=October 10, 2007|website=Space.com|access-date=2019-01-21|archive-url=https://web.archive.org/web/20190121232640/https://www.space.com/4454-scientists-design-space-currency.html|archive-date=January 21, 2019|url-status=live}}</ref>

Other possibilities include the incorporation of [[Finance:Cryptocurrency|cryptocurrency]] as the primary form of currency, as suggested by [[Biography:Elon Musk|Elon Musk]].<ref>{{Cite web|last=Delbert|first=Caroline|date=2020-12-29|title=Elon Musk Says Mars Settlers Will Use Cryptocurrency, Like 'Marscoin'|url=https://www.popularmechanics.com/space/moon-mars/a35085273/elon-musk-says-mars-settlers-will-use-cryptocurrency-like-marscoin/|access-date=2021-02-24|website=Popular Mechanics|language=en-US}}</ref>

===Resources===
{{Further|Astronomy:Asteroid mining}}

Colonies on the Moon, Mars, asteroids, or the metal-rich planet [[Astronomy:Mercury (planet)|Mercury]], could extract local materials. The Moon is deficient in [[Earth:Volatile (astrogeology)|volatiles]] such as [[Chemistry:Argon|argon]], [[Chemistry:Helium|helium]] and compounds of [[Chemistry:Carbon|carbon]], [[Chemistry:Hydrogen|hydrogen]] and [[Chemistry:Nitrogen|nitrogen]]. The LCROSS impacter was targeted at the Cabeus crater which was chosen as having a high concentration of water for the Moon. A plume of material erupted in which some water was detected. Mission chief scientist Anthony Colaprete estimated that the Cabeus crater contains material with 1% water or possibly more.<ref>{{Cite news | url=http://www.sfgate.com/science/article/NASA-s-moon-blast-called-a-smashing-success-3213973.php | work=The San Francisco Chronicle | first=David | last=Perlman | title=NASA's moon blast called a smashing success | date=2009-10-10 | access-date=2015-07-19 | archive-url=https://web.archive.org/web/20150721235224/http://www.sfgate.com/science/article/NASA-s-moon-blast-called-a-smashing-success-3213973.php | archive-date=2015-07-21 | url-status=live }}</ref> Water [[Earth:Ice|ice]] should also be in other permanently shadowed craters near the lunar poles. Although helium is present only in low concentrations on the Moon, where it is deposited into regolith by the solar wind, an estimated million tons of He-3 exists over all.<ref>[http://www.satnews.com/stories2007/4588/] {{webarchive|url=https://web.archive.org/web/20120308151604/http://www.satnews.com/stories2007/4588/|date=March 8, 2012}}</ref> It also has industrially significant [[Chemistry:Oxygen|oxygen]], [[Chemistry:Silicon|silicon]], and metals such as [[Chemistry:Iron|iron]], [[Chemistry:Aluminum|aluminum]], and [[Chemistry:Titanium|titanium]].

Launching materials from Earth is expensive, so bulk materials for colonies could come from the Moon, a [[Astronomy:Near-Earth object|near-Earth object]] (NEO), [[Astronomy:Phobos (moon)|Phobos]], or [[Astronomy:Deimos (moon)|Deimos]]. The benefits of using such sources include: a lower gravitational force, no [[Physics:Drag|atmospheric drag]] on cargo vessels, and no biosphere to damage. Many NEOs contain substantial amounts of metals. Underneath a drier outer crust (much like [[Earth:Oil shale|oil shale]]), some other NEOs are inactive comets which include billions of tons of water ice and [[Earth:Kerogen|kerogen]] hydrocarbons, as well as some nitrogen compounds.<ref>{{cite conference |title=Discovery of Abundant, Accessible Hydrocarbons nearly Everywhere in the Solar System |last1= Zuppero|first1= Anthony |year= 1996 |publisher= [[Organization:American Society of Civil Engineers|ASCE]] |book-title= Proceedings of the Fifth International Conference on Space '96 |doi= 10.1061/40177(207)107|isbn= 0-7844-0177-2}}</ref>

