roy@phri.UUCP (Roy Smith) (10/19/88)
In John Rousmaniere's "The Annapolis Book of Seamanship", in the
chapter on electronic navigation, the proposed Global Positioning System or
NAVSTAR is discussed: "it will consist of 18 satellites orbiting about 11,000
miles above the earth's surface. The signals of any four of these satellites
will be available at any time to allow instantaneous pinpoint navigation 24
hours a day. The system is expected to become operational in the late
1980's". The book is Copyright 1983, so presumably that was written 5 or 6
years ago, when America's outlook on space was a bit rosier than it is now.
Does anybody know if NAVSTAR is operational yet? Were the birds to
be launched on the shuttle (in which case, I'd expect it to be several
years behind schedule) or on disposables? Not that it makes much practical
difference; Rousmaniere estimates that a receiver will cost $25,000; it's
not likely I'll be able to afford a boat that costs $25k any time soon, let
alone a nav system.
--
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"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.
henry@utzoo.uucp (Henry Spencer) (10/22/88)
In article <3551@phri.UUCP> roy@phri.UUCP (Roy Smith) writes: > Does anybody know if NAVSTAR is operational yet? ... No, it's still experimental. The production satellites were meant for shuttle launch. They were behind schedule even before Challenger. They are now, mostly at least, going up on expendables, but that too implies delays while expendable production ramps up again. -- The meek can have the Earth; | Henry Spencer at U of Toronto Zoology the rest of us have other plans.|uunet!attcan!utzoo!henry henry@zoo.toronto.edu
Joel_F_Janosky@cup.portal.com (10/23/88)
As to the present status of the Global Positioning System : According to the October 15 issue of Practical Sailor : At this time, there are 7 first generation GPS satellites in orbit. They provide continuous two dimensional coverage up to 12 hours per day. Deployment of GPS satellites is by shuttle and now that the shuttle is flying again, deployment should resume. Full deployment calls for 18 satellites with a proposal to increase this to 24. The Magellan GPS 1000 has just been announced, at a price of $3000.00. This is a handheld unit with a built-in antenna, that runs off of 6 AA batteries. It features all the goodies LORAN-C users are used to; 50 waypoints,range and bearing to destination, course over ground and distance made good. They can be contacted at : Magellan 260 East Huntington Drive Monrovia, CA 91016 818-358-2363
wes@obie.UUCP (Barnacle Wes) (10/23/88)
In article <3551@phri.UUCP>, roy@phri.UUCP (Roy Smith) writes: > Does anybody know if NAVSTAR is operational yet? Were the birds to > be launched on the shuttle (in which case, I'd expect it to be several > years behind schedule) or on disposables? Not that it makes much practical > difference; Rousmaniere estimates that a receiver will cost $25,000; it's > not likely I'll be able to afford a boat that costs $25k any time soon, let > alone a nav system. I think the SATNAV systems you can buy from most marine supply outlets use the GPS satellites. There are several (I think 5) GPS satellites in position right now. The coverage is not continuous, there are "bands" of the eart (that move, following the satellites orbits) that cannot "see" enough of the satellites to get a fix. I think the largest gap is only 6 hours or so. The SATNAV systems for sale right now do not cost anywhere near $25,000 - the least expensive are in the $1,000 arena. Wes Peters -- Copyright 1988 Wesley R. Peters. Permission is granted to distribute this work in its entirety as long as it is not modified in any way, and this copyright remains intact. No rights other than those expressed here are granted. "How do you make the boat go when there's no wind?" -- Me
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_
karn@thumper.bellcore.com (Phil R. Karn) (10/26/88)
SATNAV does *not* use GPS satellites. They use the older Navy TRANSIT navigation satellites operating in relatively low polar orbits. A SATNAV receiver measures the Doppler shift of a satellite as it goes by, and determines position by fitting the measured curve against a predicted one based on a position estimate. You have to wait for a satellite pass to get a fix, you can't move much during the pass, and accuracy is typically several Km. GPS in the C/A (Clear Access) mode has been demonstrated to have accuracies of 30m or better. This is not much worse than GPS in the (encrypted) military mode. The original design specified that the military mode would be 10x better, but the actual ratio is more like 3 or 5:1, depending on receiver. GPS uses L-band spread spectrum. The military mode has the advantage of a 10x faster chip rate (giving ten times better theoretical resolution) plus two separate carriers to allow for ionospheric propagation delay correction. The C/A mode allows access to only frequency. Phil
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
henry@utzoo.uucp (Henry Spencer) (10/29/88)
In article <1365@thumper.bellcore.com> karn@thumper.UUCP (Phil R. Karn) writes: >SATNAV does *not* use GPS satellites. They use the older Navy TRANSIT >navigation satellites operating in relatively low polar orbits... Support for which will naturally be discontinued after GPS is operational. You just spent $nnnn on a SATNAV receiver? That's too bad. Support for GPS will continue forever, of course. Well, sort of forever. As long as the US military needs it, and maybe a little bit longer. Five minutes longer, maybe ten if you're lucky. (Do you begin to understand why a lot of potential GPS customers, notably international ones, would be a lot happier if GPS wasn't run by the US military?) -- The dream *IS* alive... | Henry Spencer at U of Toronto Zoology but not at NASA. |uunet!attcan!utzoo!henry henry@zoo.toronto.edu
dorn@fabscal.UUCP (Alan Dorn Hetzel Jr.) (11/04/88)
Once you get enough companies making GPS receivers and enough customers using them, GPS will gain some political life of its own as well. Even if the military moves on to another system, GPS would probably be converted into an all-civilian system. Dorn
roy@phri.UUCP (Roy Smith) (11/09/88)
[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"