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== Space Colonization ==
=== Introduction ===
We could state that the only function of space is to be filled. Space colonization is ultimately the only way to proceed, but still there are some that object to the idea.
The permanent autonomous (self-sufficient) human habitation of locations outside Earth, would be an insurance against a global calamity, from a devastating war to the occurrence of a deadly plague, the collapse of the ecosphere or a deadly asteroid impact to name just a few. Our blue planet is indeed a fragile home and as technology advances and the human population grows chances increase that a global catastrophe will strike humanity as it has struck other species before. We should aim to escape being replaced as the dominant species or even becoming the last.
Space colonization has been fully achieved only in science fiction. Most people will think of space colonies as being on the Moon or Mars while others will advocate that colonies will first be built in orbit, and envision huge space stations as depicted in the literature and movies.
=== Location ===
The location for colonization can be:
On a planet, natural satellite, or asteroid
In orbit around the Earth, Sun, Lagrangian point or other objectOr even a mix of the two. Humanity may find a way to transport a colony-sized population of men and women to another world, but the issue remains that each one of those people requires an amazing amount of supplies, that we here on Earth take for granted. Human space flight can be seen as prohibitively expensive, and much can be accomplished by automation and remote presence.
=== Contention ===
The issue of location and the different ways to proceed is a frequent point of contention between space colonization advocates. The way to go about colonizing outer-space has been researched and many ideas have been put forward, especially by science fiction authors, some may not even include the displacement of population from one location to another, but may consist only on a permanent remote presence, or in remotely creating "life" in situ.
Some argue that moving beyond the solar system is totally impractical in any reasonable time scale. Even so there are plans being created for that eventuality. But that should not be the primary objective, ultimately our species will be forced to do so, if not for any other reason than that our Earth and Sun have an expiration date.
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 the conquest of territory on earth. Indeed most of the ideas put forward have a logical connection to the human history regarding the colonization of new lands, with the added technological limitations and advances that a new endeavor would bring today.
Some also argue that space exploration wins the hearts and minds of voters but does little else, but in fact since the Space race during the cold war this notion does not seem to stand. 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 and so, 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. But should one proposition exclude the other ?
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.
Robotics and tele-presence seems a good start for the process of colonizing space but sadly after Lunokhod 1 in 1970 and 1971 with Mars 2 and 3, only recently in 1997, did we get to do it again with the Mars Pathfinder, that successfully exceeded expectations. It seems strange that a successful strategy can be moth-balled for so long, even in the International Space Station (ISS) only in 2011 was Robonaut been given a chance. It then becomes clear that there is a general administrative (and political) problem regarding mission planning in the USA. The problem with space program stall in the USSR/Russia was mainly economic in nature (leading to a political collapse), as the economic situation and political stability improves we may still be surprised.
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: (from http://www.space.com/missionlaunches/colonize_why_011008-1.html)
To Spread Life and Beautify throughout the Universe
To Ensure the Survival of Our Species
To Make Money
Save the Environment
Provide entertainment value in order to distract from immediate surroundingsLouis 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. (see http://www.foreignaffairs.org/19800601faessay8146/louis-j-halle/a-hopeful-future-for-mankind.html)
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.
Perhaps the most powerful justification is that colonization is employed by every successful species and civilization. Obviously, species with large, diverse habitats are less prone to extinction than those in a single niche. The Earth is a tiny fraction of the solar system, and an even smaller part of the galaxy. If life were to colonize the entire solar system via a system of tens of thousands of orbital colonies, and then send generation ships to nearby stars, it would become effectively immortal. It has been noted that life has colonized every livable niche on Earth. It would be surprising if, having developed the ability to do so, life failed to colonize the solar system.
=== Politics of Space Colonization ===
Control of the solar system's resources will provide immense power and wealth to those who grasp it. Power and wealth are well known, effective motivators.
Sadly in the current state of affairs it is with some reason that people start to give credibility to the notion that man has never gone to the moon. The Moon landing was in 1969 and since 1972 we (humans) have never gone beyond Earth's orbit. Most of the human population alive today, did not experience the occasion in the necessary context. This will assuredly be the end of the phrase "If they can put a man in the Moon why can't they...", since it is a fact that today we can not put a man on the moon. It would take a bit more than a decade to do it again. This and the fact that "they" (the Western governments) have lost much if not all of the reputation "they" had especially in the fields of management, applied science and economics, the most important fields on such endeavors.
