What Happens if GPS Fails? – The Atlantic
Blog editor’s note: This is a good popular overview of the issue, how long the government has known there is a problem, and how long the problem has gone unaddressed, in spite of a government-identified solution ready to hand.
Despite massive reliance on the system’s clocks, there’s still no longterm backup.
It only took thirteen millionths of a second to cause a whole lot of problems.
Last January, as the U.S. Air Force was taking one satellite in the country’s constellation of GPS satellites offline, an incorrect time was accidentally uploaded to several others, making them out of sync by less time than it takes for the sound of a gunshot to leave the chamber.
The minute error disrupted GPS-dependent timing equipment around the world for more than 12 hours. While the problem went unnoticed by many people thanks to short-term backup systems, panicked engineers in Europe called equipment makers to help resolve things before global telecommunications networks began to fail. In parts of the U.S and Canada, police, fire, and EMS radio equipment stopped functioning. BBC digital radio was out for two days in many areas, and the anomaly was even detected in electrical power grids.
Despite its name, the Global Positioning System is not about maps; it’s about time. Each satellite in the constellation (24 are needed, plus the U.S. has several spares) has multiple atomic clocks on board, synchronized with each other and to Coordinated Universal Time (UTC)—the time standard used across the world—down to the nanosecond. The satellites continually broadcast their time and position information down to Earth, where GPS receivers in equipment from iPhones to automated tractors acquire signals and use the minuscule differences in their arrival time to determine an exact position.