In the present case, the angle of incidence at 40° rectenna latitude will vary from about 8° to 82° daily at maximum inclination. There is also a substantial variation in azimuth of the beam. The resulting variation in the "footprint" of the microwave beam is illustrated in figure IV-A-3-21 for a typical case. The enormous increase in land area and rectenna elements required, even aside from large atmospheric losses and the difficulty of configuring a given section of the rectenna to perform efficiently over a wide range of power densities, appear to make this approach totally unacceptable. The second approach need go no higher than 9.5° inclination (in March and September). While representing a substantial penalty in land and rectenna elements (see page IV-A-3-15 for data for 7.3°), it is a great improvement over 33°. The difficulty here is the time constraint on the plane change, viz., 19° in less than 24 hours. At synchronous orbit, this involves a minimum delta-V (impulsive) of 1020 m/s. Even if the maneuver could be spread over, say, 4/5 of an orbit without penalty, the acceleration would be about 0.0015 g. At a somewhat more plausible figure of a tenth of an orbit, the acceleration would be 0.012 g, requiring a thrust of about 107 N (2.2 x 106 lb). To design the SPS to these loads appears prohibitively heavy, aside from the propellant required (about 3.6 x 10^6 kg/year) and the cost of the thrusters. Note that it will be necessary to maneuver all satellites simultaneously or nearly so; moving propulsion modules from one SPS to another to reduce propulsion system investment is therefore not possible. In summary, maneuvering solar power satellites so as to avoid eclipses by the earth appears to be completely out of the question. It will be necessary, therefore, to accept outages resulting from eclipses or to provide energy storage or standby generators to fill the gaps.
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