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Space colonization is the process of establishing human settlements beyond Earth. This is commonly for prestige, commercial or strategic benefit.[3] This is in contrast to space exploration for scientific benefit. Colonialism can involve exploitation of both resources and people by a distant entity.
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]
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 racein space between the few countries with spaceflight capabilities grew and were ultimately shared by the spacefaring countries themselves.[14] 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.[15][16][17]
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.[18][19] An international regime for lunar activity was demanded by the international Moon Treaty, but is currently developed multilaterally as with the Artemis Accords.[20][21] 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.[22] The first known work on space colonization was the 1869 novella The Brick Moon by Edward Everett Hale, about an inhabited artificial satellite.[23] 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.[24] Tsiolkovsky believed that going into space would help perfect human beings, leading to immortality and peace.[25] 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".[26] 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[27] published his ideas. Another seminal book on the subject was the book The High Frontier: Human Colonies in Space by Gerard K. O'Neill[28] in 1977 which was followed the same year by Colonies in Space by T. A. Heppenheimer.[29]Marianne J. Dyson wrote Home on the Moon; Living on a Space Frontier in 2003;[30]Peter Eckart wrote Lunar Base Handbook in 2006[31] and then Harrison Schmitt's Return to the Moon written in 2007.[32]
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."[33]
A primary argument calling for space colonization is the long-term survival of human civilization and terrestrial life.[36] 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.[37]
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.[38] 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.[39]
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.[40]
Based on his Copernican principle, J. Richard Gott has estimated that the human race could survive for another 7.8million 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".[43]
In a theoretical study from 2019, a group of researchers have pondered the long-term trajectory of human civilization.[44] 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.[44]: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.[44]: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.[45][46][47]
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.[48] 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 $100billion. If funding and technology come sooner than estimated, asteroid mining might be possible within a decade.[49]
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.[50]
Some of these high-value trade goods include precious metals,[51][52] gemstones,[53] power,[54] solar cells,[55] ball bearings,[55] semi-conductors,[55] and pharmaceuticals.[55]
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$20trillion at 2001 market prices[56]
The main impediments to commercial exploitation of these resources are the very high cost of initial investment,[57] the very long period required for the expected return on those investments (The Eros Project plans a 50-year development),[58] 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.[59][60] 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.[61]
Counterarguments state that changing only the location but not the logic of exploitation will not create a more sustainable future.[62]
Alleviating overpopulation and resource demand
An argument for space colonization is to mitigate proposed impacts of overpopulation of Earth, such as resource depletion.[63] 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.[64] Proponents of this idea include Stephen Hawking[65] and Gerard K. O'Neill.[28]
Others including cosmologist Carl Sagan and science fiction writers Arthur C. Clarke,[66] and Isaac Asimov,[67] 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".[66] The problem for these authors is not the lack of resources in space (as shown in books such as Mining the Sky[68]), 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.[69][70]
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).[71] 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.[72] Their answers were:
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.
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.
Criticisms
Space colonization has been seen as a relief to the problem of human overpopulation as early as 1758,[73] and listed as one of Stephen Hawking's reasons for pursuing space exploration.[74] Critics note, however, that a slowdown in population growth rates since the 1980s has alleviated the risk of overpopulation.[73]
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.[75]
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.[76][77][78]
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.[79]
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.[80]
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.[81]
A corollary to the Fermi paradox—"nobody else is doing it"[82]—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.[83]
Space colonization has been discussed as postcolonial[34] continuation of imperialism and colonialism,[87][88][89][90] calling for decolonization instead of colonization.[91][92] Critics argue that the present politico-legal regimes and their philosophic grounding, advantage imperialist development of space,[90] 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.[93][94] Furthermore, it is argued that there is a need for inclusive[95] and democratic participation and implementation of any space exploration, infrastructure or habitation.[96][97] 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.[91]
In regard to the scenario of extraterrestrialfirst contact, it has been argued that the employment of colonial language would endanger such first impressions and encounters.[91]
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.[34]
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.[107][108]
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).[109] There have been several planetary workshops on this issue, but with no final guidelines yet for a way forward.[110] Human explorers could also inadvertently contaminate Earth if they return to the planet while carrying extraterrestrial microorganisms.[111]
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.[112]Bone density may decrease by 1% per month,[113] which may lead to a greater risk of osteoporosis-related fractures later in life. Fluid shifts towards to the head may cause vision problems.[114] 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.[113][115]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.[116] 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.[116] 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.[117]
Locations
Location is a frequent point of contention between space colonization advocates. The location of colonization can be on a physical body planet, dwarf planet, natural satellite, or asteroid or orbiting one. Colonization of the Solar System has received the most attention.
