Space colonization (or extraterrestrial colonization) is the settlement or

colonization 475px, Map of the year each country achieved List of sovereign states by date of formation, independence. Colonization (British English: colonisation) is a process of establishing occupation of or control over foreign territories or peoples f ...

of outer space and astronomical bodies. The concept in its broad sense has been applied to any permanent human presence in space, such as a

space habitat 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 ...

or other

extraterrestrial settlement Extraterrestrial settlement can be any type of permanent habitation outside of Earth, beyond its space boundary, such as: * Space settlement ** Orbital space station **Cycler **Interstellar ark ***Generation ship * Extraterrestrial surface settle ...

s. It may involve a process of occupation or control for exploitation, such as extraterrestrial mining. Making territorial claims in space is prohibited by international

space law Space law is the body of law governing space-related activities, encompassing both international and domestic agreements, rules, and principles. Parameters of space law include space exploration, liability for damage, weapons use, rescue efforts ...

, defining space as a common heritage. International space law has had the goal to prevent colonial claims and militarization of space, and has advocated the installation of international regimes to regulate access to and sharing of space, particularly for specific locations such as the limited space of

geostationary orbit A geostationary orbit, also referred to as a geosynchronous equatorial orbit''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources. (GEO), is a circular orbit, circular geosynchronous or ...

or the Moon. To date, no permanent space settlement other than temporary space habitats have been established, nor has any extraterrestrial territory or land been internationally claimed. Currently there are also no plans for building a space colony by any government. However, many proposals, speculations, and designs, particularly for extraterrestrial settlements have been made through the years, and a considerable number of space colonization

advocates An advocate is a professional in the field of law. Different countries and legal systems use the term with somewhat differing meanings. The broad equivalent in many English law–based jurisdictions could be a barrister or a solicitor. Howeve ...

and groups are active. Currently, the dominant private launch provider

SpaceX Space Exploration Technologies Corp., commonly referred to as SpaceX, is an America, American space technology company headquartered at the SpaceX Starbase, Starbase development site in Starbase, Texas. Since its founding in 2002, the compa ...

, has been the most prominent organization planning space colonization on Mars, though having not reached a development stage beyond launch and landing systems. Space colonization raises numerous socio-political questions. Many arguments for and against space settlement have been made. The two most common reasons in favor of colonization are the survival of humans and life independent of Earth, making humans a multiplanetary species, in the event of a planetary-scale disaster (natural or human-made), and the

commercial use of space Space economy refers to the set of activities, industries, technologies, services, and resources that generate economic value through the space exploration, understanding, management, and exploitation of outer space. Commercial satellite us ...

particularly for enabling a more sustainable expansion of human society through the availability of additional resources in space, reducing environmental damage on and exploitation of Earth. The most common objections include concerns that the

commodification Commodification is the process of transforming inalienable, free, or gifted things (objects, services, ideas, nature, personal information, people or animals) into commodities, or objects for sale.For animals"United Nations Commodity Trade Stati ...

of the cosmos may be likely to continue pre-existing detrimental processes such as

environmental degradation Environment most often refers to: __NOTOC__ * Natural environment, referring respectively to all living and non-living things occurring naturally and the physical and biological factors along with their chemical interactions that affect an organism ...

, economic inequality and

war War is an armed conflict between the armed forces of states, or between governmental forces and armed groups that are organized under a certain command structure and have the capacity to sustain military operations, or between such organi ...

s, enhancing the interests of the already powerful, and at the cost of investing in solving existing major environmental and

social issue A social issue is a problem that affects many people within a society. It is a group of common problems in present-day society that many people strive to solve. It is often the consequence of factors extending beyond an individual's control. Soc ...

s. The mere construction of an extraterrestrial settlement, with the needed infrastructure, presents daunting technological, economic and social challenges. Space settlements are generally conceived as providing for nearly all (or all) the needs of larger numbers of humans. The environment in space is very hostile to human life and not readily accessible, particularly for maintenance and supply. It would involve much advancement of currently primitive technologies, such as

controlled ecological life-support system Controlled (or closed) ecological life-support systems (acronym CELSS) are self-supporting life support systems for space stations and colonies typically through controlled closed ecological systems, such as the BioHome, BIOS-3, Biosphere 2, Ma ...

s. With the high cost of

orbital spaceflight An orbital spaceflight (or orbital flight) is a spaceflight in which a spacecraft is placed on a trajectory where it could remain in space for at least one orbit. To do this around the Earth, it must be on a free trajectory which has an altit ...

(around $1400 per kg, or $640 per pound, to

low Earth orbit A low Earth orbit (LEO) is an geocentric orbit, orbit around Earth with a orbital period, period of 128 minutes or less (making at least 11.25 orbits per day) and an orbital eccentricity, eccentricity less than 0.25. Most of the artificial object ...

by SpaceX

Falcon Heavy Falcon Heavy is a super heavy-lift launch vehicle with partial reusability that can carry cargo into Earth orbit and beyond. It is designed, manufactured and launched by American aerospace company SpaceX. The rocket consists of a center core ...

), a space settlement would currently be massively expensive, but ongoing progress in

reusable launch system A reusable launch vehicle has parts that can be recovered and reflown, while carrying payloads from the surface to outer space. Rocket stages are the most common launch vehicle parts aimed for reuse. Smaller parts such as fairings, boosters ...

s aim to change that (possibly reaching $20 per kg to orbit), and in creating automated manufacturing and construction techniques.

Definition

Space colonization has been in a broad sense referred to as space settlement, space humanization or space habitation. Space colonization in a narrow sense refers to space settlements, as envisioned by

Gerard K. O'Neill Gerard Kitchen O'Neill (February 6, 1927 – April 27, 1992) was an American physicist and space activist. As a faculty member of Princeton University, he invented a device called the particle storage ring for high-energy physics experiments. ...

. It is characterized by elements such as: settlement and exploitation, as well as territorial claim. The concept in its broad sense has been applied to any permanent human presence, even robotic, particularly along with the term "settlement", being imprecisely applied to any human

, from

research station Research stations are facilities where scientific investigation, Data collection, collection, analysis and experimentation occurs. A research station is a facility that is built for the purpose of conducting scientific research. There are also man ...

s to self-sustaining communities in space. The words

colony A colony is a territory subject to a form of foreign rule, which rules the territory and its indigenous peoples separated from the foreign rulers, the colonizer, and their ''metropole'' (or "mother country"). This separated rule was often orga ...

and

are terms rooted in colonial history on Earth, making them human geographic as well as particularly political terms. This broad use for any permanent human activity and development in space has been criticized, particularly as

colonialist Colonialism is the control of another territory, natural resources and people by a foreign group. Colonizers control the political and tribal power of the colonised territory. While frequently an Imperialism, imperialist project, colonialism c ...

and undifferentiated (see below Objections). In this sense, a colony is a settlement that claims territory and exploits it for the

settler A settler or a colonist is a person who establishes or joins a permanent presence that is separate to existing communities. The entity that a settler establishes is a Human settlement, settlement. A settler is called a pioneer if they are among ...

s or their

metropole A metropole () is the homeland, central territory or the state exercising power over a colonial empire. From the 19th century, the English term ''metropole'' was mainly used in the scope of the British, Spanish, French, Dutch, Portugu ...

. Therefore, a

human outpost Human outposts

, while possibly a space habitat or even a space settlement, does not automatically constitute a space colony. Therefore, any basing can be part of colonization, while colonization can be understood as a process that is open to more claims, beyond basing. The

International Space Station The International Space Station (ISS) is a large space station that was Assembly of the International Space Station, assembled and is maintained in low Earth orbit by a collaboration of five space agencies and their contractors: NASA (United ...

, the longest-occupied extraterrestrial habitat thus far, does not claim territory and thus is not usually considered a colony. Moriba Jah has criticized existing approaches to orbital space as colonialist, such as for satellites, on the grounds that it involves claiming ownership instead of collaborative stewardship. Some advocates of peaceful human settlement of space have argued against use of the word "colony" and related terms, so as to avoid confusing their goals with

colonialism Colonialism is the control of another territory, natural resources and people by a foreign group. Colonizers control the political and tribal power of the colonised territory. While frequently an Imperialism, imperialist project, colonialism c ...

on Earth.

History

In the first half of the 17th century

John Wilkins John Wilkins (14 February 1614 – 19 November 1672) was an English Anglican ministry, Anglican clergyman, Natural philosophy, natural philosopher, and author, and was one of the founders of the Royal Society. He was Bishop of Chester from 1 ...

suggested in ''A Discourse Concerning a New Planet'' that future adventurers like

Francis Drake Sir Francis Drake ( 1540 – 28 January 1596) was an English Exploration, explorer and privateer best known for making the Francis Drake's circumnavigation, second circumnavigation of the world in a single expedition between 1577 and 1580 (bein ...

and

Christopher Columbus Christopher Columbus (; between 25 August and 31 October 1451 – 20 May 1506) was an Italians, Italian explorer and navigator from the Republic of Genoa who completed Voyages of Christopher Columbus, four Spanish-based voyages across the At ...

might reach the Moon and allow people to live there. The first known work on space colonization was the 1869 novella ''

The Brick Moon "The Brick Moon" is a novella by American writer Edward Everett Hale, published serially in the magazine ''The Atlantic Monthly'' in 1869. It is a work of speculative fiction containing the first known fictional description of an artificial sat ...

'' by

Edward Everett Hale Edward Everett Hale (April 3, 1822 – June 10, 1909) was an American author, historian, and Unitarian minister, best known for his writings such as " The Man Without a Country", published in ''Atlantic Monthly'', in support of the Union ...

