Spacewalker inspects station solar rotary joint
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: June 3, 2008
Astronaut Michael Fossum closely inspected a previously seen defect in a bearing surface on the drive gear of a space station solar array rotary joint and confirmed it is a depression and not an area where debris had accumulated. That would seem to imply that it represents an area of the hardened surface material of the bearing race that has broken down somehow or otherwise been damaged as opposed to something that could be scraped away or smoothed out.
"This is not what they were hoping to hear," Fossum said after rubbing a scraper and a gap tool over the pit. "This is definitely a depression."
"OK, how are you determining that?" astronaut Kenneth Ham asked from inside the shuttle Discovery.
"It's very, very thin, it's almost imperceptible with the scraper tool," Fossum said. "Using the gap gauge, you can feel it drop in, there's no catch on the edge as if you were running up against a bump or something. I came at it from multiple directions and I don't feel it catch. If it was a bump or something, you would catch on the edge and it would hesitate a moment. This does not. You feel it drop in."
"OK. That description sounds like it is what it is, then."
"It also catches on the outside edge as you're leaving the marred area and going back onto the undisturbed surface," Fossum reported.
"OK, that sounds like two positive indications for a depression," Ham replied."
Engineers have been struggling to figure out what has caused the drive gear bearing surface to degrade, producing large amounts of metallic shavings. Engineers theorize the surface layer suffered a crack or some other defect that got worse as the drive gear rolled through 12 bearings that hold it in place.
The SARJ is used to rotate outboard solar arrays to track the sun. The port SARJ works normally, but the right-side SARJ has been used only sparingly since the contamination and bearing surface degradation were discovered last year.
Looking over Fossum's shoulder, so to speak, via helmet-mounted television cameras, Ham observed that "it looks like, shoot, maybe 80 to 90 percent of the surface has been disturbed and eroded."
"Affirm," Fossum said. "Yep, along the outmost edge, it looks like it's eroded all the way to the boundary here."
Fossum then carried out a series of tests to find out whether he could remove contamination from a small area of the bearing surface using Braycote grease to trap the particles. He applied the grease with a scraper tool and then used the scraper to scrape it back off. He also tried wiping the particle-holding grease off with a towel and simply applying it with a wipe.
"OK, I guess I've done what I can do with a wipe," he said at one point. "It's very clean now, as far as the grease goes. The area does not look that different, there is a reduction in the little accumulations on the surface that we affectionately call pancakes, but the other surface as far as the more rigid things, I think the peninsula-type areas have been undisturbed by this process of scraping and wiping."
While Fossum was testing the debris removal techniques, crewmate Ronald Garan re-installed a bearing on the drive gear, re-installed insulation and configured a series of launch locks as required.
"Ron, you're making me look like a slacker," Fossum joked. "I'm sitting here doing one thing."
"You're doing the important thing," Garan said.
Earlier in the spacewalk, Fossum and Garan removed protective covers from the Japanese Kibo lab module, unplugged it from shuttle power and loosened window launch locks. While the spacewalkers moved onto the SARJ work, Japanese astronaut Akihiko Hoshide, assisted by Karen Nyberg, carefully pulled Kibo from its perch in the shuttle Discovery's cargo bay at 4:37 p.m. By 6:15 p.m., the huge module was positioned within inches of its docking port on the left side of the station's Harmony module.
Once the berthing mechanisms are flush together, motorized bolts will drive in to lock the laboratory to Harmony. The astronauts plan to enter the new module Wednesday.