however, the space manufacturing facility is able to produce solar power satellites purely from lunar materials. First, S.S.I. is summarized, then cost estimates are updated. Additional assumptions are necessary to determine transportation methods and costs, and are taken from SP-428. Extended S.S.I. Plan These additional assumptions allow the extension of this plan to completion of facilities independent of supply from earth with 3x10^ t/yr. (metric) throughput. Costs are estimated by determining a cost per unit mass for components of the plan, and additional assumptions are made for costs of earth computer facilities, salaries, and the first receiver. S.S.I. used lunar resources, but some materials from earth were assumed in that plan for construction of all equipment produced by the manufacturing facilities, including the solar power satellites. However, it will be assumed here in the extension of this plan that solar power satellites can be produced purely from lunar materials. This and other changes to an exact extension are made to reduce costs. The cost of designing solar power satellites will be neglected. It was also assumed in S.S.I. that one to two years are required after the space manufacturing facility reaches 3x10^ t/yr. throughput to manufacture equipment specifically for producing solar power satellites before their construction begins, but here this is assumed unnecessary. When the manufacturing facilities first reach 3x10^ t/yr. throughput, they are assumed flexible enough to manufacture anything required, without any more supplies from earth. Also, it will be assumed that all self-reproducing manufacturing facilities are completely self-repairing. Also, though it is not stated in S.S.I., it is assumed here that only one trip to the manufacturing facilities by men is needed, when first manufacturing takes place. Other Versions of Extended S.S.I Plan Two other modifications of an extension of S.S.I. are also considered. In the first, the manufacturing facilities are assumed advanced enough that they use pure selfreproduction in all generations, and no men are required in space. In the second, the assumptions are the same, except the space manufacturing facility is used while in low earth orbit to produce all other equipment, instead of constructing that equipment on earth. Both modified plans reduce costs; however, since the manufacturing facilities would be more advanced, it may be necessary to increase the cost estimates of research and construction used in this paper, and it is unknown whether the resulting costs would actually be lower. A schedule for use of the space manufacturing facility, in all three extended S.S.I. plans, is indicated beginning when its throughput reaches 3xl05 t/yr. SP-428 Plan The plan analyzed is taken without modification from SP-428, which assumed no self-reproducing factories. The plan yields the completion of a factory which constructs 2.4 solar power satellites per year. Costs are determined to the time of completion of the space manufacturing facility, though three solar power satellites are delivered by then to geosynchronous earth orbit; the cost estimates for the other plans in
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