Mars Rovers Growing Old on the Job

Winter on Mars is a cruel season.

Nights are long. The sun is a shrunken orb, appearing half its size from Earth. With temperatures plunging to a heart-stopping minus 175 degrees, there is little relief from the alien chill.

What lies ahead is even worse: dust storm season, when howling, planet-wide siroccos can claw at the surface and choke the atmosphere.

NASA’s twin rovers, Spirit and Opportunity, have been operating in this brutal environment since they landed on Mars in January.

And it shows.

Solar panels are covered with dust, cutting power by a quarter. Spirit’s right front wheel turned balky, forcing controllers to drive in reverse, dragging the wheel behind like a gangrenous leg. Two temperature sensors on Opportunity are out, and a heater on its extension arm has been stuck in the on position since its January landing.

After notching a series of scientific successes, including finding proof that water once flowed on the Red Planet, the rovers are growing creaky with age.

Rover Project Manager Jim Erickson compares them to “a middle-aged man playing softball who should be in better shape. He’s more susceptible to pulling a muscle.”

Or dropping dead of a heart attack. This month, Spirit was brought to a dead stop by steering problems; luckily, when controllers tried later Spirit responded as if nothing was wrong.

In fact, Jet Propulsion Laboratory scientists have already begun preparing for the inevitable end of the $835-million mission.

“We have two precious assets on Mars that the taxpayers bought,” Erickson said. “The best answer of what to do with them is run them into the ground.”

They’re trying hard, recently ordering the gimpy Spirit into a set of hills with inclines steeper than most ski slopes on Earth.

Intended to last three months, the mission has twice been extended.

Expected to cover just a few hundred yards, the rovers have traveled more than three miles (one mile for Opportunity and 2 1/4 for Spirit).

That’s not the farthest off-world commute. Apollo astronauts piloted a lunar rover nearly 19 miles in the heat of the space race. In 1973, the Soviets remotely drove their Lunakhod 2 robotic rover 23 miles.

But off-roading on Mars is different from cruising the Moon, which at 240,000 miles from Earth is a stone’s throw compared to the minimum distance to Mars of 40 million miles. Communication with the moon takes four seconds. Messages to Mars can take 20 minutes. In that time, a rover could roll off a cliff.

Mission scientists were surprised the rovers have lasted as long as they have, said Rick Welch, a mission manager. “It’s pretty amazing, given their age.”

The glory days of the Mars rover mission have passed. Inside mission control these days, there’s sometimes only a handful of people keeping watch over the rovers -- a far cry from the breakneck pace that swept JPL when the rovers landed nine months ago.

Each week brought new discoveries and news conferences, often accompanied by popping corks and backslaps.

As the rovers disappeared from the front pages, the rover team has been cut in half from a high of 250. Thirteen-hour work days, staggered to start an hour later each day to stay on Mars time, where the day is 40 minutes longer, are no longer de rigueur.

“It was stressful early,” said Chris Leger, one of seven robot drivers, who wore 3D goggles and T-shirts with checkered flags on the back. Compared to those high-energy days, driving time “is pretty short now.”

The rovers were launched in summer 2003 while the nation was still reeling from the loss a few months earlier of the space shuttle Columbia.

Then, as the two rovers and their orbiters closed in on the Red Planet, the European spacecraft, Beagle 2, disappeared while heading for a Mars landing Dec. 24. That solidified Mars’ long record as the place where spacecraft went to die.

As a result, observers and scientists were holding their breath as Spirit descended to the Martian surface Jan. 3. The mission was deceptively simple. To search for evidence that liquid water once flowed on the parched surface of the planet. Although it’s known that stores of water ice are locked up below-ground, it was not clear whether lakes, rivers, or even oceans ever existed. If they did, that would bolster theories that Mars could have sustained life.

From the start, fate smiled on the mission. “Opportunity hit a hole-in-one” on its landing site at Meridiani Planum, a flat plain the size of Oklahoma, Erickson said.

Two months into the planned 90-day mission, Opportunity found the evidence everyone had been awaiting. Mars had flowing water. Charles Elachi, JPL’s director, said the discovery could cause a seismic shift in human perception comparable to when 16th century astronomers determined that the Earth was not the center of the universe.

JPL threw a party. There was more backslapping, and superlatives like “history-making” were tossed around. The primary goal was met.

But Spirit and Opportunity weren’t ready to quit.

They still aren’t.

As the rovers plug along over the forbidding Martian landscape as if out for a leisurely drive, keeping them productive has required scientists to become robot gerontologists.

Spirit and Opportunity have been nagged by small problems since the beginning. First, Spirit had trouble deploying its antenna to face Earth. A piece of the crumpled air bag that had protected it during its landing prevented the rover’s exit ramp from reaching the ground. There were computer problems transmitting data and a heater on Opportunity got stuck in the on position, wasting power.

