A deployable soft airless wheel inspired by origami and the reciprocal interlocking structure of the Da Vinci bridge has been developed for operation in lunar environments. This innovation holds promise for enabling direct exploration of lunar lava tubes, a mission long deemed unachievable.

A rover with deployable soft airless wheels conducting exploration of a lava tube on Jeju Island

Lunar pits and lava tubes are geological voids formed by the collapse of underground cavities. These structures provide natural shielding from extreme temperature variation, cosmic radiation, and micrometeorite impacts. They are also valuable due to the preservation of volcanic and early planetary history. Space agencies such as NASA and ESA have identified them as promising candidates for long-term human habitation. However, entering these formations remains challenging because of vertical drops, powdery regolith, and irregular rocky terrain. Traditional methods have proposed lowering smaller rovers via tethers from larger platforms, but such systems suffer from energy loss due to friction, complex deployment procedures, and high risk of collision during descent.

To address these limitations, Professor Dae-Young Lee’s team in the Department of Aerospace Engineering at KAIST has introduced a new design: a new wheel inspired by origami and the reciprocal structure of Leonardo da Vinci’s bridge. The wheel is composed of elastic metal strips arranged in a spiral configuration that allows it to deform and recover its shape while maintaining high strength. When folded, the wheel diameter is 230 millimeters, enabling compact storage. During operation, it can expand to 500 millimeters, offering mobility comparable to larger systems. The wheel structure resists vertical impact while allowing easy deformation in rotational directions. This directional property makes it possible to absorb landing shocks effectively, enabling direct descent into pits without the need for cranes or tethers.

 Figure 1. Diagram of the wheel structure. (A) Soft deployable wheel structure with different shape modes: (i) Coiling mechanism for deployment and storage, enabled by (ii) a specialized hub set, axis and (iii) grouser design. (B) Detailed description of wheel assembly sequence and coiling mechanism.

 Experimental results showed successful traversal over 200-millimeter obstacles and the ability to climb slopes exceeding 20 degrees in simulated lunar soil. The wheel-maintained functionality under vacuum and at temperatures of up to 423K. It also continued to operate after being subjected to impact conditions equivalent to a 100-meter fall under lunar gravity, indicating excellent shock absorption capacity.

 The structural simplicity and modular configuration offer advantages for missions involving multiple exploratory units. A single lander can release several compact robotic explorers, each capable of independently entering different pit sites. This improves operational flexibility and increases the probability of mission success. In contrast to conventional approaches that concentrate all functions in a single vehicle, the distributed approach allows graceful degradation and risk reduction. The proposed system contributes to enhancing the adaptability, reliability, and efficiency of future lunar surface missions.

According to the research team, the proposed wheel is evidence that soft robotic concepts can be effectively applied in space environments. Traditionally, soft robotics has been considered unsuitable for space due to the presence of vacuum, radiation, and cryogenic temperatures. However, this study employs elastic metal rather than polymers, and achieves high deformability through structural design, overcoming many of those limitations. The reduction of mechanical components and maintenance demands, combined with structural robustness, highlights the potential of soft robotics in planetary exploration.

This work is an interdisciplinary achievement, integrating structural mechanics, materials engineering, and robotic design for space exploration. It is expected to contribute to the academic community and to future lunar missions currently being planned by the Korea Aerospace Administration for 2032. Future effort will focus on integrating the wheel into flight-grade micro-rovers to demonstrate direct entry into lunar pits during actual exploration missions.

The research was conducted in collaboration with Unmanned Exploration Laboratory (UEL), the Korea Aerospace Research Institute (KARI), and the Korea Astronomy and Space Science Institute (KASI), and is scheduled for publication in the journal Science Robotics.