The major components of the Satellite Solar Power System (SSPS) are shown in Exhibit 4 together with some of their more pertinent characteristics and overall mass estimates for the 5000 MW system. b. Efficiency Exhibit 5 indicates the efficiency goals for the various steps in the process. The solar energy conversion efficiency of 14 percent assumes a solar concentration factor of 2 and initial solar cell efficiences of 18 percent. The end-to-end efficiency is just under 8.5 percent. Efficiency of all steps other than the solar cell collection is projected to be about 60 percent. c. Transportation The SSPS will require a space transportation system capable of placing a large mass of payload into synchronous orbit at the lowest possible cost. The cost of transportation, assembly and maintenance will have the most significant impact on the economic feasibility of the SSPS. It is highly likely that a two-stage transportation system will evolve, which will carry payloads first to low-earth orbit and subsequently deliver partially assembled components to synchronous orbit or possibly to an intermediate orbital altitude for final assembly and deployment. The space transportation systems being considered are primarily an extension of existing systems. The potential systems, starting with the space shuttle now under development, vary from the use of a modified space shuttle to the development of a fully reusable liquid oxygen/liquid hydrogen heavy-lift launch vehicle (HLLV) with a potential 500,000 lb (225,000 kg) payload capability to low-earth orbit. The current shuttle or its modifications can be used for SSPS technology verification and flight demonstration and for transporting elements of the prototype SSPS into low-earth orbit. The cost for such a system capable of lifting payloads up to 160,000 lb (73,000 Kg) to low-earth orbit, is projected to be $100-200/lb. The heavy-lift launch vehicle is expected to reduce payload costs to between $20 and $60 per pound for delivery to low-earth orbit. The large mass of payloads will require about 80 to 100 flights for each SSPS assembled in synchronous orbit when an advanced space transportation
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