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{{Short description|Type of space station, intended as a permanent settlement}}
{{Ref-improve|date=January 2021}}
[[File:Stanford Torus cutaway.jpg|right|thumb|upright=1.3|A [[Stanford torus]] interior (cutaway view)]]
[[File:Spacecolony3edit.jpeg|thumb|right|upright=1.3|Interior view of a large scale [[O'Neill cylinder]], showing alternating land and window stripes]]

A '''space settlement''' (also called a '''space habitat''', '''spacestead''', '''space city''' or '''space colony''') is a [[Human settlement|settlement]] in [[outer space]], sustaining more extensively [[Space habitat (facility)|habitation facilities in space]] than a general [[space station]] or [[spacecraft]]. Possibly including [[closed ecological system]]s, its particular purpose is permanent habitation.

No space settlement has been constructed yet, but many design concepts, with varying degrees of realism, have been introduced in science-fiction or proposed for actual realization.

Space settlements include '''orbital settlements''' (also called '''orbital habitat''', '''orbital stead''', '''orbital city''' or '''orbital colony''')<ref>{{Cite web |title=The Kalpana One Orbital Space Settlement Revised |url=http://alglobus.net/NASAwork/papers/2007KalpanaOne.pdf |archive-url=https://web.archive.org/web/20240416203813/http://alglobus.net/NASAwork/papers/2007KalpanaOne.pdf |archive-date=16 April 2024}}</ref> around the Earth or any other celestial body, as well as [[cycler]]s and [[interstellar ark]]s, as [[Generation ship|generation ships]] or ''world ships''.<ref name="p523">{{cite web | title=NSS Roadmap to Space Settlement Milestone 30: Development of Interstellar Travel and Settlement | website=NSS | date=2021-05-19 | url=https://nss.org/space-settlement-roadmap-30-interstellar-settlement/ | access-date=2024-08-07}}</ref><ref name="hein-pak-putz-revisited">{{cite journal |last1=Hein |first1=Andreas M. |last2=Pak |first2=Mikhail |last3=Pütz |first3=Daniel |last4=Bühler |first4=Christian |last5=Reiss |first5=Philipp |title=World ships—architectures & feasibility revisited |journal=Journal of the British Interplanetary Society |date=2012 |volume=65 |issue=4 |page=119|url=https://www.researchgate.net/publication/236177990 }}</ref>

Space settlements are a form of [[extraterrestrial settlement]]s, which more broadly includes habitats built on or within a body other than Earth, such as a settlement developed from a [[moonbase]], a [[Mars habitat]] or an asteroid.<ref name="g324"/>

==Definition==
A space settlement is any large-scale [[space habitat (facility)|habitation facility in outer space]], or more particularly in an orbit.

The [[International Astronautical Federation]] has differentiated space settlements to space habitats and space infrastructure the following way:
{{quote|
*''Habitat'': pressurized volume(s) within which humans live and work, including relevant facilities for life support.
*''Settlement'': group of permanently inhabited habitats installed near each other, possibly interconnected.
*''Infrastructure'': set of constructed elements supporting habitats and/or settlements such as (and not limited to): power plant, water plant, greenhouse and waste management facilities, communication facilities, transportation facilities, EVAs, roads, spaceport, research platforms, and so on.<ref name="Federation 2024 q644">{{cite web | last=Federation | first=International Astronautical | title=IAF: Space Habitats Committee | website=IAF | date=2024-02-08 | url=https://www.iafastro.org/about/iaf-committees/technical-committees/space-habitats-committee.html | access-date=2024-04-25}}</ref>}}

While not automatically constituting a colonial entity, a space settlement can be an element of a [[space colonization|space colony]]. The term "space colony" has been viewed critically, prompting [[Carl Sagan]] to propose the term ''space city.''<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}}</ref><ref name="Scharmen pp. 184–196">{{cite journal | last=Scharmen | first=Fred | title=Highest and Best Use: Subjectivity and Climates Off and After Earth | journal=Journal of Architectural Education | publisher=Informa UK Limited | volume=71 | issue=2 | date=Jul 3, 2017 | issn=1046-4883 | doi=10.1080/10464883.2017.1340775 | pages=184–196| s2cid=115502023 }}</ref>

==History==
{{Further|Space station#History}}
[[File:The Brick Moon from NASA archive.jpg |thumb |upright |"[[The Brick Moon]]" – an 1869 serial by [[Edward Everett Hale]] – was the first fictional space station or habitat. (Described by other sources as a station or habitat.)]]
The idea of space settlements either in fact or fiction goes back to the second half of the 19th century. "[[The Brick Moon]]", a fictional story written in 1869 by Edward Everett Hale, is perhaps the first treatment of this idea in writing.<ref name="b368">{{cite journal | last=Ceylan | first=Salih | title=Architectural evolution of space settlements in cinema and television | journal=Journal of Design for Resilience in Architecture and Planning | volume=3 | issue=(Special Issue) | date=December 30, 2022 | issn=2757-6329 | doi=10.47818/DRArch.2022.v3si072 | pages=66–78| doi-access=free }}</ref>

