[3] The microwave power transmission system was not optimized. It required the use of far too much land area for the power receivers. The nature of optimal SPS transmitter patterns has not been thoroughly investigated, but optimal systems appear to need high-efficiency devices such as magnetrons or klystrons to generate most of the beam power, while using low-cost-per-unit-area devices such as solidstate FETs to provide the beam shaping to minimize receiver area. This approach has not been explored at all, and could yield ground receiver areas per unit power generated on the order of one-third those of the reference system. [4] The construction concepts for the reference systems were underautomated. Although space construction costs did not represent a major part of (he reference system costs, serious concerns were raised about the radiation exposure of workers in GEO orbit (12). (The cancer risk for a five-year career space worker who spends every other ninety days in GEO, with the reference system amount of shielding, would be roughly equivalent to that for a moderate smoker. Many people would consider this an unacceptably high risk.) Reducing the risk means fewer people and more shielding, and this means more automation. The reference concepts were automated in the sense that machines did most of the work, but each major machine had a human supervisor. Simply changing to a scenario in which each human supervises many machines could reduce the size of the GEO crew by half to two-thirds, and permit enough more shielding to be used on the average to greatly reduce the radiation risk. [5] The electric-propelled orbit transfer system was probably the least technically sound part of the reference system. (I have heard it called flaky.) A fleet of 25 to 30 electric vehicles was required, each itself being a large space structure a square kilometer or so in area. The six-month trip to GEO through the vanAllen belts would deliver a punishing dose of radiation to the solar array, which was then to be annealed by thermal annealers. The electric vehicles were to be served at each terminal (LEO and GEO) by smaller tugs that would load and unload cargo. Near the LEO terminal, an electric vehicle would be dangerously near the altitude at which air drag would overpower its feeble thrust and it would reenter. This was not seen as a serious risk for a normally-functioning vehicle, but one that lost thrust or control for some reason might have an orbit lifetime no more than a few days. [6] If any single thing caused the demise of SPS research in the U.S., it was the reference program. This program was not perceived by its authors as the political albatross it came to be. The reference SPS program was intended as an analytical device to identify, as best we could, all of the research, development, and investments needed to bring SPS about, and to provide a basis for comparative economic analyses. It had many faults, however, when viewed from a political standpoint. These faults mainly arose from a desire to be thorough yet simple enough to facilitate analysis. The faults included the following: (a) A high degree of arbitrariness — the reference program, after the research and development phases, presumed to emplace ten gigawatts per year of generating capacity, all with satellites of identical design, for thirty years, and then stop. This greatly simplifies comparative analysis, but is so unrealistic as to be ludicrous. A real program would start smaller, make many product improvements along the way, and eventually become bigger. (b) Liability for all space technology developments in the next twenty years. Included in the reference program’s research and development were advanced shuttles, space stations, heavy lift launch vehicles, and high-energy upper stages. All of
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