jbrown@herron.uucp (Jordan Brown) (10/20/88)
> Does anybody know if NAVSTAR is operational yet? Yes. No. Some are up; it is possible to use it a few hours a day. > Not that it makes much practical difference; Rousmaniere estimates that > a receiver will cost $25,000... I believe I've seen estimates for handheld GPS receivers in the $3k range. This was a rumor; I don't remember if the original source was an ad or a guess. Incidentally, the folks in rec.aviation would probably be interested in stuff related to GPS too. People might want to include r.a in followups.
birenboi@sal38.usc.edu (Aaron Birenboim) (10/25/88)
In article <test5@herron.uucp> jbrown@jato.jpl.nasa.gov writes: > >> Does anybody know if NAVSTAR is operational yet? > >Yes. No. Some are up; it is possible to use it a few hours a day. > >> Not that it makes much practical difference; Rousmaniere estimates that >> a receiver will cost $25,000... > >I believe I've seen estimates for handheld GPS receivers in the $3k range. I heard something about Civialian and military Navsat hardware. Real Cloak and Dagger stuff. Some how military receivers will be able to locate themsevles to within a few meters, while the civialian hardware will only work to within a few miles. Does anybody out there know how this will work? Is it classified? What will the cost be? Aaron "The Lumberjack" Birenboim|"In the begining, the Universe was created... | This made a lot of people angry, and was GO TROJANS!! | widely reguarded as a bad move." birenboi@castor.usc.edu | -Douglas Adams _The Guide_
lloyd@axecore.UUCP (Lloyd Buchanan) (10/26/88)
I presume NAVSTAR works as a variant of the same hyperbolic radionavigation as LORAN. This means that a receiver can only determine its position in relation to the transmitters. LORAN is no problem as the transmitters are in fixed, known positions. Since the satelites are not in geostationary orbits they must broadcast their positions to the receivers. Presumably they broadcast two positions, one for civilians and one more accurate but encrypted version for the military.
olsen@XN.LL.MIT.EDU (Jim Olsen) (10/26/88)
In article <test5@herron.uucp> jbrown@jato.jpl.nasa.gov writes: > Does anybody know if NAVSTAR is operational yet? The latest edition of Aviation Leak (Oct. 24) has an article on Navstar. They quote an Air Force spokesman as saying that a full constellation of Navstar satellites will be operational in the "mid-1990's". Until the constellation is complete, you can use Navstar only part of the day, and/or in only part of the world, and/or with only partial capability. Interestingly, the article suggests that there may be considerable demand for dual-mode receivers which can use both Navstar and Glonass (its Soviet counterpart). Has anyone heard when Glonass is supposed to be operational?
rgrove@pogo.GPID.TEK.COM (Robert Grove) (10/29/88)
In article <172@axecore.UUCP> lloyd@axecore.UUCP (Lloyd Buchanan) writes: > >I presume NAVSTAR works as a variant of the same hyperbolic radionavigation >as LORAN. This means that a receiver can only determine its position in >relation to the transmitters. LORAN is no problem as the transmitters >are in fixed, known positions. LORAN, which does calculate a distance difference from 2 stations to place you on a hyperbolic line, then does the same thing with two other stations and which determines your position by where the hyperbolic lines cross, requires a minimum of three transmitters to determine your position. NAVSTAR may not be the same as the older NAVSAT but, it probably works in the same way; if so, only one NAVSAT is required to get a position but, you need to already know, within a degree or so, where you are. My guess would be that the NAVSTAR station transmits its orbital information on a couple of different frequecies. This is done to resolve refraction error. By measuring the doppler of the transmission and, by knowing the orbital information of satellite and, roughly where you are, you can tell exactly where you are. Note that satellite passes that are closer to directly overhead are the least useful as there is no way to resolve which side the pass was on from the transmitted information. You need to already know that. I assume that the NAVSTARS will be in polar orbit as were the NAVSATs. -- Robert Grove rgrove@pogo.gpid.tek.com.uucp | {anybackbone != ihnp4}!tektronix!pogo!rgrove