Originally posted by the Voice of America. Voice of America content is produced by the Voice of America, a United States federal government-sponsored entity, and is in the public domain. Astronauts Begin Spacewalk to Replace Faulty Equipment VOA News 07 August 2010 'Expedition 24' Flight Engineer Doug Wheelock works outside the International Space Station during the first of two spacewalks to replace a failed ammonia pump module, 07 Aug 2010 Photo: NASA TV 'Expedition 24' Flight Engineer Doug Wheelock works outside the International Space Station during the first of two spacewalks to replace a failed ammonia pump module, 07 Aug 2010 Astronauts aboard the International Space Station have begun a challenging seven-hour spacewalk to replace faulty equipment that caused an emergency shutdown last week. American astronauts Doug Wheelock and Tracy Caldwell Dyson began exiting the orbiter (at 7:19 a.m. EDT, 1119 UTC) Saturday, about 20 minutes later than planned. NASA cited communications glitches for the delay. Crew members will work on removing an ammonia pump module that is part of the orbiter's cooling system. Astronauts hope to get a replacement pump in place Saturday.  Officials have planned a second spacewalk for Wednesday in which astronauts will connect ammonia lines to the replacement pump. NASA says the spacewalks are challenging because astronauts will be handling the ammonia lines at full operating pressure, which makes them stiff and more difficult to maneuver. 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 on the station. The U.S. space agency says the three American astronauts and three Russian cosmonauts on board the orbiting outpost are not in any danger.  Some information for this report was provided by AP and AFP. .