Discovery moves station; urine processing tests begin
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: March 22, 2009
Discovery commander Lee Archambault maneuvered the shuttle-space station "stack" today to avoid multiple close encounters with a piece of Chinese space junk that could have posed a threat during a third and final spacewalk Monday. Space station commander Mike Fincke, meanwhile, made solid progress with lab's urine recycling system and resumed testing late in the day after resolving a snag earlier in the day.
"We had a little bit of a problem loading up the RFTA, the filter assembly," outgoing station flight engineer Sandra Magnus told CBS News in a space-to-ground interview. "We ended up changing that and now Mike's back in the mode of dumping some of our urine tanks, our full urine tanks, into the processor to fill it up and start the processing. So things are moving ahead and we're hoping for a good outcome here in a few hours or a few days."
Late this evening, Fincke positioned a microphone next to the urine processors newly installed distillation assembly centrifuge for a "dry spin" test to collect acoustic data for an engineering analysis. The system's original distillation unit failed shortly after installation last year, presumably due to internal mechanical interference of some sort.
"The dry spin is going very successfully," Fincke reported as the new centrifuge spun up. "I remember the original distillation assembly and I never remember it being this quiet. ... It's looking great so far."
"Concur. We see good data as well, happy day," replied Lucia McCullough in mission control.
Fincke planned to oversee the start of the first "wet" test using stored urine later this evening.
While the Discovery astronauts enjoyed a half-day off earlier today, flight controllers at the Johnson Space Center in Houston began evaluating a predicted close encounter with a piece of Chinese space junk. Tracking data indicated the 4-inch-wide debris would repeatedly cross the space station's path Monday afternoon.
Concerned about having to carry out a debris avoidance maneuver during a spacewalk, lead flight director Kwatsi Alibaruho said mission managers decided to protectively make a subtle change today to preclude any close encounters. Rather than firing rocket thrusters and making a major change in the station's trajectory, flight planners had Archambault maneuver the combined shuttle-station stack into a normal undocking orientation with Discovery's belly pointed in the direction of travel.
In that orientation, atmospheric friction, or drag, would provide most of the energy needed to lower the station's altitude slightly with the same result as a rocket firing that changed the station's velocity by 1 foot per second. Archambault maintained that undocking attitude for about three hours before moving back to the normal orientation with the shuttle behind the station.
"Space debris is becoming an ever increasing challenge," Alibaruho agreed. "On one level, it causes us great concern, it's potentially hazardous to the spacecraft. We've been very fortunate, and also very diligent about monitoring for space debris, we do that in partnership with other government agencies that gives us the capability to try to predict when we may have a problem and adjust.
"The process of adjusting the orbit of the space station is a big deal. It requires a lot of planning, it's very resource intensive. When we do not have a shuttle there, it requires a great deal of coordination and analysis between mission control in Houston and mission control in Russia. ... It's a big deal, it's very tiring. But at the same time, we accept it as a necessary part of our business."
The threat posed by space debris has been in the news in recent weeks following a collision between to satellites in February and a predicted encounter just before Discovery's launch that forced the station crew to briefly take refuge in the lab's Soyuz lifeboat.
For his part, Archambault told CBS News he believed the events of recent weeks "seem like a coincidence. We have had a couple of these in the last couple of weeks, but as far as I know, it is coincidental."
Asked if the spacewalkers viewed space debris as a concern, astronaut Steven Swanson said "I guess I don't think too much about that. We have enough other risks and worries to take on as we go outside and I'm just trying to get the job done right. That's what I'm concentrating on."
During a spacewalk Saturday, Swanson and Joseph Acaba had problems deploying an external payload storage mechanism on the station's left-side solar power truss. During a briefing later, officials said a clamp appeared to have been installed incorrectly, preventing the mechanism from rotating into the fully deployed position.
Alibaruho said today the clamp did, in fact, appear to be in the wrong orientation, but he and Swanson both said that did not appear to be what was preventing a full deployment.
The detent that must be disengaged to allow smooth movement was "a lot stiffer than we thought it was going to be," Swanson told CBS. "And I didn't actually pull down very hard on it. So once it wouldn't come down with just a little pull, we started looking around (for what might be wrong). That pin might have been a little big out of config, but it shouldn't have actually stopped it.
"So we started looking around and we were worried about that, but now since we came back in and have more data, it looks like if I'd just pulled hard on it, it would have come on down. So tomorrow, when Joe and Ricky (Arnold) go out, that's one of the first things they're going to do ... is to pull down on it with more strength and see if it comes loose."
If that doesn't work, however, the spacewalkers likely will simply tie the mechanism down with straps to prevent inadvertent movement and move on to other tasks.
"The idea for plan B is we were probably going to just tie it down for right now until the ground can come up with more ideas on what the real problem is," Swanson said. "Because that's what all the models, all the engineering analysis, shows, it's probably just the detent position. So if it's not that, then they really don't know and we don't know exactly what the problem is and (to make sure) we don't hurt anything else, we're just going to tie it down for long duration so it can stay up here for a while while they work on the problem and come up with a solution."
Alibaruho said part of the problem Saturday was that "we train our astronauts not to apply excessive forces on any kind of rotating mechanism. So when the mechanism did not rotate freely with a slight application of force, we investigated the possibility there was some binding or some interference with the mechanism. So the fix for it may be as simple as pulling on it harder to free it from the detent.
"But this is, again, a theory, we won't really know until we get the spacewalkers at the site. ... Our first order will be to try to pull harder to try to get the mechanism to its nominal position. If we're not able to free the mechanism ... we will employ a long duration tie down, where we simply attach some very sturdy straps and tie that swinging platform into a configuration we can leave it in for an extended period."