ShadowNav: Crater-Based Localization for Nighttime and Permanently Shadowed Region Lunar Navigation

Abstract

There has been an increase in interest in missions that drive significantly longer distances per day than what has currently been performed. For example, Endurance-A proposes driving several kilometers a day in order to reach its target traverse of 2000 km in 4 years. Additionally, some of these proposed missions, including Endurance-A and rovers for Permanently Shadowed Regions (PSRs) of the moon, require autonomous driving and absolute localization in darkness. Endurance-A proposes to drive 1200 km of its total traverse at night. The lack of natural light available during these missions limits what can be used as visual landmarks and the range at which landmarks can be observed. In order for planetary rovers to traverse long-ranges, onboard absolute localization is critical to the rover's ability to maintain its planned trajectory and avoid known hazardous regions. Currently, the localization performed onboard rovers is relative to the rover's frame of reference and is performed through the integration of wheel and visual odometry and inertial measurements. To accomplish absolute localization, a "ground-in-the-loop" (GITL) operation is performed wherein a human operator matches local maps or images from onboard with orbital images and maps. This GITL operation places a limit on the distance that can be driven in a day to a few hundred meters, which is the distance that the rover can maintain acceptable localization error via relative methods. Previous work has shown that using craters as landmarks is a promising approach for performing absolute localization on the moon during the day. In this work we present a method of absolute localization that utilizes craters as landmarks and matches detected crater edges on the surface with known craters in orbital maps. We focus on a localization method based on a perception system which has an external illuminator and a stereo camera. While other methods based on lidar exist, lidar is not currently planned for deployment on the current proposed nighttime and PSR missions. In this paper, we evaluate (1) both monocular and stereo based surface crater edge detection techniques, (2) methods of scoring the crater edge matches for optimal localization, and (3) localization performance on simulated Lunar surface imagery at night. We demonstrate that this technique shows promise for maintaining absolute localization error of less than 10 m required for most planetary rover missions.