This paper describes a coherent Doppler lidar developed by NASA to address a need for a high-performance, compact, and cost-effective velocity and altitude sensor onboard its landing vehicles. Future robotic and manned missions to solar system bodies require precise ground-relative velocity vector and altitude data to execute complex descent maneuvers and soft landing at a pre-designated site. This lidar sensor, referred to as Navigation Doppler Lidar (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 with about 2 cm/sec and 2 meters precision, respectively, dominated by the vehicle motion. The NDL can also benefit terrestrial aerial vehicles that cannot rely on GPS for position and velocity data. The NDL offers a viable option for enabling aircraft operation in areas where the GPS signal can be blocked or jammed by intentional or unintentional interference. A modified version of the NDL incorporating a beam steering device can produce 3-dimensional range and Doppler images that are critical for safe andefficient operation of autonomous ground vehicles. This paper describes the design of the NDL and its capabilities as demonstrated through extensive ground tests and flight tests onboard helicopters and autonomous rocket-powered vehicles. Then, the utilization of the NDL technologies for terrestrial vehicles will be discussed.
A coherent Doppler lidar has been developed to address NASA’s need for a high-performance, compact, and cost-effective velocity and altitude sensor onboard its landing vehicles. Future robotic and manned missions to solar system bodies require precise ground-relative velocity vector and altitude data to execute complex descent maneuvers and safe, soft landing at a pre-designated site. This lidar sensor, referred to as a Navigation Doppler Lidar (NDL), meets the required performance of the landing missions while complying with vehicle size, mass, and power constraints. Operating from up to four kilometers altitude, the NDL obtains velocity and range precision measurements reaching 2 cm/sec and 2 meters, respectively, dominated by the vehicle motion. Terrestrial aerial vehicles will also benefit from NDL data products as enhancement or replacement to GPS systems when GPS is unavailable or redundancy is needed. The NDL offers a viable option to aircraft navigation in areas where the GPS signal can be blocked or jammed by intentional or unintentional interference. The NDL transmits three laser beams at different pointing angles toward the ground to measure 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. This paper describes the performance and capabilities that the NDL demonstrated through extensive ground tests, helicopter flight tests, and onboard an autonomous rocket-powered test vehicle while operating in closedloop with a guidance, navigation, and control (GN and C) system.
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