Mars Exploration Rovers (MER) use a newer modified
wheel design than what was used on the Sojourner Rover.
At 26 centimeters in diameter (a little over ten inches),
the aluminum wheels of the MER are nearly twice the
size of those used on Sojourner and are missing the
recognizable sharp cleats.
Chris Voorhees is a mobility engineer working for NASA
and is responsible for the development of the MER wheels.
He says of the new wheel design that “a big challenge
was to be able to get enough traction to get through
soil and over rocks of the Martian environment, but
also to be able to get off
of the lander without getting entangled in the deflated
airbags". The new design is "basically like
a paddlewheel that is machined onto the outside of the
wheel, providing both safety and capability."
Learn more about the MER wheels at the NASA Mars
Exploration Rover web site.