KEYNOTE: Introducing Pseudo-Range Rates and IMU Sensors to Improve Lunar Satellite Navigation System Performance

The growing interest in lunar exploration makes accurate and reliable navigation essential for future missions. Projects such as the European Space Agency’s (ESA) Moonlight are developing lunar satellite navigation systems, often based on Elliptical Lunar Frozen Orbit (ELFO) constellations and pseudorange measurements. To address the limited number of satellites during initial deployment, enhancements such as Round Trip Delay (RTD) and altimeters have been proposed. This work investigates further improvements through pseudorange rate and Inertial Measurement Unit (IMU) measurements. An Extended Kalman Filter (EKF) is developed to integrate different combinations of pseudorange, pseudorange rate, altimeter, and IMU data for position, velocity, and time (PVT) estimation. Two baseline operational modes - standard pseudorange and enhanced pseudorange with RTD and altimeter - are augmented with IMU and pseudorange rate measurements, and their performance is assessed. Montecarlo simulations of lunar landing and lunar surface rover trajectories show significant gains: position errors reduced by ≈ 25% with pseudorange rate and up to ≈ 60% with IMUs, and velocity errors reduced by up to ≈ 95%. The results also demonstrate increased robustness in ill-conditioned geometries, particularly critical during the early constellation deployment and lunar landing phases.