The seven-hour, 24-minute spacewalk completed by Mike Fincke and Greg Chamitoff at 7:39 a.m. EDT (1139 GMT) was the final spacewalk conducted by space shuttle astronauts(宇航员) before NASA turns over Endeavour and sister ships Discovery and Atlantis to museums. Space station crew will continue to make spacewalks for maintenance and repair tasks.

    At 5:02 a.m. (0902 GMT), Fincke and Chamitoff surpassed the 1, 000th hour astronauts and cosmonauts have spent spacewalking in support of space station assembly and maintenance. The milestone occurred four hours and 47 minutes into the spacewalk, the 159th in support of station assembly and maintenance, totaling 1,002 hours, 37 minutes.

    The astronauts completed their mission to stow the 50-foot-long boom on the station truss and work on some new installations to extend the space station's robotic arm. After that, shuttle commander Mark Kelly called Mission Control in Houston to mark the milestone -- after 12 years of efforts.

    "Space station assembly is complete," Kelly said.

    It was the 248th spacewalk U.S. astronauts have conducted and the 118th from space station airlocks. Landing is scheduled for 2: 32 a.m. EDT (0632 GMT) on Wednesday at the Kennedy Space Center in Florida. Shuttle Atlantis is targeted to launch on July 8 for space shuttle's final flight.

    Endeavour lifted off on May 16 from the Kennedy Space Center in Florida, to deliver to the International Space Station a 2-billion- dollar, multinational particle detector known as the Alpha Magnetic Spectrometer (AMS).

    AMS, a particle physics detector, is designed to search for various types of unusual matter by measuring cosmic rays. Its experiments are designed to help researchers study the formation of the universe and search for evidence of dark matter, strange matter and antimatter.

    NASA's 30-year-old shuttle program is ending due to high operating costs. The Obama administration wants to spur private companies to get into the space taxi business, freeing NASA to focus on deep space exploration and new technology development.

    When the U.S. space shuttle program officially ends later this year, the Russian space program's Soyuz capsule will be the only method for transporting astronauts to and from the station.(本文由在线英语听力室整理编辑)