, about an inhabited artificial satellite. In 1897, Kurd Lasswitz also wrote about space colonies. The Russian rocket science pioneer

Konstantin Tsiolkovsky Konstantin Eduardovich Tsiolkovsky (; rus, Константин Эдуардович Циолковский, p=kənstɐnʲˈtʲin ɪdʊˈardəvʲɪtɕ tsɨɐlˈkofskʲɪj, a=Ru-Konstantin Tsiolkovsky.oga; – 19 September 1935) was a Russi ...

foresaw elements of the space community in his book ''Beyond Planet Earth'' written about 1900. Tsiolkovsky imagined his space travelers building greenhouses and raising crops in space. Tsiolkovsky believed that going into space would help perfect human beings, leading to immortality and peace.The life of Konstantin Eduardovitch Tsiolkovsky 1857–1935
. One of the first to speak about space colonization was

Cecil Rhodes Cecil John Rhodes ( ; 5 July 185326 March 1902) was an English-South African mining magnate and politician in southern Africa who served as Prime Minister of the Cape Colony from 1890 to 1896. He and his British South Africa Company founded th ...

who in 1902 spoke about "these stars that you see overhead at night, these vast worlds which we can never reach", adding "I would annex the planets if I could; I often think of that. It makes me sad to see them so clear and yet so far". In the 1920s

John Desmond Bernal John Desmond Bernal (; 10 May 1901 – 15 September 1971) was an Irish scientist who pioneered the use of X-ray crystallography in molecular biology. He published extensively on the history of science. In addition, Bernal wrote popular boo ...

Hermann Oberth Hermann Julius Oberth (; 25 June 1894 – 28 December 1989) was an Austria-Hungary, Austro-Hungarian-born German physicist and rocket pioneer of Transylvanian Saxons, Transylvanian Saxon descent. Oberth supported Nazi Germany's war effort and re ...

Guido von Pirquet Guido von Pirquet (30 March 1880 – 17 April 1966) was an Austrian pioneer of astronautics and a Baron of a lower noble family. Born near Vienna, he was educated at Technische Hochschule in Vienna and Graz. He developed an interest in rocketry, b ...

and Herman Noordung further developed the idea.

Wernher von Braun Wernher Magnus Maximilian Freiherr von Braun ( ; ; 23 March 191216 June 1977) was a German–American aerospace engineer and space architect. He was a member of the Nazi Party and '' Allgemeine SS'', the leading figure in the development of ...

contributed his ideas in a 1952 ''Colliers'' magazine article. In the 1950s and 1960s, Dandridge M. Cole published his ideas. When orbital spaceflight was achieved in the 1950s

was still a strong international project, e.g. easing the United States to advance its space program and space in general as part of a "

New Frontier The term ''New Frontier'' was used by Democratic presidential candidate John F. Kennedy in his acceptance speech, delivered July 15, in the 1960 United States presidential election to the Democratic National Convention at the Los Angeles Memo ...

". As the

Space Age The Space Age is a period encompassing the activities related to the space race, space exploration, space technology, and the cultural developments influenced by these events, beginning with the launch of Sputnik 1 on October 4, 1957, and co ...

was developing,

decolonization Decolonization is the undoing of colonialism, the latter being the process whereby Imperialism, imperial nations establish and dominate foreign territories, often overseas. The meanings and applications of the term are disputed. Some scholar ...

gained again in force, producing many newly

independent Independent or Independents may refer to: Arts, entertainment, and media Artist groups * Independents (artist group), a group of modernist painters based in Pennsylvania, United States * Independentes (English: Independents), a Portuguese artist ...

countries. These newly independent countries confronted spacefaring countries, demanding an anti-colonial stance and regulation of space activity when

was raised and negotiated internationally. Fears of confrontations because of land grabs and an

arms race An arms race occurs when two or more groups compete in military superiority. It consists of a competition between two or more State (polity), states to have superior armed forces, concerning production of weapons, the growth of a military, and ...

in space between the few countries with spaceflight capabilities grew and were ultimately shared by the spacefaring countries themselves. This produced the wording of the agreed on international space law, starting with the

Outer Space Treaty The Outer Space Treaty, formally the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies, is a Multilateralism, multilateral treaty that forms the bas ...

of 1967, calling space a " province of all mankind" and securing provisions for international regulation and sharing of outer space. The advent of

geostationary satellite A geostationary orbit, also referred to as a geosynchronous equatorial orbit''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources. (GEO), is a circular geosynchronous orbit in altitud ...

s raised the case of limited space in outer space. In the 1960s and with an initial focus on communications spectrum management, the international community agreed to regulate the assignment of slots in the geosynchronous (GEO) belt through the International Telecommunication Union (ITU). Today, any company or nation planning to launch a satellite to GEO must apply to the ITU for an orbital slot. A group of

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

ial countries, all of which were countries that were once colonies of colonial empires, but without spaceflight capabilities, signed in 1976 the Bogota Declaration. These countries declared that

is a limited natural resource and belongs to the equatorial countries directly below, seeing it not as part of outer space, humanity's

common Common may refer to: As an Irish surname, it is anglicised from Irish Gaelic surname Ó Comáin. Places * Common, a townland in County Tyrone, Northern Ireland * Boston Common, a central public park in Boston, Massachusetts * Cambridge Com ...

. Through this, the declaration challenged the dominance of geostationary orbit by spacefaring countries through identifying their dominance as imperialistic. Writers continued to address space colonization concepts by publishing books in the mid-1970s such as ''The High Frontier: Human Colonies in Space'' by

and ''Colonies in Space'' by T. A. Heppenheimer. In 1975, the first international joint space mission occurred as a symbol of the policy of détente that the two superpowers were pursuing at the time. The U.S. Apollo and Soviet Soyuz spacecraft docked in earth orbit for almost two days. In 1977, the first sustained space habitat, the

Salyut 6 Salyut 6 () was a Soviet orbital space station, the eighth station of the Salyut programme, and alternatively known DOS-5 as it was the fifth of the Durable Orbital Station series of civilian space stations. It was launched on 29 September 19 ...

station, was put into Earth's orbit. Eventually the first space stations were succeeded by the ISS, today's largest

human outpost Human outposts

in space and closest to a space settlement. Built and operated under a multilateral regime, it has become a blueprint for future stations, such as around and possibly on the Moon. Additional discourse on living in space was generated by writers including Marianne J. Dyson who wrote ''Home on the Moon; Living on a Space Frontier'' in 2003; Peter Eckart wrote ''Lunar Base Handbook'' in 2006 and then

Harrison Schmitt Harrison Hagan "Jack" Schmitt (born July 3, 1935) is an American geologist, former NASA astronaut, university professor, former U.S. senator from New Mexico. He is the most recent living person—and only person without a background in military a ...

's ''Return to the Moon'' written in 2007. An international regime for lunar activity was demanded by the international

Moon Treaty The Agreement Governing the Activities of States on the Moon and Other Celestial Bodies,natural or human-made disasters on Earth. On two occasions, theoretical physicist and cosmologist

Stephen Hawking Stephen William Hawking (8January 194214March 2018) was an English theoretical physics, theoretical physicist, cosmologist, and author who was director of research at the Centre for Theoretical Cosmology at the University of Cambridge. Between ...

argued for space colonization as a means of saving humanity. In 2001, Hawking predicted that the human race would become extinct within the next thousand years unless colonies could be established in space. In 2010, he stated that humanity faces two options: either we colonize space within the next two hundred years, or we will face the long-term prospect of

extinction Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

. In 2005, then

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

Administrator Michael Griffin identified space colonization as the ultimate goal of current spaceflight programs, saying: Louis J. Halle Jr., formerly of the

United States Department of State The United States Department of State (DOS), or simply the State Department, is an United States federal executive departments, executive department of the U.S. federal government responsible for the country's foreign policy of the United State ...

, wrote in ''

Foreign Affairs ''Foreign Affairs'' is an American magazine of international relations and foreign policy of the United States, U.S. foreign policy published by the Council on Foreign Relations, a nonprofit organization, nonprofit, nonpartisan, membership or ...

'' (Summer 1980) that the colonization of space will protect humanity in the event of global

nuclear warfare Nuclear warfare, also known as atomic warfare, is a War, military conflict or prepared Policy, political strategy that deploys nuclear weaponry. Nuclear weapons are Weapon of mass destruction, weapons of mass destruction; in contrast to conven ...

. The physicist

Paul Davies Paul Charles William Davies (born 22 April 1946) is an English physicist, writer and broadcaster, a professor in Arizona State University and director of BEYOND: Center for Fundamental Concepts in Science. He is affiliated with the Institute ...

also supports the view that if a planetary catastrophe threatens the survival of the human species on Earth, a self-sufficient colony could "reverse-colonize" Earth and restore

human civilization A civilization (also spelled civilisation in British English) is any complex society characterized by the development of the state, social stratification, urbanization, and symbolic systems of communication beyond signed or spoken languag ...

. The author and journalist William E. Burrows and the biochemist Robert Shapiro proposed a private project, the Alliance to Rescue Civilization, with the goal of establishing an off-Earth "

backup In information technology, a backup, or data backup is a copy of computer data taken and stored elsewhere so that it may be used to restore the original after a data loss event. The verb form, referring to the process of doing so, is "wikt:back ...

" of human civilization. Based on his Copernican principle, J. Richard Gott has estimated that the human race could survive for another 7.8 million years, but it is not likely to ever colonize other planets. However, he expressed a hope to be proven wrong, because "colonizing other worlds is our best chance to hedge our bets and improve the survival prospects of our species". In a theoretical study from 2019, a group of researchers have pondered the long-term trajectory of human civilization. It is argued that due to Earth's finitude as well as the limited duration of the Solar System, mankind's survival into the far future will very likely require extensive space colonization. This 'astronomical trajectory' of mankind, as it is termed, could come about in four steps: First step, space colonies could be established at various habitable locations — be it in outer space or on

celestial bodies An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within the observable universe. In astronomy, the terms ''object'' and ''body'' are of ...

away from Earth – and allowed to remain temporarily dependent on support from Earth. In the second step, these colonies could gradually become self-sufficient, enabling them to survive if or when the mother civilization on Earth fails or dies. Third step, the colonies could develop and expand their habitation by themselves on their

space station A space station (or orbital station) is a spacecraft which remains orbital spaceflight, in orbit and human spaceflight, hosts humans for extended periods of time. It therefore is an artificial satellite featuring space habitat (facility), habitat ...

s or celestial bodies, for example via

terraforming Terraforming or terraformation ("Earth-shaping") is the hypothetical process of deliberately modifying the atmosphere, temperature, surface topography or ecology of a planet, moon, or other body to be similar to the environment of Earth to mak ...

. In the fourth step, the colonies could self-replicate and establish new colonies further into space, a process that could then repeat itself and continue at an exponential rate throughout the cosmos. However, this astronomical trajectory may not be a lasting one, as it will most likely be interrupted and eventually decline due to resource depletion or straining competition between various human factions, bringing about some 'star wars' scenario.

