Visual Odometry on the Mars Exploration Rovers: A Tool to Ensure Accurate Driving and Science Imaging

摘要

Keeping track of a vehicle's location is one of the most challenging aspects of planetary rover operations. The Mars Exploration Rover (MER) vehicles are typically commanded only once per Martian solar day (sol) Busing a prescheduled sequence of precise metrically specified commands (e.g., "drive forward 2.34 m, turn in place 0.3567 radians to the right, drive to location X, Y, take color pictures of the terrain at location X, Y, Z"), so having an accurate position estimate on board during the execution of all terrain-based commands is of critical importance. MER rovers onboard position and attitude estimates were updated at 8 Hz nearly every time the wheels or rover arm (instrument deployment device, or IDD) was actuated. Changes in attitude (roll, pitch, yaw) were measured using a Litton LN-200 inertial measurement unit (IMU) that has three-axis accelerometers and three-axis angular rate sensors, and changes in position were estimated based on encoder readings of how much the wheels turned (wheel odometry).