Some people argue that there will not be ever again the same level of effort put behind human space presence like we saw in the Apollo program. That all that effort was the result of the Cold War. Even considering the antagonism of the time, these arguments do not make sense, since at the time the US was already involved in a war, 1950-1973 Vietnam War and no one, especially the US was expecting the collapse of the USSR. It is then necessary to consider other complementary motivations, beyond propaganda and projection of power, and look to the continued benefits from that technological event, that lead to the advancement of numerous technologies.
With the decline of the USA supremacy, we are witnessing a downgrading of NASA (and even ESA), it is to be expected that the agencies will only support low cost projects and robotic programs fill that bill. China, the rising power has yet to build a space station (it has one programmed, Tiangong) so it will take some time for it to be able to step in as a leader in the field, even if China has also declared an interest in establishing a constant human presence on the moon.
Japan also was working in some advanced concepts, but the recent decline in its economy and stability seems bound to relegate it to a supporting role, much like Russia that lacks the political vision to see space as a viable investment beyond being a commercial orbital supplier, that holds much of the facilities, experience and know how that many others lack.
In the West this new reality puts the cards in the hands of the private enterprise, that seems to be only now taking form, even if at an accelerated pace. It is yet to be seen if they will pull anything more complex than the space tourism concept out of the bag. But the fact remains that private enterprise will not be able or willing to advance the space frontier, due to the risks involved and the higher costs of doing research and development in untested fields where unforeseen problems in development are typical. We can hope that space agencies and corporations will make improvements in already understood processes. Especially, they should adopt state of the art technology and quickly adapt to change. That was always a problem to monolithic government enterprises like NASA. This is reflected extremely well in the history of the Space Shuttle program. One lesson taken from the shuttle program may have been the need for in the future to include decision points to go along with programs that depend upon a number of untested techniques. Then progress is less likely chained to sub-optimum techniques because a commitment was made to them when a large program was undertaken as a whole.
The main problem with space exploration, that the USSR came to realize, especially after the USA won the race to put a human on the moon, was that there was no special benefit in the action itself, and that the further away from Earth the more costly it becomes. That is why the USSR has centered on and invested in establishing long human presence in near Earth orbit (holding that record). Note that the USSR was the first nation to put a satellite in orbit, a camera on the moon and to return to Earth the first piece of extraterrestrial soil. It did also extremely well in pioneering the exploration of other planets like Mars and Venus. It would be interesting to know what nations have spent more in space exploration so far.
The solution then seems to point to going out in small incremental steps.
== International Space Law ==
International Space Law is a set of documents which govern activities in outer space by the governments of the Earth. While nobody actually lives permanently outside of Earth right now, to suggest there are no existing laws governing activities in space is not accurate either. Right now outer space is governed through various international treaties regarding who is responsible for the equipment that goes beyond Earth and what legal rights may be asserted by governments of many nations. Below are some of the major documents of space law and a brief overview of each document:
Outer Space Treaty - Basic governance of extraterrestrial bodies and relinquishment of sovereignty claims by Earth governments.
Moon Treaty - Follow up treaty to Outer Space Treaty, but has not been ratified by any major space-faring nation except for France.
Nuclear Test Ban Treaty - Prohibition of nuclear weapons in space and legal consequences of nuclear detonation in space. Also affects technologies like the Orion project and nuclear rockets.
Montevideo Convention - declaring requirements to be recognized as a "state" by the UN and other nations.
The Antarctic Treaty - The original international treaty for new territories post WWII, and the basis for much of the current space law even if it doesn't explicitly deal with celestial bodies.
=== United States of America ===
In April 2, 2012 the Competitive Enterprise Institute (CEI), a non-profit think tank with the purpose of advancing economic liberty and fighting over-regulation by big government released a new study named Homesteading the Final Frontier: A Practical Proposal for Securing Property Rights in SpacePDF by Adjunct Scholar Rand Simberg. In it they argue that the U.S.A. should recognize transferable off-planet land claims. Arguing that the 1967 Outer Space Treaty only clearly prohibits declarations of national sovereignty, and noting that the U.S.A. is not a signatory of the 1979 Moon Treaty, which does outlaw private property claims in space. That a legal regime for real estate on the Moon, planets and asteroids could usher in a new era of space exploration at little or no cost to the U.S.A. government. But without off-planet property rights, investors have little incentive to fund space transportation or development.
== Space Advocacy ==
Space advocacy organizations:
The Alliance to Rescue Civilization plans to establish backups of human civilization on the Moon and other locations away from Earth. 
The Colonize the Cosmos site  advocates orbital colonies.
