Relativistic Framework for Disseminating Lunar Time for the Intuitive Machines LCRNS PNT Constellation

Jason M. Leonard, Shaun M. Stewart, David E. Gaylor

Abstract:	The initial capability for providing precise Positioning, Navigation, and Timing (PNT) services at the Moon will be enabled by a constellation of five Intuitive Machines (IM) Lunar Data Network (LDN) satellites deployed into elliptical frozen orbits (ELFOs) optimized for South Pole coverage. The LDN navigation satellites are designed to comply with NASA’s Lunar Communication Relay and Navigation System (LCRNS) requirements and will serve as the U.S. component of LunaNet, interoperable with international cislunar PNT standards jointly developed by NASA, ESA, and JAXA. Each spacecraft’s onboard time will be continually synchronized with GPS time through a GNSS receiver, with interim time accuracy maintained by an onboard ultra-stable oscillator. In the ELFO, relativistic effects caused by orbital altitude and velocity variations result in each spacecraft experiencing its own unique flow of time, referred to as Proper Time. We derive the relationship between Proper Time and the TDB, TCL, TL, and TT systems, and address the corresponding GCRS-to-BCRS state transformations required for consistent light-time and pseudorange modeling as well as BCRS-to-LCRS state and time transformations required for a consistent lunar broadcast. This paper describes the time standard to be implemented for Lunar Time dissemination for initial operating capability (IOC), including 1-way time transfer using GNSS pseudoranges at the Moon, expected clock drifts relative to the lunar time system, an error analysis with candidate simplifications, and an estimation framework using crosslinks and surface receivers to coordinate the lunar time system.
Published in:	Proceedings of the 57th Annual Precise Time and Time Interval Systems and Applications Meeting January 26 - 29, 2026 Hyatt Regency Orange County Anaheim, California
Pages:	104 - 124
Cite this article:	Leonard, Jason M., Stewart, Shaun M., Gaylor, David E., "Relativistic Framework for Disseminating Lunar Time for the Intuitive Machines LCRNS PNT Constellation," Proceedings of the 57th Annual Precise Time and Time Interval Systems and Applications Meeting, Anaheim, California, January 2026, pp. 104-124. https://doi.org/10.33012/2026.20488
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