0883-6272/86 + .00 Copyright ® 1986 SUN SAT Energy Council APPLICATIONS OF LOW-EARTH-ORBIT POWER TRANSMISSION G. D. ARNDT and E. M. KERWIN NASA Lyndon B. Johnson Space Center Houston, Texas 77058 Abstract — The use of low-earth-orbit microwave transmission systems to transfer power between two co-orbiting satellites is investigated. A microwave system with a 20 m antenna and 30 m rectenna over a 5-10 km operating range could have possible applications for transmitting 100 kW of power. Antenna/rectenna trade-off sizings, taper analyses, orbital considerations, and possible uses are discussed. INTRODUCTION Several low-earth-orbit (LEO) applications of transferring energy via microwave beam involve using a space station as either a transmitter or receiver. The feasibility of LEO power transmission has been the subject of recent studies. One concept had a space station supplying energy to nearby free-flying satellites. The prime power would be generated from a large space station solar array and then transmitted to the scientific and/or commercial free-flyers being tended by the station. A single large power source on the station would be cheaper than multiple small sources on the satellites. However, subsequent orbital analyses have shown close formation freeflyers are not feasible due to the large propellant requirements for station keeping and orbital maintenance. The reverse scenario, i.e., the space station receives electrical power from a nearby satellite, is feasible. A nuclear power satellite could generate and transmit power to a co-orbiting space station. The space station would have a conventional solar array providing its primary operating power. Growth power for conducting experiments, space manufacturing, etc., could be provided in 100 kW increments from a nuclear satellite. Locating the nuclear reactor away from the station has the advantage of reducing the considerable shielding mass required to maintain low radiation levels around the station. Orbital considerations such as space station traffic patterns, subsatellite formation flying constraints, tethered/non-tethered tradeoffs, and shielding mass as a function of separation distance will be discussed. For a tethered nuclear satellite, the power can be transferred via cable or microwaves. This study investigates only microwave transmission because of the uncertainties in allowable voltage levels through cables in the ionosphere. A number of shuttle tether experiments are planned or proposed which will provide information on power-conducting cables. If the transmission voltage is restricted to low levels or if current/magnetic field interactions are a constraint, then microwave power transmission is an attractive alternative.
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