Vast resources in space

Resources in space, both in materials and energy, are enormous. The

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

has enough material and energy to support anywhere from several thousand to over a billion times that of the current Earth-based human population, mostly from the Sun itself. Asteroid mining will likely be a key player in space colonization. Water and materials to make structures and shielding can be easily found in asteroids. Instead of resupplying on Earth, mining and fuel stations need to be established on asteroids to facilitate better space travel. Optical mining is the term NASA uses to describe extracting materials from asteroids. NASA believes by using propellant derived from asteroids for exploration to the moon, Mars, and beyond will save $100 billion. If funding and technology come sooner than estimated, asteroid mining might be possible within a decade. Although some items of the infrastructure requirements above can already be easily produced on Earth and would therefore not be very valuable as trade items (oxygen, water, base metal ores, silicates, etc.), other high-value items are more abundant, more easily produced, of higher quality, or can only be produced in space. These could provide (over the long-term) a high return on the initial investment in space infrastructure. Some of these high-value trade goods include precious metals,Asteroid Mining
. Sol Station. gemstones, power, solar cells,
– Jim Kingdon's space markets page. ball bearings, semi-conductors, and pharmaceuticals. The mining and extraction of metals from a small asteroid the size of

3554 Amun 3554 Amun is an Aten asteroid, meaning it crosses Earth's orbit, and a Venus-crosser. It was discovered on 4 March 1986 by Carolyn and Eugene Shoemaker at Mount Palomar Observatory, and named for the ancient Egyptian deity Amun. Amun was the ...

(6178) 1986 DA is a metallic asteroid, classified as near-Earth object of the Amor group, approximately 3 kilometers in diameter. It was discovered on 16 February 1986, by Japanese astronomer Minoru Kizawa at Shizuoka Observatory, Japan. 1986 DA was the fi ...

, both small near-Earth asteroids, may yield 30 times as much metal as humans have mined throughout history. A metal asteroid this size would be worth approximately US$20 trillion at 2001 market prices. The main impediments to commercial exploitation of these resources are the very high cost of initial investment, the very long period required for the expected return on those investments (''The Eros Project'' plans a 50-year development), and the fact that the venture has never been carried out before—the high-risk nature of the investment.

Expansion with fewer negative consequences

Expansion of humans and technological progress has usually resulted in some form of environmental devastation, and destruction of

ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

s and their accompanying

wildlife Wildlife refers to domestication, undomesticated animals and uncultivated plant species which can exist in their natural habitat, but has come to include all organisms that grow or live wilderness, wild in an area without being species, introdu ...

. In the past, expansion has often come at the expense of displacing many

indigenous peoples There is no generally accepted definition of Indigenous peoples, although in the 21st century the focus has been on self-identification, cultural difference from other groups in a state, a special relationship with their traditional territ ...

, the resulting treatment of these peoples ranging anywhere from encroachment to genocide. Because space has no known life, this need not be a consequence, as some space settlement advocates have pointed out. However, on some bodies of the Solar System, there is the potential for extant native lifeforms and so the negative consequences of space colonization cannot be dismissed. Counterarguments state that changing only the location but not the logic of exploitation will not create a more sustainable future.

Alleviating overpopulation and resource demand

An argument for space colonization is to mitigate proposed impacts of overpopulation of Earth, such as

resource depletion Resource depletion occurs when a natural resource is consumed faster than it can be replenished. The value of a resource depends on its availability in nature and the cost of extracting it. By the law of supply and demand, the Scarcity, scarcer ...

. If the resources of space were opened to use and viable life-supporting habitats were built, Earth would no longer define the limitations of growth. Although many of Earth's resources are non-renewable, off-planet colonies could satisfy the majority of the planet's resource requirements. With the availability of extraterrestrial resources, demand on terrestrial ones would decline. Proponents of this idea include

and

. Others including cosmologist

Carl Sagan Carl Edward Sagan (; ; November 9, 1934December 20, 1996) was an American astronomer, planetary scientist and science communicator. His best known scientific contribution is his research on the possibility of extraterrestrial life, including e ...

and science fiction writers Arthur C. Clarke, and

Isaac Asimov Isaac Asimov ( ; – April 6, 1992) was an Russian-born American writer and professor of biochemistry at Boston University. During his lifetime, Asimov was considered one of the "Big Three" science fiction writers, along with Robert A. H ...

, have argued that shipping any excess population into space is not a viable solution to human overpopulation. According to Clarke, "the population battle must be fought or won here on Earth". The problem for these authors is not the lack of resources in space (as shown in books such as '' Mining the Sky''), but the physical impracticality of shipping vast numbers of people into space to "solve" overpopulation on Earth.

Other arguments

Advocates for space colonization cite a presumed innate human drive to explore and discover, and call it a quality at the core of progress and thriving civilizations.

Nick Bostrom Nick Bostrom ( ; ; born 10 March 1973) is a Philosophy, philosopher known for his work on existential risk, the anthropic principle, human enhancement ethics, whole brain emulation, Existential risk from artificial general intelligence, superin ...

has argued that from a

utilitarian In ethical philosophy, utilitarianism is a family of normative ethical theories that prescribe actions that maximize happiness and well-being for the affected individuals. In other words, utilitarian ideas encourage actions that lead to the ...

perspective, space colonization should be a chief goal as it would enable a very large population to live for a very long time (possibly billions of years), which would produce an enormous amount of utility (or happiness). He claims that it is more important to reduce existential risks to increase the probability of eventual colonization than to accelerate technological development so that space colonization could happen sooner. In his paper, he assumes that the created lives will have positive ethical value despite the problem of

suffering Suffering, or pain in a broad sense, may be an experience of unpleasantness or aversion, possibly associated with the perception of harm or threat of harm in an individual. Suffering is the basic element that makes up the negative valence (psyc ...

. In a 2001 interview with Freeman Dyson, J. Richard Gott and Sid Goldstein, they were asked for reasons why some humans should live in space.. Their answers were: * Spread life and beauty throughout the universe * Ensure the survival of our species * Make money through new forms of space commercialization such as solar-power satellites,

asteroid mining Asteroid mining is the hypothetical extractivism, extraction of materials from asteroids and other minor planets, including near-Earth objects. Notable asteroid mining challenges include the high cost of spaceflight, unreliable identification ...

, and space manufacturing * Save the environment of Earth by moving people and industry into space Biotic ethics is a branch of ethics that values life itself. For biotic ethics, and their extension to space as panbiotic ethics, it is a human purpose to secure and propagate life and to use space to maximize life.

Opposition

Space colonization has been seen as a relief to the problem of

human overpopulation Human overpopulation (or human population overshoot) is the idea that human populations may become too large to be sustainability, sustained by their environment or resources in the long term. The topic is usually discussed in the context of wor ...

as early as 1758, and listed as one of Stephen Hawking's reasons for pursuing space exploration. Critics note, however, that a slowdown in population growth rates since the 1980s has alleviated the risk of overpopulation. Critics also argue that the costs of commercial activity in space are too high to be profitable against Earth-based industries, and hence that it is unlikely to see significant exploitation of space resources in the foreseeable future. Other objections include concerns that the forthcoming colonization and

of the cosmos is likely to enhance the interests of the already powerful, including major economic and military institutions e.g. the large financial institutions, the major aerospace companies and the

military–industrial complex The expression military–industrial complex (MIC) describes the relationship between a country's military and the Arms industry, defense industry that supplies it, seen together as a vested interest which influences public policy. A driving fac ...

, to lead to new

s, and to exacerbate pre-existing exploitation of workers and

resources ''Resource'' refers to all the materials available in our environment which are Technology, technologically accessible, Economics, economically feasible and Culture, culturally Sustainability, sustainable and help us to satisfy our needs and want ...

, economic inequality,

poverty Poverty is a state or condition in which an individual lacks the financial resources and essentials for a basic standard of living. Poverty can have diverse Biophysical environmen ...

, social division and

marginalization Social exclusion or social marginalisation is the social disadvantage and relegation to the fringe of society. It is a term that has been used widely in Europe and was first used in France in the late 20th century. In the EU context, the Euro ...

, environmental degradation, and other detrimental processes or institutions. Additional concerns include creating a culture in which humans are no longer seen as human, but rather as material assets. The issues of

human dignity Dignity is a human's contentment attained by satisfying physiological needs and a need in development. The content of contemporary dignity is derived in the new natural law theory as a distinct human good. As an extension of the Age of Enlighten ...

morality Morality () is the categorization of intentions, Decision-making, decisions and Social actions, actions into those that are ''proper'', or ''right'', and those that are ''improper'', or ''wrong''. Morality can be a body of standards or principle ...

philosophy Philosophy ('love of wisdom' in Ancient Greek) is a systematic study of general and fundamental questions concerning topics like existence, reason, knowledge, Value (ethics and social sciences), value, mind, and language. It is a rational an ...

culture Culture ( ) is a concept that encompasses the social behavior, institutions, and Social norm, norms found in human societies, as well as the knowledge, beliefs, arts, laws, Social norm, customs, capabilities, Attitude (psychology), attitudes ...

bioethics Bioethics is both a field of study and professional practice, interested in ethical issues related to health (primarily focused on the human, but also increasingly includes animal ethics), including those emerging from advances in biology, me ...

, and the threat of megalomaniac leaders in these new "societies" would all have to be addressed in order for space colonization to meet the

psychological Psychology is the scientific study of mind and behavior. Its subject matter includes the behavior of humans and nonhumans, both consciousness, conscious and Unconscious mind, unconscious phenomena, and mental processes such as thoughts, feel ...

and

social Social organisms, including human(s), live collectively in interacting populations. This interaction is considered social whether they are aware of it or not, and whether the exchange is voluntary or not. Etymology The word "social" derives fro ...

needs of people living in isolated colonies. As an alternative or addendum for the future of the human race, many science fiction writers have focused on the realm of the 'inner-space', that is the computer-aided exploration of the

human mind The mind is that which thinks, feels, perceives, imagines, remembers, and wills. It covers the totality of mental phenomena, including both conscious processes, through which an individual is aware of external and internal circumstances, ...

and human

consciousness Consciousness, at its simplest, is awareness of a state or object, either internal to oneself or in one's external environment. However, its nature has led to millennia of analyses, explanations, and debate among philosophers, scientists, an ...

—possibly en route developmentally to a Matrioshka Brain.

