The long-crippled right-front wheel of NASA's beleaguered Mars rover Spirit surprised mission managers by spinning for the first time in three years last week.

NASA engineers decided to try switching on the bum wheel to see if they could gain more traction to try to extricate the rover from the sand trap it has been stuck in since May 6.

Engineers were "totally" surprised that the wheel actually showed signs of activity last week after being switched on for the first time since 2006, when its failure due to an open circuit was thought to be permanent, said Ray Arvidson of Washington University in St. Louis. Arvidson is deputy principal investigator for the science payloads on Spirit and its twin rover, Opportunity. That wheel failure forced engineers to drive the spacecraft backwards with the crippled wheel in tow.

"We've been dragging it around Mars for three years," Arvidson said.

The attempt to switch on and move the right-front wheel was expected to be a long-shot, "but at this point we need every bit of traction we can get," Arvidson said.

The right-front wheel isn't working perfectly – while it revolved with apparently normal movement during the first three of four driving segments on Dec. 16, it stopped early in the fourth segment. Whether or not it will work again is unclear, according to the latest NASA progress report on the rover.

Spirit's right-rear wheel still isn't budging since it began experiencing a set of stalls in November.

Mission managers are unsure about the prospects of freeing the rover.

"I don't know if we're going to get it out frankly," Arvidson told SPACE.com.

But the team plans to continue the slow process of attempting to drive out of the sand trap into the new year – the seventh that Spirit and Opportunity have been on Mars, Arvidson said.