Map registration is a technique that matches (“registers”) a location in an image to the identical location on a map. Astrobotic’s landing technology registers high-quality, real-time camera images taken during the lander’s descent with terrain maps derived from orbital imagery to achieve safe landing at a precise destination. This capability is key for Astrobotic’s 2015 mission to the Lacus Mortis pit: it enables Astrobotic’s Griffin lander to fly directly over the pit, capturing close-up views of the floor and walls that cannot be seen from orbit or the ground, and then to land within 100m of the pit.
Traditionally, lunar landers have descended blind, using radio to determine their approximate trajectory during descent. They followed a pre-planned trajectory to a final descent altitude near the ground. At the final descent altitude, the computer or a human pilot used RADAR to refine the altitude and velocity estimates and gently touch down on whatever happens to lie beneath them. Because of uncertainty in radio localization and variation in lunar gravity, landing using radio and RADAR alone is accurate to approximately 10km. While this accuracy is good enough for landing in flat, safe regions of the Moon, much greater precision is necessary to safely land near a lunar pit or on the rim of a crater.
Map registration acts in place of radio orbit determination to provide better than 100m landing accuracy. As the lander descends, on-board cameras image the surface of the Moon. These images are registered to maps from the Lunar Reconnaissance Orbiter so that position and attitude can be triangulated. Velocity is then measured as the rate of change in the triangulated location.