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Space colonization

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File:Stanford-torus-by-donald-e-davis-med.jpg
Artist's conception of a space habitat called the Stanford torus, by Don Davis

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. While most people think of space colonies on the Moon or Mars, others argue that the first colonies will be in orbit. Several design groups at NASA and elsewhere have examined orbital colony feasibility. They have determined that there are ample quantities of all the necessary materials on the Moon and Near Earth Asteroids, that solar energy is readily available in very large quantities, and that no new scientific breakthroughs are necessary, although a great deal of engineering would be required.

Method

Building cities in space will require materials, energy, transportation, communications, life support, and radiation protection.

Materials

Colonies on the Moon and Mars can use local materials, although the Moon is deficient in carbon and nitrogen. For orbital colonies, launching materials from Earth is very expensive, so bulk materials should come from the Moon or Near-Earth Objects (NEOs - asteroids and comets with orbits near Earth) where gravitational forces are much less, there is no atmosphere, and there is no biosphere to damage. Our Moon has large amounts of oxygen, silicon and metals, but little hydrogen, carbon, or nitrogen. NEOs contain substantial amounts of metals, oxygen, hydrogen and carbon. NEOs also contain some nitrogen, but not necessarily enough to avoid major supplies from Earth.

Energy

Solar energy in orbit is abundant, reliable and is commonly used to power satellites today. Massive structures will be needed to convert sunlight into large amounts of electrical power for settlement use. Energy may be an export item for space settlements, using microwave beams to send power to Earth. The Moon has two-week nights and Mars has night, dust, and is much further from the Sun making nuclear power more attractive.

Transportation

Transportation is often the limiting factor in space endeavors. Present launch costs are very high - $5,000 to $ 30,000 per kilogram from Earth to Low Earth Orbit (LEO). To settle space, we need much better launch vehicles and must avoid serious damage to the atmosphere from the thousands, perhaps millions, of launches required. One possibility is air-breathing hypersonic air/spacecraft under development by NASA and others. Transportation for millions of tons of materials from the Moon and asteroids to orbital settlement construction sites is also necessary. One well-studied possibility is to build electronic catapults on the Moon to launch bulk materials to waiting settlements. There is also the NASA project to build a space elevator, which would solve the problem of high transport cost.

Communication

Compared to the other requirements, communication is relatively easy for orbit and the Moon. Much of the current terrestrial communications already pass through satellites. Communications to Mars suffer from significant delays due to the speed of light, making voice conversation impractical. Other means of communication, such as e-mail and voice mail, should pose no problem.

Life support

People need air, water, food and reasonable temperatures to survive. On Earth a large complex biosphere provides these. In space settlements, a relatively small, closed system must recycle all the nutrients without "crashing." The Biosphere 2 project in Arizona has shown that a complex, small, enclosed, man-made biosphere can support eight people for at least a year, although there were many problems. A year or so into the two year mission oxygen had to be replenished, which strongly suggests that they achieved atmospheric closure.

The relationship between organisms, their habitat and the non-Earth environment can be:

A combination of the above is also possible.

Radiation protection

Cosmic rays and solar flares create a lethal radiation environment in space. To protect life, settlements must be surrounded by sufficient mass to absorb most incoming radiation. Somewhere around 5-10 tons of material per square meter of surface area is required. This can be achieved with left over material from processing lunar soil and asteroids into oxygen, metals, and other useful materials.

Self-replication

Self-replication is an optional attribute, but many think it the ultimate goal because it allows a much more rapid increase in colonies, while eliminating costs to and dependence on Earth. It could be argued that the establishment of such a colony would be Earth's first act of self-replication. Intermediate goals include colonies that expect only information from Earth (science, engineering, entertainment, etc.) and colonies that just require periodic supply of light weight objects, such as integrated circuits, medicines, genetic material and perhaps some tools.

See also: von Neumann probe, clanking replicator, Molecular nanotechnology

Population size

In 2002, the anthropologist John H. Moore estimated that a population of 150–180 would allow normal reproduction for 60 to 80 generations—equivalent to 2000 years.

