GPS Accuracy Could Start Dropping in 2010

We've all become accustomed to using the Global Positioning System, or GPS, whether via our iPhones, car navigation devices, handheld GPS units, or even watch-based devices like the Garmin Forerunner series. The GPS system went into full operation in December of 1993, was declared a dual-use (military and civilian) system by President Bill Clinton in 1996, and in 2000 had "Selective Availability" removed to increase accuracy for civilian uses. It relies on a constellation of between 24 and 32 medium Earth orbit satellites, some of which have been operating for nearly 19 years. Unlike other national satellite navigation systems, GPS serves the entire world and is maintained by the United States Air Force 50th Space Wing.

So far, so good, but TidBITS reader Mike Craymer, a geodesist who studies the size, shape and temporal variations of the Earth, recently alerted me to a possible future problem with the accuracy of the GPS system.