NASA has come up with an innovative wheel design for its rovers that not only holds immense potential in planetary exploration, but also on our own planet.
The Superelastic Tire as they are called have been developed by NASA in collaboration with Goodyear with the inspiration derived from Apollo lunar tires. The new tires have a rather medieval look owing to its design and they have been pegged as a viable alternative to pneumatic tires here on Earth as well. These new tires that make use of shape memory alloys can withstand harsh environments like the ones present on Mars and other planets as well as greater loads. The novelty of the tires is that they can withstand excessive deformation without permanent damage.
The Superelastic Tire offers traction equal or superior to conventional pneumatic tires and eliminates the possibility of puncture failures, thereby improving automobile safety. This tire design also eliminates the need for an inner frame which both simplifies and lightens the tire/wheel assembly.
Commonly used elastic-plastic materials (e.g. spring steels, composites, etc.) can only be subjected to strains on the order of ~ 0.3-0.5% before yielding. Hence, the use of a NiTi shape memory alloy yields a superelastic tire that is virtually impervious to plastic deformation.
In addition, the utilization of shape memory alloys provides enhanced control over the effective stiffness as a function of the deformation, providing increased design versatility.
Reinventing the Wheel
NASA truly points out that exploration requires mobility. And whether you’re on Earth or as far away as the Moon or Mars, you need good tires to get your vehicle from one place to another. Tire development for space exploration has been a focus of research at NASA Glenn for a decade. Evolving since the days of Apollo, NASA engineers started examining tire designs back in the 1960’s for use on the surface of the Moon.
Three major wheel designs were introduced by NASA and other international researchers for early exploration. While they were vastly different, they were all focused on moving hardware and astronauts across the lunar surface.
The Russian vehicle Lunokhod (Moon Walker in English) used eight rigid rim wire mesh wheels with bicycle-type spokes and metal cleats for traction.
The American Modularized Equipment Transporter (MET): a two-wheeled unpowered cart used smooth rubber tires supported by nitrogen filled inner-tubes and manufactured by Goodyear to make it easier to pull the cart through soft lunar soil and over rocks.
The last NASA vehicle to visit the Moon was the Lunar Roving Vehicle. This manned vehicle used four large flexible wire mesh wheels with stiff inner frames to prevent over-deflection. Thin tread strips were attached to the carcass to enhance flotation in soft lunar soil.
While NASA was developing rovers to send to Mars, there was also interest in taking a new look at returning to the Moon. NASA Glenn engineers rebuilt Apollo era tires and developed new designs using newer materials and technology to better function on a lunar surface.
During the mid-2000s, NASA Glenn engineer Vivake Asnani worked with industry partner Goodyear to develop the Spring Tire, an airless compliant tire that consists of several hundred coiled steel wires woven into a flexible mesh, giving the tires the ability to support high loads while also conforming to the terrain. The Spring Tire has been proven to generate very good traction and durability in soft sand and on rocks. This innovation led to an R&D 100 Award for Top Inventions of the Year.
A little over a year after the Mars Curiosity Rover landed on Mars, engineers began to notice significant wheel damage in 2013 due to the unexpectedly harsh terrain, causing concern about the ability of the rover to drive far enough to complete its intended mission.
NASA Glenn engineers thought their work on Spring Tires might be a new and better solution for exploration rovers on Mars. So, they set about developing several Spring Tire prototypes to improve: traction in soft sand; durability; and reduce overall weight.
While the tires performed well, there was a problem with the steel wires deforming when rolling over punishing simulated Martian terrain at NASA’s Jet Propulsion Laboratory (JPL).
In one particular moment of serendipity, Engineer Colin Creager and Materials Scientist Santo Padula had a conversation that completely changed the path forward. [Check video below]
The game changing material that dramatically advanced the development of spring tires was nickel titanium, a shape memory alloy with amazing capabilities as explained by Santo Padula.
After building the shape memory alloy tire, Glenn engineers sent it to JPL’s Mars Life Test Facility. It performed impressively on the punishing track.
So, why are shape memory alloys the key to success for this new generation of spring tires? It has to do with the atomic structure. Take a look to find out.