[meteorite-list] NASA's Mars Rovers Roll Into Martian Winter

[Ron Baalke]

Donald Savage
Headquarters, Washington                 July 16, 2004
(Phone: 202/358-1727) 

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/354-4673)

RELEASE: 04-227

NASA'S MARS ROVERS ROLL INTO MARTIAN WINTER

     As winter approaches on Mars, NASA's Opportunity rover 
continues to inch deeper into the stadium-sized crater dubbed 
"Endurance." On the other side of the planet, the Spirit 
rover found an intriguing patch of rock outcrop while 
preparing to climb up the "Columbia Hills" backward. This 
unusual approach to driving is part of a creative plan to 
accommodate Spirit's aging front wheel.

Spirit, with an odometer reading of over 3.5 kilometers (2.2 
miles), has already traveled six times its designed capacity. 
Its right front wheel has been experiencing increased 
internal resistance, and recent efforts to mitigate the 
problem by redistributing the wheel's lubricant through rest 
and heating have been only partially successful.

To cope with the condition, rover planners have devised a 
roundabout strategy. They will drive the rover backward on 
five wheels, rotating the sixth wheel only sparingly to 
ensure its availability for demanding terrain. "Driving may 
take us a little bit longer because it is like dragging an 
anchor," said Joe Melko, a rover engineer at NASA's Jet 
Propulsion Laboratory (JPL), Pasadena, Calif. "However, this 
approach will allow us to continue doing science much longer 
than we ever thought possible," he said.

On Thursday, July 15, Spirit successfully drove 8 meters (26 
feet) north along the base of the Columbia Hills backward, 
dragging its faulty wheel. The wheel was activated about 10 
percent of the time to surmount obstacles and to pull the 
rover out of trenches dug by the immobile wheel.

Along the way, Spirit drove over what scientists have been 
hoping to find in the hills -- a slab of rock outcrop that 
may represent some of the oldest rocks observed in the 
mission so far. Spirit will continue to drive north, where it 
likely will encounter more outcrop. Ultimately, the rover 
will drive east and hike up the hills backward using all six 
wheels.

"A few months ago, we weren't sure if we'd make it to the 
hills, and now here we are preparing to drive up into them," 
said Dr. Matt Golombek, a rover science-team member from JPL. 
"It's very exciting," he added.

For the past month, the Spirit rover has been parked near 
several hematite-containing rocks, including "Pot of Gold," 
conducting science studies and undergoing a long-distance 
"tuneup" for its right front wheel.

Driving with the wheel disabled means that corrections might 
have to be made to the rover's steering if it veers off its 
planned path. This limits Spirit's accuracy, but rover 
planners working at JPL's rover test bed have come up with 
some creative commands that allow the rover to auto-correct 
itself to a limited degree.

As Spirit prepares to climb upward, Opportunity is rolling 
downward. Probing increasingly deep layers of bedrock lining 
the walls of Endurance Crater at Meridiani Planum, the rover 
has observed a puzzling increase in the amount of chlorine. 
Data from Opportunity's alpha particle X-ray spectrometer 
show that chlorine is the only element that dramatically 
rises with deepening layers, leaving scientists to wonder how 
it got there. "We do not know yet which element is bound to 
the chlorine," said Dr. Jutta Zipfel, a rover science-team 
member from the Max Planck Institute for Chemistry, Mainz, 
Germany.

Opportunity will roll down even farther into the crater in 
the next few days to see if this trend continues. It also 
will investigate a row of sharp, teeth-like features dubbed 
"razorback," which may have formed when fluid flowed through 
cracks, depositing hard minerals. Scientists hope the new 
data will help put together the pieces of Meridiani's 
mysterious and watery past. "Razorback may tell us more about 
the history of water at Endurance Crater," said Dr. Jack 
Farmer, a rover science-team member from Arizona State 
University, Phoenix.

Rover planners are also preparing for the coming Martian 
winter, which peaks in mid-September.  Dwindling daily 
sunshine means the rovers will have less solar power and take 
longer to recharge. Periods of rest and "deep sleep" will 
allow the rovers to keep working through the winter at lower 
activity levels. Orienting the rovers' solar panels toward 
the north will also elevate power supplies. "The rovers might 
work a little bit every day, or a little bit more every other 
day. We will see how things go and remain flexible," said Jim 
Erickson, project manager for the Mars Exploration Rover 
mission at JPL.

JPL, a division of the California Institute of Technology in 
Pasadena, manages the Mars Exploration Rover project for 
NASA's Office of Space Science, Washington.

Images and additional information about the project are 
available on the Internet at: 
http://marsrovers.jpl.nasa.gov 
and 
http://athena.cornell.edu.

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