Navigation Doppler Lidar: A Velocity and Altitude Sensor for Landing Vehicles
A coherent Doppler lidar has been developed to address NASA’s need for a high-performance, compact, and cost-effective velocity and altitude sensor for use onboard its landing vehicles. Future robotic and manned missions to solar system bodies require precise ground-relative velocity vectors and altitude data to execute complex descent maneuvers and safe soft landing at the pre-designated site. This lidar sensor, referred to as Navigation Doppler Lidar (NDL), can meet the required performance of landing missions while complying with most vehicle size, mass, and power constraints. Operating from several kilometers altitude, the NDL can provide velocity and range precision with about 2 cm/sec and 2 meters, respectively, dominated by the vehicle motion. The NDL transmits three laser beams at different pointing angles toward the ground and measures range and velocity along each beam using a frequency modulated continuous wave (FMCW) technique. The three line-of-sight measurements are then combined in order to determine the three components of the vehicle velocity vector and its altitude relative to the ground. After a series of flight tests onboard helicopters and rocket-powered free-flyer vehicles, the NDL is now being ruggedized for future missions to various destinations in the solar system.