For settlements not on a body see also space habitat.
Earth
It has been argued that space colonization extends from and to Earth, by colonialism having claimed space on Earth and using it for spaceflight, as with Guiana Space Centre,[118] and by building facilities for space colonization, as with Starbase.[119]
Near-Earth space
Earth orbit
A computer-generated image from 2005 showing the distribution of mostly space debris in geocentric orbit with two areas of concentration: geostationary orbit and low Earth orbit.
Geostationary orbit was an early issue of discussion about space colonization, with equatorial countries argueing for special rights to the orbit (see Bogota Declaration).[120]
Space debris, 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.[120]
The Moon is discussed as a target for colonization, due to its proximity to Earth and lower escape velocity. Abundant ice is trapped in permanently shadowed craters near the poles, which could provide support for the water needs of a lunar colony,[121] though indications that mercury is also similarly trapped there may pose health concerns.[122][123] Native precious metals, such as gold, silver, and probably platinum, are also concentrated at the lunar poles by electrostatic dust transport.[123] However, the Moon's lack of atmosphere provides no protection from space radiation or meteoroids, so lunar lava tubes have been proposed sites to gain protection.[124] The Moon's low surface gravity is also a concern, as it is unknown whether 1/6g is enough to maintain human health for long periods.[125] Interest in establishing a moonbase has increased in the 21st century as an intermediate to Mars colonization, with such proposals as the Moon Village for research, mining, and trade facilities with permanent habitation.[126]
A number of government space agencies such as Russia (2014),[127]China (2012)[128][needs update] and the US (2012)[129] have periodically floated lunar plans for constructing the first lunar outpost.
The European Space Agency (ESA) head 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 Moon Village.[130]
In a May 2018 interview, Blue Origin CEO Jeff Bezos indicated Blue Origin would build and fly the Blue Moon lunar lander on its own, with private funding, but that they would build it faster, and accomplish more, if it were done in a partnership with existing government space agencies. Bezos specifically mentioned the December 2017 NASA direction and the ESA Moon Village concepts.[130]
In 2023, the U.S. Defense Department started a study of the necessary infrastructure and capabilities required to develop a moon-based economy over the following ten years.[132]
A contour plot of the gravitational potential of the Moon and Earth, showing the five Earth–Moon Lagrange points
Another near-Earth possibility are the stable Earth–Moon Lagrange pointsL4 and L5, at which point a space colony can float indefinitely. The L5 Society was founded to promote settlement by building space stations at these points. Gerard K. O'Neill suggested in 1974 that the L5 point, in particular, 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.[133]
The inner planets
Many planets within the Solar System have been considered for colonization and terraforming. The main candidates for colonization in the inner Solar System are Mars[134] and Venus.[135] Other possible candidates for colonization include the Moon[136] and Mercury.[137]
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.[138] The planet also receives six and a half times the solar flux as the Earth/Moon system,[139] 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.[140]
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.[141]
As Mercury has essentially no axial tilt, crater floors near its poles lie in eternal darkness, never seeing the Sun. They function as cold traps, trapping volatiles for geological periods. It is estimated that the poles of Mercury contain 1014–1015kg 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.[139]
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.[140] 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 0.7m. This presence of volatiles and abundance of energy has led Alexander Bolonkin and James Shifflett to consider Mercury preferable to Mars for colonization.[139][142]
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 travels very slowly.[140]
Because Mercury is very dense, its surface gravity is 0.38g like Mars, even though it is a smaller planet.[139] This would be easier to adjust to than lunar gravity (0.16g), but presents advantages regarding lower escape velocity from Mercury than from Earth.[140] 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.[140]
