Rover takes a bite out of rock in the name of science
BY JUSTIN RAY
Posted: February 7, 2004
Its two diamond-tipped teeth gnawing at 3,000 revolutions per minute, the Mars rover Spirit has bore a hole in Adirondack, providing scientists a window inside the volcanic rock.
"It is a great day for robotics and planetary exploration," Stephen Gorevan of Honeybee Robotics, lead scientist for the drilling device, told reporters during a teleconference Saturday.
The grinding occurred on the patch of Adirondack that was brushed free of dust a day earlier using bristles on the RAT.
After the RAT was placed on the rock Friday, engineers awaited word from Spirit. But a communications session with the rover flooded Mission Control with error messages. A software bug had cropped up.
"It is associated with how we set the particular currents for the motors that drive the RAT. It just happens under certain circumstances the software decides to complain on a fairly rapid basis. The problem is that crowds out the other telemetry and data we are looking for in the downlink," mission manager Matt Wallace said.
"We were worried, but it turns out everything was fine," Gorevan said.
In a later data relay session, Spirit uplinked the news of a successful RAT'ing to the orbiting Mars Odyssey spacecraft for transmission to anxious controllers on Earth.
"We learned that we had indeed succeeded," Gorevan said. "This is an encounter with an unstructured environment all of these millions of miles away from the Earth and it was an incredible achievement. We had no idea what the strength of the rock was yet we put a nice, full circle hole in a rock on Mars for the first time."
The hole carved is 2.7 millimeters (0.1 inch) deep and 45.5 millimeters (1.8 inches) diameter.
"A lot of people asked me 'did we expected to go deeper?' All I can say is I won the pool," Gorevan joked. "It was just about right where I expected. It was very clearly a strong rock; it gave us a lot of resistance. That's why we needed at least three hours to go this deep."
The drilled area on Adirondack was slightly angled and had a few depressions. As a result, the RAT didn't affect a few areas within the grinding circle.
"When you see the image, it almost looks like a Pac Man. By that I mean it looks like it has a mouth and eye," Gorevan said, noting that those parts sit below the 2.7 millimeters.
The grinding process had several steps as Gorevan explained.
"First, the RAT is placed on the rock and if it is properly placed, switches get triggered indicating proper placement. We had to wait for a signal on the ground to show that was OK. Then we sent up essentially a 'go' to execute the rest of the sequence.
"What happens next is what we call a seek-scan. The RAT actually seeks the highest peaks in the target area, finds them and grinds them down one by one until it has achieved a full circular cut.
"And then the last 10 minutes is reserved for a cleaning operation because we produce an awful lot of cuttings. You will see them in the image on the rim. This is a 10-minute brushing by two brushes of the excavation so that we have a nice, clean surface for the MI, APXS and Mossbauer.
"I would bet, I can't prove it, but from our ground tests it's so clean that if you licked your finger, wiped it, you wouldn't see anything on your finger from the bottom of that excavation."
The RAT tools are unlike any device operated on Mars before. Both Spirit and Opportunity have RATs to strip away the weathered surfaces of rocks. The rovers are exploring the Red Planet to find evidence of past water on Mars.
"The Rock Abrasion Tool is a very sophisticated tool...It has three motors on it. We are able to grind very slowly and detect peaks in a micro sense, shave them down until we achieved a full circle," Gorevan said.
"Two little diamond heads moving at 3,000 rpm just sweep along that surface, cutting layer upon layer. If you gave us three hours, we'll cut in small layers, we'll make progress after a while. That's why we only got 2.7 millimeters. On a strong rock, we want to cut thin layers. That's the way we set the parameters."
After finishing the RAT'ing, the Mossbauer Spectrometer was placed into the hole to look for iron-bearing minerals. The rover was slated to switch instruments overnight so the Alpha Particle X-Ray Spectrometer could collect elemental composition measurements.
During the next workday at Gusev Crater, which begins Saturday afternoon (U.S. time), Spirit was scheduled to take microscopic images. Then the arm would be stowed so Spirit could drive in reverse from the pyramid-shaped rock, leaving a spot the rover has been sitting for a couple of weeks.
"The plan is to back away from the Adirondack after we finish the Microscopic Imager and instrument arm work, take a Pancam of the RAT hole and then Mini-TES of Adirondack as well," Wallace said.
Spirit was then headed for another rock nicknamed White Boat.
Upcoming for Spirit, the rover will begin the long trek to an impact crater in the distance. The first day of the trip to Bonneville Crater will extend 20 meters, setting a new Martian driving record by eclipsing the mark set by Mars Pathfinder's rover in 1997, Wallace said.
"Sojourner's longest drive was about seven meters."
The Opportunity rover on the other side of Mars, its workdays separated from Spirit's by 12 hours, continues to function successfully. The sol 14 day that ended late Saturday morning (U.S. time) saw the rover's arm study a patch of soil before Opportunity made another small drive.
"We completed that drive and the post-drive imagery indicated the targets were within the work volume of the arm."
On the sol 15 day that begins early Sunday morning (U.S time), the arm will be deployed again to snap several Microscopic Imager pictures of Snout and then place Mossbauer down on the rock. Late in the day, the Alpha Particle X-Ray Spectrometer will take over, performing an overnight observation.
Early Monday morning, the arm will be retracted so Opportunity can begin an arcing drive around the lower edge of the outcrop to survey several points, Wallace said.
"The science team is deciding how many 'bus stops' we want to hit along the way. I think the number is varying anywhere between three to six-or-seven. The total traverse distance is on the order of 30 meters. If we hit five'ish spots, we are looking at five or six meters per drive."
NASA has approved an extended mission for the Mars Exploration Rovers, handing them up to five months of overtime assignments as they finish their three-month prime mission.
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