in fact, the power redistribution network can be deposited on the interior of the sphere12. The curvature of the array causes a transmitter phase difference across the Earth-facing side, which can easily be compensated for. When designing a bicycle wheel-type SPS, an allowance must be made for the tracking loss, since the array cannot simultaneously point at both the sun and the Earth, except at midnight (and at noon, if both sides of the SPS are covered with solar cells and microwave transmitters). A tracking loss of 30% was assumed, based on Landis and Cull's (Ref. 7) figure for an SPS in orbit around the Moon. Calculations were also done for a bicycle wheel SPS with no tracking loss. This can be achieved if the array points toward the Earth and a mirror orbiting with the array reflects sunlight toward it. Such a mirror might consist of aluminum on Kapton13, plus an appropriate support structure and might weigh as much as the SPS; the increase in system mass is thus 40% over a system with a tracking loss (in which the size or number of SPS's is increased to compensate for the lost power). Such an increase in mass may be deemed worthwhile, since the power level of a non-tracking array may fluctuate throughout the day as it orbits the Earth. 6. System Efficiencies The microwave power level incident on the rectenna is considerably different from the power level of sunlight incident on the SPS. Furthermore, the power available to consumers is somewhat less than that incident on the rectenna. In addition to the inefficiency of the solar cells and tracking losses, other inefficiencies must be accounted for. The efficiencies used in this study are based on Table 1 from Vondrak (Ref. 3), but with modifications. They are shown here in Table 1.
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