Farther out, [[Astronomy:Colonization of the outer Solar System#Jupiter trojans|Jupiter's Trojan asteroids]] are thought to be rich in water ice and other volatiles.<ref>{{Cite news|last=Sanders|first=Robert|title=Binary asteroid in Jupiter's orbit may be icy comet from solar system's infancy|date=1 February 2006|publisher=UC Berkeley|url=http://www.berkeley.edu/news/media/releases/2006/02/01_patroclus.shtml|access-date=2009-05-25|archive-url=https://web.archive.org/web/20181211102116/https://www.berkeley.edu/news/media/releases/2006/02/01_patroclus.shtml|archive-date=11 December 2018|url-status=live}}</ref>

[[Physics:Recycling|Recycling]] of some raw materials would almost certainly be necessary.

====Energy====
[[Physics:Solar energy|Solar energy]] in orbit is abundant, reliable, and is commonly used to power satellites today. There is no night in free space, and no clouds or atmosphere to block sunlight. Light intensity obeys an [[Inverse-square law|inverse-square law]]. So the solar energy available at distance ''d'' from the Sun is ''E'' = 1367/''d''<sup>2</sup> W/m<sup>2</sup>, where ''d'' is measured in [[Astronomy:Astronomical unit|astronomical unit]]s (AU) and 1367 watts/m<sup>2</sup> is the energy available at the distance of Earth's orbit from the Sun, 1 AU.<ref>McGraw-Hill Encyclopedia of Science & Technology, 8th Edition 1997; vol. 16 p. 654</ref>

In the weightlessness and vacuum of space, high temperatures for industrial processes can easily be achieved in solar ovens with huge parabolic reflectors made of metallic foil with very lightweight support structures. Flat mirrors to reflect sunlight around radiation shields into living areas (to avoid line-of-sight access for cosmic rays, or to make the Sun's image appear to move across their "sky") or onto crops are even lighter and easier to build.

Large solar power photovoltaic cell arrays or thermal power plants would be needed to meet the electrical power needs of the settlers' use. In developed parts of Earth, electrical consumption can average 1 kilowatt/person (or roughly 10 megawatt-hours per person per year.)<ref>[http://www.unescap.org/esd/energy/information/ElectricPower/1999-2000/access.htm UNESCAP Electric Power in Asia and the Pacific] {{webarchive |url=https://web.archive.org/web/20110213083253/http://www.unescap.org/esd/energy/information/ElectricPower/1999-2000/access.htm |date=February 13, 2011 }}</ref> These power plants could be at a short distance from the main structures if wires are used to transmit the power, or much farther away with wireless power transmission.

A major export of the initial space settlement designs was anticipated to be large solar power satellites (SPS) that would use wireless power transmission (phase-locked [[Physics:Microwave|microwave]] beams or lasers emitting wavelengths that special solar cells convert with high efficiency) to send power to locations on Earth, or to colonies on the Moon or other locations in space. For locations on Earth, this method of getting power is extremely benign, with zero emissions and far less ground area required per watt than for conventional solar panels. Once these satellites are primarily built from lunar or asteroid-derived materials, the price of SPS electricity could be lower than energy from fossil fuel or nuclear energy; replacing these would have significant benefits such as the elimination of greenhouse gases and [[Physics:Nuclear waste|nuclear waste]] from electricity generation.<ref>{{Cite web|url=http://large.stanford.edu/courses/2015/ph240/gaertner1/|title=Solar vs. Traditional Energy in Homes|website=large.stanford.edu|access-date=2019-02-26|archive-url=https://web.archive.org/web/20181024050207/http://large.stanford.edu/courses/2015/ph240/gaertner1/|archive-date=2018-10-24|url-status=live}}</ref>

