Mitigation of lamplight-induced frequency variations in space rubidium clocks

Abstract

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 jumps into frequency jumps. In our previous work, analyzing data from GPS rubidium (Rb) clocks, we uncovered the impact of the lamp on the in-orbit clock's performance. Specifically, the Rb clock's random walk of frequency seems to be driven by a compound Poisson process associated with lamplight intensity jumps. Moreover, large lamplight-induced frequency jumps could affect the validity of the navigation message. Here, we propose an active compensation scheme for lamplight-induced Rb clock frequency variations. We show how this could be implemented as an automated on-board process, and the potential improvements this scheme might yield in timekeeping/navigation performance.