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Potentially Catastrophic GPS Rollover Due 6th April

PostPosted: March 10th, 2019, 7:02 am
by toucana

April 6th 2019 might be a poor day to take an airline flight according to some pundits, as the American GPS system is due to undergo an epoch rollover on that day.

Older satnavs and such devices won't be able to use America's Global Positioning System properly after April 6 unless they've been suitably updated or designed to handle a looming epoch rollover.

GPS signals from satellites include a timestamp, needed in part to calculate one's location, that stores the week number using ten binary bits. That means the week number can have 2^10 or 1,024 integer values, counting from zero to 1,023 in this case. Every 1,024 weeks, or roughly every 20 years, the counter rolls over from 1,023 to zero.

The first Saturday in April will mark the end of the 1,024th week, after which the counter will spill over from 1,023 to zero. The last time the week number overflowed like this was on August 21st 1999, nearly two decades on from the first epoch in January 1980. On that occasion there were barely any disruption. 

If devices in use today are not designed or patched to handle this latest rollover, they will revert to an earlier year after that 1,024th week in April, causing attempts to calculate position to potentially fail. System and navigation data could even be corrupted, we're warned.
GPS devices with a poorly implemented GPS Time-to-UTC conversion algorithm may provide incorrect UTC following a week number rollover," US Homeland Security explained in its write-up (PDF) of the issue this week.

"Additionally, some GPS devices that calculate the week number value from a device-specific date rather than the start of the current GPS Time Epoch may provide incorrect UTC at some other device-specific date."

Smartphones are unlikely to be affected because they are based on more modern GPS technology. However, Bill Malik, vice-president of Trend Micro, a cyber security company, has said he is not prepared to fly on April 6 because of the dangers.

In a worst case scenario it is claimed the problem could affect the navigation systems of ships and older aircraft and the digital timekeeping used by websites, electrical grids, financial markets, data centres and computer networks.

Re: Potentially Catastrophic GPS Rollover Due 6th April

PostPosted: April 10th, 2019, 3:05 pm
by TheVat
I wasn't paying much attention to this, last Saturday. Was there a catastrophe?

Re: Potentially Catastrophic GPS Rollover Due 6th April

PostPosted: April 10th, 2019, 3:42 pm
by toucana
Not quite a catastrophe, but there were some reports of odd and unforeseen GPS related glitches.

Probably the best came from China, where a fleet of 15 Boeing 787 Dreamliner passenger aeroplanes belonging to a number of Chinese carriers had to be grounded.
Right now, there are no less than 15 Dreamliners affected in China, most of which are grounded pending an update to the GPS. Apparently they all think that today is August 22nd, 1999, which is interesting seeing as the 787 didn’t actually exist then.

Most clocks obtain their time from Coordinated Universal Time (UTC). But the atomic clocks on satellites are set to GPS time. The timing signals you can get from GPS satellites are very accurate and globally available. And so they’re often used by systems as the primary source of time and frequency accuracy.

The rollover issue is caused by the GPS systems counting in a ten-bit parameter. They start counting at week zero and then reset when they ready week 1,024. As GPS began counting on 6th January 1980, they reset once on August 21st, 1999 and again this weekend, on April 6th.

The modernized GPS navigation message now uses a 13-bit field that repeats every 8,192 weeks. So scientists have effectively kicked this problem down the road for about another 157 years