Abstract: An earth orbit satellite control system which provides automatic, continuous correction of phase and frequency in order to maintain synchronization between the satellite and a Global Positioning System (GPS). The system achieves phase and frequency synchronization by disciplining the satellite's reference oscillator by phase locking it to timing pulses received from the GPS. The system comprising a state machine controller which cycles the disciplined oscillator into both a closed-loop operation wherein the oscillator is phase-locked to the GPS timing pulses, and an open-loop operation wherein a previously stored GPS timing pulse, or commands from a ground station, drive oscillator phase and frequency synchronization.