Key Problem with GPS is its easy to spoof on one level and have a complete denial of service on the other. Out in California a while back a malfunctioning TV distribution amplifier jammed a major harbor and surrounding almost 25 sq miles affected all because of a 49.95 TV amp had a problem. The military receivers had the same problem
LORAN is virtually jam proof unless you have a very powerful transmitter Sent from my iPhone On Jul 27, 2013, at 11:17 AM, Michael Perrett <mkperr...@gmail.com> wrote: > I have seen a lot of differing opinions on GPS Spoofing and using back up > systems on this thread. Most pretty good, but a couple off the mark a bit. > > Here are a couple of comments on GPS Spoofing. > > - There are anti-spoofing GPS receivers available - to "authorized" > users. Typically DOD. Most, if not all, military receivers utilize the > encrypted "P-Code", while civilians must use the more vulnerable clear text > "C/A code". The P-Code signals are very difficult to spoof unless you have > a-pirori knowledge. The newer satellites (GPS III) will have an even more > robust AS methodology. > - Note: beware of P-Code, or Military, receivers available on eBay. > They are useless without the encryption keys distributed by the US > Government. > - In the (near?) future there will be four civilian GPS Signals: "The > government is in the process of fielding three new signals designed for > civilian use: L2C, L5, and L1C. The legacy civil signal, called L1 C/A or > C/A at L1, will continue broadcasting in the future, for a total of four > civil GPS signals. Users must upgrade their equipment to benefit from the > new signals". ref > http://www.gps.gov/systems/gps/modernization/civilsignals/ > - Receivers utilizing the new civilian GPS frequencies can solve the GPS > equations from more than one frequency and see if any one signal is being > spoofed. The new civilian frequencies will be more spoof resistant. > > Comments on using inertial measurement units (IMUs) to back up GPS. > > - Current IMUs with even a "good" drift rate of say, 1 degree per hour, > available for around a few thousand dollars, will be off 60 nautical miles > after an hour of uncorrected operation. That can be reduced by other sensor > inputs (GPS, LORAN, pit-log or what ever you have), but the navigation > solution will eventually degrade to the accuracy of the external sensor. If > my memory serves me for a really deep pocket navigator (having tens to > hundreds of thousands of dollars, and a large amount of available mounting > space) IMUs with drift rates of up to a thousand times less can be > purchased (that's ,001 miles per hour, or around a couple of meters per > hour), think submarines, etc. > > Using a dual sensor navigation system (or timing system! ), such as > GPS/eLORAN, would obviously make the system so much more robust. > > Michael / K7HIL > > On Sat, Jul 27, 2013 at 6:43 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. _______________________________________________ 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.
