Wheel Abrasion Experiment ground tests: initial results

The Mars Pathfinder mission sent a lander and a rover to the Martian surface. Because the Martian surface dust and clay are abrasive, a Wheel Abrasion Experiment (WAE) is being carried on one of the rover wheels to evaluate wear. This experiment includes a set of three anodized aluminum strips mounted circumferentially around the center of the wheel. The strips are coated with thin, electron beam deposited coupons of aluminum, platinum, or nickel with thicknesses of 200, 400, 600, 800, and 1000 Å. (The different thicknesses allow estimates of rates of wear). As the coupons wear away, changes in reflectivity are recorded by a photovoltaic device. These data will be compared with similar data from laboratory simulations. A wear model for the Martian surface will be developed based on the results. This paper reports on the laboratory simulations. In the laboratory, an identical wheel was used in a simulated Martian environment. Three individual experiments were performed to evaluate wear of the metal coatings. A vacuum chamber which simulated the Martian surface was used. Wheel slip in the surface material (sand or clay) resulted in wear of the deposited metal layers. Wear was measured as a function of reflected light detected by a photocell. Work is in progress to finish the remaining ground tests