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Curiosity’s Wheels to Leave Morse Code on Mars’ Surface

August 05, 2012 by Jeff Shepard

Mars rover Curiosity landed on the Red Planet at 10:32 p.m. PST on August 5. Like previous rovers built by NASA’s Jet Propulsion Laboratory (JPL), Curiosity is equipped with 6 wheels in a rocker-bogie suspension. The suspension system also served as landing gear for the vehicle. Curiosity’s wheels are significantly larger than those used on previous rovers. Each wheel has a pattern which will help it maintain traction but will also leave patterned tracks in the sandy surface of Mars. That pattern is used by on-board cameras to judge the distance traveled. The pattern itself is Morse code for "JPL" (· – – – · – – · · – · ·).

"The wheels of Curiosity have begun to blaze the trail for human footprints on Mars," said NASA chief Charles Bolden. Not counting its robot arm, Curiosity is 10 feet long, nine feet wide and seven feet high measured to the top of its main camera mast. Its mobility system is similar in design to that used by Spirit and Opportunity, but its six 20-inch-wide wheels are twice the size of the earlier models. Each wheel has its own drive motor and the four corner wheels are independently steerable.

Peak power for traction and other activities is delivered by two 28V Li-ion batteries from Yardney Technical Products. They are rated to deliver 42 amp-hours each, and are expected to go through multiple charge-discharge cycles per Martian day. While the main power source is rated for 110W, the batteries can deliver a peak power of 10kW. However, the design limit of the power system is closer to 3kW as a result of limitations in the wiring harness, and other components.

Once it starts traversing the surface, Curiosity will be able to roll over obstacles approaching 75 cm (30 in) in height. Maximum terrain-traverse speed is estimated to be 90m (300 ft) per hour by automatic navigation; average traverse speeds will likely be about 30m (98 ft) per hour, based on variables including power levels, terrain difficulty, slippage, and visibility. Curiosity is expected to travel a minimum of 19km (12 mi) in its two-year mission.

NASA’s earlier rovers were solar-powered, forcing them to shut down at night and to hibernate in winter months to conserve power and heat. Curiosity is powered by a radioisotope thermoelectric generator, using the heat produced by the decay of radioactive plutonium dioxide to generate electricity. Excess heat is used to keep electronics and other sensitive systems from getting too cold. The same system that warms the rover will generate 2.5 kilowatt hours per day, much more than the Mars Exploration Rovers, that can generate about 0.6 kilowatt hours per day.

After several weeks of systems testing of nuclear-powered Curiosity and its sophisticated instruments, the six-wheel rover could take its first short drive, flex its robotic arm and formally begin its two-year surface mission. The landing site near Mars’ equator was picked because there are abundant signs of past water, meeting one of the requirements for organic life. Inside Gale Crater is a 3-mile-high mountain, and images from space show the base appears rich in minerals that formed in the presence of water.