Congressional Committee, NASA's Office of Applications became interested in further development and demonstration of microwave technology with the SPS application in mind. It initiated responsibility to carry out its sponsorship through the Jet Propulsion Laboratory and NASA's Lewis Research Center. Four activities of importance came from this support. One was a study of the complete microwave subsystem including satellite and ground rectenna [8], one was a study and technology development dealing with rectenna for the SPS application [7], a third was a demonstration of beaming significant amounts of power over a significant distance [9, 10] and a fourth was productive studies dealing with microwave power generation and antennas [11]. Of all these efforts, the 1975 JPL Goldstone demonstration of transmitting significant power over a distance of one mile and converting the incident microwave power at 84% efficiency to produce over 30 kilowatts of DC power was the most visible [9, 10] (Fig. 3). A large 18 by 24 foot rectenna composed of 18 subarrays was designed and built by the Raytheon Company for the demonstration. The efficiency and success with which the demonstration was carried out attests to the soundness and reliability of the rectenna technology involved as well as the program management. The rectenna survived and was operable after a direct lightning strike on the tower in 1980, and which destroyed equipment on the ground. The success of this demonstration was possibly essential to provide the credibility necessary to later undertake the joint DOE/NASA study of the Solar Power Satellite concept. The Solar Power Satellite and Beamed Power Transmission The Solar Power Satellite concept was introduced by Dr Peter Glaser of Arthur D. Little, Inc., in 1968 [12]. Fig. 4 illustrates the SPS concept. A satellite in geosynchronous orbit collects the sun's energy in a large array of photovoltaic cells, and converts it into microwave power which is then beamed to the Earth where it is converted back into ordinary electric power for use on Earth. Because the solar cell array is continually exposed to the sun, except for very short periods of time at midnight during the vernal and autumnal equinoxes, and because the 2.45 GHz microwave beam can penetrate the Earth's atmosphere with near negligible attenuation under all weather conditions, the Solar Power Satellite system can produce highly reliable base load electric power for use on Earth. A large Solar Power Satellite system supplying electric power for home, industry, and transportation use could reduce the amount of CO2 now being poured into the atmosphere from fossil fuel burning by a large amount. Each Solar Power Satellite and corresponding rectenna on the Earth are very large physically and electrically, involving square kilometres of area and gigawatts of power. The conceptual design presented a tremendous challenge to engineers to solve the many problems involved. Interest in the Solar Power Satellite concept grew within the Dept, of Energy and NASA until a three year study was undertaken in 1977-1980. The three-year study program was termed the ‘DOE/NASA Satellite Power system Concept Development and Evaluation Program'. The many detailed studies undertaken during this study were completed in the summer of 1980. A 670 page document summarizing the results of these studies was published [13]. A portion of the funding for the three year SPS study, administered by NASA, was used for engineering studies. The particularly difficult problem of building a high
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