Robotic spacecraft Uncrewed spacecraft or robotic spacecraft are spacecraft without people on board. Uncrewed spacecraft may have varying levels of autonomy from human input, such as remote control, or remote guidance. They may also be autonomous, in which t ...

are proposed as an alternative to gain many of the same scientific advantages without the limited mission duration and high cost of life support and return transportation involved in human missions. A corollary to the

Fermi paradox The Fermi paradox is the discrepancy between the lack of conclusive evidence of advanced extraterrestrial life and the apparently high likelihood of its existence. Those affirming the paradox generally conclude that if the conditions required ...

—"nobody else is doing it"—is the argument that, because no evidence of alien colonization technology exists, it is statistically unlikely to even be possible to use that same level of technology ourselves.

Colonialism

Space colonization has been discussed as

postcolonial Postcolonialism (also post-colonial theory) is the critical academic study of the cultural, political and economic consequences of colonialism and imperialism, focusing on the impact of human control and extractivism, exploitation of colonized pe ...

continuation of

imperialism Imperialism is the maintaining and extending of Power (international relations), power over foreign nations, particularly through expansionism, employing both hard power (military and economic power) and soft power (diplomatic power and cultura ...

and

, calling for

instead of colonization. Critics argue that the present politico-legal regimes and their philosophic grounding, advantage imperialist development of space, that key decisionmakers in space colonization are often wealthy elites affiliated with private corporations, and that space colonization would primarily appeal to their peers rather than ordinary citizens. Furthermore, it is argued that there is a need for inclusive and democratic participation and implementation of any space exploration, infrastructure or habitation. According to space law expert Michael Dodge, existing

, such as the

, guarantees access to space, but does not enforce social inclusiveness or regulate non-state actors. Particularly the narrative of the "

" has been criticized as unreflected continuation of

settler colonialism Settler colonialism is a logic and structure of displacement by Settler, settlers, using colonial rule, over an environment for replacing it and its indigenous peoples with settlements and the society of the settlers. Settler colonialism is ...

and

manifest destiny Manifest destiny was the belief in the 19th century in the United States, 19th-century United States that American pioneer, American settlers were destined to expand westward across North America, and that this belief was both obvious ("''m ...

, continuing the narrative of exploration as fundamental to the assumed

human nature Human nature comprises the fundamental dispositions and characteristics—including ways of Thought, thinking, feeling, and agency (philosophy), acting—that humans are said to have nature (philosophy), naturally. The term is often used to denote ...

. Joon Yun considers space colonization as a solution to human survival and global problems like pollution to be imperialist; others have identified space as a new sacrifice zone of colonialism. Furthermore, the understanding of space as empty and separate is considered a continuation of

terra nullius ''Terra nullius'' (, plural ''terrae nullius'') is a Latin expression meaning " nobody's land". Since the nineteenth century it has occasionally been used in international law as a principle to justify claims that territory may be acquired ...

. Natalie B. Trevino argues that not colonialism but coloniality will be carried into space if not reflected on. More specifically the advocacy for territorial colonization of Mars has been called ''surfacism'', in contrast to habitation in the atmospheric space of Venus, a concept similar to

Thomas Gold Thomas Gold (May 22, 1920 – June 22, 2004) was an Austrian-born astrophysicist, who also held British and American citizenship. He was a professor of astronomy at Cornell University, a member of the U.S. National Academy of Sciences, and a Fe ...

s '' surface chauvinism''. More generally space infrastructure such as the

Mauna Kea Observatories The Mauna Kea Observatories (MKO) are a group of independent astronomical research facilities and large telescope observatories that are located at the summit of Mauna Kea on Hawaii (island), Hawaiʻi, United States. The facilities are located i ...

have also been criticized and protested against as being colonialist.

Guiana Space Centre The Guiana Space Centre (; CSG), also called Europe's Spaceport, is a spaceport to the northwest of Kourou in French Guiana, an Overseas departments and regions of France, overseas region of France in South America. Kourou is located approxim ...

has also been the site of anti-colonial protests, connecting colonization as an issue on Earth and in space. In regard to the scenario of extraterrestrial first contact, it has been argued that the employment of colonial language would endanger such first impressions and encounters. Furthermore, spaceflight as a whole and space law more particularly has been criticized as a postcolonial project by being built on a colonial legacy and by not facilitating the sharing of access to space and its benefits, too often allowing spaceflight to be used to sustain colonialism and imperialism, most of all on Earth instead.

Planetary protection and risk of contamination

Agencies conducting interplanetary missions are guided by

COSPAR The Committee on Space Research (COSPAR) was established on October 3, 1958 by the International Council for Science, International Council for Scientific Unions (ICSU) and its first chair was Hildegard Korf Kallmann-Bijl. Among COSPAR's objec ...

's planetary protection policies, to have at most 300,000 spores on the exterior of the craft—and more thoroughly sterilized if they contact "special regions" containing water, or it could contaminate life-detection experiments or the planet itself.Queens University Belfast scientist helps NASA Mars project
"No-one has yet proved that there is deep groundwater on Mars, but it is plausible as there is certainly surface ice and atmospheric water vapour, so we wouldn't want to contaminate it and make it unusable by the introduction of micro-organisms." It is impossible to sterilize human missions to this level, as humans are host to typically a hundred trillion

microorganism A microorganism, or microbe, is an organism of microscopic scale, microscopic size, which may exist in its unicellular organism, single-celled form or as a Colony (biology)#Microbial colonies, colony of cells. The possible existence of unseen ...

s of thousands of species of the

human microbiome The human microbiome is the aggregate of all microbiota that reside on or within human tissues and biofluids along with the corresponding List of human anatomical features, anatomical sites in which they reside, including the human gastrointes ...

, and these cannot be removed while preserving the life of the human. Containment seems the only option, but it is a major challenge in the event of a hard landing (i.e. crash). There have been several planetary workshops on this issue, but with no final guidelines yet for a way forward. Human explorers could also inadvertently contaminate Earth if they return to the planet while carrying extraterrestrial microorganisms.

Challenges to overcome

Colonization beyond the Earth involves overcoming a number of difficult challenges.

Distance from
Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

The outer planets are much farther from Earth than the inner planets, and would therefore be harder and more time-consuming to reach. In addition, return voyages may well be prohibitive considering the time and distance. Even communication with Earth would be slow, with delays of 4 - 24 minutes for a message to

mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

, and 35 - 52 minutes to Jupiter and it's moons.

Extreme environments

Extreme cold – due to the distance to the sun, temperatures are near

absolute zero Absolute zero is the lowest possible temperature, a state at which a system's internal energy, and in ideal cases entropy, reach their minimum values. The absolute zero is defined as 0 K on the Kelvin scale, equivalent to −273.15 ° ...

in many parts of the outer Solar System.

Sustainable power sources

Power –

Solar power Solar power, also known as solar electricity, is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Solar panels use the photovoltaic effect to c ...

is many times less concentrated in the outer Solar System than in the inner Solar System. It is unclear as to whether it would be usable there, using some form of concentration mirrors, or whether

nuclear power Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced by ...

would be necessary. Use of geothermal systems to generate power may be practical on some of the planets and moons of the solar system.

Physical and mental health risks to colonists

The health of the humans who may participate in a colonization venture would be subject to increased physical, mental and emotional risks. * Effects of low gravity on the human body – All moons of the gas giants and all outer dwarf planets have a very low gravity, the highest being Io's gravity (0.183 g) which is less than 1/5 of the Earth's gravity. Since the

Apollo program The Apollo program, also known as Project Apollo, was the United States human spaceflight program led by NASA, which Moon landing, landed the first humans on the Moon in 1969. Apollo followed Project Mercury that put the first Americans in sp ...

all crewed spaceflight has been constrained to low Earth orbit and there has been no opportunity to test the effects of such low gravitational accelerations on the human body. It is speculated (but not confirmed) that the low gravity environments might have very similar effects to long-term exposure in

weightlessness Weightlessness is the complete or near-complete absence of the sensation of weight, i.e., zero apparent weight. It is also termed zero g-force, or zero-g (named after the g-force) or, incorrectly, zero gravity. Weight is a measurement of the fo ...

. Such effects might be avoided by rotating spacecraft creating artificial gravity. * Dust – breathing risks associated with fine dust from rocky surface objects, for similar reasons as harmful effects of lunar dust. *

learned that – without gravity – bones lose

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

s, causing

osteoporosis Osteoporosis is a systemic skeletal disorder characterized by low bone mass, micro-architectural deterioration of bone tissue leading to more porous bone, and consequent increase in Bone fracture, fracture risk. It is the most common reason f ...

Bone density Bone density, or bone mineral density, is the amount of bone mineral in bone tissue. The concept is of mass of mineral per volume of bone (relating to density in the physics sense), although medicine#Clinical practice, clinically it is measured by ...

may decrease by 1% per month, which may lead to a greater risk of osteoporosis-related fractures later in life. Fluid shifts towards the head may cause vision problems. * NASA found that isolation in closed environments aboard the

led to depression,

sleep disorder A sleep disorder, or somnipathy, is a medical disorder affecting an individual's sleep patterns, sometimes impacting physical, mental, social, and emotional functioning. Polysomnography and actigraphy are tests commonly ordered for diagnosing sle ...

s, and diminished personal interactions, likely due to confined spaces and the monotony and boredom of long space flight. *

Circadian rhythm A circadian rhythm (), or circadian cycle, is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism (i.e., Endogeny (biology), endogenous) and responds to the env ...

may also be susceptible to the effects of space life due to the effects on sleep of disrupted timing of sunset and sunrise. This can lead to exhaustion, as well as other sleep problems such as

insomnia Insomnia, also known as sleeplessness, is a sleep disorder where people have difficulty sleeping. They may have difficulty falling asleep, or staying asleep for as long as desired. Insomnia is typically followed by daytime sleepiness, low ene ...

, which can reduce their productivity and lead to mental health disorders. High-energy radiation is a health risk that colonists would face, as radiation in deep space is deadlier than what astronauts face now in low Earth orbit. Metal shielding on space vehicles protects against only 25–30% of space radiation, possibly leaving colonists exposed to the other 70% of radiation and its short and long-term health complications.

Locations to consider

Space colonization has been envisioned at many different locations inside and outside the

, but most commonly at Mars and the Moon.