The Artemis Project plans to set up a private lunar surface station. 
The British Interplanetary Society, founded in 1933, is the world's longest established space society. 
The Living Universe Foundation has a detailed plan in which the entire galaxy is colonized. 
The Mars Society promotes Robert Zubrin's Mars Direct plan and the settlement of Mars. 
The National Space Society is an organization with the vision of "people living and working in thriving communities beyond the Earth." 
The Planetary Society is the largest space interest group, but has an emphasis on robotic exploration and the search for extraterrestrial life. 
The Space Frontier Foundation promotes strong free market, capitalist views about space development. 
The Space Studies Institute was founded by Gerard K. O'Neill to fund the study of space habitats. 
Students for the Exploration and Development of Space (SEDS) is a student organization founded in 1980 at MIT and Princeton. 
Foresight Nanotechnology Institute - The space challenge
= Space Colonization =
= Living in Space =
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.
Several design groups 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.
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.
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 way-station 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, we do not classify all space stations as a space habitat since they are not a replication of the natural environment necessary to sustain a species population, they are by definition artificially maintained and temporary, 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, this concept is also referred to as the Ark model. A colony ship would be similar to a space habitat, except with major propulsion capabilities and independent power generation. 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.
The Earth is an open system, it constantly gets input from external sources from energy to matter. In a generation ship (or a long term habitat) a subset of these functions need to be mimicked as a self sustained closed system (depending on the mission and location, on a solar system energy will be possible to be introduced at no cost during a long period). Much has been learned from attempts made on Earth to simulate isolated living systems (useful for the production of food, reprocessing or gases and water in space). The Biosphere 2, originally built to be an artificial, materially closed ecological system, now a center dedicated to research, outreach, teaching of living systems. There is also the BIOS-3 dedicated to the study of am algaculture based closed system.
The generation ship concepts is proposed in several hard science fiction works and it includes:
Generation ship, hypothetical starship that would travel much slower than light between stars, with the crew going through multiple generations before the journey is complete
Sleeper ship, hypothetical spaceship in which most or all of the crew spend the journey in some form of hibernation or suspended animation
Embryo carrying Interstellar Starship (EIS), hypothetical starship much smaller than a generation ship or sleeper ship transporting human embryos in a frozen state to an exoplanet
The main disadvantage of orbital colonies in relation to a colony ship is the inability to seek them on their own, this is of course compensated by low costs (no engine, propellant) and reduction of risks. Building cities in space will require materials, energy, transportation, communications, life support, and radiation protection. These could 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.
Transportation is then the key to any space endeavor. Present launch costs are very high 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. 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 electric catapults on the Moon to launch bulk materials to waiting settlements, but then these type of solutions will get into the highest ground problem, since they can also be used as a weapon.
The issue with energy can be easily addressed by the use of solar energy, 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 even an export item for space settlements, using microwave beams to send power to Earth.
== Lagrange Points ==
== Small Asteroids ==
Some small asteroids have the advantage that they may pass closer than Earth or it'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.
A small asteroid could serve functions equal to space stations, with the benefit that some building material would already be present. Most of the disadvantages are similar to those of an artificially created space station. 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 anything else of significant mass.
== New Measuring Standards ==
Life Off-Earth is going to be different enough that a number of "standards" that we take for granted on the Earth are also going to need modification. Even very basic physical measurements like time and distance will have to be adjusted to fit with experiences on Mars as those measurements are largely associated with physical aspects of the Earth.
Units of Time - Even though target planets and the Earth may rotate at the same rate, there are can be some subtle differences that make measuring local time to be quite different from terrestrial experiences.
Distance - While standard units of measure that were developed on the Earth can be used elsewhere, it is likely that some new measurement units will result from activities on orbitally static object (like a measurement to the sun and other locations important location on that solar system, this is important for travel time and estimating costs).
Mass and Weight - The difference of gravity between the Earth and the target planet is going to have an impact on how things are built and how people live. Some things stay the same while there are some important differences as well.
= Colonizing other Celestial Bodies =
== Colonizing Mars ==
Mars is a frequent topic of discussion regarding colonization possibilities. A project for the colonization of Mars provides an opportunity to examine how we live here on Earth and what aspects of our own planet and its effects on our lives we value and would wish to re-create on Mars. The Mars Project also provides a case-study for further planetary colonization.
Mars overall surface area is similar to the dry land surface 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.
Mars's 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.