In 1903, space pioneer [[Konstantin Tsiolkovsky]] speculated about rotating cylindrical space settlements in ''Beyond Planet Earth''.<ref>K. Tsiolkovsky. ''Beyond Planet Earth.'' Trans. by Kenneth Syers. Oxford, 1960.</ref><ref>{{cite web | url=http://up-ship.com/blog/?p=6635 | title= Tsiolkovsky's Greenhouse | date= 21 July 2010 | website= up-ship.com}}</ref> In 1929 [[John Desmond Bernal]] speculated about giant space settlements. [[Dandridge M. Cole]] in the late 1950s and 1960s speculated about hollowing out asteroids and then rotating the to use as settlements in various magazine articles and books, notably ''Islands In Space: The Challenge Of The Planetoids''.<ref name="Cole">{{cite web| url=http://discoveryenterprise.wordpress.com/2007/08/08/islands-in-space-the-challenge-of-the-planetoids-the-pioneering-work-of-dandridge-m-cole/| title=Islands in Space: The Challenge of the Planetoids, the Pioneering Work of Dandridge M. Cole | author= Bonnici, Alex Michael | website= Discovery Enterprise | date= 8 August 2007 | access-date= 26 November 2014}}</ref>

=== O'Neill – The High Frontier ===
{{Main|O'Neill Cylinder}}
[[Image:Spacecolony1.jpg|thumb|right|A pair of [[O'Neill cylinder]]s]]
Around 1970, near the end of [[Project Apollo]] (1961–1972), [[Gerard K. O'Neill]], an experimental physicist at [[Princeton University]], was looking for a topic to tempt his physics students, most of them [[freshmen]] in engineering. He hit upon the idea of assigning them feasibility calculations for large space-settlements. To his surprise, the habitats seemed feasible even in very large sizes: cylinders {{convert|8|km|abbr=on|0}} in diameter and {{convert|32|km|abbr=on|0}} long, even if made from ordinary materials such as steel and glass. Also, the students solved problems such as radiation protection from cosmic rays (almost free in the larger sizes), getting naturalistic Sun angles, provision of power, realistic pest-free farming and orbital attitude control without reaction motors. O'Neill published an article about these colony concepts in ''[[Physics Today]]'' in 1974.<ref name=cos /> He expanded the article in his 1976 book ''[[The High Frontier: Human Colonies in Space]]''.

====NASA Ames/Stanford 1975 Summer Study====
[[File:Stanford Torus exterior.jpg|right|thumb|Stanford torus exterior]]
[[Image:Stanford torus-Space Settlements-A Design Study-1977.png|thumb|Collage of figures and tables of [[Stanford torus|Stanford Torus]] space habitat, from «Space Settlements: A Design Study» book. Charles Holbrow and Richard D. Johnson, NASA, 1977.]]

The result motivated [[NASA]] to sponsor a couple of summer workshops led by O'Neill.<ref>
{{cite report | url= http://www.nas.nasa.gov/About/Education/SpaceSettlement/75SummerStudy/Table_of_Contents1.html | archive-url= https://web.archive.org/web/20021119022659/http://www.nas.nasa.gov/About/Education/SpaceSettlement/75SummerStudy/Table_of_Contents1.html | archive-date= 2002-11-19 | title= Space Settlements: A Design Study | year= 1975 | publisher= NASA}}</ref><ref>{{cite report | url= http://settlement.arc.nasa.gov/spaceres/toc.html | archive-url= https://web.archive.org/web/20100528152209/http://settlement.arc.nasa.gov/spaceres/toc.html | archive-date= 2010-05-28 | title= Ames Summer Study on Space Settlements and Industrialization Using Nonterrestial Materials | year= 1977 | publisher= NASA}}</ref> Several concepts were studied, with sizes ranging from 1,000 to 10,000,000 people,<ref name="Pournelle, Jerrold E. 1977">{{cite book |last= Pournelle|first=Dr. Jerrold E. | title= A Step Farther Out | year= 1980 | isbn= 978-0-491-02941-4|url=https://www.goodreads.com/en/book/show/2362018|publisher=Ace Books}}</ref><ref>{{cite book |last= O'Neill|first=Dr. Gerard K.| title= The High Frontier: Human Colonies in Space |publisher= New York: William Morrow & Company | year= 1977| title-link= The High Frontier: Human Colonies in Space }}</ref><ref>{{cite report|author1=O'Neill, Gerard K.|author2=Reynolds, Ginie|title=Habitats in Space |jstor=24128636 }}</ref> including versions of the [[Stanford torus]]. Three concepts were presented to NASA: the [[Bernal sphere|Bernal Sphere]], the Toroidal Colony and the Cylindrical Colony.<ref>{{Cite news |url=https://edition.cnn.com/style/article/nasa-ames-oneill-space-colonies-1975/index.html |title=Space oddity: NASA's retro guide to future living |date=29 May 2016 |first=Thomas |last=Page |publisher=CNN}}</ref>

[[Image:External view of a Bernal sphere.jpg|thumb|Exterior of a 1970s Stanford adaptation of the Bernal sphere]]

O'Neill's concepts had an example of a payback scheme: construction of [[solar power satellite]]s from lunar materials. O'Neill did not emphasize the building of solar power satellites as such, but rather offered proof that orbital manufacturing from lunar materials could generate profits. He and other participants presumed that once such manufacturing facilities had started production, many profitable uses for them would be found, and the colony would become self-supporting and begin to build other colonies as well.

The concept studies generated a notable groundswell of public interest. One effect of this expansion was the founding of the [[L5 Society|L5&nbsp;Society]] in the&nbsp;U.S., a group of enthusiasts that desired to build and live in such colonies. The group was named after the space-colony orbit which was then believed to be the most profitable, a kidney-shaped orbit around either of Earth's lunar [[Lagrange point]]s 5 or&nbsp;4.

