Real-time Hazard Detection for Landers

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. The state of the art Entry, Descent, and Landing (EDL) technology can land a spacecraft on Mars somewhere within a very large landing ellipse (20-100 km). However, even if a landing ellipse is only a few kilometers long, it is very likely to contain hazards such as craters, discontinuities, steep slopes, and large rocks, regardless of how the ellipse is selected. A lander that encounters a large rock, falls off a cliff, or tips over on a steep slope can sustain mission-fatal damage. In this paper, we will briefly 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 present the hazard detection approach which fuses stereo vision and shadow based rock detection to maximize the spacecraft safety. We discuss in detail several performance models for slope estimation and rock detection within 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. We will also discuss a recent activity to convert the shadow-based rock detector into a rock detection and mapping tool that we are using to process very large, highresolution HiRISE images from the Mars Reconnaissance Orbiter (MRO) to assist in landing site selection for the Phoenix mission.