Enhancing Positioning Accuracy When Using Weak GNSS Signals on The Moon

Michael Armatys, David Anderson, Patrick Hwang

Peer Reviewed

Abstract:	Renewed interest in lunar exploration requires exploitation of the latest PNT techniques to support operations at the Moon. To provide accurate PNT, use of Earth orbiting Global Navigation Satellite Systems (GNSS) satellites shows promise, with two principal challenges: very weak signals and very poor satellite geometry. The recent National Aeronautics and Space Administration (NASA) / Italian Space Agency (ASI) Lunar GNSS Receiver Experiment (LuGRE) program demonstrated viable weak GNSS signal tracking techniques, so this paper focuses on the issue of poor geometry. GNSS positioning using pseudoranges is vulnerable to large positioning errors in the longitudinal direction between the receiver and the satellites when the satellite geometry is tightly clustered. The Dilution of Precision (DOP) results in a large position uncertainty value in the longitudinal direction, but not the lateral direction. When the satellites transmitters appear clustered to the receiving observer, the range and timing become strongly correlated and the solution struggles to separate contributions of the two. This causes the Position DOP (PDOP) in the longitudinal direction and the Time DOP (TDOP) to be very large. The vulnerability in situations associated with pseudorange-based systems involving timing uncertainty can be vastly improved if the uncertainty could be minimized independently. Time transfer via Two-Way Timing and Ranging (TWTR) is an effective method to minimize timing uncertainty that can greatly improved the DOP calculations. This paper explores the use of a clockaiding concept introduced by Collins in 2005 for Differential GPS (DGPS) applications to improve solution accuracy, called Communication-linked Time Transfer Augmentation for Geometry Enhancement (CoTTAGE), that exploits the communication data link between the reference station and the user to greatly reduce the timing uncertainty between the reference and user clocks. The paper shows through first-order error analysis and simulation that 10-meter level positioning accuracy is possible.
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:	2963 - 2976
Cite this article:	Armatys, Michael, Anderson, David, Hwang, Patrick, "Enhancing Positioning Accuracy When Using Weak GNSS Signals on The Moon," Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025), Baltimore, Maryland, September 2025, pp. 2963-2976. https://doi.org/10.33012/2025.20261
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