Ionospheric and Plasmaspheric Delay Characterization and Mitigation Methodologies for Lunar Terrestrial GNSS Receivers

Keidai Iiyama and Grace Gao

Peer Reviewed

Abstract:	Recent advancements in lunar positioning, navigation, and timing (PNT) have demonstrated that terrestrial GNSS signals, including weak sidelobe transmissions, can be exploited for lunar spacecraft positioning and timing. While GNSS-based navigation at the Moon has been validated recently, unmodeled ionospheric and plasmaspheric delays remain a significant error source, particularly given the unique signal geometry and extended propagation paths. This paper characterizes the ionospheric and plasmaspheric delay affecting GNSS signals observed at the lunar south pole and in lunar orbit using the Global Core Plasma Model (GCPM) and a custom ray-tracing algorithm to simulate both first-order delays, higher-order delays, and bending effects. Simulation results show that mean delays are on the order of 1 meter, but maximum delays can exceed 100 meters depending on the raypath, solar activity, and geomagnetic conditions. The study further compares mitigation strategies, including altitude masking, iono-free frequency combinations, and differential techniques, using simulated electron densities under high solar activity. We found that a tangential altitude cutoff of 6000 km is effective in excluding signals traversing dense ionospheric regions, and keeping 99% of the ionospheric and plasmaspheric delays below 2 m. Single differencing is able to remove over 90% of the ionospheric and plasmaspheric delays for two receivers with relative distances under 10,000 km. The iono-free combinations are effective to cancel 1st-order delays for signals that pass below 4000 km altitude, but for higher signals, the effect of inflated thermal noise due to frequency combination becomes more significant. These findings inform the design of robust lunar GNSS navigation systems that utilize terrestrial GNSS signals.
Published in:	Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025) September 8 - 12, 2025 Hilton Baltimore Inner Harbor Baltimore, Maryland
Pages:	3193 - 3210
Cite this article:	Iiyama, Keidai, Gao, Grace, "Ionospheric and Plasmaspheric Delay Characterization and Mitigation Methodologies for Lunar Terrestrial GNSS Receivers," Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025), Baltimore, Maryland, September 2025, pp. 3193-3210. https://doi.org/10.33012/2025.20343
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