Space colonization (also called space settlement, or extraterrestrial colonization) is permanent human habitation off the planet Earth.
Many arguments have been made for and against space colonization. The two most common in favor of colonization are survival of human civilization and the biosphere in the event of a planetary-scale disaster (natural or man-made), and the availability of additional resources in space that could enable expansion of human society. The most common objections to colonization include concerns that the commodification of the cosmos may be likely to enhance the interests of the already powerful, including major economic and military institutions, and to exacerbate pre-existing detrimental processes such as wars, economic inequality, and environmental degradation.
No space colonies have been built so far. Currently, the building of a space colony would present a set of huge technological and economic challenges. Space settlements would have to provide for nearly all (or all) the material needs of hundreds or thousands of humans, in an environment out in space that is very hostile to human life. They would involve technologies, such as controlled ecological life support systems, that have yet to be developed in any meaningful way. They would also have to deal with the as-yet unknown issue of how humans would behave and thrive in such places long-term. Because of the present cost of sending anything from the surface of the Earth into orbit (around $2,500 per-pound to orbit, expected to further decrease), a space colony would currently be a massively expensive project.
There are yet no plans for building space colonies by any large-scale organization, either government or private. However, many proposals, speculations, and designs for space settlements have been made through the years, and a considerable number of space colonization advocates and groups are active. Several famous scientists, such as Freeman Dyson, have come out in favor of space settlement.
On the technological front, there is ongoing progress in making access to space cheaper (reusable launch systems could reach $10 per-pound to orbit), and in creating automated manufacturing and construction techniques.
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 would provide (over the long-term) a very high return on the initial investment in space infrastructure.
Some of these high-value trade goods include precious metals, gemstones, power, solar cells, ball bearings, semi-conductors, and pharmaceuticals.
The mining and extraction of metals from a small asteroid the size of 3554 Amun or (6178) 1986 DA, both small near-Earth asteroids, would be 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.
Space colonization is seen as a long-term goal of some national space programs. Since the advent of the 21st-century commercialization of space, which saw greater cooperation between NASA and the private sector, 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.
The main impediments to commercial exploitation of these resources are the very high cost of initial investment, the very long period required for the expected return on those investments (The Eros Project plans a 50-year development), and the fact that the venture has never been carried out before — the high-risk nature of the investment.
Major governments and well-funded corporations have announced plans for new categories of activities: space tourism and hotels, prototype space-based solar-power satellites, heavy-lift boosters and asteroid mining—that create needs and capabilities for humans to be present in space.
A corollary to the Fermi paradox—"nobody else is doing it"—is the argument that, because no evidence of alien colonization technology exists, it is statistically unlikely to even be possible to use that same level of technology ourselves.
Colonizing space would require massive amounts of financial, physical, and human capital devoted to research, development, production, and deployment. Earth's natural resources do not increase to a noteworthy extent (which is in keeping with the "only one Earth" position of environmentalists). Thus, considerable efforts in colonizing places outside Earth would appear as a hazardous waste of the Earth's limited resources for an aim without a clear end.
The fundamental problem of public things, needed for survival, such as space programs, is the free rider problem. Convincing the public to fund such programs would require additional self-interest arguments: If the objective of space colonization is to provide a "backup" in case everyone on Earth is killed, then why should someone on Earth pay for something that is only useful after they are dead? This assumes that space colonization is not widely acknowledged as a sufficiently valuable social goal.
Seen as a relief to the problem of overpopulation even as early as 1758, and listed as one of Stephen Hawking's reasons for pursuing space exploration, it has become apparent that space colonisation in response to overpopulation is unwarranted. Indeed, the birth rates of many developed countries, specifically spacefaring ones, are at or below replacement rates, thus negating the need to use colonisation as a means of population control.
Other objections include concerns that the forthcoming colonization and commodification of the cosmos may be 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.
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.
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.
Robotic exploration is 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 manned missions.
Another concern is the potential to cause interplanetary contamination on planets that may harbor hypothetical extraterrestrial life.