Twin Rovers Defy Death to Continue Exploring Mars

PASADENA, Calif. — It looked like the beginning of the end for poor Spirit.

Trapped in sand in an area of Mars named Tartarus after an underworld dungeon in Greek mythology, the golf-cart-sized NASA exploratory rover was dangerously low on power and crippled by a dragging, useless wheel.

With the brutal Martian winter quickly approaching, Spirit faced almost certain doom if it couldn't get free and find a safe haven.

Here on Earth, at NASA's Jet Propulsion Laboratory near Pasadena, mission manager John Callas was noticeably worried.

"For Spirit, this could very well be the worst situation she has ever experienced," he said with the tone of a worried father.

Then, after several days of erratically moving mere inches, the rover broke free of Tartarus on Nov. 28 and started rolling feebly toward a protective rocky area known as Winter Haven 3.

And so went another week in what could well be NASA's most surprisingly successful space exploration mission ever.

When NASA's twin Mars rovers, Spirit and Opportunity, landed on opposite sides of Mars in January 2004 as part of a $820 million mission, they were programmed to wander the Red Planet for only 90 days, examining rocks and craters and searching for water.

Nearly four years later, the two rovers are miraculously still hard at work — although they're increasingly showing signs of age and wear.

Spirit has dragged its broken wheel since March 2006, and its solar panels are so obscured with thick Martian dust that they're only about 45 percent effective. It could use a new set of teeth, too. The ones on its rock-grinding tool have worn down to nubs.

Opportunity's robotic arm freezes up sometimes like an arthritic shoulder or elbow. A rock abrasion tool on the arm was accidentally bent and doesn't work like it's supposed to.

The rovers haven't covered that much ground, only about 12 miles in all. But they've made some revolutionary discoveries.

Back in 2004, Opportunity did indeed find evidence of past Martian water, essential to life as we know it.

Spirit recorded "dust devils" forming and moving, helping scientists understand better how Mars' atmosphere and surface interact. That's something that could be valuable for future robot — and possibly human — landings on Mars.

Both rovers found metallic meteorites on Mars, providing new clues about aging and weather conditions on the planet and the thickness of its atmosphere.

And together, the rovers also beamed back more than 100,000 photographs of the planet's surface and sky.

On Monday, at a scientific conference in San Francisco, Callas and other project leaders will give an update on the rovers and present the newest scientific findings.

It's hard finding anybody who knows about the rovers who isn't impressed with their longevity.

"Everyone has got to be surprised ... that these things are still going," said Mark Lemmon, a Texas A&M University professor who is part of a team of scientists studying the rovers' findings. "There were many of us who were thinking we could be working on Mars for maybe a year or so, ... but here we are now almost four years later."

In October, NASA associate administrator Alan Stern announced the agency was extending the rover mission another two years. He called the six-wheeled rolling science labs "amazing machines (that) continue to produce amazing scientific results operating far beyond their design life."

The extension will cost $20 million for the current fiscal year. It was the fifth extension of the program; NASA has spent about $106 million on previous extensions, pushing the total cost to near $1 billion.

Barry Goldstein, who was involved with the Mars rover project since the start and previously served as its deputy manager, attributed the surprising longevity of rovers to good engineering, some unexpected circumstances on Mars and simple good luck.

The motors on the rovers, for instance, have lasted substantially longer than they were designed to. If the rovers were cars, they'd have the equivalent of 800,000 miles on engines that were supposed to give out after 100,000 miles.

The biggest factor in the rovers' longevity, though, may be the surprises of the Martian atmosphere. While researchers fully expected dust to accumulate and obscure the rovers' power-supplying solar panels, they didn't anticipate the strength of Martian windstorms.

Those winds create what NASA calls "cleaning events" that blow some of the dust off the solar panels. As a result, the panels have continued to generate electricity long after researchers thought they'd be too dust-caked to do any good.

The rovers' longevity, in fact, has resulted in some unique problems.

Since they were expected to perform for only 90 days, NASA had to reprogram the rovers' internal clocks to avoid something like a Y2K computer problem.

Along with software updates, NASA engineers have attempted remote hardware fixes too, the most recent one a failed attempt to fix the broken rock abrasion tool on Opportunity.

"It's sort of like taking care of a vintage car when they don't even make any parts for it any more," said Callas.

Callas's office here is adorned with pictures of old locomotives, the sailing ship "Endurance" that Sir Ernest Shackleton piloted on his 1914 Antarctic expedition, and of course the rovers.

Though Callas fully expects to oversee the project until the rovers finally quit working, many of his original teammates, including Goldstein and Texas A&M's Lemmon, are transitioning into the next NASA mission, which is designed to land the next remote laboratory on Mars.

NASA launched a "scout" robot called Phoenix last August, and it now is almost halfway to Mars. When it lands near the planet's north pole in late May, it will drill into the permafrost and analyze the water and ice it brings up for signs of life.

Many scientists here say they fully expect the perky rovers to still be running when Phoenix lands — and long after.

"We'll have three spacecraft working on Mars at the same time for the first time ever," said Lemmon. "It's very exciting."

Callas has quit trying to guess just how much longer the rovers will survive.

It's not something he necessarily enjoys thinking about. As with others at NASA, Spirit and Opportunity have become like children to Callas, who is otherwise childless.

When they do quit working, "it will be like losing a family member," he said.

ROVER, ROVER

A look at NASA's twin Mars rovers

Dimensions: About 5 feet long by 5 feet high by 7 1/2 feet wide.

Weight: 384 pounds (on Earth)

Propulsion/suspension: Solar-powered six-wheel drive; "rocker bogie" suspension able to tilt 45 degrees without overturning.

Equipment: Robotic arm with rock abrasion tools. Spectrometers for analyzing rocks and soil. A microscope/camera. Panoramic cameras for data collection and navigation. Magnet array for collecting airborne dust.

Control chip: A radiation-hardened version of the PowerPC chip used in earlier models of Macintosh computers.

SPIRIT

Launched: June 10, 2003

Landed on Mars: Jan. 3, 2004

Current location/mission: Recently broke free after getting stuck in a sandy area named Tartarus, and moving as fast as it can to sheltered spot called Winter Haven 3 to protect itself from the coming Martian winter.

Status: If it doesn't make it to Winter Haven 3 by the end of the year, scientists fear it will be lost. Spirit is in the worse shape of the two rovers. One of its six wheels is broken and dragging like a broken foot. Its solar panels are so obscured by dust that they're only about 45 percent effective, so it can move for only 30 to 40 minutes per day. Spirit has traveled nearly five miles since landing.

OPPORTUNITY

Launched: July 7, 2003

Landed on Mars: Jan. 24, 2004

Current location/mission: Exploring rock and other features in a feature area called Victoria Crater before it heads off to its winter shelter.

Status: Opportunity is also battling age-related problems. Its robotic arm keeps stalling. Its rock abrasion tool was accidentally bent. Its solar panels are working better than Spirit's and it has traveled more than seven miles since landing.

Source: NASA

On the Web:

Mars mission: marsrovers.nasa.gov