Space colonization

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Image:Internal view of the Stanford torus.jpg
Artist's conception of a space habitat called the Stanford torus, by Don Davis

Space colonization (also called space settlement, space humanization, space habitation, etc.) is the concept of permanent autonomous (self-sufficient) human habitation of locations outside Earth. It is a major theme in science fiction, as well as a long-term goal of various national space programs.

While many 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.

In 2005 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 or 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. ”

—Michael D. Griffin[1]

Contents

Space colonization

Outer solar system

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[edit] Method

Building colonies in space will require access to space, people, food, construction materials, energy, transportation, communications, life support, simulated gravity (using steady circular rotation), and radiation protection. Colonies will presumably be situated to help fulfill those requirements.

[edit] Materials

Colonies on the Moon and Mars could use local materials, although the Moon is deficient in volatiles (principally hydrogen, and nitrogen) but possesses a great deal of oxygen, silicon, and metals such as iron, aluminum and titanium. Launching materials from Earth is very expensive, so bulk materials could come from the Moon or Near-Earth Objects (NEOs — asteroids and comets with orbits near Earth), Phobos, or Deimos where gravitational forces are much less, there is no atmosphere, and there is no biosphere to damage. Many NEOs contain substantial amounts of metals, oxygen, hydrogen and carbon. Certain NEOs may also contain some nitrogen.

Farther out, Jupiter's Trojan asteroids are thought to be high in water ice and probably other volatiles [1].

[edit] Energy

Solar energy in orbit is abundant, reliable, and is commonly used to power satellites today. There is no night in space, and no clouds or atmosphere to block sunlight. The solar energy available, in watts per square meter, at any distance, d, from the Sun can be calculated by the formula E = 1366/d², where d is measured in astronomical units.

Particularly in the weightless conditions of space, sunlight can be used directly, using large solar ovens made of lightweight metallic foil so as to generate thousands of degrees of heat at no cost; or reflected onto crops to enable photosynthesis to proceed.

Large structures would be needed to convert sunlight into significant amounts of electrical power for settlers' use. In highly electrified nations on Earth, per-capita electrical consumption can average 1 kilowatt/person (or roughly 10 megawatt-hours per person per year.)[2]

Energy has been suggested as an eventual export item for space settlements, perhaps using wireless power transmission e.g. via microwave beams to send power to Earth or the Moon. This method has zero emissions, so would have significant benefits such as elimination of greenhouse gases and nuclear waste. Ground area required per watt would be less than conventional solar panels.

The Moon has nights of two Earth weeks in duration and Mars has night, dust, and is farther from the Sun, reducing solar energy available by a factor of about ½-⅔, and possibly making nuclear power more attractive on these bodies. Alternatively, continuous[dubious – discuss] energy could be beamed to the lunar surface from a solar power satellite at the Lagrange L1 location.

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. Alternatively, the waste heat can be used to melt ice on the poles of a planet like Mars.

[edit] Transportation

[edit] Space Access

Transportation to orbit is often the limiting factor in space endeavours. Present-day launch costs are very high — $3,000 to $25,000 per kilogram from Earth to Low Earth Orbit (LEO).[citation needed] To settle space, much cheaper launch vehicles are required, as well as a way to 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 other organizations, both public and private. There are also proposed projects such as building a space elevator or a mass driver; or launch loops.

[edit] Cislunar and Solar System travel

Transportation of large quantities of materials from the Moon, Phobos, Deimos, and Near Earth asteroids to orbital settlement construction sites is likely to be necessary.

Transportation using off-Earth resources for propellant in relatively conventional rockets would be expected to massively reduce in-space transportation costs compared to the present day; propellant launched from the Earth is likely to be prohibitively expensive for space colonization, even with improved space access costs.

Other technologies such as tether propulsion, VASIMR, ion drives, solar thermal rockets, solar sails, magnetic sails, and nuclear thermal propulsion can all potentially help solve the problems of high transport cost once in space.

For lunar materials, one well-studied possibility is to build electronic catapults to launch bulk materials to waiting settlements. Alternatively, lunar space elevators might be employed.

