A Satellite System for Avoiding Serial Sun-Transit Outages and Eclipses

Communication satellite systems experience predictable service interruptions involving the sun. A sun-transit outage occurs when the pointing angles from a receiving earth terminal to a satellite and to the sun so nearly coincide that the additional noise power presented by the sun renders transmission unusable.1 When a satellite passes through the earth's shadow, its solar primary power is interrupted and its sunlight-dependent heat balance is upset. A geostationary system serving a common coverage region may include several satellites spaced less than 10° (175 mrad) in the synchronous equatorial orbit. Figure 1 illustrates the timing of sun transits and eclipses occurring in rapid series for three geostationary satellites during one day at the spring equinox, observed from an earth terminal located on the equator at longitude 0°W. One sun transit near noon and one eclipse 12 hours later are observed for each satellite served by this terminal. Eclipses of closely spaced satellites may occur at the same time, and sun transits of different satellites may also occur simultaneously within a large coverage region. Daily sun transits of all geostationary satellites serving an earth terminal occur during one week in the spring and again in the fall. Service interruptions can last five minutes or more per satellite. Affected outage regions are large and move so rapidly that terrestrial restoration is unattractive. Conversely, a minimum of one working and one spare geostationary satellite are required for restoration independent of terrestrial facilities.