NASA Astronauts John Olivas and Nicole Stott (right), STS-128 mission specialists, participate in the mission's first spacewalk as construction and maintenance continue on the International Space Station. During the six-hour, 35-minute spacewalk, Olivas and Stott removed an empty ammonia tank from the station's truss and temporarily stowed it on the station's robotic arm. Olivas and Stott also retrieved the European Technology Exposure Facility (EuTEF) and Materials International Space Station Experiment (MISSE) from the Columbus laboratory module and installed them on Discovery's payload bay for return.