The $2.5-billion Mars rover Curiosity is suffering wheel damage just two years into its long-term mission, but why and what is NASA going to do about it?

A recent, in-depth post by Emily Lakdawalla for the Planetary Society went into detail about what is going on with the wheels; why NASA didn’t anticipate this problem before the one-ton rover left Earth in 2011; and what the agency plans to do about the issue while the wheels are more than 350 million miles from a repair shop.

While NASA anticipated some wear and tear, what was causing other more concerning punctures and tears, according to Lakdawalla, took some time for NASA to figure out.

Evidence of a damaged wheel. (Image source: NASA/JPL-Caltech/MSSS)

Evidence of a damaged wheel. (Image source: NASA/JPL-Caltech/MSSS)

“Initially, this was a mystery. The mission did expect some damage to the wheels. The wheels acquired dings and scratches over time, but they were relatively unscathed until that first large puncture appeared on sol 411. They didn’t look at the wheels again until sol 463, when a large rip had opened,” she wrote, noting that rover driver Matt Heverly previously said that seeing some damage to the wheels “did not match anything we had seen in our tests. We didn’t know what was causing it. We didn’t know if it was going to continue.”

Further testing — on Earth and on Mars — revealed that tears in the wheels were caused by fatigue near the chevon features, which Lakdawalla wrote were anti-slip measures, while punctures were the result of sharp rocks.

Why hadn’t NASA anticipated the sharp rock issue? Lakdawalla wrote that “no place we’ve ever been on Mars before has these kinds of embedded, pointy rocks.”

An example of the rover encountering a sharp rock that wouldn't move. (Image source: NASA/JPL/MSSS via the Planetary Society)

An example of the rover encountering a sharp rock that wouldn’t move. (Image source: NASA/JPL/MSSS via the Planetary Society)

“There is very hard rock that doesn’t erode away uniformly. And you get ventifacts [wind-eroded pyramidal rocks] that are sharper than we’d like, and that are cemented into the ground. And so when you drive over them, they don’t skitter out of the way, they don’t get pressed into the sand, they just are something that you have to have the wheel go up and over,” Curiosity project manager Jim Erickson told Lakdawalla.

“We misunderstood what Mars was,” Erickson told Lakdawalla.

A technician conducts tests on a wheel like that on Curiosity in a laboratory on Earth. (Image source: NASA/Michelle M. Murphy)

A technician conducts tests on a wheel like that on Curiosity in a laboratory on Earth. (Image source: NASA/Michelle M. Murphy)

Curiosity, he said, was designed for a terrain experienced by the two other Mars rovers, Spirit and Opportunity, which have been on the planet for more than a decade — one is still working while the other lost communication a few years ago. The Gale crater where Curiosity has been collecting data though presented a different problem. 

She wrote that NASA’s later tests on this sharper terrain revealed a wheel could be destroyed within just 8 kilometers on these types of rocks. In order to avoid early burnout, NASA is planning on navigating more carefully around the planet and choosing routes that would put them in contact with naturally softer terrain, among other techniques.

Read more about the damage to Curiosity’s wheels and what NASA plans to do about it in Lakdawalla’s full post.

(H/T: Gizmodo)