By Leonard David
If there were mechanics on Mars, NASA may have taken the Curiosity rover into the shop by now.
The 1-ton robot has accumulated quite a bit of wheel damage since touching down inside Gale Crater in August 2012 to investigate Mars’ past and present potential to host microbial life.
“They are taking damage. That’s the surprise we got back at the end of last year,” said Jim Erickson, Curiosity project manager at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “We always expected we would get some holes in the wheels as we drove. It’s just the magnitude of what we’re seeing that was the surprise.”
But the damage has not imperiled the rover’s mission, said Curiosity’s handlers, who are employing a number of troubleshooting measures to keep the robot rolling along. They’re confident Curiosity can still reach and explore its ultimate science destination: the foothills of the 3.4-mile-high (5.5 kilometers) Mount Sharp.
Bumps and bruises
Each of Curiosity’s six aluminum wheels is independently actuated and geared, built for climbing in soft sand and rolling over rocks. However, engineers eyeing rover-snapped imagery have been taken aback by the amount of wear and tear on the wheels.
This damage comes in several forms. For example, there are punctures in the wheel skin between what are called “grousers” — traction bars that take on the form of a zigzag pattern on the wheels. Grousers help improve wheel performance and provide a better grip on the Martian terrain, rover team members said.
“We are getting punctures through there. After a while, those punctures can begin getting cracks from the puncture in different directions,” Erickson told Space.com. The entire skin between two grousers could get punched out if there are enough cracks on both sides, he added.
The damage isn’t identical from wheel to wheel. The two front wheels have worn differently than the two middle wheels, Erickson said.
It turns out that the tough-as-nails culprit playing havoc with Curiosity’s wheels is “caprock,” which is quite resistant to weathering and erosion.
“To the extent possible, we’re trying to avoid that particular kind of rock,” Erickson said. “Overall, we’re learning how to pick our poison … how to get to the right paths that are going to minimize — I repeat, minimize, not eliminate — the damage we’re going to get to the wheels. We have never encountered this kind of hard, embedded rock on Mars before.”
Lessons learned from the Curiosity wheel anxiety are expected to influence the design of NASA’s next Mars rover, which is scheduled to launch in 2020.
Choosing a path forward
Erickson told Space.com that the mission team is carefully picking Curiosity’s path forward, aided by images snapped by NASA’s sharp-eyed Mars Reconnaissance Orbiter.
“We’re looking for places that have a thin covering of sand,” he said. “If we have to drive on rock, we’re looking for areas that have softer rock types than what we’ve seen.”
This process has motivated the rover team to get better acquainted with the Martian landscape.