ROBOTIC tumbleweeds could one day meander across the surface of Mars, helping
scientists measure the Red Planet鈥檚 complex wind patterns. The Swiss inventors
say their ultra-light rolling robots, propelled only by the wind, could help
complete models of the Martian atmosphere, as well as identifying the best
landing areas for future missions.
The collapsible wire 鈥渨indballs鈥� designed by Thomas Estier of the Swiss
Federal Institute of Technology in Lausanne are temperature-activated. During
the daytime, when it鈥檚 relatively warm, the windballs will collapse into flat rings on the ground
(see picture) and study the local environment with
microsensors powered by the Sun. As the temperature drops at night, the rings
spring into action and wander the planet at the mercy of Martian winds and dust
storms. Estier says that tracking the windballs from an orbiter would give a
good idea of the wind patterns on the surface.
Estier came up with his oddball idea while he was working on a project for
the European Space Agency. 鈥淲e were asked to propose innovative ideas for
mobility on Mars,鈥� he says. 鈥淲hen I realised there was a temperature cycle on
Mars and that there were some permanent winds, I came up with the idea of
rolling robots propelled by wind.鈥�
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It won鈥檛 be easy to harness the wind on Mars. With an atmosphere only
one-75th as dense as that of Earth, even strong winds aren鈥檛 that powerful.
But Martian gravity is only a third of Earth鈥檚. 鈥淵ou want to be very
lightweight, but be as big as possible to have high wind resistance,鈥� says
Estier. He envisages balls between 0.5 and 2 metres in diameter.
To make the windballs change shape at nightfall and sunrise, Estier is
designing springs and hinges from a temperature-sensitive shape memory alloy
called nitinol. This alloy of nickel and tin can be deformed at low temperature,
but reverts to its original shape when you heat it.
At low temperatures, nitinol has a crystal structure that can easily be
deformed. The energy put into shaping the alloy is stored in the crystal
structure as stresses between adjacent nickel and tin atoms. When the alloy is
heated to a 鈥渢ransition鈥� temperature, its crystal structure begins to change,
releasing the stored stresses which then push the material back into its
original shape.
鈥淚鈥檓 intrigued by it and it should work if they get the wind resistance
right,鈥� says Ronald Greeley of Arizona State University, who has been studying
Martian winds from data collected by NASA鈥檚 1997 Mars Pathfinder mission and the
Mars Global Surveyor orbiter. Windballs could help corroborate NASA鈥檚 data, says
Greeley, and also locate areas prone to fierce dust storms. 鈥淎ny sort of
spacecraft needs to know about dust movement鈥攊t鈥檚 a factor of 10 smaller
than down here, so it gets into all sorts of places where it can gum up gears
and so on.鈥