Spacewalkers leave station airlock for 2nd outing

CAPE CANAVERAL, Fla., June 13 (Reuters) Astronauts from the visiting space shuttle Atlantis floated out of an airlock on the International Space Station today for another spacewalk on a mission overshadowed by damage to the shuttle's thermal blanket.

Aiming to boost the outpost's power supplies, Patrick Forrester and Steven Swanson began the second spacewalk of Atlantis' expanded nine-day stay at the orbital outpost shortly after 0000 IST.

Two days were added to the mission so astronauts can fix a piece of insulation protruding from the rear of their spaceship.

A corner of the thermal blanket peeled back as Atlantis climbed into orbit on Friday, leaving a triangular 4-inch by 6-inch (10 cm by 15 cm) gap.

The issue is considered minor, but managers want the crew to tuck the blanket back down to avoid damage to the shuttle as Atlantis flies through the atmosphere prior to landing.

NASA needs to keep its three-ship fleet on track for completing 12 construction missions to the space station by 2010 when the shuttles, the only vehicles suited to launching and assembling the major components, are to be retired.

The U.S. space agency also would like to fly two resupply missions to the station and make a final servicing call to the Hubble Space Telescope.

Since the loss of shuttle Columbia in 2003, NASA has been meticulous about scouring shuttles' heat shields for damage.

Columbia was hit by a piece of foam insulation that fell off its fuel tank during launch. The strike punctured heat panels, allowing superheated gases to penetrate the shuttle as it plunged through the atmosphere for landing.

The shuttle broke apart over Texas, killing the seven astronauts aboard.

EXTRA SPACEWALK NASA resumed station assembly a year ago after fuel tank redesigns, safety upgrades and two test flights. The first priority is to assemble the exterior beams and boost power supplies so long-delayed partner laboratories built by Europe and Japan can be attached to the outpost.

Atlantis delivered a pair of massive solar wing panels that were installed during the mission's first spacewalk on Monday.

Forrester and Swanson will now remove restraints so the new panels can rotate and track the sun for power.

The astronauts also will have about an hour to help fold up an older wing that will be moved to a new location on a later flight. The old panel now blocks the new wing's rotation.

NASA's last construction crew, which flew to the station in December 2006, had to make an unplanned spacewalk to coax a similar balky panel back into a storage box.

A third spacewalk on Friday by astronauts James Reilly and John ''Danny'' Olivas has been dedicated to retracting the older wing panel.

Flight directors were expected to decide today evening if Reilly and Olivas would attempt the heat shield repair on Friday as well. If not, Forrester and Swanson would pick up the task during the newly added fourth spacewalk on Sunday.

Reuters AKD VP0130