Analysis of the frequency stability of on-orbit GPS Navstar clocks

The Naval Research Laboratory analyzes the performance of the on-orbit Navstar clocks for the Global Positioning System (GPS) Joint Program Office and conducts special analyses for the GPS master control station (MCS) whenever a clock exhibits anomalous behavior. This analysis focuses on the long-term behavior of the cesium and rubidium clocks using sample times of one day or more. It includes frequency and aging histories, frequency-stability profiles, time-domain noise process profiles, and anomaly detection. Events that perturb the normal clock behavior are of particular interest. The semiannual eclipse seasons will be superimposed on selected plots to investigate the temperature sensitivity of the clocks. Of particular interest is the nonstationary stochastic behavior of one of the cesium clocks, illustrated by its frequency-stability history, showing that the frequency stability is not always time-invariant. The frequency stability is presented for sample times of one day to 300 days. Time-domain noise-process analysis shows the dominant noise type to be white frequency noise for sample times of one day to ten days