The fleet of orbiting Global Positioning System (GPS) satellites experienced what officials termed "End of Week" rollover of the spacecraft’s internal clock mechanisms at 13 seconds before 8 p.m. ET Saturday.
The rollover occurred because the clocks aboard the nation’s fleet of 27 navigation satellites count time in sequences of 1,024 weeks rather than in solar years. As a result, the clocks "rolled over" Saturday and began counting time at week zero –or 0000 –for the first time since January 6, 1980, when the satellite system’s internal clocks began.
Updates to the almanacs containing the new "week 0000" data were uplinked to each of the satellites beginning last Thursday by Air Force Space Command. As each clock "rolled over" Saturday, the GPS master control station at Shriever Air Base in Colorado Springs, Colo. verified the satellite’s navigation signals were still being transmitted and also checked out all GPS Monitoring Stations and Ground Antenna sites to make certain the change had occurred without interruption of the satellite signal or any related issues.
There were none, Schriever technicians told SMC, which has responsibility for the GPS program and is home to the joint satellite project office. The updated almanacs will now operate for another 1,024 weeks before another modification to the clocks will be needed.
The GPS satellite system was originally designed for use by U.S. military forces but has become essential for navigational needs of the U.S. and global civilian population. In a 1996 policy directive, the Clinton administration opened the GPS signal system to civilian use and guaranteed maintenance of the system well into the next century.
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