A much smaller initial 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.

Researchers in conservation biology have tended to adopt the "50/500" rule of thumb initially advanced by Franklin and Soule. This rule says a short-term effective population size (Ne) of 50 is needed to prevent an unacceptable rate of inbreeding, while a long‐term Ne of 500 is required to maintain overall genetic variability. The N e = 50 {\displaystyle N_{e}=50} prescription corresponds to an inbreeding rate of 1% per generation, approximately half the maximum rate tolerated by domestic animal breeders. The N e = 500 {\displaystyle N_{e}=500} value attempts to balance the rate of gain in genetic variation due to mutation with the rate of loss due to genetic drift.

Effective population size Ne depends on the number of males Nm and females Nf in the population according to the formula:

N e = 4 × N m × N f N m + N f {\displaystyle N_{e}={\frac {4\times N_{m}\times N_{f}}{N_{m}+N_{f}}}}

Location

Location is a frequent point of contention between space colonization advocates.

The location of colonization can be:

The most frequently mentioned locations, in rough order of popularity, are:

Mars

Main article: Colonization of Mars

Mars is a frequent topic of discussion. Its overall surface area is similar to the dry land surface Earth, it may have 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. There is a strong scientific interest in colonizing Mars due to the possibility that life could have existed on Mars at some point in its history.

However, its atmosphere is very thin (averaging 800 Pa or about 0.8% of Earth sea-level atmospheric pressure) and the climate is colder. Its gravity is only around a third that of Earth. Mars is often the topic of discussion regarding terraforming to make the entire planet or at least large portions of it habitable.

See also: Exploration of Mars

The Moon

Main article: Colonization of the Moon

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. An alternative solution is to bring hydrogen from Earth and combine it with oxygen from the Moon. Structural components of supply craft could be made of hydrogen-rich plastics. In any case, a Moon colony would carefully recycle its water.

Earth orbit

Compared to other locations, orbit has substantial advantages and one major, but solvable, problem. Orbits close to Earth can be reached in hours, whereas the Moon is days away and trips to Mars take months. There is ample continuous solar power in high Earth orbits, whereas all planets lose sunlight at least half the time. Weightlessness makes construction of large colonies considerably easier than in a gravity environment. Astronauts have demonstrated moving multi-ton satellites by hand. 0g recreation is available on orbital colonies, but not on the Moon or Mars. Finally, the level of (pseudo-) gravity is controlled at any desired level by rotating an orbital colony. Thus, the main living areas can be kept at 1g, whereas the Moon has 1/6g and Mars 1/3g. 1g is critical, at least for early colonies, to ensure that children grow up with strong bones and muscles.

The main disadvantage of orbital colonies is lack of materials. These must be imported from the Moon, which has ample metals, silicon, and oxygen, or Near Earth Asteroids, which have all the materials needed with the possible exception of nitrogen.

Lagrange points

Another Earth orbit possibility are the five Earth-Moon Lagrange points. Although they would generally also take a few days to reach with current technology, many of these points would have near-continuous solar power capability since their distance from Earth would result in only brief and infrequent eclipses of light from the Sun.

The five Earth-Sun Lagrange points would totally eliminate eclipses, but only L1 and L2 would be reachable in a few days' time. The other three Earth-Sun points would require months to reach.

In the After Colony timeline of the Gundam science fiction anime universe, there are space colonies at all five Earth-Moon Lagrange points.

The asteroids

Main article: Colonization of the asteroids

Small asteroids have the advantage that one passes closer than Earth's moon several times per decade. In between these close approaches to home, the asteroid may travel out to a furthest distance of some 350,000,000 kilometers from the Sun (its aphelion) and 500,000,000 kilometers from Earth.

Disadvantages are a lack of 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 technological advance even crossing 1/2 billion kilometers of cold vacuum. The colonists would have a strong interest in assuring their asteroid did not hit Earth or any other body of significant mass.

