7.0 COMPARISON OF CONCEPTS 7.1 APPROACH Comparison of alternative SPS concepts should ultimately be based on factors such as: size mass life cycle cost packaging capability constructability risk development cost resources consumption The scope of this study permitted evaluation of only the first three of these factors. 7.2 CONFIGURATION AND MASS COMPARISON Figure 7-1 shows the emphasized concepts to the same scale. The photovoltaic systems are shown in their end-of-life (EOL) configuration i.e., the necessary modular additions have been made to compensate for radiation-induced solar cell degradation. Fig. 7-1. Concepts to Same Scale (10 GW Ground Output) Since all systems produce the same ground output and have the same microwave power transmission systems, the "solar capture" areas are inversely proportional to the energy conversion efficiency of each. The nuclear system has no solar capture area; the projected area shown is that of radiator system (which has the same area as the solar Brayton radiator system). System masses are compared in Figure 7-2. Note the mass changes resulting from the module additions to the photovoltaic concept. The mass change to the Brayton concept results from the addition of NaK to counter creep-induced swelling of the radiator manifolds. Fig. 7-2. Mass Comparison of Concepts Cost data from the preceding section are summarized in Figure 7-3. The "life cycle" costs shown here include system ground production, launch, assembly, transfer to geosynchronous orbit and maintenance for 30 years (including modular additions where required). No costs for system disposal at end of life were included nor was any salvage value assumed. Fig. 7-3. System Life Cycle Costs The charges for electrical power produced by these SPS concepts was calculated on a 7.5% discount rate. Charges are for power at the rectenna output; no distribution charges are included (nor are taxes or profits). (See Section 6.0.)
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