Spacewalkers fit power system

So far, only one wing has been unfurled to its full length

Spacewalking astronauts have started to install a new solar power system on the International Space Station.

The mast with solar-panelled wings weighs 17 tonnes and is the largest space station segment ever to be transported on a space shuttle.

Two astronauts walking in space, and a third operating a robotic arm from inside the orbiter Endeavour, attached the mast to the space station.

Installing the panels

1830 GMT: Spacewalk begins

1900 GMT: Panels attached

2311 GMT: Panels start moving

0116 GMT Spacewalk ends

But a technical hitch has delayed the next stage of the operation: the opening out of the wings which are covered in light-gathering cells and measure 73 metres (240 feet) across.

A pin holding one of the wings in its folded position has failed to unlatch properly, and an astronaut has been trying to fix the problem, which is believed to be a minor one.

Once unfurled, the blue-and-gold-coloured solar arrays, will be the most powerful ever deployed in space.

Robot arm

Canadian astronaut Marc Garneau moved the folded arrays into place with a robotic arm.

With no direct view of the space station, Garneau had to rely on his spacewalking colleagues Joe Tanner and Carlos Noriega to relay instructions.

"Looking good. Keep it coming," Tanner urged Garneau. "You're dead centre almost, man."

Tanner and Noriega, wearing helmets equipped with small cameras, then bolted the structure onto the space station.

The ISS is in urgent need of extra power, with one of its three rooms closed off because there is not enough power to heat it.

Tanner and Noriega are to make two further spacewalks, attaching power couplings and data cables that will allow Nasa to bring the new power system online.

Brightest object

If everything goes according to plan, the $600m solar wings will make the ISS one of the brightest objects in the night sky.

The ISS is in urgent need of extra power

The wings have a total power generation capability approaching 64 kW - more than enough electricity to give the station's crew the full run of the platform and drive the equipment and experiments on the soon to arrive Destiny lab.

On Saturday, Endeavour had a flawless docking with the space station.

Waiting inside was the three-man crew - commander Bill Shepherd, an American, and Russian crew mates Yuri Gidzeko and Sergei Krikalev - who have been living there since early November.

But the two crews will not meet for some days. Because of the difference in air pressure between the two vessels, the hatches leading into the ISS's living compartment must remain sealed until the shuttle astronauts complete their spacewalks.