The Mars Exploration Rovers Descent Image Motion Estimation System

altimeter, an inertial-measurement unit, and an algorithm for combining sensor measurements to estimate horizontal velocity—the speed across the planet’s surface the lander travels as it descends. Although the sensors are not novel technology, the algorithm and flight software that combines them are new. This algorithm combines radar, image, and inertial data in a novel way to create a low-cost, robust, and computationally efficient solution to the horizontal-velocity-estimation problem. This article describes the DIMES algorithm, its testing, and its performance during both Mars Exploration Rover landings.