US astronauts from the space shuttle Atlantis have hung a window shutter on the Destiny space lab, allowing their colleagues to take pictures of unprecedented quality.

The shutter is needed to protect the finest optical-quality window ever built into a spacecraft and the installation allowed the window to be uncovered earlier than planned.

Thomas Jones and Robert Curbeam carried out a seven-hour space walk during which they made such good progress that they were able to get on with work scheduled for later in their mission.

Nasa pictures showed them moving a docking port on to the end of the Destiny module, ready for more building work during future missions, and being photographed by their colleagues inside the lab.

Shuttle Commander Bill Shepherd admires the view

Space station crew will use the window to photograph the Earth with high-powered cameras, but the first pictures were of their colleagues outside: shuttle commander Bill Shepherd described the first shot, of Jones and Curbeam, as "awesome".

The space walkers also fitted the base for a Canadian-built robot arm, due to arrive on a future mission.

They will carry out a third and final walk later in the week, Nasa said.

Space link-up

The Atlantis crew met the current three residents of the ISS on Friday and spent their first full day inside Destiny on Sunday.

Destiny facts

Weight: 16 tonnes Length: 8.5 metres Diameter: 4.3 metres Cost: $1.4bn

Now that the 1.4 billion dollar (960 million pound) Destiny lab is installed, the ISS is the biggest structure in orbit in terms of habitable space.

The space station is due to be completed in 2006. In orbit high above the Earth, it is one of the brightest objects in the night sky.

The tasks for the crew include work on how humans cope in zero-gravity.

Partners in the space station project include the United States, Russia and the European Space Agency.