Discrepancy Detected In GPS Time 187
jones_supa writes that on Tuesday, 26th January, Aalto University's Metsähovi observatory located in Kirkkonummi, Finland, detected a rare anomaly in time reported by the GPS system (Google translation). The automatic monitoring system of a hydrogen maser atomic clock triggered an alarm which reported a deviation of 13.7 microseconds. While this is tiny, it is a sign of a problem somewhere, and does not exclude the possibility of larger timekeeping problems happening. The specific source of the problem is not known, but candidates are a faulty GPS satellite or an atomic clock placed in one. Particle flare-up from sun is unlikely, as the observatory has currently not detected unusually high activity from sun.
Faulty sat? No problem... (Score:2)
...disregard it if it continues to exhibit faulty timing.
'course, there really should be a way to correct time in a GPS satellite, if only to avoid making them completely disposable (then again, maybe there is a mechanism to correct/self-diagnose timing issues on-board? One would think/hope so...)
Re:Faulty sat? No problem... (Score:4, Insightful)
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...disregard it if it continues to exhibit faulty timing.
Sure, you just have to update the configuration of all GPS devices on earth... it is more realistic to turn it off.
Re:Faulty sat? No problem... (Score:5, Informative)
Actually GPS receivers on earth are in a constant state of being updated. Part of the transmission from the satellite includes a continuous update of the orbital data for the GPS constellation, and other related data. Also, in North America, the WAAS system downlinks atmospheric correction data in real-time so that the GPS receiver can compensate for changes in the ionosphere.
Re:Faulty sat? No problem... (Score:5, Informative)
The status of each SV is also part of the datastream, and all it takes to "turn off" an errant SV is to set the flag in the data stream that says it is unusable.
WAAS doesn't know about atmospheric corrections. What WAAS does is use a network of fixed ground stations that detect deviations in position and generate data to correct those deviations. The assumption is that the WAAS receiver isn't moving, so any deviations are from propagation errors. This is the same kind of thing that has been used by surveyors and other high accuracy GPS users for decades. At the highest level of accuracy it is called realtime kinematic GPS, and it uses both the correction data and actual carrier phase information to give centimeter level accuracy. There is also "differential", which makes use of the correction data to get multi-cm level accuracy. Both were very big issues when selective availability was on.
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Ephemeris only takes a few seconds to download. I think you meant Almanac which takes ~7 minutes and describes orbit with relatively low accuracy.
Re:Faulty sat? No problem... (Score:4, Informative)
In regards to WAAS, I think you're talking about something else. WAAS was developed for the FAA to allow the use of GPS in all stages of flight, including precision landing.
It's based on a network of high precision ground receivers which are used to calculate two sets of correction information. The first is intended for all receivers in the WAAS footprint (basically North America), and consists of estimates of the error in the satellite position, and clock errors. The other breaks the continent up into a grid, and provides local estimates for errors in the ephemeris, clock errors, and ionospheric delay.
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It's based on a network of high precision ground receivers which are used to calculate two sets of correction information.
It sounds similar enough to what Obfuscant posted to be the same system. In either case, the high precision ground station is used to increase the accuracy by correcting various errors. He just simplified it more.
Though looking it up - Ephemeris is 30 seconds per satellite, Almanac takes a bit longer.
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In regards to WAAS, I think you're talking about something else. WAAS was developed for the FAA to allow the use of GPS in all stages of flight, including precision landing.
No, I was describing WAAS. A network of ground stations determining corrections. I didn't deny it was implemented by FAA.
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WAAS doesn't know about atmospheric corrections.
That is incorrect. WAAS stations create a model for the ionospheric propagation delay over the entire network and use that to provide corrections for receivers located anywhere in the area covered by the network.
WAAS also provides corrections for ephemeris and clock errors.
Re:Faulty sat? No problem... (Score:5, Funny)
>Sure, you just have to update the configuration of all GPS devices on earth...
If only they were capable of receiving signals from some sort of satellite.
Was systemd installed on any of the satellites? (Score:1, Funny)
Was systemd installed on any of the satellites recently? Maybe it was installed unintentionally, while upgrading the satellite from Debian 7 to Debian 8?
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Re:Faulty sat? No problem... (Score:5, Informative)
Re:Faulty sat? No problem... (Score:5, Funny)
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The "root cause" is that remote sensing is inherently noisy and you learn to live with it. All the cool kids now how to use a Kalman filter.
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Exactly. I know that Greyfox was making a joke, but anyone who has worked with sensors knows that intermittent anomalous readings are normal. Any sensor which doesn't produce anomalous readings almost certainly does the filtering internally.
