Precise Time and Time Interval (PTTI) Measurements From The Navigation Technology Satellites and the GPS NAVSTAR-4 Satellite

J.A. Buisson, T.B. McCaskill, O.J. Oaks, M.M. Jeffries, S.B. Stebbins

Abstract:	Since the launch of the first NTS spacecraft in 1974, international time transfer experiments have been performed as part of the concept validation phase of the Global Positioning System (GPS). Time Transfer results from both NTS-1 and NTS-2 will be presented, including recent measurements from receivers located in South America, Germany, Japan and the United States. A time link to the DOD Master clock allows sub microsecond intercomparison of UTC(USNO,MCI) with clocks in the respective countries via the NTS link. Work is progressing toward a retrofit conversion of existing NTS receivers (located at NASA and foreign observatories) into GPS time transfer receivers. Initial results will be presented on the long term rubidium frequency stability as measured from the GPS NAVSTAR-4 space vehicle (SV). Analysis has been performed for sample times varying from one to ten days. Using a 154 day data span starting on day 36, 1979, data was collected from the four GPS Monitor Stations (MS) located at Vandenberg, Guam, Alaska, and Hawaii. A time doma in estimate for the NAVSTAR-4 SV clock offset is obtained for each SV pass over the GPS monitor sites, using a smoothed reference ephemeris, with corrections for ionospheric delay, tropospheric delay, earth rotation and relativistic effects. Conversion from the time domain to the frequency domain is made using the two-sample Allan Variance; sigma-tau plots are used to identify the noise processes. Estimates of flicker and white frequency noise for the NAVSTAR-4 rubidium frequency standard are obtained. The contribution of the reference ground clocks and other error sources to the frequency stability estimates are discussed.
Published in:	Proceedings of the 11th Annual Precise Time and Time Interval Systems and Applications Meeting November 27 - 29, 1979 Goddard Space Flight Center Greenbelt, Maryland
Pages:	255 - 281
Cite this article:	Buisson, J.A., McCaskill, T.B., Oaks, O.J., Jeffries, M.M., Stebbins, S.B., "Precise Time and Time Interval (PTTI) Measurements From The Navigation Technology Satellites and the GPS NAVSTAR-4 Satellite," Proceedings of the 11th Annual Precise Time and Time Interval Systems and Applications Meeting, Greenbelt, Maryland, November 1979, pp. 255-281.
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