Characterisation of Navstar GPS and GLONASS on-board clocks

The stability of the satellite clocks of both NAVSTAR and GLONASS (the Soviet global navigation satellite system) was analyzed. The known nature of the GPS (Global Positioning System) clocks has shown that the different types of clock aboard the satellites (crystal, rubidium, and cesium) can be distinguished given a sufficient sample time. The same approach has been applied to the GLONASS satellites, and a comparison of the results obtained from GPS has enabled a conjecture on the type of clocks used by the GLONASS satellites. The analysis has involved a comparison of satellites launched during the period 1986-9, although data for the early period are sketchy. It would seem, however, that GLONASS has used clocks of the quality of rubidium atomic oscillators since 1986 at least and that there has been a steady increase in quality and performance of onboard standards with time. Some current satellites perform well enough in terms of frequency drift, flicker FM noise floor, and long-term stability to compare favorably with the cesium beam standards carried on Navstar GPS satellites launched in 1983-4