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.