From: skunk-works-digest-owner@harbor.ecn.purdue.edu To: skunk-works-digest@harbor.ecn.purdue.edu Subject: Skunk Works Digest V2 #79 Reply-To: skunk-works-digest@harbor.ecn.purdue.edu Errors-To: skunk-works-digest-owner@harbor.ecn.purdue.edu Precedence: bulk Skunk Works Digest Saturday, 13 February 1993 Volume 02 : Number 079 In this issue: DGPS D-GPS and SA Re: D-GPS and SA forwarded message from See the end of the digest for information on subscribing to the skunk-works or skunk-works-digest mailing lists and on how to retrieve back issues. ---------------------------------------------------------------------- From: THOMSONAL@CPVA.SAIC.COM Date: Fri, 12 Feb 1993 7:56:44 -0800 (PST) Subject: DGPS > Sigh... you've spent too much time inside the Beltway. Don't I know it! :-) > Frankly, you're locking the gate long after the horse got up and left > on its own. I quite agree: the purpose of the AvWeek letter was to try to get people to think about DGPS and other precision navigation techniques, and what they might mean for security-related questions. The background of the letter is that, in the second half of 1991, I started looking into DGPS and quickly found out the following interesting things (all of this is readily available in the literature). - - as noted in various messages here, DGPS typically achieves better than P-code GPS accuracies. A few meters seems to be easily obtainable. - - DGPS circumvents SA, and works just fine without reference to the P- code. - - DGPS is easily implemented: a basic reference station can consist of a commercial GPS receiver, a PC, and a radio transmitter (or other communications device, such as a telephone). Ditto for the user set, with a receiver rather than a transmitter. - - DGPS in various forms is _very_ rapidly spreading. Besides the FAA and USCG, commercial companies like Magnavox are installing reference stations using commercial FM radio stations' subcarriers for the correction data. - - People are planning to use DGPS for critical applications like landing airplanes and navigating tankers in restricted channels. - - World-wide interest in using DGPS is high, and plans are well along for supplementing and, eventually, replacing GPS by systems not under US, let alone DoD, control. (This leaves aside GLONASS, which may or may not survive.) - - the list of -'s could go on, but the upshot is clear: Precision navigation to the few-meter level is going to be available to _everybody_ in the next few years. We will not be able to deny this capability to enemies short of turning off or seriously crippling the GPS system as a whole. If we do that, we harm large parts of the world economy that will have come to rely on DGPS, possibly cause aircraft and maritime disasters, suffer great political damage, and motivate people to create other GPS-like systems even faster than they would otherwise. Therefore, it looks as if the everyone-can-have-coordinate- targeted-weapons world is almost on us. "Weapons" can be anything from PGM-ized iron bombs through mortar shells and cheap cruise missiles to ballistic missiles. Living, as noted, inside the Beltway, a colleague and I took this story to associates in the DoD and related places, and found an amazing lack of awareness of the situation. Not that they disagreed with the conclusions, it was just that they hadn't realized that DGPS defeats SA, that DGPS is cheap and easy to do, and that there will be horrendous political and economic consequences of turning off civil uses of precision navigation once it is in wide use (i.e., well before the end of the decade). This is something that needs thought, folks. Doubtless countermeasures to precision coordinate-targeted weapons are possible, but they need to be analyzed carefully and then implemented in some effective way. ------------------------------ From: rschnapp@metaflow.com (Russ Schnapp) Date: Fri, 12 Feb 93 08:58:44 PST Subject: D-GPS and SA I'm a little confused. I had assumed that US DoD was permitting D-GPS because the range of the correction signal is probably insufficient to provide correction to ballistic warheads during reentry (then again, I suppose it could still be used for delivery by an aircraft on autopilot). If they are willing to permit D-GPS only if they have a veto button, why not do away with the infrastructure and consumer expense of D-GPS by simply leaving selective availability as their veto button? Is it, perhaps, that the rest of the world governments would not adopt GPS if the U.S. DoD could zap it during a U.S. emergency? But, they could avoid this problem by providing their own D-GPS stations. I guess it's more likely that other governments would