People have been studying the mysteries of Mars for centuries. The fourth planet from the Sun is reminiscent of a fertile red desert with a rugged surface that is difficult to traverse. Although multiple robotic missions have landed on Mars, NASA has only explored 1% of the Martian surface. Ahead of future human and robotic missions to the Red Planet, NASA recently completed rigorous rover testing on simulated terrain on Mars, using a revolutionary shape developed by the agency's Glenn Research Center in Cleveland in partnership with Goodyear Tire & Rubber Company Memory alloy spring tire technology.

Rovers - mobile robots that explore the surface of the moon or planet - must be equipped with enough tires to adapt to the environment they are exploring. Because the Martian surface is rugged and rocky, durable tires are critical for mobility. Shape memory alloy (SMA) spring tires help achieve this goal.

Shape memory alloys are metals that can return to their original shape after being bent, stretched, heated and cooled. NASA has been using them for decades, but applying this technology to tires is a fairly new concept.

"We at Glenn are one of the world's leaders in providing science and understanding of how to change alloy compositions, how to change the processing of materials, and how to model these systems in a way that we can control and stabilize their behavior" so that they can truly for practical applications,” said Dr. Santo Padula II, NASA Glenn Materials Research Engineer.

Padula and his team had tested SMA in a variety of applications, but his epiphany about the tire's possibilities came about by chance.

As he left the meeting, Padula ran into Colin Creager, a mechanical engineer at NASA Glenn, whom he hadn't seen in years. Krieger used the opportunity to introduce him to the work he does at NASA's Glenn Simulated Lunar Operations (SLOPE) laboratory, which simulates the surfaces of the moon and Mars to help scientists test the rovers' performance. He brought Padula to the lab, where Padula immediately noticed the spring tires. At the time, they were made of steel.

"The moment I saw the tire, I said, 'Don't you have a problem with plasticization?'" Padula said. Plasticization is the irreversible deformation of metal that can cause component damage or failure.

"Colin told me, 'This is the only problem we can't solve.'" Padula continued, "I said, I have your solution. I'm developing a new alloy to solve this problem. That's SMA The birth of tires.”

Since then, Padula, Creager and their team have teamed up to improve NASA's existing spring tires using a game-changing material: nickel-titanium SMA. This metal can adapt to deformation when subjected to extreme stress, allowing the tire to return to its original shape even after severe impact, which is not possible with spring tires made of traditional metals .

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Since then, the research has grown, and in the fall of 2024, NASA Glenn's team traveled to Airbus Defense and Space in Stevenage, England, to test NASA's innovative SMA spring tires. The testing took place at the Airbus Mars Base, an enclosed facility designed to simulate the harsh conditions of the Martian terrain.

"We went out there with the team and we brought the motion tracking system and did different tests on the uphill and downhill," Krieger said. “We did a lot of cross-slope testing on rock and sand, focusing on understanding stability because this is something we’ve never tested before.”

During the tests, researchers monitored the rover as the wheels traveled over rocks, paying close attention to the extent of tire crown movement, any damage, and downhill slides. The team expected there would be slipping and movement, but it was minimal and the test met all expectations. The researchers also gathered insights into the tire's stability, maneuverability and rock-crossing capabilities.

As NASA continues to advance systems for deep space exploration, the agency's Extravehicular Activities and Human Surface Mobility program invited Padula to investigate other ways to improve the performance of the SMA for future Mars rover tires and other potential uses, including in the lunar environment.

"My goal is to expand the operating temperature capabilities of SMA to applications such as tires and to consider applications for these materials in habitat protection," Padula said. "We need new materials suitable for extreme environments that can provide energy absorption for micrometeorite impacts on the Moon, allowing large numbers of astronauts and scientists to work on the Moon and Mars, such as habitat structures."

Researchers say shape memory alloy spring tires are just the beginning.