Studies into future transportation systems sponsored by the Office of Space Flight are being applied to satellite power systems. These studies, along with more specific studies into heavy-lift launch vehicles and ion-powered orbit transfer vehicles, are indicating that an extension of today's known technology can yield transportation costs of $20-100/lb. to geosynchronous orbit. This is the cost range suggested by most satellite power systems studies for the system to be competitive. Our studies into transportation system technologies indicate this to be a challenging, but attainable goal. The assembly of the satellite power system is one of the most critical areas in making cost projections. Present studies into large space structures and their assembly, teleoperators, and manufacturing in space are being applied to this area. A recent Martin Marietta study to define a concept for assembling a 1 km diameter microwave transmitting antenna is summarized in Figure 5 (see p. 213). An assessment of the impacts of a satellite power system is included as part of each system study. Economic, industrial, political, and environmental impacts are considered. Preliminary assessments indicate this to be a very clean energy source. However, more detailed studies are required to fully verify that there will be no adverse effects of the microwave beam on the flora, fauna, land mass, atmosphere, and ionosphere. In addition any microwave beam interference with other users of the microwave spectrum must be determined. Some problems are anticipated in this area, but they are not expected to be severe. In addition to the specific technological experience mentioned above, past and present NASA experience in the areas of systems engineering and analysis, management of large scale programs, space operations, long lifetime space systems, solar cells, and power transfer will be applied during our studies. The ERDA Low Cost Silicon Solar Cell Array Program will contribute to the data base for satellite power systems. NASA's work on this program is adding to our experience in this area. In late 1974, the NASA Satellite Power Team was set up to investigate the potential of satellite power systems. A preliminary technology assessment, a definition of critical areas, and recommendations for a technical program plan have been prepared by the Satellite Power Team. In the Report, “Preliminary Technology Assessment of Satellite Power System Concepts,” February 1975, a tentative conclusion was made that “there appears to be a reasonable chance that power from space can compete with alternative sources in the period beyond 1995.” This conclusion is based on a six-month survey of government and industry on the state-of-the-art and projected advances of the various technology elements involved. Both photovoltaic and thermal systems were assessed, with the conclusion being that they were about equal when compared as systems. The “weak links” in the data base used for the preliminary cost projections were identified in “Critical Areas of Satellite Power Systems Concepts/' July 1975. In addition the results required to resolve each critical area were identified. In general, two types of requirements were given—better definition and advances of known technology. This is largely where we are today and what the problems are that face us. How best to proceed is the next question to address. We feel that the best programmatic approach to satellite power systems is a sequence of overlapping program phases, each phase covering a total period of about ten years. However, the great majority of the effort and funding would occur in the last five years of the phase. The major part of each phase would be committed to after successful completion of most of the objectives of the previous phase. A total program duration of 20-25 years looks reasonable at this time. System definition and a ground-based technology effort are seen as the next step (phase 1) in the orderly consideration of satellite power systems. The microwave program described earlier is an example of the nature of the ground-based technology development. The objectives of this phase of the program should be: 1. Resolve the issues critically affecting the cost projections. 2. Provide a better data base for future program decisions. 3. Begin development of the long lead-time components. In general, most of the programs proposed by others show this phase as lasting about five years and costing about $200M (1975 $). The most recent effort of the Satellite Power Team was a study to define and scope a five-year program to resolve the critical areas defined in their earlier report. This study effort indicates a program with a five-year runout cost of about $230M (1975 $) plus significant government manpower commitment as well as a large degree of industry involvement. The five-year duration was rather
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