October 29, 2007 / 2:55 AM / in 11 years

NASA extends shuttle mission

CAPE CANAVERAL, Florida (Reuters) - NASA added a day to the shuttle Discovery’s visit to the International Space Station to allow time for spacewalkers to study a troubled but critical part of the outpost’s power system, the agency said on Monday.

International Space Station flight engineer Clayton Anderson works at a computer in the Destiny module as he prepares for his return trip home aboard the Space Shuttle Discovery in this image from NASA TV October 29, 2007. REUTERS/NASA

The work will delay Discovery’s departure from the station to Monday from Sunday, a postponement that NASA said could carve a day out of the already slim six-day launch window for the next mission, when the shuttle Atlantis will fly the long-awaited Columbus laboratory to the station. That mission is targeted for launch on December 6.

For nearly two months, NASA has been aware of a potential problem with one of the station’s massive rotary joints that spin the outpost’s solar wing panels so they can track the sun and generate power.

But when spacewalker Dan Tani was dispatched on Sunday to investigate the problem during a spacewalk, he found shards of metal scrapings prevalent throughout the joint.

“I was quite sure there was something anomalous with the mechanism,” Tani said on Monday during an in-flight interview.

He collected samples to return to Earth for analysis, but space station commander Peggy Whitson, a biochemist, conducted a preliminary experiment on Monday and discovered that the metal bits contained iron.

That was not good news. NASA had hoped the debris was coming from outside the joint, such as from one of the device’s aluminum-lined thermal covers. Now engineers will be looking at parts of the rotary joint itself.

To prevent further damage, managers decided to lock the affected solar panels in place to avoid working the rotary joint. That cuts the amount of power the station can produce, a situation that must be corrected before Japan’s science laboratory, Kibo, is launched next year.

ADDITIONAL DAMAGE

“We can move it around, but without knowing what the problem is there is the risk that we could do more damage,” Whitson said.

The astronauts had planned to test a shuttle heat shield repair technique on Thursday during the fourth spacewalk of the mission, one of several safety upgrades NASA developed after the 2003 Columbia disaster. Instead they will use that outing to pull off the rest of the troubled joint’s thermal covers to see if the damage is widespread.

In addition, spacewalkers Scott Parazynski and Doug Wheelock, who are scheduled to leave the space station’s airlock early on Tuesday for the mission’s third spacewalk, will inspect the station’s healthy solar power panel joint to compare it with its troubled mate.

The primary goal of Tuesday’s outing is to move a third pair of solar wing panels to a new position on the far end of the station’s frame. The folded-up wings must then be unfurled, a maneuver that has become more critical in light of the power shortfall caused by the rotator problem.

Discovery’s astronauts arrived at the station on Thursday for what was planned to be a 10-day stay. With the extra day at the outpost, Discovery’s return to Earth is being postponed to November 7.

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