Frequency Stability of On-Orbit GPS Block-I and Block-II NAVSTAR Clocks

Thomas B. McCaskill, Wilson G. Reid, and James A. Buisson

Abstract:	On-orbit analysis of the Global Positioning System (GPS) Block-I and Block-11 NAVSTAR clocks has been performed by the Naval Research Laboratory using a multi-year database. The NAVSTAR clock phase-offset measurements were computed from pseudo-range measurements made by the five GPS monitor sites and from the U.S. Naval Observatory precise-time site using single or dual frequency GPS receivers. Orbital data was obtained from the NAVSTAR broadcast ephemeris and from the best-fit, post-processed orbital ephemerides supplied by the Naval Surface Weapons Center 01 by the Defense Mapping Agency. Clock performance in the time domain is characteriaed using frequency-stability profiles with sample times that vary from 1 to 100 days. Composite plots of NAVSTAR frequency stability and time-prediction uncertainty are included as a summary of clock analysis results. The analysis includes plots of the clock phase offset and frequency offset histories with the eclipse seasons superimposed on selected plots to demonstrate the temperature sensitivity of one of the Block-I NAVSTAR rubidium clocks. The potential impact on navigation and on transferring precise time of the degradation in the long-term frequency stability of the rubidium clocks is discussed.
Published in:	Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990) September 19 - 21, 1990 The Broadmoor Hotel Colorado Spring, CO
Pages:	131 - 137
Cite this article:	McCaskill, Thomas B., Reid, Wilson G., Buisson, James A., "Frequency Stability of On-Orbit GPS Block-I and Block-II NAVSTAR Clocks," Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990), Colorado Spring, CO, September 1990, pp. 131-137.
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