1210p 11/22 Update: Spacewalk begins; urine processor troubleshooting continues

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CBS NEWS STS-126 STATUS REPORT: 50
Posted: 1:05 PM, 11/22/08

By William Harwood
CBS News Space Analyst

Changes and additions:

   SR-46 (11/21/08): Urine processing underway; crew news conference on tap
   SR-47 (11/21/08): Urine processor shuts down again; troubleshooting continues
   SR-48 (11/21/08): Engineers troubleshoot apparent problem with motor in urine processor
   SR-49 (11/22/08): Urine processor restarted; crew gears up for third spacewalk
   SR-50 (11/22/08): Spacewalk begins; urine processor urine processor troubleshooting continues

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1:05 PM, 11/22/08, Update: Spacewalk begins

Floating in the space station's Quest airlock module, astronauts Heidemarie Stefanyshyn-Piper and Stephen Bowen switched their spacesuits to internal battery power at 1:01 p.m., 44 minutes ahead of schedule, to officially kick off a planned seven-hour spacewalk.
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The goal of today's excursion, the third of four planned for the shuttle Endeavour's mission, is to finish cleaning and lubricating the station's stalled right-side solar array rotary joint. The astronauts also plan to replace six of the joint's 12 trundle bearing assemblies, or TBAs, which grip the main drive gear on three surfaces with pressure-loaded rollers. One TBA was replaced during a shuttle flight last June, four others were replaced during spacewalks Tuesday and Thursday and a sixth was removed and re-installed after cleaning.

This is the 117th spacewalk devoted to station assembly and maintenance since construction began 10 years ago this week and the 18th so far this year. It is the second spacewalk for Bowen and the fifth overall for Stefanyshyn-Piper, who participated in two EVAs during a 2006 station assembly mission. Going into today's spacewalk, station EVA assembly time stood at 732 hours and 25 minutes. The total for Endeavour's crew through two spacewalks was 13 hours and 37 minutes.

Back at the Johnson Space Center in Houston, meanwhile, engineers are continuing efforts to figure out what's causing problems with a vacuum distillation unit in the space station's newly installed water recycling system.

The distillation unit, a critical component in a system designed to convert urine into potable water, was restarted earlier today to collect additional data and insight into what might have caused a centrifuge motor slowdown and high current draw Friday. A similar "signature" was seen again today and again, the urine processor shut itself down. Troubleshooting continues.

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Quick-Launch Web Links:

CBS News STS-126 Status Reports:
http://www.cbsnews.com/network/news/space/current.html

CBS News STS-126 Quick-Look Page:
http://www.cbsnews.com/network/news/space/currentglance.html

NASA ISS Expeditions Page:
http://www.nasa.gov/mission_pages/station/expeditions/index.html

NASA Shuttle Web: http://spaceflight.nasa.gov/shuttle/index.html
NASA Station Web: http://spaceflight.nasa.gov/station/index.html
Spaceflight Now: http://spaceflightnow.com/index.html
GoogleSatTrack: http://www.lizard-tail.com/isana/tracking/

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