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Thread: Significant Temporary GPS System Failure

  1. #1
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    Significant Temporary GPS System Failure

    Please see http://www.itnews.com.au/news/satell...anomaly-414237

    In addition to carrying a map and compass, some mitigation techniques include
    1) testing your device at the trailhead for errors
    2) keeping track or breadcrumb options on so that a sudden failure will become evident by an implausible jump in recorded track.

    (Fortunately the chance of starting a war was minimal because no guided munitions landed in the wrong country, according to an official press release from USAF. Please see https://www.mail-archive.com/time-nu.../msg76817.html
    Last edited by Remix; 01-29-2016 at 11:33 AM. Reason: grammar, rephrase

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    Senior Member DougPaul's Avatar
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    Quote Originally Posted by Remix View Post
    Please see http://www.itnews.com.au/news/satell...anomaly-414237

    In addition to carrying a map and compass, some mitigation techniques include
    1) testing your device at the trailhead for errors
    2) keeping track or breadcrumb options on so that a sudden failure will become evident by an implausible jump in recorded track.
    There are plenty of other causes of such errors and track jumps (particularly for mobile consumer units in the hands of amateurs)--such evidence is hardly definitive for finding a GPS system problem. I suspect that the probability of user or user equipment error is greater than the probability of GPS system error, although intentional jamming (illegal) or unintentional jamming (electronic interference) is also possible. And, of course, there are the usual issues of multipath, poor skyview, and poor antenna position.

    Checking the official announcements and status would generally be more reliable (see below).

    The Air Force Press release for this event:
    Air Force Official Press Release - GPS Ground System Anomaly

    On 26 January at 12:49 a.m. MST, the 2nd Space Operations Squadron at the
    50th Space Wing, Schriever Air Force Base, Colo., verified users were
    experiencing GPS timing issues. Further investigation revealed an issue in
    the Global Positioning System ground software which only affected the time
    on legacy L-band signals. This change occurred when the oldest vehicle, SVN
    23, was removed from the constellation. While the core navigation systems
    were working normally, the coordinated universal time timing signal was off
    by 13 microseconds which exceeded the design specifications. The issue was
    resolved at 6:10 a.m. MST, however global users may have experienced GPS
    timing issues for several hours. U.S. Strategic Command's Commercial
    Integration Cell, operating out of the Joint Space Operations Center,
    effectively served as the portal to determine the scope of commercial user
    impacts. Additionally, the Joint Space Operations Center at Vandenberg AFB
    has not received any reports of issues with GPS-aided munitions, and has
    determined that the timing error is not attributable to any type of outside
    interference such as jamming or spoofing. Operator procedures were modified
    to preclude a repeat of this issue until the ground system software is
    corrected, and the 50th Space Wing will conduct an Operational Review Board
    to review procedures and impacts on users. Commercial and Civil users who
    experienced impacts can contact the U.S. Coast Guard Navigation Center at
    (703) 313-5900.

    Very Respectfully,
    USCG Navigation Center
    Navigation Information Service
    NAVCEN MS 7310
    7323 Telegraph Road
    Alexandria, VA 20598-7310
    703-313-5900
    www.navcen.uscg.gov
    Intentional outage announcements and current status are available at:
    http://celestrak.com/GPS/NANU/
    http://celestrak.com/GPS/status/
    Explanation of the terms:
    http://www.navcen.uscg.gov/?pageName=nanuAbbreviations

    Doug

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    Quote Originally Posted by DougPaul View Post
    There are plenty of other causes of such errors and track jumps (particularly for mobile consumer units in the hands of amateurs)--such evidence is hardly definitive for finding a GPS system problem. I suspect that the probability of user or user equipment error is greater than the probability of GPS system error, although intentional jamming (illegal) or unintentional jamming (electronic interference) is also possible. And, of course, there are the usual issues of multipath, poor skyview, and poor antenna position.

    Checking the official announcements and status would generally be more reliable (see below).

    The Air Force Press release for this event:


    Intentional outage announcements and current status are available at:
    http://celestrak.com/GPS/NANU/
    http://celestrak.com/GPS/status/
    Explanation of the terms:
    http://www.navcen.uscg.gov/?pageName=nanuAbbreviations

    Doug

    No need to create any confusion

    1. The technology is not infallible
    2. The GPS should not be trusted if it cannot report an accurate location, or it shows implausible data.
    3. There are two simple checks to reduce the possibility of error, as well as keeping a map and compass available.


    In a perspective broader than hiking, it is very fortunate that an oil tanker did not hit a shoal, that an aircraft did not fly into a mountain. It is reported than errors of up to 4km accrued over time from Finland to Australia, and that
    fail-safe circuitry in aircraft and tankers could not detect this failure because every satellite was transmitting erroneous information...the fail safe's only detect "oddball" satellites and some jamming or spoofing.

