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Session A1: Complementary PNT: Navigation by Celestial Objects

The USNO Satellite Navigation Reference Frame
Bryan Dorland, Daniel Veillette, Gregory Hennessy, Jennifer Weston, US Naval Observatory; Christopher Dapkus, Charles Poole, Bradley Sease, Computational Physics, Inc.
Location: Ballroom A
Date/Time: Monday, Jun. 12, 1:50 p.m.

For essential position, navigation, and timing (PNT), it is vital to cross-check data and not be overly reliant on one system. GPS can act as a singular point of failure: there is potential for failure at the local level (e.g. spoofing or jamming), at the control level (the signal itself), or at the space level (the GPS satellites). The Department of Defense (DoD) has responded to this threat by developing celestial navigation systems that do not rely on GPS and instead use satellites for position reference (e.g. ACN, CELNAV). Satellites can be observed using visible or infrared sensors against the background Celestial Reference Frame (CRF) of bright stars. If extremely precise satellite ephemerides are available, a satellite based celestial navigation system could provide position and timing information that is comparable to and independent from GPS. To better support ACN and related efforts, the United States Naval Observatory (USNO) has been working on constructing a Satellite Navigational Reference Frame (SNRF): a high accuracy orbital history for a curated set of resident space objects (RSOs) with realistic uncertainties. Not only does such a system support the Navy and DoD programs, but it is useful to the Space Domain Awareness (SDA) community.
Building and maintaining the SNRF requires producing an orbit history of a diverse set of thousands of RSOs. The SNRF will degrade over time without regular observations, data processing, and published updates. Maintaining the SNRF therefore requires a network of global observation systems and data partners. RSOs in the SNRF must have orbits known to a high level of accuracy over 24 hours and have well-understood uncertainties. They must also be stable over long time periods, geographically diverse, and bright enough to be detectable by the end users. The SNRF itself must be well-calibrated to evaluate accuracy and validate results, disseminate updates at regular intervals, and provide orbit states in formats that are compatible with the user’s celestial navigation system and are at the proper levels of classification. An additional benefit of developing a functional SNRF is that taking regular, high precision measurements of even a select group of Low Earth Orbit (LEO) satellites could help to improve drag and atmospheric modeling in the SDA Community. Higher accuracy orbits could also result in more accurate collision estimates, reduction of false positives, and avoidance of unnecessary maneuvering.
USNO’s Astrometric Reference and Guidance from Observations of Satellites (ARGOS) system is an R&D program with a mission 'to maintain and disseminate a high-accuracy Satellite Navigation Reference Frame to support the needs of the Navy, Air Force, Department of Commerce and the Space Domain Awareness Community.' The ARGOS system is designed to fuse data from many sources (i.e., optical and radar), including from its own observation network, to track a set of pre-determined Earth satellites in different orbital regimes. ARGOS then will generate, maintain, and make available a standard, high-accuracy SNRF to relevant stakeholders. The basic capability of generating orbits using data obtained in an automated fashion from a persistent sensor was demonstrated successfully at the end of calendar year (CY) 17. During CY18 through CY20, the ARGOS system developed implemented and tested a software infrastructure that automatically processes images and generates navigation solutions. In CY21, CY22, and CY23 ARGOS has transitioned towards operations, utilizing assets both at USNO DC and at the USNO Flagstaff Station (USNO-FS). The USNO SNRF is currently at its initial operational capability, and is available to approved DoD and Government users by request.

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