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.[140]
Surface conditions on Venus are extremely hostile to human life: average surface temperature is 464°C (hot enough to melt lead), and average surface pressure is 92 times Earth's atmospheric pressure – roughly equivalent to a depth of one kilometre under Earth's oceans.[143] (There is some variation; due to its altitude, the peak of Maxwell Montes is 380°C and 45bar, making it the coolest and least pressurised location on the Venusian surface.[144][145] There are also some hot spots at about 700°C.) Solar energy is not available at the surface due to the constant cloud cover, and the carbon dioxide atmosphere is poisonous.[146]
However, the upper atmosphere of Venus has much more Earthlike conditions and has been suggested as a plausible colonization location since at least 1971 by Soviet scientists.[147] At just over 50km altitude (the cloud tops), atmospheric pressure is roughly equal to that on Earth's surface, and temperatures range from 0–50°C. The volatile elements necessary for life are present (hydrogen, carbon, nitrogen, oxygen, and sulfur), and above the clouds, solar energy is abundant. Pressurization would not be required; humans could even go outside the habitats safely with oxygen provision and clothing to protect against the sulfuric acid droplets. Geoffrey Landis has pointed out that breathable air is a lifting gas in Venus' atmosphere: a cubic meter of air would lift half a kilogram, and an oxygen- and nitrogen-filled aerostat the size of a city on Venus would be able to lift the mass of a city. This suggests floating aerostat cities as a colonization method for Venus. The lack of pressure differences between the outside and inside means that there is ample time to repair habitat breaches. With just over three times the land area of Earth, there would be space even for a billion such cities.[146] The atmosphere provides enough radiation shielding at this altitude, and Venus' 0.90g gravity is likely sufficient to prevent the negative health effects of microgravity.[146]
A day on Venus is very long on the surface, but the atmosphere rotates much faster than the planet (a phenomenon called superrotation), so a floating habitat would have a day of about a hundred hours. Landis compares this favorably with polar days and nights on Earth, which are much longer. A floating habitat at higher latitudes on Venus would approach a normal 24-hour cycle. Mining the surface would give access to important industrial metals, and it could be accessed via airplanes, balloons, or fullerene cables meant to withstand high temperatures. To avoid the problem of the habitat being in motion relative to its mining devices, the habitat could descend into the lower atmosphere: this region is hotter, but Landis argues that a large-sized habitat would have enough heat capacity for a short stay at higher temperatures.[146]
The colonization of Venus has been a subject of many works of science fiction since before the dawn of spaceflight and is still discussed from both a fictional and a scientific standpoint. Proposals for Venus are focused on colonies floating in the upper-middle atmosphere[148] and on terraforming.
The hypothetical colonization of Mars has received interest from public space agencies and private corporations and has received extensive treatment in science fiction writing, film, and art. The most recent[when?] commitments to researching permanent settlement include those by public space agencies—NASA, ESA, Roscosmos, ISRO, and the CNSA—and private organizations—SpaceX, Lockheed Martin, and Boeing.[citation needed]
The asteroid belt has about 1018metric tonnes of overall material available – ten thousand times more than is available in the near-Earth asteroids[149] – but it is thinly distributed as it covers a vast region of space. The largest asteroid is Ceres, which at about 940km in diameter is big enough to be a dwarf planet. The next two largest are Pallas and Vesta, both about 520km in diameter. Uncrewed supply craft should be practical with little technological advance, even crossing 500 million kilometers of space. The colonists would have a strong interest in assuring their asteroid did not hit Earth or any other body of significant mass, but would have extreme difficulty in moving an asteroid[citation needed] of any size. The orbits of the Earth and most asteroids are very distant from each other in terms of delta-v and the asteroidal bodies have enormous momentum. Rockets or mass drivers can perhaps be installed on asteroids to direct their path into a safe course.
