How NASA Reinvented The Wheel – Shape Memory Alloys

How NASA Reinvented The Wheel – Shape Memory Alloys

This episode of Real Engineering is brought
to you by the Royal Air Force and the Briggs Automotive Company, who are currently holding
an engineering design competition for Young Engineers. One of the moments that will always stand
out in my life is the watching the joy and excitement of the engineers at JPL celebrating
the monumental task they had completed. They had just landed a 900 kilogram rover
the size of a mini cooper on another planet. The Mars rover is bursting at the seams with
engineering innovation. I could detail the insane landing process
and any of the multitude of engineering marvels on board, but today I want to discuss something
you may not have put much thought into. Something we use on earth everyday. Tires. The wheels of the Mars Rover have been one
the biggest technical difficulties encountered on the mission. Accruing substantial damage though the rough
Martian terrain. Surely the engineers at NASA could have predicted
this and designed something better. Well not everything is as simple as it may
and seem. Even on flat hard ground, the rover has a
top speed of just 0.15 kilometres per hour. Yet this snail’s pace still had enough force
to tear holes into the aluminium wheels of the rover. The engineers have some strict criteria that
made the job more difficult. The wheels need to be stiff enough to support
the weight of the rover, at nearly 1 tonne that isn’t an easy task. The wheels need to be as light as possible
to reduce launch costs and must to be able maintain traction and navigate the unpredictable
martian terrain. The current record holder for longest journey
on an extraterrestrial body is held by the Opportunity Rover at 45 kilometres, with the
previous record being the Russian Lunokhod 2, a lunar rover. Curiosity has racked up just 20 kilometres
to date [1]. All Mars rovers have used solid aluminium
wheels. The Sojourner, Opportunity and Spirit rovers
all used the design successfully, but the curiosity rover is much heavier. Each wheel on the Curiosity rover is about
half a metre in diameter and 400 millimeters wide. Milled from a solid block of aluminium in
a similar fashion to the methods described in my Bloodhound SSC video, but unlike the
Bloodhound, the Mars rover wheels are milled down to just 0.75 millimeters thick over the
majority of its circumference. Damage here isn’t all that surprising, 0.75
millimeters thick is the same thickness as a credit card. Running a nearly 1 tonne vehicle over a sharp
rock would be expected to damage aluminium that thick. NASA simply underestimated the roughness of
the terrain, more worryingly though the load bearing threads which are about 6.4 millimeters
thick are also damaged, and if they continue to break the wheels will become useless. The Mars Rover cost 2.5 billion dollars to
develop and it employs a nuclear reactor for power. Extending the life of this project was top
priority for it’s engineers, and so finding a solution to this problem has been fairly
high on NASA’s list for future projects. So what other designs could we use? To reduce the chances of the wheels experiencing
a stress that could damage them we want them to be able to bend and conform to the terrain. This is what our rubber air filled tires do
on earth. Land rovers drive over similarly rough terrain
without any major problem, so why not use tires like this on Mars? Flip down of temperature with suitable image/footage
of Mars. Temperatures on Mars can dip as low as minus
130 degrees celsius. Temperatures this low would transform rubber
from an elastic material capable of absorbing stress to a brittle glass-like material, making
it useless for this application. Rubber would also degrade from the UV radiation
it would be exposed to on the surface of mars. On top of this, weight savings is also top
priority and rubber wheels with thick rubber, steel reinforcement and a rim, are actually
quite heavy. The lunar rover used flexible steel mesh wheels,
with a stiffer inner frame to prevent over deflection and thin strips of metal attached
to prevent the wheel from sinking into the lunar soil. This option was studied for applications on
Mars, but the Lunar Rover had a mass of just 450 kilograms compared to the 900 kilograms
of the Curiosity Rover, combine this with the higher gravity on Mars and it made the
wheel unsuitable for the application. The wheels would simply not be able to hold
the weight of the vehicle without deforming permanently, but Goodyear, who developed the
original Lunar wheel, has been working alongside NASA and in 2010 they were given the R&D 100
award for this spring tyre, which could be the solution to our problems. Being both light, capable of bending and conforming
to the terrain without permanently deforming and capable of holding the weight of a heavier
rover. So what is it’s secret. What makes these spring tyres different to
the ones used on the Lunar Rover. They use a new age material that has some
incredible properties, not just for applications in space, but right here on earth. This spring tyre uses a material called Nitinol. Nitinol is a nickel titanium alloy that has
