Performance of GPS Block IIR Rubidium Clocks

Wilson Reid, Thomas McCaskill, Marie Largay, O. Jay Oaks and James Buisson

Abstract:	The objective of this paper is to report to the community the performance of the Global Positioning System (GPS) Block IIR rubidium clocks. The performance of the on-orbit Block IIR rubidium clocks is, in general, superior to that of all other clocks in the constellation. The performance of some of these clocks has, however, been characterized by repetitive anomalies. For example, while the drift of most of these clocks smoothly and asymptotically approaches zero, the drift of the Navstar 46 timing signal shows a pronounced oscillation with a period of approximately 12 days. The Navstar 43 timing signal has shown small repetitive discontinuities in the frequency, as has been the performance of Serial Number 28 under test at the Naval Research Laboratory. But unlike either of the two clocks in the laboratory, or unlike any of the 59 GPS Block II/IIA on-orbit clocks activated thus far, the timing signal originating with Serial Number 6 on Navstar 43 shows repetitive spiking in the phase. There have been four episodes which occurred in February and August 1999 and in February and May 2000, which do not appear to be correlated with the occurrence of the eclipse seasons. But in spite of the reported anomalies, the frequency stability of the Block IIR rubidium clocks is superior to that of all other atomic frequency standards in the GPS constellation. Estimation of the frequency stability of the on-orbit Block IIR rubidium clocks for a sample time of one day is limited by receiver noise. However, results from the laboratory testing of this type of clock suggest that the stability for a sample time of one day may well be measurable in parts per 1015.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	937 - 946
Cite this article:	Reid, Wilson, McCaskill, Thomas, Largay, Marie, Oaks, O. Jay, Buisson, James, "Performance of GPS Block IIR Rubidium Clocks," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 937-946.
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