====Space Studies Institute====
In 1977 O'Neill founded the [[Space Studies Institute]], which initially funded and constructed some prototypes of the new hardware needed for a [[space colonization]] effort, as well as producing a number of feasibility studies. One of the early projects, for instance, involved a series of functional prototypes of a [[mass driver]], the essential technology for moving [[ore]]s efficiently from the Moon to space colony orbits.

==Motivation==
{{Also|Human presence in space#Purposes}}
There are a range of arguments for space settlements, including:
* As a base for [[human spaceflight|crewed]] [[space exploration]]
* Relieving Earth of industry and [[population pressure]]<ref name="f819">{{cite web | title=Jeff Bezos foresees a trillion people living in millions of space colonies. Here's what he's doing to get the ball rolling. | website=NBC News | date=2019-05-15 | url=https://www.nbcnews.com/mach/science/jeff-bezos-foresees-trillion-people-living-millions-space-colonies-here-ncna1006036 | access-date=2024-08-06}}</ref>
* Recreational habitation, either as visitors or residents at space (see [[space hotel]])
* Economic growth, developing access to resources in space and a [[space economy]], without destroying [[ecosystem]]s and displacing [[indigenous peoples|peoples]] on Earth
* [[Space colonization]], claiming extraterrestrial space for settler colonial independence
* [[Space and survival|For survival]] of human [[civilization]] and the [[biosphere]], in case of a disaster on the Earth (natural or man-made)<ref name=Doehring>{{cite web | author= Doehring, James| url=http://www.lifeboat.com/ex/space.habitats | title= Space Habitats | website= lifeboat.com | publisher= Lifeboat Foundation | access-date= 29 June 2011|display-authors=etal}}</ref>

==Advantages==
A number of arguments are made for space settlements having a number of advantages:

===Access to solar energy===
Space has an abundance of light produced from the Sun. In Earth orbit, this amounts to 1400 watts of power per square meter.<ref name="KoppLean11">{{cite journal |last=Kopp |first=G. |author2=Lean |first2=J. |year=2011 |title=A new, lower value of total solar irradiance: Evidence and climate significance |journal=Geophys. Res. Lett. |volume=38 |issue=1 |pages=L01706 |bibcode=2011GeoRL..38.1706K |doi=10.1029/2010GL045777 |doi-access=free}}</ref> This energy can be used to produce electricity from [[Photovoltaics|solar cells]] or [[heat engine]] based power stations, process ores, provide light for plants to grow and to warm space settlements.

===Outside gravity well===
Earth-to-space settlement trade would be easier than Earth-to-planetary habitat trade, as habitats orbiting Earth will not have a [[gravity well]] to overcome to export to Earth, and a smaller gravity well to overcome to import from Earth.

===In-situ resource utilization===
Space settlements may be supplied with resources from extraterrestrial places like [[Mars]], [[asteroid]]s, or the [[Moon]] ([[in-situ resource utilization]] [ISRU];<ref name=Doehring /> see [[Asteroid mining]]). One could produce breathing oxygen, drinking water, and rocket fuel with the help of ISRU.<ref name=Doehring /> It may become possible to manufacture solar panels from lunar materials.<ref name=Doehring />

===Asteroids and other small bodies===
Most asteroids have a mixture of materials, that could be mined, and because these bodies do not have substantial gravity wells, it would require low delta-V to [[Asteroid mining|draw materials from them]] and haul them to a construction site.<ref name="Pournelle, Jerrold E. 1977"/><!--there are issues of delta-V to access Main Belt asteroids, but for NEAs, it's less than a GEO-Luna-GEO or L5-Luna-L5... Sad to say, I don't have any of these 3 at hand...-->

There is estimated to be enough material in the main asteroid belt alone to build enough space settlements to equal the habitable surface area of 3,000 Earths.<ref>[https://web.archive.org/web/20100531200205/http://settlement.arc.nasa.gov/75SummerStudy/Chapt7.html#LIM "Limits to Growth"], Chapter 7, ''Space Settlements: A Design Study''. NASA, 1975.</ref>

===Population===
A 1974 estimate assumed that collection of all the material in the main [[asteroid belt]] would allow habitats to be constructed to give an immense total population capacity. Using the free-floating resources of the Solar System, this estimate extended into the trillions.<ref name=cos>{{cite journal | author= O'Neill, Gerard K. | title= The Colonization of Space | journal= Physics Today | volume= 27 | issue= 9 | pages= 32–40 | date= September 1974 | url= http://www.nss.org/settlement/physicstoday.htm | bibcode= 1974PhT....27i..32O | doi= 10.1063/1.3128863| doi-access= free }}</ref>

===Zero g recreation===
If a large area at the rotation axis is enclosed, various zero-g sports are possible, including swimming,<ref>{{cite conference | conference= Space 98: Sixth International Conference and Exposition on Engineering, Construction, and Operations in Space | location= Albuquerque, New Mexico | url= http://www.spacefuture.com/archive/artificial_gravity_swimming_pool.shtml | title= Artificial-Gravity Swimming-Pool | last1= Collins | first1= Patrick |display-authors=etal}} April 26–30, 1998.</ref><ref name="Kalpana" /> [[hang gliding]]<ref>{{cite web |author=Heppenheimer |first=T. A. |date=1977 |title=Colonies in Space, Chapter 11: What's to Do on Saturday Night? |url=http://www.nss.org/settlement/ColoniesInSpace/colonies_chap11.html |access-date=30 January 2012}}</ref> and the use of [[human-powered aircraft]].

