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No obvious problems found with beta gimbal assembly BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: December 18, 2007 Spacewalkers Peggy Whitson and Dan Tani found no obvious signs of damage in a mechanism used to pivot a set of space station solar arrays to keep them face on to the sun. A problem of some sort tripped circuit breakers routing power to the S4-1A beta gimbal assembly Dec. 8 and based on testing, engineers suspected possible impact damage from space debris or a micrometeoroid. But it now appears more likely the problem, whatever it might be, is internal to the mechanism or its electrical system. The beta gimbal assembly is used to pivot the starboard 1A solar blanket about its long axis to help maximize power generation. Whitson and Tani now are inspecting the right-side solar alpha rotary joint, or SARJ, a massive motorized gear assembly designed to rotate the starboard solar arrays like a giant paddlewheel to track the sun. The port SARJ is operating normally, but the starboard SARJ is locked in place because of excessive vibration and recently discovered internal metallic contamination and bearing race ring damage. Whitson and Tani removed a thermal cover protecting one of two drive motors and reported seeing metal shavings similar to what was found during earlier inspections in different areas. Based on vibration data, engineers suspected possible problems with trundle bearing assembly No. 5, one of 12 positioned around the perimeter of the 10-foot-wide rotary gear. But Tani and Whitson reported more debris concentrated around bearing No. 4. There were no obvious problems with the drive motor or gearing. Whitson and Tani originally planned to unbolt bearing No. 5 and bring it inside the station for eventual return to Earth. But engineers now are assessing whether to bring a different bearing in based on the crew's observations. In the meantime, the spacewalkers watched the drive motor gear as engineers activated it. There were no obvious problems with the gear teeth. But Tani reported metal shavings vibrating on the motor housing and moving like tiny ants. The astronauts are using adhesive tape to collect samples of the shavings before moving on to additional inspections.
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