Ceres has readily available water, ammonia, and methane, important for survival, fuel, and possibly terraforming of Mars and Venus. The colony could be established on a surface crater or underground.[150] However, even Ceres only manages a tiny surface gravity of 0.03g, which is not enough to stave off the negative effects of microgravity (though it does make transportation to and from Ceres easier). Either medical treatments or artificial gravity would thus be required. Additionally, colonizing the main asteroid belt would likely require infrastructure to already be present on the Moon and Mars.[150]
Some have suggested that Ceres could act as a main base or hub for asteroid mining.[150] However, Geoffrey A. Landis has pointed out that the asteroid belt is a poor place for an asteroid-mining base if more than one asteroid is to be exploited: the asteroids are not close to each other, and two asteroids chosen at random are quite likely to be on opposite sides from the Sun from each other. He suggests that it would be better to construct such a base on an inner planet, such as Venus: inner planets have higher orbital velocities, making the transfer time to any specific asteroid shorter, and orbit the Sun faster, so that the launch windows to the asteroid are more frequent (a lower synodic period). Thus Venus is closer to the asteroids than Earth or Mars in terms of flight time. Transfer times for the journeys Venus–Ceres and Venus–Vesta are 1.15 and 0.95years respectively along minimum-energy trajectories, which is shorter even than Earth–Ceres and Earth–Vesta at 1.29 and 1.08years respectively.[146] Anthony Taylor, Jonathan C. McDowell, and Martin Elvis suggest Mars' moon Phobos as an asteroid-belt mining hub: the main belt is more accessible from Martian orbit than from low Earth orbit in terms of delta-v, the moon provides a large platform and a mass for radiation shielding, and it is not far from Mars' surface. Hence, a Phobos base for asteroid mining works hand in hand economically with Mars settlement.[149]
Moons of outer planets
Artist's impression of a hypothetical ocean cryobot in Europa
Human missions to the outer planets would need to arrive quickly due to the effects of space radiation and microgravity along the journey.[151] 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".[152]Nuclear-thermal or nuclear-electric engines have been suggested as a way to make the journey to Jupiter in a reasonable amount of time.[153] Another possibility would be plasma magnet sails, a technology already suggested for rapidly sending a probe to Jupiter.[154] The cold would also be a factor, necessitating a robust source of heat energy for spacesuits and bases.[152] Most of the larger moons of the outer planets contain water ice, liquid water, and organic compounds that might be useful for sustaining human life.[155][156]
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 helium-3. 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.[157] 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.[158] 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.[159]
Jupiter's Galilean moons (Io, Europa, Ganymede, and Callisto) and Saturn's 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 has about half the Moon's gravity (0.08g); other round moons provide even less (starting from Uranus' Titania and Oberon at about 0.04g).[152]
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 and Europa are extreme, enough to kill unshielded humans within an Earth day.[164] Therefore, only Callisto and perhaps Ganymede could reasonably support a human colony. Callisto orbits outside Jupiter's radiation belt.[152] 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.[152]
Although Io's volcanism and tidal heating constitute valuable resources, exploiting them is probably impractical.[152] Europa is rich in water (its subsurface ocean is expected to contain over twice as much water as all Earth's oceans together)[153] 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.[152] 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.[165][166][153] Ganymede[153] and Callisto are also expected to have internal oceans.[167] 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.[168] The target chosen was 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.[152]
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.
The magnetic field of Jupiter and co-rotation rotation enforcing currents
Ganymede is the largest moon in the Solar System. Ganymede is the only moon with a magnetosphere, albeit overshadowed by 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 Sv of radiation per day. Ganymede could be terraformed.[161]
The Keck Observatory announced in 2006 that the binary Jupiter trojan617 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, Mercury and main-belt asteroids more practical.
Saturn has seven moons large enough to be round: in order of increasing distance from Saturn, they are Mimas, Enceladus, Tethys, Dione, Rhea, Titan, and Iapetus. Titan is the largest and the only one with a Moon-like gravity: it is the only moon in the Solar System to have a dense atmosphere and is rich in carbon-bearing compounds, suggesting it as a colonization target.[164] Titan has water ice and large methane oceans.[169]Robert Zubrin identified Titan as possessing an abundance of all the elements necessary to support life, making Titan perhaps the most advantageous locale in the outer Solar System for colonization.[164]
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 (1.6g/cm3) indicates that its core is rich in silicates.[157]
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.[157]
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 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.[170] On the other hand, planetary scientist 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.
Zubrin identified Titan as possessing an abundance of all the elements necessary to support life, making Titan perhaps the most advantageous locale in the outer Solar System for colonization. He said, "In certain ways, Titan is the most hospitable extraterrestrial world within the Solar System for human colonization."[164] A widely published expert on terraforming, Christopher McKay, is also a co-investigator on the Huygens probe that landed on Titan in January 2005.
The surface of Titan is mostly uncratered and thus inferred to be very young and active, and probably composed of mostly water ice, and lakes of liquid hydrocarbons (methane/ethane) in its polar regions. While the temperature is cryogenic (95 K) it should be able to support a base, but more information regarding Titan's surface and the activities on it is necessary. The thick atmosphere and the weather, such as potential flash floods, are also factors to consider.
On 9 March 2006, NASA's Cassini space probe found possible evidence of liquid water on Enceladus.[171] 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.