[edit] Communication

Compared to the other requirements, communication is relatively easy for orbit and the Moon. A great proportion of current terrestrial communications already passes through satellites. Yet, as colonies further from the earth are considered, communication becomes more of a burden. Transmissions to and from Mars suffer from significant delays due to the speed of light and the greatly varying distance between conjunction and opposition — the lag will range between 7 and 44 minutes — making real-time communication impractical. Other means of communication that do not require live interaction such as e-mail and voice mail systems should pose no problem.

[edit] Life support

People need air, water, food, gravity and reasonable temperatures to survive for long periods. On Earth, a large complex biosphere provides these. In space settlements, a relatively small, closed ecological system must recycle or import all the nutrients without "crashing."

The closest terrestrial analogue to space life support is possibly that of the 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" and typically dump carbon dioxide overboard, although they recycle oxygen. Recycling of the carbon dioxide has been approached in the literature using the Sabatier process or the Bosch reaction.

Alternatively, and more attractive to many, 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:

Note that plant based life support systems are very inefficient in their use of energy; about 1-3% energetic efficiency is common.[citation needed] This means that 97-99% of the light energy provided to the plant ends up as heat and needs to be dissipated somehow to avoid overheating the habitat.

A combination of the above technologies is also possible.

[edit] Radiation protection

Cosmic rays and solar flares create a lethal radiation environment in space. In Earth orbit, the Van Allen belts make living above the Earth's atmosphere difficult. 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 cheaply with leftover material (slag) from processing lunar soil and asteroids into oxygen, metals, and other useful materials, however it represents a significant obstacle to maneuvering vessels with such massive bulk. Inertia would necessitate powerful thrusters to start or stop rotation.

[edit] 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 (see Gaia spore). 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

[edit] 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 as little as 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 <math>N_e = 50</math> prescription corresponds to an inbreeding rate of 1% per generation, approximately half the maximum rate tolerated by domestic animal breeders. The <math>N_e = 500</math> 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:

<math>N_e = \frac{4 \times N_m \times N_f} {N_m + N_f}</math>

[edit] Location

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

The location of colonization can be:

[edit] Planetary Locations

Some planetary colonization advocates cite the following potential locations:

[edit] Mars

Main article: Colonization of Mars

Mars is a frequent topic of discussion. Its overall surface area is similar to the dry land surface of Earth, it may have large water reserves, and has carbon (locked as carbon dioxide in the atmosphere).

Mars 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, and may even still exist in some parts of the planet.

However, its atmosphere is very thin (averaging 800 Pa or about 0.8% of Earth sea-level atmospheric pressure); so the pressure vessels necessary to support life are very similar to deep space structures. The climate of Mars is colder than Earth's. Its gravity is only around a third that of Earth's; it is unknown whether this is sufficient to support human beings for extended periods of time (all long-term human experience to date has been at around Earth gravity or one g).

The atmosphere is thin enough, when coupled with Mars' lack of magnetic field, that radiation is more intense on the surface, and protection from solar storms would require radiation shielding.

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, Martian terraforming

[edit] 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. Such colonies would almost certainly be restricted to the polar regions due to the extreme daytime temperatures elsewhere on the planet.

[edit] 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 a possible 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 may have a certain benefit to colonization, as they present a possible source for the extraction of water.

See also: Venusian terraforming

[edit] Gas Giants

Main article: Colonization of Jupiter

It may also be possible to colonize the three farthest 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 for use in fusion reactors if they ever become practical.

[edit] Satellite locations

[edit] The Moon

Image:Mooncolony.jpg
Moon colony
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 proximity to Earth and lower escape velocity, 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 that may exist in some polar craters could serve as a source for these elements. An alternative solution is to bring hydrogen from NE asteroids and combine it with oxygen extracted from lunar rock.

The moon's low surface gravity is also a concern (it is unknown whether 1/6g is sufficient to support human habitation for long periods — see microgravity).

[edit] Europa, Callisto (or other Jovian moons)

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. This plan also discusses possible use of "air pockets" for human inhabitation.

See also: Colonization of Europa
See also: Colonization of Callisto
See also: Colonization of the outer solar system

[edit] Phobos and Deimos

The moons of Mars may be an appealing target for space colonization. Low delta-v is needed to reach the Earth from Phobos and Deimos, allowing delivery of material to cislunar space, as well as transport around the Martian system. The moons themselves may be inhabited, with methods similar to those for asteroids.

