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Subject: Re: GPS jammers?
From: C.L. Holm (CHolm@XXX.XXX)
Date: Mon Mar 31 2003 - 09:46:26 EST
An excellent concern, but some have already considered the problem.
Some factors to consider:
- GPS has excellent long term position accuracy and stability when values
are averaged or smoothed (i.e., no drift), but poor short term stability
(i.e., position jumps around somewhat randomly)
- INS has excellent short term position accuracy and stability without the
need to average values (i.e., no random position change), but poor long term
stability (i.e., has drift)
- Mechanical gyro INS used to be very expensive, big and prone to failure.
- Costs for an INS using a ring-laser gyro without any moving mechanical
components have reached very reasonable values with excellent reliability
- Kalman filtering of GPS and INS can provide the best of both without the
negatives.
- For a typical long range munition, in the cruise phase, smoothed GPS would
be used to eliminate drift in the INS
- In the terminal guidance phase, INS would provide the majority of the
final guidance and correction, with almost no reliance on GPS.
- Jamming effectiveness is primarily a function of jammer power and distance
between jammer and receiver
- GPS signals are radiated from space and therefore most receiver antenna
are mounted on the top
- A effective jammer is a beacon that radiates and can itself be targeted.
- Although astro-trackers are good at high altitude, it would be difficult
to put one into a precision munition, and probably not effective at low
altitude
- Few midship'n would want to ride along with a one-way munition to take
star shots.
Chris
-----Original Message-----
From: Joe Shields [mailto:jshields@XXX.XXX]
Sent: Monday, March 31, 2003 7:24 AM
To: NAVIGATION-L@XXX.XXX
Subject: GPS jammers?
It was in the news a while back, that the Russians were selling Iraq GPS
jammers. Does anybody know anything about these? What sort of range do
they have? Can they be selective so that only your enemies receivers are
jammed?
In this "smart bomb" era, I would think a network of GPS jammers that covers
your cities and extends well out over your coastal borders would provide a
pretty good safety unbrella for neutralizing a lot of expensive weopons the
U.S. now employs. Could make GPS-guided missles the next "Maginot Line" type
boo boo. If I was Commandant of the U.S. Naval Academy, it might make me
re-think taking Celestial Navigation out of the cadets curriculum.
-- Joe Shields
40d34' lat, 80d03' long
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