Roving on Mars

On May 6, 2009, Spirit got stuck. The Mars rover, about the size of a go-kart, was traveling south on the red planet when it found itself hubcap-deep in loose, flourlike sand. To make matters worse, the rover’s right front wheel had locked up three years earlier, leaving it with only five working ones. Fearful of its digging in deeper with every turn of the wheels, Spirit’s controllers at JPL called a halt until they could find a way to get it out. Since then, the engineers have been testing maneuvers here on Earth in a big sandbox with two rovers—an exact replica and a lighter one that’s closer to what Spirit weighs on Mars. The team is still at it as of this writing, and so far this Spirit is anything but free. Such setbacks aren’t new, however. Less than three weeks after Spirit landed on January 4, 2004, it fell silent. Engineers scrambled to solve the problem, hoping there wouldn’t be a repeat of the previous two American missions to Mars. On December 3, 1999, the Mars Polar Lander had been lost, apparently due to a software error that shut off its descent engine too soon. Accompanying the lander was the Mars Climate Orbiter, which was incinerated when a mix-up between metric and imperial units caused it to enter the Martian atmosphere too low. Mars is an unforgiving destination—in fact, more than a third of all spacecraft sent there have never made it. The memory of past failures was still fresh and, with Spirit, the future of the entire Mars program might well have been hanging in the balance. Meanwhile, Spirit’s twin was