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I presume you're talking about RAIM: https://en.wikipedia.org/wiki/... [wikipedia.org]
Basically if your GPS receiver can hear more than the minimum (4 satellites usually) at once, the simultaneous equation solutions are overdetermined. This makes it possible for software to detect and ignore outliers in the solution set.
I heard of a GPS failure back in the mid 90's that caused the entire Los Angeles area CDMA cellular network to stop working - because US CDMA (as opposed to UMTS CDMA) is exceedingly sensitive to timing e
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The time discrepancy is 13.7 microseconds [not milliseconds]. I don't know how that translates to position accuracy, but, to me, even that seems a bit large for something derived from an atomic clock.
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Several AC's replied to me about speed of light being [roughly] one foot per nanosecond [which I had forgotten]. So, 13.7 us is 13,700 ns, or 13,700 feet, or 2.5 miles [just as you said]. Wow! I know that GPS receivers [try to] use several satellites. Can they compensate for this without an almanac update [automatic or manual]? Or, if they use the faulty one, what happens? Would they try to average it in or reject it as too far off the average of the others?
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Re:Faulty sat? No problem... (Score:5, Funny)
there really should be a way to correct time in a GPS satellite
1) Press and hold the Set Time button until the indicator lamp lights (5 seconds)
2) Press + or - until the correct time is reached
3) Release Set Time button.
Re:Faulty sat? No problem... (Score:4, Insightful)
I just put some black electrical tape over the flashing 12:00.
I suppose it's a good thing I'm not running the system.
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You expect to get some kind of UI feedback that you've successfully long-pressed? Luxury!
The long press is, hands down, the absolute worst invention of my lifetime.
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Worse than Windows 10 and systemd?
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Oh gawd, they put systemd in Windows 10?
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...disregard it if it continues to exhibit faulty timing.
I'm not sure of the specs of block III, but in the case of block II, each satellite has three atomic clocks each (i.e. two hot spares) and the constellation as a whole has a few hot spare satellites (my memory is telling me four, but this may be wrong). However, this may not be a single-satellite failure.
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I believe that is the responsibility of the Ground Segment http://www.navipedia.net/index... [navipedia.net]
It's a hacker or NK trying to start a war (Score:2)
It's a hacker or NK trying to start a war.
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Using only the exact time from it and not having it calculate your location would only be useful for something like dead reckoning. They are not looking at a clock and deciding when to turn, they are looking at a GPS device to tell it where they are. The GPS is using the exact timing data to calculate it's location and even tiny errors can cause big errors in your location.
For every nanosecond off you get about 1 foot (0.3 meters) off on your location, 13.7 microseconds is enough for the GPS to think your l
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Shouldn't that be... compare number of bankruptcies... jobs destroyed.
Don't understand how you Americans worship people who game the system, destroy jobs and outsource wealth to your enemies/competitors, though I guess being smart enough to be born in a position to get a large inheritance does take skill.
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My business isn't big enough to qualify for the government handouts unlike some.
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They're using Slackware for nefarious purposes? Oh the horror!
Post your awesome and crazy theories here!!! (Score:2)
I think the clock went through a pocket of dark matter and the time dilation caused the time discrepancy.
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After reviewing the current state of Earth, in general, and of US politics and their recent "debates", in specific, Judiciary Pag [wikipedia.org] has realized that the Earth population will not be satisfied alongside the existence of the rest of the Universe, and has sentenced Earth and its sun sealed in a Slo-Time envelope within which time will pass almost infinitely slowly until the end of the Universe, thus serving the dual purpose of protecting the Universe from Earth, and allowing us Earthlings to enjoy a solitary e
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Sounds kind of familiar... [wikipedia.org]
Thanks, I hadn't heard of that book/author.
You do realize that what I wrote is a direct ripoff from The Hitchhiker's Guide to the Galaxy and what happened to planet Krikkit - right? If not, hand in your geek card. :-)
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> It's a glitch in the simulation.
They still got buggy pentiums in the renderfarm?
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It's a glitch in the simulation.
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The machine that is running the simulation we experience as our universe had a data fault, and we had to back up to the last savepoint.
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God is save-scumming.
It was just a test... (Score:2)
They where checking if they could skew the accuracy of GPS and if anybody would notice when they did. Oops, somebody noticed.
Well, that's my theory.. Don't ask me who "they" are because I left my tinfoil hat at home today.
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Moving at the speed of light, 13 microseconds is only 4 kilometers, at the speed most normal things move, you're looking at less than 10 millimeters.
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With a good GPS fix, the receiver should throw out the 13 microsecond delayed data as being anomalous. If you only had a 3 satellite fix though, it could cause a significant positioning error.
