Not only designed for Mars missions, this tire may soon be used here on Earth as well.
The harsh environment of Mars rapidly wears down the tires of the Curiosity rover – a one-ton, nuclear-powered robot tasked with exploring the red planet. After just one year of travel at a mere speed of 0.14 mph (0.04 m/s), rocks on Mars had caused several large holes in the rover's tires.
It’s difficult to repair a flat tire on Mars or the Moon. In fact, it's nearly impossible. Therefore, when NASA sends any rover or wheeled exploration vehicle into space, they must ensure the wheels are virtually puncture-proof. And this is where the Superelastic Tire was born.
Developed by NASA for future Moon and Mars missions, the Superelastic Tire could also serve as a viable alternative to traditional pneumatic tires here on Earth.
NASA states, “The use of new shape-memory alloys allows the wheels to withstand high levels of deformation. Unlike conventional elastic materials, these alloys create a tire that can endure extreme deformation without permanent damage.”
NASA created a nearly eternal tire, woven from metal fibers, that “remembers” its optimal shape and can return to it after being deformed by external forces.
The research and design of this special tire took place at NASA’s Glenn Research Center in Cleveland, Ohio. Engineer Colin Creager and his team wove steel springs together to form the tire. It has excellent traction on soft soil and sand, while also being capable of carrying heavy loads. However, there was still one issue.
“We had one problem: the tires always started to dent after some time,” said engineer Creager.
Then he met Santo Padula, a material scientist. Creager was advised to use shape-memory alloys – a type of superelastic metal that can revert to its original shape after deformation.
“From that point on, we started collaborating… to create a new type of tire that we believe could revolutionize the tires used by planetary exploration vehicles and even innovate tires here on Earth,” Creager said excitedly.
Driving in space is as difficult as launching a spacecraft.
NASA has been researching and developing tires suitable for planetary exploration since the 1960s, when the Moon program began. First, there was the Lunar Roving Vehicle (LRV), which was used during Apollo missions 16 and 17. The metal pads on the tires allowed easy movement over the Moon’s surface, which included lunar dust and small pebbles.
But the surface of Mars is much more complex. To travel there, a vehicle must meet a long and complicated list of requirements, such as:
- The tire must traverse all terrains: Mars’ surface includes sand, gravel, sharp rocks, and small pebbles.
- The vehicle must be lightweight: It costs $30,000 to land about half a kilogram on Mars, so the lighter the vehicle, the less it costs.
- The tire must last long: Solar and nuclear power will keep the vehicle operating for many years, even decades.
- It must withstand extreme weather: Ordinary rubber tires cannot survive in a vacuum, where temperatures fluctuate from -129°C to 21°C in a short time.
Curiosity’s tires are 50 cm tall, made of aluminum, and reinforced with metal rings inside and out. The tire surface has V-shaped grooves for better traction, while the spoke-based suspension system helps absorb shocks.
Today, the rover must avoid areas with small pebbles to minimize damage, but the tires still continue to wear down over time.
A new tire emerges.
After many years of research, the team decided to use a nickel-titanium alloy (NiTi). Steel springs can only be stretched 0.3% (the distance between atoms changes) before becoming permanently dented. However, NiTi alloy can stretch up to 10% and still return to its original shape, making it 30 times more elastic than steel springs.
Using shape-memory alloys as a reinforcing component also increases the tire’s load-bearing capacity. The Superelastic Tire provides traction equal to or better than traditional pneumatic tires while eliminating the risk of punctures, improving fuel efficiency, and vehicle safety. Additionally, the design of this tire does not require an inner frame, simplifying and lightening the tire/wheel assembly.
Research results show that this new tire can support more than 10 times the weight Curiosity’s tires can bear. It operates in a temperature range from -130°C to 90°C, grips rocks and sand better, and climbs hills 23% better.
In the most extreme test, over a 10-kilometer course filled with challenging terrain, the tire performed excellently. Currently, NASA is building an ultra-cold testing facility to test the tire under low-temperature conditions.
A long road ahead.
In five years, NASA will launch Mars 2020 – a vehicle similar to Curiosity but heavier. According to Creager, unfortunately, the great tire may not be applicable for Mars 2020 due to time constraints and limited testing opportunities. There's still much testing to be done, and the launch deadline is fast approaching.
Good news for us on Earth: this tire may be applied here as well. The research team is collaborating with Goodyear – an American tire manufacturer founded in 1898 – to apply this tire technology to vehicles that travel on rough, dirt roads.
For now, it may be used in military vehicles designed to operate on rugged, difficult terrain. Creager hopes that this advanced tire technology will eventually be used on vehicles that travel on paved roads as well.
