Astronauts Hunt for Space Station Ammonia Leak (Spacewalk Photos)

Spacewalkers Replace Ammonia Pump on ISS: May 11, 2013.

NASA astronauts Chris Cassidy (top) and Tom Marshburn work outside the International Space Station after replacing an ammonia coolant pump on May 11, 2013.

Spacewalks Inspect Ammonia Pump Box

NASA astronaut Chris Cassidy (striped spacesuit) holds an ammonia pump control box during a spacewalk to hunt for an ammonia leak outside the International Space Station on May 13, 2013. The spacesuit of astronaut Tom Marshburn can be seen behind him.

Astronaut Shutterbug: Spacewalker Tom Marshburn

NASA astronaut Tom Marshburn snaps a photo of crewmate Chris Cassidy during a May 11, 2013 spacewalk in this view from Cassidy's helmet camera. The spacewalkers replaced an ammonia pump box while seeking a coolant leak outside the International Space Station.

Spacewalkers Install New ISS Ammonia Pump

This view from NASA astronaut Chris Cassidy's helmet camera shows a new ammonia pump being installed during a May 11, 2013 spacewalk.

Spacewalk at Night: May 11, 2013

Canadian astronaut Chris Hadfield captured this view of astroanut Chris Hadfield outside the International Space Station on May 11, 2013, during an ammonia leak-hunting spacewalk.

Emergency Spacewalk Suit Up: May 11, 2013

NASA astronauts Chris Cassidy and Tom Marshburn don their NASA-issue Extravehicular Mobility Units for an emergency spacewalk to find an ammonia link outside the International Space Station. Canadian astronaut Chris Hadfield (center) and Russian cosmonaut Pavel Vinogradov assist in the May 11, 2013 spacewalk work.

How ISS's Ammonia Cooling System Works (Infographic)

The ammonia system is one of several cooling loops that circulate liquids throughout the International Space Station. See how the space station's cooling system works here.

Emergency Spacewalk Astronauts: May 11, 2013

NASA astronaut Chris Cassidy and Tom Marshburn will perform an emergency spacewalk outside the International Space Station on May 11, 2013, to identify and perhaps fix an ammonia coolant leak.

Emergency Spacewalk Worksite: May 11, 2013

This NASA graphic shows the location of the ammonia leak on the International Space Station to be inspected by astronauts in an emergency spacewalk on May 11, 2013.

Emergency Spacewalk Astronaut Path: May 11, 2013

This NASA graphic shows the path astronauts Tom Marshburn and Chris Cassidy will take to reach an ammonia leak outside the International Space Station in an emergency spacewalk on May 11, 2013.

Mission Management Team Discusses Station Ammonia Leak

On May 10, 2013, members of the International Mission Management Team convene for a session in the Christopher C. Kraft Mission Control Center to discuss the status of a recently discovered ammonia leak on the International Space Station and the likelihood of a space walk over the coming weekend. The extravehicular activity would likely be performed by two Expedition 35 crew members to resolve the issue.