0191 -9067/82/020099-21 $03.00/0 Copyright ® 1982 SUNS AT Energy Council TRANSMISSION OF MICROWAVE BEAMED-POWER FROM AN ORBITING SPACE STATION TO THE GROUND R. M. WELCH* Institute of Meteorology Johannes Gutenberg University 6500 Mainz, West Germany J, M. DAVIS and S. K. COX Department of Atmospheric Science Colorado State University Fort Collins, Colorado 80523, USA Abstract — Transmission efficiencies and surface power densities are calculated from the interaction of a 10 GW microwave beam with rain clouds. Computations are made as a function of [a] frequency (2.45 to 10 GHz); [b] beam nadir angle; [c] raindrop size distribution; and [d] cloud shape. Scattered surface power densities outside of the receiving rectenna do not exceed 10 gW/cm2 for frequencies of 2.45 and 3.3 GHz, even for extremely heavy rainfall rates. At higher frequencies exposure levels outside of the rectenna may reach 100 q.W/cm2, or two orders of magnitude less than the U.S. safety standard. From the standpoint of public health and safety, the scattering of microwaves by rain clouds is not a serious problem, with scattered fluxes outside of the rectenna much smaller than sidelobe fluxes. Beam losses due to absorption in rain clouds are significant in some cases, with absorption losses far more important than scattering losses. The amount of scattering increases with increasing microwave frequency, increasing drop size and drop concentration and increasing nadir angle of the beam. I. INTRODUCTION The concept of a geosynchronous solar power satellite (SPS) has been given increased attention as an alternative energy source. In spite of the costs associated with construction in orbit, the power satellite would be competitive with nuclear energy production. The proposed system would provide energy all but 72 min during the day and would be immune to various ground-based limitations such as dust and clouds. Studies of the SPS concept have been reported by many authors (1-8). The current SPS proposal centers around a 21.3 x 5.3 km2 silicon-solar-cell array, oriented towards the sun and providing 17 GW of continuous power to one or two 1 km-in-diameter slotted waveguide transmitters. The transmitter(s) consists of approximately 104 klystron or amplitron oscillators. The surface rectenna consists of large arrays of dipole antennas with a solid-state rectifier at each dipole to collect the microwave energy and convert it to d.c. The microwave d.c. power then is collected, converted to a.c. and distributed over conventional power grids. A review of the various efficiencies and design criteria has been given (9). An extensive review of the *Present address: Department of Geophysical Sciences, Old Dominion University, Norfolk, VA 23508.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==