OBSERVATIONS ON THE RELIABILITY OF RUBIDIUM FREQUENCY STANDARDS ON BLOCK II/IIA GPS SATELLITES

Currently, the B h k IlllIA Gbbal Positioning System (GPS) sateUites are equipped with lwo rubidium frequency standards. These frequency standards were or ig i~Uy intended to serve 4s the back-ups to two cesium frequency standards. As the constellation ages, the Master Control Station is forced to initialize 4n increasing number of rubidium frequency standards. Unfortunately, the operational use of these frequency standards has not lived up to initial expectations. Although the performance of these rubidium frequeneg standards has net and even exceeded GPS requirements, their reliclbilily has not. The number of unscheduled oufage times and the short operational I i fe t im of the rubidium froquency standards compare poorly to the tmek record o f the cesium froquency standards. Only 4 SIMU number of rubidiumfrequency standards have actually been made operational Of these, 4 large percenkage have exhibited poor reliability. If this trend continues, it is unlikolg that the rubidium frequency standards will he4 contribute to the navigation payload meting program specifiation