Transmitting solar energy wirelessly from the Earth to the Moon and back is also an idea proposed for the benefit of space colonization and energy resources. Physicist Dr. David Criswell, who worked for NASA during the Apollo missions, came up with the idea of using power beams to transfer energy from space. These beams, microwaves with a wavelength of about 12&nbsp;cm, will be almost untouched as they travel through the atmosphere. They can also be aimed at more industrial areas to keep away from humans or animal activities.<ref name="i2massociates.com">{{Cite web |url=http://www.i2massociates.com/downloads/AAPG_Memoir_101-July18-2012.pdf |title=Nuclear Power and Associated Environmental Issues in the Transition of Exploration and Mining on Earth to the Development of Off-World Natural Resources in the 21st Century |access-date=2017-09-18 |archive-url=https://web.archive.org/web/20150214125331/http://i2massociates.com/downloads/AAPG_Memoir_101-July18-2012.pdf |archive-date=2015-02-14 |url-status=live }}</ref> This will allow for safer and more reliable methods of transferring solar energy.

In 2008, scientists were able to send a 20 watt microwave signal from a mountain in Maui to the island of Hawaii.<ref>{{Cite journal|last=Dance|first=Amber|date=2008-09-16|title=Beaming energy from space|journal=Nature|doi=10.1038/news.2008.1109|issn=0028-0836}}</ref> Since then [[Organization:JAXA|JAXA]] and Mitsubishi has teamed up on a $21&nbsp;billion project in order to place satellites in orbit which could generate up to 1 gigawatt of energy.<ref>{{cite web|url=https://www.popsci.com/technology/article/2011-06/satellites-could-gather-energy-sun-and-beam-it-down-earth/ |title=Space Based Solar Power |first=Corey|last=Binns|archive-url=https://web.archive.org/web/20170927054041/http://www.popsci.com/technology/article/2011-06/satellites-could-gather-energy-sun-and-beam-it-down-earth |archive-date=2017-09-27|publisher=Popular Science| date=June 2, 2011}}</ref> These are the next advancements being done today in order to make energy be transmitted wirelessly for space-based solar energy.

However, the value of SPS power delivered wirelessly to other locations in space will typically be far higher than to Earth. Otherwise, the means of generating the power would need to be included with these projects and pay the heavy penalty of Earth launch costs. Therefore, other than proposed demonstration projects for power delivered to Earth,<ref name="NatSecSpaceOffice2007">{{cite web |date=10 October 2007 |title=Space-Based Solar Power As an Opportunity for Strategic Security: Phase 0 Architecture Feasibility Study |url=https://apps.dtic.mil/sti/pdfs/ADA473860.pdf |url-status=live |archive-url=https://web.archive.org/web/20220926134325/https://apps.dtic.mil/sti/pdfs/ADA473860.pdf |archive-date=26 September 2022 |access-date=26 September 2022 |website= |publisher=U.S. National Security Space Office}}</ref> the first priority for SPS electricity is likely to be locations in space, such as communications satellites, fuel depots or "orbital tugboat" boosters transferring cargo and passengers between [[Astronomy:Low Earth orbit|low Earth orbit]] (LEO) and other orbits such as [[Astronomy:Geosynchronous orbit|geosynchronous orbit]] (GEO), [[Astronomy:Lunar orbit|lunar orbit]] or [[Astronomy:Highly elliptical orbit|highly-eccentric Earth orbit]] (HEEO).<ref name="Lewis1997">[[Astronomy:Mining the Sky|Mining the Sky]]</ref>{{rp|132}} The system will also rely on satellites and receiving stations on Earth to convert the energy into electricity. Because of this energy can be transmitted easily from dayside to nightside meaning power is reliable 24/7.<ref>[https://www.wired.co.uk/article/moon-solar-energy-power Beaming solar energy from the Moon could solve Earth's energy crisis] {{Webarchive|url=https://web.archive.org/web/20171011044359/http://www.wired.co.uk/article/moon-solar-energy-power |date=2017-10-11 }}; March 29, 2017; Wired]</ref>