Near-Earth space

Earth orbit

Geostationary orbit A geostationary orbit, also referred to as a geosynchronous equatorial orbit''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources. (GEO), is a circular orbit, circular geosynchronous or ...

was an early issue of discussion about space colonization, with equatorial countries argueing for special rights to the orbit (see Bogota Declaration).

Space debris Space debris (also known as space junk, space pollution, space waste, space trash, space garbage, or cosmic debris) are defunct human-made objects in spaceprincipally in Earth orbitwhich no longer serve a useful function. These include dere ...

, particularly in low Earth orbit, has been characterized as a product of colonization by occupying space and hindering access to space through excessive pollution with debris, with drastic increases in the course of military activity and without a lack of management. Axiom modules connected to ISS

Most of the delta-''v'' budget, and thus propellant, of a launch is used bringing a spacecraft to low Earth orbit. This is the main reason why

Jerry Pournelle Jerry Eugene Pournelle (; August 7, 1933 – September 8, 2017) was an American scientist in the area of operations research and ergonomics, human factors research, a science fiction writer, essayist, journalist, and one of the first bloggers. ...

said "If you can get your ship into orbit, you're halfway to anywhere". Therefore, the main advantages to constructing a space settlement in Earth orbit are accessibility to the Earth and already-existing economic motives such as space hotels and space manufacturing. However, a big disadvantage is that orbit does not host any materials that is available for exploitation. Space colonization altogether might eventually demand lifting vast amounts of payload into orbit, making thousands of daily launches potentially unsustainable. Various theoretical concepts, such as orbital rings and skyhooks, have been proposed to reduce the cost of accessing space.

Moon

The

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

is discussed as a target for colonization, due to its proximity to Earth and lower

escape velocity In celestial mechanics, escape velocity or escape speed is the minimum speed needed for an object to escape from contact with or orbit of a primary body, assuming: * Ballistic trajectory – no other forces are acting on the object, such as ...

. The Moon is reachable from Earth in three days, has a near-instant communication to Earth, with minable minerals, no atmosphere, and low gravity, making it extremely easy to ship materials and products to orbit. Abundant

ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...

is trapped in permanently shadowed craters near the poles, which could provide support for the water needs of a lunar colony, though indications that mercury is also similarly trapped there may pose health concerns. Native

precious metal Precious metals are rare, naturally occurring metallic chemical elements of high Value (economics), economic value. Precious metals, particularly the noble metals, are more corrosion resistant and less reactivity (chemistry), chemically reac ...

s, such as

gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...

silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...

, and probably

platinum Platinum is a chemical element; it has Symbol (chemistry), symbol Pt and atomic number 78. It is a density, dense, malleable, ductility, ductile, highly unreactive, precious metal, precious, silverish-white transition metal. Its name origina ...

, are also concentrated at the lunar poles by electrostatic dust transport. There are only a few materials on the Moon which have been identified to make economic sense to ship directly back to the Earth, which are

helium-3 Helium-3 (3He see also helion) is a light, stable isotope of helium with two protons and one neutron. (In contrast, the most common isotope, helium-4, has two protons and two neutrons.) Helium-3 and hydrogen-1 are the only stable nuclides with ...

(for

fusion power Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions. In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices d ...

) and rare-earth minerals (for

electronics Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...

). Instead, it makes more sense for these materials to be used in-space or being turned into valuable products for export. However, the Moon's lack of atmosphere provides no protection from space radiation or meteoroids, so

lunar lava tube file:Mare Tranquillitatis pit crater.jpg, The Mare Tranquillitatis pit has been associated with a lava tube. Lunar lava tubes are lava tubes on the Moon formed during the eruption of Basalt, basaltic lava flows. When the surface of a lava flow co ...

s have been proposed sites to gain protection. The Moon's low surface gravity is also a concern, as it is unknown whether 1/6g-force, g is enough to maintain human health for long periods. Since the Moon has extreme temperature swings and toxic lunar regolith, it is argued by some that the Moon will not become a place of habitation, but instead attract polluting Primary sector of the economy, extraction and Secondary sector of the economy, manufacturing industries. Furthermore, it has been argued that moving these industries to the Moon could help protect the Earth's environment and allow poorer countries to be released from the shackles of neocolonialism by wealthier countries. In the space colonization framework, the Moon will be transformed into an industrial hub of the Solar System. Interest in establishing a moonbase has increased in the 21st century as an intermediate to Mars colonization. The European Space Agency (ESA) head Johann-Dietrich Wörner, Jan Woerner at the International Astronautical Congress in Bremen, Germany, in October, 2018 proposed cooperation among countries and companies on lunar capabilities, a concept referred to as ''Moonbase#Moon Village, Moon Village''. In a December 2017 Space Policy Directive 1, directive, the First presidency of Donald Trump, first Trump administration steered

to include a lunar mission on the pathway to other beyond Earth orbit (BEO) destinations. In 2023, the U.S. Defense Department started a DARPA lunar programs, study of the necessary infrastructure and capabilities required to develop a moon-based economy over the following ten years. As of 2024, on one side, China, along with other partner countries, has announced its intention to establish the International Lunar Research Station. On the other side, the United States, in collaboration with international partners, is advancing its Artemis program, which includes plans to build Moonbases near the lunar poles, close to permanently shadowed craters, in the 2030s. The Chinese Lunar Exploration Program is seen as a means to bolster China's political influence and support its aspirations for superpower status, while the United States aims to maintain its position as the leading space power.

Lagrange points

Another near-Earth possibility are the stable Earth–Moon Lagrangian point, Lagrange points and , at which point a space colony can float indefinitely. The L5 Society was founded to promote settlement by building space stations at these points.

suggested in 1974 that the stable region around L₅ could fit several thousand floating colonies, and would allow easy travel to and from the colonies due to the shallow effective potential at this point.

Mars

The hypothetical colonization of Mars has received interest from public space agencies and private corporations and has received extensive treatment in science fiction writing, film, and art. While there have been many plans for a Human mission to Mars, human Mars mission, including affordable ones such as Mars Direct, none has been realized as of 2025. Both the United States and China have plans to send humans to Mars sometime in the 2040s, but these plans are not backed with hardware and funding. However,

is currently developing SpaceX Starship, Starship, a Super heavy-lift launch vehicle, super-heavy-lift reusable launch vehicle, with a vision of sending humans to Mars. As of November 2024, the company plans to send five uncrewed Starships to Mars in either 2026 or 2028–2029 launch windows and SpaceX's CEO Elon Musk has repeatingly stated his support for the Mars efforts, both financially and politically. Mars is more suitable for habitation than the Moon, with a stronger gravity, rich amount of materials needed for life, day/night cycle nearly identical to Earth, and a thin atmosphere to protect from Micrometeoroid, micrometeroids. The main disadvantage of Mars compared to the Moon is the six-to-nine-month transit time and the lengthy launch window, which occurs approximately every two years. Without in situ resource utilization, Mars colonization would be nearly impossible as it would require bringing thousands of tons of payload to sustain a handful of astronauts. If Martian materials can be used to make propellant (such as methane with the Sabatier reaction, Sabatier process) and supplies (such as oxygen for crews), the amount of supplies needed to bring to Mars can be greatly reduced. Even then, Mars colonies will not be economically viable in the near term, thus reasons for colonizing Mars will be mostly ideological and prestige-based, such as a desire for freedom.

Other inner Solar System bodies

Mercury

Mercury is rich in metals and volatiles, as well as solar energy. However, Mercury is the Delta-v budget, most energy-consuming body on the Solar System to land for spacecraft launching from Earth, and astronauts there must contend with the extreme temperature differential and radiation. TerraformedMercuryGlobe

Once thought to be a volatile-depleted body like the Moon, Mercury is now known to be volatile-rich, surprisingly richer in volatiles than any other terrestrial body in the inner Solar System. The planet also receives six and a half times the solar flux as the Earth/Moon system, making solar energy an effective energy source; it could be harnessed through orbital solar arrays and beamed to the surface or exported to other planets. Geologist Stephen Gillett suggested in 1996, that this could make Mercury an ideal place to build and launch solar sail spacecraft, which could launch as folded "chunks" by a mass driver from Mercury's surface. Once in space, the solar sails would deploy. Solar energy for the mass driver should be easy to produce, and solar sails near Mercury would have 6.5 times the thrust they do near Earth. This could make Mercury an ideal place to acquire materials useful in building hardware to send to (and terraform) Venus. Vast solar collectors could also be built on or near Mercury to produce power for large-scale engineering activities such as laser-pushed light sails to nearby star systems. As Mercury has essentially no axial tilt, crater floors near its poles lie in crater of eternal darkness, eternal darkness, never seeing the Sun. They function as cold trap (astronomy), cold traps, trapping volatiles for geological periods. It is estimated that the poles of Mercury contain 10¹⁴–10¹⁵ kg of water, likely covered by about 5.65×10⁹ m³ of hydrocarbons. This would make agriculture possible. It has been suggested that plant varieties could be developed to take advantage of the high light intensity and the long day of Mercury. The poles do not experience the significant day-night variations the rest of Mercury do, making them the best place on the planet to begin a colony. Another option is to live underground, where day-night variations would be damped enough that temperatures would stay roughly constant. There are indications that Mercury contains lava tubes, like the Moon and Mars, which would be suitable for this purpose. Underground temperatures in a ring around Mercury's poles can reach room temperature on Earth, 22±1 °C; and this is achieved at depths starting from about 0.7 m. This presence of volatiles and abundance of energy has led Alexander Bolonkin and James Shifflett to consider Mercury preferable to Mars for colonization. Yet a third option could be to continually move to stay on the night side, as Mercury's 176-day-long day-night cycle means that the terminator (solar), terminator travels very slowly. Because Mercury is very dense, its surface gravity is 0.38g like Mars, even though it is a smaller planet. This would be easier to adjust to than lunar gravity (0.16g), but presents advantages regarding lower escape velocity from Mercury than from Earth. Mercury's proximity gives it advantages over the asteroids and outer planets, and its low synodic period means that launch windows from Earth to Mercury are more frequent than those from Earth to Venus or Mars. On the downside, a Mercury colony would require significant shielding from radiation and solar flares, and since Mercury is airless, decompression and temperature extremes would be constant risks.

Venus

Though the surface of Venus is extremely hostile, habitats high above the atmosphere of Venus are fairly habitable, with temperatures ranging from 30 °C to 70 °C (86 to 158 °F) and a pressure similar to the Earth's sea level at an altitude of 50 kilometers (30 miles). However, beside tourism opportunities, the economic benefit of a Venusian colony is minimal.

