Elliptical orbit constellations-a new paradigm for higher efficiency in space systems?

Abstract

Several systems are being developed for satellite cellular telephone use. Examples are Iridium, Globalstar, ICO, and ELLIPSO. Systems designers seem to prefer sub-synchronous multi-satellite arrays over geostationary satellites as they can more easily communicate with small low-power handheld cellular telephones, and they also have less signal latency (time delay). The flexibility of the elliptic orbit allows a biasing of earth coverage towards a given latitude. Increased coverage is obtained by placing apogees in a stable orbit over a preferred latitude. If the orbit is both elliptical and sun-synchronous, it can also be biased towards a given (local) time of day. With apogees appearing during daytime, greater capacity is ensured during the peak usage hours for telephone communications. Tailored elliptical-orbit constellations may well become the paradigm for many of these new telecommunications space systems. Lower cost elliptic-orbit constellations, with fewer satellites, may well prove more profitable than circular arrays for many other space applications, as well.