Spirit Wheel Problem

NASA's Mars rovers each have six wheels. Opportunity, after nearly six years on the planet, continues to roll right along.

Spirit, however, has had more problems. It has been functioning without an operating right front wheel since 2006, and for the past several months has been stuck in deep sand. During NASA's recent attempts to extricate Spirit, the right rear wheel has stopped spinning, perhaps permanently. The rovers were designed to function on four wheels if necessary-- three, if the right three-- but NASA isn't sure Spirit can get out of its current predicament with two dead wheels.

A time factor is also beginning to loom. Winter at Spirit's location on Mars begins in May 2010. Given the precise way the rover is situated, NASA doesn't believe it could gather enough solar energy to survive the winter. So, the fight to save Spirit might be reduced to a simple imperative. Move or die. In six months.