Lunar Augmented Navigation Service Interoperability Demonstration - Reference Products and Expected PVT Accuracy

Currently, NASA, ESA, and JAXA are defining the LunaNet Interoperability Specification (LNIS). This specification will enable interoperable communication and Position, Navigation, and Timing (PNT) services on the Moon. Within the LunaNet framework, the Lunar Augmented Navigation Service (LANS) aims to provide Regional Navigation Satellite Systems (RNSS)-like services to lunar users (i.e., rovers, landers, and orbiters). The service will be provided by different LunaNet service provider (LNSP) nodes each broadcasting the Augmented Forward Signal (AFS) to form regional coverage with appropriate geometry.
Currently, ESA, NASA, and JAXA are developing LunaNet instantiations with industrial partners; respectively, Moonlight Lunar Communication and Navigation System (LCNS), Lunar Communication Relay and Navigation System (LCRNS), and Lunar Navigation Satellite System (LNSS) that each contribute to the LANS. By 2029, the first five nodes (1 LCNS node, 3 LCRNS nodes, and 1 LNSS node) are planned to be in lunar orbit broadcasting the AFS and thus contributing to the LANS. Along with the LNSS satellite and the demonstration payload including the LANS receiver to be delivered to the Moon, JAXA is planning to perform a joint ESA-JAXA-NASA LANS interoperability demonstration.

This mission will aim to:
1) Acquire and track in-situ AFS signals from all LNSP nodes and assess the signal quality.
2) Estimate the signal-in-space error (SISE) of each LNSP node.
3) Demonstrate the interoperable approach is viable for a user to produce their position, velocity, and time (PVT) estimate.
4) Perform additional experiments concerning, among others, lunar time and reference systems.

To this end, the lander aims to embark a set of LANS receivers, an atomic clock (e.g., MiniRAFS), a laser retroreflector, and a Tracking, Telemetry, and Command (TT&C) transponder for Direct with Earth (DWE) communication and ranging.
Due to the availability of precise geodetic techniques (e.g., a laser retroreflector), the position of the lander should be well surveyed providing a high-accuracy reference location. This reference position should enable the validation of the PVT solution achieved through combined usage of the LNSPs by NASA, ESA, and JAXA and thus demonstrate interoperability as achieved at the AFS level for the user. Moreover, when the precise a-posteriori LNSP products are available (similarly to GNSS precise products), the UERE (User Equivalent Ranging Error) can be characterized which should enable the estimation of the LNSP SISE.

Moreover, having precise PVT, a stable, free-running atomic clock, and time-transfer capabilities could support the characterization of relativistic offsets between Moon- and Earth-based clocks. Furthermore, as part of the interoperable PVT, the impact of the different system time realizations of each LNSP and the provided offsets to relate back to LunaNet Reference Time (LRT) can be assessed. Finally, the presence of the lunar laser retroreflector (LRR) can support further improvements of the lunar reference frame realizations.

This paper will analyze the different aspects of the LANS interoperability demonstration mission. First, it will simulate the accuracy of the reference PVT that can be achieved with the embarked geodetic techniques. Secondly, a preliminary assessment of the accuracy of the interoperable user PVT will be provided. This assessment will consider the latest information concerning the LNSP orbits and system design parameters (e.g., SISE). Finally, this paper aims to characterize the accuracy with which the reference user clock offset can be obtained by adding GNSS receiver capabilities on the lander.