Certain programmatic guidelines were chosen to initiate the study and bound the study effort. 1. Program plans and technology projections will be developed based on deployment of the first operational SPS as early as 1990. 2. The capability will be provided as early as 1995 to deploy two to four SPS1 s per year. 3. Dedicated transportation systems will be developed and optimized specifically for use in deploying and operating the SPS network. 4. Materials used in fabricating and operating an SPS will be obtained only from the Earth. 5. The SPS will be deployed in appropriate geosynchronous orbits only. 6. The lifetime of an SPS will nominally be 30 years, although liberal refurbishment/replacement of parts may be assumed. 7. The SPS will be designed in a manner to optimize participation of man in its fabrication, assembly, and operation. 8. Availability of scarce resources will be a major consideration in projecting technologies to be used in fabricating the SPS network. 9. Energy as well as economic payback will be assessed in determining the SPS development strategy. 10. Aspects of social and environmental impact will be assessed. 11. Assembly fabrication strategies for SPS will be developed such as to minimize overall costs. The first two guidelines were modified slightly as the study progressed in that various scenarios were defined and evaluated. Available resources defined the scope and depth of the study. For example, the study was primarily limited to consideration of the photovoltaic concept for solar energy collection and conversion, although a rather thorough review of past system studies involving the use of the thermal energy conversion concept was accomplished (Vol. II). Similarly, the more detailed design studies were limited to consideration of silicon solar cells. Given these restrictions, a range of power station sizes and weights was determined based on conservative and optimistic estimates of collection, conversion, transmission, and receiving efficiencies. Analyses and/or design studies were conducted for each element of the systems to varying degrees. These studies included several satellite configurations, construction concepts, crew requirements, alternate microwave generator concepts, rotary joint designs, attitude and control concepts, and structural designs. Several program scenarios were developed that defined the number and schedule of space power satellites required to provide varying percentages of the Nation's energy needs in the 1995-2025 period.
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