Analyses of the reference concept will be based on the use of gallium-alminum-arsenide (GaAlAs) solar cells. In the time frame of interest, advances in GaAlAs cell technology and increased cell efficiencies may decrease blanket weights. The greater cell efficiency will permit a reduction in overall blanket area; however, the slightly greater weight of GaAlAs cells may not permit a significant cell blanket weight reduction. The reduced blanket area will require less supporting structure, resulting in reduced structural weight. The reference microwave antenna structure being investigated is a hexagonal compression frame with a tension web. The dominant advantage of such a structure will be to minimize its on-orbit construction time. All construction operations for the SPS will take place at geosynchronous orbit, and the primary mode of transfer from low to geosynchronous orbit will be conventional chemical propulsion. Advantage will be taken of the previous NASA- contracted studies of future transportation systems and power transfer via microwave radiation. The major study tasks are shown in Figure D-2, illustrating the degree of emphasis on analyses and definition of the reference satellite and on assembly operations — Tasks 1 and 2. The vehicles required for transport from Earth will be defined in Task 3, and capital cost estimates will be made in Task 4 together with the definition of significant technological advancements needed to successfully accomplish the program.
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