Mercury

Main article: Colonization of Mercury

There is a suggestion that Mercury could be colonized using the same technology, approach and equipment that is used in colonization of the Moon. However, Mercury's very hostile environment, such as its extremely hot temperature would likely make such a colonization impossible.

Venus

Main article: Colonization of Venus

While the surface of Venus is far too hot and features atmospheric pressure at least 90 times that at sea level on Earth, its massive atmosphere offers an alternate location for colonization. At a height of approximately 50 km, the pressure is reduced to a few atmospheres, and the temperature would be between 40-100° C, depending on the height. This part of the atmosphere is probably within dense clouds which contain some sulfuric acid. Even these have a certain benefit to colonization, as they present a possible source for the extraction of water. Thus, the most likely colony on Venus would be a floating city in the clouds that stays 50 km or more above the surface.

Europa

The Artemis Project designed a plan to colonize Europa, one of Jupiter's moons. Scientists were to inhabit igloos and drill down into the Europan ice crust, exploring any sub-surface ocean. It also discusses use of "air pockets" for human inhabitation.

See also: Colonization of the outer solar system

Gas Giants

It may also be possible to colonize the three furthest gas giants with floating cities in their atmospheres. By heating hydrogen balloons large masses can be suspended underneath at roughly Earth gravity. Jupiter would be less suitable for habitation due to its high gravity, escape velocity and radiation. Such colonies could export Helium-3 which would be used to fuel fusion reactors for energy.

Advanced concepts

Space habitats

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 space habitat could serve as a proving ground for how well a generation ship would function as a home for hundreds or thousands of people. Such a space habitat could be isolated from the rest of humanity for a century, but near enough to Earth for help. This would test if thousands of humans can survive a century on their own before sending them beyond the reach of any help.

See also: Orbital Megastructures

Spaceship

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:

Tau Ceti

The star Tau Ceti, about eleven light years away, has an abundance of cometary and asteroidal material in orbit around it. These materials could be used for the construction of space habitats for human settlement.

Terrestrial analogues

The most famous attempt to build an analogue 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.

Remote research stations in inhospitable climates, such as the Amundsen-Scott South Pole Station or Devon Island Mars Arctic Research Station, can also provide some practice for off-world outpost construction and operation. The Mars Desert Research Station has a habitat for similar reasons, but the surrounding climate is not strictly inhospitable.

Justification

See also: Space and survival

In 2001, the space news website SPACE.com asked Freeman Dyson, J. Richard Gott and Sid Goldstein for reasons why some humans should live in space. Their respective answers were:

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.

Other important reasons: To increase the knowledge and technological abilities of Humanity.

Advocacy

Space advocacy organizations:

Objections

There are many who object to the idea of colonizing space as being too expensive and a waste of time. There is nothing in space that we really need, they say, adding that moving beyond the solar system is totally impractical in any reasonable time scale.

The pragmatic argument to 'live together on the earth we have' is a powerful one, suggesting that if even half the money of space exploration were spent for terrestrial betterment, there would be greater good for a greater number of people, at least in the short term.

The anti-space arguments have gone so far as to suggest that space colonization is a remnant of historical colonization - it is (the idea at least) a lingering desire left over from a romanticized notion of the 'founding fathers' and the conquest of territory on earth. As such, the argument goes, space exploration wins the hearts and minds of voters but does little else. Worse still, it could be said that the objective of colonizing space adds fuel to the patriotic dogma of conquest, and thus reinforces negative national prejudice rather than helping to unify earth.

As an alternative for the future of the human race, many science fiction writers have instead focused on the realm of the 'inner-space', that is the (computer aided) exploration of the human mind and human consciousness. Perhaps one example of this trend is the popular movie The Matrix, where all the action takes place on (under the surface of) Earth, and in a computer generated reality in cyberspace. However, this form of exploration need not be exclusive to space colonization, as exemplified by Transhumanist philosophies.

See also

Space colonization
Core concepts
Space habitats
Colonization targets
Terraforming targets
Organizations

External links

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