Figure 7-44. Cool-down rate in Earth's shadow. 7. 3. 4 MICROWAVE GENERATION SUBSYSTEM 7. 3. 4.1 INTRODUCTION The amplitron or crossed-field amplifier was selected as the candidate RF generator for this study. It is to be emphasized that a final selection cannot be made at this time because of necessary technological advancements in all RF generators under consideration. There are no known RF generators available today that have the required characteristics to make the SPS economically or technically feasible; however, the required advancements are within the forecast technology with little risk or need for technological breakthroughs. Primary factors to be considered in the selection of the generators are reliability, efficiency, lifetime, size, mass, and radio frequency characteristics. The selection was narrowed to vacuum tube devices, since solid state devices, at present, produce lower power and have low efficiency compared to vacuum devices. The most promising vacuum devices are the klystron and the amplitron, which have the best potential of being developed to the extent necessary for the SPS.
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