In this still image taken from NASA TV, International Space Station (ISS) astronauts Chris Cassidy takes photos as he works on repairs to the ISS on May 11, 2013. Cassidy and crewmate Tom Marshburn are working to repair an ammonia leak which was discovered May 9. NASA emphasised that the lives of the multinational crew were not in danger but both Russian and US space experts were scrambling to swiftly fix the problem. NASA said the leak of ammonia, which is used to cool the station’s power system, was coming from the same general area as in a previous episode in November 2012. == RESTRICTED TO EDITORIAL USE / MANDATORY CREDIT: “AFP PHOTO / NASA TV / NO SALES / NO MARKETING / NO ADVERTISING CAMPAIGNS / DISTRIBUTED AS A SERVICE TO CLIENTS ==