SYSTEM CONCEPT A typical geometry for a space-to-earth microwave power transmission system is shown in Figure 1. As was shown in other studies (references 3,6-9), the required transmitter diameter is nominally 1 km and the receiver, nominally 10 km, is sized to intercept 90 percent of the main lobe. More interception can be realized by increasing the transmitter or receiver diameter but cost analyses have shown (references 6-9) a diminishing return above 90-95 percent interception. Typically the transmitter might be a planar array segmented into many small arrays of the order of 20 meters on a side. Each of these smaller arrays might be attached to a monolithic support structure having means for independent pointing and positioning. This concept is a consequence of relaxing the mechanical rigidity requirements in the interest of reducing on-orbit weight of the transmitter. As a consequence, gravity gradient perturbations, variations in solar pressure, periodic thrusting for attitude control, and thermal cycling will perturb the structure. Without compensation the resulting deformations would be of sufficient significance to degrade the transmission efficiency and pointing to an intolerable level. To compensate for these deformations and maintain efficiency as well as precise pointing, it has been proposed that a retro-directive phase control approach (references 3.6-9) be used.
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