Space colonization

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Space colonization is the process of establishing human settlements beyond Earth for prestige, commercial or strategic benefit,^[3] in contrast to space exploration for scientific benefit. Colonialism in this sense is multi-dimensional, including the exploitation of labor, resources and rights.

While there have been initiatives to start space colonization programs in the past, none have been feasible due to the extreme cost of space launch. As reusable launch systems are becoming the norm in the 2020s, launch cost will decrease and colonization projects will become feasible. Space colonization is likely to begin with the establishment of a lunar base with either United States's Artemis Base Camp or China's International Lunar Research Station.^[3] While SpaceX, the main launch provider for NASA, has expressed interest in establishing a Mars base, SpaceX is currently contracted to perform lunar landings for the Artemis program and has no detailed plans for a Mars base.^[4] The first entity to have a Moon base will have an immense first-mover advantage to the point of shaping human history and geopolitics in the 21st century. However, collaboration can also be extremely beneficial to all entities.^[3]

In the near term, the Moon is believed to contain various types of metal and rare earth metals, which can be mass-extracted in space without causing environmental damage on Earth. Space manufacturing would allow human organs to be 3D printed and exotic pharmaceuticals to be produced which have the potential to improve healthcare. However, the great potential of space colonization would be the many unknown technological, economic and societal advancements that can be made with space bases.^[3] Once lunar or Mars-based infrastructure is sufficiently well-developed, other bodies in the Solar System could be subject to human colonization and exploitation, making humans a multiplanetary species.^[5]

Space colonization is an important topic in academic debates across many disciplines. Space colonization will ensure human survival in case of a planetary disaster and accessing space resources to expand society, but it could also benefit the ruling class like traditional colonialism and worsen existing problems like war, economic inequality, and environmental damage.^[6][7][8] There has been calls to halt space colonization process before major social issues are solved,^[9] but the momentum of United States and Chinese space program have made this less viable.

As Christopher Wanjek pointed out, space colonization is a project that require political goodwill and great sums of money. There are three main reasons why a nation or benefactor might sponsor such a project: prestige, militaristic, or economic. These reasons, combined with lower costs, hedged risks, and increased returns could enable settlement and trade, could potentially lead to a successful large-scale colonization effort beyond a few small habitats like in Antarctica.^{[10]: 10–15}

Until the 2010s, space travel was extremely expensive because expendable launch vehicles, making the cost of each launch equal to the manufacturing cost of a launch vehicle. With the development of reusable launch vehicle, the manufacturing cost is amortised and with multiple flights the only significant costs are propellant and operational cost. When space launch cost decreases, the cost of space hardware will significantly decrease, which would allow more payload and astronauts to be sent to space.^{[11]: 21–25} In addition, most of the delta-v budget, and thus propellant, is in bringing a spacecraft to low Earth orbit.^[10]: 100 This is the main reason why Jerry Pournelle said "If you can get your ship into orbit, you're halfway to anywhere".^[12]

The major advantages to construct a space habitat 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. Thus, outer space will not be a destination by itself, but as a place to host space infrastructures and an exploitation point for the service industry. Space colonization eventually will 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.^{[10]: 142–147}

As of 2024, both China and the United States plan to establish scientific Moonbases at the poles near permanently shadowed craters in the 2030s. The Chinese Lunar Exploration Program aims to bolster its political influence and enhance its bid for superpower status, and the United States’ Artemis program seeks to maintain its position as the leading space power. A prestige imperative means that converting a scientific Moonbase into a Moon colony is likely to receive political and financial support.^{[10]: 154–158}

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.^[10]: 175 There are only a few materials on the Moon which make economic sense to ship directly back to the Earth, which are helium-3 (for fusion power) and rare-earth minerals (for electronics). Instead, it makes more sense for these materials to be used in-space or being turned into valuable products for export. Since the Moon has extreme temperature swings and toxic lunar regolith, it is likely that the Moon will not a place of habitation, but instead attract polluting extraction and manufacturing industries. Moving these industries to the Moon will help protect the Earth's environment and allow poorer countries to be released from the shackles of neocolonialism by wealther countries. In the space colonization framework, the Moon will be transformed into an industrial hub of the Solar System.^{[10]: 161–172}

