Flight engineers on the International Space Station (ISS), including U.S. astronaut Chris Cassidy (pictured), completed a 5.5-hour spacewalk on May 11 to repair a leaky coolant pump.

The pump provides ammonia coolant to systems on the ISS responsible for generating electricity for the station.

The leak was initially discovered on May 9 by Canadian astronaut Chris Hadfield, who reported seeing flakes coming off the ISS. (Related: "Serious Space Station Leak Provokes Weekend Spacewalk.")

—Jane J. Lee