Old page wikitext, before the edit (old_wikitext) | '{{refimprove|date=January 2021}}
{{short description|Type of space station, intended as a permanent settlement}}
{{Distinguish|Space habitat (facility)|Space station|Space colonization}}
[[Image:Spacecolony1.jpg|thumb|right|A pair of [[O'Neill cylinder]]s]]
[[File:Spacecolony3edit.jpeg|thumb|right|Interior view of an O'Neill cylinder, showing alternating land and window stripes]]
A '''space habitat''' (also called a '''space settlement''', '''space colony''', '''spacestead''', '''space city''', '''orbital habitat''', '''orbital settlement''', '''orbital colony''', '''orbital stead''' or '''orbital city''') is a more advanced form of living quarters than a [[space station]] or [[space habitat (facility)|habitation module]], in that it is intended as a permanent settlement or green habitat rather than as a simple way-station or other specialized facility. No space habitat has been constructed yet, but many design concepts, with varying degrees of realism, have come both from engineers and from science-fiction authors.
The term ''space habitat'' sometimes includes more broadly habitats built on or in a body other than Earth—such as the Moon, [[Mars habitat|Mars]] or an asteroid. This article concentrates on self-contained structures envisaged for [[micro-g environment]]s.
==Definition==
A space habitat, or more precisely a space settlement, is any large-scale [[space habitat (facility)|habitation facility in space]], or more particularly in [[outer space]] or an orbit. A space habitat is typically designed to rotate so as to prevent long-term exposure of its residents to the peril of weightlessness or microgravity; studies have shown rotation to be a healthy substitute for gravity.
While not automatically constituting a colonial entity, a space habitat 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==
The idea of space habitats 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. In 1903, space pioneer [[Konstantin Tsiolkovsky]] speculated about rotating cylindrical space habitats, with plants fed by the sun, 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 the 1920s [[John Desmond Bernal]] and others speculated about giant space habitats. [[Dandridge M. Cole]] in the late 1950s and 1960s speculated about hollowing out asteroids and then rotating them 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>
==Motivation==
{{Also|Human presence in space#Purposes|Space colonization#Reasons|Space and survival}}
[[File:Stanford Torus interior.jpg|right|thumb|A [[Stanford torus]] interior]]
[[File:Stanford Torus exterior.jpg|right|thumb|Stanford torus exterior]]
There are a range of reasons for space habitats. Beside [[human spaceflight]] supported [[space exploration]] and [[space colonization]], reasons for space habitats include:
* 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>
* Huge resources in space for expansion of human society
* Expansion without any [[ecosystem]]s to destroy or [[indigenous peoples]] to displace
* It could help the Earth by relieving [[population pressure]] and taking industry off-Earth.
==Advantages==
A number of arguments are made for space habitats 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=G. Kopp|author2=J. Lean |title=A new, lower value of total solar irradiance: Evidence and climate significance|journal=Geophys. Res. Lett.|volume=38 |issue=1 |year=2011|pages=L01706|doi=10.1029/2010GL045777|bibcode = 2011GeoRL..38.1706K |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 habitats.
===Outside gravity well===
Earth-to-space habitat 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 habitats 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 habitats 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 | url=http://www.nss.org/settlement/ColoniesInSpace/colonies_chap11.html | title=Colonies in Space, Chapter 11: What's to Do on Saturday Night ? |date=1977 | access-date=30 January 2012 | author=T. A. Heppenheimer}}</ref> and the use of [[human-powered aircraft]].
===Passenger compartment===
{{See|Space and survival}}
A space habitat 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:Cupola above the darkened Earth.jpg|thumb|400px|The [[airglow]] above the horizon, captured from the [[International Space Station|ISS]]]]
The requirements for a space habitat 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.
===Atmosphere===
Air [[pressure]], with normal partial pressures of [[oxygen]] (21%), [[carbon dioxide]] and [[nitrogen]] (78%), is a basic requirement of any space habitat. Basically, most space habitat 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 habitats.
===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}}
===Protection from radiation===
[[File:Mars Ice Home concept.jpg|thumb|300px|Langley's Mars Ice Dome design from 2016 for a Mars base uses frozen water to enhance protection.]]
If a space habitat is located at [[Lagrangian point#L4 and L5|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]]''). 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/enwiki/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 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>
===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.