As of 2011, according to the Journal of Cosmology, an interplanetary trip to Mars from Earth, could take as little as 10 months, and it would be possible for a privately-funded one-way mission to Mars to depart as soon as 20 years from now. But returning would be virtually impossible (due to payload and energy restrictions).
In regards to volunteers, in 2011 a special edition of the Journal of Cosmology, detailing and promoting a privately-funded one-way mission to Mars prompted more than 400 readers to volunteer as colonists. This leads to the conclusion that there are people willing to take on the risk, but it also creates the need to select those that should and are more capable of being successful.
Solar energy would be a problem in mars, there is not only night time to consider but a large amount of dust.
There is an ongoing debate on this topic on the Mars Civil-Cultural mailing list. One way that this topic can be explored is to look at the lessons learned from science fiction.
=== Life and fossils ===
There is increasing evidences that point to the, at least ancient, presence of life on Mars, this has created a strong scientific interest in colonizing Mars. A study from 2011 from NASA indicates that if life existed on at some point in Mars history, the best chances for it to have survived (or at least to have persisted longer) would have been below the surface. This hypothesis is based in geological studies performed by probes from NASA and the European Space Agency in more than 350 sites, along with what is known of mars today.
=== Water ===
Water is one of the most important substances for life as we know it. In the last three decades upon reviewing images of the surface of Mars taken by the Viking orbiters in the 70s, scientists became puzzled by the apparent sloping of rocky material around mountains and cliffs, these deposits, referred to as lobate debris apron, seems to extend sometimes for tens of miles. The debate around those formations generated the theory that they may have been formed by the lubrication of the rocky debris by a thin layer of ice, since similar features can be observed on Earth, for instance in Antarctica.
A new indication that water seems to exist on the planet came from data collected by the Shallow Subsurface Radar (SHARAD) instrument aboard the Mars Reconnaissance Orbiter probe, lunched in August 12, 2005 and operating at destination from 2006 onward. The radar results are consistent with massive deposits of water in middle latitudes, providing further support for the debris covered glacier hypothesis.
Equipment is available to extract in situ resources (water, air, etc.) from the Martian ground and atmosphere.
=== Agriculture ===
Martian soil contains several nutrients required to support to plant life. With fertilizer and environmental control, it could be used to grow plants.
=== Artifacts and equipment already available ===
There are several artifacts left on the surface of Mars from previous exploration and still working equipment, like monitoring satellites.
== Colonies on the Moon ==
The Moon is Earth's only natural satellite, it is also known as Luna in Latin and other languages. Due to its proximity and relative familiarity, Earth's Moon is also frequently discussed as a target for colonization.
A colony on Luna has several important advantages over a colony on any other celestial body outside Earth.
One big advantage is that it is close proximity to Earth. It would be comparatively easy to supply any colonization process, place and evacuate colonists, and use radio signals for reprogramming and remote control of robots and other devices on the Moon's surface. Another advantage is the low gravity, allowing for easier exchange of goods and services. But the topmost advantage is that we already have been there.
Solar energy on the moon is a possibility by the moon has two week nights and similar to Mars dust will constitute a problem, not atmospheric dust but the surface regolith is an extreme problem, making nuclear power more attractive.
A major drawback of the Moon is its low abundance of volatiles necessary for life such as hydrogen and carbon. Water ice deposits was found in relative abundance, especially in some polar craters, that could serve as significant sources for these elements.
India's first unmanned lunar probe, launched in 22 October 2008, Chandrayaan-1 intended to last for 2 years in a compressive mapping of moon resources has generated data that leads NASA's scientists to estimate the existence of 600 million metric tons of water ice in craters around the Moon's north pole.
The existence of numerous craters near the poles of the Moon that have interiors that are in permanent sun shadow, makes them capable of maintaining very low temperatures. Without the effects from the Sun's radiation water can be indefinitely kept as ice. If this estimation is verified, mining this resource, could serve as a source of life support for future lunar bases as water and oxygen or as propellant for future spacecraft if converted to methane, dramatically reducing the cost of space exploration. NASA in April 2012 contracted Astrobotic Technology Inc. to determine whether its polar rover can deploy an ice-prospecting payload to the Moon, aiming for such verification.
There are also several magma caves that would facilitate the creation of protected habitats.
According to M.J. Fogg, "it is just possible to terraform the Earth's moon, so long as you are prepared to keep its imported volatiles topped up every few thousand years or so".
The lunar space elevator
=== Planed Moon Colonies ===
== 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.
== 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 sulphuric 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 above 50 km 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.
== 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 unsuitable 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.
== Stars ==