Coolant

In a six-hour procedure, space station commander Sunita Williams and Japanese astronaut Akihiko Hoshide successfully reconfigured ammonia coolant lines to bypass the suspect radiator, which may have been hit by space debris months earlier.

The U.S. space agency, NASA, says astronauts aboard the International Space Station will perform a previously unscheduled spacewalk Saturday to deal with an ammonia coolant leak outside the station.

The coolant is leaking.

Water will suffice as coolant in a pinch.

Coolant is used in car engines and industrial processes, where excess heat could cause machine damage.

Anti-freeze has not been found necessary, even in the most severe conditions, since the water is drained out if a locomotive spends any appreciable time out of service and in normal working conditions the coolant is always warm.