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Discrepancy Detected In GPS Time
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.
I think they have to be updated pretty much constantly. Their orbits aren't perfect and they have to be adjusted for relativity in their orbits.
"Some books contain the machinery required to create and sustain universes."-Tycho
http://www.navcen.uscg.gov/?Do...
That's it exactly! Had they executed their turn 13.7 microseconds earlier as planned, they would've avoided Iranian waters and been left alone.
This is the second time a bug in the firmware of Motorola Oncore GPS receivers have manifested itself. There is a bug relating to a 32 bit wide bitmap, and DoD just took the GPS satellite numbered 32 out of the constellation and that seems to be the cause. I have data for two such receivers showing the anomaly and for one different receiver seeing no trouble at all.
Poul-Henning Kamp -- FreeBSD since before it was called that...
What the hell are you driving, the Millenium Falcon?
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.
...si hoc legere nimium eruditionis habes...
"(...) 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
Lots of folks on the time-nuts mailing list have GPS-based systems to maintain not only precision time, but also precision frequency standards, and many of them saw and recorded this one.
It's a glitch in the simulation.
But it's aliens
Have you ever fallen asleep at the keybhanusdiog?
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."
-Styopa
As someone who works in GPS software, you see these kinds of off-by-miles readings from time to time. If it was one time and not constant, we already have software in place to ignore the anomalous reading.
Peter predicted that you would "deliberately forget" creation 2000 years ago...
When the atomic clocks in GPS satellites have a discrepancy, you don't report a discrepancy. You report you have done some experiments that suggest faster than light travel across some 30 km apart in the Swiss Alps. By the time they track it down and attributed to some discrepancy in some atomic clock, you got your headlines, the 15 minutes of fame.
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
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 location is 2.55 miles (4.11 KM) away from where you really are. That is also the error from only one satellite so the error from other ones adds even more error to where the GPS thinks you are.
http://www.montana.edu/gps/und...
https://en.wikipedia.org/wiki/...
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.
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.
A GPS clock comes with the time already set. Your private rubidium clock needs someone to tell it what time it is, which is probably going to be GPS-based anyway.
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.
Ephemeris only takes a few seconds to download. I think you meant Almanac which takes ~7 minutes and describes orbit with relatively low accuracy.
Clock speeds are sensitive to the structure of the gravitational field. Maybe other aspects of the Universe.
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.
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.
...si hoc legere nimium eruditionis habes...
>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.
Oh yeah, don't do any root cause analysis or anything, just keep ignoring all those gravity waves jittering the clocks on our orbiting atomic clock satellite network :-P
I'm trying to teach myself to set people on fire with my mind... Is it hot in here?
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 evil empowerment of the self - the lowest form of humanity. Humans are brainwashed stupid and indoctrinated evil. A human will rotate around 4-corner lifetime stages within a family metamorphosis - baby, child, parent and grandparent. Name your 4/16 greatgrandparents.
All Educated are Stupid from brainwashing and indoctrination. Pedants cannot comprehend that there are 4 simultaneous Years within a single rotation of Earth about the Sun.Each season has its own separate Year.
Required reading for internet skeptics
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.
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... is the posting from a gentlemen at Meinberg that has the details. http://www.usno.navy.mil/USNO/... 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...), 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.
...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.
sub f{($f)=@_;print"$f(q{$f});";}f(q{sub f{($f)=@_;print"$f(q{$f});";}f});