Twin Mars rovers still exploring after two years
BY SPACEFLIGHT NOW
Posted: January 24, 2006
With a longevity unthinkable even to the humans that built them, NASA's remarkable Mars rovers remain hard at work after two years on the Red Planet's surface.
"We take every day as if it could be our last day and we really push hard to keep driving, keep going," said rover mission manager Beth Dewell.
With Spirit working within the vast Gusev Crater and Opportunity exploring on the other side of Mars in Meridiani Planum, both rovers found evidence that Mars was wet in its ancient past.
"Putting all the clues together -- the mineral, chemical and textural clues -- we have found good evidence that there was ground water," said project scientist Joy Crisp.
Answering the water question is critical in the broader quest to determine if life ever arose on Mars. The two rovers aren't equipped to answer the life questions, however. Future missions will try to do that.
Spirit and Opportunity have driven a collective eight miles, crawling in and out of craters, climbing tricky terrain and beaming home pictures by the tens of thousands of never-before-seen territory and breath-taking vistas.
"With the rovers we've actually been able to go look and pick the things we wanted to see whether it was up on top of hills or whether it was down inside the craters, you name it," said Jim Erickson, rover project manager.
But it hasn't been all smooth sailing for the craft. Spirit's rock-grinding tool is no longer usable because the diamond-tipped teeth have worn away. Opportunity's front right wheel steering motor stopped working eight months ago, although the rover can still drive with its other steerable wheels. And a motor at the shoulder joint of the Opportunity's instrument-laden arm has a broken wire.
"As they age, we learn how to deal with the symptoms of old age whether it's the equivalent of arthritis in our joints or senility in our memory," Erickson said.
Tuesday marked the second anniversary of Opportunity's landing. A special celebration at the Jet Propulsion Laboratory, where the rovers are controlled, included speeches and remembrances of the past two years. U.S. Rep. David Dreier presented JPL officials with special certificates from Congress for each rover.
NASA Administrator Mike Griffin wasn't in attendance. But he offered these thoughts in a taped message to the rover team:
"As both the NASA administrator and an alumnus of JPL, I am delighted to add my voice to those saluting NASA's Mars rover team for your dedicated contributions to one of the grandest achievements in the annals of planetary exploration. By demonstrating that the spirit of robust scientific inquiry is alive and well at NASA, you have brought honor to this agency. I am extremely proud of what you have accomplished.
"In the summer of 2003 we launched the twin Mars rovers with the hope that at least one would safely reach its designated landing site and roam the surrounding Martian terrain for three months. Now, 24 months and over 700 sols (Martian days) later having both successfully and dramatically bounced to their duty posts, both Spirit and Opportunity and the people who operate them continue to astound the world.
"To be certain, there were logical reasons for supposing the rovers would have a more limited life span. A combination of the planet's cold temperatures and dust building up on the rovers' power-providing solar panels were expecting to bring their scientific missions to a swift end. However, your ability to find creative ways to work around problems and the dynamic character of the Martian environment -- the very thing we came to study -- helped to extend the rovers' missions well beyond anyone's wildest imagination.
"Last March, for example, a whirlwind in the Martian atmosphere blew the dust off Spirit's solar panels, allowing it to regenerate its batteries and its mission could continue.
"And last April, we had a different sort of problem with Opportunity, which gave the rover team a chance to prove that you are not only lucky but very, very good. When Opportunity's wheels dug into a dune, members of the team did their best to replicate the dune's soil conditions by clearing out the stock of swimming pool filter material from several home supply stores in the San Gabriel Valley and trying out various soil combinations in JPL's in-situ instrument lab's sandbox.
"I'm certain that in the history of NASA procurement we've never pulled off that feat before. And I'll bet there is some auditor, somewhere, still scratching head about this one.
"Fortunately, the confidence we gained from operating the test rover in the simulated Martian sand paid off handsomely. Despite wheel slippage exceeding 99 percent several days in a row, the team persevered and gave Opportunity renewed life.
"Because you have kept at your work with unbridled enthusiasm in the past year, we have added to the rovers' already impressive scientific findings concerning the presence of water in Mars' ancient history. Spirit's extended mission has allowed time for the rover to explore the Columbia Hills and find clues to a complex history in the bedrock that included some periods with enough water to alter some of the rocks. Additionally, Spirit was able to capture from the summit of Husband Hill those stunning images of dust devils swirling out on the plains below -- a dramatic vista of an active planet.
"As mission principal investigator Steve Squyres said about Spirit, every time we turn a corner, every time we go over a ridge, it seems like there is something new. All of that diversity, all of those discoveries were really enabled by the extraordinarily long life of the rovers.
"Also with its extended time on the surface, Opportunity was able to reach what appeared to be higher and younger layers at Merdiani Planum that demonstrated a record of alternating wet and dry conditions. As it continues its work, Opportunity is headed for a deeper crater where the layers exposed could extend the geological record to an earlier time.
"In summary, I'm convinced that when the history of the 21st century is written the exploits of the Mars rovers and the team that operated them will be recognized for heralding a great age of exploration and discovery as NASA took the first steps of implementing the Vision for Space Exploration. For this accomplishment, I salute you."
The rover engineers and scientists know that someday Spirit and Opportunity will succumb. No one knows when or how. But losing the craft is something the team thinks about.
"Everybody knows that eventually we will die. They are metal. They are machines. So sooner or later the tool will break," Erickson said.
"Despite the fact that it continues to this day, well in excess of anything we ever expected, it will still be incredibly painful when the two vehicles cease to function," said mechanical systems engineer Chris Voorhees.
"It will be a sad day for all of us when we have to actually let go of these rovers. They have become such a large part of our lives at this point," added Dewell.
"There's going to be quite a period of mourning once we lose one, just one. We know these creatures, these robotic creatures on Mars, pretty well now. It is going to take some digesting to get used to them not being there everyday," said deputy project scientist Albert Haldemann.
"The whole point is keep it running as long as you can, get as much data as you can, using it until it breaks because that is the best thing you can do for it. And when it finally breaks you say 'we did a job, we did a great job, the vehicles helped us do that, let's go celebrate,'" Erickson said.