T. Myrick

The RAT as a Mars Rock Physical Properties Tool

The Rock Abrasion Tool (RAT) is a compact three-axis mechanism mounted to the Mars Exploration Rover’s (MER) Instrument Deployment Device (IDD) that grinds away the surface of rocks, to expose the interior while brushing debris from the excavation site thus revealing a clean surface. Additionally, the RAT can be used to perform science investigations. The data products generated by the RAT on Mars include position, angular velocity, and current, for each of the three motors, and temperature of the z-axis motor, in addition to the state of the control algorithm. These data can be used to determine the specific grind energy, a normalized value of energy required to grind a unit volume, for the rocks of Mars. The RAT engineering models use a library of terrestrial rocks specifically assembled to create a set of similar grind energy data products for comparison against Mars rocks in order to estimate Martian rock physical properties. Initial results indicate that the Martian rocks at Meridiani Planum are analogous to a range of terrestrial rocks from chalk to limestone in terms of “grindability,” a bulk property that relates to hardness, compression strength, shear strength, coefficient of friction, density, etc. The RAT measurement of various Mars rocks represents the most comprehensive physical properties database created of Martian rocks and will be of enormous value in our understanding of the geologic history of Mars, instrument design, and planning of future Mars missions.