Xref: utzoo sci.space.shuttle:1886 rec.boats:1065 Path: utzoo!attcan!uunet!husc6!mailrus!nrl-cmf!cmcl2!phri!roy From: roy@phri.UUCP (Roy Smith) Newsgroups: sci.space.shuttle,rec.boats Subject: Navstar (aka GPS) Message-ID: <3588@phri.UUCP> Date: 8 Nov 88 19:04:09 GMT Organization: Public Health Research Institute, NYC, NY Lines: 60 Followups-To: rec.boats [This is only marginally about the shuttle, so followps to rec.boats only] A few weeks ago I asked about Navstar, also know as Global Positioning System or GPS. Thanks for everyone for all the replies I've gotten. It seems the New York Today has been reading the net too; this mornings Science Times sections has a feature article about GPS. It's long (and copyrighted) so I'll leave it to people to get their own copies, but here are some interesting tidbits: A picture of a hand-held GPS system. Various people had mentioned this. It's from Magellan Systems Corporation in Monrovia Ca. It costs about $3k, runs on 6 penligh (AA?) batteries, and looks like an slightly oversize hand calculator with a bump on the side containing a 3-inch spiral antenna. Takes about 4 minutes to lock on to 3 birds. The CPU in the rcvr is based on gallium arsenide and is "the same chip as an IBM personal computer" whatever that means. A gallium arsenide 80286?? Unfortunately, you can't make out what all the 20 or so buttons say except for 0-9, enter, clear, and on/off. The LCD display in the picture reads "TO NASSAU" and on the line below, "174 degree T 29.65 NM". The stated goal is "guiding missiles, bombers, warships, and ground troops with pinpoint accuracy". Feh! But we knew that already. Burlington Northern Railroad has installed experimental GPS receivers in 17 of its locomotives. BN says their engineers know the position of the locomotives to within 150 feet. A Small Lighweight GPS Receiver will be a "S.L.G.R." or "Slugger". There are currently 7 birds up, in 10,900 mile, 63 degree orbits, making 2 orbits a day each. Future birds will be in 55 degree orbits, and (if I understand it properly) 4 other inclinations eventually to give pole-to-pole coverage. Ground stations track the birds and broadcast the time (atomic clock) and position of each; they in turn rebroadcast that information to the recievers. The receivers need to see 3 birds to get a fix, but will use as many as they can see to increase the accuracy (and speed of lock?). When the full set is up, a given rcvr may be able to see as many as 8 at a time. By 2001, the system will have cost $8.4 billion. The Air Force plans to launch 6 a year on Delta-2's. By year's end, there will be 13 up there, giving 24-hour coverage everywhere. Eventually there will be 21 working satelites, with 3 in-orbit spares. The first went up on Feb 22, 1978 (10-1/2 years ago!). They have a design useful life of 5 years which means 5 launches a year just to keep up with failures. There have been 9 successful launches and one failure. Of the 7 operating birds, 2 have been up for 10 years. Future plans call for shuttle launches as well as Delta-2's. An anonymous Air Force officer is quoted as saying "GPS will have an impact on navigation nearly as important as the invention of the compass". Actually, considering that the $3k price will surely drop a lot and the current price of high-quality magnetic compasses, I wonder how long it will be before GPS is actually *cheaper* than a compass? -- Roy Smith, System Administrator Public Health Research Institute {allegra,philabs,cmcl2,rutgers}!phri!roy -or- phri!roy@uunet.uu.net "The connector is the network"