l.-Iniroduction The SSI-sponsored study of low-mass solar power satellites has been completed. The following is a report on results. Information from the progress report dated October 15, 1993 is included. The report was written by Seth Potter, except for Sections 8 through 8.5 (including Table 3 and Figures 1 through 5), which were based on reports submitted by Dr. Gregory Matloff. 2, Goals and Ground Rules for Study As stated in the Proposal on September 9,1993, the primary goal of this study is to design a lightweight solar power satellite (SPS) which makes use of thin-film photovoltaic materials and solid state microwave transmitters deposited on lightweight substrates. The SPS is then to be redesigned to use lunar materials, if possible. The desirability of using lunar materials will then be assessed. Throughout the study, "traditional" requirements on SPS's will be adhered to whenever possible (e.g., geostationary orbit, microwave power transmission, etc.), but will be altered if necessary to facilitate the design of a simple, easily launched SPS (e.g., new materials; integrated, rather than gimbaled, antennas; etc.). The study is a “first order” design. Future designers may need to alter such things as frequency (depending on federal and international frequency allocations) and total mass (depending on an eventual selection of type of thrusters). 3. Power Transmission One of the major constraints on SPS design is the need to transmit power from geostationary orbit to the Earth. The NASA/US Department of Energy reference design1 utilized microwaves at a frequency of 2.45 GHz. This is a well-understood frequency, with equipment such as magnetron tubes readily available. Since the physics of power transmission causes the beam to spread out into a 10 x 13 km area on Earth (for a 1 km transmitting antenna), the reference SPS had to transmit large amounts of power (5 gigawatts) in order to be economical. One of the advantages of a thin-film SPS is that with
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