By Irene Klotz
Cape Canaveral, Florida - A pair of Nasa astronauts ventured outside the International Space Station on Saturday to try to repair a faulty cooling system, but their attempt was thwarted by a stubborn ammonia line fitting.
Spacewalkers Doug Wheelock and Tracy Caldwell Dyson plan to make a second spacewalk on Wednesday to resume working on the failed coolant system, which shut down on July 31.
The system is one of two aboard the station needed to control heat generated by equipment in the US, Japanese and European laboratories. The station, a $100-billion project involving 16 nations, has been under construction 352km above the Earth since 1998.
Wheelock struggled to free an unyielding quick-disconnect fitting on one ammonia line feeding the failed system, before ground controllers told him to move on to the other lines, where the astronauts made better progress.
With time running short, the pair returned to the trapped line and were able to release it, but they noted crystals of ammonia leaking out.
Flight directors at Nasa's Mission Control Centre in Houston decided not to attach the line to a bypass mechanism holding the other three lines and told Wheelock to re-attach the fitting while they figured out what to do next.
Because of the leak, the spacewalkers spent extra time in the airlock to flush out any ammonia that may have attached to their spacesuits. The decontamination procedure is routine whenever spacewalkers are exposed to free-flying ammonia, which can be a hazard if it gets into the space station's air.
Nasa had hoped to replace the cooling system's failed pump module with a spare during Saturday's spacewalk, which had been slated to last seven hours. The second spacewalk on Wednesday was intended to reattach electrical and fluid lines.
Wheelock and Caldwell Dyson ended up spending more than eight hours outside the space station on Saturday, with the bulk of the work still to come.
Flight directors had said before Saturday's outing that three spacewalks might be needed to complete the repair.
Most of the station's science experiments and some backup life support equipment have been turned off to cut the amount of heat generated with only one cooling loop available.
Nasa says the crew of three Russian cosmonauts and three Nasa astronauts aboard the station are not in any danger, though it would like to return the station to full normal systems as soon as possible. - Reuters