The ExoMars rover locomotion subsystem

ExoMars is the European Space Agency (ESA) mission to Mars planned for launch in 2018, focusing on exobiology with the primary objective of searching for any traces of extant or extinct carbon-based micro-organisms. The on-surface mission is performed by a near-autonomous mobile robotic vehicle (also referred to as the rover) with a mission design life of 180 sols. The rover has a 6 × 6 × 6 with 6 wheel-walking drive configuration (all 6 wheels are driven, steered and have a ‘walking’ capability) and has flexible wheels providing enhanced traction compared to rigid wheels of the same diameter. The suspension is a passive ‘3-bogie’ system which offers the same 6 wheel contact on uneven ground and mobility performance as the NASA-JPL ‘rocker-bogie’ suspension used on previous Mars rovers, but permits elimination of the differential linkage present in that design. Mars presents several challenges to the rover locomotion subsystem with its rock-strewn surface, sand dunes, rocky outcrops, craters and slopes. The unknown nature of the terrain to be traversed imposes several constraints on the locomotion subsystem design that need to be evaluated and incorporated within the flight model for its successful operation on Mars. In addition, accommodation within the confines of the lander and successful egress from it over deflated airbags places stringent constraints on locomotion subsystem mass, stowage envelope, deployment and wheel design. This paper documents the evolution of the ExoMars rover vehicle locomotion configuration from an early design concept to the current mission baseline design. The discussion involves various tradeoffs supported by mechanical and terramechanical analyses, simulations and testing performed on full-scale locomotion breadboard models at single wheel level and system level.