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Sure, if "most normal things move" around 0.77 km/s.
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What? [wolframalpha.com]
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I don't understand your confusion:
1) 500 knots is 1/3 of 0.77 km/s. 3.3 mm is 1/3 of 10 mm.
2) 10 mm is the number you provided, so it's the number I calculated. 3.3 mm is significantly less than 10 mm, so if you meant that, why not say "around 3 mm" or "less than 4 mm" or "3.3 mm"?
3) I don't know too many "normal things" that move even at 500 knots.
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It's also about 10% of a Sonet frame. Fortunately most telecom clocks don't blindly repeat GPS time, but instead use it to gradually steer their internal rubidium and quartz clocks so there wouldn't be an abrupt change in the output.
Wormhole (Score:2)
Going back in time by a mere 13.7uS doesn't seem very exciting though.
Temporal Anomaly! (Score:1)
It's about to get exciting, folks!
Crap! Trouble now (Score:1)
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Surely if you have more than a couple of satellites in view it will discard the 13.7mS one as a multipath. The chance of it actually giving you a reading thats off by 4km would be quite low I'd say
What if you're coming out of a tunnel or out of a parking garage?
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From U.S. COAST GUARD NAVIGATION CENTER (Score:5, Informative)
http://www.navcen.uscg.gov/?Do... [uscg.gov]
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While likely related, Martin Burnicki posted a more detailed explanation of the actual event to the time-nuts mailing list:
https://www.febo.com/pipermail... [febo.com]
GOOD. (Score:2)
Mr. President, they are using our own satellites against us and the clock is ticking.
Just a Motorola Oncore Receiver bug (Score:4, Interesting)
Redundancy (Score:2)
This is why there's redundancy built into the system, more satellites than are strictly needed for operation. If one's clock goes out-of-spec, you notice that it's not agreeing with the rest of the constellation and drop it from your sources. If it's a transient glitch it'll come back in-spec and come back into use, if it's a permanent problem they decommission it and schedule a replacement. Redundancy makes the difference between a major crisis and a minor annoyance.
Tiny? (Score:3, Insightful)
"(...) reported a deviation of 13.7 microseconds. While this is tiny (...)"
Tiny ? It's huge.
If such an error occurs every hour, the total accumulated error would be more than 7 seconds. It's tiny if you look at it individually (well, not so tiny - your 2GHz CPU clock has a period of 500ps (picosseconds) - that's 0.0000005 microseconds).
The atomic clock period (based on Cs-133) is 108.78278 picosseconds. So this is very very large.
Alvie
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1us = 1000ns = 100000 ps hence 500ps=0.5ns=0.0005us=0.0000000005s=5e-10s
but yes, not a tiny error given expected GPS accuracy.
pulse-per-second signal derived from GPS should be accurate to tens of ns...
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1us = 1000ns = 100000 ps
You missed a 0 here. Not complaining, just point it out.
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Absultely right. Thanks for the correction. Too many zeroes too keep track of.
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Indeed. My point was that despite being considered "tiny", you have to contextualize it. It's tiny if it's a single event (well it's rather big even for a single event), it's huge if such errors accumulate.
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No it wouldn't.
Time-Nuts... (Score:5, Interesting)
I'm not saying it's aliens..... (Score:2)
But it's aliens
OK finally (Score:5, Funny)
Reading this, I really feel like I'm living in the future:
"The automatic monitoring system of a hydrogen maser atomic clock triggered an alarm which reported a deviation of 13.7 microseconds."
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Wasted ooportunity! (Score:3)
Cover your heads! (Score:2)
Root Cause: Chuck Norris (Score:2)
Chuck Norris did some push ups so aggressivly that in contrast to his normal work out he liftet his body upwards and did not push the earth down,
thus generated a gravitational wave hitting the gps satellite.
The other explanation is:
It is a black hole and we all are doomed.
new physics? (Score:5, Interesting)
GPS times have all sort of noise. Some geophysicists use this "noise" to figure things like the atmospheric temperature and density. The GPS signal wavefront bend slightly then. You can tomographically invert for spatial location of the travel time anomalies to locate temperature and density changes. There are papers on this every year at the American Geophysical Union meeting.
Microsecond size anonalies are huge and may have more mudane causes like software.
It's not a problem (Score:2)
It's not a problem unless all four corner days are off and thus the four corners of the cube.
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You educated evil human have not the education or rationale to comprehend Nature's Simultaneous 4-Day Cube. who can't understand 4-day simultaneous cubic time. You are probably brainwashed, indoctrinated, educated stupid and cannot comprehend Nature's Harmonic Simultaneous 4-Day
No single corner human can occupy or experience more than a single corner at the same time during a 4-corner rotation within the 4/16 creation principle. Earth sphere rotates within an invisible Time Cube.
