Astronauts from the shuttle Atlantis began today the first space walk of their mission to store hardware and conduct repairs on the exterior of the International Space Station.

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

After switching his suit to battery power, signifying the start of his first ever space walk, Satcher rode the station's robotic arm carrying a vital communications antenna, which he and Foreman then bolted into place.

The spacewalk was scheduled to last six-and-a-half hours.

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

The crew of Atlantis docked yesterday at the International Space Station as part of an 11-day voyage to deliver a 9,071-kilogram haul of spare parts.

The fifth and final shuttle mission for 2009 is scheduled to include three space walks to store hardware on the exterior of the space station and bring US astronaut Nicole Stott, who has been on the ISS since August, back to Earth.

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