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    Senior Member iAmKrzys's Avatar
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    Quote Originally Posted by Remix View Post
    In a perspective broader than hiking, it is very fortunate that an oil tanker did not hit a shoal, that an aircraft did not fly into a mountain. It is reported than errors of up to 4km accrued over time from Finland to Australia, and that
    fail-safe circuitry in aircraft and tankers could not detect this failure because every satellite was transmitting erroneous information...the fail safe's only detect "oddball" satellites and some jamming or spoofing.
    I don't quite get this error estimate. As I understand it, most gps receivers don't have clocks that are accurate enough for the purpose of calculating position and instead use differences in time of arrival between signals coming from different satellites https://en.wikipedia.org/wiki/Global...llite_geometry. Now, if signals coming from all satellites were broadcasting time that was off by 13 microseconds then it would not affect *differences* in times of signal arrivals, sort of like we are ok with switching to daylight savings time as long as we all do it on the same day. I think the estimate is meant to exemplify how far the light can travel in such a short period of time (13 microseconds * 300,000,000 m/s = 3.9 km) but I doubt anyone's gps would be really off in such scenario. The article mentions that it was some observatory with atomic clock that noticed the discrepancy while it doesn't say anything about any gps users complaining.

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    Next thing you know we will have magnetic pole reversal and my maps and compass wont work

    The military is working on alternatives to GPS due to spoofing technology that various countries have developed. Could be that GPS will turn into Loran C someday

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    Senior Member jniehof's Avatar
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    Quote Originally Posted by iAmKrzys View Post
    Now, if signals coming from all satellites were broadcasting time that was off by 13 microseconds then it would not affect *differences* in times of signal arrivals
    It would affect the receiver's knowledge of the satellite location...the ephemeris is tied to the time in the GPS signal. Not sure exactly how that propagates down to the actual error estimates.

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    Quote Originally Posted by iAmKrzys View Post
    I don't quite get this error estimate. As I understand it, most gps receivers don't have clocks that are accurate enough for the purpose of calculating position and instead use differences in time of arrival between signals coming from different satellites https://en.wikipedia.org/wiki/Global...llite_geometry. Now, if signals coming from all satellites were broadcasting time that was off by 13 microseconds then it would not affect *differences* in times of signal arrivals, sort of like we are ok with switching to daylight savings time as long as we all do it on the same day. I think the estimate is meant to exemplify how far the light can travel in such a short period of time (13 microseconds * 300,000,000 m/s = 3.9 km) but I doubt anyone's gps would be really off in such scenario. The article mentions that it was some observatory with atomic clock that noticed the discrepancy while it doesn't say anything about any gps users complaining.
    I can't pretend to know the GPS system from end-to-end, but reading the first article about a time to distance computation error, and reading the statement from JSOC concerning munitions, it is inferred that location would be computed incorrectly. The statement from the Air Force says they are accepting reports from commercial operators. Regarding your point, I am curious why the story is not in the general media yet.

    Whatever the end result, its important to be mindful that a system failure is in the realm of possibility, some possible ways to detect it, and to keep an alternate means of navigation handy. For instance, in the recent past, the GLONASS system was reported to be down for about a day because of a software error.

    The stuff about war, well, thats some dark Dr. Strangelove humor.

    The last block II satellite was scheduled to be launched this past friday; block III, with improved accuracy and stronger signals, deployment was orignally supposed to occur in 2014 but has slipped to 2017. See https://en.wikipedia.org/wiki/GPS_Block_IIIA
    Last edited by Remix; 01-30-2016 at 03:51 PM.

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    Senior Member Stan's Avatar
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    Quote Originally Posted by peakbagger View Post
    ... The military is working on alternatives to GPS due to spoofing technology that various countries have developed. Could be that GPS will turn into Loran C someday
    Oh good. In that case I won't bother to buy a GPS, I'll wait for the next generation of navigation equipment.

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    Senior Member DougPaul's Avatar
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    From the official AF press release:
    Further investigation revealed an issue in
    the Global Positioning System ground software which only affected the time
    on legacy L-band signals. This change occurred when the oldest vehicle, SVN
    23, was removed from the constellation. While the core navigation systems
    were working normally, the coordinated universal time timing signal was off
    by 13 microseconds which exceeded the design specifications. The issue was
    resolved at 6:10 a.m. MST, however global users may have experienced GPS
    timing issues for several hours.
    (Background note: the GPS system is used for both position determination and timing distribution. A number of computers and many cellphone towers use the time info.)

