PRN01/SVN49: Another GPS Satellite Anomaly
September 8, 2009From monitoring at the University of New Brunswick and elsewhere around the globe, it appears that normal signals from the L1 and L2 transmitters on the GPS satellite PRN01/SVN49 were unavailable for more than two hours on the morning of September 4.
The satellite was not transmitting useful signals on L1 and L2 from about 12:00 to 14:11 UTC, as evidenced by the observation records of some International GNSS Service stations in Europe. The L5 test signal continued to be tracked by some receivers but not others.
“A report has come from Europe that some receivers are tracking L5 (but not L1 or L2) signals, so, it seems that only the L1 and L2 transmitters are affected at the moment,” explained Richard Langley, GPS World’s Innovation and Almanac contributing editor.
One possible explanation for the inability to track PRN01 is that the satellite rejected an upload and automatically went into non-standard mode, resulting in GPS receivers being unable to track the L1 and L2 signals. In other words, the L1/L2 transmitters were still on but transmitting a non-standard signal.
“It is not known for sure what actually happened with the satellite, but perhaps it is related to the ongoing issues with the signal reflections on the satellite and that the GPS Wing was conducting further tests,” Langley said. “Luckily, the problem was short lived.” And as to why some receivers continued to track the L5 signal but others did not, Langley speculates that some receivers may need to acquire and track the L1 signal before they can track the L5 test signal.
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