The crew of the space Shuttle Discovery have completed their second space walk, spending just over six and three quarter hours outside the shelter of the Shuttle.

Mission specialists Piers Sellers and Mike Fossum spent the first part of their time outdoors installing a spare thermal control system pump on the outside of the Quest Airlock on the International Space Station. The pump is used to move liquid ammonia to the space station's cooling system.

Once that was done, the pair replaced a cable on the mobile transporter, part of the ISS that gives extra mobility to the space station's robotic arm - Canadarm2 - which will be used in the station's construction. This means the platform now has full primary and back-up power systems.

Fossum had earlier told reporters that the space walk would be a kind of "ballet", adding that the choreography of the space would would be the most challenging aspect of the work.

On Wednesday, the crew has one final space walk scheduled for Wednesday this week. The astronauts will be outside testing repair techniques. ®

Related stories

• Woman sets new spacewalking record (5 February 2007)
• NASA reports mystery 'bad smell' on space station (18 September 2006)
• ISS inhabitants plan space stroll (31 July 2006)
• Discovery touches down in Florida (18 July 2006)
• Shuttle, plus leak, set to land today (17 July 2006)
• Discovery cleared for landing (10 July 2006)
• Delayed Discovery takes to the skies (5 July 2006)
• Hubble's vision saved (3 July 2006)
• NASA's next-gen launch vehicles dubbed 'Ares' (3 July 2006)
• Shuttle mission postponed 'til Independence Day (3 July 2006)