Shuttle commander Lee Archambault used Discovery's steering jets today to re-orient the shuttle-space station "stack" and in so doing, slightly lower their altitude. The maneuver was ordered to reduce the odds of a potential close encounter, or conjunction, with a 4-inch-long piece of Chinese rocket debris.

Station commander Mike Fincke, meanwhile, replaced a filter assembly in the lab's finicky urine processor assembly late today and was cleared to load the processor with stored urine for a delayed processing test. Fincke spent most of the morning troubleshooting a lower-than-expected flow rate that delayed plans to start a test run before noon.

Flight controllers later told Fincke to stand down while engineers on the ground tried to figure out what the problem might be. Later, they suggested swapping out a filter and Fincke was cleared to make another attempt to load urine for the so-called "wet" test. A complete processing cycle takes about five hours to complete.

"Houston, station, on space-to-ground 2 for UPA," Fincke called. "We took it up to 65 percent and we can see it's going through the filter now with the nominal, so far, apparently, decrease rate."

"And Mike, we copy and concur based on what we're seeing," Rick Davis replied from Houston. "So hopefully it'll continue that way, that would be great."

While Fincke was resuming work with the urine processor, Archambault was maneuvering the shuttle-station stack into the same orientation that will be used next week for undocking, one in which the belly of the orbiter is pointed in the direction of travel.

"Just looking to make our conjunction numbers better during tomorrow's EVA (spacewalk), we want to do a very minor orbit adjust," astronaut Stephen Robinson called from mission control. "So at 20:46 MET (mission elapsed time, or 4:29 p.m. EDT), we'll have you maneuver to the undock attitude using the shuttle, hold that attitude for three hours, then we'll move back to (the normal orientation) and give attitude back to station. We're putting a note together with the details, but that's the big picture."

By maneuvering to the undocking attitude, the shuttle-station vehicle will experience slightly more atmospheric friction, or orbital drag, than usual, causing a very slight change in altitude. The maneuver will have the same result as a rocket firing that changed the station's velocity by about 1 foot per second.

A NASA spokesman said the attitude maneuver will be enough to make sure the debris in question, identified by catalog number 26264 (CZ-4 DEB) and believed to be a 4-inch-long piece of debris from an upper stage, does not get close enough to cause any problems.

"They want to adjust the attitude slightly in order to ensure that they're able to avoid a piece of debris that has been identified in the area," said mission control commentator Nicole Cloutier. "This small maneuver will ensure there is no collision concern."

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.

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