Sept. 22, 2004 — NASA's robotic explorers are back at work on Mars following an extended siesta that had left mission managers with only hope and optimism that the rovers would survive the darkest days of Martian winter.

With the sun squarely blocking direct communications between Earth and Mars, the Spirit and Opportunity rovers were left on their own for nearly two weeks.

"When we're in this position it's very difficult for us to communicate with Mars. You have to kind of go through the sun or past the sun, get real close to the sun with our radio signal which creates a lot of noise. We miss about 60 percent of our signal," said Jeff Fabretto, a Mars rover flight director with NASA's Jet Propulsion Laboratory in Pasadena, Calif.

So, it was with a sigh of relief that first Opportunity and then Spirit readily responded to flight controllers' commands to begin restarting their interrupted science programs.

"Not only were communications disrupted, but the rovers were also going through the worst part of Mars' southern-hemisphere winter from a solar-energy standpoint," said project manager Jim Erickson. "It is a relief to get past this past couple of weeks."

The rovers are positioned on opposite sides of Mars' equatorial region in identical quests for signs of past water, which in turn could provide evidence of Martian life at some time in the planet's history.

Both vehicles are well past their design lifetimes and engineers have been able to work around the minor mechanical glitches that have developed over the past eight months. In a show of confidence, NASA managers recently approved $2.8 million for an additional six-month extension for the mission.

"Although Spirit and Opportunity are well past warranty, they are showing few signs of wearing out," Erickson said. "We really don't know how long they will keep working, whether days or months."

Managers intend to drive Spirit to the top of what has been named Husband Hill, part of a region known as the Columbia Hills. Rick Husband was the commander of the ill-fated shuttle Columbia mission. The rover currently is positioned about halfway up the hill.

Opportunity is inside a crater and will be dispatched to an area of exposed bedrock to hunt for chemical and physical signs of past water. Managers intend to drive Opportunity out of Endurance Crater and continue the rover's mission at another site.