The Mars Pathfinder Wheel Abrasion Experiment

Abstract

On board the Mars Pathfinder spacecraft, launched in December of 1996, was a small roving vehicle named Sojourner. On Sojourner was an experiment to determine the abrasive characteristics of the Martian surface, called the Wheel Abrasion Experiment (WAE). The experiment worked as follows: one of the wheels of the rover had a strip of black anodized aluminum bonded to the tread upon which was deposited five patches or samples of three different metals ranging in thickness from 200Å to 1000Å. A series of candidate metals (Ag, Al, Au, Cu, Ni, Pt and W) were tested for suitability for the WAE. Optical, corrosion, abrasion and adhesion criteria were used to select aluminum, platinum and nickel. The photovoltaic sensor or photodetector developed for the WAE is described. As the wheel was spun in the Martian soil, thin patches of metal were abraded away, exposing the black surface. Abrasion of those samples was detected by the change in specular reflectance of sunlight as measured by a photodetector mounted above the wheel. The degree of abrasion occurring on the samples is discussed, along with comparisons to the abrasion seen in Earth-based laboratory experiments using Martian soil. Conclusions are reached about the hardness, grain size and angularity of the Martian simulant soil particles and about precautions to be undertaken to avoid abrasion on moving parts exposed to Martian dust.