While there has been many plans for a human Mars mission, including affortable ones such as Mars Direct, none has been realized as of 2024. Both the United States and China has plans to send humans to Mars sometime in the 2040s, but these plans are backed with hardware and funding.^{[10]: 219–223} However, SpaceX is currently developing Starship, a 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^[14] and SpaceX's CEO Elon Musk has repeatingly stated to back the Mars efforts financially and politically.^[15]

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 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.^[10]: 175 Without in situ resource utlization, 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 process) and supplies (such as oxygen for crews), the amount of supplies needed to bring to Mars can be greatly reduced.^{[10]: 228–230} 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.^{[10]: 267–270, 280}

Once Earth orbit becomes a gateway point for spaceships, the Moon becomes an industrial hub and Mars becoming a place for space settlement, settling on other bodies in the Solar System become more attractive. These bodies are ordered based on economic feasibility.

• Asteroids: 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.^{[10]: 203, 204, 218}
• Venus: Though the surface of Venus is extremely hostile, habitats high above the atmosphere of Venus are fairly habitable, with a temperature of around 50°C and a pressure similar to the Earth's sea level. However, beside tourism opportunities, the economic benefit of a Venusian colonies is minimal.^{[10]: 308–310}
• Titan: Among all moons around Saturn, Titan is the most attractive to colonization because of its dense atmosphere and vast lakes of hydrocarbons. The biggest challenges for colonists are the distance from Earth, extreme cold, low gravity and the lack of solar energy on the surface.^{[10]: 320–326}
• Galilean moons around Jupiter: Radiation levels on Io and Europa are extreme, enough to kill unshielded humans within an Earth day.^[16] Therefore, only Callisto and perhaps Ganymede could reasonably support a human colony. Callisto orbits outside Jupiter's radiation belt.^[17] However, due to the extreme radiation and these moons do not contain precious minerals, it might be more practical to setup an orbiting space hub around Jupiter and visit these moons only briefly.^{[10]: 318–319}
• Mercury: Mercury is rich of metals and volatiles, as well as solar energy. However, Mercury is the 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.^{[10]: 311–314}
• Moons of Uranus and Neptune, and trans-Neptunian objects: Due to the lack of scienfific knowledge, it is unknown whether settling on these worlds are feasible and economically viable.^[10]: 333

When the first space flight programs commenced, they partly used – and have continued to use – colonial spaces on Earth, such as places of indigenous peoples at the RAAF Woomera Range Complex, Guiana Space Centre or contemporarily for astronomy at the Mauna Kea telescope.^[18][19][20] When orbital spaceflight was achieved in the 1950s colonialism was still a strong international project, e.g. easing the United States to advance its space program and space in general as part of a "New Frontier".^[21]

At the same time of the beginning of the Space Age, decolonization gained again in force, producing many newly independent countries. These newly independent countries confronted spacefaring countries, demanding an anti-colonial stance and regulation of space activity when space law was raised and negotiated internationally. Fears of confrontations because of land grabs and an arms race in space between the few countries with spaceflight capabilities grew and were ultimately shared by the spacefaring countries themselves.^[22] This produced the wording of the agreed on international space law, starting with the Outer Space Treaty of 1967, calling space a "province of all mankind" and securing provisions for international regulation and sharing of outer space.

