Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!burl!mgnetp!ihnp4!zehntel!hplabs!sri-unix!dietz%USC-CSE@ECLA From: dietz%USC-CSE%ECLA@sri-unix.UUCP Newsgroups: net.space Subject: Re: How Does Geostar Work? Message-ID: <645@sri-arpa.UUCP> Date: Thu, 2-Aug-84 11:49:00 EDT Article-I.D.: sri-arpa.645 Posted: Thu Aug 2 11:49:00 1984 Date-Received: Sun, 5-Aug-84 00:34:17 EDT Lines: 20 Geostar works by triangulation. A signal addressed to a portable tranceiver is sent from the central ground station via one of the satellites. The ground unit then emits a very short omnidirectional microwave pulse (with ID information included). All four satellites receive this pulse, and transmit it back to the ground station. Time delays are used to compute position. The position is then transmitted back to the ground unit. The Geostar ground unit is simply a microwave tranceiver capable of emitting high power (500 watts, I believe) short duration pulses, along with some fast control logic to detect when the unit is being polled and to receive and display position information. Average power consumption is low, because the pulses are so short (a microsecond?). The Navstar system uses passive ground units, since they must operate in combat conditions where radio silence is critical. These passive units must do the triangulation themselves, so they are expensive. Paul Dietz dietz%usc-cse@usc-ecl