Freeman Dyson suggested that within a few centuries, human civilization will have relocated to the Kuiper belt.[172][173] Several hundred billion to trillion comet-like ice-rich bodies exist outside the orbit of Neptune, in the Kuiper belt and Inner and Outer Oort cloud. These may contain all the ingredients for life (water ice, ammonia, and carbon-rich compounds), including significant amounts of deuterium and helium-3. Since Dyson's proposal, the number of trans-Neptunian objects known has greatly increased.
Colonists could live in the dwarf planet's icy crust or mantle, using fusion or geothermal heat[citation needed] and mining the soft-ice or liquid inner ocean for volatiles and minerals. Given the light gravity and resulting lower pressure in the ice mantle or inner ocean, colonizing the rocky core's outer surface might give colonists the largest number of mineral and volatile resources as well as insulating them from cold.[citation needed] Surface habitats or domes are another possibility, as background radiation levels are likely to be low.[citation needed]
Orbit around 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 helium-3, which could have a very high value per unit mass as a thermonuclear fuel.[174][159]
It is hypothesized that one of Neptune's satellites could be used for colonization. Triton's surface shows signs of extensive geological activity that implies a subsurface ocean, perhaps composed of ammonia/water.[175] 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.[citation needed]
Looking beyond the Solar System, there are up to several hundred billion potential stars with possible colonization targets. The main difficulty is the vast distances to other stars: roughly a hundred thousand times farther away than the planets in the Solar System. This means that some combination of very high speed (some more-than-fractional percentage of the speed of light), or travel times lasting centuries or millennia, would be required. These speeds are far beyond what current spacecraft propulsion systems can provide.
Space colonization technology could in principle allow human expansion at high, but sub-relativistic speeds, substantially less than the speed of light, c. An interstellar colony ship would be similar to a space habitat, with the addition of major propulsion capabilities and independent energy generation.
A generation ship would travel much slower than light, with consequent interstellar trip times of many decades or centuries. The crew would go through generations before the journey was complete, so none of the initial crew would be expected to survive to arrive at the destination, assuming current human lifespans.
An 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 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-ship, a nuclear-powered concept proposed by Freeman Dyson which would use nuclear explosions to propel a starship. A special case of the preceding nuclear rocket concepts, with similar potential velocity capability, but possibly easier technology.
Laser propulsion concepts, using some form of beaming of power from the Solar System might allow a 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.
The above concepts appear limited to high, but still sub-relativistic speeds, due to fundamental energy and reaction mass considerations, and all would entail trip times which might be enabled by space colonization technology, permitting self-contained habitats with lifetimes of decades to centuries. Yet human interstellar expansion at average speeds of even 0.1% of c would permit settlement of the entire Galaxy in less than one-half of the Sun's galactic orbital period of ~240,000,000 years, which is comparable to the timescale of other galactic processes. Thus, even if interstellar travel at near relativistic speeds is never feasible (which cannot be determined at this time), the development of space colonization could allow human expansion beyond the Solar System without requiring technological advances that cannot yet be reasonably foreseen. This could greatly improve the chances for the survival of intelligent life over cosmic timescales, given the many natural and human-related hazards that have been widely noted.
If humanity does gain access to a large amount of energy, on the order of the mass-energy of entire planets, it may eventually become feasible to construct Alcubierre drives. These are one of the few methods of superluminal travel which may be possible under current physics. However, it is probable that such a device could never exist, due to the fundamental challenges posed. For more on this see Difficulties of making and using an Alcubierre Drive.
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.[176][177][178]
Implementation
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,[179] an argument made by John Hickman[180] and Neil deGrasse Tyson.[181]
Migration
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.[182][183]
Governance
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.[184]
Federalism has been studied as a remedy of such distant and autonomous communities.[185]
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.[186] Another commonly proposed life-support system is a closed ecological system such as Biosphere 2.[187]
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.[188] 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.[189] Radiation risk may be reduced for astronauts by frequent monitoring and focusing work to minimize time away from shielding.[117] Future space agencies can also ensure that every colonist would have a mandatory amount of daily exercise to prevent degradation of muscle.[117]
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.[190] In the case of Van Allen belts, these could be drained using orbiting tethers[191] or radio waves.[192]
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.[193] 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).[190] 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.[194]
Economics
Space colonization can roughly be said to be possible when the necessary methods of space colonization become cheap enough (such as space access by cheaper launch systems) to meet the cumulative funds that have been gathered for the purpose, in addition to estimated profits from 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,[195] 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 13,150kg (28,990lb) payload[196] to low Earth orbit, SpaceXFalcon 9 rockets are already the "cheapest in the industry".[197] 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."[197] 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.[198]
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.[200]
Other possibilities include the incorporation of cryptocurrency as the primary form of currency, as suggested by Elon Musk.[201]
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.[202] 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.[203] 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.[204]
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/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.[206]
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.)[207] 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.[208]
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 12cm, 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.[209] 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.[210] Since then JAXA and Mitsubishi have been working together on a $21billion project to place satellites in orbit which could generate up to 1 gigawatt of energy.[211] 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,[212] 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).[213]: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.[214]
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.[215] 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.[209]
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.[216] It could be argued that the establishment of such a colony would be Earth's first act of self-replication.[217] 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.