[[Physics:Nuclear power|Nuclear power]] is sometimes proposed for colonies located on the Moon or on Mars, as the supply of solar energy is too discontinuous in these locations; the Moon has nights of two Earth weeks in duration. Mars has nights, relatively high gravity, and an atmosphere featuring [[Astronomy:Climate of Mars#Effect of dust storms|large dust storms]] to cover and degrade solar panels. Also, Mars' greater distance from the Sun (1.52 astronomical units, AU) means that only ''1/1.52<sup>2</sup>'' or about 43% of the solar energy is available at Mars compared with Earth orbit.<ref>[https://www.sciencedaily.com/releases/2009/10/091004020806.htm 'Trash Can' Nuclear Reactors Could Power Human Outpost On Moon Or Mars] {{Webarchive|url=https://web.archive.org/web/20170918154323/https://www.sciencedaily.com/releases/2009/10/091004020806.htm |date=2017-09-18 }}; October 4, 2009; ScienceDaily</ref> Another method would be transmitting energy wirelessly to the lunar or Martian colonies from solar power satellites (SPSs) as described above; the difficulties of generating power in these locations make the relative advantages of SPSs much greater there than for power beamed to locations on Earth. In order to also be able to fulfill the requirements of a Moon base and energy to supply life support, maintenance, communications, and research, a combination of both nuclear and solar energy will be used in the first colonies.<ref name="i2massociates.com"/>

For both solar thermal and nuclear power generation in airless environments, such as the Moon and space, and to a lesser extent the very thin Martian atmosphere, one of the main difficulties is dispersing the [[Physics:Carnot cycle|inevitable heat generated]]. This requires fairly large radiator areas.

===Self-replication===

Space manufacturing could enable self-replication. Some consider it the ultimate goal because it would allow an [[Exponential growth|exponential]] increase in colonies, while eliminating costs to and dependence on Earth.<ref>{{Cite magazine |first=Ian |last=Crawford |title=Where are they? |magazine=Scientific American |volume=283 |number=1 |date=July 2000 |pages=38–43 |jstor=26058784 |url=https://www.jstor.org/stable/26058784}}</ref> It could be argued that the establishment of such a colony would be Earth's first act of self-replication.<ref>{{cite journal | last1 = Margulis | first1 = Lynn |  last2 = Guerrero | first2 = Ricardo | year = 1995 | title = Life as a planetary phenomenon: the colonization of Mars | journal = Microbiología | volume = 11 | pages = 173–84 | pmid = 11539563 }}</ref> Intermediate goals include colonies that expect only information from Earth (science, engineering, entertainment) and colonies that just require periodic supply of light weight objects, such as [[Engineering:Integrated circuit|integrated circuit]]s, medicines, [[Biology:DNA|genetic material]] and tools.

===Population size===
In 2002, the [[Social:Anthropology|anthropologist]] John H. Moore estimated<ref>{{Cite web |url=https://www.newscientist.com/article/dn1936-magic-number-for-space-pioneers-calculated |title="Magic number" for space pioneers calculated |date=15 February 2002 |work=New Scientist |first=Damian |last=Carrington}}</ref> that a population of 150–180 would permit a stable society to exist for 60 to 80 generations—equivalent to 2,000 years.

Assuming a journey of 6,300 years, the astrophysicist Frédéric Marin and the particle physicist Camille Beluffi calculated that the minimum viable population for a [[Engineering:Generation ship|generation ship]] to reach [[Astronomy:Proxima Centauri|Proxima Centauri]] would be 98 settlers at the beginning of the mission (then the crew will breed until reaching a stable population of several hundred settlers within the ship) .<ref>{{cite journal |arxiv=1806.03856|last1=Marin|first1=F|title=Computing the minimal crew for a multi-generational space travel towards Proxima Centauri b|journal=Journal of the British Interplanetary Society|volume=71|pages=45|last2=Beluffi|first2=C|year=2018|bibcode=2018JBIS...71...45M}}</ref><ref>{{cite magazine |url=https://www.technologyreview.com/s/611485/this-is-how-many-people-wed-have-to-send-to-proxima-centauri-to-make-sure-someone-actually/amp/ |magazine=MIT Technology Review |title=This is how many people we'd have to send to Proxima Centauri to make sure someone actually arrives |date=June 22, 2018 |quote="We can then conclude that, under the parameters used for those simulations, a minimum crew of 98 settlers is needed for a 6,300-year multi-generational space journey towards Proxima Centauri b," say Marin and Beluffi.}}</ref>

