0191-9067/81/030225-24S02.00/0 Copyright ® 1981 SUNSAT Energy Council SOLAR POWER SATELLITES: THE IONOSPHERE AND COMMUNICATIONS L. M. DUNCAN Los Alamos National Scientific Laboratory Los Alamos, New Mexico 87545 W. E. GORDON Rice University Houston, Texas 77001 Abstract — The proposed solar power satellite collects solar energy above the earth in geosynchronous orbit, converts it to microwaves, and beams it to a receiver on the ground where it is suitably processed and delivered to the electric transmission system as base-load power. The microwave beam will heat the earth's ionosphere and the responses include electron temperature enhancement, plasma striations from thermal self-focusing, and parametric interactions. These responses are described and the possible impacts of these responses on telecommunications and on the system itself are outlined. The heavy lift vehicles needed to launch into space the materials to be used in constructing solar power satellites emit water and other contaminants that react with the ionized gases in ways to speed up the recombination of ions and electrons. Near the launch trajectory and over a volume centered on the region of rocket engine burn the recombination may be complete. The recombination chemistry is indicated and the impact of this effect on telecommunications discussed. The reference solar power satellite system had a design limit of 23 mW/cm2 for the power density in the microwave beam based on estimates of a threshold of nonlinear interaction of the radio waves and the ionosphere. Experiments have shown that the limit is too low, and theory now suggests that the threshold is soft. The current consensus is that the limit of 23 mW/cm2 can be at least doubled, and perhaps more, pending further tests. 1. INTRODUCTION The Solar Power Satellite (SPS) concept proposes to collect solar energy in space and beam it via microwaves to ground-based receiving antennas, where it can be converted to electrical power. A network of these space power stations, each generating 5 to 10 GW of power, could make a substantial contribution toward satisfying future energy needs. The microwave beam and the emissions from the launch vehicles needed to construct the SPS will modify the ionosphere, which in turn may impact telecommunications, and the ionosphere may affect the operation of the SPS. Each of these relations is considered using the available theory and observations. The theoretical gaps and the observational needs are listed. The ionosphere is defined as that part of the earth’s upper atmosphere where free electrons exist in sufficient numbers to affect radio-wave propagation. Numerous telecommunications systems rely on ionospheric reflections or transionospheric propagation as part of the communications signal path. Any system which can significantly modify the ionosphere has the potential to produce telecommunications interference and/or additional radio paths that may be usefully employed. In addition, the role of the ionosphere in solar-terrestrial coupling and climate change is just beginning to be investigated.
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