Rover Finds Way To Brush Rock Surfaces Despite Setbacks

Grind testing will continue next week using a rock abrasion tool with new grind bits on a surrogate rover on Earth in preparation for grinding new targets on Smith.

by Staff Writers

Pasadena CA (JPL) Nov 15, 2007

Opportunity is still parked in front of the rock layer known as "Smith" inside Victoria Crater. The rover has now lost two encoders that operate motors on the rock abrasion tool during the grinding and brushing of surfaces. Science team members and engineers have been working in test beds and computer sequencing rooms to devise creative ways of using the rock abrasion tool without the grind and revolve encoders.

On sol 1347 (Oct. 7, 2007), they achieved their goal when Opportunity successfully completed a new, seek-scan procedure. Using this technique, the rover locates a rock surface by simultaneously spinning its grind teeth and wire brush while also extending toward the rock surface.

Normally, the rock abrasion tool software monitors the safe operation of the grind or brush using the two encoders, which detect stalls that can occur during grinding and encoding. In the event of a stall, the encoders measure the z-axis position (the point where the rock abrasion tool contacts the rock surface). Without the encoders, engineers must rely on current limits and contact switches to know when grind teeth come into contact with a rock surface.

Opportunity followed a command to run both the grind and revolve motors along with a parallel command to move in toward the rock surface. When the rock abrasion tool made contact with the surface, contact switches disengaged, ending the activity. The following day, sol 1348 (Oct. 8,

2007) , the science team directed the rover to retract the rock abrasion tool 1 millimeter and brush the surface. The brushing proceeded as planned!

Grind testing will continue next week using a rock abrasion tool with new grind bits on a surrogate rover on Earth in preparation for grinding new targets on Smith.

Opportunity is also scheduled to test communications next week with NASA's Mars Reconnaissance Orbiter. This test, along with other tests conducted recently with the European Space Agency's Mars Express orbiter, are demonstrations of the capability to conduct UHF communications in preparation for next year's arrival of the Phoenix lander.

Opportunity's solar array energy has been approximately 670 watt-hours (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour) per sol with atmospheric dust opacity, known as tau, of 0.87.

Full report here:

http://www.marsdaily.com/reports/Rover_Finds_Way_To_Brush_Rock_Surfaces_Despite_Setbacks_999.html