In 2020, Jean-Marc Salotti proposed a method to determine the minimum number of settlers to survive on an extraterrestrial world. It is based on the comparison between the required time to perform all activities and the working time of all human resources. For Mars, 110 individuals would be required.<ref>{{cite journal |last1=Salotti |first1=Jean-Marc |title=Minimum Number of Settlers for Survival on Another Planet |journal=Scientific Reports |date=16 June 2020 |volume=10 |issue=1 |page=9700 |doi=10.1038/s41598-020-66740-0 |pmid=32546782 |pmc=7297723 |bibcode=2020NatSR..10.9700S |doi-access=free }}</ref>

==Advocacy==
Several private companies have announced plans toward the [[Astronomy:Colonization of Mars|colonization of Mars]]. Among entrepreneurs leading the call for space colonization are [[Biography:Elon Musk|Elon Musk]], Dennis Tito and Bas Lansdorp.<ref>[https://www.nytimes.com/2013/03/09/business/global/reality-tv-for-the-red-planet.html Reality TV for the Red Planet] {{Webarchive|url=https://web.archive.org/web/20170629013428/http://www.nytimes.com/2013/03/09/business/global/reality-tv-for-the-red-planet.html |date=2017-06-29 }}, by Nicola Clark; The New York Times, March 8, 2013</ref><ref>[http://news.nationalgeographic.com/news/2013/02/130222-manned-mission-mars-tito-space-science/ Businessman Dennis Tito Financing Manned Mission to Mars] {{Webarchive|url=https://web.archive.org/web/20130301012114/http://news.nationalgeographic.com/news/2013/02/130222-manned-mission-mars-tito-space-science/ |date=2013-03-01 }}, by Jane J. Lee; National Geographic News, February 22, 2013</ref>

===Involved organizations===
Organizations that contribute to space colonization include:

