GNSS space clocks: Performance analysis

Atomic clocks are fundamental elements of a Global Navigation Satellite System (GNSS). Currently, several GNSSs are operational and the different clock technologies employed onboard their satellites benefit from the technological improvements achieved during the last decades. To ensure the timing capabilities needed for correct positioning, the analysis of GNSS clock performances is essential. We have recently started a performance analysis for GPS and GLONASS clocks, by using the satellite clock estimates produced by the Information-Analytical Centre (IAC) of the Russian Federal Space Agency. In this paper we discuss a few preliminary results of this analysis. We analyze the time deviation, frequency deviation, and frequency stability of the Cesium and Rubidium clocks onboard three GPS and GLONASS satellites. The obtained results highlight the presence of two common space clock anomalies, namely, deterministic oscillations and frequency jumps. Our final goal is to build a detailed statistics of the clock anomalies for all GNSSs.