Long-Term Stability of a Rubidium Atomic Clock in Geosynchronous Orbit

J. G. Coffer, J. C. Camparo

Abstract:	In general for a well-stabilized rubidium (Rb) atomic clock (i.e., the type flown on M&tar satellites), the output frequency of the device ages slowly over time in a linear fashion. However, when a Rb atomic clock is first turned on, the output frequency of the device changes relatively rapidly as the physics package “warms up,” and it requires some time before the clock’s frequency settles down to its quiescent aging behavior. This warm-up period is important to Milsatcom system planners, as it defines the time interval following turn-on before a satellite clock may be said to be “reference quality.” We have assessed this warm-up period for the Milstar Flight-2 (FLT-2) Rb atomic clock using 2 1/2 years of timekeeping data archived at the Milstar Auxiliary Support Center (MASC). The change in the clock’s frequency aging rate is consistent with an exponential decay from an initially large absolute value (- -7x10^-12/day) to asmall steady-state value (+7x10^-14/day). The time constant for this decay is - 50 days, indicating that stabilization of a newly turned-on Rb atomic clock may take several months. In addition, we show that for 427 days of running at a stable aging rate, the Allan variance random-walk coefficient is 1x10^-15/day.
Published in:	Proceedings of the 31th Annual Precise Time and Time Interval Systems and Applications Meeting December 7 - 9, 1999 Marriott's Laguna Cliffs Resort Dana Point, California
Pages:	65 - 74
Cite this article:	Coffer, J. G., Camparo, J. C., "Long-Term Stability of a Rubidium Atomic Clock in Geosynchronous Orbit," Proceedings of the 31th Annual Precise Time and Time Interval Systems and Applications Meeting, Dana Point, California, December 1999, pp. 65-74.
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