Asteroid belt

Asteroids can provide enough material in the form of water, air, fuel, metal, soil, and nutrients to support ten to a hundred trillion humans in space. Many asteroids contain minerals that are inheriently valuable, such as rare earths and precious metals. However, low gravity, distance from Earth and disperse nature of their orbits make it difficult to settle on small asteroids.

Giant planets

There have also been proposals to place robotic aerostats in the upper atmospheres of the Solar System's giant planets for exploration and possibly mining of

, which could have a very high value per unit mass as a thermonuclear fuel. Robert Zubrin identified Saturn, Uranus and Neptune as "the Persian Gulf of the Solar System", as the largest sources of deuterium and helium-3 to drive a nuclear fusion, fusion economy, with Saturn the most important and most valuable of the three, because of its relative proximity, low radiation, and large system of moons. On the other hand, planetary scientist John S. Lewis, John Lewis in his 1997 book '' Mining the Sky'', insists that Uranus is the likeliest place to mine helium-3 because of its significantly shallower gravity well, which makes it easier for a laden tanker spacecraft to thrust itself away. Furthermore, Uranus is an ice giant, which would likely make it easier to separate the helium from the atmosphere. Because Uranus has the lowest

of the four giant planets, it has been proposed as a mining site for

. As Uranus is a gas giant without a viable surface, one of Uranus's natural satellites might serve as a base. It is hypothesized that one of Neptune's satellites could be used for colonization. Triton (moon), Triton's surface shows signs of extensive geological activity that implies a subsurface ocean, perhaps composed of ammonia/water. If technology advanced to the point that tapping such geothermal energy was possible, it could make colonizing a cryogenic world like Triton feasible, supplemented by nuclear fusion power.

Moons of outer planets

Human missions to the outer planets would need to arrive quickly due to the effects of space radiation and microgravity along the journey. In 2012, Thomas B. Kerwick wrote that the distance to the outer planets made their human exploration impractical for now, noting that travel times for round trips to Mars were estimated at two years, and that the closest approach of Jupiter to Earth is over ten times farther than the closest approach of Mars to Earth. However, he noted that this could change with "significant advancement on spacecraft design". Nuclear thermal rocket, Nuclear-thermal or nuclear-electric engines have been suggested as a way to make the journey to Jupiter in a reasonable amount of time. Another possibility would be plasma Magnetic sail, magnet sails, a technology already suggested for rapidly sending a probe to Jupiter. The cold would also be a factor, necessitating a robust source of heat energy for spacesuits and bases. Most of the larger moons of the outer planets contain Ice, water ice, liquid water, and organic compounds that might be useful for sustaining human life. Robert Zubrin has suggested Saturn, Uranus, and Neptune as advantageous locations for colonization because their atmospheres are good sources of fusion fuels, such as deuterium and

. Zubrin suggested that Saturn would be the most important and valuable as it is the closest and has an extensive satellite system. Jupiter's high gravity makes it difficult to extract gases from its atmosphere, and its strong radiation belt makes developing its system difficult. On the other hand, fusion power has yet to be achieved, and fusion power from helium-3 is more difficult to achieve than conventional deuterium–tritium fusion. Jeffrey Van Cleve, Carl Grillmair, and Mark Hanna instead focus on Uranus, because the delta-v required to get helium-3 from the atmosphere into orbit is half that needed for Jupiter, and because Uranus' atmosphere is five times richer in helium than Saturn's. Jupiter's Galilean moons (Io, Europa, Ganymede, and Callisto) and Saturn's Titan (moon), Titan are the only moons that have gravities comparable to Earth's Moon. The Moon has a 0.17g gravity; Io, 0.18g; Europa, 0.13g; Ganymede, 0.15g; Callisto, 0.13g; and Titan, 0.14g. Neptune's Triton (moon), Triton has about half the Moon's gravity (0.08g); other planetary-mass moon, round moons provide even less (starting from Uranus' Titania (moon), Titania and Oberon (moon), Oberon at about 0.04g).

Jovian moons

The Jupiter, Jovian system in general has particular disadvantages for colonization, including a deep gravity well. The magnetosphere of Jupiter bombards the moons of Jupiter with intense ionizing radiation delivering about 36 Sievert#Dose examples, Sv per day to unshielded colonists on Io (moon), Io and about 5.40 Sv per day on Europa (moon), Europa. Exposure to about 0.75 Sv over a few days is enough to cause Acute radiation syndrome, radiation poisoning, and about 5 Sv over a few days is fatal. Jupiter itself, like the other gas giants, has further disadvantages. There is no accessible surface on which to land, and the light hydrogen atmosphere would not provide good buoyancy for some kind of aerial habitat as has been proposed for Venus. Radiation levels on Io (moon), Io and Europa (moon), Europa are extreme, enough to kill unshielded humans within an Earth day. Therefore, only Callisto (moon), Callisto and perhaps Ganymede (moon), Ganymede could reasonably support a human colony. Callisto orbits outside Jupiter's radiation belt. Ganymede's low latitudes are partially shielded by the moon's magnetic field, though not enough to completely remove the need for radiation shielding. Both of them have available water, silicate rock, and metals that could be mined and used for construction. Although Io's volcanism and tidal heating constitute valuable resources, exploiting them is probably impractical. Europa is rich in water (its subsurface ocean is expected to contain over twice as much water as all Earth's oceans together) and likely oxygen, but metals and minerals would have to be imported. If alien microbial life exists on Europa, human immune systems may not protect against it. Sufficient radiation shielding might, however, make Europa an interesting location for a research base. The private ''Artemis Project'' drafted a plan in 1997 to colonize Europa, involving surface igloos as bases to drill down into the ice and explore the ocean underneath, and suggesting that humans could live in "air pockets" in the ice layer. Ganymede and Callisto are also expected to have internal oceans. It might be possible to build a surface base that would produce fuel for further exploration of the Solar System. In 2003, NASA performed a study called ''HOPE'' (Revolutionary Concepts for Human Outer Planet Exploration) regarding the future exploration of the Solar System. The target chosen was Callisto (moon), Callisto due to its distance from Jupiter, and thus the planet's harmful radiation. It could be possible to build a surface base that would produce fuel for further exploration of the Solar System. HOPE estimated a round trip time for a crewed mission of about 2–5 years, assuming significant progress in propulsion technologies. Io (moon), Io is not ideal for colonization, due to its hostile environment. The moon is under influence of high tidal forces, causing high volcanic activity. Jupiter's strong radiation belt overshadows Io, delivering 36 Sv a day to the moon. The moon is also extremely dry. Io is the least ideal place for the colonization of the four Galilean moons. Despite this, its volcanoes could be energy resources for the other moons, which are better suited to colonization. Currents in Jovian Magnetosphere

Ganymede (moon), Ganymede is the largest moon in the Solar System. Ganymede is the only moon with a magnetosphere, albeit overshadowed by Magnetosphere of Jupiter, Jupiter's magnetic field. Because of this magnetic field, Ganymede is one of only two Jovian moons where surface settlements would be feasible because it receives about 0.08 Sievert, Sv of radiation per day. Ganymede could be terraformed. The Keck Observatory announced in 2006 that the binary Jupiter trojan 617 Patroclus, and possibly many other Jupiter trojans, are likely composed of water ice, with a layer of dust. This suggests that mining water and other volatiles in this region and transporting them elsewhere in the Solar System, perhaps via the proposed Interplanetary Transport Network, may be feasible in the not-so-distant future. This could make colonization of the Moon, Colonization of Mercury, Mercury and main-belt Colonization of the asteroids, asteroids more practical.

Saturn

Saturn's radiation belt is much weaker than Jupiter's, so radiation is less of an issue here. Dione, Rhea, Titan, and Iapetus all orbit outside the radiation belt, and Titan's thick atmosphere would adequately shield against cosmic radiation. Saturn has seven moons planetary-mass moon, large enough to be round: in order of increasing distance from Saturn, they are Mimas (moon), Mimas, Enceladus, Tethys (moon), Tethys, Dione (moon), Dione, Rhea (moon), Rhea, Titan (moon), Titan, and Iapetus (moon), Iapetus.

=Enceladus

= The small moon Enceladus is also of interest, having a subsurface ocean that is separated from the surface by only tens of meters of ice at the south pole, compared to kilometers of ice separating the ocean from the surface on Europa. Volatile and organic compounds are present there, and the moon's high density for an ice world (1.6 g/cm³) indicates that its core is rich in silicates. On 9 March 2006,

's ''Cassini–Huygens, Cassini'' space probe found possible evidence of liquid water on Enceladus. According to that article, "pockets of liquid water may be no more than tens of meters below the surface." These findings were confirmed in 2014 by NASA. This means liquid water could be collected much more easily and safely on Enceladus than, for instance, on Europa (see above). Discovery of water, especially liquid water, generally makes a celestial body a much more likely candidate for colonization. An alternative model of Enceladus's activity is the decomposition of methane/water clathrates – a process requiring lower temperatures than liquid water eruptions. The higher density of Enceladus indicates a larger than Saturnian average silicate core that could provide materials for base operations.

=Titan

= Authors like Robert Zubrin have offered that Saturn is the most important and valuable of the four gas giants in the

, because of its relative proximity, low radiation, and excellent system of moons. He named Titan as the best candidate on which to establish a base to exploit the resources of the Saturn system. He pointed out that Titan possesses an abundance of all the elements necessary to support life, saying "In certain ways, Titan is the most hospitable extraterrestrial world within our solar system for human colonization." To consider a colony on Saturn's largest moon Titan (moon), Titan, protection against the extreme cold must be a primary consideration. Titan offers a gravity of approximately 1/7 of Earth gravity, in the same range as Earth's Moon. Atmospheric pressure at the surface of the planet is about 1.5x that of the surface of the Earth; there is however, no oxygen present in the environment. The atmosphere is about 95% nitrogen and 5% methane. Some estimates suggest that abundant energy resources on Titan could power a colony with a population size of the United States. The dense atmosphere of Titan shields the surface from radiation and would make any structural failures problematic, rather than catastrophic. With an oxygen mask and thermal clothing protection, humans could roam Titan's surface in the dim sunlight. Or, given the low gravity and dense atmosphere, they could float above it in a balloon or on personal wings.

