Mars Curiosity Rover Wheels, Low Cycle Fatigue Cracks

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Curiosity is a car-sized robotic rover exploring Gale Crater on Mars as part of NASA’s Mars Science Laboratory mission (MSL).

Curiosity was launched from Cape Canaveral on November 26, 2011 aboard the MSL spacecraft and landed on Aeolis Palus in Gale Crater on Mars on August 6, 2012.

Each of the six wheels has its own motor.

Each wheel tire was machined from a single block of aluminum alloy 7075-T7351.

The wheel is 50 centimeters in diameter and 40 centimeters wide. It has grousers (treads) that protrude 7.5 millimeters from the wheel skin. Grousers are spaced 15 degrees apart. Unlike the Spirit and Opportunity rovers, the grousers are not straight; they have chevron features designed to prevent sideways slip.

The skin of the wheel is 0.75 millimeters thick — the absolute thinnest that could be machined. The grousers provide structural strength; the skin is for floating the rover atop loose sand.

The rocks in the Gale Crater region where Curiosity landed are basalt, formed from the rapid cooling of lava.   The rover’s wheels have been worn down by driving over these sharp, embedded igneous rocks.   Furthermore, the rocks in this region have proven to be more severe than the other regions where previous rovers have landed.

The damage in the front wheels has thus been much greater than that in the rear wheels.

Emily Stewart Lakdawalla, Senior Editor of The Planetary Society, explained that there are mechanical aspects of the mobility system that actively shove the front wheels into pointy rocks. A wheel can resist the force of one-sixth of the rover’s weight pressing down on a pointy rock, but it can’t resist the rover’s weight plus the force imparted by five other wheels shoving the sixth wheel into a pointy rock. The forces are worse for the middle and front wheels than they are for the rear wheels.

“Dents and holes were anticipated,” said Jim Erickson, project manager for the NASA Mars Science Laboratory Project, which operates Curiosity,” but the amount of wear appears to have accelerated in the past month or so. It appears to be correlated with driving over rougher terrain. The wheels can sustain significant damage without impairing the rover’s ability to drive.”

The wheel damage prompted a slow-down in driving, and the mission team has adjusted routes and driving methods to reduce the rate of damage.

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See also:  fatigue

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– Tom Irvine

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