Educated people are the evi
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I don't think that I can ever comprehend the 4 simultaneous years within a single rotation of Earth about the Sun.
What makes it hard for me is that I now know that I am educated stupid.
I understand that this is the truth, but I cannot occupy more than a single corner at the same time.
This is so hard for me - the not occupying or experiencing.
The actual problem is CERN (Score:2)
The activation of the Large Hadron Collider with full power this past year has ripped a hole in the space time continuum and has been jumping the planet forwards in time by nanoseconds, now milliseconds. If the rift is not contained it will eventually grow exponentially from seconds, minutes, hours, days, months, years, centuries, millenniums to eventually eons, and may forward us in time past the moment of when Sol had collapsed killing us all!!!
History channel says..... (Score:2)
More info -- the last of the Block IIA birds (Score:2)
It was the last of the Block IIA birds, and had an expected 8 year lifetime, which it beat by quite a few years!
It featured a combination of cesium and rubidium clocks -- two of each. Now decommissioned -- http://www.navcen.uscg.gov/?Do... [uscg.gov]
Read more of this bird's interesting history -- http://www.schriever.af.mil/ne... [af.mil]
The actual problem: Bad data upload (Score:5, Interesting)
It looks like the actual problem was a bad data upload; Specifically, some satellites were transmitting incorrect parameters for UTC offset correction. https://www.febo.com/pipermail... [febo.com] is the posting from a gentlemen at Meinberg that has the details. http://www.usno.navy.mil/USNO/... [navy.mil] has more information about the time offset parameters (A0 and A1) and how they interact with GPS and UTC time.
According to another message (https://www.febo.com/pipermail/time-nuts/2016-January/095686.html), PRNs 2, 6, 7, 9, and 23 got hit. It is interesting to note that the satellite that was taken out of service this morning (PRN 32) is not in this list. It looks like the decommissioning of PRN32 was quite possibly scheduled (see http://gpsworld.com/last-block... [gpsworld.com]), and even if not, a failure of that specific satellite could not have caused multiple satellites to start broadcasting incorrect offset data.
I'm really looking forward to the postmortem on this.
13.7 us is a small eternity. (Score:2)
And if you're measuring the distance that radio signals travelled, that's a whopping 4 km.
That's funny (Score:2)
Is this one of those "that's funny" events that lead to world shattering discoveries?
Or just a bug...?
Schroedinger's cat at play... (Score:2)
Just patted a passing bird(in orbit)
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Agreed, 13.7 microseconds is a substantial error. Large enough that this isn't some obscure esoteric unexplained phenomena; one of the two devices being compared is essentially broken.
It's like reporting that somebody has a car that's supposed to get 30mpg but mysteriously they only get 22mpg. Is it aliens, sunspots, quantum thingamajiggery or just poor maintenance.
Re:That's a lot (Score:4, Insightful)
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Except he is using GPS as a very precise 10MHz signal, not a clock. The private rubidium clock (about 1500USD from memory) will provide that very nicely.
Personally if I was running an experiment that required that sort of precision then the private highly accurate frequency source is going to be fairly small beer in the total cost of the experiment and freezes you from the trouble of getting the GPS signal into your lab, which for most labs I know is going to be a right pain in the backside because GPS sign
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The normal process is to use a very high quality short-term stable oscillator, e.g. a temperature controlled quartz crystal oscillator - but discipline it to the long-term stable GPS signal. Over periods of hours to days, the quartz oscillator can drift in frequency due to aging, shifts in environmental factors which affect
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Except he is using GPS as a very precise 10MHz signal, not a clock. The private rubidium clock (about 1500USD from memory) will provide that very nicely.
$1500 clock vs. $100 clock. Hmmm. And how do you know the shift was 13.7ms as TFA reports unless you know which clock is right?
and freezes you from the trouble of getting the GPS signal into your lab, which for most labs I know is going to be a right pain in the backside because GPS signals don't extend indoors.
I understand they're developing a solution to that problem, and it will be distributed once the patent has been issued. They're taking a wire, surrounding it with some insulation, then around that goes a mesh of copper to make a second conductor, and then around that all more insulation. I hear they're calling it cropaxial cable or something like that. They claim, but I don't beli
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Its 2016. We have a widely available set of external reference signals from multiple governments running multiple satellites providing redundant sources of a stable reference. It is far more sensible to use something highly accurate and easily available than spend many thousands of dollars rolling your own.
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