Trans-Neptunian region

Beyond the Solar System

Beyond the Solar System colonization targets might be identified in the List of nearest stars, surrounding stars. The main difficulty is the vast distances to other stars. To reach such targets travel times of millennia would be necessary, with current technology. At average speeds of even 0.1% of the speed of light (''c'') interstellar expansion across the entire Milky Way galaxy would take up to one-half of the Sun's galactic orbital period of ~240,000,000 years, which is comparable to the timescale of other galactic processes. Due to fundamental energy and reaction mass consideration such speeds would be with current technology limited to small spaceships. If humanity would gain access to a large amount of energy, on the order of the mass-energy of entire planets, it may become possible to construct spaceships with Alcubierre drives. The following are plausible approaches with current technology: * A generation ship which would travel much slower than light, with consequent interstellar trip times of many decades or centuries. The crew would go through generations before the journey was complete, so none of the initial crew would be expected to survive to arrive at the destination, assuming current human lifespans. * A sleeper ship, where most or all of the crew spend the journey in some form of hibernation or suspended animation, allowing some or all to reach the destination. * An embryo space colonization, embryo-carrying interstellar starship (EIS), much smaller than a generation ship or sleeper ship, transporting human embryos or DNA in a frozen or dormant state to the destination. (Obvious biological and psychological problems in birthing, raising, and educating such voyagers, neglected here, may not be fundamental.) * A nuclear fusion or nuclear fission, fission powered ship (e.g. ion drive) of some kind, achieving velocities of up to perhaps 10% ''c'' permitting one-way trips to nearby stars with durations comparable to a human lifetime. * A Project Orion (nuclear propulsion), Project Orion-ship, a nuclear-powered concept proposed by Freeman Dyson which would use nuclear bomb, nuclear explosions to propel a starship. A special case of the preceding nuclear rocket concepts, with similar potential velocity capability, but possibly easier technology. * Solar sail, Laser propulsion concepts, using some form of beaming of power from the Solar System might allow a solar sail, light-sail or other ship to reach high speeds, comparable to those theoretically attainable by the fusion-powered electric rocket, above. These methods would need some means, such as supplementary nuclear propulsion, to stop at the destination, but a hybrid (light-sail for acceleration, fusion-electric for deceleration) system might be possible. * Mind uploading, Uploaded human minds or artificial intelligence may be transmitted via radio or laser at light speed to interstellar destinations where self-replicating spacecraft have traveled subluminally and set up infrastructure and possibly also brought some minds. Extraterrestrial intelligence might be another viable destination.

Intergalactic travel

The distances between galaxies are on the order of a million times farther than those between the stars, and thus intergalactic colonization would involve voyages of millions of years via special self-sustaining methods.

Implementation

Building colonies in space would require access to water, food, space, people, construction materials, energy, transportation, communications, life support system, life support, simulated gravity, radiation protection, migration, governance and capital investment. It is likely the colonies would be located near the necessary physical resources. The practice of space architecture seeks to transform spaceflight from a heroic test of human endurance to a normality within the bounds of comfortable experience. As is true of other frontier-opening endeavors, the capital investment necessary for space colonization would probably come from governments, an argument made by John Hickman and Neil deGrasse Tyson.

Life support

In space settlements, a life support system must recycle or import all the nutrients without "crashing." The closest terrestrial analogue to space life support is possibly that of a nuclear submarine. Nuclear submarines use mechanical life support systems to support humans for months without surfacing, and this same basic technology could presumably be employed for space use. However, nuclear submarines run "open loop"—extracting oxygen from seawater, and typically dumping carbon dioxide overboard, although they recycle existing oxygen. Another commonly proposed life-support system is a closed ecological system such as Biosphere 2.

Solutions to health risks

Although there are many physical, mental, and emotional health risks for future colonists and pioneers, solutions have been proposed to correct these problems. Mars500, HI-SEAS, and SMART-OP represent efforts to help reduce the effects of loneliness and confinement for long periods of time. Keeping contact with family members, celebrating holidays, and maintaining cultural identities all had an impact on minimizing the deterioration of mental health. There are also health tools in development to help astronauts reduce anxiety, as well as helpful tips to reduce the spread of germs and bacteria in a closed environment. Radiation risk may be reduced for astronauts by frequent monitoring and focusing work to minimize time away from shielding. Future space agencies can also ensure that every colonist would have a mandatory amount of daily exercise to prevent degradation of muscle.

Radiation protection

Cosmic rays and solar flares create a lethal radiation environment in space. In orbit around certain planets with magnetospheres (including Earth), the Van Allen belts make living above the atmosphere difficult. To protect life, settlements must be surrounded by sufficient mass to absorb most incoming radiation, unless magnetic or plasma radiation shields are developed.Spacecraft Shielding
engineering.dartmouth.edu. Retrieved 3 May 2011. In the case of Van Allen belts, these could be drained using orbiting tethers or radio waves. Passive mass shielding of four metric tons per square meter of surface area will reduce radiation dosage to several Sievert#Yearly dose examples, mSv or less annually, well below the rate of some populated Background radiation#Natural background radiation, high natural background areas on Earth. This can be leftover material (slag) from processing lunar soil and asteroids into oxygen, metals, and other useful materials. However, it represents a significant obstacle to manoeuvering vessels with such massive bulk (mobile spacecraft being particularly likely to use less massive active shielding). Inertia would necessitate powerful thrusters to start or stop rotation, or electric motors to spin two massive portions of a vessel in opposite senses. Shielding material can be stationary around a rotating interior.

Psychological adjustment

The monotony and loneliness that comes from a prolonged space mission can leave astronauts susceptible to cabin fever or having a psychotic break. Moreover, lack of sleep, fatigue, and work overload can affect an astronaut's ability to perform well in an environment such as space where every action is critical.

Law, governance, and sovereignty

A range of different models of transplanetary or extraterrestrial governance have been sketched or proposed. Often envisioning the need for a fresh or independent extraterrestrial governance, particularly in the void left by the contemporarily criticized lack of space governance and inclusivity. It has been argued that space colonialism would, similarly to terrestrial

, produce colonial national identities. Federalism has been studied as a remedy of such distant and autonomous communities. Space activity is legally based on the

, the main international treaty. But

has become a larger legal field, which includes other international agreements such as the significantly less ratified

Moon Treaty The Agreement Governing the Activities of States on the Moon and Other Celestial Bodies,terra nullius ''Terra nullius'' (, plural ''terrae nullius'') is a Latin expression meaning " nobody's land". Since the nineteenth century it has occasionally been used in international law as a principle to justify claims that territory may be acquired ...

'' but as ''res communis'', which subsequently influenced the work of the United Nations Committee on the Peaceful Uses of Outer Space.

Economics

Space colonization can roughly be said to be possible when the necessary methods of space colonization become Economic behavior, cheap enough (such as space access by cheaper launch systems) to meet the cumulative funds that have been gathered for the purpose, in addition to estimated profits from

Overcoming access-to-space barriers

Although there are no immediate prospects for the large amounts of money required for space colonization to be available given traditional launch costs, there is some prospect of a radical reduction to launch costs in the 2010s, which would consequently lessen the cost of any efforts in that direction. With a published price of million per launch of up to payload to low Earth orbit,

Falcon 9 rockets are already the "cheapest in the industry". Advancements currently being developed as part of the SpaceX reusable launch system development program to enable reusable Falcon 9s "could drop the price by an order of magnitude, sparking more space-based enterprise, which in turn would drop the cost of access to space still further through economies of scale." If SpaceX is successful in developing the reusable technology, it would be expected to "have a major impact on the cost of access to space", and change the increasingly competition (economics), competitive market in space launch services. The President's Commission on Implementation of United States Space Exploration Policy suggested that an Inducement prize contest, inducement prize should be established, perhaps by government, for the achievement of space colonization, for example by offering the prize to the first organization to place humans on the Moon and sustain them for a fixed period before they return to Earth.

Money and currency

Experts have debated on the possible use of money and currencies in societies that will be established in space. The Quasi Universal Intergalactic Denomination, or QUID, is a physical currency made from a space-qualified polymer Polytetrafluoroethylene, PTFE for inter-planetary travelers. QUID was designed for the foreign exchange company Travelex by scientists from Britain's National Space Centre and the University of Leicester. Other possibilities include the incorporation of cryptocurrency as the primary form of currency, as suggested by Elon Musk.

Socio-economic issues

Human spaceflight has enabled only temporarily relocating a few privileged people and no permanent space migrants. The societal motivation for space migration has been questioned as rooted in colonialism, questioning the fundamentals and inclusivity of space colonization. Highlighting the need to reflect on such socio-economic issues beside the technical challenges for implementation.

Resources

Raw materials

Colonies on the Moon, Mars, asteroids, or the metal-rich planet Mercury (planet), Mercury, could extract local materials. The Moon is deficient in Volatile (astrogeology), volatiles such as argon, helium and compounds of carbon, hydrogen and nitrogen. The LCROSS impacter was targeted at the Cabeus (crater), Cabeus crater which was chosen as having a high concentration of water for the Moon. A plume of material erupted in which some water was detected. Mission chief scientist Anthony Colaprete estimated that the Cabeus crater contains material with 1% water or possibly more. Water

should also be in other permanently shadowed craters near the lunar poles. Although helium is present only in low concentrations on the Moon, where it is deposited into regolith by the solar wind, an estimated million tons of He-3 exists over all. It also has industrially significant oxygen, silicon, and metals such as iron, aluminium, and titanium. Launching materials from Earth is expensive, so bulk materials for colonies could come from the Moon, a near-Earth object (NEO), Phobos (moon), Phobos, or Deimos (moon), Deimos. The benefits of using such sources include: a lower gravitational force, no Drag (physics), atmospheric drag on cargo vessels, and no biosphere to damage. Many NEOs contain substantial amounts of metals. Underneath a drier outer crust (much like oil shale), some other NEOs are inactive comets which include billions of tons of water ice and kerogen hydrocarbons, as well as some nitrogen compounds. Farther out, Colonization of the outer Solar System#Jupiter trojans, Jupiter's Trojan asteroids are thought to be rich in water ice and other volatiles. Recycling of some raw materials would almost certainly be necessary.

