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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, 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 most people think of space colonies on the Moon or Mars, others argue that the first colonies will be in orbit (see International Space Station). 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.

Current NASA chief Michael Griffin has 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."[1]

Method

Building colonies in space will require 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.

Materials

Colonies on the Moon and Mars could use local materials, although the Moon is deficient in volatiles (principally hydrogen, carbon 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. 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.

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

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 solar ovens made of lightweight metallic foil so as to generate thousands of degrees of heat. Large structures would be needed to convert sunlight into significant amounts of electrical power for settlers' use in space. The energy requirements of a non-terrestrial colony are heavily dependent on the purpose and usage of the colony. For example, a colony that exists for mass production of energy intensive products such as metallic products or high-precision electronics components would require much more energy than an agrarian colony.

Energy has been suggested as an export item for space settlements, perhaps using microwave beams to send power to Earth or the Moon. see also Solar Power Satellite

In many areas, the Moon has nights of two Earth weeks in duration reducing solar energy available and possibly making nuclear power more attractive there, unless energy storage can meet the night-time demand. Mars is further from the sun, thus it receives less solar energy available in orbit. However, the thinner atmosphere of Mars reflects and absorbs less of the energy than Earth's thick atmosphere does, thus making the surface differences much less than is widely noted.

For both solar thermal and nuclear power generation in airless environments, such as the Moon and space, one of the main difficulties is dispersing the inevitable heat generated. This requires fairly large radiator areas that are placed "in shadow" of the panels or other large blocking structures. This increases launch mass, costs, and complexity of orbital and free-space colonies.

On the lunar surface, the moon itself can be used as a heat sink using Heat conduction to bleed the heat off. Mars power generation can use ground storage as well as some atmospheric convection to manage thermal extremes generated by solar or thermal power systems. The key to managing thermal aspects of solar or nuclear power are the same as most aspects of colonization: maximum use and reuse of available resources.

Transportation

Space Access

Transportation to orbit is often the limiting factor in space endeavors. Present-day launch costs are very high - $5,000 to $ 30,000 per kilogram from Earth to Low Earth Orbit (LEO). 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 to build a space elevator.

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, 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.

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 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, such as e-mail and voice mail systems should pose no problem.

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 system must recycle or import all the nutrients without "crashing."

The closest terrestrial analogue to space life support is possibly that of Nuclear submarines. 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. 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.

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.

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 prescription corresponds to an inbreeding rate of 1% per generation, approximately half the maximum rate tolerated by domestic animal breeders. The 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:

Location

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

The location of colonization can be:

Planetary Locations

Planetary colonization advocates cite the following potential locations:

Mars

Main article: Colonization of Mars

Mars is a frequent topic of discussion among space colonization enthusiasts and scientists. Its overall surface area is similar to the dry land surface of Earth, it's water reserves are known to exist and may be large. It has a very large supply of carbon (predominantly as carbon dioxide in the atmosphere). Carbon Dioxide provides Mars with a significant readily available resource when the Sabatier reaction is utilized.

Mars may have gone through similar geological and hydrological processes as Earth, but this is debated. Mars is known to possess valuable metals and minerals, some in larger proportion than Earth, other is lesser proportion. 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. Yet the atmosphere that is provided by Mars gives it several advantages over a free-space colony. Among these are radiation protection and readily available resources for processing via simple technology (Zubrin & Wagner 2006).

The climate of Mars is colder than Earth's. However, in comparison to other non-planetary locations for space colonies or settlements, the temperature swings are much less, as are the extremes. This provides significant benefit and advantage due to a wider variety of habitat material construction. Compared to free-space colony locations, Mars is warmer. 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


Mars gravity is only around a third that of Earth; it is unknown whether this is sufficient to support human beings for long periods (all long term human experience to date has been at around Earth gravity or zero-g). Much of the literature and research has out of necessity been concerned primarily with Earth return. In a settlement or colony situation, Earth visits may not be an issue. To date, research has not found that the bone and muscle tissue loss associated with low-to-no gravity situations has been a health concern as long as the subject remains in such an environment. However, terrestrial research into Martian gravity level effects on humans is ongoing. [1] Ultimately, short of gravity control which renders the concern moot anyway, the only way to answer the concerns over long-term low-to-no gravity effects on biological entities is to put the entities in these environments long-term and observe.

The atmosphere is thin enough, when coupled with Mars' weaker (compared to Earth) magnetic field, that radiation is more intense on the surface in comparison to Earth surface norms. Protection from solar storms would require radiation shielding, though less than free-space colonies. The presence of the planetary body with atmosphere also provides significant protection from cosmic radiation radiation compared to free-space colonies. When comparing exposed surface exposure to GCR on Mars to, for example, the International Space Station, one finds the levels are similar.[2] Rudimentary radiation protection for Martian settlers and visitors reduces the exposure to less than is currently found on the ISS.

It should also be noted that the increased levels of GCR compared to Earth surface are not necessarily a large risk factor. Research and rigorous study has shown that a Martian surface colony with minor shielding (as in sandbags on the roof of a metal habitat) represent an increase in cancer risk of low single digits. (“Single Track Effects and New Directions in GCR Risk Assessment,” Adv. Space. Res., Vol. 14, No. 10, pp.(10)885-(10)894, 1994 ) Dr. Curtis breaks down the incremental risk to each organ of the body (Table 1, p.(10)888.) It has been noted [3] that stays on Mars for a period of years represents an increased risk in a nonsmoker approximately equal to smoking for that period of time - including a round trip Mars from Earth.

