Monday, November 24, 2008

730p 11/23 Update: Urine processor runs past point of earlier shutdowns; engineers hopeful fix worked


Posted: 7:30 PM, 11/23/08

By William Harwood
CBS News Space Analyst

Changes and additions:

   SR-57 (11/23/08): Urine distillation unit maintenance procedure completed; crew stands by for test run
   SR-58 (11/23/08): With dampers removed, urine processor re-started in critical test of recycling system
   SR-59 (11/23/08): Urine processor continues working beyond earlier failure point; engineers hopeful about fix


07:30 PM, 11/23/08, Update: Urine processor continues working beyond earlier failure point; engineers hopeful about fix

An improvised fix to overcome subtle vibration issues that triggered premature shutdowns of the space station's new urine processor assembly may have paid off Sunday. Engineers say an initial test run continued past the point of earlier failures, raising hopes the critical system can be coaxed into normal operation.

Test runs Friday and Saturday ended after about two hours when telemetry indicated a centrifuge motor in the unit's vacuum distillation assembly began slowing down and drawing higher than normal currents. When programmed safety limits were exceeded, the unit shut itself down.

Today, the astronauts removed rubber vibration dampers from the distillation unit's rack mounting system in a bid to reduce, if not eliminate, physical interference between the spinning centrifuge and a speed sensor caused by a subtle interplay between thermal expansion, vibration frequencies and the inertia of the liquid circulating in the system.

After two hours of operation this evening, engineers reported seeing a motor speed decrease and current drop similar to what was observed during test runs Friday and Saturday. But this time around, the processor did not shut itself down, indicating the removal of the vibration dampers helped improve performance.

"We saw the same signature that we saw yesterday and the day before," an engineer radioed the astronauts. "It was a small decrease in speed and a small increase in current that steadied itself back out. It did not fail off and it's still processing."

"That sounds dandy news," station commander Mike Fincke replied. "We've been watching it and actually have the PCS plot function up (on a computer display) for the first time in my life and we saw that yeah, we saw it's still going and the current is about one point four. ... So Megan, the big picture plan is to keep processing, and that means I'll probably need to do another fill in about another hour, hour and a half?"

"We're actually going to let it run through this (four-hour) process and then probably talk about it a little bit and I'm guessing we can do a fill tomorrow, maybe," she replied.

"OK, well we have quite a collection (of urine) up here," Fincke quipped. "So anytime you need a fill, we'll be happy to unload it as opposed to loading it up. So that's good news so far, we'll keep our fingers crossed."


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