Second spacewalk a success; water recycling glitch studied
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: November 20, 2008
Despite a tool shortage, a spacesuit carbon dioxide buildup late in the day and communications problems, spacewalkers Heidemarie Stefanyshyn-Piper and Robert "Shane" Kimbrough accomplished the primary goals of a six-hour 45-minute spacewalk, officials said today, moving two equipment carts, servicing the space station's robot arm and continuing work to clean and lubricate a jammed solar array rotary joint. Inside the lab complex, meanwhile, other astronauts ran into start-up glitches with the lab's new urine processor.
"These are the growing pains we expect to see," space station Flight Director Ginger Kerrick told reporters late today. "We have had similar experience when we first activated the oxygen generation system, it took us quite a while to work out the kinks. These are very complicated pieces of equipment with a very complicated software system to control them and this is the first time they are all being put together in space, so it takes a while to learn lessons from that.
"Does this set us back from what we hope to accomplish? Right now, we can incorporate about a 24-hour delay in the tasks we had planned in the timeline and still be able, assuming everything else goes nominally, to accomplish our sampling objectives ,... without requesting (an extra) day. We think this is just a small setback, we'll take some time and figure out what exactly caused the situation that we saw today and we have hopes that we can still accomplish everything."
A major goal of the current assembly mission is to install complex water recycling gear in the space station that can convert urine and condensate into pure water for drinking, meal preparation, personal hygiene and oxygen generation. Water recycling is required for NASA to expand station crew size from three to six next year.
Two water recovery system racks were installed in the Destiny lab module earlier this week and the astronauts spent much of the day today hooking the equipment up to begin initial shakedown runs. The goal is to produce samples of potable water from processed urine before Endeavour departs. Those samples will be returned to Earth for a detailed chemical analysis to confirm water quality and to help calibrate an on-board analyzer. The astronauts were beginning initial tests with stored urine as today's spacewalk was winding down.
Toward the end of the excursion, Kimbrough's spacesuit showed a buildup of carbon dioxide that exceeded NASA's safety limits. While he was in no immediate danger, flight controllers told him to terminate his portion of the spacewalk and return to the station's Quest airlock module as a precaution. The call came as he was winding up work anyway.
On the way back to the airlock, however, he ran into problems hearing his crewmates and flight controllers in Houston, apparently because his headset volume knob had been bumped and accidentally turned down earlier. At around the same time, an alarm sounded that got Stefanyshyn-Piper's attention.
"The EVA trip back into the airlock was a little eventful," Kerrick said. "We had some comm issues, we also had a crew member who was having elevated CO2. But all those are under investigation and it was no problem getting the crew member back in the airlock and Shane is fine.
"While that was going on, on the inside, we had a caution alarm ring and the EVA crew heard that in their headsets. That caution was associated with some commanding that we were doing for the urine processor assembly. We have downlinked some date, we think we understand what the problem is and the teams will be off assessing that tonight to determine how much of the commanding that was planned for this evening can still be performed."
The alarm sounded as commands were being sent to the urine processor.
"We ran into a snag, I guess it was last night, with the amount of cooling we were providing to the WRS rack, the water recovery system, rack," Kerrick, said. "Folks met this morning and we got comfortable with that so we started on with our procedures. The point to where we got to tonight, we were getting ready to command the urine processor to actually process the urine. And one of the commands we sent annunciated the caution alarm.
"The standard response for that particular caution is to remove power to the unit and have the crew member take (a reading) looking for signs that there were combustion products. That's our typical response for an RPC trip. This particular time, we were suspicious of the response because we knew the commands we were sending at that time should not have initiated that response. When the crew members confirmed that they had no concerns, no smell of smoke or no odor, especially when they told us the combustion products were all reading zero, we began to think it was a false indication. That was indeed the case."
But the urine processor assembly was halted and engineers ordered a data downlink to find out exactly what happened.
"We think we have a handle on what caused the caution to annunciate, but we're going to have to think about it some more and talk with our engineering counterparts before we get comfortable sending any commands to the UPA again tonight," Kerrick said. "We are still going to continue with our water processing activities for this evening. Even if the UPA does not process the urine, there is a possibility to take condensate, run that through the water processor and still get a sampling out of the water processor assembly and later on, the potable water bus and the potable water dispenser."
Going into Endeavour's mission, managers were holding open the option of extended the docked portion of the flight by one day to give the astronauts extra time to install and test the potable water dispenser. The astronauts were running well ahead of schedule installing the water recycling gear and mission managers were optimistic the extra day would not be needed. Whether that will change if the current glitch cannot be quickly resolved remains to be seen.