The Moon's large surface holes, or "pits," and underground lava tubes are drawing attention as natural shelters that can avoid space radiation and extreme temperature swings, but steep cliffs and rockfall risks have made them hard for rovers to reach. A Korean research team developed a wheel based on origami principles that can fold and unfold its diameter without complex machinery, boosting small rovers' ability to overcome obstacles.
A team led by Professor Lee Dae-young of the KAIST Space Research Institute and the Department of Aerospace Engineering said on the 18th that, together with the Institute of Unmanned Exploration, the Korea Astronomy and Space Science Institute (KASI), the Korea Aerospace Research Institute (KARI), and Hanyang University, it has developed the world's first "deployable airless wheel." An airless wheel does not use air, making it easier to maintain its shape in extreme environments, and is considered well-suited for space exploration equipment.
Moon pits and lava tubes are considered prime targets not only for their habitability potential but also for their research value. Shim Chae-kyung, head of the KASI Planetary Exploration Center, said in an interview that day, "A pit is a place where geological strata are naturally exposed, making it a good spot to glimpse how the surface crust is composed," adding, "A lava tube is close to a 'record archive' of past volcanic activity. By analyzing traces on the walls, we can infer the composition of the magma and how it flowed."
The problem is the approach. Major space agencies have suggested sending a large rover close to the site and then deploying a small rover. But the small rover's small wheels are at a disadvantage in getting over obstacles such as ledges and rocks, making it hard to secure mobility. There have been ideas for variable wheels that change shape, but the Moon's large day-night temperature differences can cause uneven expansion and contraction of materials, and lunar dust could enter mechanical gaps and cause wear.
The team combined origami structures with soft robotics concepts to develop a deployable airless wheel that can fold and unfold. Instead of increasing complex parts like hinges or gears, they wove and interlocked thin, strip-shaped metal plates with good elasticity that can withstand the space environment to form a wheel.
Professor Lee said, "We weave flat strips into a wheel shape, and as that structure deforms, the diameter increases and decreases," adding, "We used stainless steel, a type of alloy, as the material."
It's easy to understand if you think of an umbrella or a collapsible camping cup. An umbrella is thin and long when folded but expands to a much larger area when opened. This wheel works the same way, with bendable sections predesigned into the metal plates so it can move between a compact folded state and a large deployed state.
When folded, the developed wheel has a diameter of about 23 cm, but it expands to 50 cm when deployed. You can reduce wheel size to load it on a small rover, and in rough terrain, increase the wheel diameter to improve the ability to climb over ledges.
The team verified driving performance at a test site that mimicked lunar soil conditions. They also confirmed impact resistance sufficient to maintain shape and function even when subjected to shocks equivalent to being dropped from a height of 100 m under lunar gravity.
Cho Nam-seok, head of the Institute of Unmanned Exploration, said, "It took nearly three years to develop, and it was more difficult to identify and improve the parts that deformed during testing than the design itself," adding, "Repeated validation, including drop tests using drones, took up most of the time."
They also conducted field tests tailored to cave exploration. The team ran driving tests on sloped and step sections inside a cave on Jeju Island. Although Jeju caves are UNESCO World Heritage sites with restricted access, they obtained permission from relevant agencies to carry out the first domestic robot experiment inside a cave.
However, the wheel seen that day showed relatively large vibration during the demonstration. Asked whether vibration during lunar exploration would be a problem, Jang Jong-tae, a principal researcher at KARI, said, "Because the wheel has an elastic structure like a spring, vibration can occur and could affect the stability of camera footage mounted on the rover," adding, "Going forward, we will optimize the wheel material and combine algorithms or stabilization technologies that can compensate for vibration."
Heat is also cited as an important variable. Jang said, "Temperatures at the lunar equator rise to as high as 120 degrees, but simulations showed the wheel surface reaching a much higher 230 degrees," adding, "Since this could burden the motors connected to the wheel, we need to apply thermal barriers or refine the heat dissipation design."
This achievement is also significant in that it was the result of voluntary collaboration among researchers from universities, corporations, and government-funded institutes who met at seminars and workshops. Cho said, "In the United States and Japan, it is common for universities, corporations, and government agencies to build space robots together, and we have shown such a collaborative model can produce tangible results in Korea as well."
Professor Lee said, "This is the world's first technology to offer an answer to the problem of accessing pits and lava tubes, which no one had properly solved," adding, "Although a lunar exploration robot project has not yet fully begun in Korea, we plan to propose and participate if related calls are announced in the future."
Earlier, the Korea AeroSpace Administration presented a plan to launch an unmanned lunar lander in 2032. Shim said, "Korea is a latecomer in lunar exploration, but there are still many things we can be the first in the world to discover," adding, "Including this research, I hope we can design and carry out our own original exploration missions."
The research was published on the 18th in the international robotics journal "Science Robotics."
References
Science Robotics (2025), DOI: https://doi.org/10.1126/scirobotics.adx2549