Exploration requires mobility. And whether you’re on Earth or as far away as the Moon or Mars, you need good tires to get your vehicle from one place to another. Tire development for space exploration has been a focus of research at NASA Glenn for a decade. Evolving since the days of Apollo, NASA engineers started examining tire designs back in the 1960's for use on the surface of the Moon.
The Mars Curiosity rover has been a big success, but NASA's modern tech couldn't save its tires from breaking down in the harsh conditions of Mars. For future missions, the agency has gone back to the age of knights. Based on the principles of chainmail armor, the "Superelastic" tires can withstand more deformation than any other non-pneumatic tire. At the same time, they could potentially withstand extraplanetary abuse and provide better traction for next-generation rovers.
So, why are shape memory alloys the key to success for this new generation of spring tires? It has to do with the atomic structure. Take a look to find out.
A great deal of time and energy is put into designing the instruments and cameras that go to Mars on rovers, but none of those will do any good if the vehicle is dead in the sand after a few weeks. After all, it’s a few million miles to the nearest mechanic. That’s why NASA engineers are designing a new generation of rover wheels that can cope with the rugged terrain of the red planet. The newly unveiled shape memory tire uses innovative design and advanced material for increased survivability in harsh environments.
NASA’s current Mars rover, the famed Curiosity, was designed with six aluminum wheels, each milled from a solid block of metal. Engineers decided on that design to make sure the wheels didn’t change shape over time. However, aluminum is inflexible, and the Martian surface is a bit more pointy than anyone expected. As a result, NASA began to notice punctures and dents in the wheels after just a year of operation on Mars.
Curiosity has been a real trooper on Mars, logging more distance than any other rover and far exceeding the expectations of NASA. That’s thanks not only to solid engineering but an abundance of caution as well. Mission operators take care to avoid obstacles that could damage the wheels further — even a single mistake could render a wheel useless. NASA knew it needed a new generation of rover wheel, and that’s where the spring tire came in.
NASA initially worked with Goodyear in the mid-2000s to develop a prototype spring tire. These tires were composed of a flexible mesh with hundreds of coiled steel wires. It gave the tires the ability to support heavy loads with good traction, but even the strongest steel springs deform. On Mars, rolling over rocks while carrying a heavy loadout of instruments would cause the steel to change shape over time.
The answer was a new material based on a stoichiometric nickel-titanium alloy. Like regular spring tires, there’s no air inside. It’s just a lattice of coiled metal that flexes as it rolls over obstacles. That means it won’t get punctured by sharp Martian rocks. The bonds in the nickel-titanium alloy can rearrange in response to stress instead of stretching, so the tire snaps back — no deformation.
The game changing material that dramatically advanced the development of spring tires was nickel titanium, a shape memory alloy with amazing capabilities as explained by Santo Padula.
NASA plans to use shape memory tires on future Mars rovers, possibly even on the upcoming 2020 rover that will take over for Curiosity in the next few years. It’s even possible we could see this design on Earth-based tires one day.