been named a shape memory alloy, and for good reason. You can bend and deform it, and then just
apply a little bit of heat and it magically returns to its original shape. It remembers its original shape. That is incredible, but nothing is magic in
this world and everything has an explanation. Here is how it works. Typically when a material is stressed one
of two things can happen. If the stress is below it’s yield point,
the material will deform elastically like a rubber band, and return to its original
shape when the stress is released. Alternatively, if the material is stressed
beyond its yield point the material will deform permanently and when the stress is released
the material will be not return to its original shape. So how does this permanent deformation occur? If bonds are not broken, the material should
return to its original preferred crystal lattice orientation, but when sufficient force is
applied small defects in the crystal lattice are able to move. This is what is happening to the wheels of
the Mars Rover. When driving over pointed rocks and gravel
the stress exceeds the yield stress, and thus the wheels are gradually picking up permanent
damage, and eventually cracks will form and the material will fracture. Deformation occurs slightly differently for
Nitinol, as it has some unique properties due to the internal crystal structure. When Nitinol is below a certain temperature
it has a crystal structure called martensite. It’s crystal structure is arranged in such
a way that it can accommodate deformation very easily. Martensitic nitinol forms grains of twinned
atoms where the direction aligns. When stress is applied these twin grains deform
and align to best absorb the stress. Particular twin grains can grow at the expense
of others. This is called detwinning. This, like the dislocation movement in other
metals is permanent, without external energy providing the energy needed to revert backwards,
but Nitinol can get that energy from heat. Upon heating the nitinol forms austenite,
an ordered and regular crystal structure, which effectively resets the crystal structure,
and when the nitinol cools again the nitinol remembers its original shape. What makes nitinol even more amazing and useful,
is that this transformation temperature can be tailored for different applications. In general, increasing the titanium content
of the metal will increase the transformation temperature. This is an incredibly useful property and
it has found many applications across many industries. Let’s say we want the metal to remember
its shape at 37 degrees celsius, body temperature. Can you think of any applications when this
would be useful? I’ll give you one. Traditionally when stents, which are tiny
tubes used to clear blockages in arteries, are being deployed, a small balloon is used
to inflate it and plastically deform the stent into shape. However this often places force on the lining
of the blood vessel, which can damage it and cause it to form scar tissue. Many stent designs now employ nitinol which
has been tailored to remember it’s shape at 37 degrees celsius, and so when unsheathed
it automatically expands into place without placing excessive force on the blood vessel. [7] So how is this useful for the Mars rover? Do we have to apply heat to the metal so it
can recover its shape after running over a particularly big rock? No, luckily nitinol can also be induced into
that martensite to austenite transformation through stress and strain, and so when the
stress passes a threshold it actually causes the crystal lattice to transform to austenite,
and when the stress is released it returns to martensite and the metal recovers its shape. This is called super elasticity and it is
the property that allows these new Mars rover wheels to deform right down to the rim and
still recover its shape after. This combined with the interlocking coil design
allows the tyre to tolerate strains in a way no other tyre could, while surviving the harsh
Martian environment. These tyres could appear in NASA’s designs
for future Mars Rovers, like those planned for launch in 2020. It’s easy to think something as simple as
a wheel will never be reinvented, but there are always ideas and opportunities for people
willing to put the work into thinking about them. That’s why I have teamed up with the Royal
Air Force and the Briggs Automotive Company to bring you an exciting design competition
for Young Engineers. We want you to brainstorm designs for a new
Mars Transport Vehicle that improves on previous designs in some way. We want your most innovative and creative
ideas. Think from the ground up, what problems will
Mars rovers encounter, have you ever thought about how we communicate with a vehicle on
another planet. The top prize winner will have their idea
developed and made into a 3D model by the Briggs Automotive Company. They’ll also win work experience at the
pioneering BAC factory in Liverpool that produces the world’s only road legal single-seater
supercar. For more information head over to the STARRSHIP
YouTube Channel, a link for that is on screen now. As always thanks for watching and thank you
to all my Patreon supporters. If you would like to see more from me the
links to my instagram, twitter, subreddit and discord server are below.

