About 25 years ago, I bought a bunch of LORAN-C receiver boards at the Appelco bankrupcy auction. Despite zero doc, I got a couple running.
They had to 8085 uPs, one to compute the TDs and a second,on a daughter board, to compute Lat/Long. The unit would repeatably hit my location w/in a couple of hundred feet. A trivial uP in a box could easily subtract the GPS and LORAN positions and sound an alarm if they differed by more than a set limit, and sound an alarm. Furthermore, I suspect the cost to operate a set of worldwide LORAN chains is far less than launching a single GPS bird. -John ================== > LORAN can be good to 60 ft. > > > On 7/27/13 12:21 AM, Jim Lux wrote: >> On 7/26/13 8:45 PM, J. Forster wrote: >>> I gather from the article, the GPS position was spoofed and the >>> autopilot, >>> in bringing it back to where it was supposed to be, actually took it >>> off >>> course. >>> >>> There are places where a few hundred feet makes a big difference, >>> viz. the >>> Costa Concordia. >>> >>> IMO, this is a very convincing reason for something like LORAN. >> >> I think it's a convincing argument for a captain who pays attention to >> the other navigation instruments and doesn't blindly follow the GPS. >> >> It's also a convincing argument that shipboard >> automation/autopilot/autocontrol vendors need to make more >> sophisticated software (which I suspect they do, particularly on 200+ >> foot ships.. I would imagine that there are some aspects of this demo >> that are contrived.) The ship making and driving business is pretty >> unregulated. It's all about what the owner of the ship is willing to >> pay (or what he needs to get liability insurance, if he wants). >> There's nothing even remotely like DO-178 for shipboard stuff. >> >> The folks doing stabilized oil rigs probably have sophisticated >> systems, but they're also using IMUs and other stuff. Ditto for high >> value things (oil tankers, warships). Molasses tankers? They're >> probably lucky to have a functioning compass and some old charts. >> >> >> I'm not sure, though, that looking at the big picture, whether your >> tax dollars are better spent on LORAN, or on some other precision >> navigation method or on making jam resistant GPS receivers (which do, >> in fact exist, and make use of things like direction of arrival of the >> signal..) >> >> Note that a GPS system with 3 antennas (as is common in systems that >> use GPS to derive attitude/orientation) would be extremely difficult >> to spoof, and would be VERY inexpensive to implement. Either the >> carrier phases and code phases are consistent for all the received >> signals or they're not. A jamming signal coming from the wrong >> direction will not have the right direction of arrival relative to the >> platform orientation. One wrong signal might be tolerable (multipath, >> etc.) but with a multi satellite fix, I suspect it would be hard to do >> it. >> >> Sure, one could throw up N pseudolites on a bunch of UAVs, etc., but >> that's getting to be a bit noticeable. >> >> >> For what it's worth, I don't know that LORAN has the performance to >> avoid a Costa Concordia type foul up (assuming they were crazy enough >> to do the near pass in the fog, so visual navigation didn't work) >> >> I seem to recall that LORAN had 1/4 nmi kinds of accuracy. it would >> get you to the channel or mouth of the harbor, but not get you into >> your berth. You might be familiar with the local propagation anomalies >> and get better accuracy with experience in your local waters. >> >> >> >> >> >> >>> >>> -John >>> >>> ================= >>> >>> >>> >>>> I boat? The backup is a competent captain. He'd see the compass >>>> heading >>>> move and quickly disengage the autopilot. I had a boat for years >>>> I'd >>>> notice a 5 degree change. Mine was a sailboat so I'd be more >>>> sensitive to >>>> heading changes than a power boater but still the human is the backup. >>>> >>>> Most autopilots don't directly follow GPS, they use GPS to determine a >>>> heading, follow it then use GPS to detect drift and re-compute the >>>> heading. >>>> the heading would be held by a compass sensor in a low-cost setup >>>> or in a >>>> larger setup a lazer ring gyro backed up by a compass. So a >>>> spoofed >>>> GPS >>>> would cause the autopilot to "think" there was a bigger crooswnd or >>>> current >>>> and make a bigger heading change. >>>> >>>> I bet you could hijack a drone not a manned vehicle the pilot is >>>> trained >>>> to >>>> monitor the automation and he'd very quickly turn it off thinking it >>>> was >>>> broken. >>>> >>>> >>>> >>>> >>>> >>>> >>>> On Fri, Jul 26, 2013 at 8:41 AM, J. Forster <j...@quikus.com> wrote: >>>> >>>>> Prof. Humphry from Texas just reported being able to spoof GPS in the >>>>> Med >>>>> and take over the nav system of a luxury yacht. He's done this before >>>>> with >>>>> a drone in the US. >>>>> >>>>> LORAN as a backup, at least? >>>>> >>>>> -John >>>>> >>>>> ============== >>>>> >>>>> >>>>> >>>>> _______________________________________________ >>>>> time-nuts mailing list -- time-nuts@febo.com >>>>> To unsubscribe, go to >>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>>> and follow the instructions there. >>>>> >>>> >>>> >>>> >>>> -- >>>> >>>> Chris Albertson >>>> Redondo Beach, California >>>> >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.