Astronauts on first spacewalk of Discovery mission

Wednesday, September 02, 2009 WASHINGTON: Two US astronauts gingerly stepped out of the shuttle Discovery on Tuesday and began the first spacewalk of the mission's nine-day stay at the International Space Station (ISS).Astronaut Nicole Stott emerged from the orbiter's decompression chamber at 2149 GMT some 350 kilometers (255 miles) above the Pacific ocean and was joined in the blackness of space by Mission Specialist Danny Olivas for what is expected to be a walk of 6.5 hours, according to US space agency NASA. With the help of the station's robotic arm and guided by shuttle Commander Rick Sturckow and spacewalk choreographer Pat Forrester, the duo will be removing an old liquid ammonia coolant tank from the ISS truss. A new, 800-kilogram (1,760-pound) replacement will be installed during the second spacewalk. They will also be retrieving experiment equipment from the outside of the ISS, from the European Columbus module, and returning it to Earth for processing.Astronauts are scheduled to conduct two more spacewalks during the mission, the fourth of five planned for the shuttle program this year. The last is scheduled for November.