Landing Hazard Detection with Stereo Vision and Shadow Analysis

Under a Phase A Concept Study for the NASA New Millennium Program (NMP) ST9 mission, the Terrain Relative Guidance System (TRGS) project developed an approach to landing hazard detection with descent imagery for missions to most solid-surfaced bodies of the solar system. Unmanned planetary landers to date have landed “blind”; that is, without the benefit of onboard landing hazard detection and avoidance systems. This constrains landing site selection to very benign terrain, which in turn constrains the scientific agenda of missions. In this paper we review sensor options for landing hazard detection and identify an approach based on stereo vision and shadow analysis that addresses the broadest set of missions. We then develop performance models for slope estimation and rock detection with this approach and validate those models experimentally. Instantiating our model of rock detection reliability for Mars predicts that this approach will reduce the probability of failed landing by at least a factor of 4 in any given terrain. Conversely, for the safety level desired for the 2009 Mars lander, this approach would roughly triple the fraction of the planet that is accessible for landing. The key contributions of this work are identifying the most appropriate sensor approach, developing and validating the performance models, and quantifying the impact this could have on missions.