Monday, November 24, 2008

230p 11/24 Update: 'Wear' seen on port SARJ bearing race


Posted: 2:20 PM, 11/24/08

By William Harwood
CBS News Space Analyst

Changes and additions:

   SR-61 (11/24/08): Astronauts gear up for final spacewalk; urine processor troubleshooting continues
   SR-62 (11/24/08): Shuttle mission extended one day
   SR-63 (11/24/08): Spacewalk begins
   SR-64 (11/24/08): Inspection of port SARJ shows signs of wear on bearing race


2:20 PM, 11/24/08, Update: Inspection of port SARJ shows signs of wear on bearing race

Astronauts inspecting the space station's left-side solar alpha rotary joint, or SARJ, prior to lubrication intended as preventive maintenance, reported seeing signs of wear on a bearing race that appears similar to, though not nearly as extensive as, damage to the right-side SARJ.

The astronauts spent most of the first three spacewalks of Endeavour's mission cleaning and lubricating the starboard SARJ's three bearing races and installing new trundle bearing assemblies to reduce friction and fatigue-inducing vibration. One bearing race, called the outer canted surface, was heavily damaged by pressure-loaded rollers in the bearing assemblies because of a lubrication failure.

The port SARJ has been operating normally and Kimbrough plans to spend most of today's spacewalk applying lubrication as preventive maintenance. But during an inspection before the work began, Bowen reported seeing signs of wear on the port SARJ's outer canted surface.

"If you look at the outer canted surface, you can see two dark lines, one above and one below the track where the trundle bearings are riding, it looks at though there is some wear where the trundle bearings are riding," Bowen said. "You can see ... a little wear pattern in there that's sort of a junior version of what we have on the other side."

The SARJ mechanisms are critical to space station power generation, rotating outboard solar panels to keep them face-on to the sun as the lab orbits the Earth. The damaged right-side SARJ can no longer operate in auto-track mode, but engineers hope the cleaning, lubrication and bearing replacement carried out during Endeavour's mission will permit occasional sun-tracking to improve power output.

The port SARJ has been operating normally, although Bowen's report today would seem to indicate the planned lubrication could be of more immediate benefit than initially thought.


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