Washington - Two astronauts from the space shuttle Discovery completed a more than 6-hour-long spacewalk outside the International Space Station (ISS) Friday, installing a new ammonia tank used in the cooling system, NASA said. US astronaut John "Danny" Olivas and Swede Christer Fuglesang ended their mission successfully at 0451 GMT. They got started nearly an hour later than planned because of problems with a communications device in Olivas' spacesuit.
The pair removed an 816-kilogramme ammonia tank from a cargo carrier attached to the station and moved it with a robotic arm to its home outside the station. The tank was the largest item ever moved by astronauts during a spacewalk.
Much of the work involved connecting bolts and cables to hook the tank into the station's cooling system.
Kevin Ford and Nicole Stott operated the robotic arm.
Earlier this week, Olivas and Stott removed an empty ammonia tank from the station. The old tank was put into the carrier to be brought back to Earth at the end of the shuttle's mission.
The planned 13-day mission is designed to transport new equipment and experiments to the space station to boost its capacity as an orbiting laboratory.
The crew of six US and a Swedish astronaut brought two "racks" for scientific experiments and a freezer to store experiments set to be sent back to Earth. One of the racks will be used to conduct research on metals, semiconductors, crystal, glass and other materials in microgravity. The other will be used to study liquids and gels in space.
The racks were transferred to the station Wednesday.
