The potential for short-term flexibility of power delivery could be exploited most fully if satellites had two transmitting antennas with the capability to transmit two power beams simultaneously of which the power levels could be varied smoothly. Technically it would be possible to vary the output of an SPS continuously, but whenever power was being delivered at less than the maximum rate possible, some of the system capacity would be being wasted. The use of a satellite with two antennas, of which the combined capacities exceeded the capacity of the satellite, would enable the power output of the two antennas to be adjusted inversely. In this way the load factor on the satellite could be kept at its maximum, and the power delivered to the two rectennas be adjusted to match best the requirements of the two utilities. Figure 3 illustrates a possible pattern for sharing of the output of an 8 GW satellite between two 5 GW antennas. (An alternative means of transmitting two microwave beams from a single satellite has been proposed by Arndt and Kerwin [7] who have described single antennas capable of transmitting two and four microwave beams at an overall cost of power very similar to that of single beam antennas. However, the efficiency of power transmission falls off as the separation between rectennas increases, which would greatly restrict the scope for long distance power switching). The cost per kilowatt of an 8 GW satellite with two 5 GW transmitting antennas would be some 12% more than the cost of a 5 GW system [5]. This margin
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