Astronauts have attached an enormous laboratory to the International Space Station, in a complex operation involving spacewalks and a robot arm.

The Japanese lab - which was carried into orbit on the shuttle Discovery - is now the biggest room at the station.

Named Kibo, Japanese for hope, it is 37 feet long and weighs 32,000 pounds.

Astronaut Akihiko Hoshide had the honour of operating the robot arm that installed the lab, after colleagues Michael Fossum and Ronald Garan Jr prepared the way on a spacewalk.

"We have a new hope on the international space station," Mr Hoshide declared.

The lab, which cost around $1 billion (£507 million) to build and will allow for more sophisticated space research, will be in use from today.

More equipment - including another robot arm and an an outdoor porch for holding experiment packages - will be delivered next spring.

Discovery arrived at the station on Monday, having begun its two-week mission from the Kennedy Space Center in Florida on Saturday.

The shuttle also brought spare parts to repair the station's broken toilet. The space station's two Russian residents are due to spend the morning installing the new pump.

It was the fourth spacewalk for Mr Fossum, a colonel in the Air Force Reserves who is making his second shuttle flight, and the first for Mr Garan, an Air Force pilot.

As the spacewalk got under way, Mr Fossum told his colleague: "Enjoy the view, but don't look down."

Two more spacewalks are planned before the Discovery sets off back to Earth.