Rover for Martian exploration: linear flexible wheel model in multibody environment

The main objective of this thesis is to develop a linear flexible wheel model that, implemented in a multibody model of the ExoMars rover, allows to simulate and predict the real behavior of the rover on the Martian surface. ExoMars is the mission managed by the European Space Agency (ESA) and the Russian Federal Space Agency (Roscosmos), with the aim to deliver a surface platform and a rover on Mars, in search of a sign of life. The Martian soil is not regular, but rocky and mostly covered with loose soil. Therefore, the study of the rover mobility becomes a crucial aspect for the mission success. ExoMars rover is equipped with flexible wheels that facilitate the overcoming of obstacles. Multibody software is a fundamental tool to simulate the static and dynamic behavior of the rover on the Martian surface. ??First, a non-linear static analysis is performed on a finite element model (FEM model) of the rover wheel to obtain the static radial stiffness curves. The numerical data acquired are thus compared with the available experimental data on the wheel stiffness, to verify the "goodness" of the FEM model. The FEM model of the rover wheel is built using HyperMesh, a finite element pre-processor, and analyzed through OptiStruct solver. In the second part of the thesis work, starting from the FEM model, using OptiStruct, a Component Mode Synthesis (Craig-Bampton Method) is carried out to obtain the linear flexible wheel model, which is then implemented in a Multi-Body System (MBS) model of the ExoMars rover. Subsequently, to verify the validity of the modal reduction operation carried out, the deformation of the flexible wheels, due only to the action of the rover weight, is checked and compared with the numerical data obtained from the FEM analysis. Finally, a multibody simulation of a real test in which the rover is engaged in overcoming an obstacle is performed. The multibody model of the ExoMars rover is made with MotionView pre-processor and simulated through MotionSolve solver. As result, the simulation reproduces in a rather faithful way the real rover behaviour. The positive comparison with the experimental test validates the goodness of the linear flexible wheel model realized. ??The thesis has been developed at the Thales Alenia Space Italia S.p.A., Prime Contractor for ESA contributions to the ExoMars mission.