===Passenger compartment===
{{See|Space and survival}}
A space settlement can be the passenger compartment of a large spacecraft for colonizing [[asteroid]]s, moons, and planets. It can also function as one for a [[generation ship]] for travel to other planets or distant stars (L. R. Shepherd described a generation starship in 1952 comparing it to a small planet with many people living in it.)<ref>{{cite journal | last= Shepherd | first= L. R. | title= Interstellar Flight | periodical= Journal of the British Interplanetary Society | volume= 11 | date= July 1952 | pages= 149–167}}</ref><ref>{{cite web | title= Les Shepherd, RIP | author= Gilster, Paul | date= 28 February 2012 | website= centauri-dreams.org | url= http://www.centauri-dreams.org/?p=21895 | access-date= 1 January 2015}}</ref>

==Requirements==
[[File:Stanford torus configuration.gif|right|thumb|Configuration of a Stanford torus]]

The requirements for a space settlement are many. They would have to provide all the material needs for hundreds or thousands of humans, in an environment out in space that is very hostile to human life.<ref>{{cite journal |last1=Chen |first1=Muhao |last2=Goyal |first2=Raman |last3=Majji |first3=Manoranjan |last4=Skelton |first4=Robert E. |title=Review of space habitat designs for long term space explorations |journal=[[Progress in Aerospace Sciences]] |date=2021 |volume=122 |article-number=100692 |doi=10.1016/j.paerosci.2020.100692|doi-access=free }}</ref>

===Regulation===
The governance or regulation of space settlements is crucial for responsible habitation conditions. The physical as well as socio-political architecture of a space settlement, if poorly established, can lead to tyrannical and precarious conditions.<ref name="g324">{{cite journal | last=Cockell | first=C. S. | title=Essay on the Causes and Consequences of Extraterrestrial Tyranny | journal=Journal of the British Interplanetary Society | volume=63 | date=2010 | issn=0007-084X | pages=15–37 | url=https://ui.adsabs.harvard.edu/abs/2010JBIS...63...15C/abstract | access-date=2024-08-07}}</ref>

===Initial capital outlay===
Even the smallest of the settlement designs mentioned below are more massive than the total mass of all items that humans have ever launched into Earth orbit combined.{{Citation needed|date=February 2011}} Prerequisites to building settlements are either cheaper launch costs or a mining and manufacturing base on the Moon or other body having low [[delta-v]] from the desired habitat location.<ref name="Pournelle, Jerrold E. 1977"/><!--Sad to say, I don't have these at hand...but it's in there.-->

===Location===
[[File:Figure4.13, Baseline transportation system, Space Settlements, A Design Study.NASA.gif|thumb|A 1970s NASA concept for routs and locating a [[Stanford torus]] in [[cis-lunar space]]]] 
The optimal settlement orbits are still debated, and so [[orbital stationkeeping]] is probably a commercial issue. The lunar {{L4}} and {{L5}} orbits are now thought to be too far away from the Moon and Earth. A more modern proposal is to use a two-to-one resonance orbit that alternately has a close, low-energy (cheap) approach to the Moon, and then to the Earth.{{Citation needed|date=June 2018}} This provides quick, inexpensive access to both raw materials and the major market. Most settlement designs plan to use [[tether propulsion|electromagnetic tether propulsion]], or [[mass driver]]s used instead of rocket motors. The advantage of these is that they either use no reaction mass at all, or use cheap reaction mass.{{Citation needed|date=February 2011}}

===Protection from radiation===
If a space settlement is located at {{L4}} or {{L5}}, then its orbit will take it outside of the protection of the Earth's [[magnetosphere]] for approximately two-thirds of the time (as happens with the Moon), putting residents at risk of [[Proton#Human exposure|proton exposure]] from the [[solar wind]] (see ''[[Health threat from cosmic rays]]'').

Protection can be attained through passive or active shielding.<ref name="h447">{{cite web | title=Radiation Shielding Techniques for Human Spaceflight | website=Professor Robert B. Laughlin, Department of Physics, Stanford University | date=2015-07-17 | url=http://large.stanford.edu/courses/2015/ph241/clark1/ | ref={{sfnref | Professor Robert B. Laughlin, Department of Physics, Stanford University | 2015}} | access-date=2024-08-08}}</ref> Passive shielding through the use of materials has been the method to shield current spacecrafts.

Water walls or ice walls can provide protection from solar and cosmic radiation, as 7 cm of water depth blocks approximately half of incident radiation.<ref>{{cite report|title=Water Walls Architecture: Massively Redundant andn Highly Reliable Life Support for Long Duration Exploration Missions|url=https://ntrs.nasa.gov/api/citations/20190001191/downloads/20190001191.pdf|access-date=November 13, 2022|publisher=NASA}}</ref> Alternatively, rock could be used as shielding; 4 metric tons per square meter of surface area could reduce radiation dosage to several mSv or less annually, below the rate of some populated [[background radiation|high natural background areas]] on Earth.<ref>[https://web.archive.org/web/20100531210412/http://settlement.arc.nasa.gov/75SummerStudy/5appendE.html "Mass Shielding"], Appendix E, ''Space Settlements: A Design Study''. NASA (SP-413), 1975.</ref>

