Comments pertinent to the activities in this phase are presented in the following paragraphs. Solar energy conversion.- The most significant contribution to technical and economic feasibility of SPS can be obtained by increase of solar cell array power per unit mass (kilowatts/kilogram) and decrease in cost. It is also expected that solar cell life will play a key role in determining economic feasibility. Structures.- Although structures appear to be a relatively low weight item in current SPS configurations, it is expected that significant analytical and test efforts will be required to develop and qualify these systems. The main difficulty in this area is the inability to ground test (simulate) the large, lightweight systems. Microwave conversion and control.- The satisfactory performance of dc/rf power converters is essential to the success of the SPS concept. The key performance parameters are efficiency, lifetime, and noise characteristics. Low component weight is desirable, but it is of secondary importance to conversion efficiency, which directly affects solar array size and weight. Environmental impact.- The design and performance of SPS is directly influenced by allowable microwave radiation intensity levels on the ground and in the upper atmosphere. It is expected that a major test program will be required to resolve environmental issues and to establish practical but safe design criteria. Space transportation.- The installed cost of SPS is strongly influenced by space transportation costs. Although the HLLV development appears to be primarily a scale-up and product improvement of existing rocket technology, such as was accomplished in the Saturn V development, significant testing and development will be required to demonstrate low- cost operations and efficient equipment reuse concepts. Development of a suitable low-cost, long-life OTV propulsion system is also mandatory regardless of SPS design configuration. D. System Development Detailed plans for the system development phase would be developed during the Technology Advancement phase of the program. The scope of the effort would exceed that required for the Apollo Program, particularly since a continuing commercial phase would be envisaged requiring a large industrial capacity. The ability to accomplish this in the period between 1985 and 1987 will be dependent upon the planning, organization, and long lead-time activities conducted during the preceding phase. The transportation and associated launch and recovery (or landing) facility development will constitute a particularly significant theme of the overall activities of this phase. E. Program Costs The program plan (fig. X-l) shows preliminary estimates of costs by major phase. The initial phase (system definition and exploratory technology) is estimated to cost between $40 and $50 million. The major elements in this estimate are as follows:
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