Mass of Space Habitats Assumptions Assumptions used in determining the mass of habitats follow. Approximate scaling laws will be used to find the habitat mass. 1. The colonies are rotating cylinders with gravity 1 g at the perimeter of the cylinder. 2. Atmosphere is the standard earth atmosphere. 3. Shielding thickness is 10 m instead of the 2.04 m used in the 106 person habitat of SP-428 [52], because the larger amount is required for permanent safety from cosmic rays [53], 4. Attached radiation shielding is used to avoid the use of bearings between shielding and structure, since bearings on Skylab, which functioned in zero-gravity, had shorter lifetimes than expected, indicating unreliability. 5. The structural mass of a cylindrical habitat for 106 people, with about half normal atmospheric pressure and minimum gravity 0.7g, is given in SP-428. With attached radiation shielding 2.04 m thick, the structural mass is 1.6 x 107 t; with separate shielding, the structural mass is 107 t [54], For spherical habitats with the same population capacity, the structural masses are identical to this, for both the attached and separate shielding cases [55], It will be assumed therefore that when additional stress is exerted on the habitat structure, as described later, the structural mass of the cylindrical habitat varies in the same way as, and is identical to, that of the spherical habitat. 6. The structural mass of the spherical habitat with separate shielding 2.04 m thick increases 60% as the atmospheric pressure increases from about half normal to normal [56], The structural mass of the cylindrical habitat with attached shielding and normal atmospheric pressure therefore is also 60% greater, with mass 1.6 1.6 x 107 t = 2.56 x 107 t. 7. As discussed above, the structural mass of the spherical habitat is increased by 60% when the radiation shielding is attached; since the total mass exclusive of shielding
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