production plant would be 6.7 x 1010 kWh (provided by two 5 GW SPS in nine months). The capital cost of the industrial plants would be about $2.7 billion and require integrated but not necessarily colocated plants with an area of 260,000 m2 which is comparable to the Boeing 747 aircraft plant. The magnitude of the photovoltaic subsystem production requirements would result in the creation of a significant new industrial capability which would affect several industrial sectors.3 Expansion of production capacity to meet both SPS and the terrestrial photovoltaic markets would reduce the potential business risk to industry participants implied by a buildup of industrial capacity for a single large program. 2. Ion Engines The production requirements for ion engines are about 40,000 per year, primarily for replacement or refurbishment in the SPS. The characteristics of the production plant will depend critically on the design lifetime of the engine and the use of either readily available or exotic materials, degree of quality control, labor skills, and required tolerances. The production steps for ion engines are comparable to those now in use in the aerospace and electronic industries. The ion engine production rate will be modest compared to analogous production requirements of, for example, color television. 3. Dipole Rectifiers To support the SPS buildup at a rate of 10 GW per year, a continuous production process capable of delivering completed dipole rectifier elements at the rate of 625 per second would be needed to produce 2 x 1010 dipoles per year. This process will consume about 42,000 mt of aluminum for the dipole strip, and 14 mt for gallium arsenide Schottky diodes per year. Divided between several hundred automated machines, these production rates would not be of sufficient magnitude to stress the capabilities of electronics and related industries. Receiving antenna design changes could reduce diode production requirements and avoid handling of very large numbers of discrete components. 4. Microwave Generators Figure 2 shows the gross annual power output of microwave generators as part of U. S. microwave oven sales. The annual production requirements for a 2.5 GW SPS pilot plant of about 600 MW per year would be well within current production capabilities of the microwave industry of close to 2 GW per year, if the microwave generator would be a magnetron rather than a klystron, which has only a limited market. The existing microwave industry capacity appears adequate to meet SPS microwave generator production requirements. 5- Graphite Fiber Reinforced Composite Structures About 4000 mt of graphite fiber composite structures may be required for a 5 GW SPS. As Figure 3 shows, projections of the U.S. market for graphite fibers indicate that this production level will be reached by about 1990. Furthermore, extensive use of graphite composite structures in automobiles could result in
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