The durable twin rovers on Mars have gotten yet another lease on life, with NASA announcing Tuesday it would fund another 18 months of operations.
Spirit and Opportunity were originally designed for a three-month effort. Engineers knew all along that if nothing unexpected happened, they could last longer. But few expected them to be still roving after more than 14 months.
The new extension, which covers the costs of running mission control and analyzing images and data, could mean the rovers would operate in three separate Earth-years (early 2004 into 2006) if they continue to operate.
"The rovers have proven their value with major discoveries about ancient watery environments on Mars that might have harbored life," said Ghassem Asrar, deputy associate administrator for NASA's Science Mission Directorate. "We are extending their mission through September 2006 to take advantage of having such capable resources still healthy and in excellent position to continue their adventures."
The original three months of operations was not surprisingly extended by 11 months.
It's not yet clear exactly how the mission might change, or if the robots will actually run for a year and a half more.
"We now have to make long-term plans for the vehicles because they may be around for quite a while," Jim Erickson, rover project manager at NASA's Jet Propulsion Laboratory, said in a statement. "Either mission could end tomorrow with a random part failure. With the rovers already performing well beyond their original design lifetimes, having a part wear out and disable a rover is a distinct possibility at any time."
For now, the rovers are in "amazingly good shape," Erickson said. "We're going to work them hard to get as much benefit from them as we can, for as long as they are capable of producing worthwhile science results."
Is NASA surprised by the longevity of the bots?
"Spirit and Opportunity are approaching targets that a year ago seemed well out of reach," said Doug McCuistion, director of NASA's Mars Exploration Program. "Their successes strengthen NASA's commitment to a vision with the ambitious targets of returning samples from Mars and sending human explorers to Mars."
While the discoveries of past water by both rovers has made the dual mission successful by any measure, scientists are still interested what the future might hold.
Opportunity is approaching a region called "Etched Terrain," where scientists hope to find rocks exposed by gentle wind erosion rather than by disruptive cratering impacts, and rocks from a different time in Mars' history than any examined so far.
"This is a journey into the unknown, to something completely new," said Steve Squyres of Cornell University, Ithaca, N.Y. and principal investigator for the rover's science instruments.
Opportunity has overtaken Spirit in total distance driven. It has rolled more than 3 miles -- eight times the original goal. On March 20, Opportunity also set a new Martian record of 722 feet in a single day's drive. Drive-distance estimates can vary by a few percent. The long drives take advantage of crossing a plain so smooth it's "like an East Coast beach," said JPL's Jeff Favretto, mission manager on the Opportunity shift in recent weeks.
Opportunity's solar panels, though now dustier than Spirit's, still generate enough power to allow driving for more than three hours on some days.
Spirit is in much rougher terrain than Opportunity, climbing a rocky slope toward the top of "Husband Hill." However, with a boost in power from wind cleaning its solar panels on March 9 and with its formerly balky right-front wheel now working normally, Spirit made some longer one-day drives last week than it had for months. "We've doubled our power," said JPL's Emily Eelkema, mission manager. "It has given us extra hours of operations every day, so we can drive longer and we've used more time for observations."
With Mars now beginning southern-hemisphere spring, the Sun is farther south in the sky each day. If not for panel-cleaning, Spirit might be facing the prospect of becoming critically short of power if still on the north-facing slope by early June.
"We still want to get to the summit of Husband Hill and then head down into the 'Inner Basin' on the other side," Squyres said. "But now we have more flexibility in how we carry out the plan. Before, it was climb or die."
Both rovers show signs of wear. Spirit's rock abrasion tool shows indications that its grinding teeth might be worn away after exposing the interiors of five times more rock targets than its design goal of three rocks. Researchers probably won't know the extent of wear until Spirit's next rock-grinding attempt, which may be weeks away.
Troubleshooting continues for determining whether Opportunity's miniature thermal emission spectrometer is still usable despite tests indicating a problem last month. All other instruments on both rovers are still working normally.
- Mars Rover Special Report