[edit] Titan

Main article: Colonization of Titan

Titan has been suggested as an appealing target for colonization,[3] because it is the only moon in our solar system to have a dense atmosphere and is rich in carbon-bearing compounds.[4]

[edit] Free space locations

[edit] Space habitats

Main article: Space habitat

Free space locations in space would necessitate a space habitat, also called space colony and orbital colony, or a space station which would be 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. Many design proposals have been made with varying degrees of realism by both science fiction authors and engineers.

A space habitat would also serve as a proving ground for how well a generation ship could function as a long-term 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.

[edit] Earth orbit

Compared to other locations, Earth 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. It's not known what the minimum g-force is for ongoing health but 1g is known to ensure that children grow up with strong bones and muscles.

The main disadvantage of orbital colonies is lack of materials. These may be expensively imported from the Earth, or more cheaply from extraterrestrial sources, such as the Moon (which has ample metals, silicon, and oxygen), Near Earth Asteroids, which have all the materials needed (with the possible exception of nitrogen[citation needed]), comets, or elsewhere.

[edit] Lagrange points

Image:Lagrange points.jpg
A contour plot of the effective potential (the Hill's Surfaces) of a two-body system (the Sun and Earth here), showing the five Lagrange points.

Another near-Earth 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.

However, the fact that Lagrange points L4 and L5 tend to collect dust and debris, while L1-L3 require active station-keeping measures to maintain a stable position, make them somewhat less suitable places for habitation than was originally believed.

[edit] Asteroids

Main article: Colonization of the asteroids
[edit] Near Earth Asteroids

Many small asteroids in orbit around the Sun have the advantage that they pass 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.

[edit] Main Belt Asteroids

Colonization of asteroids would require space habitats. The asteroid belt has significant overall material available, although it is thinly distributed as it covers a vast region of space. 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 that their asteroid did not hit Earth or any other body of significant mass, but would have extreme difficulty in moving an asteroid 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.

[edit] Statites

Main article: Statite

Statites or "static satellites" employ solar sails to position themselves in orbits that gravity alone could not accomplish. Such a solar sail colony would be free to ride solar radiation pressure and travel off the ecliptic plane. Navigational computers with an advanced understanding of flocking behavior could organize several statite colonies into the beginnings of the true "swarm" concept of a Dyson sphere.

[edit] Outside the Solar system

Colonization of the entire Solar system would take hundreds or thousands of years. Looking beyond our solar system, there are billions of potential suns with possible colonization targets.

Physicist Stephen Hawking has said:[5][6]

“ The long-term survival of the human race is at risk as long as it is confined to a single planet. Sooner or later, disasters such as an asteroid collision or nuclear war could wipe us all out. But once we spread out into space and establish independent colonies, our future should be safe. There isn't anywhere like the Earth in the solar system, so we would have to go to another star. ”

[edit] Starship

An interstellar colony ship would be similar to a space habitat, except with major propulsion capabilities and independent energy generation.

Concepts proposed both by scientists and in hard science fiction include:

[edit] Example

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.

[edit] Terrestrial analogues to space colonies

The most famous attempt to build an analogue to a self-sufficient 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 permanent 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.

[edit] Literature

The literature for space colonization began in 1869 when Edward Everett Hale wrote about an inhabited artificial satellite.[7]

The Russian schoolmaster and physicist Konstantin Tsiolkovsky foresaw elements of the space community in his book Beyond Planet Earth written about 1900. Tsiolkovsky had his space travelers building greenhouses and raising crops in space.[8]

Others have also written about space colonies as Lasswitz in 1897 and Bernal, Oberth, Von Pirquet and Noordung in the 1920s. Wernher von Braun contributed his ideas in a 1952 Colliers article. In the 1950s and 1960s, Dandridge M. Cole[9] and Krafft Ehricke published their ideas.[citation needed]

Another seminal book on the subject was the book The High Frontier: Human Colonies in Space by Gerard K. O'Neill[10] in 1977 which was followed the same year by Colonies in Space by T. A. Heppenheimer.[11]

M. Dyson wrote Home on the Moon; Living on a Space Frontier in 2003;[12] Paul Eckart wrote Lunar Base Handbook in 2006[13] and then Harrison Schmitt's Return to the Moon written in 2007.[14]

[edit] Justification

Main article: 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:[15]

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.[16]

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.[17]

Another important reason used to justify space is the effort to increase the knowledge and technological abilities of humanity.

