Examination of a crystal oscillator's frequency fluctuations during the enhanced space-radiation environment of a solar flare

Though the ubiquitous quartz crystal oscillator finds application onboard diverse spacecraft, the space-radiation environment can be severe, particularly during periods of enhanced solar activity. The question 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, can have a pronounced effect on the oscillator's timekeeping ability. Examining the response of the Milstar FLT-1 spacecraft's crystal oscillator to the large solar flares of July 14 and November 9, 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. Though limited to a somewhat unique satellite experiment, this result nonetheless suggests that spacecraft timekeeping need not be unduly perturbed during periods of enhanced solar activity, so long as the spacecraft can compensate for the deterministic change in crystal oscillator frequency.