On-Orbit Frequency Stability Analysis of the GPS Navstar's 3 and 4 Rubidium Clocks and Navstar's 5 and 6 Cesium Clocks

Thomas B. McCaskill, James A. Buisson, Sarah B. Stebbins

Abstract:	This paper describes the on-orbit frequency stability performance analysis of the GPS NAVSTARs 3 and 4 rubidium clocks, and the NAVSTARs 5 and 6 cesium clocks. Time-domain measurements, taken from the foul- GPS monitor sit,es, have been analyzed to estimate the short and long-term frequency stability performance of the NAVSTAR clocks. The data analyzed includes measurements from 1981, 1982, and the first 100 days of 1983. Short and long-term results are presented for data collected during 1982. The Allan variance was used as the measure of frequency stability performance in the time domain. The time-domain noise analysis results indicate a white noise FM process is present, in both rubidium and cesium clocks, for sample times of 900- and 1800-seconds. The projected value of this white noise FM process to a 1-day sample time agrees closely with the 1-day sample time stability results, for both rubidium and cesium clocks, indicating an underlying white noise FM process for sample times ranging from 900 seconds to 1 day. A random walk FM process was measured for the NAVSTARs 3 and 4 rubidium clocks for sample times of 1 to 10 days. A flicker noise FM process was measured for the NAVSTARs 5 and 6 cesium clocks, for sample times of 1 to 10 days. The NAVSTARs 3 and 4 rubidium clock long-term frequency stability values are in good agreement with the expected performance. The NAVSTAR3 short-term stability results indicate an anomaly which has peak effect at a 1 .25-hour sample time. The NAVSTARs 5 and 6 cesium clock long-term frequency stability values are in god agreement with the expected performance. For sample times of 2- to 10-days the cesium clocks have better frequency stability results than the rubidium clocks.
Published in:	Proceedings of the 15th Annual Precise Time and Time Interval Systems and Applications Meeting December 6 - 8, 1983 Naval Research Laboratory Washington, DC
Pages:	171 - 209
Cite this article:	McCaskill, Thomas B., Buisson, James A., Stebbins, Sarah B., "On-Orbit Frequency Stability Analysis of the GPS Navstar's 3 and 4 Rubidium Clocks and Navstar's 5 and 6 Cesium Clocks," Proceedings of the 15th Annual Precise Time and Time Interval Systems and Applications Meeting, Washington, DC, December 1983, pp. 171-209.
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