* The [[Organization:National Space Society|National Space Society]] is an organization with the vision of people living and working in thriving communities beyond the Earth. The NSS also maintains an extensive library of full-text articles and books on space settlement.<ref>{{cite web |url=http://www.nss.org/settlement/library.html |title=NSS Space Settlement Library |publisher=Nss.org |date=2011-12-16 |access-date=2013-12-14 |archive-url=https://web.archive.org/web/20110612005613/http://www.nss.org/settlement/library.html |archive-date=2011-06-12 |url-status=dead }}</ref>
* The [[Organization:Space Frontier Foundation|Space Frontier Foundation]] performs [[Engineering:Space advocacy|space advocacy]] including strong [[Social:Free market|free market]], [[Philosophy:Capitalism|capitalist]] views about space development.
* The [[Organization:Mars Society|Mars Society]] promotes [[Biography:Robert Zubrin|Robert Zubrin]]'s [[Astronomy:Mars Direct|Mars Direct]] plan and the settlement of Mars.
* The Space Settlement Institute is searching for ways to make space colonization happen within a lifetime.<ref>{{cite web|url=http://www.space-settlement-institute.org|title=The Space Settlement Institute|work=space-settlement-institute.org|access-date=13 June 2015|archive-url=https://web.archive.org/web/20150428202903/http://www.space-settlement-institute.org/|archive-date=28 April 2015|url-status=live}}</ref>
* [[Company:SpaceX|SpaceX]] is developing extensive [[Astronomy:SpaceX Mars transportation infrastructure|spaceflight transportation infrastructure]] with the express purpose of enabling long-term human settlement of Mars.<ref name=trati20181224>{{cite news |last=Ralph |first=Eric |url=https://www.teslarati.com/spacex-elon-musk-starship-prototype-three-raptors-mirror-finish/ |title=SpaceX CEO Elon Musk: Starship prototype to have 3 Raptors and "mirror finish" |work=Teslarati |date=24 December 2018 |access-date=30 December 2018 |archive-url=https://web.archive.org/web/20181224133103/https://www.teslarati.com/spacex-elon-musk-starship-prototype-three-raptors-mirror-finish/ |archive-date=24 December 2018 |url-status=live }}</ref><ref name=sn20181224>
{{cite news |last=Foust|first=Jeff |url=https://spacenews.com/musk-teases-new-details-about-redesigned-next-generation-launch-system/ |title=Musk teases new details about redesigned next-generation launch system |work=SpaceNews |date=24 December 2018 |access-date=27 December 2018 }}</ref>
* The [[Organization:Space Studies Institute|Space Studies Institute]] funds the study of outer space settlements, especially [[Astronomy:O'Neill cylinder|O'Neill cylinder]]s.
* The [[Astronomy:Alliance to Rescue Civilization|Alliance to Rescue Civilization]] plans to establish [[Backup|backup]]s of human civilization on the Moon and other locations away from Earth.
* The [[Astronomy:Artemis Project|Artemis Project]] plans to set up a private lunar surface station.[https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930008978.pdf]
* The [[Organization:British Interplanetary Society|British Interplanetary Society]] promotes ideas for the exploration and utilization of space, including a [[Astronomy:Project Boreas|Mars colony]], future propulsion systems (see [[Engineering:Project Daedalus|Project Daedalus]]), terraforming, and locating other habitable worlds.<ref>{{Cite web |title=Journal of the British Interplanetary Society |url=https://www.bis-space.com/publications/jbis/ |access-date=2022-09-26 |website=The British Interplanetary Society |language=en-GB}}</ref>
** In June 2013 the BIS began the SPACE project to re-examine Gerard O'Neill's 1970s space colony studies in light of the advances made since then. The progress of this effort were detailed in a special edition of the journal in September 2019.<ref name=":2">{{Cite journal |date=September 2019 |title=BIS SPACE Project special issue |url=https://www.bis-space.com/membership/jbis/2019/JBIS-v72-no09-September-October-2019_dk64ll.pdf |journal=[[Organization:Journal of the British Interplanetary Society|Journal of the British Interplanetary Society]] |volume=72 |issue=9/10}}</ref>
* Asgardia (nation) – an organization searching to circumvent limitations placed by [[Engineering:Outer Space Treaty|Outer Space Treaty]].
*The [[Organization:Cyprus Space Exploration Organisation|Cyprus Space Exploration Organisation]] (CSEO) promotes space exploration and colonization, and fosters collaboration in space.

==Terrestrial analogues to space settlement==
[[File:Wiki bio2 sunset 001.jpg|thumb|right|200px|Biosphere 2 is a test habitat on Earth for space flight.]]
Many space agencies build "testbeds", which are facilities on Earth for testing advanced life support systems, but these are designed for long duration [[Astronomy:Human spaceflight|human spaceflight]], not permanent colonization.

*The most famous attempt to build an analogue to a self-sufficient settlement is Biosphere 2, which attempted to duplicate Earth's biosphere. 
*BIOS-3 is another closed ecosystem, completed in 1972 in Krasnoyarsk, Siberia.<ref>{{Cite news|url=https://www.ecowatch.com/the-worlds-largest-earth-science-experiment-biosphere-2-1882107636.html|title=The World's Largest Earth Science Experiment: Biosphere 2|date=2015-10-16|work=EcoWatch|access-date=2018-08-14|language=en|archive-url=https://web.archive.org/web/20180814040305/https://www.ecowatch.com/the-worlds-largest-earth-science-experiment-biosphere-2-1882107636.html|archive-date=2018-08-14|url-status=live}}</ref>
*The Mars Desert Research Station has a habitat for similar reasons, but the surrounding climate is not strictly inhospitable.<ref>{{Cite news|url=https://news.nationalgeographic.com/2016/12/exploring-mars-utah-mock-mission-simulation-space-science/|title=8 Amazing Places You Can Visit 'Mars' on Earth|date=2016-12-12|access-date=2018-08-13|archive-url=https://web.archive.org/web/20180814040445/https://news.nationalgeographic.com/2016/12/exploring-mars-utah-mock-mission-simulation-space-science/|archive-date=2018-08-14|url-status=dead}}</ref>
*Devon Island [[Place:Flashline Mars Arctic Research Station|Mars Arctic Research Station]], can also provide some practice for off-world outpost construction and operation.<ref>{{Cite news|url=https://www.mnn.com/earth-matters/wilderness-resources/stories/devon-island-close-mars-you-may-get|title=Devon Island is as close to Mars as you may get|work=MNN - Mother Nature Network|access-date=2018-08-13|language=en|archive-url=https://web.archive.org/web/20180814040256/https://www.mnn.com/earth-matters/wilderness-resources/stories/devon-island-close-mars-you-may-get|archive-date=2018-08-14|url-status=live}}</ref>