be nervous about having high accuracy GPS available 99% of the time without their veto power. Still, that's a lot of bucks for general aviation consumers and U.S. taxpayers to cough up... ...Russ ------------------------------ From: gwh@lurnix.COM Date: Fri, 12 Feb 93 14:28:07 -0800 Subject: Re: D-GPS and SA What this kluge of a system (dithering, then D-GPS around airports) allows is the capability to deny precision targeting to the rest of the world (i.e. a regional conflict, like Iraq) while still letting US airliners land on GPS navigation systems. If you don't think this is important, go back and look at how airlines howled when the US dithered a lot back at the beginning of the gulf conflict. A better idea might have been to allow selective area dithering (shut it off over the US) but that capability isn't in the sattelites as I understand them. This allows the DOD to keep going with their system as-is and gives the same results for the FAA, albeit causing a bit of technical insanity. - -george ------------------------------ From: rick@ssg.com (Rick Emerson) Date: Fri, 12 Feb 93 20:49:09 GMT Subject: forwarded message from Russ Schnapp writes: > > I'm a little confused. I had assumed that US DoD was permitting D-GPS > because the range of the correction signal is probably insufficient to > provide correction to ballistic warheads during reentry (then again, I > suppose it could still be used for delivery by an aircraft on > autopilot). If they are willing to permit D-GPS only if they have a > veto button, why not do away with the infrastructure and consumer > expense of D-GPS by simply leaving selective availability as their veto > button? DGPS is inherently a limited area feature. Beyond a certain range the satellite constellation seen by a mobile station will not be the same as that seen at the benchmark station. The USCG DGPS facilities, which rely on RDF beacons, have ranges of approximately 75-100 nm. Clearly, this isn't much good for an incoming SS-18 except in the terminal phase and when attacking a coastal target. But don't get hung up on directing busloads of MIRV's. Attacks, as we know from Lebanon, don't require high tech navigation systems to be effective. Engaging S/A and strangling DGPS won't be effective in this case. And this is the basic fallacy of DoD's argument that using S/A at all times makes the world safe. There are many different electronic navigation systems. Few of them are under the direct control of DoD. The biggest risk probably comes from sources whose technical capabilities are limited which reduce the potential risk even more. > Is it, perhaps, that the rest of the world governments would not adopt > GPS if the U.S. DoD could zap it during a U.S. emergency? But, they > could avoid this problem by providing their own D-GPS stations. > > I guess it's more likely that other governments would be nervous about > having high accuracy GPS available 99% of the time without their veto > power. Still, that's a lot of bucks for general aviation consumers > and U.S. taxpayers to cough up... > > ...Russ There is a growing demand in the civilian sector for accurate geodetic and navigation data. Applications range from simple "where am I now" problems for pilots and boat captains to position fixes for emergency vehicles, surveying data to fixes for problems in plate tectonics, and on and on. If the Navstar system won't provide this data, commercial sources will (e.g., Inmarsat's nav systems). Moreover, other countries (e.g., Russia, France) can develop simialr systems and clearly in at least one case DoD has no control over such systems. The simple truth is DoD's demands for S/A are being overrun by reality. Rick | Richard B. Emerson | Replies may be sent to: | | System Support Group | rick@ssg.com | | 940 Delaware Avenue |-------------------------------------------------+ | Lansdale, PA 19446 USA | "When you ski, you dance with the mountain -- | | Voice: 215.855.1607 | and the mountain always leads." | ------------------------------ End of Skunk Works Digest V2 #79 ******************************** To subscribe to skunk-works-digest, send the command: subscribe skunk-works-digest in the body of a message to "listserv@harbor.ecn.purdue.edu". If you want to subscribe something other than the account the mail is coming from, such as a local redistribution list, then append that address to the "subscribe" command; for example, to subscribe "local-skunk-works": subscribe skunk-works-digest local-skunk-works@your.domain.net To unsubscribe, send mail to the same address, with the command: unsubscribe skunk-works-digest in the body. 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