The advent of geostationary satellites raised the case of limited space in outer space. A group of equatorial 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 geostationary orbit is a limited natural resource and belongs to the equatorial countries directly below, seeing it not as part of outer space, humanity's common. Through this, the declaration challenged the dominance of geostationary orbit by spacefaring countries through identifying their dominance as imperialistic. Furthermore this dominance in space has foreshadowed threats to the Outer Space Treaty guaranteed accessibility to space, as in the case of space debris which is ever increasing because of a lack of access regulation.^[23][24][25]

In 1977, the first sustained space habitat, the Salyut 6 station, was put into Earth's orbit. Eventually the first space stations were succeeded by the ISS, today's largest human outpost in space and closest to a space settlement. Built and operated under a multilateral regime, it has become a blueprint for future stations, such as around and possibly on the Moon.^[26][27] An international regime for lunar activity was demanded by the international Moon Treaty, but is currently developed multilaterally as with the Artemis Accords.^[28][29] The only habitation on a different celestial body so far have been the temporary habitats of the crewed lunar landers. Similar to the Artemis program, China is leading an effort to develop a lunar base called the International Lunar Research Station beginning in the 2030s.

In the first half of the 17th century John Wilkins suggested in A Discourse Concerning a New Planet that future adventurers like Francis Drake and Christopher Columbus might reach the Moon and allow people to live there.^[30] The first known work on space colonization was the 1869 novella The Brick Moon by Edward Everett Hale, about an inhabited artificial satellite.^[31] In 1897, Kurd Lasswitz also wrote about space colonies. The Russian rocket science pioneer Konstantin Tsiolkovsky 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.^[32] Tsiolkovsky believed that going into space would help perfect human beings, leading to immortality and peace.^[33] One of the first to speak about space colonization was Cecil Rhodes 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".^[34] In the 1920s John Desmond Bernal, Hermann Oberth, Guido von Pirquet and Herman Noordung further developed the idea. Wernher von Braun contributed his ideas in a 1952 Colliers magazine article. In the 1950s and 1960s, Dandridge M. Cole^[35] published his ideas. Another seminal book on the subject was the book The High Frontier: Human Colonies in Space by Gerard K. O'Neill^[36] in 1977 which was followed the same year by Colonies in Space by T. A. Heppenheimer.^[37] Marianne J. Dyson wrote Home on the Moon; Living on a Space Frontier in 2003;^[38] Peter Eckart wrote Lunar Base Handbook in 2006^[39] and then Harrison Schmitt's Return to the Moon written in 2007.^[40]

Space activity is legally based on the Outer Space Treaty, the main international treaty. But space law has become a larger legal field, which includes other international agreements such as the significantly less ratified Moon Treaty and diverse national laws.

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

And continued in article two by stating: "Outer space, including the Moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means."^[41]

The development of international space law has revolved much around outer space being defined as common heritage of mankind. The Magna Carta of Space presented by William A. Hyman in 1966 framed outer space explicitly not as terra nullius but as res communis, which subsequently influenced the work of the United Nations Committee on the Peaceful Uses of Outer Space.^[42][43]

A primary argument calling for space colonization is the long-term survival of human civilization and terrestrial life.^[44] By developing alternative locations off Earth, the planet's species, including humans, could live on in the event of natural or human-made disasters on Earth.^[45]

On two occasions, theoretical physicist and cosmologist Stephen Hawking argued for space colonization as a means of saving humanity. In 2001, Hawking predicted that the human race would become extinct within the next thousand years unless colonies could be established in space.^[46] 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.^[47]

In 2005, then NASA Administrator Michael Griffin identified space colonization as the ultimate goal of current spaceflight programs, saying:

... the goal isn't just scientific exploration ... it's also about extending the range of human habitat out from Earth into the solar system as we go forward in time ... In the long run, a single-planet species will not survive ... If we humans want to survive for hundreds of thousands of millions of years, we must ultimately populate other planets. Now, today the technology is such that this is barely conceivable. We're in the infancy of it. ... I'm talking about that one day, I don't know when that day is, but there will be more human beings who live off the Earth than on it. We may well have people living on the Moon. We may have people living on the moons of Jupiter and other planets. We may have people making habitats on asteroids ... I know that humans will colonize the solar system and one day go beyond.^[48]

