Robotics Trends Feature

Rovers on a Roll

Whatever happened to NASA’s intrepid little rovers on Mars?

Before news organizations virtually lost track of them last spring—turning their collective attention to the presidential race for the rest of the year—the mobile robots known as Spirit and Opportunity seemed to be performing admirably.

Not least of all by landing safely and soundly at their respective targets on Mars after traveling 283 million miles from Earth.

For a while, the rovers’ daily accomplishments made headlines around the world, as first Spirit touched down on Jan. 4, then Opportunity arrived three weeks later on the opposite side of the planet. Both vehicles sent back a stunning array of photographic postcards.

Among them were images showing that a portion of Mars used to be covered in water—a condition necessary to sustain life—which thoroughly thrilled the scientists who received the pictures at the NASA Jet Propulsion Laboratory in Pasadena, Calif.

“The rovers have been phenomenal,” says mission science manager John Callas, who’ll deliver a free public lecture on the subject this evening at the University of Alaska Anchorage. “And they continue to be. ... They’re performing very well.”

Which might come as news to anyone who hasn’t been following the rovers’ most recent progress that closely. It would be easy to assume that their mission had already concluded—as it was supposed to have in April.

By late March, Opportunity had already confirmed that a significant body of salty water once flowed over a broad Martian plain known as the Meridiani Planum, and Spirit had found a separate indication of water inside volcanic rocks in a depression called Gusev Crater.

The discovery by Opportunity was especially exciting, Callas says.

“Wherever the rover has driven at that site, we’ve found that water has influenced the formation of geology.”

Moving slowly and deliberately on six wheels attached to six spindly legs while stopping frequently to stare intently at rocks, the rover Opportunity hasn’t even traveled a mile so far. So Callas and the other scientists don’t know yet if what they’re looking at is the remnant of a small lake, a broad river or even a giant sea.

“As the rover goes further, we’re finding continuing evidence of water—and this body of water grows larger and larger,” he says.

Since the rovers are powered by solar panels and fuel isn’t an issue, NASA administrators decided in late April to extend their mission for six months, allowing Spirit to creep its way overland on a two-mile journey to the Columbia Hills. Then in September they decided to extend the mission for another six months.

But that might be wishful thinking. Spirit and Opportunity are beginning to show their age, NASA engineers say. Moving metal parts eventually wear out, especially on a planet as cold as Mars, which is about 50 percent farther from the sun than Earth is.

Daytime temperatures on Mars sometimes rise above freezing, but all the heat escapes during the night (due to the thin atmosphere), resulting in a daily temperature differential of about 180 degrees—roughly the equivalent of a noontime temperature of 60 degrees on Earth falling to minus 120 degrees at night.

“That’s every day,” Callas says. “That kind of normal stress fatigues components. It’s almost like the rovers could have a massive stroke at any time. There’s no way of predicting it.”

On its recent journey into the hills, Spirit’s right front wheel finally succumbed to damage by friction, so the rover controllers turned it around and began driving it in a reverse gear, which allowed it to proceed with its damaged wheel dragging.

What do they expect to find?

“We don’t know what we’ll find next—that’s the nature of the explorer,” says Callas, who oversees about 200 rover geologists and planetary scientists in JPL headquarters at the California Institute of Technology.

The rover mission is unique for NASA, Callas says, since a lot of the decisions on what to explore next are made on an impromptu basis determined almost hourly by what they’ve just seen, sometimes with the help of a spectrometer or a microscope attached to the rover’s robotic arm.

“The scientists may decide, ‘OK, let’s stay at this rock. It’s interesting and there’s some other measurements we want to do.’ Or they may say, ‘No, there’s an interesting geologic (feature) that’s four meters away. Why don’t we drive over there and take some measurements?’ “

Over the past two months, Callas says, the rovers have managed to survive the Martian winter as well as a two-week shutdown while Mars slipped behind the edge of the sun and radio transmissions to Earth became unreliable. Full operations resumed when Mars re-emerged. Then in late October, NASA scientists celebrated the reception of the 50,000th picture transmitted by the rovers.

For Opportunity, the plan calls for it to leave Endurance Crater, motor over to the lander’s heat shield to make some observations for the engineering crew, then proceed south toward Victoria Crater, which is about five times larger than Endurance.

Spirit, meanwhile, will continue to explore the Columbia Hills, possibly reaching their 100-meter summit, which would allow a 360-degree view that might result in some of the best photographs yet.

“The hills are interesting because they’re much older geologically than the surrounding material,” Callas says. “From there, we’re looking at traversing down the back side (of Victoria). As long as these rovers are healthy, we can continue to go further.”

Of course, NASA’s exploration of Mars will continue long after the Spirit and Opportunity rovers finally roll to a stop.

The space agency is planning to launch another Mars orbiter next year, Callas says. In 2007, a scout mission called Phoenix will land at a far-northern latitude near the Martian ice sheet.

In 2009, a rover mission equipped with vehicles large enough to carry more instrumentation and travel farther than Spirit and Opportunity will pick up where the present mission ends.

Copyright 2004 Anchorage Daily News

Copyright © 2002 LexisNexis, a division of Reed Elsevier Inc.