Mobility Mode Evaluation of a Wheel-on-Limb Rover on Glacial Ice Analogous to Europa Terrain

Mobile, in-situ exploration of Europa's rugged, icy surface holds the potential for enabling discovery across multiple geologic units outside the exhaust-contaminated landing zone. The spatial and compositional diversity of surface salts and organics are of significance to our understanding Europa's history and biological potential. Our knowledge of Europa's surface properties, both topographic and mechanical, is extremely limited. Furthermore, additional data will not become available prior to the arrival of the Europa Clipper spacecraft. If the exploration of Europa continues to be an area of high science-value, this work postulates that solutions to the challenges of mobility on uncertain, but likely challenging, surfaces should be developed now. In this paper, we discuss the development of a multi-modal locomotion system and the results of field trials performed on fractured, glacial ice. Work was performed using the RoboSimian rover: a 32 degree-of-freedom, actively articulated mobility system. Three modes of mobility are compared: wheel-rolling, inchworming (push-rolling) and wheel-walking. Each mobility mode is designed to operate with articulated suspension whereby the normal load per wheel, body orientation, and available limb workspace are actively controlled. Each mode is presented individually alongside a discussion of its performance on terrain of varied slope and topographic roughness. Further, the utility of a multi-modal approach is presented, whereby rover immobilization was avoided during field trials through the selection of appropriate mobility modes as a function of terrain properties. Lastly, the results of trials performed using a body-mounted sampling system and its ability to collect and process samples taken 10 cm beneath the surface are discussed.