Population size
In 2002, the anthropologistJohn H. Moore estimated[218] 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).[219][220]
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.[221]
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.[224]
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.[229]
Biosphere 2 is a test habitat on Earth for space flight.
Many space agencies build "testbeds", which are facilities on Earth for testing advanced life support systems, but these are designed for long duration 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.
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:[233]
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)
Interplanetary spaceflight or interplanetary travel is the crewed or uncrewed travel between stars and planets, usually within a single planetary system. In practice, spaceflights of this type are confined to travel between the planets of the Solar System. Uncrewed space probes have flown to all the observed planets in the Solar System as well as to dwarf planets Pluto and Ceres, and several asteroids. Orbiters and landers return more information than fly-by missions. Crewed flights have landed on the Moon and have been planned, from time to time, for Mars, Venus and Mercury. While many scientists appreciate the knowledge value that uncrewed flights provide, the value of crewed missions is more controversial. Science fiction writers propose a number of benefits, including the mining of asteroids, access to solar power, and room for colonization in the event of an Earth catastrophe.
Space exploration is the use of astronomy and space technology to explore outer space. While the exploration of space is currently carried out mainly by astronomers with telescopes, its physical exploration is conducted both by uncrewed robotic space probes and human spaceflight. Space exploration, like its classical form astronomy, is one of the main sources for space science.
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 make it habitable for humans to live on.
Deimos is the smaller and outer of the two natural satellites of Mars, the other being Phobos. Deimos has a mean radius of 6.2 km (3.9 mi) and takes 30.3 hours to orbit Mars. Deimos is 23,460 km (14,580 mi) from Mars, much farther than Mars's other moon, Phobos. It is named after Deimos, the Ancient Greek god and personification of dread and terror.
A space settlement is a settlement in outer space, sustaining more extensively habitation facilities in space than a general space station or spacecraft. Possibly including closed ecological systems, its particular purpose is permanent habitation.
The Discovery Program is a series of Solar System exploration missions funded by the U.S. National Aeronautics and Space Administration (NASA) through its Planetary Missions Program Office. The cost of each mission is capped at a lower level than missions from NASA's New Frontiers or Flagship Programs. As a result, Discovery missions tend to be more focused on a specific scientific goal rather than serving a general purpose.
Asteroid mining is the hypothetical extraction of materials from asteroids and other minor planets, including near-Earth objects.
In the colonization of Mars humans would inhabit Martian territory and exploit resources there, possibly enabling the settlement of Mars. Most Mars colonization concepts focus on settling, but colonization is a broader ethical concept, which international space law has limited, and national space programs have avoided, instead focusing on human missions to Mars for exploring the planet. The exploitation of native resources might include in situ resource utilization to produce consumables like propellants and life support gasses which would otherwise need to be imported from Earth. Currently there are only proposals for Mars colonization and no humans have yet lived on or visited Mars.
The colonization of Venus has been a subject of many works of science fiction since before the dawn of spaceflight, and is still discussed from both a fictional and a scientific standpoint. However, with the discovery of Venus's extremely hostile surface environment, attention has largely shifted towards the colonization of the Moon and Mars instead, with proposals for Venus focused on habitats floating in the upper-middle atmosphere and on terraforming.
The NASA Innovative Advanced Concepts (NIAC) is a NASA program for development of far reaching, long term advanced concepts by "creating breakthroughs, radically better or entirely new aerospace concepts". The program operated under the name NASA Institute for Advanced Concepts from 1998 until 2007, and was reestablished in 2011 under the name NASA Innovative Advanced Concepts and continues to the present. The NIAC program funds work on revolutionary aeronautics and space concepts that can dramatically impact how NASA develops and conducts its missions.
