Mars Rover Steers Into Steep Crater

Sept. 11, 2007 — -- Opportunity, one of the two hardy rovers that have been exploring Mars since 2004, is now beginning what engineers on Earth say could be its final mission.

But after what the rover's been through in the last couple of months, that's a chance that mission managers at NASA's Jet Propulsion Laboratory are willing to take.

Today, they sent commands that will start Opportunity moving down the side of a steep, half-mile crater called Victoria, where exposed rocks may offer clues to what Mars was like millions of years ago, when scientists believe its climate was warmer and wetter.

The mission's managers say there's a bit of a risk that the crater's walls will be so steep the rover will not be able to climb out. But it's been through worse.

Opportunity and its twin, Spirit, which landed on opposite sides of the red planet in 2004, have become symbols of endurance. They were expected to survive the temperature swings on Mars for three months; they've now been going for 43.

In July and August, though, they came very close to dying. A massive dust storm engulfed most of the planet -- bad enough to block 99 percent of the sunlight reaching the surface in many places.

Such storms have been seen before. But to the rovers, which run on solar power, this was serious trouble. The dust was so thick that the rovers were not getting enough power for basic systems, such as heaters to keep internal parts from freezing.

Anxiously, controllers at the Jet Propulsion Lab sent commands for both rovers to turn almost everything off. No roving. No pictures. They even ordered the rovers to suspend their daily radio transmissions back to Earth. Every little bit of power saved mattered.

Opportunity, on a vast plain called Meridiani, was cutting it especially close. In one transmission it reported that with heaters turned down, its inside temperature had dropped, at times, to minus 35 degrees Fahrenheit. If it had dropped to minus 38, emergency heaters would have come on, possibly draining the rover's power system for good.

Scientists say the dust was thick enough that a person standing next to Opportunity would have not been able to see the disk of the sun. What's more, the blowing dust was slowly building up on the solar panels that cover the rover's top deck, meaning that even if the storm eased, the rover might not get enough power to continue functioning.

By early this month, though, NASA said the air was clearing. The rovers had pulled through.

"These rovers are tough. They faced dusty winds, power starvation and other challenges -- and survived," said Alan Stern, NASA's associate administrator for science, in a statement. "Now they are back to doing groundbreaking field work on Mars. These spacecraft are amazing."