Astronauts on the International Space Station (ISS) will conduct spacewalks this Friday to repair a pump module on its broken cooling system, NASA said Monday. Four spacemen will spend two spacewalks replacing the broken ammonia pump module on the station’s starboard truss with a new one. An underwater practice run was conducted Monday to help the ISS team identify challenges that will need to be addressed. The pump failed Saturday night after a spike in the electric current tripped a circuit breaker, cutting half of the station’s cooling system. Efforts to restart the pump were not successful. The station remains in a stable condition but many planned activities this week have been cancelled or postponed in order to prepare for the spacewalks