Effects of a satellite power system on ground‐based radio and radar astronomy

Abstract

Intensive studies of the feasibility of a satellite power system (SPS) are currently being carried out under a program initiated by the U.S. Department of Energy and the National Aeronautics and Space Administration. In such a system, satellites in the geostationary orbit convert solar radiation to microwaves, which are beamed to collecting stations on earth in order to provide electric power. An envisioned reference system for such studies is composed of 60 satellites spaced at 1° intervals, each radiating 6.7 GW at 2.45 GHz. Such a system can interact with radio and radar astronomy systems in a number of ways. The power signal and its harmonics, which fall close to radio astronomy bands, can cause overloading of input stages, and mitigation will require development of cryogenically cooled filters. Radiation within radio astronomy bands can result from transmitter‐generated noise, thermal noise from the large solar cell arrays, and possibly from intermodulation, component failures, and turn‐on transients. Noise and harmonics can also be generated by the power‐collecting rectennas. There may be propagation effects resulting from ionospheric heating. For those effects for which the magnitude can be estimated from present data, comparison is made with the interference thresholds for various types of radio telescopes. It is concluded that for any radio telescope, a zone of sky will be centered on the arc of satellites, in which observations with high sensitivity are precluded. The width of this zone, as determined by thermal radiation, is estimated to vary from about 30° for single‐antenna telescopes to a few degrees for high‐resolution arrays and interferometers. There will be some degradation in performance in bands close to the power signal and its second harmonic, and it will be necessary to insure that adequate shielding by terrain exists between radio observatories and the power receiving sites. The interference thresholds are higher for radar astronomy than for radio astronomy, but one of the main frequencies, 2.38 GHz, is very close to the power transmission frequency, and targets are usually close to the ecliptic and therefore at declinations close to the arc of satellites. Coexistence of radio and radar astronomy with the SPS will be crucially dependent upon the quality of engineering and maintenance of the satellites.