Footage from the JPL In-Situ Instruments Laboratory, or "testbed," shows engineers rehearsing a crucial maneuver called egress in which the Mars Exploration Rover Spirit rolls off its lander platform and touches martian soil. Engineers at JPL used a test rover to perform this maneuver as if they were at the rover's landing site, Gusev Crater on Mars. Spirit successfully completed its roll-off early Thursday morning.