Energy

Solar energy in orbit is abundant, reliable, and is commonly used to power satellites today. There is no night in free space, and no clouds or atmosphere to block sunlight. Light intensity obeys an inverse-square law. So the solar energy available at distance ''d'' from the Sun is ''E'' = 1367/''d''² W/m², where ''d'' is measured in astronomical units (AU) and 1367 watts/m² is the energy available at the distance of Earth's orbit from the Sun, 1 AU. In the weightlessness and vacuum of space, high temperatures for industrial processes can easily be achieved in solar ovens with huge parabolic reflectors made of metallic foil with very lightweight support structures. Flat mirrors to reflect sunlight around radiation shields into living areas (to avoid line-of-sight access for cosmic rays, or to make the Sun's image appear to move across their "sky") or onto crops are even lighter and easier to build. Large solar power photovoltaic cell arrays or thermal power plants would be needed to meet the electrical power needs of the settlers' use. In developed parts of Earth, electrical consumption can average 1 kilowatt/person (or roughly 10 watt-hour, megawatt-hours per person per year.) These power plants could be at a short distance from the main structures if wires are used to transmit the power, or much farther away with wireless power transmission. A major export of the initial space settlement designs was anticipated to be large solar power satellites (SPS) that would use wireless power transmission (phase-locked microwave beams or lasers emitting wavelengths that special solar cells convert with high efficiency) to send power to locations on Earth, or to colonies on the Moon or other locations in space. For locations on Earth, this method of getting power is extremely benign, with zero emissions and far less ground area required per watt than for conventional solar panels. Once these satellites are primarily built from lunar or asteroid-derived materials, the price of SPS electricity could be lower than energy from fossil fuel or nuclear energy; replacing these would have significant benefits such as the elimination of greenhouse gases and nuclear waste from electricity generation. Transmitting solar energy wirelessly from the Earth to the Moon and back is also an idea proposed for the benefit of space colonization and energy resources. Physicist Dr. David Criswell, who worked for NASA during the Apollo missions, proposed the idea of using power beams to transfer energy from space. These beams, microwaves with a wavelength of about 12 cm, would be almost untouched as they travel through the atmosphere. They could also be aimed at more industrial areas to keep away from humans or animal activities. This would allow for safer and more reliable methods of transferring solar energy. In 2008, scientists were able to send a 20 watt microwave signal from a mountain on the island of Maui to the island of Hawaii. Since then JAXA and Mitsubishi have been working together on a $21 billion project to place satellites in orbit which could generate up to 1 gigawatt of energy. These are the next advancements being done today to transmit energy wirelessly for space-based solar energy. However, the value of SPS power delivered wirelessly to other locations in space will typically be far higher than to Earth. Otherwise, the means of generating the power would need to be included with these projects and pay the heavy penalty of Earth launch costs. Therefore, other than proposed demonstration projects for power delivered to Earth, the first priority for SPS electricity is likely to be locations in space, such as communications satellites, fuel depots or "orbital tugboat" boosters transferring cargo and passengers between low Earth orbit (LEO) and other orbits such as geosynchronous orbit (GEO), lunar orbit or Highly elliptical orbit, highly-eccentric Earth orbit (HEEO). The system will also rely on satellites and receiving stations on Earth to convert the energy into electricity. Because this energy can be transmitted easily from dayside to nightside, power would be reliable 24/7. Nuclear power is sometimes proposed for colonies located on the Moon or on Mars, as the supply of solar energy is too discontinuous in these locations; the Moon has nights of two Earth weeks in duration. Mars has nights, relatively high gravity, and an atmosphere featuring Climate of Mars#Effect of dust storms, large dust storms to cover and degrade solar panels. Also, Mars' greater distance from the Sun (1.52 astronomical units, AU) means that only ''1/1.52²'' or about 43% of the solar energy is available at Mars compared with Earth orbit. Another method would be transmitting energy wirelessly to the lunar or Martian colonies from solar power satellites (SPSs) as described above; the difficulties of generating power in these locations make the relative advantages of SPSs much greater there than for power beamed to locations on Earth. In order to also be able to fulfill the requirements of a Moon base and energy to supply life support, maintenance, communications, and research, a combination of both nuclear and solar energy may be used in the first colonies. For both solar thermal and nuclear power generation in airless environments, such as the Moon and space, and to a lesser extent the very thin Martian atmosphere, one of the main difficulties is dispersing the Carnot cycle, inevitable heat generated. This requires fairly large radiator areas.

Self-sustainment

In situ manufacturing

Space manufacturing could enable self-replication. Some consider it the ultimate goal because it would allow an exponential growth, exponential increase in colonies, while eliminating costs to, and dependence on, Earth. It could be argued that the establishment of such a colony would be Earth's first act of self-replication. Intermediate goals include colonies that expect only information from Earth (science, engineering, entertainment) and colonies that just require periodic supply of light weight objects, such as integrated circuits, medicines, DNA, genetic material and tools.

Sustaining a population

In 2002, the Anthropology, anthropologist John H. Moore estimated that a population of 150–180 would permit a stable society to exist for 60 to 80 generations—equivalent to 2,000 years. Assuming a journey of 6,300 years, the astrophysicist Frédéric Marin and the particle physicist Camille Beluffi calculated that the minimum viable population for a generation ship to reach Proxima Centauri would be 98 settlers at the beginning of the mission (then the crew will breed until reaching a stable population of several hundred settlers within the ship). In 2020, Jean-Marc Salotti proposed a method to determine the minimum number of settlers to survive on an extraterrestrial world. It is based on the comparison between the required time to perform all activities and the working time of all human resources. For Mars, 110 individuals would be required.

Advocacy

Several private companies have announced plans toward the colonization of Mars. Among entrepreneurs leading the call for space colonization are Elon Musk, Dennis Tito and Bas Lansdorp.

Involved organizations

Organizations that advocate for space colonization include: * Blue Origin and Jeff Bezos are pursuing plans for space colonization starting with a base on the moon. Blue Origin is developing the New Glenn launcher to significantly reduce access to space cost with use of a re-useable booster and is building the Blue Moon lunar lander. * The Mars Society promotes Robert Zubrin's Mars Direct plan and the settlement of Mars. * The National Space Society (NSS) is an organization with the vision of people living and working in thriving communities beyond the Earth. The NSS also maintains an extensive library of full-text articles and books on space settlement. * The Space Frontier Foundation performs space advocacy including strong free market, capitalism, capitalist views about space development. * The Space Settlement Institute is searching for ways to make space colonization happen within a lifetime. *

is developing extensive SpaceX Mars transportation infrastructure, spaceflight transportation infrastructure with the express purpose of enabling long-term human settlement of Mars. * The Space Studies Institute funds the study of outer space settlements, especially O'Neill cylinders. * The Alliance to Rescue Civilization plans to establish

s of human civilization on the Moon and other locations away from Earth. * The British Interplanetary Society (BIS) promotes ideas for the exploration and use of space, including a Project Boreas, Mars colony, future propulsion systems (see Project Daedalus), terraforming, and locating other habitable worlds. In June 2013 the BIS began the SPACE project to re-examine Gerard O'Neill's 1970s space colony studies in light of the advances made since then. The progress of this effort were detailed in a special edition of the BIS journal in September 2019. * Asgardia (nation) – an organization searching to circumvent limitations placed by

. *The Cyprus Space Exploration Organisation promotes space exploration and colonization, and fosters collaboration in space.

Experiments with terrestrial analogues

Many space agency, space agencies build "testbeds", which are facilities on Earth for testing advanced life support systems, but these are designed for long duration human spaceflight, not permanent colonization. *The most famous attempt to build an analogue to a self-sufficient settlement is Biosphere 2, which attempted to duplicate Earth's biosphere. *BIOS-3 is another closed ecosystem, completed in 1972 in Krasnoyarsk, Siberia. *The Mars Desert Research Station has a habitat for similar reasons, but the surrounding climate is not strictly inhospitable. *Devon Island Flashline Mars Arctic Research Station, Mars Arctic Research Station, can also provide some practice for off-world outpost construction and operation.

Influence of science fiction

Space colonization is a recurring theme in science fiction. NASA began to assess space colonization issues as early as 1975 with their Space Settlements Design Study. The report directly acknowledges the foundation of various ideas for colonization in science fiction. It quotes author Robert Salkeld and highlights the role of the precursors of science fiction alongside the founders of astronautics, where for example Jules Verne rubs shoulders with Constantin Tsiolkovsky. Indeed, colonization as a fictional theme and colonization as a research project are not independent. Research feeds fiction and fiction sometimes inspires research. Many of the most fascinating ideas in science originated not in the laboratory but in the minds of such science fiction writers as Arthur C. Clarke and Ray Bradbury. Clarke's 1945 article on communications satellites was the original idea behind modern communications satellites. Bradbury's The Martian Chronicles explores the exploration and settlement of Mars and has been attributed as the main inspiration behind NASA's many missions to Mars. Communicators and tricorders from the science fiction of Star Trek are said to be inspirations for cell phones and wireless medical triage devices. Fiction inspired innovation and invention to develop new technologies. Communications, governance principles, and advanced technological devices, all speculated by science fiction, are all precursors to survival of an extraterrestrial colony. The European Space Agency ITSF project (Innovative Technologies in Science Fiction for Space Applications) study offers similar consideration for the cross-fertilization between fiction and science. Science fiction writer Norman Spinrad highlights the role of science fiction as a visionary force that spawned the conquest of space, a term he believes betrays its imperialist tendencies, and the colonization of space. He also shows that political scientist and science fiction writer Jerry Pournelle, in wanting to revive the conquest of space for this purpose in the early 1980s, actually launched the Reagan administration's Strategic Defense Initiative project, which he considers a failure, because instead of the military program reviving the space program, the opposite happens: the $40 billion cost of the program is actually taken away from the construction of a base on the Moon. One of the great names in science fiction, Arthur C. Clarke, a supporter of Marshall Savage's ideas, announced in a 2001 article, the date appearing in one of his most famous titles 2001: A Space Odyssey, that by 2057 there would be humans on the Moon, Mars , Europa, Ganymede, Titan and in orbit around Venus, Neptune and Pluto. Contemporary science fiction has extended the colonization vision further. The TV series The Expanse (TV series), The Expanse which is based on a series of novels of the same name by James S. A. Corey, addresses the politics and conflict of humanity hundreds of years in the future after it has colonized the solar system and Mars has become an independent military power. In Theresa Hutchin's essay on the series in 2021, comparisons are drawn between the fiction of the story and the reality of current corporate led development of space exploration activities.