Doug Wheelock & Tracy Caldwell Dyson Conduct Second ISS Cooling System Repair Spacewalk

August 11, 2010

NASA says two astronauts are conducting a spacewalk outside the International Space Station, continuing efforts to repair faulty cooling equipment that caused an emergency shutdown in the station last week.

'Expedition 24' Flight Engineer Doug Wheelock works outside International Space Station during first of two spacewalks to replace failed ammonia pump module, 07 Aug 2010

This is the second spacewalk in the past four days for Americans Doug Wheelock and Tracy Caldwell Dyson. The two are trying to remove a broken ammonia pump that is expect to be replaced in a third spacewalk later this week.

Wheelock and Dyson tried but failed to disconnect the pump from the space station's cooling system Saturday, in a spacewalk that lasted more than eight hours.

Mission controllers say the astronauts had difficulty disconnecting an ammonia hose from the pump and had to use a hammer to loosen the hose's fittings. The astronauts also found a leak in one of the hoses attached to the pump.

The faulty pump is supposed to feed ammonia into cooling loops to maintain the proper temperature for the station's electrical and flight systems. When the pump failed, it shut down half of the space station's cooling system.

Astronauts had to switch off some equipment to reduce the amount of heat in the station.

The U.S. space agency says the three Americans and three Russians on the orbiting outpost are not in any danger.