Ray Tracing and Use of Shadows as Features for Determining Location in Lunar Polar Terrain

Ice is the most valuable resource on the Moon. It exists only at the poles where shadows are extensive and drivable routes are short. Robot routes to reach this ice are tenuous. Sun-synchronous lunar polar routes offer order-of-magnitude greater duration and range if such routes are achievable. Sun-synchrony is brittle in the sense that a rover must be at precisely scheduled time and place, so special localization techniques are warranted. Methods for terrain-based localization that work at equatorial regions are challenged at the lunar poles, where the grazing sunlight casts long shadows that obscure and change views over time. The shadows are shown here to accentuate craters as localization features. This paper presents a method that improves terrain registration at the poles of the Moon by probabilistically considering sensor and terrain uncertainty, and exploiting shadows as semantic features for localization. This method is validated and evaluated in simulated experiments.