ERJ staff report (DS)
Gale Crater, Mars - Mars exploration vehicle 'Curiosity' runs on 20-inch wheels. Not a scrap of rubber there, but the wheels are made from aluminium supported on titanium suspension legs.
The vehicle has a maximum speed of around 4cm/sec (or 0.144 km/hour), but speed is unlikely to be an issue, as the vehicle is only expected to travel some 20 km during the whole of its prime mission, scheduled to last around two years.
Each of the six electrically-powered wheels include cleats (similar to the studs on a fooballer's boot) made from titanium. These are used by the on-board intelligence to compare wheel rotations against distance travelled. If the cameras show that the imprint left by the cleats is less than the distance calculated from the wheel rotation information, then the computers realize that the machine might be stuck or slipping in soft terrain.
Those cleats? According to Emily Lakdawalla of The Planetary Society in her blog, the design team at the Jet Propulsion Lab (JPL), put them in a particular pattern . _ _ _ / . _ _ . / . _ . .
Those who can read Morse Code will realise that spells out J / P / L.
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Press release from NASA (Includes close-up images of wheels)
Emily Lakdawalla's blog about the Morse Code