Apparent problem with motor in station's water system
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: November 21, 2008
Engineers believe the problem with the space station's new urine processor assembly, a key component in the water recycling system needed to boost the space station's crew size from three to six, involves trouble with a motor or associated sensors in a centrifuge that helps separate pure water from urine in a vacuum distillation system.
The motor ran normally for two hours earlier today before shutting down when sensors indicated the motor in question began slowing down and drawing more current than normal. Station flight director Courtenay McMillan said engineers do not yet understand the nature of the problem or what might be needed to fix it. The astronauts do not have spare parts for major components in the system, but engineers may be able to come up with a work around.
"What we saw earlier today when we brought the UPA back on line, it looks like there is a problem on the motor on the centrifuge in the distillation assembly of that system," McMillan said. "Right now, folks are still looking at the data, we got some conflicting information from a couple of different sensors so we're really still trying to understand the signature. It doesn't match anything specifically that we saw, it doesn't identically match something we've seen in ground testing. So they're really still investigating and determining forward steps. They may be able to mask it if it is a sensor, but we don't know that for sure yet."
One of the primary goals of the shuttle Endeavour's on-going mission was to install the new water recycling system, activate it and begin initial urine processing runs. Engineers want the astronauts to bring fully processed samples back to Earth aboard Endeavour for detailed chemical analysis of water quality and to help calibrate an on-board analyzer.
The plan called for a 90-day checkout in orbit and analysis of additional samples after a February shuttle flight before the system would be deemed operational, clearing the way for the station's crew to increase to six next May.
Going into Endeavour's mission, NASA managers held open the option of adding a docked day to the shuttle flight to give the crews time to get the equipment installed and operating. The astronauts were running well ahead of schedule and as of Thursday, it did not appear an additional day would be necessary. But as of this writing, it's not known whether the urine processor assembly can be re-activated in time to generate the needed samples or even whether an extra day would help.
If the hardware is, in fact broken or unable to operate properly, the station crew could be forced to wait for a spare distillation unit to be launched on the next shuttle flight in February, a delay that presumably would impact NASA's plans to boost the station crew to six next May.
But McMillan said that level of concern was premature.
"We were running for two hours with no issues prior to this so we know the system was running pretty well prior to this point," she said. "So we have some pretty good confidence there. But yeah, without this (motor), we can't get much further. So we do need to figure this out before we can proceed."
Station commander Mike Fincke took a philosophical view, telling reporters earlier today "as a flight test engineer, I fully expected things not to work perfectly."
"No matter how well we plan on the ground or test on the ground, you really need to test fly it," he said. "And that's what we're doing here. I think we found a sensor that's not working correctly, so we're going to look into it and see if we can bypass the sensor, replace the sensor. But so far, everything else is looking really clean and looking really good. So we're very hopeful we can still get the first round of samples through during this mission while the STS-126 (crew) and Endeavour are still here. So we're not worried so far. We've got the right team up here if we need any fixes."
The urine processor is in one of the two water recovery system racks delivered to the space station aboard Endeavour, along with a new toilet, a potable water dispenser, a new galley and two new crew sleep stations. The WRS racks were mounted in the floor of the Destiny laboratory module and connected to a potable water bus that eventually will feed urine from the toilet and route pure water to the galley and the potable water dispenser.
For readers unfamiliar with the intricacies of the station's new water recycling equipment, here's how Endeavour astronaut Don Pettit described its operation before launch:
"The key to the urine processing uses the age old practice of distillation," Pettit explained. "This is a vacuum distillation apparatus, which will put a partial vacuum on urine concentrate and it will allow the water to boil off at a lower temperature than if you just cooked it under the standard atmosphere of space station. And so the water that comes off from this distillation outfit is going to be pretty pure.
"But any distillation process has a little bit of carry over. It's kind of like the backwash when you drink in your water bottle. And so, to get rid of this little bit of backwash, we run it through a catalytic converter, which will oxidize any of the backwash. The catalytic converter actually has a supply of oxygen running into it to provide an oxidation material to go with the catalyst to convert the backwash, so to speak. And then from there, it goes into a series of ion exchange beds.
"At that point, it's almost like deionized water," Pettit said. "It also goes through a charcoal bed that gets rid of a few other impurities and then it finally gets analyzed by a couple of on-line boxes. One of them just checks the bulk resistivity and if that doesn't satisfy the box, it opens up a valve and sends that splash of water back to go again. It's kind of like a Monopoly game where you don't get to go by go and get $200. You just go straight back to the distillation unit.
"And then, from there it goes through this TOCA machine, this Total Organic Carbon Analyzer. Organic carbon is the kind of stuff you don't want. If the feed stock is urine and you're having potable water come out, you don't want organic carbon in there. So, the total Organic Carbon Analyzer lets you know whether any of that stuff has come through. And then from there, it can branch out into the oxygen generator or go to the galley. In the galley, they add some salts just to make the water taste a little bit better. if you drink distilled water, it doesn't taste as good as regular water and there's a few mineral salts in there that for some reason or another makes it more palatable to human beings.
"From there, we can use it to make our dinner or our coffee with," Pettit said. "I like to refer to this whole process as a coffee machine. Because it's going to take yesterday's coffee and make it into today's coffee."