the refining site to the mining site). Crew only travels between a site and low earth orbit. Bulk cargo from earth only travels from low earth orbit to the destination site. Two general-purpose transport designs (one manned, one unmanned) travel between low earth orbit and all sites. Route-specific transport designs may be chosen for transport between sites. Site locations are specified in terms of velocity increments between site and adjacent sites and low earth orbit. The output mass from the assembly site is the production rate of N satellites per year times the mass of a single SPS, taken to be 50 x 106 kg. The output mass of site i is identical to the input mass of site i+ 1 (assuming no losses in transport), so the site-to-site mass flows may be calculated by The fraction of output at each site not available from the moon must be brought from earth, so the first estimate of bulk cargo mass is Since site output is known, crew needed can be calculated from the productivity parameters. This, however, brings up the question of the learning curve. It has been clearly shown that production increases in a repetitive task exponentially with the number of times the task is performed. It is obvious that much of the SPS will be constructed of highly repetitive subassemblies, thus there will be a learning period even during construction of a single unit. However, as a conservative assumption the repetitive unit in the learning curve will be taken as the SPS itself. The necessary crew can then be expressed as At this point, enough information exists to allow the estimation of logistics costs for the industrial system as a function of time. Cost elements are wages and training costs of the crew and transport costs of crew and cargo. Transport costs may be separated into earth launch and interorbit transport. Earth launch costs were analyzed in Appendix B: therefore, they will enter into this analysis only as a flat rate per kilogram of mass launched, which is the optimized average launch cost as derived in the previous appendix. In order to keep the analysis manageable, the cost of intraspace transportation will be assumed to consist of only the initial R&D and procurement, and the launch costs of any propellants needed from earth. This neglects such factors as vehicle refurbishment and amortization of capital over the long trip times of low thrust systems. From past studies, the simplification should not have a significant impact on costing accuracy. To determine the propellant launch mass, it is necessary to find a relation for propellant mass in terms of vehicle parameters, AV increment, and payload carried. Defining a propellant fraction p. = MP/MPL, and the basic relations derived in Appendix B, it is possible to derive analytical relations for in the general case of arbitrary fractions of propellant reloaded at each end of a round trip, with pay loads carried one way or both ways. Restricting the problem somewhat to single fraction refuelings (e.g., oxidizer and fuel are each loaded at only one end of the round trip, although they need not be loaded at the same end), the expression for n if payload is carried in both directions can be derived to be In both (C6) and (C7), y is the fraction of fuel added at the outbound end (the destination if payload is carried only one way). For example, the personnel carrier between low earth orbit and the refining site in
RkJQdWJsaXNoZXIy MTU5NjU0Mg==