The ground control center does not play a direct role unless the onboard control system fails. In this event, direct ground control would be limited to performing emergency shutdown using separate and redundant control links in critical systems' areas. The rectenna control center (Figure 4) would monitor startup sequencing to provide any necessary ground support to the satellite. This includes antenna boresighting, pilot beam control and initiation of power reception, conversion, and distribution to the utility customer interfaces. Special coordination functions may be needed from the ground center to avoid power surges and to provide load leveling. Emergency shutdown of satellite operations also may be required if a major ground system failure occurs. During the operational phase the satellite and GRS have reached stabilized power conversion and transmission to the utility network. The rectenna control center will receive periodic updates of scheduled power requirements from the utility area control center (Figure 5). These load schedules are translated by the ground center into satellite power output schedules which take into account RF transmission, rectenna conversion, dc-to-dc/ac conversion efficiencies, and related factors. This scheduling facilitates matching of generated power to load levels. If for some reason the entire utility network or a dedicated customer drops off the line, the SPS power output may be shut down, adjusted, or switched to other loads. The ground center must accommodate these and other contingencies such as problems in rectenna dc-to-dc/ac conversion and distribution. Emergency shutdowns or load adjustments require authenticated commands, rather than enabling messages, to be transmitted to the satellite. Figure 4. Rectenna Control Center Concept
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