astroengine writes "During an unscheduled spacewalk on the space station's exterior on Saturday morning, NASA astronauts Tom Marshburn and Chris Cassidy carried out the mother of all plumbing jobs: They detached a suspect ammonia pump, replaced it with a spare and watched for any further ammonia leakage. The emergency spacewalk was carried out in response to a troubling ammonia coolant leak that was discovered on Thursday. The coolant is used to maintain the temperature of the vast solar arrays the space station uses to generate electricity for its systems. 'It will take some diagnostics, still, over the course of the next several days by the thermal systems specialists to fully determine that we have solved the problem of the ammonia leak," said NASA commentator Rob Navias during the live NASA TV spacewalk broadcast. 'But so far, so "good."'"