Low Earth Orbit Navigation System (LEONS): Scalable GNSS-Independent Time Transfer and Positioning for Space Users

Paul Anderson, George Schmitt, Patrick Shannon

Peer Reviewed

Abstract:	Commercial and government LEO satellites often rely on low power, unencrypted GNSS signals transmitted from MEO to derive their onboard time and position. This GNSS-based solution has proliferated in the commercial sector due to its low SWaP and high performance. Unfortunately, GNSS susceptibility to jamming and spoofing makes it a fragile service even for satellites. Loss of accurate time and position quickly degrades a system’s ability to conduct nominal operations, including targeting a ground site for EO or RF collection, planning orbital maneuvers in support of on-orbit servicing or collision avoidance, or slewing to make contact on a routine TT&C pass. TrustPoint is currently developing a commercial GNSS system based on our patent-pending signal technology and COTS satellite hardware to provide alternative and innovative PNT RF signals to terrestrial users. In support of this effort, TrustPoint is developing a ground network of transceivers that will both monitor our constellation’s signals and broadcast GNSS-like signals upwards from the ground towards our satellites for purposes of time transfer and positioning. This GNSS-independent capability, named the Low Earth Orbit Navigation System (LEONS), can be extended beyond TrustPoint-only use and offered as an alternative or complementary PNT service for third-party commercial and government LEO satellites. By providing a higher-power, ground-based, RF-broadcast PNT signal set coupled with a purpose-built satellite receiver alongside an integrated on-board clock and precision orbit determination system, TrustPoint will establish a precise and resilient time and positioning capability, fully independent of existing GNSS. Further, the broadcast nature of such a system and service means it can serve an indefinite number of users simultaneously, like GNSS, and avoid the limited scalability, cost concerns, and weather dependence of alternatives like laser ranging or point-to-point RF systems. In this paper, we will provide an overview of the LEONS architecture and present reference designs for space and ground segment hardware that will enable GNSS-independent PNT services for LEO users. Preliminary link budgets and modeling and simulation results will be presented to survey system coverage and PNT performance trades.
Published in:	Proceedings of the 2023 International Technical Meeting of The Institute of Navigation January 24 - 26, 2023 Hyatt Regency Long Beach Long Beach, California
Pages:	65 - 76
Cite this article:	Anderson, Paul, Schmitt, George, Shannon, Patrick, "Low Earth Orbit Navigation System (LEONS): Scalable GNSS-Independent Time Transfer and Positioning for Space Users," Proceedings of the 2023 International Technical Meeting of The Institute of Navigation, Long Beach, California, January 2023, pp. 65-76. https://doi.org/10.33012/2023.18591
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