Global satellite communication (SATCOM) networks and positioning, navigation, and timing (PNT) services are both critically important to DoD for rapid, high-bandwidth dissemination of data, command and control, and PNT services to support joint all-domain operations. Optical crosslink in SATCOM networks has been identified as an enabling technology to provide low latency, high throughput SATCOM services with enhanced security and anti-jamming capabilities. However, the operation of SATCOM networks with Free Space Optical Communications (FSOC) heavily relies on Medium-Earth-Orbit (MEO) based Global Navigation Satellite System (GNSS) systems, e.g., GPS, for accurate satellite orbit determination. GPS and GNSS constellations in general are subject to a variety of interference and spoofing threats. Loss or compromises of GNSS services would have significant implications to satellite constellations using optical crosslinks. As a result, it is of great interest to reducing the reliance of SATCOM networks on GNSS systems. In addition to high-speed space data transfer, optical crosslinks can also provide time synchronization, accurate range measurements, and angle measurements, which can be utilized to not only determine orbital states of the satellites but also to assist and/or PNT in satellite systems. Such a capability will potentially enable SATCOM systems to operate when GNSS services are interrupted. In addition, SATCOM systems using optical crosslinks can be extended to provide on-demand PNT services to users, when satellites in the constellations are accurately tracked and synchronized in time. Especially, proliferated Low-Earth-Orbit (LEO) SATCOM networks can provide global PNT coverage with much stronger signals than MEO-based GNSS constellations. This makes the jamming and spoofing of PNT signals from LEO-based satellite constellations much harder and allows resilient PNT services to warfighters in GNSS-denied environments.

To develop SATCOM networks supporting integrated communications and PNT over optical crosslinks, the following challenges need to be addressed. Optical crosslinks need to support accurate time synchronization and ranging with minimal impact on communications. Ranging and time synchronization using optical crosslinks need to be optimized to achieve required PNT performance without consuming excessive system resources away from communications. Advanced asynchronous fusion and estimation algorithms are required for satellite orbital state determination. In order to provide on-demand PNT services to users from communication satellites an integrated communication and PNT system also need to be investigated.

References

1. K. D. Pham, “Integrated Navigation and Communications: A Conformance Framework,” IEEE Aerospace Conference, Big Sky, MT, 2023

2. C. Carrizo, M. Knapek, J. Horwath, D. Gonzalez, and P. Cornwell "Optical inter-satellite link terminals for next generation satellite constellations", Proc. SPIE 11272, Free-Space Laser Communications XXXII, 1127203 (2 March 2020); https://doi.org/10.1117/12.2545629.

3. J. Garnham, P. Shubert, and J. McNally "Position and time information via free space optical communications", Proc. SPIE 11272, Free-Space Laser Communications XXXII, 1127208 (2 March 2020); https://doi.org/10.1117/12.2547401.

4. K. Iwamoto, et.al., "Small optical inter-satellite communication system for small and micro satellites", Proc. SPIE 10096, Free-Space Laser Communication and Atmospheric Propagation XXIX, 100960T (24 February 2017); https://doi.org/10.1117/12.2251610.

key words

GPS, GNSS, Optical Crosslinks, Laser Communications, Precision Timing, Precision Positioning

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