Clock Resiliency Test Results with GPS Prototype Hardware
Michael R. Jones, John P. Janis, Nick Quackenbush, Amy Caprioni, Robert Montana, L3 Harris Technologies
Location: Ballroom E
Date/Time: Wednesday, Aug. 25, 10:50 a.m.
The GPS Navigation Payload Time Keeping System (TKS) utilizes three Rubidium Atomic Frequency Standards (RAFS) to provide redundancy. These frequency standards are installed on every Navigation Payload Element (NPE) navigation panel, which can also accommodate a 4th RAFS via a spare slot. Operational practice has been to use a single RAFS on each vehicle as the primary frequency standard, reserving the other two as cold spares. RAFS in the current GPS constellation have exhibited exceptional reliability over the past two decades, leading to the possibility of using them both for clock ensembling and advanced clock anomaly detection with autonomous on-board anomaly correction. L3Harris has previously presented the results of a successful laboratory demonstration of GPS clock ensembling using the L3Harris GPS-IIIF prototype mission data unit (MDU). L3 Harris has also previously presented high fidelity simulation results for GPS advanced clock anomaly detection and correction. In this paper we present an extension of the previous clock ensembling hardware demo to include advanced anomaly detection and correction. This hardware demo verifies the simulation predictions and proves the viability of implementing anomaly detection and autonomous correction in real GPS hardware. Clock ensembling plus anomaly detection and on-board correction are GPS enhancements that can integrated with the existing GPS-III SV hardware through a MDU Flight Software (FSW) upload. These two innovations improve the overall resiliency and stability of the GPS MDU 10.23 MHz system clock, which is the time basis for all L-band navigation signal generation for GPS users. Users will benefit from less SV operational downtime in the event of a frequency standard anomaly and better long-term User Range Error (URE) for scenarios where the SVs are out of ground contact for an extended period of time.