Washington: Two space shuttle Discovery astronauts moved a failed ammonia cooling pump during a more than six-hour spacewalk outside the International Space Station.
NASA officials called Monday`s work a "textbook" spacewalk, after overcoming a problem with the station`s robotic arm that left astronaut Steve Bowen holding the weightless pump for a bit longer than expected.
It was the first of two spacewalks in the shuttle mission, which is Discovery`s last before the spacecraft is retired.
NASA said after the spacewalk that it had decided to add another day to the mission, making it a 12-day affair, in order to allow Discovery astronauts to help with work setting up a new room that it carried aloft.
Astronauts Bowen and Alvin Drew also installed a back-up power extension cable and camera equipment and did other work to make future spacewalks easier.
Before heading back inside, they filled a metal container with the vacuum of space as part of a Japanese experiment called "Message in a Bottle" that will later be displayed on Earth.
The cooling pump broke last year and had to be relocated from a temporary storage location where it had been stashed on an earlier spacewalk. It had to be moved before it can be taken back to Earth for analysis.
The six-hour, 34-minute spacewalk wrapped up at 2220 GMT.
A second spacewalk is set for Wednesday.
Two more shuttle flights are planned for later this year in the final missions for the rest of the fleet, Endeavour and Atlantis.
Discovery`s mission is delivering the last major US contribution to the ISS - an extra room - along with supplies and equipment, including a human-like robot, known as Robonaut 2 (R2), the first such robot ever sent to space.