‘Tumbleweed ball’ set for Mars?

Researchers exploring different methods to deliver scientific instruments to various Martian locations are studying the potential for a giant, lightweight, two-story tall beach ball.

Equipped with scientific instruments, the so-called ‘tumbleweed ball’ conceived by NASA’s Jet Propulsion Laboratory (JPL) researchers could potentially explore vast tracts of planetary terrain, blown by the wind.

The wind blowing across the face of Mars would be the only engine needed to move the giant tumbleweed ball from place to place, said Jack A. Jones, who is leading JPL’s research into various inflatable machines for exploring space.

JPL’s Inflatable Technology for Robotics Program aims to create rugged, all-terrain vehicles and other devices with low mass and low-packing volume.

A scientific payload, carrying instruments such as magnetometers or water-seeking radar, would be held in place by tension cords at the tumbleweed’s centre.

Cameras mounted inside the ball would peer out at the local terrain.

When scientists identify a promising spot and want the tumbleweed to put down roots and sit for a spell, the ball could be partially deflated. Then, when it’s time to move along again, the ball could be reinflated to roll on toward new frontiers. Much of Mars’ terrain is sloping and littered with boulders.

But researchers were excited by the results of tests this summer of a 1.5 metre-tall version of the tumbleweed.

The tests confirmed that 6-metre diameter balls should be able to climb over or around one-metre rocks and travel up slopes as high as 25-degrees in the thin, but breezy Martian air.

The team, which includes senior engineer Sam Kim and design engineer Jay Wu is now preparing for desert tests later this month that will incorporate a radar into the ball’s centre to test the prototype’s ability to find underground water.

Such instrumentation could eventually be used to search for possible water hidden beneath Mars’ surface.

The ball is weighted so that it has a preferred axis of rotation. It tends to roll with the heaviest part down, so two weights opposite each other send the ball along a straight path.

The upcoming tests will also try out a centre-of-mass control device that would allow the ball to be steered by pumping contained fluid to the left, right or centre of the tyre, which will be slightly oblong.

‘With a 20 kilogram ball and 20 kilogram payload, the 6-metre diameter tumbleweed ball is light enough that it could be added on to another lander and deployed from the ground, or it could be in its own delivery vehicle,’ said Jones.

The large, lightweight ball could possibly also serve as its own parachute and landing airbag, he said, able to withstand the bounce following a 30-metre per second terminal velocity descent at Mars.