Robots become master geologists

The $800 million effort by NASA is designed to gather data that could reveal whether Mars ever could have supported life.

Brace yourself, Mars. The alien robots are returning.

Six years ago, a small mechanical rover named Sojourner Truth grabbed international headlines and lucrative toy contracts with its two-week travels over a tiny patch of the Martian surface. Now, NASA is sending a pair of more muscular descendants to the red planet to range farther afield - each with an eye (actually, two pairs of eyes) toward answering the question: Could conditions on Mars ever have supported life?

With six wheels, wing-like solar panels, and two pairs of lenses on a tiltable mount atop a slender mast, the high-tech rovers look like a cross between a horsefly and a toy giraffe. But they are the most sophisticated robots ever sent to explore another world, packed with high-tech tools designed to help Earthbound scientists read the climate history recorded in Martian rocks.

It's a mission that awes even the scientists working on it.

NASA is sending what in effect are two heavily tested prototypes "to a alien environment and an inhospitable one," says Robert Sullivan Jr. of Cornell University, a member of the Mars Exploration Rover (MER) team. "We have to go through outer space to get there. And we're shaking the whole thing up on a rocket launch. It really is amazing that we can even think this is going to work."

That expectation marks a departure from the 1997 Mars Pathfinder mission, scientists say.

"We had very low sights," says Rob Manning, who was chief engineer for Pathfinder. The message then was: "Do the best you can, land on Mars, and do whatever science you can get away with."

Coffee table on wheels?

The new rovers reflect more ambitious objectives. Where Sojourner was the size of a microwave oven, the MERs have been likened to everything from a small golf cart to an oversized coffee table on wheels. Their camera masts can rise to roughly 5 feet above the surface. Designed to operate for at least three months, the rovers tip the scales at 384 pounds each, more than 16 times heavier than Sojourner, which nuzzled "Yogi" and a host of other rocks in 1997.

In addition to the brawn, the rovers also pack plenty of digital smarts.

"These vehicles are the brains of the whole operation," explains Mr. Manning, who has served as spacecraft systems manager for the MER mission at Cal Tech's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. In effect, the rovers' computers control the trip to Mars as well as the cross-country jaunts once they arrive.

Manning notes that the rovers "molt." First, they will shed first their protective covers, or fairings, after launch. They will doff various heat shields, parachutes, braking rockets, and air bags that protect them as they bounce like basketballs to a stop. Finally, they will roll off their landing platforms onto the Martian surface.

The rovers aren't designed to break speed records. Their velocities will be measured in inches per minute - what one colleague has dubbed "a contemplative pace," Manning says. If it travels 30 feet a day, it will have had a good trip, although on a pancake-flat surface "we can haul."

Remote-control geology

Using hazard-avoidance software to get from rock A to rock B, these robo-geologists will perform many of the tasks a human geologist would when visiting a new site, says Dr. Sullivan. Landing in two Martian hemispheres, they will feed data to researchers looking for minerals and other rock types that form in the presence of water.

Two cameras at the top of the mast serve as reconnaissance tools and can glean some initial information about rock types. If ground-based geologists find a rock interesting, the rover activates an arm carrying a special tool to scrape away the outer, weathered layers and expose pristine rock. The rover can take images of the exposed rock with a small camera that acts like a geologist's magnifying glass. Two spectrometers will determine its chemical makeup. The data will be beamed back to Earth via any of two satellites NASA currently has orbiting Mars.

To people back on Earth, this $800 million mission will look much different from Mars Pathfinder. While rover-retrieved images may make the evening news, don't expect to see shots of the rover as it travels across the Martian landscape, since the mission contains no cameras on the landers to view what the rovers are doing. For the Martian's-eye view, Earthlings will have to depend on the folks in JPL's animation department.

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