[edit] Objections

There are some who object to the idea of colonizing space as being "too expensive and a waste of time". According to this view, there is nothing in space that we really need, adding that moving beyond the solar system is totally impractical in any "reasonable" time scale[citation needed].

The argument to live together on the earth we have suggests 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. This argument assumes that money not spent on space would automatically go toward socially beneficial projects. It also assumes that space colonization is not itself a valuable goal (see Space and survival).

Some anti-space arguments have gone so far as to suggest that space colonization is a remnant of historical colonization, an idea which is said to be 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. It is even said by some 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[citation needed].

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.

[edit] Counter arguments

The argument of need: The population of Earth continues to increase, while its carrying capacity and available resources do not. If the resources of space are opened to use and viable life-supporting habitats can be built, the Earth will no longer define the limitations of growth (see extraterrestrial population growth).

The argument of cost: Very many people greatly overestimate how much money is spent on space, and underestimate how much money is spent on defense or health care. For example, as of June 13, 2006, over $320 billion has been allocated by the US Congress for the current war in Iraq, in comparison it only cost $2 billion to create the Hubble Space Telescope, and NASA's yearly budget averages only about $16 billion a year, in other words the money that has been spent on the Iraq war could have funded NASA for approximately 21 years.

The argument of Nationalism: Space proponents counter this argument by pointing out that humanity as a whole has been exploring and expanding into new territory since long before Europe's colonial age, going back into prehistory (the nationalist argument also ignores multinational cooperative space efforts); that seeing the Earth as a single, discrete object instills a powerful sense of the unity and connectedness of the human environment and of the immateriality of political borders; and that in practice, international collaboration in space has shown its value as a unifying and cooperative endeavor.[16]

The argument of 'Inner Space': This form of exploration need not be exclusive to space colonization, as exemplified for example by Transhumanist philosophies.

[edit] Advocacy

Space advocacy organizations:

[edit] In fiction

Although established space colonies 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 much rarer. The following list is restricted to works dealing primarily with the initial stages of colonization.

[edit] Written works

[edit] Games

  • Alien Legacy (1994), computer game. Player has to manage new colonies on the planets of Beta Caeli.
  • Ascendancy (1995), computer game. Player tries to grow a colony into a spacefaring civilization.
  • Outpost (1994), computer game. Player plans and manages a colony on another planet.
  • Outpost 2 (1997), computer game. Player manages a colony on the fictional planet of New Terra.
  • Sid Meier's Alpha Centauri (1999), computer game. Player tries to expand a human colony on Alpha Centauri.
  • Starfarers of Catan (1999), tabletop game. Player manages trade and colonization in the fictional planetary system of Catan.

[edit] Comics

[edit] Television

  • Earth 2 (1994-1995), television series. A refugee group travels to and tries to colonize a distant Earth-like planet.
  • Mobile Suit Gundam (1979-1980), animated television series. The series as well as its sequels and spin-offs mostly revolve around the conflicts between the Earth and the space colonies.
  • Firefly (2002-2003), a television series. The series, and the followup film Serenity, dealt with a mass exodus from an overcrowded Earth to a new solar system, involving the terraforming and colonisation of these new worlds.

[edit] RPG's

[edit] See also

[edit] References

  1. ^ "NASA's Griffin: 'Humans Will Colonize the Solar System'", Washington Post, September 25, 2005, pp. B07. 
  2. ^ http://www.unescap.org/esd/energy/information/ElectricPower/1999-2000/access.htm
  3. ^ Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: Titan, pp. 163-166, Tarcher/Putnam, 1999, ISBN 978-1-58542-036-0
  4. ^ NASA page: News-Features-the Story of Saturn saturn.jpl.nasa.gov. Retrieved 8 January 2007.
  5. ^ Move to new planet, says Hawking (2006).
  6. ^ Mankind must colonise other planets to survive, says Hawking (2006).
  7. ^ E. E. Hale. The Brick Moon. Atlantic Monthly, Vol. 24, 1869.
  8. ^ K. E. Tsiolkovsky. Beyond Planet Earth. Trans. by Kenneth Syers. Oxford, 1960
  9. ^ Dandridge M. Cole and Donald W. Cox Islands in Space. Chilton, 1964
  10. ^ G. K. O'Neill. The High Frontier: Human Colonies in Space. Morrow, 1977.
  11. ^ T. A. Heppenheimer. Colonies in Space. Stackpole Books, 1977
  12. ^ Marianne J. Dyson: Living on a Space Frontier. National Geographic, 2003
  13. ^ Paul Eckart. Lunar Base Handbook. McGraw-Hill, 2006
  14. ^ Harrison H. Schmitt. Return to the Moon. Springer, 2007.
  15. ^ Britt, Robert Roy. "The Top 3 Reasons to Colonize Space", Space.com, 08 October 2001. 
  16. ^ Halle, Louis J. (Summer 1980). "A Hopeful Future for Mankind". Foreign Affairs.
  17. ^ Life After Earth: Imagining Survival Beyond This Terra Firma. New York Times.
  18. ^ http://space.alglobus.net/
  19. ^ http://www.space-settlement-institute.org
  20. ^ http://www.seds.org/
  21. ^ http://www.foresight.org/challenges/space.html

