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There are two main types of space colonies: Surface-based examples that would exist on or below the surfaces of planets, moons, etc. Space habitats — free-floating stations that would orbit a planet, moon, etc. or in an independent orbit around the sun. There is considerable debate among space settlement advocates as to which type (and associated locations) represents the better option for expanding humanity into space. Space habitats Main article: Space habitat Interior view of an O'Neill cylinder 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 designs have been proposed with varying degrees of realism by both science fiction authors and scientists. Such a space habitat could be isolated from the rest of humanity but near enough to Earth for help. This would test if thousands of humans can survive on their own before sending them beyond the reach of help. O'Neill cylinders space colony (Island Three design from the 1970s) Method Building colonies in space would require access to water, food, space, people, construction materials, energy, transportation, communications, life support, simulated gravity, radiation protection and capital investment. It is likely the colonies would be located by proximity to the necessary physical resources. The practice of space architecture seeks to transform spaceflight from a heroic test of human endurance to a normality within the bounds of comfortable experience. As is true of other frontier opening endeavors, the capital investment necessary for space colonization would probably come from the state,[29] an argument made by John Hickman[30] and Neil deGrasse Tyson.[31] Materials Colonies on the Moon, Mars, or asteroids could extract local materials. The Moon is deficient in volatiles such as argon, helium and compounds of carbon, hydrogen and nitrogen. The LCROSS impacter was targeted at the Cabeus crater which was chosen as having a high concentration of water for the Moon. A plume of material erupted in which some water was detected. Anthony Colaprete estimated that the Cabeus crater contains material with 1% water or possibly more.[32] Water ice should also be in other permanently shadowed craters near the lunar poles. Although helium is present only in low concentrations on the Moon, where it is deposited into regolith by the solar wind, an estimated million tons of He-3 exists over all.[33] It also has industrially significant oxygen, silicon, and metals such as iron, aluminum, and titanium. Launching materials from Earth is expensive, so bulk materials for colonies could come from the Moon, a near-Earth object, Phobos, or Deimos. The benefits of using such sources include: a lower gravitational force, there is no atmospheric drag on cargo vessels, and there is no biosphere to damage. Many NEOs contain substantial amounts of metals. Underneath a drier outer crust (much like oil shale), some other NEOs are inactive comets which include billions of tons of water ice and kerogen hydrocarbons, as well as some nitrogen compounds.[34] Farther out, Jupiter's Trojan asteroids are thought to be high in water ice and other volatiles.[35] Recycling of some raw materials would almost certainly be necessary. Further information: Asteroid mining Energy Solar energy in orbit is abundant, reliable, and is commonly used to power satellites today. There is no night in free space, and no clouds or atmosphere to block sunlight. Light intensity obeys an inverse-square law. So the solar energy available at distance d from the Sun is E = 1367/d2 W/m2, where d is measured in astronomical units (AU) and 1367 watts/m2 is the energy available at the distance of Earth's orbit from the Sun, 1 AU.[36] In the weightlessness and vacuum of space, high temperatures for industrial processes can easily be achieved in solar ovens with huge parabolic reflectors made of metallic foil with very lightweight support structures. Flat mirrors to reflect sunlight around radiation shields into living areas (to avoid line-of-sight access for cosmic rays, or to make the Sun's image appear to move across their "sky") or onto crops are even lighter and easier to build. Large solar power photovoltaic cell arrays or thermal power plants would be needed to meet the electrical power needs of the settlers' use. In developed nations on Earth, electrical consumption can average 1 kilowatt/person (or roughly 10 megawatt-hours per person per year.)[37] These power plants could be at a short distance from the main structures if wires are used to transmit the power, or much farther away with wireless power transmission. A major export of the initial space settlement designs was anticipated to be large solar power satellites that would use wireless power transmission (phase-locked microwave beams or lasers emitting wavelengths that special solar cells convert with high efficiency) to send power to locations on Earth, or to colonies on the Moon or other locations in space. For locations on Earth, this method of getting power is extremely benign, with zero emissions and far less ground area required per watt than for conventional solar panels. Once these satellites are primarily built from lunar or asteroid-derived materials, the price of SPS electricity could be lower than energy from fossil fuel or nuclear energy; replacing these would have significant benefits such as elimination of greenhouse gases and nuclear waste from electricity generation. However, the value of SPS power delivered wirelessly to other locations in Space will typically be far higher than to locations on Earth. Otherwise, the means of generating the power would need to be included with these projects and pay the heavy penalty of Earth launch costs. Therefore, other than proposed demonstration projects for power delivered to Earth,[38] the first priority for SPS electricity is likely to be locations in space, such as communications satellites, fuel depots or "orbital tugboat" boosters transferring cargo and passengers between Low-Earth Orbit (LEO) and other orbits such as Geosynchronous orbit (GEO), lunar orbit or Highly-Eccentric Earth Orbit (HEEO).