Monday, November 24, 2008

630p 11/23 Update: Urine processor test run begins; Fincke reports unusual noise from system


Posted: 6:25 PM, 11/23/08

By William Harwood
CBS News Space Analyst

Changes and additions:

   SR-56 (11/23/08): Urine processor repair attempt; Monday spacewalk replanned
   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


6:25 PM, 11/23/08, Update: With dampers removed, urine processor re-started in critical test of recycling system; Fincke reports unusual noise in system

After work to remove rubber vibration dampers from a centrifuge assembly inside the space station's new urine recycling system, the astronauts and flight controllers began another test run Sunday evening to find out if the improvised fix will eliminate a vibration-related problem that triggered pre-mature shutdowns.

The urine processor facility is designed to run about four hours at a time converting urine in a standard Russian container into potable water. During test runs Friday and Saturday, the motor driving a centrifuge in the processor's vacuum distillation sub-system slowed down after about two hours, forcing shut downs.

Telemetry indicated the problem involves physical interference between the spinning centrifuge and a speed sensor, possibly caused by thermal effects and/or a frequency mode the device gets into after extended operation.

"It could be thermal expansion and then two pieces actually rubbing up against each other inside or the outside of the case rubbing up against something," station Flight Director Courtenay McMillan told reporters late today. "It could be the combination of fluid dynamics and the ability of the whole drum to move. In previous tests, we've had the drum essentially fixed so it can't move at all, the whole centrifuge drum was fixed."

Aboard the station, however, the centrifuge assembly is mounted inside a water recovery system (WRS) rack with bolts running through thick rubber washers to serve as vibration dampers. The idea was to reduce the noise produced by the spinning centrifuge.

"We think with the dampers, it allows for some slight amount of movement that might exacerbate the dynamics of the fluid that's moving inside the centrifuge in such a way that it could slow it down," McMillan said. "We're not a hundred percent sure by any means that this is the mechanism causing the problem. But it is one way it could try to slow the motor down, just the interaction of the inertia of the fluid with how the drum itself is behaving. So by taking out those dampers, you reduce the ability for it to move at the drum level. That will increase some of the noise the system makes overall, but we think if we can actually make this work, we can find another way to deal with that if we have to."

Station commander Mike Fincke and Endeavour astronaut Don Pettit removed the dampers this afternoon, bolting the centrifuge directly to its support tray. Late in the afternoon, another test run was started. After the unit was restarted, Fincke reported hearing an unusual noise in the centrifuge section of the processor.

"I can hear, I don't know what you'd call it, like a sound coming from the WRS rack No. 2, near the distillation unit and I don't know if that's the centrifuge misbehaving or the centrifuge behaving," Fincke radioed a few minutes after 6 p.m. "I just wanted to let you know I'm starting to hear some slight noises that weren't there before."

"Houston copies and we appreciate those words. From all the data we've got on the ground, it looks like WRS is working nominally," replied Mark Vande Hei from mission control.

"OK, then we'll pay no attention to that noise. But it did sound like it was something that was spinning and had a slight imbalance to it. But maybe it's just a normal noise. These are new racks ... so I'll pay no attention to it. However, if you see (a computer) caution pop up, let us know and maybe we can hear something or stop by and take a look and give you some other data besides the telemetry you've got."

A few minutes later, Vande Hei reconfirmed that no problems were showing up in telemtry from the centrifuge.

Earlier Sunday, FIncke praised engineers at the Johnson Space Center in Houston for coming up with the damper-removal fix.

"We're not picking at straws here," Fincke told CBS News in a post-repair interview. "These guys (in Houston) did a great job in a very short period of time to come up with an analysis for some tricky problem. The centrifuge, it would spin around for two hours and then all of the sudden would get a little bit unbalanced and we think it's partly because maybe it had a little bit too much play in the mounts, because that helps reduce vibrations.

"In this case, by nailing it down a little bit, by bolting it down, we'll reduce the vibration. It may make things a little bit louder on the space station but maybe good enough to keep the centrifuge in balance while it processes the urine. So we're very hopeful for this and if not, we have a few other tricks up our sleeves. Ultimately, we could even take the distillation unit back with Endeavour. So right now it's a good time to test all these things out."

If the repair work does not resolve the problem, McMillan said engineers will consider other alternatives, including the possibility of shipping the centrifuge unit back to Earth aboard Endeavour for repairs and re-launch aboard the next shuttle bound for the space station in February.

But that would throw a wrench into NASA's plans to thoroughly test the new hardware before expanding the station's crew size from three to six.

"We really want to be confident the system will run long term and 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," McMillan said. "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," she said. "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."


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