PRELIMINARY SPS MATERIALS ASSESSMENT R. R. Teeter and W. M. Jamieson Battelle Columbus Laboratories - 505 King Avenue, Columbus, Ohio 43201 Presently, there are two SPS reference design concepts (one using silicon solar cells; the other using gallium arsenide solar cells). A materials assessment of both systems was performed based on the materials lists set forth in the DOE/NASA SPS Reference System Report: "Satellite Power System Concept Development and Evaluation Program" ^October, 1978. This listing identified 22 materials (plus "miscellaneous and organics") used in the SPS. Tracing the production processes for these 22 materials, a total demand for over 50 different bulk materials (copper, silicon, sulfuric acid, etc.) and nearly 20 raw materials (copper ore, sand, sulfur ore, etc.) was revealed. Assessment of these SPS material requirements produced a number of potential materials supply problems. The more serious problems are those associated with the solar cell materials (gallium, gallium arsenide, sapphire, and solar grade silicon), and the graphite fiber required for the satellite structure and space construction facilities. In general, the gallium arsenide SPS option exhibits more serious problems than the silicon option, possibly because gallium arsenide technology is not as well developed as that for silicon. The table on the next page summarizes potential material problems that have been identified. Problems of serious concern are denoted by an "A" in the table, and those of lesser but possible concern are denoted by a "B." The "A" materials are discussed briefly below. For more complete discussions including the "B" materials the reader is referred to the full report on this subject.^) As shown in the table, the gallium required for solar cells in the gallium arsenide option represents a potentially serious problem from a number of standpoints. It is a by-product of aluminum ore (bauxite) much of which is imported. It is also a high-cost material for which the SPS would be the primary consumer. This last problem could be alleviated if concurrent development of terrestrial photovoltaic programs or other uses for gallium emerged. However, this would also drive up the demand for what would be an already scarce commodity. The production of gallium arsenide is also a problem in that it would need to be greatly expanded and the SPS would again be the dominant consumer. Also, the arsenic and arsenic trioxide needed to produce gallium arsenide represent additional problems due to the weak position of the U.S. arsenic industry (only one plant in operation). Synthetic sapphire used as the substrate for gallium arsenide solar cells is extremely expensive. The SPS program would require major production expansion and would become the primary consumer. The cost and energy requirements (electricity) associated with the production of solar grade silicon has been and remains a significant problem. In addition, the SPS again would dominate the market, unless parallel terrestrial photovoltaic programs or other applications for high purity silicon were developed. Additional demand would have less impact on silicon than on gallium since the raw material is plentiful. However, it would compound production growth rate problems for the high purity material.
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