A Polar Orbit Solar Power Satellite JOHN W. FREEMAN Jr Summary We propose placing the solar power satellite (SPS) in a polar elliptic orbit with apogee over the north pole and placing the rectenna at a high latitude location. The satellite's long dwell time near apogee would allow it to follow the circumpolar motion of the rectenna for a large fraction of an orbit period. The long distance between the rectenna and the consumer could be accommodated by energy storage such as the conversion of electricity to hydrogen. The advantages of this scheme are that it would confine the microwave beam near the Earth to the polar regions which are sparsely populated and it would permit a total power requirement of less than 5 GW for early versions of the SPS since the geostationary orbit distance would no longer be mandatory. The purpose of this paper is to suggest a variation to the SPS concept that addresses areas of concern that have arisen from previous SPS studies. This variation invites the marriage of the satellite power system idea with a hydrogen-based energy system [1] and proposes the elimination of the geostationary orbit as the orbit of choice for the SPS. Since the SPS concept was first introduced in 1968 by Dr Peter Glaser, it has been subjected to considerable study. Much of this study has focused on methods of implementing the basic concept of an energy collector in geostationary orbit. There has not been much effort to investigate orbits other than the geostationary orbit. The reason for this is the obvious appeal of a continuous, fixed orientation between the satellite and the rectenna. There are, however, certain disadvantages of the geostationary orbit itself and there are disadvantages to the location of the rectenna which the geostationary orbit mandates. To begin with, the intrinsic altitude of the geostationary orbit, 36000 km, together with the minimum power density required for efficient reconversion of energy at the rectenna require a very high total beam power of about 5 GW and a large rectenna area of about 100 km2. A lower orbit altitude would permit a lower initial power level and rectenna area and hence lower front-end or start up costs or lower costs for pilot or prototype plants. Next, the geostationary orbit, being an equatorial orbit, requires that the rectenna be located at low or mid-latitudes. These latitudes also include a substantial majority of human activity on the earth. This is convenient for the distribution of power from the rectenna to the consumer but it also invites potential interference between the SPS energy beam and other electronic devices as well as concern about hazards to biological John W. Freeman Jr, Assistant Chairman and Professor, Department of Space Physics and Astronomy, Rice University, Houston, TX 77251, USA.
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