Originally posted by the Voice of America. Voice of America content is produced by the Voice of America, a United States federal government-sponsored entity, and is in the public domain. Spacewalking Astronauts to Fix ISS Cooling System Suzanne Presto 11 August 2010 A NASA video image of astronaut Douglas Wheelock working on the International Space Station to restore a crucial cooling system, 11 Aug 2010 Photo: AP A NASA video image of astronaut Douglas Wheelock working on the International Space Station to restore a crucial cooling system, 11 Aug 2010 NASA astronauts are conducting the second of three spacewalks in an effort to replace a faulty ammonia pump module on the International Space Station's truss. The astronauts encountered some problems with this task during their first spacewalk August 7. Astronauts Doug Wheelock and Tracy Caldwell Dyson are working to replace a pump that failed July 31.  The faulty pump is supposed to feed ammonia into cooling loops to maintain the proper temperature for the station's electrical and flight systems. When it failed, it took down half of the space station's cooling system. For the past week and a half, the space station has been operating at half its usual cooling capacity, forcing the astronauts to power down equipment to prevent overheating on the ISS.   Before this spacewalk, the team reduced the pressure in the hoses carrying ammonia, making the task of removing the tubes easier for the astronauts.  It was the pressurized ammonia hoses that caused some problems during the first spacewalk of the repair mission Saturday. That spacewalk clocked in at more than eight hours - one of the longest spacewalks in history.  NASA has had to schedule a third spacewalk to complete the repairs. Officials say the spare pump will be installed during this third spacewalk, which is planned for Sunday, at the earliest. .