Smooth is Fast

Astronaut's enthusiasm causes spacewalk breathing problem

NASA has some advice for the elite U. S. navy diver-turned-astronaut whose first spacewalk was cut short because of an air issue: Breathe easily.

Endeavour astronaut Chris Cassidy and partner David Wolf were nearing the end of a spacewalk on Wednesday when carbon dioxide, a byproduct of breathing, started to build up in Cassidy's suit. The poisonous gas is chemically removed from the sealed spacesuit by a canister of lithium hydroxide.

Engineers believe Cassidy's enthusiastic and strenuous start to his outing led to a failure of the canister later in the spacewalk. Cassidy was never in any danger, as the spacewalk was cancelled before the carbon dioxide levels came anywhere close to being a concern.

"There's a feature with how the (lithium hydroxide) works where if you go out and have a very high metabolic rate at the very beginning, then the canister doesn't work as well for the duration," space station flight director Holly Ridings said.

"Chris is a navy SEAL," Ridings said, referring to the U. S. navy's special forces who operate on sea, air and land.

"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 (canister) to work right, so just slow down a little and take your time,' " Ridings said. "He took that with good humour."

On Friday, Cassidy and crewmate Tom Marshburn conducted an extended 71/2-hour spacewalk to finish replacing batteries in the solar power system aboard the International Space Station.

Also Friday, a Russian cargo ship blasted off from the Baikonur Cosmodrome in Kazakhstan with more than 1,200 kilograms of equipment and supplies, as well as 800 kg of fuel for the station's steering thrusters.

The vessel is scheduled to dock at the orbital outpost on Wednesday.