Astronauts from the International Space Station will start their space walk Saturday about 5:45 a.m. Pacific time, in an effort to locate and fix an ammonia leak in a coolant system, NASA officials said Friday.
The unscheduled emergency walk was "precedent setting" for the station, although similar impromptu tasks had been performed during the Space Shuttle program, said Norm Knight, NASA chief flight director.
“The team is ready to go,” International Space Station program manager Michael Suffredini said.
“Things are really progressing in the right direction,” added Knight.
Ground managers at the Johnson Space Center in Houston suspect the leak comes from a pump that circulates ammonia coolant to one of eight solar panel systems that provide electricity to the station. That coolant loop has caused trouble for some time, and crew member attempted to locate and repair a leak last November, Suffredini said.
“This is the system that has been leaking for some time, a very small amount, for years,” Suffredini said. The rate of the leak, formerly about five pounds per year, escalated to about five pounds per day, he added.
The volume of the leak should make it easier to pinpoint, he added. Previous leaks were very hard to find. The crew reported seeing small white flakes floating away from an area on the station’s Port 6 truss structure Thursday night, NASA said.
Astronauts Chris Cassidy and Tom Marshburn, who have worked together on two previous space walks during a 2009 mission, were expected to replace the pump with one of three spares aboard the station, the NASA officials said. If they cannot complete the repair, a subsequent crew may have to take up the task, Suffredini said.
The six-member Expedition 35 crew, commanded by Chris Hadfield, was not in danger, NASA said. The station continued to operate normally while crew members and mission managers routed power through another of the station’s eight channels.
"The whole team is ticking like clockwork, readying for tomorrow. I am so proud to be Commander of this crew. Such great, capable, fun people," Hadfield tweeted Friday morning.
"What a fun day! This type of event is what the years of training were for," Hadfield tweeted later. "A happy, busy crew, working hard, loving life in space."
But by Friday afternoon, the tone and mood became more business-like: "Tomorrow we send 2 crew out into the thermal vacuum wearing cloth-and-rubber pressure suits to repair ISS. Extra study of procedures tonight," Hadfield tweeted.