April 14, 2010

NASA May Call For Unplanned Fourth Space Walk

NASA officials said Wednesday that astronauts on board the International Space Station (ISS) might have to perform an unscheduled fourth space walk due to a malfunctioning valve on a newly installed ammonia tank. 

The tank was installed Tuesday during what was considered to be the last space walk by U.S. shuttle astronauts.  It is a key part of the cooling system on the ISS.

Dan Huot, a spokesman for NASA in Houston, said a faulty nitrogen valve on the pressurizer for the ammonia has prevented the new cooling system from working.

"Right now, ground controllers are going through their procedures," Huot said.

"They have been doing a couple of calling procedures to try to get the valve to respond, but it is not responding. They are trying to figure it out."

Huot said a fourth space walk could be needed in order to fix the valve.

"That's one potential way, because they do have a spare box with a nitrogen pump in it" at the ISS, he said.

Astronauts Rock Mastracchio and Clayton Anderson installed the tank on Tuesday during a six-and-a-half hour space walk.  The walk was supposed to be the final outing for the astronauts before they return home on the Discovery on Monday.

The space walk took longer than planned because the astronauts had problems stowing the empty ammonia tank assembly on a carrier in the shuttle's cargo bay in order to bring it back to Earth.

The shuttle will carry about 2.5 tons back to Earth from the station in its cargo bay.

Flight Director Ron Spencer said NASA is concerned about having the astronauts go back out for a fourth space walk because they did not train for this particular situation.

"We want to make sure we get it right before we go out there," Spencer told reporters. "We're still sharpening our pencils on what the options are."

Spencer said that it is possible NASA may be able to operate with the stuck valve through May.  That would allow flight controllers more time to prepare for the spacewalk repairs.

Mastracchio told reporters in a news conference that he and Anderson were both feeling fine and would be happy to go out again if necessary.

"It may have seemed like we were working hard," Mastracchio told reporters. "But actually as we were struggling with those bolts, we were just doing a lot more thinking than we were actually working."

"Today, Clay and I feel fine. And if necessary, we'll go out for future spacewalks, but hopefully, none of those will be required."


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