The Wheels on Mars Go Round and Round
- Raissa Senoaji
- May 5
- 5 min read
NASA’s Curiosity Rover (2023)
Elon Musk has a lot of work to do if he’s serious about migrating humanity to Mars in the near future. Why? So far, there has been a grand total of zero astronauts who have explored this red planet. The robots and rovers sent on these suicide missions are not doing much better, often breaking down before they even touch down while those that do get to Mars have never returned to Earth in one piece. This is why Martian missions tend to stress engineers out. After all, sending a little robot 225 million kilometres away is no cheap feat. One little mistake, and it’s goodbye to billions of dollars. So, they need to do everything they can to make Mars rovers perfect.
A Mars rover is like a little animal created to explore an intended terrain—it even has its own body, but instead of brains, eyes, and vital organs, it has supercomputers, color cameras, and complex electronics. Consider this, though: What body part would an explorer and adventurer of unknown lands need most? Legs! How else could the rover trek through the iron oxide-filled soils of Mars if not with the best wheels on Earth—or more accurately, in the galaxy?
How do we make the perfect wheel?
According to NASA’s Jet Propulsion Laboratory, roughly 60% of all missions to Mars (by any space agency) fail, and most of the failures were due to technical difficulties related to wheels. Mars has a terrain that is unheard of by humans. It’s dry and rocky, with mountain ranges and dunes bigger than any on Earth. It is also substantially colder, with an average temperature of -46°C, making it clear that our rubber Michelin tires wouldn’t be enough to withstand the conditions on Mars, but this concern has stumped astronomers and engineers since the first Mars rover mission in 1997.
For the vast history of space exploration, rovers would have had aluminium wheels because it was lightweight and durable enough for past missions. But as rovers needed to cover more ground on rougher terrain, it became clear that aluminum wasn’t cutting it. They were outstandingly slow, travelling at a maximum speed of 0.18 kilometers per hour. That’s the average WALKING speed of a giant tortoise. Even then, the force of Mars’s terrain punctured holes into the pure aluminium wheels.
Thus there are strict criteria when it comes to designing these wheels. They need something that can handle extreme pressures and temperatures. Not too thick since heavy wheels would be more expensive to send. Not too thin either, or the wheels can’t endure the pointy rocks on Mars’s mountains. For decades, countries from all over the world have tried to find this ‘Goldilocks’ material for a wheel that’s just right for Martian travel, and in 1959, scientists William J. Buehler and Frederick E. Wang found the next big step to finding it: Nitinol.
What is Nitinol?
Nitinol is a material like no engineer has seen before. It’s an alloy of 45% titanium and 55% nickel, often called a ‘shape memory alloy.’ This means that it can be bent and deformed but still can return to its original shape when heated.
With a normal piece of metal, like a paper clip, applying enough stress or force will permanently bend or even break it because the strain fractures the bonds between the metal atoms. Nitinol, however, behaves differently. Under stress, nitinol undergoes a structural transformation at the atomic level while remaining solid. In other words, rather than cracking or deforming permanently, its internal arrangement shifts, allowing it to be stretched, bent, or compressed like rubber without breaking. Nitinol can endure over ten times the strain of an average steel wire, stretching up to 8% of its length and still snapping back to its original shape when heated. Talk about superelastic!
Originally, it was founded in 1959 in search of a heat and corrosive-resistant alloy, and when it was produced commercially in the 1980s, it was primarily used for biomedical applications. For years, nitinol was used in orthodontic braces, surgical staples, and bone anchors. With how versatile and unique nitinol is, though, engineers have found applications everywhere, including space exploration.
Nitinol wheels?
At high temperatures, nitinol is stiff and springy (which we call the Austenite phase), and at low temperatures, it bends like rubber (the Martensite phase). With just a temperature change, nitinol can switch between these two phases. Luckily for nitinol, temperature change isn’t very hard to find on Mars. This might just be the 'Goldilocks' solution engineers have been searching for. With nitinol, NASA engineers have developed spring tires, essentially a big spring of nitinol in the shape of a circle. It doesn’t take up much space or weight, nor does it need to be pressurized. Most importantly, though, it can be hit by Martian rocks and whatever otherworldly materials on the Red Planet and spring back to its original shape like nothing happened. Simply put, it can act as both rubber tires that we’ve been using on Earth and resilient aluminium tires that can handle wear and tear.
(NASA’s design of Nitinol mesh-wire tires)
Nitinol in the future
Nitinol wheels are set to step foot on Mars in the next Mars rover mission called the Mars Sample-Return Mission, which NASA has called one of their most ambitious multi-mission campaigns. Absolutely everything must be spot-on. If things go right, it could mark the first time we ever gain samples from Mars’s surface. If it goes south, though, billions of dollars from multiple world governments are gone just like that! With such high stakes, it’s no wonder that engineers have been banging their heads with designing the rover. Nitinol has given them a helping hand in this. Apart from wheels, NASA is considering the use of nitinol to build sensors and actuators due to its durability and versatility.
Space exploration is something that we can never be sure will succeed. After all, we’re predicting and designing machines for conditions that we have never seen and don’t know much about. What’s sure is that nitinol has opened the doors to milestones in space exploration that we wouldn’t have thought possible a couple of years ago. The new design of the nitinol mesh wheel is expected to comply with Mars’s unforgiving terrain and could do wonders in getting to know this faraway planet better. We can know so much more about our world and innovate beyond our known limits, all because of a piece of metal, nitinol: one small step for material science, one giant leap for space exploration.
References
b.marcotulli. “Nitinol, the Versatile Metal: From Blood Vessels to Mars.”
Maker Faire Rome, 6 Apr. 2021,
“How Perseverance Drives on Mars - NASA Science.”
Science.nasa.gov, 8 Apr. 2022,
“InSight Landing Press Kit | Home Page.”
Nasa.gov, 2018,
Mamoozadeh, Arsha. THE AEROSPACE APPLICATIONS of NICKEL-TITANIUM as a SUPERELASTIC MATERIAL. 2018.
NASA. “Mars Sample Return - NASA Science.”
Science.nasa.gov, science.nasa.gov/mission/mars-sample-return/.
Williams, Matt. “Mars Compared to Earth.”
Phys.org, 7 Dec. 2015,
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