Explain how we developed our approach and why we believe it merits consideration. Give you our thoughts on some future development steps the U.S. can take. We have attempted to approach space-based solar power as a total concept. In addition to the satellite itself, we have addressed our efforts to the system's other needs: New modes of space transportation; unique support systems, including space assembly facilities; launch facilities; maintenance and resupply systems; ground systems, including receiving antennas, grid interfaces and control systems. Like Dr. Glaser's satellite, our Powersat would generate electricity in geosynchronous orbit and transmit that energy to Earth. The satellite would be illuminated more than 99 percent of the time by sunlight undisturbed by Earth's atmosphere or weather. The essential difference between our configuration and Dr. Glaser's resides in the method of converting this sunlight to electrical power. We would utilize a heat engine converter rather than solar cells. Thousands of acres of plastic film mirrors much like those being developed under our ERVA contract would concentrate sunlight into a solar cavity. This heat would drive a set of helium gas turbines which, operating on a closed Brayton cycle, drive alternators. Waste heat is radiated into space. We have emphasized turbine heat engine converters because we feel that they are achievable within a natural growth of existing technology. In other words, we believe that we have developed a concept which does not demand any great technological breakthrough. The solar cell option, however, also is attractive. If the necessary technological breakthroughs do occur, the economics of photovoltaic power satellites could compare favorably with the heat engine option. Once the electric power is generated—whether by heat engines or solar cells— it is routed to a phased array RF generator where it is converted to a narrow microwave beam. This beam can be directed to ground-based receiving antennas located at any point on Earth visible to the satellite. These ground receiving antennas would be about five miles in diameter. They would be elevated, allowing the land beneath them to be farmed. The RF field strength below these antennas would be less than the current U.S. public safety standard of 10 milliwatts per square centimeter. The D.C. power would be converted to high voltage A.C. at these rectennas and fed to the nation's power grids. An essential element of the Powersat or any other concept for power generated in space is an economical space transportation system. A major share of our effort has gone toward defining this need. The heavy weight of this system would be a launch vehicle shorter but larger in diameter than the Saturn Five moonrocket. It would transport Powersat parts and subassemblies to low Earth orbit, burning nonpolluting hydrogen fuel. This vehicle would look something like a huge Apollo command module—except its landing would be rocket-arrested rather than parachute-assisted. Its shape would provide a large-volume payload bay and enable a controlled aerodynamic return to Earth. Using Space Shuttle engine technology and a water-cooled heat shield this space freighter would be totally reusable and would have a turn-around time between flights of about one day. The massive payloads of these space freighters would be destined for a low- Earth-orbit assembly station where several hundred workers would build the Powersat from parts prefabricated on Earth. Electric rockets, drawing power from the already-operating solar generators, slowly would propel the modules into their 22,000-mile stationary orbit. They would be assembled there into a four-module Powersat unit. We can envision a Powersat with a mass of about 100,000 tons, stretching about nine miles across space. It would pour enough energy to Earth to produce about 10,000 megawatts of net useful output from the ground receiver—-enough to power about a million households. It is immense and mind boggling—but possible according to our preliminary studies. The cost? My apologies, gentlemen, but I cannot be entirely responsive to your request for the economic viability of Powersat as compared to likely alternatives. Projecting cost is uncertain, at best, and tends to develop at these early stages into a numbers game. This is a game I do not play. The truth is that we do not know at this time what these costs will be. We have, however, done enough homework to believe that
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