High-Resolution Clock Control for the TIP Satellite.

Abstract : The Transit Improvement Program (TIP) satellite clock is controlled by the IPS (Incrementally Programmable Synthesizer) and flight computer subsystems. Together they provide a synthesis of frequency offset and frequency drift that can be used to compensate for such errors in satellite crystal oscillator. To do this, the ground software must estimate the oscillator offset and drift and then compute the proper control parameters to be injected into the satellite to steer the clock. The system provides a resolution of control of 1 part in 10 to the 13th power in frequency and 1 part in 10 to the 13th power per day in drift. Estimation of oscillator offset and drift from high-resolution pseudo-random noise epoch measurements is accomplished by a discrete Kalman filter, based upon a three-state model with continuous random walks in frequency and frequency drift as the driving noise in the oscillator. A ground software program has been provided to implement the Kalman filter and compute the control parameters required to steer the satellite clock to the reference ground clock. The programs are written in Fortran 4. Complete listings of the software and operating procedures are provided. (Author)