Development Challenges of a GNSS SDR Receiver for Moon Landing

Abstract

NASA, in the frame of the Commercial Lunar Payload Services (CLPS) initiative, has established a partnership with the Italian Space Agency (ASI) to procure a commercial GNSS payload for the Lunar GNSS Receiver Experiment (LuGRE). The project main objective is to achieve GNSS-based Positioning, Navigation, and Timing (PNT) on the Moon. By collecting GPS and Galileo raw measurements and IQ samples on both L1 and L5 bands, LuGRE will pave the way for the use of GNSS-based navigation systems in future moon missions. The LuGRE payload will fly on board the US Firefly Blue Ghost Mission 1 Lander (BGM1), landing on the Moon’s Mare Crisium in 2024. Moreover, the project oversees the development of a GNSS Software Defined Radio (SDR) receiver, which is a moon-customized version of Qascom QN400-SPACE. The receiver processor has been upgraded to support the mission operational modes for standard acquisition and tracking (i.e., Real Time Processing) and Sample Capture, which allows the collection of IQ samples batches for post-processing activities on-ground. High sensitivity acquisition and tracking techniques have been embedded to acquire and track GNSS signals as weak as 23 dB-Hz. Specialized navigation plugins have been added for Moon Transfer Orbit (MTO) and Moon Surface (MS) static positioning. The SDR technology allows for high flexibility and reconfigurability throughout the mission, during which Positioning and Timing are assisted with the uplink of GPS/Galileo ephemeris and time. The software can be incrementally updated via telecommand, and software-based radiation resilience mechanisms have been introduced to improve the robustness against memory corruptions. The payload includes a High-Gain Antenna (HGA) and a Front-End Assembly (FEA) containing a multi-stage Low Noise Amplifier (LNA) with dual-band filtering at L1 and L5. The High Gain Antenna consists in a passive RHCP L-band antenna obtained with a planar array of 3x3 elements operating in the L1/E1 and L5/E5a bands with a gain pattern up to 15dBi. After the HGA, the received signal is then processed through the LNA in the FEA, which boosts the signal power in order to properly feed the receiver stage.