However, the biological effects of low level ionizing radiation (such as cosmic radiation) depend on the body's ability to replace cells killed by the radiation - there is no buildup to be dealt with. The comparatively increased radiation exposure of a human/animal on Mars versus Earth is not confirmed to be it levels beyond average human recovery. There are studies and research that show that a slight increase in ionizing radiation can be beneficial to plant and animal life. [4] [5] [6] [7] [8] [9]

Mars has also been suggested as forming a critical part in interplanetary trade by Zubrin in his book The Case for Mars. In this scenario Mars serves as the primary center of operations for asteroid belt mining. It is argued that due to costs involved with asteroid belt mining based on Earth or in Earth orbit, that a Mars settlement would be a cheaper base of operations. Zubrin envisions Mars processes raw materials from the belt and ships finished goods (such as free-space colony parts, water, food, air) to Earth orbit, with Mars providing the means for using the existing body of knowledge in construction and material processing, and possibly developing new techniques and process improvements that may have relevance to terrestrial production. Of the four common locations for non-terrestrial human colonization (Luna, Mars, Earth orbit, Asteroid belt), only Mars provides a mixture of available resources and accessibility. The other intra-system locations have (known or potential) high amounts of a few needed resources combined with a lack of other critical resources.

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.

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

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 for use in fusion reactors if they ever become practical.

Satellite locations

The Moon

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 close 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 Earth 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).

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

See also: Colonization of the outer solar system

Phobos and Deimos

Phobos may possess water in the form of ice. Due to the low delta-v needed to reach the Earth, this would permit delivery of propellant and other materials to cis-lunar space as well as transport around the Martian system. This makes these locations economically advantageous, since it is within easy reach of much of the solar system, as they have resources at a high potential energy. Phobos and Deimos themselves are probably suitable for sourcing materials for production of space habitats, or for living within.

Free space locations

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.

Earth orbit

See also: Orbital Megastructures

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 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 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.

The Asteroids

Main article: Colonization of the 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.

Colonization of Asteroids requires Space habitats, the asteroid belts have 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 asteroids are very distant from each other and the asteroidal bodies have enormous momentum. Rockets can perhaps be installed on asteroids to direct their path into a safe course.

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. This topic begins to exceed the scope of encyclopedia articles and enters the realm of science fiction. Even there, however, some work has been done to explore the possibilities.[citation needed]

Starship

An interstellar 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:

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.

Terrestrial analogues to space colonies

A colonization or settlement analogue research station seeks to replicate on a full-scale or near-full scale basis specific subsets of an entire settlement, with some attempting to do as many as possible. Example analogue stations may include habitat analogues, horticultural or agricultural analogues, psychological, usability analogues. In particular analogues are generally noted to be human-scale production that exceed small laboratory based studies. Many space agencies build testbeds for advanced life support systems, but these are designed for long duration human spaceflight, not colonization.

Biosphere 2 is often cited as an attempt to test a fully self-sufficient life support system on a large scale. However, it was actually an to duplicate Earth's biosphere to conduct a "hundred year study of complex ecological systems interactions" [10] Indeed, it's failures centered around terrestrial causes that would not likely be found in non-terrestrial applications.

Remote research stations have generally been placed inhospitable climates, such as the Amundsen-Scott South Pole Station or Devon Island Mars Arctic Research Station, or the Mars Desert Research Station. Each of the aforementioned analogues emphasize various aspects of a remote settlement. Devon Island, for example, has similar light levels as the surface of Mars. The MDRS is primarly running as an analogue for day-to-day life of a theoretical mission, covering such areas as suit design and usability to communication and hab usability concerns. [11]. In the Mars Society analogue stations crew members rotate through a period of weeks or months depending in the the mission being run. Several Mars Society additional analogues are in development and planning stages.

While there are currently no similar analogue stations for free-space or Lunar colonies, there is nothing inherent in their design that certain aspects could not be research terrestrially in this fashion.

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:[2]

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.[3]

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.

Another important reason used to justify Space is the effort 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 and under the surface of the Earth, and in a computer generated reality in cyberspace.

Counter Arguments

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 $15 billion a year, in other words the money that has been spent on the Iraq war could have funded NASA for approximately 21 years. They also underestimate the extent that space technologies such as communications and weather satellites help them in their everyday lives. This argument also assumes that money not spent on space would automatically be spent in ways that would benefit humanity.

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; 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.[8]

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

See also

References

  1. ^ "NASA's Griffin: 'Humans Will Colonize the Solar System'". Washington Post. September 25, 2005. pp. B07.
  2. ^ Britt, Robert Roy (08 October 2001). "The Top 3 Reasons to Colonize Space". Space.com. {{cite news}}: Check date values in: |date= (help)
  3. ^ Halle, Louis J. (1980). "A Hopeful Future for Mankind". Foreign Affairs. {{cite journal}}: Unknown parameter |month= ignored (help)
  4. ^ http://space.alglobus.net/
  5. ^ http://www.space-settlement-institute.org
  6. ^ http://www.seds.org/
  7. ^ http://www.foresight.org/challenges/space.html
  8. ^ Pale Blue Dot: A Vision of the Human Future in Space, Carl Sagan
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