Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!linus!security!genrad!grkermit!masscomp!clyde!floyd!harpo!seismo!hao!hplabs!sri-unix!REM@MIT-MC From: REM%MIT-MC@sri-unix.UUCP Newsgroups: net.space Subject: re: G.K. O'Neill's satellite plan Message-ID: <16109@sri-arpa.UUCP> Date: Sat, 28-Jan-84 16:27:00 EST Article-I.D.: sri-arpa.16109 Posted: Sat Jan 28 16:27:00 1984 Date-Received: Thu, 2-Feb-84 01:00:05 EST Lines: 38 From: Robert Elton MaasLet me step back and analyze this system from an abstract viewpoint. Why would anybody want to know their position (relative to a coodinate system fixed on the Earth; as we all know absolute position is either nonsense or useless as the Earth spins thru space) anyway?? To establish rendezvous with some desired target (a fixed object or somebody else who you're trying to meet), to prevent rendezvous with some undesired object (a hazardous area), or to estimate distance between the current location and a potential target to determine feasibility of rendezvous, or to find the set of all potential targets within some prescribed radius. Following a route on a computerized map is merely a combination of using the navigation system to get a direction vector to achieve approximate rendezvous with the next map target, and using local feedback to avoid local obstacles and to improve the proximity of rendezvous, this procedure being followed over and over for different intermediary rendezvous points along a route. Can anybody think of any other fundamental use for a locator system? In the woods/mountains, getting within a few hundred meters should be sufficient. When your two locators say you are "at the same location" but you still can't see each other, you shout or fire a gunshot or use a local radiobeacon or radio-describe landmarks. In a crowded city you need more accurate information, both because normal city noises tend to drown out your shouts and the like, and because gunshots tend to disturb the residents and the police. It would be nice if a single system could handle both country and city, but perhaps cellular radio in cities will do a better locator job anyway, as well as provide other services that are too compute-intensive for the satellite to handle (the satellite would have to handle a whole world's load whereas the corner radio-cell-transceiver would have to hande only one square block's worth of load, about 9 orders of magnitude less), so maybe a dual city/country system is inevitable and having the satellite accuracy be insufficient to handle crowded cities is a minor inconvenience?