jim.grubs@w8grt.fidonet.org (Jim Grubs) (01/28/91)
> From: michael@vk2bea.UUCP (Michael G. Katzmann) > Date: 25 Jan 91 14:09:22 GMT > Organization: Broadcast Sports Technology., Crofton, MD > Message-ID: <846@vk2bea.UUCP> > Newsgroups: rec.ham-radio,sci.electronics,sci.physics > > Has anyone noticed a degradation of the Navstar GPS system since the > outbreak of unpleasentness in the middle east? > > The implication, when GPS was first started, was that during times of > crisis the C/A code would be degraded so that an enemy could not use it. > > Does differential GPS totally get around this, or is there a trick > they can use to defeat this technique? Jeepers, Michael, why don't we just invite Saddam to sit in on JCS planning sessions and be done with it? -- Jim Grubs - Support OPERATION DESERT STORM - the 9th Crusade! UUCP: ...!uunet!w8grt!jim.grubs INTERNET: jim.grubs@w8grt.fidonet.org
henry@zoo.toronto.edu (Henry Spencer) (01/29/91)
> > From: michael@vk2bea.UUCP (Michael G. Katzmann) > > Has anyone noticed a degradation of the Navstar GPS system since the > > outbreak of unpleasentness in the middle east? > > The implication, when GPS was first started, was that during times of > > crisis the C/A code would be degraded so that an enemy could not use it. The last word I heard was that accuracy had actually improved, because the US military forces in the Gulf are making extensive use of commercial Navstar receivers, while the Iraqis have little or no Navstar equipment, so the public-access code is being kept as undegraded as possible. In article <1154.27A2ECFD@w8grt.fidonet.org> jim.grubs@w8grt.fidonet.org (Jim Grubs) writes: >Jeepers, Michael, why don't we just invite Saddam to sit in on JCS planning >sessions and be done with it? Why bother? There is nothing secret about any of this. There is nothing to be gained, and a fair bit to be lost, by keeping the public in ignorance of things Saddam already knows. -- If the Space Shuttle was the answer, | Henry Spencer at U of Toronto Zoology what was the question? | henry@zoo.toronto.edu utzoo!henry
marty@puppsr.Princeton.EDU (Marty Ryba) (01/31/91)
In article <1991Jan29.044137.20914@zoo.toronto.edu>, henry@zoo.toronto.edu (Henry Spencer) writes: |> The last word I heard was that accuracy had actually improved, because the |> US military forces in the Gulf are making extensive use of commercial |> Navstar receivers, while the Iraqis have little or no Navstar equipment, |> so the public-access code is being kept as undegraded as possible. A little deeper information: all the new GPS/Navstar satellites (so-called "Block II") have what is called SA, Selective Availability. SA allows the DoD to dither the effective phase and frequency in the pseudocode that contains the range information. I forget, but I think they are also allowed to lie a little about their orbits. Anyway, they can then add uncertainty in several places. Starting in April or so of last year, they turned on SA on the Block II satellites, but only part way: they just added about 100 ns pure white phase noise. So, if you had time to track for a while (say, if you are NIST and want to transfer atomic time accurately) you could get around this. The SA limits triangulation accuracy for positioning to about 100 meters, compared to 10 m or so with SA off. Note the few older Block I satellites still in operation have no SA capability; if you can control which satellite you talk to, you can get around it (until they launch enough new ones to retire the old ones). In August, when Desert Shield started, the DoD realized they needed Navstar stuff, but their military versions of the receivers are not yet ready, so they switched SA off. As Henry stated, this is little strategic loss, with much to gain (the commercial Navstar receivers are portable enough for infantry). If anything, I'd imagine the Iraqis may have some GLONASS equipment from the Soviets, if they trusted them enough. GLONASS is just as good as GPS (but I think the receivers are a little less portable). -- Marty Ryba | slave physics grad student Princeton University | They don't care if I exist, Pulsars Unlimited | let alone what my opinions are! marty@pulsar.princeton.edu | Asbestos gloves always on when reading mail
nagle@well.sf.ca.us (John Nagle) (02/03/91)
The Trimble Navigation portable GPS receiver, a handheld device
intended for small boat navigation and available in boat shops, is being
used by U.S. troops. Trimble is manufacturing them as fast as possible,
but can't keep up with the sudden demand. They're made in here in Silicon
Valley. The militarized portable GPS receivers aren't available in
quantity yet, so this commercial unit is being pressed into service.
It's a cute little device. It takes about 30 seconds for it to get
a fix, it runs on batteries, and it's watertight. (It even floats.)
Trimble doesn't promise accuracy better than a few hundred meters,
though, so signal degradation for security reasons probably isn't
an issue.
John Naglemcovingt@athena.cs.uga.edu (Michael A. Covington) (02/04/91)
Assuming the supply catches up with the demand and these widgets are available again, how much does a GFS receiver cost? I'd like to be the first on my block with satellite navigation in my car, maybe...
bhoughto@hopi.intel.com (Blair P. Houghton) (02/05/91)
In article <1991Feb4.062853.21374@athena.cs.uga.edu> mcovingt@athena.cs.uga.edu (Michael A. Covington) writes: >Assuming the supply catches up with the demand and these widgets >are available again, how much does a GFS receiver cost? >I'd like to be the first on my block with satellite navigation in >my car, maybe... About $3K. --Blair "Nobody ever said that knowing your exact position wouldn't affect your momentum..."