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Press Release Images: Opportunity
In this image Dr. Trebi-Ollennu, a thirty-something man of African descent, stares intently at the extended 'arm' of the test rover.  The arm appears, blurry, in the foreground of the image.  The arm cuts diagonally across the image and the 'wrist,' that houses the RAT and other instruments, is on the far right.
RAT Modifying Its Bite

What once would have taken one sol (or day) is now going to take Opportunity two sols. With age often comes a slower pace and, although JPL engineers have brilliantly figured out a solution to a potentially mission-cramping problem, their "senior" rover must move cautiously to preserve herself.

An encoder on the rock abrasion tool (RAT) is no longer working. The encoder indicates when the grinding teeth have detected a rock surface. However, another of its vital functions - being able to detect stalls - is no longer working. Stalls may indicate a problem for the RAT (for example a surface that is too tough to grind). If the tool stalls and that stall is not detected, the tool will continue to draw a current in an effort to keep moving, threatening to overheat and ruin the instrument.

When you are drilling, say, into a wall, if you hit an obstacle, the drill might jerk and damage the wall or the tool itself. This is a situation engineers are trying to avoid with Opportunity. After all, the rover has many more rocks to examine.

As they have done throughout both rovers' amazing over three-year run, engineers have taken the challenge to the testbed in order to come up with a solution or, in engineer-ease, a "work around."

"We are very fortunate that the encoder failed on the RAT grind motor because it is one of the few motors on the rover that we can safely operate without an encoder," said rover driver and technical lead for the RAT anomaly Dr. Ashitey Trebi-Ollennu. "However, during RAT operations, an abrupt contact of the RAT grinding bit with a rock can cause the RAT grind motor to stall or kick back and result in damage to the IDD, or rover arm. This is a situation we are trying to avoid because the IDD carries two-thirds of the science payload."

Image credit: NASA/JPL-Caltech
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