Although JPL referred to these as hiccups, no problem is minor when you’re driving on another planet.

JPL engineers addressed the glitches one by one.

Sometimes doing nothing is the best solution. After a pebble recently fouled Opportunity’s rock-grinding device, JPL scientists began concocting plans to jar it loose. Instead, it dropped out on its own.

Other problems have been more difficult to solve.

In early July, during Spirit’s two-month trek to the 330-foot-tall Columbia Hills, scientists found a problem in the right front wheel. “It was drawing three times the current of the other wheels,” said Erickson, the project manager. “We were concerned it would fail.”

The culprit was friction. Joe Melko, a systems engineer on the rover project, said only a small amount of lubricant was used in the wheel housings; the weather on Mars is so extreme that extra lubricant would just freeze and gum things up.

Melko wondered if driving the rover in reverse would take some pressure off the bad wheel. After testing the idea with a replica rover at JPL’s Martian test bed, an indoor lab covered in ruddy ground rock, the team decided to apply the strategy on Mars.

It worked.

Just as worrisome was the buildup of dust on the 14-square-foot solar panels. When full, the batteries store 900 watt-hours of power (enough to keep a 100-watt light bulb illuminated for nine hours). Driving the rovers doesn’t use much power. The real energy drain was communicating with Earth. Running the few dozen mini-heaters that keep equipment warm was another high-cost item.

Going into the project, some engineers figured the buildup of dust after a few months would so interfere with the ability of the rovers to recharge their batteries that the rovers would die of power starvation.

As the weeks passed and dust built up, available power fell by as much as 28%. With the Martian winter coming on, the rovers needed more frequent rests.

As the power drained, there was nothing to do but watch and hope.

“You live with it,” Erickson said.

Finally, the power situation seemed to stabilize, with a 25% drain on Spirit and 15% on Opportunity.

Given the age of the rovers and the array of glitches, one might think rover minders would be nursing Spirit and Opportunity into their dotage.

Nope.

Having completed the prime mission, JPL decided there was no reason to coddle its wandering robots.

“We’d gone way, way past what anybody expected us to do,” said Steve Squyres of Cornell University, the principal investigator for the science instruments. “Now we’ve become much more aggressive.”

Managers decided to see what these vehicles could do. With a top speed of 600 feet an hour, the drivers couldn’t leave skid marks, but they found other ways to challenge the equipment.

After its trek to the Columbia Hills, named for the lost shuttle crew, Spirit went rock-climbing. It’s ascended 38 feet, climbing grades as steep as 34 degrees.

Opportunity, now in Endurance Crater, may head for a piece of broken landscape about 3 miles away. Beyond that is the pit of Victoria Crater.

If it makes it that far, “we’ll have a very old, tired rover,” Squyres said.

The rovers have entered a new phase of exploration, in which discoveries are incremental.

In the Columbia Hills, Spirit has found “lots of soft, crumbly rock,” the product of tens of millions of years of weather and water. These rocks are different from the hard rock the rover encountered on the plain, which scientists said meant the warm, wet period was early in Mars’ existence.

“I envision something like salt flats,” Squyres said. “They may have been knee-deep.”

Some of the latest findings, based on analysis of a rock called Escher, have raised the possibility that there could have been two wet periods, at least where Opportunity is working.

As for the nature of the bodies of water, scientists had expected to find chemical carbonates in the rocks. “That was supposed to be the Holy Grail,” Squyres said. “We found instead we were barking up the wrong tree.”

Researchers kept finding rocks rich in sulfates. At first frustrated, the scientists now think the Martian seas could have been moderately acidic.

There are acidic bodies of water on Earth, notably some South American lakes and the Rio Tinto in Spain, a 58-mile-long, ruby-red river that is an other-worldly place all its own.

Squyres cautioned that “it would be a bad idea to swim in the Tinto. But these are environments teeming with life.”

It doesn’t prove life developed on Mars, but “it’s a promising line of research,” Squyres said.

No one is certain how much longer the rovers can survive -- it could be days or years.

The mission got some good news in September when NASA extended funding for another six months. Mission manager Mark Adler said he thought that “as long as we’re rolling we will continue to get funding.”

After all, the twin Voyager spacecraft, now 9 billion miles from the sun, recently passed their 27th anniversaries on their way out of the solar system. Yet 12 people are still employed on the Voyager missions.

That type of longevity is unlikely for the rovers.

NASA’s first rover on Mars, Sojourner, explored the planet for about three months in 1997 before it lost contact with mission control. The problem appeared to be with the spacecraft that landed on Mars and discharged the rover.

The craft mysteriously stopped sending signals to Earth, and Sojourner had no way to communicate on its own.

In case of a serious problem, Sojourner was programmed to drive back to the spacecraft.

As far as anyone knows, it is still waiting there.