Figure 39 estimates the number of flights required, payload characteristics, packing factors assumed, and numbers of people associated with building two SPS's over a one-year period. Data is presented for both silicon and gallium options. Table 6 shows the fleet sizes of HLLV's, PLV's, COTV's, and POTV's needed (1) for the buildup period prior to SPS construction and (2) for the construction of two SPS's per year. Data is presented for both silicon and gallium options. Fewer COTV's are needed for the gallium option due to the following combination of factors: different COTV design and flight times, different satellite weights, and different packing factors. Besides space construction, there is the task of constructing the ground rectenna. Techniques for accomplishing this have not yet been developed; however, some of the relevant issues are present under the construction discussion in Appendix A. 2. Commercial Operations Once the SPS and rectenna are constructed, the SPS begins to produce commercial power. The main tasks are to operate the interface with the grid and maintain both the SPS and the rectenna. With regard to the grid interface, it would be ideal if the SPS power would remain uniform at all times. In reality, however, there will be variations from a number of seasonal, daily and orbital path causes. Also, periodic shutdowns due to earth eclipses will occur. Thus, ground-based power generation systems must have a throttling capability to smooth out the demand load. With regard to maintenance, the large number of components (e.g., 10$ klystrons) will result in random failures. Also, it is probable that sections of solar blankets will have to occasionally be replaced due to meteoroid damage or part failures. It is estimated that between 5 and 20 people would be required in GEO per SPS, probably stationed at the construction base. Parts and personnel are transported from LEO to GEO and between SPS's in GEO using OTV stages.
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