Positioning, Navigation, and Timing for Lunar Descent and Landing with Joint Doppler and Ranging

Lunar descent and landing requires accurate position, velocity, and timing (PVT) knowledge in real-time. This paper introduces the use of Joint Doppler and Ranging (JDR) fused with additional sensors to estimate PVT for a lunar lander. JDR is a radiometric navigation method that utilizes geometric constraints with a surface reference station to reduce Doppler measurement errors and improve positioning performance. Previous papers introduced PVT estimation for surface users and lunar orbiters utilizing JDR with a three-satellite constellation and a self-positioned reference station. A well-known reference station enables measurement corrections through single and double differencing. Double differencing with JDR (DD-JDR) provides highly accurate navigation under significant range and Doppler bias, drift, and noise. This analysis fuses DD-JDR with an altimeter and an inertial measurement unit to achieve high accuracy navigation during active descent and landing. During the simulated lunar descent, the lander receives one-way range and Doppler from the navigation constellation and reference station. The navigation simulation generates high-fidelity Doppler shift measurements including instrumentation and propagation errors. Oscillator models generate frequency errors from local oscillators in the lander, orbiters, and reference station. An extended Kalman filter fuses the DD-JDR, inertial, and altimeter measurements and estimates the lander’s PVT. A Monte Carlo analysis describes the distribution of PVT performance. The analysis compares the performance of fused DD-JDR for lunar landers against traditional radiometric methods fused with the same inertial and altimeter measurements. Fusion of additional sensors with DD-JDR further improves PVT performance and navigation robustness.