Session A4: PNT Solutions for Space Applications

The Design of a Flexible, Interoperable Navigation Signal for Future Lunar Missions
Philip Dafesh, Nathan Wong, Gourav K. Khadge, Goran Djuknic, The Aerospace Corporation; Juan Crenshaw, Brian C. Peters, The National Aeronautics and Space Administration; Floor Melman, Cosimo Stallo, Richard Swinden, The European Space Agency; Masaya Murata, Japan Aerospace Exploration Agency
Location: Beacon A

The LunaNet Interoperability Specification (LNIS) is a set of standards currently under development by NASA, ESA, and JAXA which define a common, interoperable set of services and interfaces for lunar communication and navigation. The LNIS includes specifications for the GNSS-like Augmented Forward Signal (AFS). The LANS (Lunar Augmented Navigation Service) will be comprised of Multiple LunaNet Service Providers (LNSP) such as NASA’s LCRNS (Lunar Communications Relay and Navigation Systems), ESA’s Moonlight LCNS (Lunar Communication and Navigation Services) and the Japan LNSS (Lunar Navigation Satellite System) broadcasting the AFS. The LANS will provide a GNSS-like capability enabling orbiting and surface users in lunar space (such as Artemis) to estimate their position, velocity and time. Initial capabilities will focus on providing service to the lunar South pole region.
The specification of AFS defines two orthogonal signal components on a single carrier, with the in-phase component (AFS-I) being a lower-chip-rate data channel tailored for applications where low SWaP is critical (e.g., IoT devices or search and rescue), and the quadrature component (AFS-Q) being a high-chip-rate data-less pilot signal for high-precision, robust lunar navigation and positioning applications.
An initial description of AFS was provided in [1] and initial analysis results were shown in [2]. In this work, we provide rationale for updates to the LNIS that define key aspects of the signal including the primary spreading code designs for the data and pilot channels, and a three-tiered overlay code approach for the pilot channel that provides flexible signal acquisition alternatives, rapid time dissemination and robust frame synchronization. The paper also describes a robust data sync word that is designed to enable frame synchronization for low-SWaP receivers that only use the I channel, as well as a low-density parity check code (LDPC) data message encoding design and interleaving definition.
The work further describes the impact of the updated AFS design in terms of improved acquisition performance, interference resistance, navigation message capabilities and rapid absolute time dissemination for users able to access clock and ephemeris data over an external network. The cross-correlation and synchronization performance of the AFS design is also compared to potential alternatives, further providing rationale for the final signal design configuration.
[1] Pietro Giordano, European Space Agency (ESA), Richard Swinden, European Space Agency (ESA), Cheryl Gramling, National Aeronautics and Space Administration (NASA), Juan Crenshaw, National Aeronautics and Space Administration (NASA), Javier Ventura-Traveset, European Space Agency (ESA), “LunaNet Position, Navigation, and Timing Services and Signals, Enabling the Future of Lunar Exploration,” ION GNSS+ 2023.