Management of Phase and Frequency for GPS IIR Satellites

Marvin Epstein, Todd Dass

Abstract:	The ITT-Industries-developed GPS IIR satellite payloads have been on orbit since 1997, providing outstanding signal-in-space performance. The GPS IIR satellites have the capability of adjusting the phase, frequency, and frequency drift of their broadcast clocks. This paper discusses the intricacies of phase and frequency management in the GPS IIR Time Keeping System. During the initial years of the GPS IIR operation, the only clock correction technique used was the traditional technique of phase adjustment. In year 2000, the GPS IIR clock management operation started to use the full GPS IIR capability of adjusting phase, frequency, and frequency drift. Two approaches were employed. The fist approach was applied to GPS satellites SVN43 and SVN46, where the phase, frequency, and frequency drift errors were zeroed during off-line maintenance. The phase and frequency of the other IIR satellites were managed by the second approach using on-line frequency drift adjustments to correct for phase, frequency, and frequency drift errors; and does not require the satellite to be taken out of service. The operation of the two phase and frequency management approaches is compared in this paper. We have the results of over a year of operation of the new phase and frequency management techniques. As a result of these management approaches, the phase and frequency errors due to the GPS IIR rubidium frequency drift are now much smaller, with minimal load on the operation of the GPS system. This improvement is described in this paper by plots of the clock performance before and after the use of the phase and frequency management techniques. The cost of the improvement is minimal, as illustrated by a table of the ground control operations used to obtain these results.
Published in:	Proceedings of the 33th Annual Precise Time and Time Interval Systems and Applications Meeting November 27 - 27, 2001 Hyatt Regency Long Beach Long Beach, California
Pages:	481 - 492
Cite this article:	Epstein, Marvin, Dass, Todd, "Management of Phase and Frequency for GPS IIR Satellites," Proceedings of the 33th Annual Precise Time and Time Interval Systems and Applications Meeting, Long Beach, California, November 2001, pp. 481-492.
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