Array

HOUSTON, Sep 15 (Reuters) Two astronauts floated out of the International Space Station today to complete work on new solar energy panels in the third and final spacewalk of a shuttle mission to restart construction of the half-finished outpost.

Joe Tanner and Heidemarie Stefanyshyn-Piper were to prepare an instrument-cooling radiator on the 73-metre solar array that was unfurled on Thursday and will double the amount of electricity available on the station.

They also were to perform some station maintenance work during the 6 1/2 hour walk and retrieve a materials science experiment.

The deployment of the solar panels was the major task of this flight by shuttle Atlantis, which launched September 9 from Florida and arrived at the station on Monday.

Atlantis carried up a 14-metre truss structure that contained the folded-up solar panels.

When the truss was attached to the space station on Tuesday, it marked the first major addition to the outpost in almost four years.

Construction of the $100 billion complex came to a halt when NASA grounded the shuttles after the Columbia disaster in 2003.

Now, after more than $1 billion in safety upgrades and two shuttle test flights, NASA has begun an ambitious program of at least 15 shuttle missions to finish the station before the shuttles are retired in 2010.

The additional power generated by the new solar panels will be needed as the station expands, but will not be activated until December.

Solar arrays installed in 2000 currently provide power to the station. Two more solar power units will be added later.

Tanner and Stefanyshyn-Piper made the first spacewalk of the mission on Tuesday, while astronauts Dan Burbank and Steve MacLean went out into space on Wednesday.

On both spacewalks, the astronauts lost bolts they had removed during their work, raising fears the hardware could damage the station or the new solar power assembly.

But in an e-mail message to the astronauts today, NASA managers said they estimated the bolts were at least 18 km away from the station and not a danger.

''This issue is now considered to be closed,'' it said.

Atlantis was scheduled to return to Earth on Wednesday.

Reuters AB DB1854