PSNDL (Space Navigation Doppler Lidar)
A laser sensor that measures a lander's velocity and distance to the ground during descent, so it can touch down softly and on target.
Why it matters
Several commercial Moon landers have tipped over or crashed because they misjudged speed or altitude in the last seconds. A direct, precise measurement of motion relative to the surface lowers that risk, and the same sensor can guide spacecraft docking.
How the technology works
The lidar fires laser beams at the surface and reads the Doppler shift of the reflections, using coherent detection to reject background light. The lunar version, PSNDL-L, gives three-axis velocity better than 2 cm/s and range better than 1 meter.
The design is licensed from NASA.