The robotic arm used by the Phoenix Mars Lander to scoop up samples of Martian soil employs thin-section bearings in its key positioning joints to keep down weight whi le managing appreciable loads.
The robot ic arm was built by Alliance Spacesystems of Pasadena, Calif., for NASA’s Jet Propulsion Laboratory. It is designed to trench the surface, pick up soil and ice samples, and deposit them in the Lander’s instruments for testing (electrochemistry, conductivity, and thermal analysis). The 7-ft, 7-in. arm attaches to the deck of the Lander and has a garden- sized trowel on its end. A camera mounted above the trowel sends color photographs of the samples to scientists on Earth.
The arm has four types of motion: up-and-down, side-to-side, backand- forth, and rotational. Three of the joints for these movements use sets of custom-engineered Reali-Slim thin-section bearings from Kaydon Corp. Bearings Div. Used partly because they are lightweight and small enough to fit in the tight space, the bearings take a heavy load during digging, as up to 100 lb or more of force is needed to break through the ice and dig down about 20 in. They are made of heattreated 440C stainless steel and mechanically honed for a superfine finish. The bearings are heated to operate in extreme cold (the joints are designed to survive in –108°C) and use a low-outgassing lubricant that neither gets too viscous in extreme cold nor evaporates in the thin atmosphere, according to Kaydon officials.
The Phoenix Lander is expected to be on the job for three months, digging for evidence that Mars could sustain life. This is the second Mars mission for Reali-Slim bearings. They were also used in the two 2004 Mars Exploration Rovers, which are still sending geologic findings back to Earth.
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The robotic scooper arm under development at Alliance.
