Assembly in Action: Bearings Ensure Effective Arm Performance
August 21, 2008
NASA’s Phoenix Mars Lander, which arrived at the Martian north pole in late May, carries an assortment of instruments, including cameras, an onboard meteorological station, a thermal and evolved-gas analyzer, and a robotic arm.
The latter, built for NASA’s Jet Propulsion Laboratory by Alliance Spacesystems (Pasadena, CA), is designed to pick up soil and ice samples, and then present them to the Lander’s instruments for analysis. The 7-foot, 7-inch arm is attached to the deck of the Lander and equipped with a garden-sized trowel. Adjacent to the trowel is a camera, which sends color photographs of each sample back to Earth.
To ensure that the arm would be utterly reliable and as light at possible, Alliance Spacesystems equipped its joints with Reali-Slim thin-section bearings from Kaydon Corp. (Muskegon, MI). In fact, the Phoenix application represents the third time a Kaydon product has made the trip to Mars. The company’s bearings were also used in the two Exploration rovers that landed on the planet in 2004.
“The Kaydon bearings give us plenty of load capacity, even though they are lightweight and small enough to fit in the tight space,” says Alliance mechanical engineering group supervisor Richard Fleischner. “They have a full complement of balls to withstand the force and vibration of the launch. We [also] get good engineering support and a reasonable lead time from Kaydon.”
According to Fleischner, the bearings have to be robust enough to accommodate the heavy loads that result when the arm is in operation. Specifically, the arm needs to exert up to 100 pounds of force if it is to successfully break through the polar ice and dig up useful samples.
The bearings are made of heat-treated stainless steel and mechanically honed to achieve a super-fine finish and improve torque. They are specially treated to operate in temperatures as low as -162 F, and employ a low-outgassing lubricant that won’t become overly viscous in extreme cold, but also won’t evaporate in the thin Martian atmosphere.
For more on precision bearings, visit www.kaydonbearings.com or call 800-514-3066.