lower than shown in Figure 4-31 the optimum concentration ratio will be below 4.3, and conversely. Consequently a modular configuration was developed. In this concept the SPS would begin life with the number of modules required to produce somewhat more than the required 10 GW ground output. After a period of time, cell degradation would have brought the output to 10 GW and additional area would have to be added. This process would be repeated over the 30 year life of the SPS. Fig. 5-17. Cost and Mass Minima are not Coincident The microwave power transmission system efficiency was taken as 0.62; thus for a 10.0 GW ground output 16.17 GW must be supplied to the transmitter. Figure 5-18 shows the total orbit busbar power is determined. Fig. 5-19. Approaches to SPS Maintenance Figure 5-20 shows the selected silicon SPS configuration. The system begins life with 12 modules installed. At the end of life 18 modules are installed; during the 30 year life the system output does not drop below 10 GW (ground). Figure 5-21 shows the main frame of the SPS to which the 18 Fig. 5-18. Silicon SPS Efficiency Chain With a concentration ratio of 4.3, the operating temperature of the cells is 367 K (201 °F). Due to this elevated temperature, the cell efficiency (beginning of life) is only 11.23%. (A lower concentration ratio would yield higher efficiency, but as previously explained, higher cost.) At end of life (30 years) the cell efficiency is 7.5%, or 68% of the original. Figure 5-19 shows the approaches considered to compensate for cell radiation degradation. Annealing of the damage (by thermal effects) is an apparently very desirable solution. However, pending tests which accurately and repeatedly duplicate the geosynchronous environment, including solar flares, annealing must be considered as uncertain. As shown, the concept of periodic cell/concentra- tion addition was selected as the most promising of solutions other than annealing. Fig. 5-20. Silicon SPS End-of-Life Configuration Fig. 5-21. Main Frame, Silicon SPS
RkJQdWJsaXNoZXIy MTU5NjU0Mg==