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." [Amazing Mars Rover Curiosity's Martian Views (Latest Photos)]
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.
Curiosity Rover Wheel Wear Pin It Curiosity rover wheel wear on Mars has become the number-one issue for engineers to cope with and develop work-around strategies for.
Credit: NASA/JPLView full size image
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.
Troublesome caprock
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."
NASA's Curiosity Mars Rover Route
This recent map shows in red the route driven by NASA's Curiosity Mars rover from the "Bradbury Landing" location where it touched down in August 2012 (blue star at upper right) through the 663rd Martian day, or sol, of the rover's work on Mars. The white line shows the planned route ahead to reach "Murray Buttes" (at white star), the chosen access point to destinations on Mount Sharp.
Credit: NASA/JPL-Caltech/Univ. of Arizona/USGSView full size image
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. [NASA's 2020 Mars Rover (Images)]
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.
"Since we first recognized that wheel damage had occurred more rapidly than expected, we have learned to read the terrain," said John Grotzinger, Curiosity project scientist at the California Institute of Technology in Pasadena.
Grotzinger told Space.com that wheel damage is not simply related to driving distance. Rather, it relates more to terrain type.
"The last few months have seen us pull together as scientists and engineers to understand how to avoid the 'briar patches' formed of broken-up fragments of hard sandstone, and drive in the valleys made of softer rock and sometimes partially filled with sand," Grotzinger said.
Can't fathom how boring they've made this mission. About half way now... how long after touchdown?Funny. As I posted the OP, I was thinking/remembering about you and I complaining about how boring the mission was a week from landing.