HAZARD AVOIDANCE TECHNIQUES FOR VISION BASED LANDING

Hazard Avoidance is a key technology for a safe landing of future planetary landing missions. During Hazard Avoidance, sensors and computers onboard the lander are used to detect hazards in the landing zone, autonomously select the most suitable region for landing, and generate the trajectory that retargets the lander to the safer landing site. In this paper, algorithms are described for vision-based hazard detection, safe site selection and powered landing guidance designed for landing in planets without atmosphere. The performance of these algorithms is currently under assessment through closed-loop simulation of the Hazard Avoidance system. Preliminary results show that the developed Hazard Avoidance algorithms are effective at detecting hazards and guiding the lander to a safe landing site. 1. ABBREVIATIONS AND ACRONYMS ESA European Space Agency FOV Field-Of-View GNC Guidance Navigation and Control HA Hazard Avoidance HG High Gate HM Hazard Map IMU Inertial Measurement Unit LDS Landing Site Reference Frame LG Low Gate LS Landing Site LS0 Nominal Landing Site PANGU Planetary and Asteroid Natural Scene Generation RCS Reaction Control System RSF Structural Reference Frame S/C Spacecraft TCT Transverse Control Thrusters VBNAT Vision-Based Navigation Analysis Tool VBRNAV Visual-Based Relative Navigation VGP Visual Guidance Phase 2. INTRODUCTION Technologies for planetary landing have been studied and developed since the late fifties during the Moon race, which culminated in 1969 with the first human landing on the Moon. Nowadays, instead of humans, small probes/landers are sent to distant planetary bodies, as more recently to Titan. These landings are often performed by a pre-programmed time sequence of events that bring the lander to a full stop in a desired area at the planet surface (e.g. ‘pathfinder-type’ is a open-loop landing with airbags; ‘Viking-type’ a semiautomatic landing). Future exploration missions envisage landing on planetary surfaces that are not known apriori, or in areas that are not flat and hazard free as the nominal selected Landing Sites (LS) of the current exploration missions. Landers also tend to become smaller and lighter, not so robust to surface hazards. Autonomous pinpoint soft-landing systems that include Hazard Avoidance (HA) capability are therefore required to guarantee safe landing. An HA system is responsible for the detection of any hazards that put in risk the landing mission and pathplanning to avoid the detected hazards. Hazard detection implies the lander to be equipped with a proper sensing device. In the frame of this study, an optical sensor, onboard camera, is used to detect hazards (e.g. craters, rocks, boulders, high slopes, etc.) in the landing zone. This paper presents the developed HA algorithms, namely the three functions that comprise: Hazard Mapping, Piloting and Guidance functions.