Back to newsletter listDate:
Tue, June 03, 2008 04:17:02 PMFrom:
CBS Space News
Subject:
4p 6/3 Update: Kibo prepped for attachment to station; astros an hour ahead of schedule
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CBS NEWS STS-124 STATUS REPORT: 27
Posted: 4:00 PM, 6/3/08
By William Harwood
CBS News Space Analyst
Changes and additions:
SR-23 (06/02/08): Cain says pad damage not likely to delay Hubble mission
SR-24 (06/03/08): Astronauts gear up for spacewalk
SR-25 (06/03/08): Spacewalk begins
SR-26 (06/03/08): Heat shield inspection boom unlatched from station
SR-27 (06/03/08): Kibo prepped for attachment to station
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4:00 PM, 6/3/08, Update: Kibo prepped for attachment to station
Spacewalkers Ronald Garan and Michael Fossum removed protective covers, released window cover launch locks and disconnected shuttle power to prepare Japan's 15-ton Kibo laboratory module for its move from Discovery to the international space station. The astronauts are running about an hour ahead of schedule, more than making up for a 50-minute late start due to problems with a headset cable.
Fossum and Garan have two more major tasks to complete, both involving the station's right-side solar alpha rotary joint, or SARJ. The station is equipped with two motor-driven SARJ mechanisms, one on each side of the lab's main power truss, to turn outboard solar arrays like giant paddle wheels to keep them face on to the sun.
The left-side SARJ works normally in "auto-track" mode, but the left-side gear has been used sparingly since last year when engineers discovered extensive metallic contamination on one of the drive gear's bearing surfaces. Engineers are not certain what's causing the problem, but they suspect it might be due to an initially small breakdown in the super-hard outer layer of the bearing surface that worsened as the gear rotated through the tight grip of 12 bearing assemblies.
During today's spacewalk, Garan will re-install trundle bearing No. 5, which was removed earlier as part of NASA's on-going troubleshooting. Fossum, meanwhile, will inspect the damaged bearing surface and attempt to clean a small section, spreading on Braycote grease to trap small shavings and other debris and then wiping it off. He plans to test several techniques and tools to see what works best.
If he is successful, future spacewalkers may attempt to clean the entire drive gear enough to permit at least partial use of the drive assembly. The SARJ is equipped with two drive gears, and the backup is pristine. But NASA does not want to change gears unless absolutely necessary because of the possibility of additional problems down the road.
"They'll start off by using the scraper," said David Beaver, lead spacewalk officer for Discovery's mission at the Johnson Space Center. "He'll first try just scraping the ring just with the scraper with no grease and see how much material does that remove. And then also try to characterize when the material comes off, is this going to cause a huge mess if we do this on the entire race ring? Or is this manageable?
"The next thing to try out is to use the Braycote grease along with the scraper and apply the grease and then try to remove it with the scraper and see does that pull up, attract more of the debris. The scraper is basically a putty knife, so you would use it to spread the grease out and then come back over it with the scraper and try to remove the grease and debris with it.?
"The final thing is to just take a wipe with grease and spread just grease with the wipe," he said. "The reason for that is, the crew reports (have indicated) there's some fine particulate on the ring as well as, obviously, there are some parts that are a little bit more substantial that are either pressed on debris or damage sites. So the question is, does going over it with the scraper remove any of this bigger stuff to help get this ring any smoother? Or does it do nothing more than what just a wipe with the grease does to remove this fine particulate?
"You don't want to waste time using a scraper if it doesn't do much for you. So really, this is just a test of several different techniques to try to narrow down which ones are most effective so we can better plan spacewalks on (future) missions."
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