Asteroids, including those in the asteroid belt, have been suggested as possible sites of space colonization. Motives include the survival of humanity, and the specific economic opportunity for asteroid mining. Obstacles include transportation distance, temperature, radiation, lack of gravity, and psychological issues.
In space exploration, in situ resource utilization (ISRU) is the practice of collection, processing, storing and use of materials found or manufactured on other astronomical objects that replace materials that would otherwise be brought from Earth.
The following outline is provided as an overview of and topical guide to space exploration.
Discovery and exploration of the Solar System is observation, visitation, and increase in knowledge and understanding of Earth's "cosmic neighborhood". This includes the Sun, Earth and the Moon, the major planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune, their satellites, as well as smaller bodies including comets, asteroids, and dust.
Asteroid capture is an orbital insertion of an asteroid around a larger planetary body. When asteroids, small rocky bodies in space, are captured, they become natural satellites, specifically either an irregular moon if permanently captured, or a temporary satellite.
The Planetary Science Decadal Survey is a serial publication of the United States National Research Council produced for NASA and other United States Government Agencies such as the National Science Foundation. The documents identify key questions facing planetary science and outlines recommendations for space and ground-based exploration ten years into the future. Missions to gather data to answer these big questions are described and prioritized, where appropriate. Similar decadal surveys cover astronomy and astrophysics, earth science, and heliophysics.
The following outline is provided as an overview of and topical guide to the Solar System:
The future of space exploration involves both telescopic and physical explorations of space by robotic spacecraft and human spaceflight. Near-term physical exploration missions, focused on obtaining new information about the Solar System, are planned and announced by both national and private organisations.
↑ See for example, the work of Dr. Alan Marshall in Alan Marshall (1993) 'Ethics and the Extraterrestrial Environment', Journal of Applied Philosophy, Vol. 10, No 2, pp227-237; Alan Marshall (1994) 'Martians Beware', New Zealand Science Monthly, December 1994 issue; Alan Marshall (1997) 'Extraterrestrial Environmentalism', Australian Science, Vol. 18, No. 2, Winter issue, pp. 25–27. July 1997; and "Cosmic Preservationist", The Word: New Scientist, January 4th, 2003 issue.
↑ Vajk, J.Peter (1976-01-01). "The impact of space colonization on world dynamics". Technological Forecasting and Social Change. 9 (4): 361–99. doi:10.1016/0040-1625(76)90019-6. ISSN0040-1625.
↑ O'Neill, Colonies in Space; Pournelle, A Step Farther Out.
↑ Marshall, P. (1981). "Nicole Oresme on the Nature, Reflection, and Speed of Light". Isis. 72 (3): 357–374 [367–374]. doi:10.1086/352787. S2CID144035661.
↑ Queens University Belfast scientist helps NASA Mars projectArchived 2018-11-19 at the Wayback Machine "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."
↑ Safe on Mars page 37Archived 2015-09-06 at the Wayback Machine "Martian biological contamination may occur if astronauts breathe contaminated dust or if they contact material that is introduced into their habitat. If an astronaut becomes contaminated or infected, it is conceivable that he or she could transmit Martian biological entities or even disease to fellow astronauts, or introduce such entities into the biosphere upon returning to Earth. A contaminated vehicle or item of equipment returned to Earth could also be a source of contamination."
1 2 Abadie LJ, Lloyd CW, Shelhamer MJ (11 June 2018). "The Human Body in Space". NASA. Archived from the original on 26 July 2019. Retrieved 2019-03-04.
1 2 Weir, Kirsten (1 June 2018). "Mission to Mars". American Psychological Association. Archived from the original on 12 December 2019. Retrieved 2019-03-04. We are a circadian species, and if you don't have the proper lighting to maintain that chronobiology, it can create significant problems for crew members
1 2 Platts, Warren J.; Boucher, Dale; Gladstone, G. Randall (12 December 2013). "Prospecting for Native Metals in Lunar Polar Craters". 7th Symposium on Space Resource Utilization. doi:10.2514/6.2014-0338. ISBN978-1-62410-315-5.
↑ Taylor, R. L. (March 1993). "The effects of prolonged weightlessness and reduced gravity environments on human survival". Journal of the British Interplanetary Society. 46 (3): 97–106. PMID11539500.
