Two astronauts were set to make a hastily planned spacewalk yesterday to try to fix an ammonia leak in the International Space Station’s (ISS) power system.
NASA officials emphasized that the six-member crew is not in danger.
The leak in a cooling system was discovered on Thursday when “snowflakes” of ammonia were seen flying away from the station. Spacewalks are rarely done on such short notice, but the US space agency wanted to check out the leak before all the ammonia escaped.
They also want to take advantage of a spacewalking crew member who is about to return home.
Officials said the space station has plenty of power, even though the leak forced NASA to shut off the power channel from one of eight solar panels that supply electricity.
The station can operate fine with only seven electrical channels, space station program manager Michael Suffredini said on Friday.
Power from the affected panel was re-routed to the other seven systems.
Suffredini said the chief suspect for the leak is space junk hitting a cooling tube, but he said the area had a slow small leak for many years that suddenly accelerated on Thursday.
“You’re talking a very, very, very small hole,” Suffredini said at a news conference.
While he described it as a “serious situation,” he characterized it more as an annoyance.
NASA hopes the leak is in a small pump box. During the six-hour spacewalk, US astronauts Chris Cassidy and Tom Marshburn plan to replace the 118kg box with a nearby spare.
While NASA has had to do impromptu spacewalks before, they have not been done on the space station since it was completely built and operating as a finished lab, chief flight director Norm Knight said.
Station Commander Chris Hadfield of Canada told NASA flight controllers on Friday that the crew is completely ready for the spacewalk.
“It’s the right thing to do,” he radioed down to Earth.
Hadfield tweeted that the crew was working “like clockwork” and said the two spacewalkers were already getting their spacesuits ready.
If the cooling system could not be fixed in yesterday’s spacewalk, it could be fixed in later spacewalks, Suffredini said. NASA can and has operated the station fully on seven power channels, he said.
However, that would leave the station little margin for error. If there are more problems, some experiments on board may have to be shut down to conserve power.
NASA spokesman Rob Navias said the repair is what the agency calls one of the “Big 12” types of emergency repair work that all spacewalking astronauts are trained for in advance.
In 2009, Cassidy and Marshburn flew to the space station on the shuttle Endeavour and walked in space together to swap out a battery in the same location, so “they know this worksite inside and out,” Navias said.
Marshburn, Hadfield and Russia’s Roman Romanenko are set to return to Earth tomorrow. NASA administrator Charles Bolden told reporters on Friday that their return will go ahead as planned.