Navigation Doppler Lidar Performance Assessment and Trajectory Reconstruction of the Intuitive Machines IM-1 Lunar Landing

The Navigation Doppler Lidar instrument was developed at NASA Langley Research Center to support precision landing at locations such as the Moon and Mars. The instrument uses a frequency modulated continuous wave method that provides simultaneous range and velocity measurement data that can be processed in an onboard navigation filter for vehicle state estimation. The sensor has been tested thoroughly in laboratory settings and on various helicopter and suborbital rocket flight tests. The Navigation Doppler Lidar instrument was recently flown as a payload onboard the Intuitive Machines mission IM-1, which was designed to soft-land on the surface of the Moon on February 22, 2024. The instrument provided valid measurements at ranges that exceeded preflight expectations. This paper describes the post-flight data processing and trajectory reconstruction of the IM-1 lander based on data from the Navigation Doppler Lidar and an onboard Inertial Measurement Unit. An Unscented Kalman Filter was used to combine the data sources to reconstruct the approximate final three minutes of the trajectory prior to touchdown, where both sets of data were available. A digital elevation map was used to model the lunar surface terrain, and a ray tracing terrain engine was used to model the lidar beams. The results of the reconstruction show agreement between the lidar and modeled measurements to within approximately 5 m and 0.5 m/s, indicating that the Navigation Doppler Lidar produced accurate measurements and the reconstruction results provided additional flight validation of the ray tracing terrain engine and underlying digital elevation map.