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Session A1: Complementary PNT: Navigation by Celestial Objects

Celestial-Aided Navigation Capabilities in GPS-Denied Flight
Trevor Stephens, Ross Merritt, Brian Schipper, Paul Samanant; Honeywell International
Location: Ballroom A
Date/Time: Monday, Jun. 12, 2:10 p.m.

Navigation systems for many military aircraft have become overly reliant on GPS, rendering adversarial attacks on GPS detrimental to the success of the aircraft’s mission. This vulnerability creates a need for alternative PNT solutions capable of providing near-GPS performance during GPS-denied conditions. Candidate alternative PNT technologies include vision, magnetic, gravitational, radar, and celestial aiding. These technologies work in a complementary fashion to provide a navigation solution suitable across a variety of missions. This work focuses on celestial-aided navigation and the role it plays in meeting navigation needs during GPS denial, especially as the only alternative PNT technology capable of providing near-GPS performance when flying over water.
The key enabling technology for celestial navigation to achieve near-GPS performance is the ability to observe resident space objects (RSOs) in conjunction with traditional star observations using a star tracker. Star observations compared with their known position in space provides knowledge of the vehicle attitude. Whereas, observing RSOs relative to these background stars provides knowledge of vehicle position when compared against RSO ephemeris data. Utilizing these types of celestial observations, Honeywell has repeatedly demonstrated better than 30-meter navigation performance during GPS-denied flights on current prototype hardware, and now aims to develop a low-SWaP celestial navigation product for use on military aircraft to provide this same capability. This presentation will overview recent GPS-denied flight test results and present our low-SWaP design with discussion on key challenges including daytime tracking and accurate RSO ephemeris data.
Honeywell’s low-SWaP celestial navigation design utilizes a Ball Aerospace star tracker, which can observe RSOs and stars as dim as magnitude 9. Through these observations, a full navigation solution including position, velocity, and attitude is computed using an extended Kalman filter, which includes robust modelling of sensor and system level errors. As part of the new design, daytime tracking is realized through changes in the optics as well as enhanced RSO selection logic to view appropriate RSOs despite the challenge of background light. These enhancements provide a core capability to operate celestial navigation during both day and night. Celestial navigation also remains the sole alternative navigation technology capable of operating over water with near-GPS performance.
Our celestial navigation flight results in GPS-denied regions have repeatedly demonstrated better than 30 meters of accuracy including at PNTAX (Positioning, Navigation, and Timing Assessment Exercise) and flight demonstrations at various DoD locations in 2022. The current limiting factor on performance is accurate RSO ephemeris data. We will present results to show the improvement gains that can be realized with improved RSO ephemeris data and discuss the work we are doing in this area including utilization of USNO’s recently curated VCM catalogs. Recent refinements in system-level modelling within our extended Kalman filter has also led to performance gains, which will also be discussed.
The benefits of this low-SWaP celestial navigation system, including day and night capability as well as operability over water, offers great benefits for the overall success of missions when GPS is unavailable. The capabilities and unique benefits of celestial navigation renders it a crucial technology in providing an overall alternative PNT solution.

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