An Improved GPS Cesium Frequency Standard

Terry Flanagan, Dennis Breuner, Charles McKnett, Leonard Cutler, Robin Giffard, Jack Kusters, Robert Kern, Michael Delaney, and Jeffry Wisnia

Abstract:	The GPS/NAVSTAR Navigation Satellite System will be the mainstay of the NSS and must provide a global full coverage system through the late 90’s and beyond. The heart of the GPS Satellite System is an atomic clock which maintains synchronous system time to generate range and range-rate data for global users. Current GPS satellite Cesium frequency standards on which GPS timing depends, were designed in the early to mid 1980s. While these clocks have performed admirably on orbit, a new design for a Cesium frequency standard utilizing modem digital and RF technology offers significant advantages with respect to stability and environmental insensitivity, which taken together eliminate any perceived need for a clock temperature controller in the satellite. In this paper we describe a Cesium design that takes advantage of the fact that the Cesium standard is the only primary standard. The approach builds on the Cesium beam tube design and flight worthyness of our previous successful GPS Cesium standards married to Hewlett Packard’s world recognized 5071A Cesium standard electronic and software design to achieve an optimized clock for GPS space application. The design provides advancements in the areas of performance optimization, stability, accuracy, extended useful life, reduction in environmental sensitivities, state of health diagnostics and clock system simplicity. In particular, the new design provides: immunity to environmental and aging effects, e.g., temperature, loop gain variations, magnetic and RF stability, and radiation response. Thus, the requirement for auxiliary environmental temperature control on the GPS satellite can be eliminated. Telemetry monitors that can indicate ciock health and longevity, supplemented with additional data available to telemetry on command will allow engineering specialists to interpret trends and predict future performance and could even permit on orbit optimization of all performance determining operating parameters.
Published in:	Proceedings of the 1995 National Technical Meeting of The Institute of Navigation January 18 - 20, 1995 Disneyland Hotel Anaheim, CA
Pages:	431 - 437
Cite this article:	Flanagan, Terry, Breuner, Dennis, McKnett, Charles, Cutler, Leonard, Giffard, Robin, Kusters, Jack, Kern, Robert, Delaney, Michael, Wisnia, Jeffry, "An Improved GPS Cesium Frequency Standard," Proceedings of the 1995 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 1995, pp. 431-437.
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