Why can't traditional rubber tires be used on the Moon or Mars?

Rubber becomes brittle at the extreme low temperatures experienced in space and can degrade under vacuum conditions. The lack of atmospheric pressure also prevents pneumatic tires from functioning correctly.

How does NiTi alloy remember its shape?

NiTi undergoes a solid-state phase transformation between Austenite and Martensite. When heated above a certain temperature, the atoms rearrange back to their original 'parent' shape, a property known as the shape memory effect.

What are the benefits of airless tires made from NiTi?

Airless NiTi tires eliminate the risk of flats, do not require inflation, can operate in extreme temperatures, offer improved fuel efficiency, and can provide integrated shock absorption, simplifying vehicle design.

How is the shape memory temperature of NiTi adjusted?

The transition temperature at which NiTi changes between its Austenite and Martensite phases can be precisely tuned by altering the ratio of nickel to titanium and through specific heat treatments.

What are some non-space applications of shape memory alloys?

Shape memory alloys are used in medical stents, self-deploying aircraft components like vortex generators and flaps, actuators, and potentially in elasto-caloric cooling systems.

What does 'superelasticity' mean for NiTi?

Superelasticity in NiTi refers to its ability to undergo large deformations (up to 8% strain) and spring back to its original shape, not because it's in the elastic regime, but due to a stress-induced phase transformation it undergoes and reverses.

Key Moments

How NASA Reinvented The Wheel

Veritasium

Education3 min read26 min video

Apr 29, 2023|17,351,809 views|256,643|8,107

veritasium science physics

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Key Moments

TL;DR

NASA reinvents the wheel with a shape memory alloy, creating indestructible, airless tires for space and Earth.

Key Insights

NASA is developing novel airless tires using shape memory alloys (SMAs) like Nitinol for extreme environments like Mars.

Traditional pneumatic tires fail on other planets due to extreme temperatures and lack of atmospheric pressure.

Metal mesh tires, used in early rovers, suffered from plastic deformation and wear, limiting mission durability.

Shape Memory Alloys possess superelasticity, allowing them to stretch significantly (up to 8%) and return to their original shape.

Nitinol can also exhibit a 'shape memory effect,' returning to a pre-set shape when heated, useful for actuators and self-deploying structures.

These advanced tires offer enhanced durability, fuel efficiency, and can even act as integrated suspension systems for vehicles.

THE CHALLENGE OF EXTRATERRESTRIAL WHEELS

Exploring planets like Mars and the Moon presents unique challenges for wheel design. The absence of atmospheric pressure means traditional pneumatic tires would essentially explode, while extreme temperature fluctuations (from over 250°F in sunlight to below -250°F in shadow) can make rubber brittle or cause it to permanently deform. Early rovers used solid aluminum wheels, but these are heavy and prone to damage from aggressive terrain, leading to cracks and reduced operational efficiency. The need for lightweight, durable, and flexible wheels capable of withstanding harsh conditions necessitates unconventional solutions.

INTRODUCING SHAPE MEMORY ALLOYS (SMAS)

NASA's innovative approach leverages Shape Memory Alloys (SMAs), particularly Nitinol (Nickel-Titanium). Discovered serendipitously, Nitinol can undergo a reversible solid-state phase change. In its 'austenite' phase, atoms are in a specific cubic lattice structure. Upon cooling, it transforms into 'martensite,' a less symmetrical arrangement. This martensite phase allows the material to be deformed significantly without breaking atomic bonds or causing permanent plastic deformation. When heated back to the austenite phase, the atoms return to their original positions, restoring the material's 'memory' shape.

SUPERELASTICITY: THE KEY TO DURABILITY

Beyond the shape memory effect, SMAs like Nitinol exhibit 'superelasticity' or 'pseudoelasticity.' This property allows the material to undergo substantial strain—up to 8%—and return to its original shape upon removal of stress, even without a significant temperature change. This is not true elasticity but rather a stress-induced phase transformation between austenite and martensite. This remarkable flexibility means the material can absorb impacts and conform to terrain without permanent damage, a crucial capability for navigating rugged extraterrestrial surfaces.

FROM SCIENCE TO APPLICATION: THE AIRLESS TIRE

These unique properties of SMAs are being applied to create revolutionary airless tires. Instead of air pressure, these tires utilize a structure made of woven Nitinol springs. This design eliminates the risk of flats and ensures consistent performance, as there's no need to maintain air pressure. The resulting tires are not only incredibly resilient to punctures and impacts but also possess integrated shock absorption capabilities due to the material's ability to deform and dissipate energy.

ADVANTAGES FOR SPACE EXPLORATION

The airless SMA tires offer significant advantages for space missions. Their inherent toughness means they can withstand the abrasive Martian regolith and extreme temperature swings without degradation. The superelasticity allows them to absorb impacts from rocks and uneven terrain, protecting the vehicle's structure. Furthermore, by integrating load-bearing elements with the tire structure itself, these wheels can act as advanced suspension systems, simplifying vehicle design and enhancing mobility across challenging planetary surfaces.

