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    ATMOSPHERE

    People need an atmosphere of acceptable composition and pressure. On earth the pressure of Oxygen at sea level is 22.7 kPa. For general populations deviations of more than 9 kPa seems unwise. Nitrogen is also needed to provide an inert gaseous buffer against combustion and to prevent certain respiratory problems. Our default values based on NASA-Space Settlements, A design Study, provide 22.7 kPa Oxygen pressure, and 26.6 kPa Nitrogen pressure at half the atmospheric pressure on Earth at sea level. Maintaining a proper atmosphere also implies monitoring and controlling trace elements. In particular, many materials outgas, i.e., molecules of materials like plastic leave the material and enter the atmosphere. Outgassing is responsible for the smell of new cars and some new plastic toys. On Earth, these sometimes unpleasant and even dangerous gasses disperse in our large atmosphere. On a space colony of limited size, outgassing could quickly poison the atmosphere.


    MATERIALS

    Once built and populated, a colony with excellent recycling will need only a few materials to replace leaks and losses. However, a great deal of materials will be needed to build a space colony, particularly shielding. If a colony expands, builds new colonies, or builds solar power satellites or other export products, a lot of material will be necessary. There are several sources of materials to consider: Earth, the Moon, asteroids, other planets, and other moons. All the materials necessary for space colonies are available on Earth. In addition, manufacturing facilities to provide finished products are readily available. However, launch from Earth is difficult, expensive, and can damage the atmosphere. Thus, only high value finished products and materials unavailable from other sources should be shipped from Earth. Because of the Apollo missions, we know that the Moon has plenty of oxygen, silicon and metals but apparently little nitrogen, or carbon. There is a possibility of water at south pole which is under current research.  Fortunately, radiation shielding can be made out of anything and shielding is most of the mass of most colony designs. Thus, all the shields, most structural materials, and about 20% of the atmosphere can be taken from the Moon. Launch from the Moon is much easier than from Earth as the Moon's gravity is much less (about 1/6 Earth normal) and the Moon has very little atmosphere. In fact, it is possible to launch small buckets of lunar soil from the Moon with an electromagnetic catapult. Such a catapult uses the same physical principles as maglev trains. The Moon is fairly accessible from Earth. Launch opportunities are frequent and it only takes a few days for conventional rockets to get between the Earth and the Moon. Asteroids are believed to have substantial amounts of metals, carbon, and water. Most asteroids are in the asteroid belt between Mars and Jupiter, but some are in orbits close to Earth and thus more accessible. Asteroids are attractive sources of material because they have water and launch and landing is very easy due to the small gravitational attraction of asteroids. However, even though asteroids exist in near Earth orbits, launch opportunities are relatively rare and transit times are long compared to the Moon. Planets are a poor source of materials in the early stages of space colonization because launch and landing is difficult or, in the case of the gas giants, impossible. Planets are also very hard to get to from Earth with launch opportunities being rare and transit times measured in years assuming current rocket technology. Planets do, however, have a wide variety of materials. The moons of other planets are as difficult to get to as planets, but are easier to land on and launch from. These moons vary widely in their composition.

    SHIELDING - Radiation Protection

     
    There is a great deal of radiation in space. This radiation primarily comes from deep space (cosmic rays) and the Sun (solar flares). Deep space radiation is substantially in excess of permissible radiation limits on Earth, and a large solar flare can kill an unprotected human very quickly. On Earth, we are protected from this radiation by the Earth's atmosphere and magnetosphere(for more information on Magnetosphere go to this link, select earth, select magnetosphere.. A space colony must be encased in sufficient mass to shield colonists from radiation. This can be done with any mass; for example, large amounts of lunar soil. A 4.5 meter thick layer of lunar soil may be able to provide adequate protection. Active shielding by creating an electro-magnetic field tries to change the trajectories of charged particles, somewhat like Earth's magnetoshpere (see above link).
    Name  Relative Biological Effectiveness RBE  Source 
    X-Rays and Gamma Ray Radiation belts, solar radiation, and bremsstrahlung electrons 
    Electrons
    1.0 MeV
    0.1 MeV 

    1
    1.08 

    Radiation belts 
    Protons
    100 MeV
    1.5 MeV
    0.1 MeV 

    1-2
    8.5
    10 

    Cosmic rays, inner-radiation belts, and solar cosmic rays 
    Neutrons
    0.05 ev (thermal)
    1.0 MeV
    10 MeV 

    2.8
    10.5
    6.4

    Nuclear interactions in the sun 
    Alpha Particles
    5.0 MeV
    1.0 MeV
    Heavy Primaries 

    15
    20
    varies widely 

    Cosmic rays 


    ENERGY

    Energy is needed for lights and to power equipment. Fortunately, for colonies sufficiently far from planets and large moons, solar energy is continuously available. In the weightless environment of space, large solar collectors can be built to convert sunlight to electricity which can then be beamed to space colonies using microwaves and/or lasers. If a colony is near a planet or moon, there will be periodic eclipses when solar energy will not be available. Only 40% to 50% of solar energy reaches the earth's surface. 22% of solar energy is absorbed in the atmosphere and between 30% to 40% is reflected into space. Outside earth's atmosphere 1.35*103 watts per cubic meter of solar energy is available. On earth's surface the solar energy is about 630 watts/m2.
    The royal blue surface is the solar panel that provides Pathfinder with electricity while on route to Mars.

    What is RBE?

    Different forms of radiation with different energies may have different effects upon orgainic tissue; so the radiation dose from each must be multiplied by the RBE. Thus, a low-energy thermal neutron would have 2.8 times the effect of a 1-rad exposure of X-Rays.

    MeV or Million Electron Volts

    1 eV or electron volts is an extremely small unit of energy. (.000000000000000000038 Calories) 1 MeV mega or million electron volts is still a small unit of energy(.000000000000038 Calories), however its biological effects may be quite significant.
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