==In media and fiction==
Although established space habitats are a stock element in science fiction stories, fictional works that explore the themes, social or practical, of the settlement and occupation of a habitable world are much rarer.{{Citation needed|date=December 2022}}

* ''Solaris'' is noted for its critique of space colonization of inhabited planets. At one point, one of the characters says:<ref>{{cite journal|url=https://www.jstor.org/stable/4240332|title=Resisting Monsters: Notes on "Solaris"|author=Ann Weinstone|journal=Science Fiction Studies|date= July 1994|volume=21|number=2|pages=173–190|publisher=SF-TH Inc|jstor=4240332|access-date=4 February 2021}}"Lem's critique of colonialism, as he broadly defines it, is articulated by
Snow, one of the other scientists on the space station, who says in the book's most frequently quoted passage.</ref>
{{blockquote|We are humanitarian and chivalrous; we don't want to enslave other races, we simply want to bequeath them our values and take over their heritage in exchange. We think of ourselves as the Knights of the Holy Contact. This is another lie. We are only seeking Man. We have no need of other worlds. We need mirrors. (§6:72)}}

In 2022 Rudolph Herzog and Werner Herzog presented an in-depth documentary with [[Biography:Lucianne Walkowicz|Lucianne Walkowicz]] called ''Last exit: Space''.<ref name="Machkovech 2022">{{cite web | last=Machkovech | first=Sam | title=Why Werner Herzog thinks human space colonization "will inevitably fail" – Ars Technica | website=Ars Technica | date=2022-03-12 | url=https://arstechnica.com/gaming/2022/03/ars-talks-to-werner-herzog-about-space-colonization-its-poetry/?amp=1 | access-date=2022-10-15}}</ref>

==See also==
{{Div col|colwidth=20em}}
* [[Astronomy:Asteroid mining|Asteroid mining]]
* Bernal sphere
* [[Engineering:Billionaire space race|Billionaire space race]]
* [[Biology:Colonisation|Colonisation]]
* [[Unsolved:Colonization of Antarctica|Colonization of Antarctica]]
* [[Unsolved:Directed panspermia|Directed panspermia]]
* [[Engineering:Domed city|Domed city]]
* [[Astronomy:Extraterrestrial liquid water|Extraterrestrial liquid water]]
* [[Astronomy:Extraterrestrial real estate|Extraterrestrial real estate]]
* Human outpost
* [[Astronomy:Human presence in space|Human presence in space]]
* Lagrange point colonization
* [[Astronomy:Mars analog habitat|Mars analog habitat]]
* [[Organization:Mars One|Mars One]]
* [[Astronomy:Mars to Stay|Mars to Stay]]
* [[Engineering:Megastructure|Megastructure]]
* [[Company:NewSpace|NewSpace]]
* [[Engineering:MELiSSA|MELiSSA]]
* [[Earth:Ocean colonization|Ocean colonization]]
* O'Neill Cylinder
* [[Astronomy:Planetary habitability|Planetary habitability]]
* Solar analog
* Space archaeology
* [[Astronomy:Space habitat|Space habitat]]
* [[Social:Politics of outer space|Politics of outer space]]
* {{annotated link|Research station}}
* [[Astronomy:Space law|Space law]]
* [[Astronomy:Spome|Spome]]
* [[Astronomy:Stanford torus|Stanford torus]]
* [[Earth:Terraforming|Terraforming]]
* [[Astronomy:Timeline of Solar System exploration|Timeline of Solar System exploration]]
* Underground city
{{Div col end}}

