By Staff Writer Jerri Clewis
One of the arguably more annoying things about driving is the occasional flat tire. It is an easy enough fix to swap out tires or get some air, but it is a different story in space when no one is around to change an all-important rover tire. That was one of the problems NASA had to solve to carry out space exploration in uncrewed missions.
NASA engineers had to find a way to create self-sufficient tires that could handle unknown terrain on the moon and, decades later, on Mars. Tire development at NASA began as far back as the 1960s during preparations for the Apollo missions. During that development, NASA and international researchers introduced three significant wheel designs suitable for planetary exploration.
The first development was the Russian rover, Lunokhod (Moon Walker). According to NASA, Lunokhod 1 landed on the moon in 1970 as part of the uncrewed Luna 17 mission and was the first successful rover to explore another world. The Lunokhod model had eight wheels, each made of rigid rim wire mesh, bicycle-type spokes, and metal cleats for traction.
While the Luna missions were making history, NASA introduced the American Modularized Equipment Transporter (MET). The MET was a two-wheeled unpowered, hand-pulled cart that used smooth rubber tires supported by nitrogen filled inner-tubes. The tires, which looked like inflatable tires without tread, were designed by Goodyear for use in the 1971 Apollo 14 mission.
The third development was the Lunar Roving Vehicle, which served in Apollo missions 15, 16, and 17 during 1971-1972. The Lunar Roving Vehicle tires looked more like traditional tires than the previous models. The rover model had four large flexible wire mesh wheels with stiff inner frames to prevent over-deflection.
Decades after the Apollo missions ended, NASA’s Glenn Research Center partnered with Goodyear to develop a new airless compliant tire known as the “Spring Tire.” The Spring Tire, designed in the mid-2000s, consisted of several hundred coiled steel wires woven into a flexible mesh, allowing the tire to support high loads while conforming to the terrain. NASA engineers planned for these tires to provide better functionality for the next generation of moon rovers. Still, a twist of fate led to a very different planet.
The Mars Curiosity Rover sustained significant wheel damage in 2013, just a little over a year since it landed, which NASA attributed to the harsh terrain of the planet. The problem inspired NASA Glenn engineers to reimagine and repurpose the Spring Tire for Mars exploration, which resulted in new prototypes designed to improve traction in soft sand, improve durability, and reduce overall weight.
The prototypes performed well, but the steel wires deformed when rolling over simulated Martian terrain at NASA’s Jet Propulsion Laboratory (JPL). Later, Engineer Colin Creager and Materials Scientist Santo Padula discovered they could use nickel titanium, a shape memory alloy, to create tires capable of flexing with the terrain while enveloping rocks without risk of puncture. The resulting creation looked and behaved like a traditional rubber tire, but with more robust viability against the rocky terrain and cold temperatures of Mars.