[66788] in Cypherpunks
Re: GPS and other Dual-use technologies
daemon@ATHENA.MIT.EDU (jim bell)
Sun Sep 29 15:27:20 1996
Date: Sun, 29 Sep 1996 12:14:59 -0800
To: azur@netcom.com (Steve Schear), tcmay@buckeye.got.net
From: jim bell <jimbell@pacifier.com>
Cc: cypherpunks@toad.com
At 10:34 AM 9/29/96 -0700, Steve Schear wrote:
>I used to be an avid RC modeler and have contemplated organizing an
>on-going amateur cruise missile contest. The object would be to accurately
>deliver various payload weights over courses of various terrain and
>distances (perhaps out to a hundred miles or more in the case of Giant
>Scale craft). Judging would be based on speed, stealth (noise, IR
>emissions and radar cross section) and accuracy.
>
>Craft are free to use any navigational technology, but must be autonomous
>from launch to delivery. To aid navigation I was considering the design of
>a substitute differential GPS beacon functionally interchangable with those
>offered by the USCG. My device would work on a different frequency,
>possibly using very wideband direct sequence spread spectrum (for low
>probability of intercept/detection) and be actuated by the missile as it
>neared the target in order to refine its position.
The data standard for differential corrections is called "RTCM-104", and
it's the signal you input into differential-capable GPS receivers. Boxes to
generate RTCM-104 are probably relatively cheap, primarily needing a
multi-channel GPS receiver and another processor for coding. Differential
corrections can, of course, be transmitted on any frequency you'd like,
including frequency-hopping if you're really concerned about intercept.
(which you won't be...)
Incidentally, GPS receivers are getting REALLY small these days,
particularly for just the module-level products. A size like about 1 inch
by 2-inches is pretty close to state-of-the-art. Power consumption is about
3/4 watt.
Jim Bell
jimbell@pacifier.com