Alternative concepts based on active shielding are untested yet and more complex than such passive mass shielding, but usage of magnetic and/or electric fields, like through spacecraft encapsulating wires,<ref name="z986">{{cite web | last=Williams | first=Matt | title=Plans for a modular Martian base that would provide its own radiation shielding | website=Phys.org | date=2018-10-17 | url=https://phys.org/news/2018-10-modular-martian-base-shielding.html | access-date=2024-08-08}}</ref> to deflect particles could potentially greatly reduce mass requirements.<ref name = spacecraftshielding>{{cite web | url= http://engineering.dartmouth.edu/~simon_g_shepherd/research/Shielding/ | title= Spacecraft Shielding | author= Shepherd, Simon George | website= dartmouth.edu | publisher= Thayer School of Engineering, Dartmouth College | access-date= 3 May 2011}}</ref>

===Atmosphere===
[[File:Cupola above the darkened Earth.jpg|thumb|The [[airglow]] above the horizon at the atmospheric and orbital [[Outer space#Boundary|boundary to space]], captured from the [[International Space Station|ISS]]]]
Air [[pressure]], with normal partial pressures of [[oxygen]] (21%), [[carbon dioxide]] and [[nitrogen]] (78%), is a basic requirement of any space settlement. Basically, most space settlement designs concepts envision large, thin-walled pressure vessels. The required oxygen could be obtained from lunar rock. Nitrogen is most easily available from the Earth, but is also recycled nearly perfectly. Also, nitrogen in the form of ammonia ([[ammonia|{{chem|NH|3}}]]) may be obtainable from comets and the moons of outer planets. Nitrogen may also be available in unknown quantities on certain other bodies in the [[outer Solar System]]. The air of a habitat could be recycled in a number of ways. One concept is to use [[photosynthesis|photosynthetic]] [[gardening|garden]]s, possibly via [[hydroponics]], or [[forest gardening]].{{Citation needed|date=November 2009}} However, these do not remove certain industrial pollutants, such as volatile oils, and excess simple molecular gases. The standard method used on [[nuclear submarines]], a similar form of closed environment, is to use a [[catalytic]] burner, which effectively decomposes most organics. Further protection might be provided by a small cryogenic distillation system which would gradually remove impurities such as [[mercury (element)|mercury]] vapor, and noble gases that cannot be catalytically burned.{{Citation needed|date=November 2009}}

===Food production===
[[Organic chemistry|Organic]] materials for food production would also need to be provided. At first, most of these would have to be imported from Earth.{{cn|date=January 2018}} After that, feces recycling should reduce the need for imports.{{cn|date=January 2018}} One proposed recycling method would start by burning the cryogenic distillate, plants, garbage and sewage with air in an electric arc, and distilling the result.{{Citation needed|date=November 2009}} The resulting carbon dioxide and water would be immediately usable in agriculture. The nitrates and salts in the ash could be dissolved in water and separated into pure minerals. Most of the nitrates, potassium and sodium salts would recycle as fertilizers. Other minerals containing iron, nickel, and silicon could be chemically purified in batches and reused industrially. The small fraction of remaining materials, well below 0.01% by weight, could be processed into pure elements with zero-gravity [[mass spectrometry]], and added in appropriate amounts to the fertilizers and industrial stocks. It is likely that methods would be greatly refined as people began to actually live in space settlements.

===Artificial gravity===
{{Main|Artificial gravity}}
{{unreferenced section|date=February 2011}}
Long-term on-orbit studies have proven that zero gravity weakens bones and muscles, and upsets [[calcium metabolism]] and [[immune systems]]. Most people have a continual stuffy nose or sinus problems, and a few people have dramatic, incurable motion sickness. Most habitat designs would rotate in order to use [[inertia]]l forces to [[Artificial gravity|simulate gravity]]. NASA studies with chickens and plants have proven that this is an effective physiological substitute for gravity.{{Citation needed|date=November 2009}} Turning one's head rapidly in such an environment causes a "tilt" to be sensed as one's inner ears move at different rotational rates. [[Centrifuge]] studies show that people get motion-sick in habitats with a rotational radius of less than 100 metres, or with a rotation rate above 3 rotations per minute. However, the same studies and statistical inference indicate that almost all people should be able to live comfortably in habitats with a rotational radius larger than 500 meters and below 1 RPM. Experienced persons were not merely more resistant to motion sickness, but could also use the effect to determine "spinward" and "antispinward" directions in the centrifuges.{{Citation needed|date=November 2009}}

===Meteoroids and dust===
The habitat would need to withstand potential impacts from [[space debris]], [[meteoroid]]s, dust,&nbsp;etc. Most meteoroids that strike the earth vaporize in the atmosphere. Without a thick protective atmosphere meteoroid strikes would pose a much greater risk to a space settlement. [[Radar]] will sweep the space around each habitat mapping the trajectory of debris and other man-made objects and allowing corrective actions to be taken to protect the habitat.{{citation needed|date=September 2012}}<!-- on what basis is this claim made? "will sweep ..." and "allowing corrective action...". Even in low-Earth orbit, these orbital speeds are thousands of meters per second, and there is no source to show that large habitats might easily avoid them with radar. -->

In some designs (O'Neill/NASA Ames "Stanford Torus" and "Crystal palace in a Hatbox" habitat designs have a non-rotating cosmic ray shield of packed sand (~1.9 m thick) or even artificial aggregate rock (1.7 m ersatz concrete). Other proposals use the rock as structure and integral shielding (O'Neill, "the High Frontier". Sheppard, "Concrete Space Colonies"; Spaceflight, journal of the B.I.S.). In any of these cases, strong meteoroid protection is implied by the external radiation shell ~4.5 tonnes of rock material, per square meter.<ref>{{cite web| url=http://www.quadibloc.com/science/spaint.htm | title=A Space Habitat Design | website=quadibloc.com | date= | access-date= 8 February 2021 }}</ref>

Note that Solar Power Satellites are proposed in the multi-GW ranges, and such energies and technologies would allow constant radar mapping of nearby 3D space out-to arbitrarily far away, limited only by effort expended to do so.

