Technology transfer has been part of NASA’s culture for quite some time. Collaborations between NASA and private companies to develop technologies for space missions have accelerated the transfer to earthbound projects or products that benefit humans around the globe. In this article, we talk about a space-focused technology innovation that seems to have the potential to revolutionize a well-known and more ordinary product here on Earth - the tire.
For quite some time, NASA has been developing special tires to fit the needs of missions going to the Moon and Mars. By the mid 70's, while working with the Apollo program, NASA engineers had already gone through several designs. The technical memoranda for the development of wheels for the lunar rover stated that because of the unique lunar environment, the creation of flexible wheels was the most challenging and time-consuming aspect of the Lunar Roving Vehicle (LRV) development.[1].
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Compared to the distances we drive on Earth, the distances traveled by these are insignificant; however, a wheel/tire for the Moon or Mars had to be more reliable and specially designed to not need repairs or go flat. The wheels also had to be light and small and operate in a vacuum, extreme temperatures, and low gravity. On top of that, these had to be flexible and be able to deform to facilitate slope climbing. From all those, flexibility was the most critical and difficult aspect of the design. Due to the range of temperatures on the Moon, typical flexible materials like rubber are unusable, so the only alternative was to create a metal mechanism that could deform repeatedly, resist impacts, and not slide in loose soil.
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To support the Apollo 14 mission, Goodyear manufactured a more earth-like wheel that the American Modularized Equipment Transporter (MET) used. This was an unpowered, two-wheeled cart that moved equipment with tires that had inner tubes filled with nitrogen[4]. It was the Apollo 15 mission that took the first rover to the Moon. This rover had tires with a mesh structure, made of zinc-coated steel strands of 0.083 cm in diameter, attached to the rim. It also had discs of formed aluminum attached to a hub of spun aluminum. The dimensions of this tire were 81.8 cm in diameter by 23 cm wide[5].
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After the Apollo program, NASA Glenn Research Center in Cleveland, Ohio, focused on designing tires for the Mars rovers. Sojourner, the first rover sent to Mars, was part of the Mars Pathfinder mission, which landed on Mars on July 4, 1997. The wheels of this small vehicle were only 13 cm in diameter and the rover didn’t go far. Subsequent rovers were larger, so the wheels were too. The Mars Exploration Rovers Spirit and Opportunity, launched in 2003, had wheels 0.02 inches thick and 10.2 inches in diameter. Curiosity, which landed on Mars in 2012, also had thin wheels; these were 0.03 inches thick and 19.7 inches in diameter. All these wheels were made of aluminum with cleats for traction and curved titanium springs for springy support.
Micro rover [5]
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Due to the unexpectedly harsh terrain on Mars, a little over a year after the Mars Curiosity Rover landed on the red planet, engineers began to notice significant damage in its wheels. Looking to extend the rover’s life and allow it to complete its mission, the development team had to engineer smart-driving algorithms to reduce forces on Curiosity’s wheels as the rover climbed over rocks and therefore reduce damage.
Even before this problem was realized, NASA Glenn engineers had already started working on different designs. For this, NASA created partnerships with private companies, like Goodyear, and worked on the design of an airless-compliant tire. The result of this partnership was the Spring Tire, which was made of hundred coiled steel wires woven into a flexible mesh. This design could support high loads while conforming to the terrain and have good traction. However, even though it performed quite well on sand, testing showed that the steel wires would deform in the harsh Mars terrain.
The solution to the deformation problem was addressed by the serendipitous collaboration between two NASA employees. In this case, the engineer Colin Creager, working on the tire problem, had a conversation with Sato Padula, a Materials Scientist, also working at NASA Glenn. Padula had experience with superelastic materials and told Creager that the solution was to use nickel-titanium (NiTinol), which is a shape memory alloy (SMA). In this case, the material goes through an atomic rearrangement to accommodate deformation and then rearranges back into shape. This superelasticity allows a tire to have 30 times the maximum deformation possible of a conventional material and end up without permanent deformation. The superelastic tire technology also makes a tire an excellent shock absorber and allows it to effortlessly move through rough terrain without breaking or damaging. Subsequent research and testing changed the design of the Spring Tire from a woven wire to a series of interconnected coils.
This brings us back to the topic of technology transfer. Excited about this new technology, Brian Yennie and Earl Cole, two entrepreneurs, reached out to engineers in NASA Glenn Research Center to explore commercial applications of this breakthrough tire technology. Conceived in 2020 as part of the FedTech NASA Startup Program, The SMART Tire Company (STC) has been developing the Martensite Elasticized Tubular Loading (METL™) tire that uses the SMA technology and works for street and trail bicycles[8]. Their goal is for the tire to be lightweight, durable, and that never goes flat. In early 2022, the company came back to the spot after appearing on Shark Tank to look for more funding, and early this year their METL™ airless bike tire won two 2023 Consumer Technology Association (CES) Innovation awards. Unfortunately, these tires are not yet available, although we hear they will be available soon. Some speculate that the hold-up might be due to the cost of NiTinol and funding[7].
In the meantime, it looks like engineers and materials scientists at NASA continue testing a spinoff tire version that would work on cars and trucks on Earth[9]. More recently, Fort Wayne Metals in Fort Wayne, Indiana, started a collaboration with NASA to begin producing NiTinol materials to create rover tires[10]. The goal of this collaboration is to support the Moon exploration; however, it also has the potential to speed up the development of these superelastic tires for general use.
Besides the exciting technology, there are two things mentioned in this article that I would like to highlight. First, the importance of collaboration. More than once, I have heard stories about simple conversations between colleagues with different expertise who end up helping find the solution to a big problem. Therefore, we should not be afraid to share successes and failures because it might help us achieve our objectives and also result in great things. Second, not only big companies can take advantage of this technology. The SMART Tire company is a small starting company, which despite possible hurdles, seems to be close to achieving a goal that might be a game changer for all and the end of flat tires.
References:
[1] https://ntrs.nasa.gov/citations/20100000019
[2] https://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_lrv.html
[3] Smithsonian National Air and Space Museum https://airandspace.si.edu/collection-objects/wheel-lunar-rover/nasm_A19750830000— Image first wheel with aluminum center, steel wire, and aluminum “treads”
[4] https://www.nasa.gov/specials/wheels/
[5] https://mars.nasa.gov/MPF/rover/descrip.html
[6] https://mars.nasa.gov/resources/6265/rover-wheel-sizes-isometric/
[7] https://bikerumor.com/astronauts-on-bikes-rubber-tread-smart-airless-metl-tire-prototype-is-50-lighter/
[8] https://technology.nasa.gov/page/nasas-airless-tire-technology-re
[9] https://technology.nasa.gov/patent/LEW-TOPS-99
[10] https://www.wane.com/news/local-news/fort-wayne-metals-nasa-team-up-to-advance-tech-that-could-support-moon-exploration/