Like any travelers worth their frequent flyer miles, the twin rovers of the Mars Exploration Rover Mission must prepare for a long journey. Unlike airline passengers, however, the rovers won’t have an attentive flight crew to tend to their needs. Instead, the twins face a daunting 460 million kilometer (286 million mile) voyage to Mars. To ensure their readiness, scientists and engineers at JPL are testing the rovers by simulating conditions they’ll experience en route to and upon arrival at the red planet.