Hi Which is why the regulations (air or sea) *require* you to be using at least two nav systems to check each other. If you are depending on only one system, your breaking the rules. It's not a matter of weather there are 100,000 systems available or not. It's a matter of weather they follow the rules.
Bob On Jul 27, 2013, at 9:43 AM, Scott McGrath <scmcgr...@gmail.com> wrote: > Key here is how does the captain know that GPS is no longer providing an > accurate fix? You need 2 or more independent systems to cross check each > other. > > Sent from my iPhone > > On Jul 27, 2013, at 12:21 AM, Jim Lux <jim...@earthlink.net> 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.
