NASA is constantly trying to reinvent the wheel, both literally and figuratively. While satellites and probes are exploring undiscovered reaches of space, engineers and scientists are attempting to create the perfect wheel and tire combination down here on Earth. NASA’s latest innovation is based on an idea that has been around for years, the airless tire, but uses shape-memory alloys as radial stiffening elements to maximize the advantages and capabilities. It goes by the uninspired name of Superelastic Tire.
Like many breakthroughs, NASA’s newest development was born from an issue with its previous tire. In the late 2000s, NASA was doing testing for motorhome-size lunar rovers. Back then, the airless spring tires utilized spring steel, and although they worked well, they were vulnerable to plastic deformation or dents when put under heavy loads. A chance visit from materials scientist Santo Padula to the Simulated Lunar Operations (SLOPE) lab at NASA’s Glenn Research Center resulted in a potentially revolutionary merging of technology. Padula suggested using shape-memory alloys in the form of radial stiffeners on the tire instead of spring steel.
The material used for this technology on this tire is an alloy based on stoichiometric nickel titanium. To get technical about it, other material atoms stretch to the point of breaking when taking on the duress of heavy loads. This nickel titanium alloy rearranges at an atomic level and regains its shape once the load is taken off. Hence, memory. According to Padula, this allows for 30 percent more deformation without permanent changes or damage. The memory alloys can take up to 10 percent “reversible strain,” as opposed to 0.3 to 0.5 percent the spring steels or composites are capable of. In prototype form, the tire looks like pliable chain mail.
