One paper suggests “shedding” its wheels may save the rover’s ability to move around as intended.
Curiosity is NASA’s fifth rover to roam the red planet, landing on Mars in August of 2012. But within just a year of driving around there were reports of damage to its wheels. As time goes on, the wheels tear due to repeated bending of the metal as they traverse hard rocky surfaces and are punctured by driving over sharp pointed rocks, according to solar system specialist and science communicator Emily Lakdawalla writing for the Planetary Society in 2014.
The pointed rocks weren’t thought to be a problem during testing, but it turns out that, while the wheels can withstand 1/6 of the rover’s weight (one wheel) sitting on a pointed rock, they have trouble withstanding the full weight of the rover pushing the front wheels into pointed rocks. This is why the front wheels are most affected by the punctures while the back wheels are least affected.
Since sending a pit crew out to Mars to give Curiosity a tune up is out of the question, rover operators have had to focus on cautiously driving to avoid pointed rocks and further damage to prolong the integrity of the wheels.
A paper published by NASA’s Jet Propulsion Laboratory (JPL) in March of 2020 provides some insights on what the future of Curiosity’s wheels may hold in a worst-case scenario.
In the paper, titled “Rimmed Wheel Performance on the Mars Science Laboratory Scarecrow Rover,” authors Evan Graser, Sean McGill, Arturo Rankin, and Alex Bielawiec warn that if enough of the grousers (the parts that stick out of the wheel and dig into the sand) break then the wheel could essentially split into two pieces. In this scenario, the rover would be dragging a loose portion of the metal wheels, which could pose a threat to the cabling that runs from the wheels to the rest of the rover.
Graser, et al. propose that strategically shedding 2/3 of the wheel by driving it over a sturdy rock embedded in the ground may be a valid way to mitigate the risks. After all, if that portion of the wheel is broken off completely and left behind on the Martian surface, it will pose no threat to the cabling on the rover. They claim that this shedding will not affect the rover’s ability to drive around.
“Test results indicate that if wheel shedding could be successfully executed in flight, Curiosity could continue to drive indefinitely on rimmed wheels.” — Graser, et al.
Readers are highly encouraged to check out the paper themselves. It includes interesting insights and images about how engineers test ideas regarding Curiosity.
So, could the solution to damaged wheels be as simple as having less wheel? Possibly.