(MOSCOW) -- An ammonia gas leak has been discovered on the American side of the International Space Station.
According to Russian news reports, the leak is serious but not critical. NASA says the crew is not in danger.
The ammonia is part of a cooling system for the circuits that supply power to the space station from its solar panels.
Astronauts Thomas Mashburn and Chris Cassidy are expected to make an unscheduled space walk on Friday to inspect the problem.
Copyright 2013 ABC News Radio