===Meteoroids and dust===
The habitat would need to withstand potential impacts from [[space debris]], [[meteoroid]]s, dust, 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 habitat. [[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 habitat and any arbitrarily large shield, but not in any timely or rapid manner, the thrust being very low compared to the huge mass.
===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.
==Considerations==
===Initial capital outlay===
Even the smallest of the habitat 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 habitats 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===
The optimal habitat 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 habitat 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}}
==Conceptual studies==
[[File:Noordung space station.jpg|thumb|Description of a rotating wheel space station in [[Hermann Noordung]]'s ''The Problem of Space Travel'' (1929)]]
===O'Neill - The High Frontier===
{{Main|O'Neill Cylinder}}
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-habitats. 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 /> (See the above illustration of such a colony, a classic "O'Neill Colony"). He expanded the article in his 1976 book ''[[The High Frontier: Human Colonies in Space]]''.
====NASA Ames/Stanford 1975 Summer Study====
The result motivated [[NASA]] to sponsor a couple of summer workshops led by O'Neill.<ref>
{{citation | 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 | url-status= dead | archive-date= 2002-11-19 | title= Space Settlements: A Design Study | year= 1975 | publisher= NASA}}</ref><ref>{{citation | 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 | url-status= dead | 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= 978-0491029414|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|website=jstor.org|jstor=24128636 |access-date=April 22, 2023|url=http://www.jstor.org/stable/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=http://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 |work=CNN}}</ref>
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 Society]] in the 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 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.
===NASA concepts===
Some NASA concept studies included:
* [[Bernal sphere#Island One|Island One]], a Bernal sphere habitat for about 10,000–20,000 people.
* [[Stanford torus]]: an alternative to Island One.
* [[O'Neill cylinder]]: "Island Three", an even larger design (3.2 km radius and 32 km long).
* 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 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.
* 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 |url-status=dead |archive-url=https://web.archive.org/web/20130215204552/https://settlement.arc.nasa.gov/Kalpana/KalpanaOne.html |archive-date=2013-02-15}}</ref>
* A bola: a 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" />
* Beaded habitats:<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}} 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 |url-status=dead |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 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.
===Other concepts===
*Bubbleworld: The Bubbleworld or Inside/Outside concept was originated by [[Dandridge MacFarlan Cole|Dandridge M. Cole]] in 1964.<ref name="Cole" /> The concept calls for drilling a tunnel through the longest axis of a large asteroid of iron or nickel-iron composition 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 artificial gravity by centrifugation, 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]].
* [[Terrarium (space habitat)|Asteroid terrarium]]: a similar idea to the bubble world, the asteroid terrarium, appears in the 2012 novel ''[[2312 (novel)|2312]]'', authored by [[hard science fiction]] writer [[Kim Stanley Robinson]].
*[[Bishop Ring (habitat)|Bishop Ring]]: a speculative design using [[carbon nanotube]]s, a Bishop Ring is a torus 1000 km in radius, 500 km in width, and with atmosphere retention walls 200 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>
*[[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 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>
==Gallery==
<gallery>
File:Curreri space habitat.png|Bola space station
File:Nasa mars artificial gravity 1989.jpg|Bola Mars spacecraft
Kalpana One space station.png|Kalpana One Orbital space station
File:Concepts from 1975 NASA Summer Study at Stanford.png|Various concepts
</gallery>
==Current projects==
The following projects and proposals, while not truly space habitats, incorporate aspects of what they would have and may represent stepping stones towards eventually building of space habitats.
The [[Nautilus-X]] Multi-Mission Space Exploration Vehicle (MMSEV): this 2011 NASA proposal for a long-duration crewed space transport vehicle included an [[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 [[International Space Station|ISS]] [[Nautilus-X#ISS centrifuge demonstration|Centrifuge Demo]], also proposed in 2011 as a demonstration project preparatory to the final design of the larger torus centrifuge space habitat for the Multi-Mission Space Exploration Vehicle. The structure 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 [[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.
==See also==
{{commons category|Space habitats}}
* [[Bioastronautics]]
* [[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==
*[http://lifeboat.com/ex/space.habitats Lifeboat Foundation Space Habitats], a space habitat advocacy group.
