The transmitting antenna consists of a number of subarrays, each of which is phase controlled as a unit. Increasing the size of individual subarrays reduces the number of receivers and phasing electronics required, and therefore the cost of the phasing control system. Decreasing the size of the subarrays reduces thermal distortion and the probable need for active positioning to compensate for misalinement. Subarray sizes of 4, 10, and 18 m (square) were studied. The 10-m size was selected as a reference, because it required less phase-control equipment than the 4-m size while not needing the active mechanical alinement of the 18-m size. A summary of the microwave system(s) parameters is presented in table IV-1. These parameters were utilized in the calculation of the power density distribution across the rectenna, which is presented in figure IV-4. Power densities of 23 mW/cm2 and 1 mW/cm? exist at the center and edge (5 km) of the rectenna, respectively. The latter density corresponds to one-tenth of the current U.S. standard for allowable human exposure to microwave radiation. 3. Orbit Considerations There are three orbit perturbations of importance. The Earth's equatorial ellipticity, solar and lunar gravity gradients, and solar radiation pressure result in satellite movement that must be assessed and possibly counteracted. The equatorial ellipticity causes a drift in longitude centered about either longitude 120° W or 60° E. Such a drift is unacceptable in view of an expected large number of satellites in this orbit and the need to maintain a proper relationship between the satellite and the receiving antenna. The velocity increment required to counteract this drift, however, is less than 1 m/s/yr. Solar and lunar gravity gradients cause an initial inclination of zero to grow to about 15° in 27 years. Nonzero inclinations require larger rectennas (approximately 10 to 30 percent for 7.3° inclination). Zero inclination can be maintained with a velocity increment of 46 m/s/yr; this appears to be a reasonable price. Solar radiation pressure produces an eccentricity in the orbit. To maintain the eccentricity at zero requires a velocity increment of a few hundred m/s/yr. The problems associated with a slightly eccentric orbit, primarily a moderate departure from constant velocity antenna rotation and a small (on the order of +1 percent) variation in rectenna output, do not appear to warrant the expenditure.
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