Algorithm for On-Orbit GPS III Clock Correction

The Atomic Frequency Standards in each GPS satellite form the basis for global navigation. As reported previously, the Rubidium Atomic Frequency Standards (RAFS) occasionally experience frequency and phase anomalies that impact operational availability and system performance. In GPS III currently, RAFS anomaly detection is based on fixed limits. When an anomaly is detected, the satellite is automatically switched to Non-Standard Code (NSC), requiring Control Segment intervention to resume standard code operation. We present the results of an advanced algorithm to automatically detect and correct for these anomalies. The algorithm employs adaptive thresholding to minimize time to correction for the largest anomalies while maximizing detection sensitivity and correction accuracy, taking advantage of the capabilities of the GPS III Navigation Payload TKS to simultaneously measure the phase of multiple onboard clocks.