Louis J. Halle, formerly of the United States Department of State, wrote in Foreign Affairs (Summer 1980) that the colonization of space will protect humanity in the event of global nuclear warfare.^[49] The physicist Paul Davies also supports the view that if a planetary catastrophe threatens the survival of the human species on Earth, a self-sufficient colony could "reverse-colonize" Earth and restore human civilization. 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" of human civilization.^[50]

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".^[51]

In a theoretical study from 2019, a group of researchers have pondered the long-term trajectory of human civilization.^[52] 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.^{[52]: 8, 22f} 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 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 stations or celestial bodies, for example via terraforming. In the fourth step, the colonies could self-replicate and establish new colonies further into space, a process that could then repeat itself and continue at an exponential 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.^{[52]: 23–25}

Resources in space, both in materials and energy, are enormous. The Solar System 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.^[53][54][55]

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.^[56] 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.^[57]

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.^[58]

Some of these high-value trade goods include precious metals,^[59][60] gemstones,^[61] power,^[62] solar cells,^[63] ball bearings,^[63] semi-conductors,^[63] and pharmaceuticals.^[63]

The mining and extraction of metals from a small asteroid the size of 3554 Amun or (6178) 1986 DA, 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^[64]

The main impediments to commercial exploitation of these resources are the very high cost of initial investment,^[65] the very long period required for the expected return on those investments (The Eros Project plans a 50-year development),^[66] and the fact that the venture has never been carried out before—the high-risk nature of the investment.

Expansion of humans and technological progress has usually resulted in some form of environmental devastation, and destruction of ecosystems and their accompanying wildlife. In the past, expansion has often come at the expense of displacing many indigenous peoples, the resulting treatment of these peoples ranging anywhere from encroachment to genocide. Because space has no known life, this need not be a consequence, as some space settlement advocates have pointed out.^[67][68] 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.^[69]

Counterarguments state that changing only the location but not the logic of exploitation will not create a more sustainable future.^[70]

An argument for space colonization is to mitigate proposed impacts of overpopulation of Earth, such as resource depletion.^[71] 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.^[72] Proponents of this idea include Stephen Hawking^[73] and Gerard K. O'Neill.^[36]

Others including cosmologist Carl Sagan and science fiction writers Arthur C. Clarke,^[74] and Isaac Asimov,^[75] 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".^[74] The problem for these authors is not the lack of resources in space (as shown in books such as Mining the Sky^[76]), but the physical impracticality of shipping vast numbers of people into space to "solve" overpopulation on Earth.

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.^[77][78]

Nick Bostrom has argued that from a utilitarian 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).^[79] 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.

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.^[80] 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, 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.

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There would be many problems in colonizing the outer Solar System. These include:

• Distance from Earth – The outer planets are much farther from Earth than the inner planets, and would therefore be harder and more time-consuming to reach. In addition, return voyages may well be prohibitive considering the time and distance.
• Extreme cold – temperatures are near absolute zero in many parts of the outer Solar System.
• Power – Solar power is many times less concentrated in the outer Solar System than in the inner Solar System. It is unclear as to whether it would be usable there, using some form of concentration mirrors, or whether nuclear power would be necessary. There have also been proposals to use the gravitational potential energy of planets or dwarf planets with moons.
• 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 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. Such effects can 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.

Space colonization has been seen as a relief to the problem of human overpopulation as early as 1758,^[81] and listed as one of Stephen Hawking's reasons for pursuing space exploration.^[82] Critics note, however, that a slowdown in population growth rates since the 1980s has alleviated the risk of overpopulation.^[81]

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.^[83]

Other objections include concerns that the forthcoming colonization and commodification of the cosmos is likely to enhance the interests of the already powerful, including major economic and military institutions e.g. the large financial institutions, the major aerospace companies and the military–industrial complex, to lead to new wars, and to exacerbate pre-existing exploitation of workers and resources, economic inequality, poverty, social division and marginalization, environmental degradation, and other detrimental processes or institutions.^[84][85][86]

