Sending a rover into space to explore other celestial bodies comes with a dizzying array of challenges, and one of the most complex is ensuring the vehicle doesn't break down out there.
To largely mitigate that, a team of aerospace engineers from South Korea has designed a flexible wheel that doesn't require an air-filled tube, can change its size, and can take a serious beating.
In fact, it survived a fall from a height of over 13 ft (4 m) and even drove through fire without falling apart. Here's a clip:
The researchers believe this could be useful for lunar exploration vehicles that have to traverse uneven sandy and rocky terrain to find sites of interest, as well as lunar pits. The latter refers to areas on the Moon that can shelter astronauts from radiation and the wild temperature variations on the surface – from 260 °F (127 °C) during the day to minus 280 °F (-173 °C) at night) – but getting there is no mean feat.
This wheel utilizes elastic steel strips arranged in a woven, crossed-helical pattern suitable for load bearing. This is similar to the principle of a Da Vinci bridge’s self-supporting structure, so the strips mutually support one another without the need for adhesives or additional binding components.
The wheel’s hub connects two sides that can rotate in opposite directions, so the current design can expand radially from a compact diameter of 9 in (230 mm) all the way up to 19.7 in (500 mm) without a hinge in sight.
"Unlike previous shape-variable structures that rely on mechanical revolute joints or soft materials like fabrics and elastomers, our design utilizes continuum deformation driven by a coiling mechanism," said lead researcher Seong-Bin Lee from the Aerospace Robotics & Mechanisms Laboratory at South Korea's KAIST university. "This flexibility in material selection allows the structure to be customized to meet the demands of various extreme mission environments."
Interestingly, this prototype wheel uses the same heat-treated SK5 carbon steel that you'll find in commercial tape measures.
The helical strip configuration allows for the wheel's load to be distributed throughout the wheel body. This creates an anisotropic behavior where the wheel requires minimal energy to coil for storage but resists deformation under vertical loads. It also enables the wheel to absorb shocks effectively, mitigating damage from uneven terrain during driving, tumbles and vertical descents.
The team tested this wheel design by fitting two of the prototypes to a dummy rover, and put the vehicle through its paces in an outdoor environment simulating lunar soil with large obstacles. It not only made its across the area successfully, but also tackled a steep stair-like obstacle with a 34-degree incline, survived big drops from several feet up, and chugged along after driving through fire.
Advancements in component design like this are important because wheel failure would literally stop an extraterrestrial exploration mission in its tracks. Rovers are subject to all kinds of impact damage and abrasive conditions, and there are no ways to repair rovers remotely.
Durability requirements fundamentally shape rover design, and that's why material selection is one of the most critical engineering decisions in space exploration.
Last September, an image of NASA's Curiosity rover on Mars (which landed there in 2012) revealed its wheels had taken significant damage traversing the Red Planet's rugged landscape. The varied dents and punctures thankfully didn't prevent its operation over the years, but they could well have. Rovers can weigh a lot (Curiosity came in at a ton) and that can make it even more challenging to stand up to wear and tear over extended missions.
The team hopes its wheel design might eventually be integrated into rover systems for future exploration missions. Thanks to the way it's configured, it could feature stainless steel like in this prototype, high-strength elastic materials, or various other metals that are suitable for space environments.
Source: KAIST via Eurekalert
