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Space colonization, also called space settlement and space humanization, is the hypothetical permanent autonomous (self-sufficient) human habitation of locations outside Earth. It is a major theme in science fiction. Several design groups at NASA and elsewhere have examined the feasibility of various schemes.
For humans to live permanently outside Earth, the habitat must maintain variables within an appropriate range, ie. homeostasis. The habitat must contain non-human species--for example, microorganisms and crop plants.
The relationship between organisms, their habitat and the non-Earth environment can be:
A combination of the above is also possible.
Self-replication is an optional attribute, but highly desirable because it allows an exponential increase in colonies.
It could be argued that the establishment of a colony would be Earth's first act of self-replication.
See also: von Neumann probe, von Neumann machine, clanking replicator, self-replication
In 2002, the anthropologist Dr. John Moore estimated that a population of 150-180 would allow normal reproduction for 60-80 generations--equivalent to 2000 years.
A much smaller inital population of two female humans should be viable as long as human embryos are available from Earth. Use of a sperm bank from Earth also allows a smaller starting base with negligible inbreeding.
The location of colonization can be:
Location is a frequent point of contention between space colonization advocates.
Small asteroids have the advantage that one passes closer than Earth's moon several times per decade. In between close approaches to Earth, 1/2 billion kilometers from Earth is not unusual.
Disadvantages are that significant gravity, a population of more than ten and self sufficiency may be far in the future on/in very small asteroids. Unmanned supply craft should be practical with little technology advance even at 1/2 billion kilometers. The colonists would have a strong interest in making sure their asteroid did not hit Earth or anything else of significant mass.
The most famous attempt to build an analog colony is Biosphere 2, which attempted to duplicate Earth's biosphere.
Many space agencies build testbeds for advanced life support systems, but these are designed for long duration human spaceflight, not colonization.
Mars is a frequent topic of discussion. Its size is similar to Earth, it has large water reserves, and has carbon (locked as carbon dioxide in the atmosphere). It may have gone through similar geological and hydrological processes as Earth and contain valuable mineral ores, but this is debated. Equipment is available to extract in situ resources (water, air, etc.) from the Martian ground and atmosphere.
However, its atmosphere is very thin (averaging 800 Pa or about 0.8% of Earth sea-level atmospheric pressure) and the climate is colder. It's gravity is only around a third that of Earth. There is also the problem of native bacteria, which may live on Mars. Mars is often the topic of discussion regarding terraforming to make the entire planet or at least large portions of it habitable.
See : Exploration of Mars
Due to its proximity and relative familiarity, Earth's Moon is also frequently discussed as a target for colonization. It has the benefits of close proximity to Earth and lower gravity, allowing for easier exchange of goods and services. A major drawback of the Moon is its low abundance of volatiles necessary for life such as hydrogen and carbon. Water ice deposits thought to exist in some polar craters could serve as significant sources for these elements.
See also : Moon colonization.
The Artemis Project designed a plan to colonize Europa, one of Jupiter's moons. It would use igloos made of ice refrozen melted by the microwaves on the surface. For submarine/drill would be use for drilling into the Europan ice crust, as well as any sub-surface ocean. It also discusses use of "air pockets" for human inhabitation.
A space habitat, also called space colony and orbital colony, is a space station which is intended as a permanent settlement rather than as a simple waystation or other specialized facility. They would be literal "cities" in space, where people would live and work and raise families. No space habitats have yet been constructed, but many design proposals have been made with varying degrees of realism by both science fiction authors and engineers.
A colony ship would be similar to a space habitat, except with major propulsion capabilities and independent power generation.
Concepts proposed in hard science fiction include:
In 2001, the space news website SPACE.com asked Freeman Dyson, J. Richard Gott and Life and Beautify the Universe"
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.
The scientist 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" the 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.
See also: Space and survival
Alliance to Rescue Civilization plans to establish backups of human civilization on the Moon and other locations away from Earth.
Films and books that depict space colonies of Earth include:
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