Investigation of Upload Anomalies Affecting IIR Satellites in October 2007

Karl Kovach, John Berg, Victor Lin

Abstract:	The GPS Operational Control System (OCS) successfully transitioned to the use of a new operational architecture, known as the Architecture Evolution Plan (AEP) on September 14, 2007. A string of anomalies, first occurring on 8 October 2007, affected the broadcast navigation signals output from six Block IIR satellites. These anomalies were directly related to the periodic navigation data uploads that the Control Segment makes to all GPS satellites. This paper presents the results of the National Space- Based PNT Engineering Forum (NPEF) investigation into the navigation signals broadcast by the Block IIR satellites affected by the six upload anomalies which occurred from 8 October 2007 thru 10 October 2007. The information presented includes a detailed timeline of events from a satellite command and control perspective, satellite by satellite, and a corresponding characterization of the output navigation signals drawn from multiple sources of GPS performance observers (including pseudorandom noise code, navigation message content, and pseudorange errors). This work summarizes the impacts of the anomalies on various classes of user equipment. The conclusions herein are drawn very carefully to accurately portray the sequence of events and prevent promulgation of misleading data regarding the anomalies. Certain classes of user equipment experienced nothing worse than a simple satellite outage, while other classes of user equipment data experienced huge pseudorange errors (tens or even hundreds of kilometers). These striking differences in the impacts of the anomalies are shown to be the result of variations in how user equipment implements the capability to coast on previously collected navigation message data for the duration of a curve fit interval (reference IS-GPS-200, paragraph 20.3.4.4). Finally, some very specific user equipment recommendations are provided to mitigate the impacts of potential future occurrences of similar anomalies.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	1679 - 1687
Cite this article:	Kovach, Karl, Berg, John, Lin, Victor, "Investigation of Upload Anomalies Affecting IIR Satellites in October 2007," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 1679-1687.
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