GWMAW writes "NASA Astronauts will conduct a spacewalk on Thursday to repair part of the cooling system of the International Space Station. The cooling system is essential for maintaining the temperature inside the station. There are two 'loops' in the system, one that uses water and draws heat from the inside of the station, and one uses ammonia and dumps the heat into space. Ammonia is used because it freezes at a much lower temperature than water. On Saturday the pump that controls the flow of ammonia through the system shut down."