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More GPS problems?

May 22, 2009 In the March issue of ON, I wrote about a Government Accounting Office report that indicated that 19 of the current GPS satellites are hanging by a thread. The loss of a single major system on one of these spacecraft and they would be unable to broadcast usable signals. Should enough of them fail, gaps in GPS coverage could occur. Now this story has been picked up by the mainstream media. A recent story on possible loss of GPS coverage appeared in the British paper The Guardian, and that story has been quoted online at several sailing sites.

One mitigating factor in this looming problem with GPS is the considerable number of spare satellites the Air Force controllers of the system have placed in orbit. The system needs 24 satellites to provide full coverage. There are currently 30 spacecraft in orbit, giving the Air Force a healthy margin of error until the next block of satellites can be built and launched.

To add to the Air Force's problems, however, the trade magazine Inside GNSS is reporting that the latest operational satellite to reach orbit, SVN 49, a Block IIR (example of a Block IIR is shown here in a Lockheed Martin photo) is having signal problems. SVN 49 carries a test package on board for evaluating a new second civilian signal (called L5). This spacecraft is experiencing problems with its signals being what the Air Force calls "out of family." The Air Force is reporting that when the L5 package began transmitting, the other frequencies on board the spacecraft experienced anomalies. The Air Force is reportedly investigating the problem. The issue needs to be fixed before the next group of satellites is launched starting late this year or early 2010.


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