Spacewalkers Continue Replacing Batteries

(CBS)  Mission Specialists Christopher Cassidy and Thomas Marshburn switched their spacesuits to battery power at 9:54 a.m. EDT to officially begin a planned seven-and-a-half hour spacewalk today.

CBS News space analyst Bill Harwood reports that the astronauts will replace a final four batteries in the International Space Station's oldest set of solar arrays, a critical task that was interrupted during a spacewalk Wednesday because of elevated carbon dioxide levels in Cassidy's spacesuit.

Spacewalks are normally scheduled for no more than six-and-a-half hours, but today's excursion was extended to give the astronauts time to complete the battery swap out.

NASA reported that by 11:17 a.m. EDT, the first of four batteries has already been replaced.

Cassidy and David Wolf attempted to replace four of the six batteries during a spacewalk Wednesday, but the excursion was cut short after just two batteries were installed when engineers noticed rising CO2 levels in Cassidy's suit.

The spacewalker never experienced any symptoms of hypercapnia, which include headaches, confusion and lethargy, and he said Thursday he was surprised when the spacewalk was called off.

"They're getting telemetry from each of our suits," Cassidy said. "They're able to detect any problems long before we inside would have any idea. In fact, it was a total surprise to me that the CO2 was climbing high, and we aborted at conservative numbers, so I felt no symptoms and really was not that concerned. I was confident they had my safety in mind."

Space station Flight Director Holly Ridings said Thursday engineers believe the problem was triggered when Cassidy, a former Navy SEAL, got off to a fast start in his first spacewalk, overtaxing the lithium hydroxide, or LIOH, that is used to scrub carbon dioxide from his air supply.

"There is a feature of the way LIOH works where if you go out and you have a very high metabolic rate at the very beginning, then the canister doesn't work as well for the duration," she said. "It's kind of got a metabolic rate that it's expecting.

"So we talked to the crew and we explained ... to them that it's important that they don't go out really excited and really fast like you normally would on your first spacewalk. They understand they need to take it slow at the beginning and let the LIOH can do its thing and then it will work efficiently for the duration."

Asked if the crew was told to do anything different procedurally, Ridings laughed and said, "Chris is a very motivated, very intelligent guy and he was excited about his first spacewalk. And he went all the way from the airlock ... out to the end very, very quickly. He's a Navy SEAL, he's in great shape and so we really just needed to tell him, 'Hey, we know you can do this really well and really fast, but we need the LIOH to work right for us.' He took that with good humor."

It will be the 129th spacewalk devoted to station assembly and maintenance since construction began, the 10th so far this year and the fourth of five planned by Endeavour's crew.


For more info:

Space Shuttle Main Page (NASA)

CBS News space analyst Bill Harwood's "Space Place" updates