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, morality, philosophy, culture, bioethics, and the threat of megalomaniac leaders in these new "societies" would all have to be addressed in order for space colonization to meet the psychological and social needs of people living in isolated colonies.^[87]

As an alternative or addendum for the future of the human race, many science fiction writers have focused on the realm of the 'inner-space', that is the computer-aided exploration of the human mind and human consciousness—possibly en route developmentally to a Matrioshka Brain.^[88]

Robotic spacecraft are proposed as an alternative to gain many of the same scientific advantages without the limited mission duration and high cost of life support and return transportation involved in human missions.^[89]

A corollary to the Fermi paradox—"nobody else is doing it"^[90]—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.^[91]

Space colonization has been discussed as postcolonial^[42] continuation of imperialism and colonialism,^{[95][96][97][98]} calling for decolonization instead of colonization.^[99][100] Critics argue that the present politico-legal regimes and their philosophic grounding, advantage imperialist development of space,^[98] 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.^[101][102] Furthermore, it is argued that there is a need for inclusive^[103] and democratic participation and implementation of any space exploration, infrastructure or habitation.^[104][105] According to space law expert Michael Dodge, existing space law, such as the Outer Space Treaty, guarantees access to space, but does not enforce social inclusiveness or regulate non-state actors.^[99]

Particularly the narrative of the "New Frontier" has been criticized as unreflected continuation of settler colonialism and manifest destiny, continuing the narrative of exploration as fundamental to the assumed human nature.^{[106][107][96][101][97]} Joon Yun considers space colonization as a solution to human survival and global problems like pollution to be imperialist;^[108] others have identified space as a new sacrifice zone of colonialism.^[109]

Natalie B. Trevino argues that not colonialism but coloniality will be carried into space if not reflected on.^[110][111]

More specifically the advocacy for territorial colonization of Mars opposed to habitation in the atmospheric space of Venus has been called surfacism,^[112][113] a concept similar to Thomas Golds surface chauvinism.

More generally space infrastructure such as the Mauna Kea Observatories have also been criticized and protested against as being colonialist.^[114] Guiana Space Centre has also been the site of anti-colonial protests, connecting colonization as an issue on Earth and in space.^[42]

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.^[99]

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.^[42]

Robotic spacecraft to Mars are required to be sterilized, to have at most 300,000 spores on the exterior of the craft—and more thoroughly sterilized if they contact "special regions" containing water, or it could contaminate life-detection experiments or the planet itself.^[115][116]

It is impossible to sterilize human missions to this level, as humans are host to typically a hundred trillion microorganisms of thousands of species of the human microbiome, and these cannot be removed while preserving the life of the human. Containment seems the only option, but it is a major challenge in the event of a hard landing (i.e. crash).^[117] There have been several planetary workshops on this issue, but with no final guidelines yet for a way forward.^[118] Human explorers could also inadvertently contaminate Earth if they return to the planet while carrying extraterrestrial microorganisms.^[119]

The health of the humans who may participate in a colonization venture would be subject to increased physical, mental and emotional risks. NASA learned that – without gravity – bones lose minerals, causing osteoporosis.^[120] Bone density may decrease by 1% per month,^[121] which may lead to a greater risk of osteoporosis-related fractures later in life. Fluid shifts towards to the head may cause vision problems.^[122] NASA found that isolation in closed environments aboard the International Space Station led to depression, sleep disorders, and diminished personal interactions, likely due to confined spaces and the monotony and boredom of long space flight.^[121][123] Circadian rhythm may also be susceptible to the effects of space life due to the effects on sleep of disrupted timing of sunset and sunrise.^[124] This can lead to exhaustion, as well as other sleep problems such as insomnia, which can reduce their productivity and lead to mental health disorders.^[124] 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.^[125]

Building colonies in space would require access to water, food, space, people, construction materials, energy, transportation, communications, 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,^[126] an argument made by John Hickman^[127] and Neil deGrasse Tyson.^[128]

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.^[129][130]