Proposals are available to move even kilometer-sized NEOs to high Earth orbits, and reaction engines for such purposes would move a space settlement and any arbitrarily large shield, but not in any timely or rapid manner, the thrust being very low compared to the huge mass.

===Heat rejection===
The habitat is in a vacuum, and therefore resembles a giant thermos bottle. Habitats also need a [[radiator]] to eliminate heat from absorbed sunlight. Very small habitats might have a central vane that rotates with the habitat. In this design, [[convection]] would raise hot air "up" (toward the center), and cool air would fall down into the outer habitat. Some other designs would distribute coolants, such as chilled water from a central radiator.

===Attitude control===
Most mirror geometries require something on the habitat to be aimed at the Sun and so [[Spacecraft attitude control|attitude control]] is necessary. The original O'Neill design used the two cylinders as [[momentum wheel]]s to roll the colony, and pushed the sunward pivots together or apart to use [[precession]] to change their angle.

=== Interior design ===
The interior of a space settlement should always have areas out of sight, to avoid the psychological effect of all reality being visible simultaneously, while also allowing for landscapes and wide vistas, so there is no sensation of living in a theater stage-like situation. Because of psychological reasons, the design should also avoid the perception that everything is human-controlled (for example, by having random artificial weather, or vegetation developing in a natural way).<ref>{{Cite web |url=https://nss.org/settlement/nasa/75SummerStudy/3appendA.html |access-date=2025-06-10 |website=nss.org |title=Space Settlements: A Design Study, chapter 3, appendix A}}</ref>

==Concepts==
===Base concepts===
The two common original concepts are the [[Bernal sphere]] and the [[O'Neill cylinder]].

====Dumbbell-shape assembly concept====
[[File:Curreri space habitat.png|thumb|A dumbbell-shaped self-sufficient and self-reproducible habitat for 10 persons]]
[[File:Concepts from 1975 NASA Summer Study at Stanford.png|thumb|Various concepts merging into a cylindrical station]]

A [[dumbbell]]-like spacecraft or habitat, connected by a cable to a [[counterweight]] or other habitat. This design has been proposed as a Mars ship, initial construction shack for a space habitat, and [[transhab|orbital hotel]]. It has a comfortably long and slow rotational radius for a relatively small station mass. Also, if some of the equipment can form the counter-weight, the equipment dedicated to artificial gravity is just a cable, and thus has a much smaller mass-fraction than in other concepts. For a long-term habitation, however, radiation shielding must rotate with the habitat, and is extremely heavy, thus requiring a much stronger and heavier cable.<ref name="minimized">{{cite conference |last= Curreri |first= Peter A. |title= A Minimized Technological Approach towards Human Self Sufficiency off Earth |conference= Space Technology and Applications International Forum (STAIF) Conference |location= Albuquerque, NM |url= https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070032685_2007018823.pdf |archive-url=http://web.archive.org/web/20110606010920/http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070032685_2007018823.pdf |archive-date=2011-06-06}} 11–15 February 2007. Retrieved 18 December 2010</ref> This speculative design was also considered by the NASA studies.<ref>{{Cite web |url=https://settlement.arc.nasa.gov/75SummerStudy/Chapt4.html |title=Space Settlements: A Design Study -- Chapter 4: Choosing Among Alternatives |archive-url=https://web.archive.org/web/20091103221336/https://settlement.arc.nasa.gov/75SummerStudy/Chapt4.html |archive-date=2009-11-03}}</ref> Small habitats would be mass-produced to standards that allow the habitats to interconnect. A single habitat can operate alone as a [[Bolas|bola]]. However, further habitats can be attached, to grow into a "[[dumbbell]]" then a "bow-tie", then a ring, then a cylinder of "beads", and finally a framed array of cylinders. Each stage of growth shares more radiation shielding and capital equipment, increasing redundancy and safety while reducing the cost per person. This concept was originally proposed by a professional architect because it can grow much like Earth-bound cities, with incremental individual investments, unlike those that require large start-up investments. The main disadvantage is that the smaller versions use a large structure to support the radiation shielding, which rotates with them. In large sizes, the shielding becomes economical, because it grows roughly as the square of the colony radius. The number of people, their habitats, and the radiators to cool them grow roughly as the cube of the colony radius.

