Mission specialists Mike Foreman and Robert Satcher completed their task with two hours to spare and so began work, intended for a second space walk, on a new system for storing spare parts, NASA said.

After "camping out" overnight in the Quest airlock, which purges nitrogen from their bloodstream to prevent decompression sickness, Foreman and Satcher moved out into the vacuum of space at 1424 GMT.

Satcher, on his first space walk, was lifted by the station's robotic arm carrying the antenna equipment that he and Foreman then bolted into place.

Lead spacewalker Foreman, wearing a suit with solid red stripes, and Satcher, in an all-white spacesuit, also re-routed cables and lubricated key moving parts on the space station during their six-hour and 37-minute outing.

Choreographing the space walk and coordinating with Mission Control in Houston was mission specialist Randy Bresnik, who earlier woke the crew up with his choice of song for the day -- "In Wonder" by the Newsboys.

Meanwhile, back on the space station, crucial rewiring was carried out on the hatch where the new Tranquility node is to be connected early next year, allowing more berths for astronauts and an all-round view of the station.

The crew of Atlantis docked on Wednesday at the International Space Station as part of an 11-day voyage to deliver a 20,000-pound (9,071-kilogram) haul of spare parts.

With only five launches left before the 2010 retirement of the shuttle fleet, NASA officials said the parts were essential for extending the life of the space station.

This fifth and final shuttle mission for 2009 is scheduled to include a further two space walks before bringing US astronaut Nicole Stott, who has been on the ISS since August, back to Earth.

Stott, who celebrated her 47th birthday Thursday in space, and the rest of the crew will also be conducting scientific experiments that could explain muscle loss in space.

Thousands of the microscopic worms have been sent from Britain's University of Nottingham to study the effect of zero gravity on the human body's muscle development and physiology.

The worms will be stashed inside the Japanese Kibo laboratory on the ISS where they will be tested with several potential treatments for muscle loss.

NASA's shuttle program is due to be mothballed next year, but the White House could still decide to extend it through 2011 to reduce America's future reliance on Russia for transporting astronauts to the space station.

Last month NASA successfully launched the prototype Ares I-X rocket that it hopes will launch the Orion, a new generation of manned space exploration vehicle that is still under development.

Orion, which is not expected to be ready until at least 2015, is being designed to take a crew of up to six astronauts on flights to the International Space Station, or a crew of four on lunar missions lasting up to 210 days.

But America's human space flight program, which swallows up 10 billion dollars of NASA's 18-billion-dollar annual budget, is at great risk of being grounded.

A panel set up by President Barack Obama and tasked with assessing its future has said an additional three billion dollars a year is needed for NASA to meet its goals.

All rights reserved. © 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.