An investigation into optimal mobility system for planetary rovers.

This thesis outlines a systematic study of different mobility/suspension systems that have been proposed for Martian robotic rovers. One of the lessons learned during the 1997 US Mars Pathfinder mission was that mobility over the rock-strewn terrain was severely limited. This limited the Sojourner rover's traverse to only 106m in total during the entire 30-sol mission. Similar problems were also encountered by the twin Mars Exploration Rovers - Spirit and Opportunity. The investigation serves to analyse different mobility configurations - wheels, tracks, rocker-bogie and suspended track (Elastic Loop Mobility System - ELMS) over a terrain typical to the Viking Landing Sites - VL1 and VL2, Pathfinder Landing Site and MER landing sites. Given that there are severe mass and power constraints, these factors will also have to be considered in selecting the optimal mobility system configuration. The approach to soil-wheel and soil-track interaction modelling incorporating wheel/track slips, the vehicle slip angle and forces acting on the wheels/tracks is presented. The equations developed characterise the relationship between the forces acting on the vehicle, the vehicle parameters and key soil properties. This interaction model is then used in the developed software architecture RPET (Rover Performance Evaluation Tool). This represents an effort to develop a comprehensive method for evaluating the effectiveness of a presented mobility/suspension concept under a particular choice of operating environment. Incorporating the kinematic and dynamic equations of vehicle motion in the tool along with the wheel/track-soil interaction model allow a very accurate and near-realistic performance estimation. This allows ranking individual concepts on the basis of respective performance on a variety of terrain and operating environments. The RPET comprises of several modules each responsible for a dedicated computational task. The analytical performance metrics are well complemented by 3D simulation metric and prototype testing of a fully resolved vehicle configuration for both wheeled and tracked concepts. The field trials indicate that the RPET tool determines the performance of a system with considerable accuracy. This thesis makes a considerable contribution to reduce the time and effort required for evaluation and determining the suitability of a candidate vehicle mobility concept for a mission during the initial stages of a project. This work was implemented in a European Space Agency (ESA) project - Rover Chassis Evaluation Tool (RCET) and developed further to suit the project requirements