Two U.S. astronauts have conducted the first spacewalk for space shuttle Atlantis and installed an antenna on the International Space Station (ISS). NASA said the spacewalk of mission specialists Michael Foreman and Dr. Robert Satcher Jr. lasted six hours and 37 minutes. The duo installed a spare antenna to the outside of the ISS in just two hours after venturing out. They also hooked up cables and a handrail, and greased some mechanisms.After finishing all their scheduled chores, Foreman and Satcher carried out a task that had been planned for the second spacewalk. Atlantis lifted off from Kennedy Space Center in Florida on Monday.Its 11-day flight will include three spacewalks and the installation of two platforms to the station's truss, or backbone. Atlantis' STS-129 mission is NASA's fifth and last shuttle mission for 2009.