EXECUTIVE SUMMARY This volume summarizes results obtained in the study concerning, design approaches, estimated costs and technology requirements for systems that transmit power from space to earth, a concept leading to a potential source of comparatively pollution-free power. Basic elements of such systems are an extraterrestrial power source, e.g., a solar powered device or a nuclear reactor, and a transmission system to condition the power, beam it to earth and again condition it for distribution. The transmission system uses microwave technology which has the potential for high efficiency, large power handling capability and controllability. The transmitting antenna would be in geosynchronous orbit on a fixed line of sight to the ground antenna. The work was conducted in 1974-1975 by the Raytheon Company. Raytheon was supported by the Grumman Aerospace Corporation on mechanical systems and flight operations, and by Shared Applications, Inc. on klystrons for microwave conversion. The transmitting antenna is a planar phased array about 1 km in diameter constructed of aluminum or composites and weighing about 6 x 106 kg. It consists ofj 18M x 18M slotted waveguide subarrays which are electronically controlled to direct the power beam at the ground receiving antenna with an rms error of only 10M. The subarrays use groups either of 5 kW amplitrons in series or 50 kW klystrons in parallel to convert input de power to microwave power. The receiving antenna is an array about 10 km in diameter consisting of dipole elements each connected to a solid state diode which converts microwave power back to de power. An operating frequency of 2.45 GHz in the USA industrial band re- bulls in near optimum efficiency, avoids brownouts in rain and should have minimal problems in radio frequency interference and allocation. A 5 GW ground power output provides economy of scale while keeping the peak microwave power density in the center of the beam at earth about 20 mW/cm^. Microwave system transmission efficiency is about 60% and cost is about 500 $/kW including assembly and transport of the transmitting antenna to geosynchronous orbit at 200 $/kg. The orbital transportation and assembly cost should not exceed about 200 $/kg if a satellite power system is to have energy costs comparable with projections for ground based fossil and nuclear plants. The recommended flight plan is transport to low earth orbit using a reusable heavy lift launch vehicle, assembly in low earth orbit and then transport to synchronous orbit usirg a solar electric propulsion stage. Emphasis is placed on orbital manufacture and assembly to achieve faborable launch vehicle packaging densities. The critical technology items needing early development are the de to microwave converters, materials, electronic phase control subsystems and the transmitting antenna waveguide and structure including their interfaces with the microwave converters. A
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