===Further concepts===
[[File:Bernal sphere interior.jpg|thumb|Interior of a Bernal sphere]]
* [[Bernal sphere#Island One|Island One]], a Bernal sphere settlement for about 10,000–20,000 people.
* [[Stanford torus]]: an alternative to Island One.
* Lewis One,<ref>{{cite web| url=http://alglobus.net/NASAwork/papers/RNR-91-018/RNR-91-018.html| title=Lewis One Space Colony| first=Al| last=Globus| access-date=2006-05-28}}</ref> a cylinder of radius 250&nbsp;m with a non-rotating radiation shielding. The shielding protects the micro-gravity industrial space, too. The rotating part is 450m long and has several inner cylinders. Some of them are used for agriculture.
* Island Three or [[O'Neill cylinder]], an even larger  cylindrical design (3.2<ref>{{Cite web |date=2017-08-03 |title=O'Neill Cylinder Space Settlement |url=https://nss.org/o-neill-cylinder-space-settlement/ |access-date=2025-01-09 |website=NSS |language=en-US}}</ref> or 4<ref>{{Cite web |date=2014-10-02 |title=How We Could Actually Build a Space Colony |url=https://www.popularmechanics.com/space/deep-space/a11351/how-we-could-actually-build-a-space-colony-17268252/ |access-date=2025-01-09 |website=Popular Mechanics |language=en-US}}</ref> km radius and 32 km long).
*[[McKendree cylinder]], another concept that would use carbon nanotubes, a McKendree cylinder is paired cylinders in the same vein as the Island Three concept, but each 460 km in radius and 4600 km long (versus 3.2-4 km radius and 32 km long in the Island Three).<ref>{{cite conference | title= Implications of Molecular Nanotechnology Technical Performance Parameters on Previously Defined Space System Architectures | conference= The Fourth Foresight Conference on Molecular Nanotechnology | first= Thomas Lawrence | last= McKendree | location= Palo Alto, California, USA | url= http://www.zyvex.com/nanotech/nano4/mckendreePaper.html#RTFToC17}} 9–11 November 1995.</ref>
* Kalpana One, revised,<ref name="Kalpana">{{cite web| url=http://alglobus.net/NASAwork/papers/2007KalpanaOne.pdf|title=The Kalpana One Orbital Space Settlement Revised|first=Al|last=Globus|access-date=2009-08-29}}</ref> a short cylinder with 250 m radius and 325 m length. The radiation shielding is 10 t/m<sup>2</sup> and rotates. It has several inner cylinders for agriculture and recreation. It is sized for 3,000 residents.<ref>{{Cite web |url=https://settlement.arc.nasa.gov/Kalpana/KalpanaOne.html |title=Kalpana One Space Settlement |archive-url=https://web.archive.org/web/20130215204552/https://settlement.arc.nasa.gov/Kalpana/KalpanaOne.html |archive-date=2013-02-15}}</ref>
[[File:Kalpana One space station.png|thumb|Kalpana One concept]]
*Bubbleworld or Inside/Outside concept, originated by [[Dandridge MacFarlan Cole|Dandridge M. Cole]] in 1964,<ref name="Cole" /> calls for drilling a tunnel through the longest axis of a large metallic asteroid and filling it with a [[Volatility (chemistry)|volatile]] substance, possibly water. A very large solar reflector would be constructed nearby, focusing solar heat onto the asteroid, first to weld and seal the tunnel ends, then more diffusely to slowly heat the entire outer surface. As the metal softens, the water inside expands and inflates the mass, while rotational forces help shape it into a cylindrical form. Once expanded and allowed to cool, it can be spun to produce centrifugal pseudogravity, and the interior filled with soil, air and water. By creating a slight bulge in the middle of the cylinder, a ring-shaped lake can be made to form. Reflectors would allow sunlight to enter and to be directed where needed. This method would require a significant human and industrial presence in space to be at all feasible. The concept was popularized by [[science fiction]] author [[Larry Niven]] in his [[Known Space]] stories, describing such worlds as the primary habitats of the [[Belter (Niven)|Belters]], a civilization who had [[Colonization of the asteroids|colonized the asteroid belt]].
**"Bubbleworld" is also the name of a different concept of space settlement thought of by Dani Eder in 1995<ref>{{Cite web |title=Bubbleworld (Dani Eder) |url=https://yarchive.net/space/exotic/bubbleworld.html |access-date=2024-01-09 |website=yarchive.net}}</ref> (it is alternatively known as an Ederworld<ref>{{Cite web |title=Ederworlds |url=http://www.orionsarm.com/eg-article/48472f9d56859 |access-date=2024-01-09 |website=Orion's Arm - Encyclopedia Galactica}}</ref>). This is a relatively thin, spherical shell surrounding a mass of gas great enough to be held together by gravity. If hydrogen is used as the gas, the shell would have a radius of about 240,000 km. The outside of the shell would have a living space 2,400 km thick (filled with breathable air) with an additional outer shell (possibly made of 500 m of steel) above it to hold in the air.
* [[Terrarium (space habitat)|Asteroid terrarium]], a similar idea to the bubble world, in the 2012 novel ''[[2312 (novel)|2312]]'' by [[hard science fiction]] writer [[Kim Stanley Robinson]].
*[[Bishop Ring (habitat)|Bishop Ring]], a speculative design using [[carbon nanotube]]s: a torus 1000&nbsp;km in radius, 500&nbsp;km in width, and with atmosphere retention walls 200&nbsp;km in height. The habitat would be large enough that it could be "roofless", open to outer space on the inner rim.<ref>{{cite web | url= http://www.iase.cc/openair.htm | title= Open Air Space Habitats | first= Forrest | last= Bishop | website= iase.cc | publisher= Institute of Atomic-Scale Engineering | year= 1997}}</ref>
[[File:Orbitale.jpg|thumb|Artist's impression of a [[Bishop Ring (habitat)|Bishop Ring]]]]

==Space station projects==
Space settlements are in principle space stations, developments in space station construction therefore share many elements. 
The following projects and proposals, while not truly space settlements, incorporate aspects of what they would have and may represent stepping stones towards eventually building of space settlements.
[[File:Gateway and Orion in lunar orbit (5).jpg|thumb|left|Concept art of the [[Lunar Gateway]]]]
The [[Lunar Gateway]] is a planned lunar space station, the first outside of [[Low Earth Orbit]], therefore being the first spacecraft designed in unshielded space.

