Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site cornell.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxl!houxm!houxz!vax135!cornell!dietz From: dietz@cornell.UUCP (Paul Dietz) Newsgroups: net.space Subject: Re: Relative costs of Geostar and Navstar Message-ID: <158@cornell.UUCP> Date: Tue, 7-Aug-84 01:52:47 EDT Article-I.D.: cornell.158 Posted: Tue Aug 7 01:52:47 1984 Date-Received: Wed, 8-Aug-84 19:19:53 EDT References: <742@sri-arpa.UUCP> Reply-To: dietz@gvax.UUCP (Paul Dietz) Organization: Cornell Univ. CS Dept. Lines: 17 A Navstar ground unit must receive signals from four navstar satellites simultaneously, so it must have 4 receivers (actually, two frequencies are transmitted by each satellite, so the unit must receive 8 signals). A Geostar ground unit need only have one receiver. Geostar ground unit must transmit a powerful microwave pulse, but the average power is very low (milliwatts), so microwave semiconductors can be used. There is some contention about the accuracy of the Geostar system. The Navstar system uses two different frequency signals from each satellite in order to compensate for the slowing of microwaves passing through the ionosphere (a frequency dependent effect). Geostar could do this also by having the ground unit transmit two reply pulses at different frequencies, but I don't know if O'Neill has put this feature in. The biggest gain for Geostar is the added functionality. Since signals are transmitted from ground units, they can be used for communication as well as position location.