0883-6272/86 + .00 Copyright ® 1986 SUNSAT Energy Council GEOSTAR: A MULTI-PURPOSE SATELLITE SYSTEM TO SERVE CIVIL AVIATION NEEDS* GERARD K. O’NEILL President and C.E.O. Geostar Corporation 101 Carnegie Center Princeton. New Jersey 08540 INTRODUCTION The Geostar System is a proposed space/ground or air concept that would link mobile terminals through satellites to a computer on the ground. It is designed to provide many services: navigational positioning, radiolocation (return of position information to a central site), emergency location, terrain warning to pilots, warnings of potential collisions between Geostar-equipped aircraft, approach guidance, two- way digital message service and interconnection to ground data bases. Where other systems are already in place to satisfy one or more of these needs, the Geostar System can operate in a supplemental or advisory mode. The Geostar System combines the existing technologies of orbital satellites, computers and integrated circuits. It consists of three parts: a ground station with a computer, two or more satellites at fixed locations in Earth orbit, and the terminals (transceivers) carried by aircraft, surface vehicles or even individual people. The ground station sends digital messages to the transceivers and receives replys from them through the satellite relays. In an airborne application, the times of reply are measured at the ground station and are combined with transmitted digital information on altitude for calculation of aircraft position. That information is sent to the aircraft and to central dispatch locations. The transceivers are designed to be simple and low in cost. All use the same wideband radio channel for transmit and another for receive. The single channel can accommodate a large number of users for three reasons: • Each transceiver is silent most of the time, transmitting only in short, occasional bursts. • Transceivers use “spread-spectrum” transmissions which permit many messages to occupy the same channel simultaneously without interference. • The satellites have spot beams for different geographical areas. A minimal Geostar System consists of one ground station, one satellite able to relay outbound messages from the ground station to the users and to relay inbound *This paper originally appeared in the ICAO bulletin.
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