[edit] External links

 v • d • e The Solar System
<imagemap>

Image:Solar System XXVII.png

  1. The Sun

circle 0 0 90 35 The Sun

  1. Mercury

circle 112 18 6 Mercury

  1. Venus

circle 153 18 8 Venus

  1. Earth and the Moon

circle 203 8 4 The Moon circle 194 18 8 Earth

  1. Mars and satellites

circle 239 13 3 Phobos and Deimos circle 233 18 8 Mars

  1. Ceres and the asteroid belt
  2. - by placing the rectangle code for the asteroid belt AFTER Ceres, Ceres is "on top" (and can co-exist)

circle 271 18 8 Ceres rect 256 0 288 35 The asteroid belt

  1. Jupiter and satellites

circle 316 18 15 Jupiter circle 329 5 6 Moons of Jupiter

  1. Saturn and satellites

circle 372 18 10 Saturn circle 381 7 6 Moons of Saturn

  1. Uranus and satellites

circle 418 18 9 Uranus circle 427 10 6 Moons of Uranus

  1. Neptune and satellites

circle 471 10 3 Moons of Neptune circle 462 18 12 Neptune

  1. Pluto, satellites, and the Kuiper belt
  2. - by placing the rectangle code for the Kuiper belt AFTER Pluto, Pluto is "on top" (and can co-exist)

circle 508 13 3 Moons of Pluto circle 504 18 8 Pluto rect 492 0 527 35 The Kuiper Belt

  1. Eris, Dysnomia, and the Scattered disc
  2. - by placing the rectangle code for the Scattered disc AFTER Eris, Eris is "on top" (and can co-exist)

circle 544 14 3 Dysnomia circle 540 18 8 Eris rect 528 0 567 35 The Scattered Disc rect 568 0 597 35 The Oort Cloud

desc none

  1. - setting this to "bottom-right" will display a (rather large) icon linking to the graphic, if desired
  1. Notes:
  2. Details on the new coding for clickable images is here: [3]
  3. The smaller planets have a bit of an overlap just to ensure they're locatable, especially in the belts.
  4. While it may look strange, it's important to keep the codes for a particular system in order. The clickable coding treats the first object created in an area as the one on top.
  5. - I've placed moons on "top" so that their smaller circles won't disappear "under" their respective planets or dwarf planets.
  6. The "poly" code would be more appropriate for the moons of Jupiter, Saturn, and Uranus. However, there appears to be a bug with that aspect of the code.
  7. - I've compensated by using oversized circles for those moon groups, and tucking them UNDER their planets for now.
  8. The Sun is a rectangle as that approximates the edge closely enough for the purposes of this template.
  9. I've guessed as to the boundaries for the KB, SD, and OC - if they need adjustment, load the image into Paint and use the pencil tool to find the appropriate coordinates.

</imagemap>

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See also astronomical objects, the solar system's list of objects, sorted by radius or mass, and the Solar System Portal
es:Colonización del espacio

fr:Colonisation de l'espace id:Kolonisasi angkasa it:Colonizzazione dello spazio he:מושבת חלל nl:Ruimtekolonisatie ja:宇宙移民 pt:Colonização espacial ru:Колонизация космоса sr:Колознизација свемира fi:Avaruuden kolonisaatio sv:Rymdkolonisation zh:太空移民

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