EARTHBOUND APPLICATIONS AND FUTURE POTENTIAL

The benefits of SMA technology extend beyond space exploration. These airless tires are being considered for terrestrial applications, including aircraft and rugged off-road vehicles. For aircraft, they eliminate the need for high-pressure tires prone to explosion and reduce maintenance related to air pressure checks. On vehicles like Jeeps, they promise improved fuel economy by eliminating underinflation and the risk of flats. The ability of SMAs to generate force upon heating also opens possibilities for actuators, replacing hydraulic systems in everything from aircraft flaps to medical devices.

Mentioned in This Episode

●Supplements

●Products

●Companies

●Organizations

●Concepts

Shape Memory Alloy (NiTi) Properties and Applications

Practical takeaways from this episode

Do This

Utilize NiTi's shape memory effect for self-deploying or self-stowing mechanisms (e.g., aircraft vortex generators, flaps).

Leverage superelasticity for durable, airless tires that can withstand significant deformation without permanent damage.

Consider NiTi for applications requiring high forces or precise actuation when heated.

Explore elastocaloric effects for cooling and heat pumping applications.

Use NiTi in medical devices like stents that require precise expansion.

Consider NiTi for load-bearing structures in harsh environments due to its strength and flexibility.

Avoid This

Do not rely on rubber pneumatic tires in extreme temperatures (hot or cold) or vacuum environments.

Avoid using conventional metals for components requiring large elastic deformation, as they risk plastic deformation or fracture.

Do not assume simple mechanical designs are insufficient; a woven slinky can form a functional airless tire.

Avoid designs with potential stress concentration points in wheels intended for aggressive terrain.

Do not overlook non-aerospace products that may share precision engineering principles (e.g., razors from aerospace shops).

Common Questions

Nickel-Titanium (NiTi) alloy exhibits superelasticity, allowing it to deform significantly (up to 8%) and return to its original shape repeatedly without permanent damage. This makes it ideal for durable, airless tires that can withstand extreme conditions.

Topics

Shape Memory Alloy NiTi Nickel-titanium Airless Tires Mars Rover Superelasticity Mechatronics Stents

Mentioned in this video

conceptShape memory alloy

Materials like NiTi that can return to a predetermined shape after being deformed, due to solid-state phase changes.

productHenson AL13 razor

A specific razor model from Henson Shaving, highlighted for its aerospace-grade precision, durability, and cost-effectiveness compared to conventional razors.

conceptTwinned Martensite phase

A lower symmetry, 'messier' arrangement of atoms in NiTi alloys formed upon cooling from the Austenite phase, allowing for deformation without breaking atomic bonds.

productApollo Lunar Roving Vehicle (LRV)

The electric vehicle used by astronauts on the Moon during the Apollo missions, featuring mesh wheels designed to minimize sinking into the lunar surface.

conceptAustenite phase

A high-temperature phase of NiTi alloys where atoms are arranged in a cubic lattice, which can transform into Martensite upon cooling and revert upon heating.

supplementNickel-Titanium (NiTi)

A shape memory alloy composed of nickel and titanium, discovered at the Naval Ordnance Laboratory, known for its ability to return to a predetermined shape after deformation.

organizationNaval Ordnance Laboratory

The institution where NiTi (Nickel-Titanium) alloy was discovered during experiments with different alloys.

productSlinky

A coiled spring toy used as a structural component in airless bicycle tires, demonstrating the potential of simple designs in advanced applications.

product737 aircraft

A commercial aircraft model where shape memory alloys have been demonstrated to operate wing flaps, potentially replacing hydraulic systems.

conceptElastocalorics

A field that utilizes the transformation properties of materials like NiTi to perform heat pumping and cooling effects.

companyHenson Shaving

The sponsor of the video, an aerospace-derived company producing durable, high-precision razors, presented as an example of long-lasting products.

productJeep

A vehicle that has been tested with airless tires, showcasing potential terrestrial applications for the technology by improving fuel economy and eliminating flats.

conceptDetwinned Martensite phase

The crystal structure of NiTi that results from applying stress to the twinned Martensite phase, enabling significant deformation.

productVortex generators

Small fins on aircraft wings that create turbulence to keep airflow attached, improving performance during takeoff and landing. Shape memory alloys can be used to make them stowable.

productCuriosity Rover

A Mars rover developed by NASA, for which aluminum wheels were machined. Its wheel issues highlight the need for more durable materials.

conceptSuper elasticity

A property of NiTi alloys, often misnomered, allowing them to undergo large strains (e.g., 6-8%) and return to their original shape due to stress-induced phase changes.