Flat tires are frustrating for anyone, but they're especially frustrating for NASA. After all, if a rover or a vehicle breaks down on an extraterrestrial surface, you can't call AAA.
This has been an issue for NASA. Earlier this year, cracks were detected in the Mars Curiosity rover's left middle wheel. The rover's wheel are solid aluminum with thick threads and grousers, so while they can take some wear and tear, the cracks form after only traveling 10 miles over the Martian surface. That's well within NASA's expectations for the rover, but it's a reminder of why the space agency has been working on a way to make better wheels.
And now the agency may have a solution that could be the future of tires in space — and possibly on Earth.
An armored tire
That tire is the Shape Memory Alloy (SMA) tire. It's essentially a chain mail tire made up of stoichiometric nickel titanium, an alloy that remembers its original shape after it has rolled over something.
Scientists at NASA's Glenn Research Center were working on tires for the new rover, what one researcher described as "lunar Winnebago-type" rover. The scientists, in partnership with Goodyear, developed what are called "spring tires" back in 2009. These are airless tires composed of hundreds of coiled steel wires woven into a flexible mesh. The result was a tire that delivered good traction and durability.
The issue with the steel spring tires, however, is that they got dented upon repeated use and under heavier loads. Obviously it was a good tire, but the material itself wasn't the right match, especially for the heavier loads and rough terrain. A chance meeting between NASA engineer Colin Creager, who had been working on the spring tire, and a material scientist, Santo Padula, changed the conversation. Creager invited Padula to the lab, and Padula immediately identified the issue Creager was having with the tires. More importantly, Padula also had the solution: shape memory alloys, specifically nickel titanium.
Unlike other materials, like the steel springs used for the earlier models, the atomic bonds of the nickel titanium don't break apart as they're stressed by wear and tear. Instead, the nickel titanium can rearrange its molecules to "accommodate deformation," according to Padula. Indeed, as you can see in the video below, the SMA tire can be pressed all the way to the axle and keep its shape.
New tires for new (and old?) worlds
This SMA tire isn't quite ready for Martian prime time yet, but that's the goal. Such a durable tire would allow rovers to explore even more areas, including some extremely rough and rocky surfaces. Given their strength, the SMA tires could also allow rovers to carry heavier loads, and that means more equipment for analyzing samples and conducting other experiments. Finally, these tires could also be used on manned vehicles and could move at much higher speeds than current tires and rovers can.
And if you read "manned vehicles" and thought to yourself, "Wait, could I get these tires for my car?" the answer is "No." Currently, there aren't any plans to release the tires onto Earth roads, but NASA researchers have developed a SMA tire that fits on cars and trucks. It looks pretty impressive when rolling over dirt and rocks:
Of course, plenty of NASA inventions that started off as space-age feats of engineering we now use every day, including freeze-dried foods, invisible braces and, fittingly enough, memory foam. So maybe we'll see some version of these airless and armored tires on the highway one day in the future.