A PAIR of astronauts carried out a rare spacewalk yesterday in hurried efforts to patch a dangerous ammonia leak at the International Space Station.
American astronauts Christopher Cassidy and Thomas Marshburn completed the emergency task by replacing a pump that had been leaking white frozen ammonia flakes 48 hours earlier.
The fault was discovered on a cooling system on one of the station’s solar panel arrays that provide electricity to the orbital outpost.
Mission Control’s radio response declared “so far, so good” after no new leakage was detected following the mission.
But it could still be days before the attempt to repair the mystery leak is declared an ultimate success, with Nasa saying it will continue watching for any fresh seepage.
Cassidy and Marshburn initially reported nothing amiss around the old pump after hunting in vain for an obvious leak.
“All the pipes look shiny clean, no crud,” Cassidy said as he used a mirror to peer into the panel’s narrow openings.
“I can’t give you any good data other than nominal, unfortunately. No smoking guns.”
Mission Control noted: “There’s nothing to lose by putting in a fresh pump and pressing ahead with additional detective work. The mystery mounts.”
The astronauts remained outside the space station after fixing the replacement, looking out for any visible icy flecks. The spacewalk lasted five and a half hours.
Managers of the space station had wanted to solve the problem before Marshburn left to return to Earth late tomorrow.
Nasa said the leak, while significant, had never jeopardised the six-man crew’s safety.
Yesterday’s was the first impromptu spacewalk for a station crew ordered by the space agency in such a short period of time.
Unplanned spacewalks were uncommon even during the heyday of the Nasa programme.
Ammonia is used to cool the power systems that operate each of the eight solar arrays on the $100 billion (£65bn) space station, which orbits 250 miles above Earth.
The area on the space station where the fault happened is prone to leaks.
Flight controllers in Houston, Texas, had to work furiously to get ready for yesterday’s operation, with all preparations carried out in less than 48 hours.
Both astronauts had been trained for the emergency scenario before being rocketed into orbit. The repair job ranks among Nasa’s so-called Big 12 operations.
Nasa’s space station program manager Mike Suffredini said it remained a mystery as to why the leak happened.
Possibilities include a micrometeorite strike or a leaky seal. A tiny amount of ammonia had been seeping from the location earlier, but had increased dramatically on Thursday.
It is not the first time that Nasa has experienced problems with the station’s cooling systems.
A very small leak was found in 2007 in the same location, with a spacewalk organised last year to reconfigure coolant lines and isolate the fault.