    The press release says an issue "only affected the time on legacy L-band signals" and "While the core navigation systems were working normally, the coordinated universal time timing signal was off by 13 microseconds". (Consumer GPSes use the legacy signals--military users (including munitions) do not.)

    This suggests that hikers using GPSes were probably not affected. (It is my understanding that the coordinated UTC signal is derived from GPS time. It is possible that GPS time (used in position determination) was unaffected.)

    Exactly which ground users were affected and how they were affected depends on which signals they were using, how they were using them, and exactly what happened on each satellite. I'll reserve personal speculation until I see a professional quality description of the details.


    The GPS signals are constantly monitored world-wide and any problems will be detected rapidly and be communicated to the controllers who will attempt to fix it ASAP. They also send out notifications to users so critical users (eg military and human safety) can respond appropriately.


    GPS is currently being used in many military, safety, and economically critical applications with no backup in the US. Thus many US systems are vulnerable to a GPS problem or enemy action interfering with GPS operation. Loran used to be available as a backup, but the US shut its Loran down in 2010. An enhanced form of Loran (named eLoran) has been proposed as a replacement and is being installed in several countries, including the US. http://gpsworld.com/eloran-progresse...in-u-s-europe/

    Doug

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    Senior Member DougPaul's Avatar
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    Quote Originally Posted by peakbagger View Post
    Next thing you know we will have magnetic pole reversal and my maps and compass wont work
    The latest analyses that I have seen project that a pole reversal is not in progress. Your compass should be safe (at least from this problem...) for the foreseeable future.

    The military is working on alternatives to GPS due to spoofing technology that various countries have developed. Could be that GPS will turn into Loran C someday
    The alternative is intended as a backup rather than as a replacement. Loran-C was shut down in 2010--the new system is eLoran (enhanced Loran). eLoran uses (and Loran-C used) terrestrial transmitters. The signals are at very different frequencies and a single event is unlikely to interfere with both simultaneously--Loran works on low frequencies (LF) which bend around the curvature of the earth while GPS uses ultra-high frequency (UHF) signals which are line of sight (and must pass through the ionosphere).

    Doug

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    Senior Member ChrisB's Avatar
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    Quote Originally Posted by peakbagger View Post
    Next thing you know we will have magnetic pole reversal and my maps and compass wont work
    This is an easy to fix problem: turn all your maps upside down and subtract 180 degs from your usual headings.

    Boom. Done.

    cb
    A man needs to know his limitations -- Dirty Harry / Clint Eastwood

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    Senior Member iAmKrzys's Avatar
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    Quote Originally Posted by peakbagger View Post
    Next thing you know we will have magnetic pole reversal and my maps and compass wont work
    Another way to look at this is that compass will work but current maps will become really obsolete... The magnetic North has been observed to drift long time ago (apologies, I can't find a good historic reference) and so the maps that show magnetic declination are slowly becoming out-of-date right from the moment they get printed! http://www.ngdc.noaa.gov/geomag/GeomagneticPoles.shtml

    The subject of magnetic pole reversal is also pretty fascinating: https://en.wikipedia.org/wiki/Geomagnetic_reversal

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    Quote Originally Posted by peakbagger View Post
    Next thing you know we will have magnetic pole reversal and my maps and compass wont work

    The military is working on alternatives to GPS due to spoofing technology that various countries have developed. Could be that GPS will turn into Loran C someday
    The only solution for non military users is GPS Block III, which has been delayed due to technical problems--probably specification changes.

    Block IIIa has stronger signals to address tree canopy and indoor applications, as well as reduced systemic error. It will support existing users AFAIK.

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    Senior Member Stan's Avatar
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    The last pole reversal was swift and believed to have occurred some 800,000 years ago. The odds are it won't happen in our lifetimes but I couldn't find if Las Vegas is making book on it.

    I don't believe it would make maps obsolete. Being a mapaholic it would make me weep if they were. True north is based on the earth's axis, which has a normal wobble, and as long as any resulting magnetic polarity can be adjusted to true north, the maps will still be valid. Aside from polarity, there are other navigational clues on maps which would remain functional. Maybe the worse case would be that we'd rename the poles to keep their present names and read the other end of the needle.

    Can dead men vote twice?

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    Senior Member jniehof's Avatar
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    Quote Originally Posted by Stan View Post
    The last pole reversal was swift and believed to have occurred some 800,000 years ago. The odds are it won't happen in our lifetimes but I couldn't find if Las Vegas is making book on it.
    "Swift" on geological timescales, last I saw it may have been several hundred to a thousand years (obviously there's little in the way of an observational lower bound). During that time the dipole field more or less goes away and all we have are higher moments, i.e. there's no pair of dominant poles. Also has solar wind shielding implications....

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