A complete transportation system from earth to geosynchronous orbit that is located in the equatorial plane also has the well recognized advantages of minimum ground-to-space launch cost, because of the earth’s high rotational speed at the equator, and the elimination of cross-range maneuvers later. The new rectenna format is a key element of the proposed vehicle. In addition to its low mass and flexibility as demonstrated in Figure 2, the rectenna converts over 80% of the impinging microwave power directly to DC power. Sections of the rectenna can be connected in series or parallel to give almost any value of output voltage and current that is desired. The efficiency of the rectenna is relatively independent of its orientation to the microwave beam, up to an angle of 30°, so that the rectenna need not be kept normal to the microwave beam even in low earth orbit. Its usual position would be parallel to the earth’s surface where drag would be minimal and gravitational gradient forces would be zero. The life and reliability of the rectenna in space should be excellent. The Kapton film is highly resistant to ultra violet radiation. The rectifying diodes are made from gallium arsenide and their combined area is less than a hundred-thousandth of the rectenna area so that they could be easily shielded if necessary with minimal weight penalty. The rectenna is so efficient that it generates very little heat and the heat that it does generate can be radiated to space by its own structure without exceeding the 200°C operating temperatures that are tolerable to both Kapton and the diodes. The rectenna in its previous format has received extensive and successful evaluation^, its new thin-film, etched-circuit format, has also received extensive laboratory testing for efficiency and reliability. The interorbital vehicle, comprised essentially of the rectenna and electric propulsion engines, is shown schematically in Figure 3. In concept, the sections of rectenna are carried in rolled- up form in the space shuttle to low earth orbit where the sections are assembled with the electric engines to form the interorbital vehicle. One shuttle load could provide the needed rectenna area for two interorbital vehicles. Once assembled and placed in operation with the ground-based transmitter, the interorbital vehicle is assumed to ascend with the spiral geometry shown in Figure 4. This is the known flight profile if the satellite were continuously propelled with the accelerating force always parallel to the earth's surface^. Although the flight profile actually consists of a large number of intermittent accelerations, they are angularly distributed rather uniformly if projected on a polar plot. It is quite likely, then, that a flight profile would also be that of a spiral. 12r.m. Dickinson, "Evaluation of a microwave high-power reception-conversion array for wireless power transmission," Tech. Memo 33-741, Jet Propulsion Lab., Cal. Inst. Technol., Sept. 1, 1975. ^E. Sthulinger, "Ion Propulsion for Space Flight", Sec. 4.3, McGraw-Hill, NY (1964).
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