8.5 PRECURSOR SYSTEM DEVELOPMENT AND DEMONSTRATION (PART III) ■ The necessity for, and form of, an SPS precursor system has been a subject of debate by those studying the SPS concept. Views of the precursor program have ranged from none, to a small "pilot plant" of perhaps 1 MW orbit busbar, to a larger pilot plant of perhaps 50 MW orbit busbar (1 MW rectenna output) to a 1000 MW ground output "commercial demonstrator." A significant aspect of this range of options is that the space shuttle is adequate to launch all except the commercial demonstrator, although there would be a cost and environmental impact benefit to the use of a liquid booster "growth shuttle." In general, space projects are lowest in total cost, if performed expeditiously, i.e., in an accelerated fashion; "stretchouts" are costly. An early commitment to a large scale precursor program entails more financial risk, but could speed the date of space power availability. Selection of a detailed precursor program plant will probably involve analysis and trades in Part I and Part II, followed by "national" decisions, i.e., Presidential and Congressional approval. As a "middle-of-the-road" approach to selection of a precursor program activity level a 50 MW orbit busbar, 1 MW ground output pilot plant is here baselined. Program elements are: 1. Selection and design of the orbital power generation system and the microwave power transmitter. 2. Ground and shuttle sortie tests of elements of the above. 3. Selection and design of orbital assembly equipment for the "pilot plant." 4. Equipment ground fabrication. 5. Launch, assembly and checkout of the orbital assembly facility. 6. Launch of the pilot plant system hardware. If low orbit assembly and "self-power" transfer is selected approximately 50 shuttle flights would be required. Assembly at geosynchronous orbit, with parts transfer from low orbit by chemical OTV, would require approximately 100 shuttle flights. 7. Construction and tests of the ground test rectenna system. 8. Assembly and checkout of the orbital systems. 9. Long term microwave power transmission tests, including ionospheric effects tests. 8.6 OPERATIONAL SYSTEM DEVELOPMENT & DEMONSTRATION (PART IV) In addition to the full size SPS system, rectenna, construction facilities, etc., the heavy lift launch vehicle and high orbit transfer systems must be developed. The HLLV might conceivably be begun quite early, perhaps even in Part II.
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