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.