About the Author: Michael Flood


  1. – RealEngineering:
    So what other uses can we give to this material?"
    – Sex toy and dildo companies:

  2. Elon needs to launch Starship to Mars, unload a supercharger, unload a Tesla, make software to autonomously drive itself.

  3. The old man's spares were tires in the academic sense. They were round…..once made of rubber. Ralphie from The Christmas Story.

  4. What prevents the accumulation of dirt and rocks inside the tire? It seems like it wouldn't take long before it would be full of debris that would increase the weight, and start to wear at the metal fibers (getting wedged into the gaps, and preventing the fibers from elastically reshaping). I assumed the Curiosity's tires were open-sided to allow this kind of debris to simply 'roll out'…

  5. Hi very interesting channel. 8:59 I was thinking if you would changhe the position of the exhaust in front of the supercar also you need to modify the shape to a wide cone somehow that when the car is running at high speeds the hot gases mixes with the air that is in friction with the body of the car and somehow to improve the out come in speed? Can you rap your head arround this idea? Include aspects of thermodynamics in your imagination:d

  6. Please with the Bullshit. Start with whom keeps the solar panels clean. This shit is no where near Mars. NASA never a straight answer.

  7. A wheel is a circular object around a central axle, and is not be reinvented. A tire is a type of wheel used to bare a load and provide mobility, and tires get reinvented all the time.

  8. Why not make a rover that can hover to avoid some obstacle along the way .. just like a drone with wheels 😊✌🏻

  9. I only wonder howmuch taxpayers money they wasted on reinventing metal sponge into a wheel. What a dumbass invention for I believe only 5,000,000,000,000.99 if not more us dollars. Just like using pen vs pencil in space which wasnt even done directly by nasa. Totally wasted money in the air, just like fireworks or tomahawk missiles. And some people still support this, with grace and pride. Why care about 3rd world countries and their problems, those are their problems afterall. I'd say, first worry about the earth and once you got all done fixed down here, only then fuck yourself up to the moon, mars or wherever the shit ya want.
    EDIT: Cakeportal, agreed. And those funds come from nasa, get it? Carlos didnt think deep in the irony of my comment… Yeah, maybe I should be thankful to nasa for having food on the table every day, only thanks to them. Or is it that they come up with their stupid ideas realized thanks to all of ours pockets? You tell me mr. Righteous.
    You do know that GPS is a triangulation system right? Because you dont seem so intelligent yourself claiming gps works thanks to satellites. lol seriously. Do you even know what all information the cell towers contain and distribute? Calling half century used weather balloons = satellites, really dawg? REALLY?

  10. What about the possibly better aerospike rocket engines what are the true material difficulties we are facing to get these engine online as operational devices.


  12. I'm sure th ORKZ at NAZI did NOT INVENT ANYTHNG ITZ all stolen INTEL from some1 ELZE we WILL SOON dismantle NAZI az they did NOT hav PERMISSION 2 conduct any of thoze testz they hav been a part of ABORT program AT ONCE!!!

  13. According to a information first wheel was invented in sindh Pakistan mohenjodaro and also world first swimming pool and world first WC you can see on google that what is mohenjodaro is 2500 bce old

  14. Design a mars rover… Fine. I have a design. It's a crewed mobile base, so it's a little bigger than a rover. It doesn't need wheels, as it uses electromagnetic repulsion. It "lands" on legs when it's powered down. It's powered by a matter-antimatter reactor and has a top speed of 560kmh and can "fly" as high as 80 meters. It's armor is also photovoltaic, so it can generate power during the daytime, or radiate heat, should temperatures rise too much.The cockpit is similar to that of a helicopter. Keeping the thing operational at all times is a Virtual intelligence system. There is no way one pilot could control all of the repulsors, so the VI handles that and aids the pilot via a system that links with their brain. System comes from military spaceships. The vehicle is half the size of a football field and it even has armaments should they be needed. It also has a force field to limit radiation and minimize damage.

    Now I need a genius to invent all the nonsense I described and a bunch of other geniuses to put the damn thing together.

    On a serious note, that's a lot of stuff to think about when designing a wheel and memory metals seem like the best option.

  15. There is NOT a nuclear reactor on Curiosity. It's an RTG or Radio-thermal Generator. It generates electricity thermo-electrically from the heat of decaying plutonium.

  16. The casual certainty of the thinking behind the phrase "nothing is magic in this world" (well, that's how it comes across to me) is a good example of someone who knows nothing at all about how much he doesn't know.

  17. Gentle Reminder: The dry MASS of the rover is 899kg/1982lb; however, the WEIGHT, on Mars, is 38% of that, or 341kg/752 lbs. Still substantial, but not nearly a ton.

  18. Make a rock analyzer where it can analyze the rocks through away ones that have been found before and keep ones that have not and if we colonize mars then we can get the rocks from the rovers for further analyzation.

  19. The curiosity rover wheel is not the problem the problem is the rover is to slow that means the wheel have alot of friction from the ground keep the rover moving

  20. Arkadaşlar bir sorum var
    Bu youtuberlar video yaparken videoları ve fotorafları nereden buluyorlar
    Nereden indiriyorlar???

  21. Add leg instead of Wheel's put AI and 5 G to the autonomous legs and put feet that mimic a chicken so it can't stuck when pull up with sensors under the feets Add also to AI then steer it

  22. The saying "Don't invent the wheel…" is only a partial one.
    "Don't invent the wheel when traveling the beaten path.".
    … I'd say a completely different planet calls for a little tinkering. :3

  23. Considering curiosity has gone more than 7 years past it’s predicted lifespan, I’d say they did a pretty good job on the wheels

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