The [[International Space Station|ISS]] [[Nautilus-X#ISS centrifuge demonstration|Centrifuge Demo]] was proposed in 2011 as a demonstration project for an [[artificial gravity]] compartment, preparatory for a similar module of a [[Nautilus-X]] Multi-Mission Space Exploration Vehicle (MMSEV). The ISS module would have an outside diameter of {{convert|30|ft}} with a {{convert|30|in}} ring interior cross-section diameter and would provide 0.08 to {{nowrap|0.51g}} partial gravity. This test and evaluation centrifuge would have the capability to become a Sleep Module for ISS crew. The subsequent vehicle design would be a long-duration crewed space transport vehicle including the artificial gravity compartment intended to promote crew-health for a crew of up to six persons on missions of up to two years duration. The [[gravity|partial-g]] [[torus|torus-ring]] [[centrifuge]] would utilize both standard metal-frame and [[Inflatable space habitat|inflatable]] spacecraft structures and would provide 0.11 to {{nowrap|0.69[[Standard gravity|g]]}} if built with the {{convert|40|ft}} diameter option.

The [[Bigelow Commercial Space Station]] was announced in mid-2010. Bigelow has publicly shown space station design configurations with up to nine modules containing {{convert|100000|cuft|abbr=on}} of habitable space. Bigelow began to publicly refer to the initial configuration as "Space Complex Alpha" in October 2010.

==In fiction==
{{Also|Space stations in fiction}}
Space settlements have been elements of different science-fiction stories, across different media, from books to movies like [[Elysium (film)|Elysium]] (2013) for a wheel shaped [[Stanford torus]] type and [[Interstellar (film)|Interstellar]] (2014) for a [[O'Neill cylinder|cylindrical O'Neill type]].<ref name="b368"/>

==See also==
{{commons category|Space habitats}}
* [[Arcology]]
* [[Bioastronautics]]
* [[Closed ecological system]]
* [[Domed city]]
* [[Dyson sphere]]
* [[Floating cities and islands in fiction]]
* [[Human outpost]] (artificially created controlled human habitat)
* [[Locomotion in space]]
* [[Megastructure]]
* [[Planetary chauvinism]]
* {{annotated link|Research station}}
* [[Space architecture]]
* {{annotated link|Space observatory}}
* [[Space stations and habitats in fiction]]
* [[Spaceflight]]
* [[Space station]]
* [[Spome]]
* [[Underground living]]
* [[Underground city]]
* [[Underwater habitat]]

==Notes==
{{Reflist|30em}}

==References==
{{Refbegin}}
*[https://web.archive.org/web/20021027010824/http://www.nas.nasa.gov/About/Education/SpaceSettlement/ NASA's table of contents for the studies] See the "online books" about halfway down the page.
{{Refend}}

==External links==
*[https://commons.wikimedia.org/wiki/Space_habitats Gallery about space habitats], in [[Wikimedia Commons]].
*[http://lifeboat.com/ex/space.habitats Lifeboat Foundation Space Habitats], a space habitat advocacy group.
*[https://upload.wikimedia.org/wikipedia/commons/f/ff/Space_Settlements_-_A_Design_Study_%281977%29.pdf ''Space Settlements: A Design Study''], 1977 book by NASA about designing a space settlement
*{{Cite web |first=Paul |last=Lucas |date=21 February 2005 |url=http://www.strangehorizons.com/2005/20050221/homesteading-a.shtml |archive-url=https://web.archive.org/web/20061114035834/http://www.strangehorizons.com/2005/20050221/homesteading-a.shtml |archive-date=2006-11-14 |title=Homesteading the High Frontier: The Shape of Space Stations to Come |work=Strange Horizons}}
*{{Cite news |url=https://www.npr.org/blogs/13.7/2011/05/01/135895195/visions-of-the-high-frontier-space-colonies-of-1970 |title=Visions Of The High Frontier: Space Colonies of 1970 |date=1 May 2011 |first=Adam |last=Frank |work=NPR}}
*[https://www.youtube.com/watch?v=EgrdAUFFMrA NASA video about space habitats and space settlements construction as seen around 1970"s (5 min)].
* [https://www.youtube.com/watch?v=86JAU3w9mB8 Video explaining rotating space habitats].
* [https://vimeo.com/306453241 Opening the High Frontier], a video about affordable spaceflight and building a spacefaring civilization.
*[https://youtube.com/watch?v=DM88sUBTTRM The 1975 space habitat video credited with inspiring Blue Origin (Jeff "Amazon" Bezos as a boy).]
*[https://www.ria.edu/Segits Segits.com], a website that refers to Space habitats as Segits or Self-sufficient Extra-terrestrial Green-habitat Intentional Transparent self-replicating communities.

{{Space stations}}
{{Spaceflight}}
{{Space colonization}}

{{DEFAULTSORT:Space Habitat}}
[[Category:Space habitats| ]]
[[Category:Human habitats]]
[[Category:Space farming]]