The Phoenix Mars Lander that began scooping up samples of Martian soil June 4 depends on Reali-Slim® thin-section bearings to position its robotic arm for digging in the permafrost.
This is the second Mars mission for Reali-Slim® bearings, manufactured by Kaydon® Corp Bearings Div of Muskegon, MI. They were also used in the two 2004 Mars Exploration Rovers, which are still sending geological findings back to earth, some 171 million miles away.
The robotic arm was built by Alliance Spacesystems of Pasadena, CA 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, attached to the deck of the Lander, has a garden-sized trowel on the end and a camera mounted above it that sends color photographs of the samples to scientists on earth.
The arm has four types of motion: up-and-down, side-to-side, back-and-forth, and rotating. Three of the joints that accomplish these movements use sets of custom-engineered Reali-Slim® thin-section bearings. According to Richard Fleischner, mechanical engineering group supervisor at Alliance, they were specified for several reasons.
"The Kaydon bearings give us plenty of load capacity, even though they are lightweight and small enough to fit in the tight space," he said. "They also have a full complement of balls to withstand the force and vibration of the launch. And we get good engineering support and a reasonable lead time from Kaydon."
The bearings take a heavy load during digging, Fleischner said, as up to 100 lb or more of force is needed to break through the ice and dig down about 20 inches. They are made of heat-treated 440C stainless steel and mechanically honed to achieve a super-fine finish and improve torque. 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.
The Phoenix Lander is expected to be on the job for three months, digging for evidence that Mars could sustain life.
