The transportation system selected for the point design includes: (1) a horizontal takeoff HLLV (one or two stage) for earth to LEO operation; (2) a dedicated electric ion thruster OTV for cargo transport; (3) a two stage LO2/LH2 OTV for personnel and priority cargo transport; and (4) a single-stage LO2/LH2 vehicle for orbit transfer (short distance and small AV)of personnel and cargo. These elements are illustrated in a low earth orbit scenario in Figure R-2. An alternative 2 stage vertical takeoff earth to LEO operation has also been defined as a viable option for SPS. The electric ion thruster OTV utilizes the satellite solar array design of GaALAs solar cells at a concentration ratio of 2. The basic approach for satellite construction assumes that the entire satellite is constructed in geosynchronous orbit and that the necessary construction material is transported from low earth orbit to GEO using the OTV's. The OTV's are constructed in LEO. Three orbital bases have been identified to support GEO construction: (1) satellite construction base; (2) operations and maintenance base; and (3) low earth orbit base. A crew size of 640 has been established for accomplishing the construction in a scheduled 90 days. An additional crew of 20 has been estimated for satellite maintenance and operations. A description of the system and subsystems is given in Table R-l. Figure R-3 shows the end-to-end efficiency chain for the system which has been sized to provide 5 GW of electrical power to the utility busbar. With an overall efficiency of 6.29 percent, it is necessary to size the solar arrays to intercept 79.0 GW of solar energy. The quoted efficiency is the minimum efficiency, including the worst-case seasonal variation (91%), the end-of-life (30-year) concentrator reflectivity (91.5%), and the end-of-life (30-year) solar cell efficiency (15.4%). C. Solar Cells and Blankets Figure R-4 shows the solar array blanket description and array characteristics. The point design utilizes a GaAlAs solar cell efficiency of 20-percent
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