- The Washington Times - Monday, January 3, 2005

The six-wheel Spirit rover celebrated its first anniversary on Mars yesterday. The golf cart-size rover was designed with a goal to last at least 90 Martian days and has exceeded that almost fourfold.

“I’m amazed. I thought we were going to last longer than 90 days,” said Mars scientist Steve Squyres. “I would have told you if we can get down safely down on the surface that we’ll last not 90 days but 120, 150, maybe on the outside 180.”

A Martian day is about 41 minutes longer than an Earth day, so its actual Martian anniversary won’t be for awhile.

Project manager Jim Erickson said Spirit, and its sister rover, Opportunity, have sent back 62,000 images, as well as other scientific data, and that the rovers “are in great shape for their age.”

Opportunity, which landed several weeks after Spirit, is in even better shape than Spirit, Mr. Squyres said

“Opportunity looks like she just came off the showroom floor,” he said.

Apparently, wind blew the dust off of its solar arrays, so it’s generating almost as much power as when it arrived on Mars three weeks after Spirit.

The big question is how long can Spirit and Opportunity last? A random failure could doom a rover without warning.

“What we try to do is plan for hundreds of sols [Martian days] of operation, but on each sol we drive it like there’s no tomorrow,” Mr. Erickson said. “As long as we have them we’re going to use them to the best of our abilities.”

The known limitation is the amount of dust that collects on the solar arrays. That reduces the amount of power that can be generated. Spirit’s arrays generate about 500 watts of power, enough to operate a small microwave oven.

In September, Mars was at its farthest point from the sun and in its winter, generating far less power. Many days had to be spent recharging batteries instead of collecting science data or moving to new locations. But now with the Martian spring, there’s more power.

Mr. Squyres said dust buildup eventually could doom the crafts.

“Dust is inherently unpredictable,” he said, but “it’s possible a well-timed gust could clear the dust off of the solar arrays and restore them to full power.”

Mechanically, there’s no one thing which could go bad and permanently disable a rover. For example, if a motor operating one of the six wheels goes bad, it could drag the bad wheel. Even if the motor that turns the mast around goes bad, the engineers could compensate by turning the entire rover.

On the other hand, there are many electrical parts that could go bad and instantly doom a rover.

“We have a lot of electrical components in that if they failed, we’re just done — you’d never see it coming,” Mr. Squyres said.

One of the most unpredictable factors affecting the rovers’ future is NASA’s budget. Many working spacecraft have been shut off because of a lack of funds. The relative cost of continuing to operate the rovers is much cheaper than the cost of building the spacecraft and getting it to Mars — about $3 million per month.

“So far, NASA’s been very cooperative in providing our funding, and every indication I’ve had is they’ll continue to do so,” Mr. Squyres said.

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