Assessment of Tractive Performances of Planetary Rovers with Flexible Wheels Operating in Loosely Packed Soils

In view of project support work for ExoMars and possible subsequent Martian and Lunar ESA rover missions, a preliminary assessment has been made of the influence of a number of variables on wheel tractive performances on a loose fine sand, using state-of-the-art soil mechanics models and tools, i.e. the Abaqus Finite Element Method software with a Drucker-Prager Cap hardening 3-dimensional model mimicking a “Modified Cam-Clay Model” from Critical State Soil Mechanics. Especially for wheels with a deformable rim operating on loosely packed compressible soils this method of predicting tractive performances is expected to be more accurate than the currently existing semi-empirical models from classical terramechanics. For the currently baselined ExoMars Rover wheel design and a set of properties assumed for a fine sand which is expected to be representative for part of the Martian surface, the effects of wheel flexibility and wheel diameter on the tractive performances have been assessed, for a given load on the wheels and for a wide range of slip values. Moreover an assessment has been made, for this type of soil, of the effect of the gravity level on the load sinkage, within a range of wheel loads. This work can be considered a pilot project for exploring the possibilities of this method for future research and development.