ing module in the array. The resulting low level signal is then amplified to a high power level by a phase-locked amplifier which preserves the phase of the drive signal. The net orchestrated effect is to keep the beam electronically pointed towards the rectenna even though there may be considerable physical deviation. The subarray is boresighted by making certain that it is physically flat and then by adjusting the phase references in all radiating modules to the same value. This can be accomplished by an alignment procedure utilizing laser beams modulated by the microwave frequency selected for the power beam”. In the ground-based phased array, whose physical flatness can always be maintained, an appropriate change in the digital signals sent out in the row-column matrix can be used to make a first order correction of the focussing of the beam by changing the curvature of its wave front. The analagous use of this feature in the subarray in space is to first-order correct for subarray warping whose nature and magnitude can be obtained from operational experience. A change in the two digital signals can also be used to compensate for the linear expansion or contraction of the array, which can be predicted from temperature sensors and observational data^. APPLICATION OF MICROWAVE POWER TRANSMISSION TECHNOLOGY TO A LOW-COST, LOW-EARTH-ORBIT TO GEOSYNCHRONOUS ORBIT TRANSPORTATION SYSTEM NEEDED TO CONSTRUCT THE SOLAR POWER SATELLITE The thin-film, etched-circuit rectenna^»shown in Figure 2 provides a continuous source of electric power in space, at the very low specific mass of two kilograms for each kilowatt of DC power output. When this new development is combined with a ground-based microwave transmitter, a high-specific-impulse LEO to GEO transportation system becomes technically feasible. If the ground-based transmitter is located on the equator and the inter orbital vehicle is in the equatorial plane the proposed transportation system becomes economically very attractive. The transportation system benefits greatly from this arrangement in that the vehicle passes directly over the transmitter on each revolution. An obvious benefit is that the minimum distance between transmitter and satellite, important in low orbits, is maintained. A more important, not-so- obvious, benefit is that the cost of the transmitter which needs to be electronically steered through a +50° angle in the east to west direction only is a small fraction of the cost of a transmitter that is able to scan throughout a 50° cone angle. ^W.C. Brown, J.F. Triner, "Experimental thin-film, etched-circuit rectenna," 1982 IEEE-MMT-S International Microwave Symposium Digest, IEEE Cat. No. 82CH1705-3. ^W.C. Brown, "Performance characteristics of the thin-film, etched circuit rectenna," 1984 IEEE MTT-S International Microwave Symposium Digest.
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