*{{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]]' |
New page wikitext, after the edit (new_wikitext) | '{{refimprove|date=January 2021}}
{{short description|Type of space station, intended as a permanent settlement}}
{{Distinguish|Space habitat (facility)|Space station|Space colonization}}
[[Image:Spacecolony1.jpg|thumb|right|A pair of [[O'Neill cylinder]]s]]
[[File:Spacecolony3edit.jpeg|thumb|right|Interior view of an O'Neill cylinder, showing alternating land and window stripes]]
A '''space habitat''' (also called a '''space settlement''', '''space colony''', '''spacestead''', '''space city''', '''orbital habitat''', '''orbital settlement''', '''orbital colony''', '''orbital stead''' or '''orbital city''') is a more advanced form of living quarters than a [[space station]] or [[space habitat (facility)|habitation module]], in that it is intended as a permanent settlement or green habitat rather than as a simple way-station or other specialized facility. No space habitat has been constructed yet, but many design concepts, with varying degrees of realism, have come both from engineers and from science-fiction authors.
The term ''space habitat'' sometimes includes more broadly habitats built on or in a body other than Earth—such as the Moon, [[Mars habitat|Mars]] or an asteroid. This article concentrates on self-contained structures envisaged for [[micro-g environment]]s.
==Definition==
A space habitat, or more precisely a space settlement, is any large-scale [[space habitat (facility)|habitation facility in space]], or more particularly in [[outer space]] or an orbit. A space habitat is typically designed to rotate so as to prevent long-term exposure of its residents to the peril of weightlessness or microgravity; studies have shown rotation to be a healthy substitute for gravity.
While not automatically constituting a colonial entity, a space habitat 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==
The idea of space habitats 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. In 1903, space pioneer [[Konstantin Tsiolkovsky]] speculated about rotating cylindrical space habitats, with plants fed by the sun, 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 the 1920s [[John Desmond Bernal]] and others speculated about giant space habitats. [[Dandridge M. Cole]] in the late 1950s and 1960s speculated about hollowing out asteroids and then rotating them 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>
==Motivation==
{{Also|Human presence in space#Purposes|Space colonization#Reasons|Space and survival}}
[[File:Stanford Torus interior.jpg|right|thumb|A [[Stanford torus]] interior]]
[[File:Stanford Torus exterior.jpg|right|thumb|Stanford torus exterior]]
There are a range of reasons for space habitats. Beside [[human spaceflight]] supported [[space exploration]] and [[space colonization]], reasons for space habitats include:
* 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>
* Huge resources in space for expansion of human society
* Expansion without any [[ecosystem]]s to destroy or [[indigenous peoples]] to displace
* It could help the Earth by relieving [[population pressure]] and taking industry off-Earth.
==Advantages==
A number of arguments are made for space habitats 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=G. Kopp|author2=J. Lean |title=A new, lower value of total solar irradiance: Evidence and climate significance|journal=Geophys. Res. Lett.|volume=38 |issue=1 |year=2011|pages=L01706|doi=10.1029/2010GL045777|bibcode = 2011GeoRL..38.1706K |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 habitats.
===Outside gravity well===
Earth-to-space habitat 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 habitats 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 habitats 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 | url=http://www.nss.org/settlement/ColoniesInSpace/colonies_chap11.html | title=Colonies in Space, Chapter 11: What's to Do on Saturday Night ? |date=1977 | access-date=30 January 2012 | author=T. A. Heppenheimer}}</ref> and the use of [[human-powered aircraft]].
===Passenger compartment===
{{See|Space and survival}}
A space habitat 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:Cupola above the darkened Earth.jpg|thumb|400px|The [[airglow]] above the horizon, captured from the [[International Space Station|ISS]]]]
The requirements for a space habitat 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.
===Atmosphere===
Air [[pressure]], with normal partial pressures of [[oxygen]] (21%), [[carbon dioxide]] and [[nitrogen]] (78%), is a basic requirement of any space habitat. Basically, most space habitat 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 habitats.
===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}}
===Protection from radiation===
[[File:Mars Ice Home concept.jpg|thumb|300px|Langley's Mars Ice Dome design from 2016 for a Mars base uses frozen water to enhance protection.]]
If a space habitat is located at [[Lagrangian point#L4 and L5|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]]''). 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/enwiki/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 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>
===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.
===Meteoroids and dust===
The habitat would need to withstand potential impacts from [[space debris]], [[meteoroid]]s, dust, 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 habitat. [[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 habitat and any arbitrarily large shield, but not in any timely or rapid manner, the thrust being very low compared to the huge mass.
===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.