1 2 3 4 Bolonkin, Alexander A. (2015). "Chapter 19: Economic Development of Mercury: A Comparison with Mars Colonization". In Badescu, Viorel; Zacny, Kris (eds.). Inner Solar System: Prospective Energy and Material Resources. Springer-Verlag. pp.407–419. ISBN978-3-319-19568-1.
↑ Stanley Schmidt and Robert Zubrin, eds., "Islands in the Sky: Bold New Ideas for Colonizing Space"; Wiley, 1996, pp. 71–84.
↑ Shifflett, James (n.d.). "A Mercury Colony?". einstein-schrodinger.com. Retrieved 31 July 2021.
↑ Williams, David R. (25 November 2020). "Venus Fact Sheet". NASA Goddard Space Flight Center. Archived from the original on 11 May 2018. Retrieved 2021-04-15.
↑ R. Walker Fillius, Carl E. McIlwain, and Antonio Mogro-Campero, Radiation Belts of Jupiter: A Second Look, Science, Vol. 188. no. 4187, pp. 465–467, 2 May 1975.
↑ Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: Colonizing the Jovian System, pp. 166–170, Tarcher/Putnam, 1999, ISBN1-58542-036-0.
1 2 3 4 Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: Titan, pp. 163–170, Tarcher/Putnam, 1999, ISBN978-1-58542-036-0
↑ Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: The Persian Gulf of the Solar System, pp. 161–163, Tarcher/Putnam, 1999, ISBN1-58542-036-0.
↑ Freeman Dyson, The Sun, The Genome, and The Internet (1999), Oxford University Press. ISBN0-19-513922-4.
↑ Freeman Dyson, "The World, the Flesh, and the Devil", Third J.D. Bernal Lecture, May 1972, reprinted in Communication with Extraterrestrial Intelligence, Carl Sagan, ed., MIT Press, 1973, ISBN0-262-69037-3.
↑ Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: Settling the Outer Solar System: The Sources of Power, pp. 158–160, Tarcher/Putnam, 1999, ISBN1-58542-036-0.
↑ Klass, Morton (2000). "Recruiting new "huddled masses" and "wretched refuse": a prolegomenon to the human colonization of space". Futures. 32 (8). Elsevier BV: 739–748. doi:10.1016/s0016-3287(00)00024-0. ISSN0016-3287.
↑ Crawford, Ian A. (2015). "Interplanetary Federalism: Maximising the Chances of Extraterrestrial Peace, Diversity and Liberty". The Meaning of Liberty Beyond Earth. Cham: Springer International Publishing. p.199–218. doi:10.1007/978-3-319-09567-7_13. ISBN978-3-319-09566-0.
↑ Zuppero, Anthony (1996). "Discovery of Abundant, Accessible Hydrocarbons nearly Everywhere in the Solar System". Proceedings of the Fifth International Conference on Space '96. ASCE. doi:10.1061/40177(207)107. ISBN0-7844-0177-2.
↑ Marin, F; Beluffi, C (2018). "Computing the minimal crew for a multi-generational space travel towards Proxima Centauri b". Journal of the British Interplanetary Society. 71: 45. arXiv:1806.03856. Bibcode:2018JBIS...71...45M.
↑ Weinstone, Ann (July 1994). "Resisting Monsters: Notes on "Solaris"". Science Fiction Studies. 21 (2). SF-TH Inc: 173–190. JSTOR4240332. Retrieved 4 February 2021."Lem's critique of colonialism, as he broadly defines it, is articulated by Snow, one of the other scientists on the space station, who says in the book's most frequently quoted passage.
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. ISBN978-3-319-39825-9.
Harrison, Albert A. (2002). Spacefaring: The Human Dimension. Berkeley, CA, US: University of California Press. ISBN978-0-520-23677-6.
Seedhouse, Erik (2009). Lunar Outpost: The Challenges of Establishing a Human Settlement on the Moon. Chichester, UK: Praxis Publishing Ltd. ISBN978-0-387-09746-6. Also see .
Seedhouse, Erik (2012). Interplanetary Outpost: The Human and Technological Challenges of Exploring the Outer Planets. Berlin: Springer. ISBN978-1-4419-9747-0.
Cameron M. Smith, Evan T. Davies (2012). Emigrating Beyond Earth: Human Adaptation and Space Colonization. Berlin: Springer-Verlag. ISBN978-1-4614-1164-2.
Sarmont, Eagle (December 2018). Opening the High Frontier.Affordable to everyone spaceflight is the key to building a spacefaring civilization. Posted on Vimeo.
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