Spacewalk Preps Running About 30 Minutes Behind Schedule

Two U.S. astronauts are suited up in the International Space Station's U.S. Quest airlock this morning, but preps for their excursion outside the outpost are running about a half-hour late.

Overnight, Tracy Caldwell-Dyson had to refit part of the lower torso of her spacesuit, and that stalled the beginning of a procedure in which the astronauts breathe pure oxygen to remove nitrogen gas bubbles from the bloodstream. The so-called "pre-breathing" procedure is designed to prevent decompression sickness while the astronauts are working in the vacuum environment in low Earth orbit.

Consequently, Caldwell-Dyson and fellow flight engineer Doug Wheelock probably won't exit the hatch of the Quest airlock until about 8:30 a.m. The start-time already had been slipped an hour to 7:55 a.m. to provide more prep time to refine robot arm support operations and give flight control teams in Mission Control extra rest.