It’s a rollover

Finnish researchers are building a wind-propelled ‘tumbleweed’ Mars rover capable of rolling hundreds of kilometres, which they claim is more efficient and easier to control than previous designs.

The University of Helsinki’s early prototype, funded by ESA, takes the concept a step further than previous attempts to develop a tumbleweed rover with a central ballast weight used to steer the device and more efficient turbine ‘wings’ to capture the wind. In 2001 Swiss researchers revealed a design for an ultra-light wire sphere that would collapse into flat rings during the Mars daytime high temperatures then spring into action at night.

NASA’s Jet Propulsion Laboratory also tested a 1.5m-diameter tumbleweed rover in the Antarctic earlier this year that inflated like a beachball. NASA’s rover could deflate to stop or slow down, but both designs only had limited control of their travel direction. The Helsinki team’s device combines lightweight longitudinal carbon-fibre or mylar wings with a ballast drive inside to steer the rover or propel it in low winds. An unbalanced weight suspended within the rover is shifted from the centre to make the sphere rotate, and to turn left and right.

Prof Aarne Halme, head of the Automation Technology Laboratory at Helsinki, said that the rover instruments that caused difficult weight problems for previous wind-powered designs could be used to provide the ballast propulsion. ‘We would have active mobility using the unbalanced mass to control forward motion and a turning radius, combining that with the wind thrust,’ he said.

The key advantage of the Helsinki team’s tumbleweed rover is the long distance it could travel from a lander, said Halme. ‘Current rovers on Mars can only travel around 20km,’ he said. ‘Our rover would be capable of long distances up to 100km.’

In addition, the rover’s turbine wings are much more efficient in the wind compared with other designs like NASA’s inflatable device, he said.

The rover turbine wings could also be used to generate electricity to power instruments or recharge itself. ‘There is the possibility of using the motor in the unbalanced mass as a generator. It would recharge when the wind was high,’ said Halme.

The rover would sit on its axis and rotate like a windmill. Solar cells and gas-expansion turbines could also provide additional energy to power the unbalanced mass during exploration.

The team plans to test the rover on an ice plateau this winter, and use the data to optimise turbine blade shape, number and material to maximise wind efficiency.

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