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Session C8: Military GPS User Equipment and Related Programs 3

EGI with Resilient Timing Results
Joe Franiak, Darryl Larson, Neal Dahlen, Steve Jefferts, Steven Kim, Northrop Grumman
Location: Ballroom B
Date/Time: Tuesday, Jun. 2, 4:05 p.m.

An Embedded GPS/INS (EGI) system combines tightly integrated inertial navigation sensors (accelerometers and gyros) with GNSS positioning to deliver continuous, high-rate, and robust navigation and attitude solutions that maintain accuracy during GNSS outages, resist multipath and jamming better than GNSS alone, and provide low-latency, vehicle-dynamic-aware outputs for flight control, guidance, and sensor registration; adding a Chip Scale Atomic Clock (CSAC) provides the following benefits:
1) Knowing time more accurately when Satellite data comes back after a period of loss will help the receiver find SVs more quickly. The current project provides accurate 1PPS even after GPS loss. Additional work will be performed to maintain and send accurate time to the receiver, so that this benefit can be fully realized.
2) Northrop Grumman is working on EGIM enhancements that make use of Iridium PNT receiver and Starlink terminal provided Satellite LOS measurements to aid navigation. This capability can significantly improve INS velocity and position performance when GPS is not available. The degree of improvement is however affected by time accuracy since the alternate LOS measurements are time-tagged in GPS time. Aligning these measurements with INS velocity and position is required to form Kalman Filter observations and this process is more accurate when GPS time is precisely known.
NGC has tested a CSAC as a timing source in Legacy Navigation system: LN-251, LN-260, & LN-270. This resilience testing aims to validate continuity, accuracy, and holdover performance under realistic stressors (power interruptions, temperature changes, RF interference, and host-system faults). Key objectives are to confirm the CSAC’s Allan deviation and phase noise meet system requirements, to verify the system’s ability to maintain time and frequency during loss or degradation of reference input, and to ensure graceful recovery and bounded time error when the CSAC is reconnected or when the system switches back from an alternate reference (e.g., GNSS or network time). Define quantitative pass/fail criteria up front (maximum allowed time error, reacquisition time, frequency offset limits, and jitter thresholds).

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