==Considerations==
===Initial capital outlay===
Even the smallest of the habitat 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 habitats 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===
The optimal habitat 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 habitat 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}}
==Conceptual studies==
[[File:Noordung space station.jpg|thumb|Description of a rotating wheel space station in [[Hermann Noordung]]'s ''The Problem of Space Travel'' (1929)]]
===O'Neill - The High Frontier===
{{Main|O'Neill Cylinder}}
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-habitats. 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 /> (See the above illustration of such a colony, a classic "O'Neill Colony"). He expanded the article in his 1976 book ''[[The High Frontier: Human Colonies in Space]]''.
====NASA Ames/Stanford 1975 Summer Study====
The result motivated [[NASA]] to sponsor a couple of summer workshops led by O'Neill.<ref>
{{citation | 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 | url-status= dead | archive-date= 2002-11-19 | title= Space Settlements: A Design Study | year= 1975 | publisher= NASA}}</ref><ref>{{citation | 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 | url-status= dead | 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= 978-0491029414|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|website=jstor.org|jstor=24128636 |access-date=April 22, 2023|url=http://www.jstor.org/stable/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=http://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 |work=CNN}}</ref>
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 Society]] in the 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 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.
===NASA concepts===
Some NASA concept studies included:
* [[Bernal sphere#Island One|Island One]], a Bernal sphere habitat for about 10,000–20,000 people.
* [[Stanford torus]]: an alternative to Island One.
* [[O'Neill cylinder]]: "Island Three", an even larger design (3.2 km radius and 32 km long).
* 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 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.
* 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 |url-status=dead |archive-url=https://web.archive.org/web/20130215204552/https://settlement.arc.nasa.gov/Kalpana/KalpanaOne.html |archive-date=2013-02-15}}</ref>
* A bola: a 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" />
* Beaded habitats:<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}} 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 |url-status=dead |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 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.
===Other concepts===
*Bubbleworld: The Bubbleworld or Inside/Outside concept was originated by [[Dandridge MacFarlan Cole|Dandridge M. Cole]] in 1964.<ref name="Cole" /> The concept calls for drilling a tunnel through the longest axis of a large asteroid of iron or nickel-iron composition 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 artificial gravity by centrifugation, 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 habitat thought of by Dani Eder in 1995 (it is alternatively known as an Ederworld). 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.<ref>{{Cite web |title=Bubbleworld (Dani Eder) |url=https://yarchive.net/space/exotic/bubbleworld.html |access-date=2024-01-09 |website=yarchive.net}}</ref><ref>{{Cite web |date=2013-12-11 |title=Gravitational Space Balloons: Ederworld Analyzed (Concentric Gravity Balloons to Maximize Volume) |url=http://gravitationalballoon.blogspot.com/2013/12/ederworld-analyzed-concentric-gravity.html |access-date=2024-01-09 |website=Gravitational Space Balloons}}</ref>
* [[Terrarium (space habitat)|Asteroid terrarium]]: a similar idea to the bubble world, the asteroid terrarium, appears in the 2012 novel ''[[2312 (novel)|2312]]'', authored by [[hard science fiction]] writer [[Kim Stanley Robinson]].
*[[Bishop Ring (habitat)|Bishop Ring]]: a speculative design using [[carbon nanotube]]s, a Bishop Ring is a torus 1000 km in radius, 500 km in width, and with atmosphere retention walls 200 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>
*[[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 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>
==Gallery==
<gallery>
File:Curreri space habitat.png|Bola space station
File:Nasa mars artificial gravity 1989.jpg|Bola Mars spacecraft
Kalpana One space station.png|Kalpana One Orbital space station
File:Concepts from 1975 NASA Summer Study at Stanford.png|Various concepts
</gallery>
==Current projects==
The following projects and proposals, while not truly space habitats, incorporate aspects of what they would have and may represent stepping stones towards eventually building of space habitats.
The [[Nautilus-X]] Multi-Mission Space Exploration Vehicle (MMSEV): this 2011 NASA proposal for a long-duration crewed space transport vehicle included an [[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 [[International Space Station|ISS]] [[Nautilus-X#ISS centrifuge demonstration|Centrifuge Demo]], also proposed in 2011 as a demonstration project preparatory to the final design of the larger torus centrifuge space habitat for the Multi-Mission Space Exploration Vehicle. The structure 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 [[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.
==See also==
{{commons category|Space habitats}}
* [[Bioastronautics]]
* [[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==
*[http://lifeboat.com/ex/space.habitats Lifeboat Foundation Space Habitats], a space habitat advocacy group.
*{{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]]' |
