Fig. 1-2. Receiving Antenna The receiving stations for the SPS consist of a large number («*109) of small receiving antennas integrated in an oval array. Rectification of the received energy to direct current is accomplished by circuit elements which are integral to the antennas. Figure 1-2 shows such an array. Since the antenna may block most of the microwave energy but would be nearly transparent to sunlight, it is possible that agriculture could be accomplished beneath it. Surrounding the antenna is a buffer zone to contain those microwave "side-lobes" which are more energetic than the continuous exposure standard (assumed to be more than 10 times more stringent than the current standard which is 10 mW/cm2). These antennas could be placed relatively near demand points (note the city in the background of Figure 1-2). Figure 1-3 shows, as an example, one of the concepts studied; a solar Brayton SPS. Four power generator modules feed the circular microwave transmitter. Each power module consists of a reflector which concentrates solar energy into a cavity absorber at the focal point. The resultant high temperatures are used to energize turbomachines which turn electrical generators which power the transmitter. In this study the technical and economic practicality of these systems was investigated. While these systems produce large quantities of power (e.g., 10,000,000 kilowatts per satellite), the forecasted demands of the United States alone are sufficient to require a significant number of satellites. In the program baselined in this study, 60 satellites are made operational by the year 2016. 1.2.2 Auxiliary Systems The criterion for optimization of these systems was minimum cost per kilowatt hour of energy produced (while maintaining set standards on factors such as environmental impact). To achieve low cost
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