The International Space Station’s active thermal control systems (ATCS) pump fluids through closed-loop pipes. A liquid-ammonia coolant loop along the station’s main truss keeps the station’s electricity-generating solar panels cool.
An ammonia pump on the main truss failed in 2010 and had to be replaced by spacewalking astronauts. The Expedition 35 crew on the International Space Station reported an ammonia leak near the same location on May 9, 2013.
Liquid ammonia circulates through the pipes, carrying waste heat from the solar panels to the photovoltaic radiator panels, where the heat escapes into space. This keeps the solar panels cool.
The International Space Station is the largest man-made structure ever built in space. From end to end, it is as long as a football field and can be seen from the ground by the unaided eye by observers who know when and where to look.
The $100 billion space station is the product of international cooperation among 15 different countries and five national space agencies representing the United States, Russia, Europe, Canada and Japan. Construction began in 1998 and the first crew, Expedition 1, took up resident in 2000. Rotating crews of between three and six crewmembers have kept the space station permanently manned ever since.