Solar Flares and Precise Satellite Timekeeping

J.C. Camparo, S.C. Moss

Abstract:	On 14 July 2000 and 9 November 2000 two large solar flares occurred. As measured by the GOES-8 and GOES-10 satellites, these flares were accompanied by an increase in the flux of energetic particles at geosynchronous altitudes. Here, we discuss the effect of these flares on communication satellite timekeeping, specifically timekeeping onboard the Milstar FLT-1 and FLT-2 satellites. FLT-1 ’s timekeeping device is a crystal oscillator clock, whose time-reading and oscillator frequency are tied through a satellite crosslink to the atomic clock carried onboard Milstar FLT-2. It is well known that crystal oscillator clocks have sensitivity to radiation, while atomic clocks, like the one onboard FLT-2, are relatively insensitive to space radiation. The solar &res had a noticeable impact on the FLT-1 quartz crystal Oscillator, causing the oscillator frequency to change by - 2x10”. However, the flares had little if any observable effect on the FLT-2 Rb atomic clock. Since the crystal oscillator’s frequency was “slaved” via crosslinks to FLT-2, the slaving procedure compensated for the radiation induced changes in the quartz crystal oscillator. Consequently, crosslink slaving of FLT-1 to FLT-2 mitigated the influence of the flares on FLT-1’s actual timekeeping, and hence the satellite communications system.
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:	89 - 98
Cite this article:	Camparo, J.C., Moss, S.C., "Solar Flares and Precise Satellite Timekeeping," Proceedings of the 33th Annual Precise Time and Time Interval Systems and Applications Meeting, Long Beach, California, November 2001, pp. 89-98.
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