Using GPS & VLBI Technology to Maintain 14 Digit Syntonization

Samuel C. Ward

Abstract: To facilitate the navigation of spacecraft to the outer planets, Jupiter and beyond, the JPL/NASA Deep Space Network (DSN) has implemented three ensembles of atomic clocks at widely separated locations (Goldstone, California/Canberra , Australia/Madrid,Spain). These clocks must be maintained, syntonized to within a few parts in 10^13 of each other and the entire group must be maintained, to a lesser degree, in synchronism with UTC (NBS/USNO). Over the last 1.5 years, the DSN has been used in Global Positioning Satellites (GPS) and Very Long Baseline Interferometry (VLBI) technology to perform these critical Frequency anti Time (F&T) synchronization tasks. Both techniques are required because: 1 ) Though VLBI techniques permit direct F&T measurements on widely dispersed clocks, it is relatively insensitive to drift. Drift of the group away from UTC and second order drift of individual member clocks, 2) The present constellation of GPSs is quite sensitive to clock offset from UTC and to second order drift hut simultaneous direct measurements on widely separated clocks (Australia to Spain) cannot be made. This report covers a year of F&T synchronization data collected from the intercomparison of 3 sets of cesium and hydrogen maser driven clock ensembles through the use of GPS and VLHI techniques. Also covered, are some of the problems met and limitations of these two techniques at their present level of technology.
Published in: Proceedings of the 16th Annual Precise Time and Time Interval Systems and Applications Meeting
November 27 - 29, 1984
NASA Goddard Space Flight Center
Greenbelt, Maryland
Pages: 447 - 465
Cite this article: Ward, Samuel C., "Using GPS & VLBI Technology to Maintain 14 Digit Syntonization," Proceedings of the 16th Annual Precise Time and Time Interval Systems and Applications Meeting, Greenbelt, Maryland, November 1984, pp. 447-465.
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