Astronauts Dave Wolf and Piers Sellers have completed their first planned spacewalk to extend the backbone on the International Space Station.

The two men were outside working on the platform for seven hours and a minute.

Wolf and Sellers were outside for seven hours - longer than planned

The primary construction task involved the fitting of a large girder, or truss, brought up into orbit by the shuttle Atlantis.

Motorized bolts were used to lock the 14-tonne truss in place before Wolf and Sellers connected cables and released its equipment.

The $390m aluminium girder contains a new external cooling system for the ISS and is part of a framework that will hold electricity-generating solar wings and radiators needed for future laboratories.

It will form part of a structure that will eventually stretch 107 metres (350 ft) - the longest structure ever built in space.

Sellers is only the third British-born astronaut in space

This was British-born Sellers' first spacewalk. "Yippee," he shouted as he went outside. He was astonished by the view of Earth almost 390 kilometres below.

"Where am I?" Sellers asked at one point. When told he was flying over the Pacific and coming up on South America, he observed, "Wow - it's too beautiful for words - unbelievable."

Wolf and Sellers will go back outside on Saturday and on Monday to complete the installation work.

Atlantis is due back on Earth on Friday 18 October.