The time and frequency control subsystem onboard Navstar/GPS

The purpose, objectives, and design of atomic clocks used by the Global Positioning System Navstar satellites are discussed. The latest models of cesium crystal clocks are described and illustrated with block diagrams. Advanced models, Model 4401 and 4401A, feature program-approved parts, full radiation screening, worst case circuit analysis, failure mode effects analysis, parts stress analysis, and reliability prediction. The clocks provide nanosecond timing accuracy and 10 to the -13th or better frequency accuracy.