[39]:132 The Moon has nights of two Earth weeks in duration. Mars has nights, relatively high gravity, and an atmosphere with dust storms to cover and degrade solar panels. Also, its greater distance from the Sun (1.5 astronomical units, AU) translates into E/(1.52 = 2.25) only ½-⅔ the solar energy of Earth orbit. For these reasons, nuclear power is sometimes proposed for colonies in these locations.[40] Another alternative would be transmitting energy wirelessly to the lunar or Martian colonies from solar power satellites (SPSs) as described above—note again that the difficulties of generating power in these locations make the relative advantages of SPSs much greater there than for power beamed to locations on Earth. 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. Transportation Delta-v's in km/s for various orbital maneuvers[41][42] using conventional rockets. Red arrows show where optional aerobraking can be performed in that particular direction, black numbers give delta-v in km/s that apply in either direction. For velocity change requirements to get to different places in the solar system, see delta-v budget. For cargo see Interplanetary Transport Network optimized for minimum energy. For people see Interplanetary spaceflight optimized for minimum time. Space access Further information: Non-rocket spacelaunch Transportation to orbit is often the limiting factor in space endeavours. 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.[citation needed] One possibility is the air-breathing hypersonic spaceplane under development by NASA and other organizations, both public and private. Other proposed projects include space elevators, mass drivers, launch loops, and StarTrams. 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 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 mass drivers to launch bulk materials to waiting settlements. Alternatively, lunar space elevators might be employed. Local transport Lunar rovers and Mars rovers are common features of proposed colonies for those bodies. Space suits would likely be needed for excursions, maintenance, and safety. Communication Compared to the other requirements, communication is 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. Life support In space settlements, a life support system must recycle or import all the nutrients without "crashing." The closest terrestrial analogue to space life support is possibly that of a 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"—extracting oxygen from seawater, and typically dumping carbon dioxide overboard, although they recycle existing oxygen. Recycling of the carbon dioxide has been approached in the literature using the Sabatier process or the Bosch reaction. Although a fully mechanistic life support system is conceivable, a closed ecological system is generally proposed for life support. 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: Organisms and their habitat fully isolated from the environment (examples include artificial biosphere, Biosphere 2, life support system) Changing the environment to become a life-friendly habitat, a process called terraforming. Changing organisms to become more compatible with the environment, (See genetic engineering, transhumanism, cyborg) A combination of the above technologies is also possible. Further information: Effect of spaceflight on the human body, Space medicine, and Space food 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, unless magnetic or plasma radiation shields were developed.[43] Passive mass shielding of four metric tons per square meter of surface area will reduce radiation dosage to several mSv or less annually, well below the rate of some populated high natural background areas on Earth.[44] This can be 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 (mobile spacecraft being particularly likely to use less massive active shielding).[43] Inertia would necessitate powerful thrusters to start or stop rotation, or electric motors to spin two massive portions of a vessel in opposite senses. Shielding material can be stationary around a rotating interior. See also: Health threat from cosmic rays Self-replication Space manufacturing could enable self-replication. Some 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) and colonies that just require periodic supply of light weight objects, such as integrated circuits, medicines, genetic material and tools. See also: von Neumann probe, clanking replicator, molecular nanotechnology Psychological adjustment The monotony and loneliness that comes from a prolonged space mission can leave astronauts susceptible to cabin fever or having a psychotic break. If this wasn't enough, lack of sleep, fatigue, and work overload can affect an astronaut's ability to perform well in an environment such as space where every action is critical.[45] 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 women 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 Ne = 50 prescription corresponds to an inbreeding rate of 1% per generation, approximately half the maximum rate tolerated by domestic animal breeders. The Ne = 500 value attempts to balance the rate of gain in genetic variation due to mutation with the rate of loss due to genetic drift. |
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