Astronauts aboard the International Space Station will venture outside on three spacewalks to replace a malfunctioning pump that has shut down part of the station’s cooling system, NASA announced on Tuesday.

The space agency also postponed until January the launching of a cargo supply ship, which had been scheduled to lift off on Thursday.

The first spacewalk is on Saturday, with the second on Monday and the third next Wednesday.

Two loops of circulating ammonia cool equipment on the station. The problem started last Wednesday with a malfunction of a valve inside the pump, which is on one of the station’s exterior trusses. Flight controllers shut down that cooling loop. The remaining loop is sufficient for regulating the temperature of critical equipment, and NASA said there was no immediate danger to the six crew members.

NASA managers want both cooling loops to be operating before the cargo ship is sent into orbit. The Orbital Sciences Corporation, a private company hired by the space agency to bring cargo to the space station, had rolled out its Antares rocket, carrying 3,230 pounds of supplies, to the launching pad on Wallops Island in Virginia. The launching will now occur no earlier than Jan. 13.