Long Term Frequency Stability Analysis of the GPS NAVSTAR 6 Cesium Clock

Thomas B. McCaskill, Sarah Stebbins, Clarence Carson, James Buisson

Abstract:	Time domain measurements, taken between the NAVSTAR 6 Spacecraft Vehicle (SV) and the Vandenberg GPS Monitor Site (SV), by a pseudo random noise (PRN) receiver, have been collected over an extended period of time and analyzed to estimate the long term frequency stability of the NAVSTAR 6 onboard frequency standard, referenced to the Vandenberg frequency standard. The technique employed separates the clock offset from the composite signal by first applying corrections for equipment delays, ionospheric delay, tropospheric delay, earth rotation and the relativistic effect. The data, are edited and smoothed using the predicted SV ephemeris to calculate the geometric delay. Then all available passes from each of the four GPS monitor stations are collected a 1-week intervals and used to calculate the NAVSTAR orbital elements. The procedure is then completed by subtracting the corrections and the geometric delay, using the final orbital elements, from the composite signal, thus leaving the clock offset and random error. Frequency stability estimates of clock performance are then made using the clock offsets to calculate the Allan Variance for the spacecraft oscillator, using sample times that vary from 1 to 10 days. The results indicate a combined clock/ephemeris frequency stability of 1.7~10 , or less, for sample times varying from one day up to ten days. Future work will include analysis of cesium standards on SV 5 and 6 as well as a rubidium standard on SV 5.
Published in:	Proceedings of the 13th Annual Precise Time and Time Interval Systems and Applications Meeting December 1 - 3, 1981 Naval Research Laboratory Washington, DC
Pages:	451 - 468
Cite this article:	McCaskill, Thomas B., Stebbins, Sarah, Carson, Clarence, Buisson, James, "Long Term Frequency Stability Analysis of the GPS NAVSTAR 6 Cesium Clock," Proceedings of the 13th Annual Precise Time and Time Interval Systems and Applications Meeting, Washington, DC, December 1981, pp. 451-468.
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