Better Tires to Drive on Mars

A future rover on Mars may include shape-shifting capabilities. This innovative tech won’t quite be like the liquid-metal polymorphing robot from “Terminator 2,” but will solve a problem that have plagued previous rovers: wheel wear and tear.

NASA’s Glenn Research Center is now using shape memory alloys (SMA) to build better wheels for driving on Mars.

Engineers at NASA’s Glenn Research Center assemble the new shape memory alloy rover tire prior to testing in the Simulated Lunar Operations Laboratory.
Credits: NASA

“Glenn began working with the U.S. tire industry years ago to develop a better non-pneumatic, or airless, tire for the Moon,” said Vivake Asnani, lead tire engineer at Glenn. “This led to an advanced tire known as the Spring Tire, constructed using a network of steel springs, that adapted and contoured to terrain like a traditional rubber tire.”

Tires made from these shape-shifting materials can “flex” with the terrain. This means the tires would basically adapt to the topography, whether it was rocky, sandy, sloped, or flat. These new types of tires can withstand the brutal, sharp, pointy rocks that have gouged holes in the Curiosity rover’s wheels by enveloping the rocks instead of being punctured by them. NASA Glenn engineers say the shape-shifting tires also provide a smoother ride – almost like adding shock absorbers – which helps minimize potential damage to systems on the rover.

Close-up image of the broken grousers on Curiosity’s left-middle wheel. Credit: NASA/JPL-Caltech/MSSS

Curiosity rover project scientist Ashwin Vasavada said they weren’t expecting to encounter the kind of ‘pointy’ rocks that have damaged the rover’s wheels. Gale Crater – where Curiosity has been roving since it landed in 2012 – has a more rocky and hard terrain than anticipated. Plus, just the physics of how the rover drives has actually created some of the holes and tears, which show up mostly in the front wheels.

“We did some testing and saw how one wheel could push another wheel into a rock, making the damage worse,” Vasavada told me in 2016. “We now drive more carefully and don’t drive as long as we have in the past. We’ve been able to level off the damage to a more acceptable rate.” 

Each of Curiosity’s wheels, as well as the wheels for the Mars 2020 Perseverance rover tire, are machined from a block of flight-grade aluminum and equipped with titanium spokes. Perseverance’s wheels are slightly larger in diameter and narrower than Curiosity’s, with skins that are almost a millimeter thicker. (Curiosity’s are 0.75 millimeters thick.) They also feature new treads, or grousers: In place of Curiosity’s 24 chevron-pattern treads are 48 gently curved ones.

The aluminum wheels of NASA’s Curiosity (left) and Perseverance rovers. Slightly larger in diameter and narrower, 20.7 inches (52.6 centimeters) versus 20 inches (50.8 centimeters), Perseverance’s wheels have twice as many treads, and are gently curved instead of chevron-patterned. Credit: NASA/JPL-Caltech.

Extensive testing in the Mars Yard at NASA’s Jet Propulsion Laboratory has shown these treads better withstand the pressure from sharp rocks and grip just as well or better than Curiosity’s when driving on sand.

Perseverance is now packed up and ready to fly to Mars, with launch scheduled for July 2020. But future rovers could use the new shape-shifting tires to improve a rover’s ability to operate in extremely rocky terrain and at the cold temperatures of Mars. This is appealing to mission planners for future use on Mars because of its lighter weight, traction performance and durability.

“We’re developing a Mars-grade material that greatly improves SMA capability and makes reversible material deformations possible in the harsh Martian environment without sacrificing performance,” said Dr. Santo Padula, lead SMA materials and design engineer at Glenn.

The SMA tires are now undergoing testing at Glenn’s Simulated Lunar Operations Lab. Rigorous tests have proven the tire’s grip meets or exceeds all traction performance demands and will give rover drivers the ability to cross varying terrains.  The more capable tires also allow for a rover design using four tires as opposed to the past six-tire configurations. So, NASA says, in the case of future human exploration or robotic missions, these tires can provide valuable flexibility in the vehicle and spacecraft design.

Not only could this technology be used on Mars, but also for Earth. NASA says a concept SMA passenger tire has been tested, and could eventually replace conventional air-filled tires, eliminating the risk of punctures and driving with under-inflated tires, while improving fuel efficiency and safety.

More info:

NASA Glenn
Perseverance Rover info
Detailed information on Curiosity rover wheel damage by Emily Lakdawalla, The Planetary Society