IONOSPHERIC EFFECTS With the ground based dosed loop interferometer phase control approach, ionospheric effects are limited to phase errors introduced into the space- to-earth transmission path only. Although, the PMA is shown to be at the center of the Rectenna, it is not necessary that it be located there or even within the Rectenna site. Off-site measurement has the advantage that the signals being phase tuned do not have to pass through an ionosphere that may be subjected to undetermined heating effects by the power beam. An important advantage of Interferometric Phase Control is its inherent ability to make use of statistical error reduction techniques to minimize any ionospheric effects. This includes time averaging and/or spatial averaging using several on and off-site phase measurement antennas. PREDICTION OF DEFORMATION DYNAMICS/MAPPI NG It should be pointed out that once the Spacetenna has been initially phase tuned, learning curves or adaptive modeling techniques could be used to predict the dynamics of Spacetenna structural deformations. With such predictions, it is felt that the capability would then exist to phase tune the entire Spacetenna based on frequency measurements of only a "few" key power modules and occasional measurements of the rest. By adding two additional receiving antennas on the earth so that there are three earth antennas spaced a few kilometers apart and not in a straight line, additional phase measurements can be made. These measurements provide information to "map" the face of the Spacetenna, that is, to determine the relative distance, direction and motion of each power module with respect to the SRT. This provides the capability for performing a transverse modal analysis from the earth, of select samples of power modules on the face of the Spacetenna. In addition, the interferometer phase control technique provides the ability to automatically identify defective power modules. REFERENCES 1. J. H. Ott and J. S. Rice: "Digital SPS Phase Control Using Traveling Wave Interferometry" Novar Electronics Corporation Technical Report, October, 1978. 2. Ibid., p. 32.
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