Development of a Lunar Surface Navigation Pseudolite Testbed

Interest in the Moon has grown significantly over the past few years as NASA works to return astronauts to the lunar surface. Historically, lunar missions have primarily been supported by Earth-based ground stations for communication and radionavigation. However, the quantity and scope of proposed lunar exploration, science, and commercial missions require in-situ infrastructure for continuous communication support and precision navigation services. We propose a lunar surface-based Position, Navigation, and Timing (PNT) and emergency broadcast pseudolite system as a cost-effective solution to support regional operations over exploration critical areas, and have previously explored architecture design characteristics, defined the pseudolite concept of operations, and identified potential navigation performance. This research is focused on developing a lunar pseudolite testbed with two primary objectives: demonstrating lunar surface communication and radionavigation techniques and characterizing the performance of low-cost, commercially available radio frequency (RF) hardware alternatives for supporting lunar operations. The work is comprised of four primary phases: (1) integration of the terrestrial pseudolite testbed, (2) development and testing of the communication and radionavigation protocols in a benchtop environment, (3) characterizing the relative range and time synchronization performance with different reference oscillators, and (4) over-the-air demonstrations with multiple pseudolite units. Pseudorandom noise (PRN) code ranging is the baseline relative positioning methodology, with signal tracking, range estimation, and absolute position estimates obtained by modifying open-source Global Navigation Satellite System (GNSS) software engines. Hardware tests were conducted to characterize the ranging performance, with average range error of less than 1.3 meters, primarily driven by time synchronization offsets. Initial tests demonstrate how low SWaP pseudolites can provide communication coverage and < 10 m error absolute positioning accuracy over critical lunar regions, helping to jumpstart exploration and commercialization on the lunar surface.