The astronauts are scheduled to make five spacewalks

ISS spacewalk

Scott Parazynski and Doug Wheelock moved about the 14-tonne unit as it was hauled by robotic arm from Discovery's cargo bay and put in a temporary site.

The "Harmony" node will be locked into a permanent position once the shuttle has left the station.

Harmony gives station crews 18% more room in which to move about.

It is the first expansion of living and working space since 2001.

It will provide a passageway between three science laboratories: the existing US Destiny lab; the European Space Agency's Columbus module; and the Japanese Kibo experimental units.

Safety inspection

Built in Italy by the company Thales Alenia Space, Harmony is 7m by 4.6m (23ft by 15ft).

The installation was being led by Italian astronaut and mission specialist Paolo Nespoli. It has been attached to the US Unity module for now but will be moved to the end of the Destiny unit in due course.

Shuttle Discovery performed a back-flip as it approached the ISS, allowing crew members aboard the station to inspect its wings and nose for any launch damage.

The shuttle then docked with the orbiting space platform high above the Earth, both travelling at 28,000km/h (17,400mph)

On Wednesday, astronauts used a robot arm to check the shuttle's wings and nose for signs of damage in what has become a routine inspection since the loss of space shuttle Columbia in 2003.

Nasa engineers did not spot anything significant in a preliminary look at images captured during Wednesday's examination, said John Shannon, head of the mission management team.