RESPONSE OF A GEOSYNCHRONOUS SPACECRAFT'S CRYSTAL OSCILLATOR TO SOLAR FLARES: RESULTS OF A 'SPACE EXPERIMENT'

摘要

Viewing the frequency history of the high-quality quartz crystal oscillator onboard Milstar FLT-1 as a "space experiment," we examined the response of the crystal to various solar flares occurring over the past 4 years. One of the questions we address concerns the influence of enhanced space radiation on a crystal oscillator's random frequency fluctuations, which, in addition to radiation-induced deterministic effects, could affect the oscillator's timekeeping ability. Examining the response of the Milstar FLT-1 crystal oscillator to the large solar flares of 14 July and 9 November 2000, we find clear evidence of a flare-induced deterministic change in oscillator frequency. However, examining the random fluctuations of the oscillator's frequency about this deterministic variation, we find no evidence of a concomitant change in the nature of the oscillator's stochastic behavior. Additionally, we examined the magnitude of the radiation-induced frequency excursion for a number of solar flares, obtaining a scaling relation between maximum frequency excursion and solar proton fluence as measured by GOES satellites. The results show that even for the largest flares, timekeeping onboard a geosynchronous communications satellite need not be unduly perturbed by the enhanced space-radiation environment of a solar flare, so long as a ground station can take mitigating action within a few hours of the flare's onset. Though limited to a unique satellite experiment, the results reported here bode well for satcom timekeeping during periods of solar maximum.