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NASA's Opportunity rover is still around to celebrate Friday's 10th anniversary of its landing on Mars mostly due to the skill of the engineers and scientists who built it and are guiding it to this day — but some of the credit has to go to the Red Planet's winds.
Those strong winds are a big reason why a solar-powered robot that was expected to last only 90 Martian days has been able to keep going since the night of Jan. 24-25, 2004, project manager John Callas said.
The engineers learned during the 1997 Mars Pathfinder mission that dust could accumulate on the solar panels, gradually reducing the amount of electricity that could be generated. That factored into the design of Opportunity as well as its twin, the Spirit rover, which landed on Mars three weeks earlier.
"We sized the arrays to give us enough power to last 90 days," Callas explained during a Thursday news briefing at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "What we didn't expect was that the wind would blow the dust off the arrays. In fact, we all thought that the wind wouldn't blow the dust off the arrays, because it might cling electrostatically to the surfaces. So this has been a tremendous benefit."
It turned out that Spirit and Opportunity kept going, and going, and going. Spirit was finally done in when it got stuck in a sand trap in 2009 and couldn't position its solar arrays to soak up power during the Martian winter that followed. But Opportunity is still plugging along, despite a gimpy wheel, an arthritic robotic arm and a couple of scientific instruments that have gone on the fritz.
Just this week, the Opportunity science team reported fresh geological evidence suggesting that Mars might have been quite livable for hundreds of millions of years. And earlier this month, the 10-year-old model stole the show from Curiosity, NASA's bigger and newer Mars rover, by coming across a mysterious rock that looks like a jelly doughnut.
During Thursday's news conference, actor William Shatner of "Star Trek" fame asked in a tweet whether the doughnut-shaped rock was thrown into Opportunity's field of view by aliens. "I think Martian rock throwers are unlikely, but we'll keep our eyes open for that," Cornell astronomer Steve Squyres, who's been the mission's principal investigator since the beginning, quipped in reply. (Squyres and other scientists suspect that one of Opportunity's wheels flipped the rock over.)
Opportunity's firstsThere's much more to Opportunity's record than a jelly doughnut: When it bounced to the surface in 2004, cushioned by airbags, it had the good luck to roll right into a shallow crater that served as its first geological laboratory. The rover was the first to come up with evidence that parts of Mars were once covered with standing water. It was the first to find the bizarre-looking "Martian blueberries" that have provided further clues about the planet's warmer, wetter past.
During the years that followed, Opportunity made epic treks across a plain called Meridiani Planum to survey Mars' layered bedrock — first at the 430-foot-wide (130-meter-wide) Endurance Crater, then at the half-mile-wide (800-meter-wide) Victoria Crater, and then at the 14-mile-wide (22-kilometer-wide) Endeavour Crater. Along the way, it came across several meteorites and a whirling dust devil.
Today, Opportunity is hunkered down for the Martian winter at a spot named Cook Haven, along Endeavour Crater's rim. Yes, it's covered with a layer of dust, but Callas said the solar arrays can still hit 60 percent of their electricity-generating capacity, which is an improvement over the past two Martian winters. The rover's flash memory suffers an occasional "amnesia event," but Callas said that so far the fault is "just an operational annoyance."
What next?Once springtime brings more daylight to Opportunity's locale, the rover's control team at JPL plans to send it heading up a rise called Murray Ridge. "We are going to ascend this ridge, we hope, all the way to its summit," Squyres said. He estimated that the trip could take a year or two, depending on whether the rover lasts that long.
"What are we going to see? We don't know. We'll find out when we get there," Squyres said.
A decade ago, $800 million was budgeted for Opportunity and Spirit to get to Mars and conduct their 90-day primary mission. Since then, the rover mission has been repeatedly extended. Callas said NASA's current funding level for the Opportunity mission is $14 million a year. NASA managers are to rule on another extension during a senior review meeting this spring.
Opportunity's team members hope NASA will keep the project going as long as the rover keeps going. "We're getting a good return on investment on this vehicle," said Ray Arvidson, a planetary scientist at Washington University in St. Louis who is the mission's deputy principal investigator.
Callas said the most important measuring stick for Opportunity's performance is "not how long the rover has lasted, or even how far it's driven, but the amount of scientific exploration it has accomplished at that time."
And there's yet another measure to consider: How much does it change our perspective, to know that a machine made on Earth has been at work on another planet for 10 years? Callas argued that Opportunity's mere presence on Mars has made all of us more than mere Earthlings.
"We have become Martians, too," Callas said. "Dual citizens, as it were."
Opportunity by the numbers:
- In 10 years, the rover has traveled 24.07 miles (38.73 kilometers), or roughly the distance between Denver and Boulder, Colo.
- About 187,000 raw images have been sent back to Earth.
- Opportunity transmitted 32.7 gigabytes of data as of the end of 2013, which would take up half of the memory available on the most expensive iPhone. More than 93 percent of Opportunity's data was relayed to Earth by NASA's Mars Odyssey orbiter.
- Opportunity's solar panels are currently generating about 350 watt-hours of electricity per day, which is only enough to keep a 15-watt light bulb lit continuously. The rover needs 180 watt-hours per day for basic survival and communication. Peak power generation was 900 watt-hours per day.
- The steepest slope that Opportunity has tackled had a 31-degree tilt, which is steeper than the most hazardous stretch of road going up Hawaii's Mauna Kea volcano.
For still more about the 10th anniversary, check out the "MER10" presentation on the Jet Propulsion Laboratory's website.