Mitigation of Lamplight-Induced Frequency Jumps in Space Rubidium Clocks

Rubidium clocks are currently the most common atomic clocks for space applications, playing a fundamental role in global navigation satellite systems. Their stability is affected by the light-shift effect, turning lamplight variations into frequency variations, e.g., lamplight intensity jumps into frequency jumps. In our previous work, analyzing data from GPS rubidium clocks, we uncovered the impact of the lamp on the in-orbit clock's performance. Specifically, the rubidium clock's random walk of frequency seems to be driven by a compound Poisson process associated with lamplight intensity jumps. Most important, large lamplight-induced frequency jumps could affect the validity of the navigation message. Here, we propose and test on simulated data, a software compensation scheme for lamplight-induced rubidium clock frequency jumps. We show how this could be implemented as an automated onboard process, and the potential improvements this scheme might yield in timekeeping and navigation performance. In particular, we demonstrate the possibility to correct large lamplight-induced frequency jumps in a time smaller than the interval between consecutive navigation message upgrades, thus improving the quality of the navigation message.