==References==
{{reflist}}

==Further reading==
{{Library resources box}}
;Papers
* Yap, Xiao-Shan & Rakhyun E. Kim (2023). "Towards Earth-Space Governance in a Multi-Planetary Era". ''Earth System Governance'', 16: 100173.
* {{cite book| last = Ferrando | first = Francesca | chapter = Why Space Migration Must be Posthuman | publisher = Springer | pages = 137–152| date = July 2016| location=New York, US| isbn = 978-3-319-39825-9 | doi = 10.1007/978-3-319-39827-3_10 | title = The Ethics of Space Exploration | series = Space and Society }}
* {{cite journal | last = Tiziani | first = Moreno | title = The Colonization of Space - An Anthropological Outlook | journal = Antrocom Online Journal of Anthropology | publisher = Antrocom | volume = 9 | pages = 225–236 | date = Jun 2013 | location = Rome, Italy | issn = 1973-2880 | url = http://www.antrocom.net/upload/sub/antrocom/090113/21-Antrocom.pdf | issue = 1 | access-date = 2013-12-01 | archive-date = 2013-12-02 | archive-url = https://web.archive.org/web/20131202223755/http://www.antrocom.net/upload/sub/antrocom/090113/21-Antrocom.pdf | url-status = dead }}
* {{cite book |last=Foss |first= Nicole |date= December 2016 |title=Mass Extinction and Mass Insanity |url= https://www.theautomaticearth.com/2016/12/mass-extinction-and-mass-insanity/}}
* {{cite book| last = Harrison | first = Albert A. |title=Spacefaring: The Human Dimension|year=2002 |publisher=University of California Press |location=Berkeley, CA, US |isbn=978-0-520-23677-6}}
* {{cite book|last=Seedhouse|first=Erik|title=Lunar Outpost: The Challenges of Establishing a Human Settlement on the Moon|year=2009 |publisher=Praxis Publishing Ltd. |location=Chichester, UK |isbn=978-0-387-09746-6}} Also see [https://www.springer.com/astronomy/space+exploration/book/978-0-387-09746-6]
* {{cite book|last=Seedhouse|first=Erik|title=Martian Outpost: The Challenges of Establishing a Human Settlement on Mars|journal=Popular Astronomy |year=2009 |publisher=Praxis Publishing Ltd. |location=Chichester, UK |isbn=978-0-387-98190-1|bibcode=2009maou.book.....S}}
* {{cite book|last=Seedhouse|first=Erik|title=Interplanetary Outpost: The Human and Technological Challenges of Exploring the Outer Planets|year=2012 |publisher=Springer |location=Berlin |isbn=978-1-4419-9747-0}}
* {{cite book| last = Cameron M. Smith | first = Evan T. Davies |title=Emigrating Beyond Earth: Human Adaptation and Space Colonization|year=2012 |publisher=Springer-Verlag |location=Berlin |isbn=978-1-4614-1164-2}}
;Video
*{{cite book| last=Rees|first=Martin|url=https://www.youtube.com/watch?v=ngrJLQjZqY4 |archive-url=https://ghostarchive.org/varchive/youtube/20211211/ngrJLQjZqY4| archive-date=2021-12-11 |url-status=live|title=Brief talk on some key issues in space exploration and colonization|date=March 2017}} <small>Posted on the official YouTube channel of ''Casina Pio IV.''</small>
*{{cite book| last=Sarmont|first=Eagle|url=https://vimeo.com/306453241|title=Opening the High Frontier|date=December 2018}} <small>Affordable to everyone spaceflight is the key to building a spacefaring civilization. Posted on Vimeo.</small>

{{Spaceflight}}
{{Space tourism}}
{{inspace}}
{{Solar System}}

{{DEFAULTSORT:Space Colonization}}
[[Category:Spaceflight concepts]]
[[Category:Open problems]]

{{Sourceattribution|Space colonization}}