Lunar PNT: Enabling Sustainable Infrastructure for Lunar Missions
Author: Peng hu, Open lunar fellowThis work is completed by Peng Hu, an Open Lunar Fellow, undertaking research on Lunar Position, Navigation, and Timing (PNT).
Lunar position, navigation, and timing (PNT) services are essential for supporting future lunar exploration missions, scientific research, and potential commercial activities. They enable precise landing, long-distance transportation of goods and humans, facility deployment, tracking of surface vehicles and astronauts, and facilitating scientific investigations on both the near and far sides of the Moon.
Earth-based PNT services provided through Global Navigation Satellite Systems (GNSS) such as GPS, Galileo, GLONASS, and BeiDou include a wide range of fundamental services, such as location tracking and navigation for humans, mapping, vehicle guidance, and time synchronization. Similar to Earth-based PNT, Lunar PNT services refer to a system of technologies and infrastructure designed to provide accurate position, velocity, and timing information on and around the Moon.
Planned PNT Infrastructure
To support lunar missions, PNT services will need to be available in cislunar space and on the lunar surface, particularly in key regions such as the South Pole, a prime location for a human outpost due to its water ice deposits and scientific potential. The challenge lies in determining the necessary infrastructure to achieve this vision. Addressing this will involve multiple phases and options. In the initial phase, the feasibility of leveraging existing signals from GNSS constellations, such as GPS and Galileo, for Lunar PNT services will be evaluated, along with an assessment of their performance. In the subsequent phase, a dedicated Lunar PNT infrastructure will be developed and deployed, which will include lunar orbiters and satellites. Notable initiatives include NASA’s Lunar Communications Relay and Navigation Systems (LCRNS) in 2026, ESA’s Moonlight Lunar Communications and Navigation Services (LCNS) constellation in 2028, and Japan’s Lunar Navigation Satellite System (LNSS) in 2028, aligned with space assets planned under NASA’s Moon to Mars architecture [1], gradually enhancing service coverage and accuracy.
Lunar orbiting spacecraft require precise time synchronization to maintain a globally recognized reference time, such as Coordinated Universal Time (UTC). However, due to the limited visibility of Earth from many potential lunar landing sites [2], relying on Earth-based GNSS or ground stations for time reference is challenging, which is being assessed by the Lunar GNSS Receiver Experiment (LuGRE) in 2025. A study [3] has shown that using one or more lunar orbiting satellites can provide navigation through Doppler shift observables, measurable changes in the frequency or wavelength of a wave between the source and the observer. An alternative solution is the deployment of lunar surface stations (LSS) that provide a local reference time closer to the orbiting spacecraft. This reduces dependence on Earth-based systems. Additionally, LSS can enhance PNT service coverage across lunar surface regions, similar to how the enhanced long-range navigation system (eLoran) supports terrestrial navigation on Earth. The use of LSS also reduces latency and improves reliability, particularly for missions operating in rugged terrain, such as craters, or near the lunar poles, where Earth visibility is sporadic and signal occlusion is common.
The Importance of Interoperability
Combining signals from both ground and space assets is essential to ensure high-performance, reliable Lunar PNT services and expand coverage. Achieving this, however, requires interoperability and open standards, which presents a significant challenge. NASA’s Moon to Mars architecture [1] highlights the importance of PNT asset interoperability to support the expansion of service regions. To facilitate this, the LunaNet Interoperability Specification (LNIS) [4] has been developed to enable seamless lunar interoperability between space assets as LunaNet Service Providers (LNSP). With the Augmented Forward Signal (AFS) [5], a multi-access forward link broadcast standard, LNSP assets can interoperate to enhance PNT services, improving performance (e.g., from meter-level to centimeter-level positioning accuracy) and expanding coverage (e.g., from the South Pole region to other lunar locations, orbits, and beyond). Through international cooperation, it is anticipated that new communication protocols will be developed to ensure configurable, secure, and resilient PNT service delivery, tailored to meet the unique challenges of the lunar environment and missions.
Lunar PNT services will be a cornerstone of sustainable lunar operations, enabling mission safety and precision. As lunar exploration expands, PNT systems will evolve to offer enhanced accuracy, coverage, and resilience, supporting commercial and scientific endeavors on and around the Moon.
References
[1] NASA, "Moon to Mars Architecture Definition Document (ESDMD-001) – Revision B," 2024.
[2] K. -M. Cheung, W. W. Jun, S. Bhamidipati and P. Carter, "Ground-Assisted Position Navigation and Timing (PNT) for Moon and Mars," 2024 IEEE Aerospace Conference, Big Sky, MT, USA, 2024, pp. 1-19.
[3] Kaila M. Y. Coimbra, Marta Cortinovis, Tara Mina, and Grace Gao, Stanford University, "Single-Satellite Lunar Navigation via Doppler Shift Observables for the NASA Endurance Mission," ION GNSS+ 2024, September 16-20, Baltimore, MD, USA.
[4] NASA, "LunaNet Interoperability Specification," Version 5, Feb. 7th, 2025.
[5] NASA, "LunaNet Signal-In-Space Recommended Standard - Augmented Forward Signal (LSIS - AFS) Volume A," Version 1, Jan. 29th, 2025.