NASA scientists were concerned when the harsh terrain on Mars took a toll on the tires of their Curiosity rover. But nickel-titanium shape memory alloys held the key to indestructible space roving, so NASA applied it to their space-grade tires and managed to reinvent the wheel in the process. Matmatch.com explores uncharted territory.
NASA began producing tires suitable for space travel in the 1960’s since the conventional air-filled varieties used on Earth were not appropriate in orbit. Design breakthroughs over the decades that followed led to successful lunar roving with mesh wheels and Martian roving with off-planet wheels. But the original steel spring wheels used for lunar roving deform over time, and the wheels developed for the Mars Curiosity rover are also showing signs of significant wear and tear due to the unforeseen rough terrain. So NASA Glenn Research Center diligently continued to research the design of impermeable tires for future space travel.
The metal spring wheels used on the Lunar Roving Vehicle still have many favourable properties. Further engineering work performed by Vivake Asnani in collaboration with Goodyear soon resulted in an airless “Spring Tire” consisting of spring steel wires, coiled and woven into a malleable mesh form to facilitate terrain conformity. This tire was indeed suitable for travel over soft sand and rocks, but testing revealed similar problems with deformation as experienced on the Lunar Roving Vehicle years earlier.
Now, NASA has taken the Spring Tire concept and applied brand new materials technology, with a view to reduce weight, eliminate deformation and increase durability and traction in sandy environments. Engineer Colin Creager and materials scientist Santo Padula collaborated to find the solution. Padula suggested using a shape memory alloy (SMA). This rare nickel-titanium alloy has a unique characteristic – it can rearrange itself atomically to accommodate the terrain and then recover its original shape, even when significant opposing forces are applied all the way to the axel. Such a pressure simply results in a stretching and subsequent shortening of bonds. Additionally, as no air means no punctures, these new tires are almost completely indestructible.
So far, the lab testing performed on the shape memory alloy tire has yielded impressive results, including several kilometres of lab roving without any signs of wear. The next step of the testing process will involve a cryogenic chamber that reconstructs Martian temperature extremes. The future looks bright for NASA’s airless nickel-titanium SMA tires – in addition to their work in outer space, we might also expect to see them fitted on Earthly vehicles in the military or even the passenger sectors in the future.
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