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 settler colonialism, produce colonial national identities.^[131]

Federalism has been studied as a remedy of such distant and autonomous communities.^[132]

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.^[133] Another commonly proposed life-support system is a closed ecological system such as Biosphere 2.^[134]

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.^[135] 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.^[136] Radiation risk may be reduced for astronauts by frequent monitoring and focusing work to minimize time away from shielding.^[125] Future space agencies can also ensure that every colonist would have a mandatory amount of daily exercise to prevent degradation of muscle.^[125]

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.^[137] In the case of Van Allen belts, these could be drained using orbiting tethers^[138] or radio waves.^[139]

Passive mass shielding of four metric tons per square meter of surface area will reduce radiation dosage to several mSv or less annually, well below the rate of some populated high natural background areas on Earth.^[140] 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).^[137] 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.

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.^[141]

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

Although there are no immediate prospects for the large amounts of money required for space colonization to be available given traditional launch costs,^[142] 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 US$56.5 million per launch of up to 13,150 kg (28,990 lb) payload^[143] to low Earth orbit, SpaceX Falcon 9 rockets are already the "cheapest in the industry".^[144] 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."^[144] 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 competitive market in space launch services.^[145]

The President's Commission on Implementation of United States Space Exploration Policy suggested that an inducement prize should be established, perhaps by government, for the achievement of space colonization, for example by offering the prize to the first organization to place humans on the Moon and sustain them for a fixed period before they return to Earth.^[146]

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 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.^[147]

Other possibilities include the incorporation of cryptocurrency as the primary form of currency, as suggested by Elon Musk.^[148]

Colonies on the Moon, Mars, asteroids, or the metal-rich planet Mercury, could extract local materials. The Moon is deficient in volatiles such as argon, helium and compounds of carbon, hydrogen and nitrogen. The LCROSS impacter was targeted at the Cabeus crater which was chosen as having a high concentration of water for the Moon. A plume of material erupted in which some water was detected. Mission chief scientist Anthony Colaprete estimated that the Cabeus crater contains material with 1% water or possibly more.^[149] Water ice should also be in other permanently shadowed craters near the lunar poles. Although helium is present only in low concentrations on the Moon, where it is deposited into regolith by the solar wind, an estimated million tons of He-3 exists over all.^[150] 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, or Deimos. The benefits of using such sources include: a lower gravitational force, no 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.^[151]

Farther out, Jupiter's Trojan asteroids are thought to be rich in water ice and other volatiles.^[152]

Recycling of some raw materials would almost certainly be necessary.

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/d² 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.^[153]

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

Large solar power photovoltaic cell arrays or thermal power plants would be needed to meet the electrical power needs of the settlers' use. In developed parts of Earth, electrical consumption can average 1 kilowatt/person (or roughly 10 megawatt-hours per person per year.)^[154] 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.^[155]

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.^[156] 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.^[157] 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.^[158] 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,^[159] 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-eccentric Earth orbit (HEEO).^[160]: 132 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.^[161]

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 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.^[162] 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.^[156]

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 inevitable heat generated. This requires fairly large radiator areas.

Space manufacturing could enable self-replication. Some consider it the ultimate goal because it would allow an exponential increase in colonies, while eliminating costs to, and dependence on, Earth.^[163] It could be argued that the establishment of such a colony would be Earth's first act of self-replication.^[164] 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, genetic material and tools.

In 2002, the anthropologist John H. Moore estimated^[165] 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).^[166][167]

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.^[168]

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.^[169][170]

Organizations that contribute to space colonization include:

• 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.^[171]
• The Space Frontier Foundation performs space advocacy including strong free market, capitalist views about space development.
• The Mars Society promotes Robert Zubrin's Mars Direct plan and the settlement of Mars.
• The Space Settlement Institute is searching for ways to make space colonization happen within a lifetime.^[172]
• SpaceX is developing extensive spaceflight transportation infrastructure with the express purpose of enabling long-term human settlement of Mars.^[173][174]
• The Space Studies Institute funds the study of outer space settlements, especially O'Neill cylinders.
• The Alliance to Rescue Civilization plans to establish backups of human civilization on the Moon and other locations away from Earth.
• The Artemis Project plans to set up a private lunar surface station.[2]
• The British Interplanetary Society (BIS) promotes ideas for the exploration and use of space, including a Mars colony, future propulsion systems (see Project Daedalus), terraforming, and locating other habitable worlds.^[175]
  • 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.^[176]
• Asgardia (nation) – an organization searching to circumvent limitations placed by Outer Space Treaty.
• The Cyprus Space Exploration Organisation promotes space exploration and colonization, and fosters collaboration in space.

Many 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.^[177]
• The Mars Desert Research Station has a habitat for similar reasons, but the surrounding climate is not strictly inhospitable.^[178]
• Devon Island Mars Arctic Research Station, can also provide some practice for off-world outpost construction and operation.^[179]

Although established space habitats are a stock element in science fiction stories, fictional works that explore the themes, social or practical, of the settlement and occupation of a habitable world are more rare.^{[citation needed]}

• Solaris is noted for its critique of space colonization of inhabited planets. At one point, one of the characters says:^[180]

We are humanitarian and chivalrous; we don't want to enslave other races, we simply want to bequeath them our values and take over their heritage in exchange. We think of ourselves as the Knights of the Holy Contact. This is another lie. We are only seeking Man. We have no need of other worlds. We need mirrors. (§6:72)

In 2022 Rudolph Herzog and Werner Herzog presented an in-depth documentary with Lucianne Walkowicz called Last exit: Space.^[181]

Papers

• Yap, Xiao-Shan & Rakhyun E. Kim (2023). "Towards Earth-Space Governance in a Multi-Planetary Era". Earth System Governance, 16: 100173.
• Ferrando, Francesca (July 2016). "Why Space Migration Must be Posthuman". The Ethics of Space Exploration. Space and Society. New York, US: Springer. pp. 137–152. doi:10.1007/978-3-319-39827-3_10. ISBN 978-3-319-39825-9.
• Tiziani, Moreno (Jun 2013). "The Colonization of Space - An Anthropological Outlook" (PDF). Antrocom Online Journal of Anthropology. 9 (1). Rome, Italy: Antrocom: 225–236. ISSN 1973-2880. Archived from the original (PDF) on 2013-12-02. Retrieved 2013-12-01.
• Foss, Nicole (December 2016). Mass Extinction and Mass Insanity.
• Harrison, Albert A. (2002). Spacefaring: The Human Dimension. Berkeley, CA, US: University of California Press. ISBN 978-0-520-23677-6.
• Seedhouse, Erik (2009). Lunar Outpost: The Challenges of Establishing a Human Settlement on the Moon. Chichester, UK: Praxis Publishing Ltd. ISBN 978-0-387-09746-6. Also see [3].
• Seedhouse, Erik (2009). Martian Outpost: The Challenges of Establishing a Human Settlement on Mars. Chichester, UK: Praxis Publishing Ltd. Bibcode:2009maou.book.....S. ISBN 978-0-387-98190-1. {{cite book}}: |journal= ignored (help).
• Seedhouse, Erik (2012). Interplanetary Outpost: The Human and Technological Challenges of Exploring the Outer Planets. Berlin: Springer. ISBN 978-1-4419-9747-0.
• Cameron M. Smith, Evan T. Davies (2012). Emigrating Beyond Earth: Human Adaptation and Space Colonization. Berlin: Springer-Verlag. ISBN 978-1-4614-1164-2.

Video

• Rees, Martin (March 2017). Brief talk on some key issues in space exploration and colonization. Archived from the original on 2021-12-11. Posted on the official YouTube channel of Casina Pio IV.
• Sarmont, Eagle (December 2018). Opening the High Frontier. Affordable to everyone spaceflight is the key to building a spacefaring civilization. Posted on Vimeo.