NASA reimagined the wheel by using Shape Memory Alloys: Nitinol

 Space missions have always been a challenge for humanity. Launching a rocket from the earth and carrying out the mission safely is no easy task. But as technology is advancing, we are getting more closer to exploring different planets. We first went to the moon, carried out manned as well as unmanned missions successfully and now, the whole world has its focus on Mars as the next celestial body to visit. With speculations suggesting that the earth will become unfit for living in the coming centuries, Mars is being seen as the second home for humanity. But of course, setting up human settlements on Mars is not that easy. A large amount of research needs to be done regarding the atmosphere, the weather conditions, availability of water and oxygen, and many other aspects of survival. So, NASA and other space agencies are using unmanned rovers to study all the necessary conditions on Mars. NASA has launched Curiosity, Opportunity to study Mars.

These rovers used Aluminium tyres for manoeuvering on the surface of Mars. But, the terrain is not uniform. The martian surface is rough. The aluminium tyres that were used in earlier rovers were less than a centimetre thick. Opportunity rover had these aluminium tyres and they are deteriorating because of the rough terrain. Rubber wheels could not be used on Mars because the temperature there fluctuates highly. At low temperatures, rubber loses its elasticity and becomes brittle. So, NASA along with Goodyear has developed a wheel from Nitinol, a shape memory alloy (SMA) of Nickel and Titanium. The major characteristic of shape memory alloys is that they remember their shape and can change back to it after deformation. This transition is aided by heat. The amount of heat required to regain the shape can be determined by the amount of Titanium in the wheel. So, Goodyear developed a tyre made from chains on Nitinol. The transition temperature is tailored to fit the martian temperature so that when the tyre gets deformed, say by going over a sharp rock, it will regain its shape due to the shape memory effect. 

These alloys add another benefit. They are lightweight. Launching stuff in space requires crazy amounts of energy. Weight has always been a limiting factor in space missions. The tyres made from Nitinol are lighter, so, it won't add extra cost to the mission as well as they are durable for heavy rovers.  

Let's have a quick look at how shape memory alloys work. Typically, when stress is applied to a material, if the stress is below the material's yield point, it regains its shape back. But, if the material is stressed beyond its yield point, it deforms permanently. Normally when metals are stretched, defects are formed in them. But Nitinol has a Martensite structure. In this structure, when stress is applied, the layers in the material just realign to absorb the stress and when sufficient energy is provided, they come back to their original position. So, this leads to the Shape Memory Effect.

Now that NASA is planning to use these wheels, a lot of new possibilities are unlocked as the rovers will be able to travel longer distances. The wheel is the most important invention in human history, and now, NASA reimagined it!

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