Two astronauts left the International Space Station on Saturday to perform a complicated spacewalk to fix a broken cooling system that last weekend prompted the shutdown of some systems onboard the orbiting spacecraft, reported dpa. Doug Wheelock and Tracy Caldwell Dyson will replace the broken 350-kilogramme ammonia cooling loop with a spare part stored about 10 metres away outside the ISS during the planned seven-hour spacewalk that began at 1119 GMT. A second spacewalk to hook up cables and wire the part into the station is scheduled for Wednesday. The system is one of two used to keep electronics on the ISS from overheating. Last Saturday, alarms were triggered signalling that the ammonia-based refrigeration system on the ISS had failed due to a power surge. NASA officials stressed that the six crew members were in no danger, and all critical and many non-critical systems on the ISS were since operating as normal despite the malfunction. The ISS could continue to operate without the cooling system indefinitely, but would be in trouble if the second ammonia cooling loop were to also fail before the first is replaced. Wheelock and Caldwell Dyson had already trained to replace this part, despite the effort being unplanned, as part of NASA's efforts to prepare ISS crew members for contingencies aboard the station.
