Station's recycling gear shuts down again after repair
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: November 23, 2008
An improvised fix to overcome subtle vibration issues that triggered premature shutdowns of the space station's new urine processor assembly appeared to have paid off Sunday. Engineers said an initial test run continued past the point of earlier failures, raising hopes the critical system can be coaxed into normal operation. But less than an hour later, the processor shut itself down again after experiencing problems similar to those that interrupted test runs Friday and Saturday.
"Teams on the ground who have been watching the test of the urine processor over the last, almost, three hours now are reporting that, although it was initially running well and ran longer than the earlier tests of it, it has again shut down," said mission control commentator Brandi Dean. "They're looking at different possibilities of what could be causing that problem and will be troubleshooting it overnight."
The newly installed water recycling system aboard the space station is crucial for NASA's plans to boost the lab's crew size from three to six next May. NASA managers had hoped to collect test data on the urine recycling system for the next 90 days before a dress-rehearsal in February using the crew of the next shuttle mission to simulate the "load" the lab's life support system will experience when the station' crew size jumps to six.
As it is, time is running out for NASA managers to make a decision about how to proceed. Engineers still hope to figure out a solution that would permit normal, or near-normal, operations with the urine processor "as is." But if a solution is not found in fairly short order, the astronauts could be forced to ship the hardware back to Earth for repairs. While the distillation unit presumably could be repaired and relaunched in February, it wouldn't leave much time to complete testing before it would have to go on line to support six crew members.
"Clearly, we want to get the system running as soon as possible so we can start processing urine and verify that we do have good potable water coming out the other side," space station flight engineer Sandra Magnus told CBS News Sunday. "I know there are some plans when the (shuttle) arrives to pick me up in February to also have the toilet up and running and have the maximum loading of six to 10 people using the toilet, working through the urine processor, to get the system into a test run, if you will, for the six-person crew.
"So it's really important that we get this up and running and again, we want to do that to make sure it's set and ready to go when we send up our six-person crew next summer."
Endeavour currently is scheduled to undock from the space station Thanksgiving day. NASA managers could delay undocking at least one day if engineers determine the extra time could help in the troubleshooting effort. Shipping the distillation unit back to Earth would be a worst-case scenario, delaying tests and checkout until February and possibly disrupting NASA's plans to boost crew size in May. Engineers remain hopeful it won't come to that.
"We really want to be confident the system will run long term so that when we begin six-person crew operations in May, we know we've got essentially a stable platform in the life support systems operation," station Flight Director Courtenay McMillan said earlier today. "So the longer we can actually perform the checkouts prior to that, the better off we are.
"The reason we really targeted this flight for performing the analysis, we still have some margin in case something goes wrong and we need to do any replanning or fly up any additional equipment or consumables on the mission in February. So we do still have some room and some runway ahead of us in this case. If we wait until February, we may not get all the engineering requirements to be sure that all the systems are working as required in order to support six-person crew."
If the distillation assembly is shipped back to Earth aboard Endeavour, "we may still be able to make it in May in that case," McMillan said. "We would need to look at do we need the full checkout period and what type of evaluation we have to do of samples and so forth and what that does to the schedule as well. Those conversations haven't started yet, we're tying to get all we can out of this mission."
Initial urine processing runs Friday and Saturday ended after about two hours when telemetry indicated the 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 presumably 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 may have 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."
But the optimism was premature.
"For the first more than two hours, that fix seemed to be working, although the motor was giving a similar signature to the one they'd seen in the past just before it shut down," Dean said. "However, just a few moments ago it shut down again. So they will be continuing troubleshooting of that problem tonight."