(Recasts, adds Shannon, astronaut quotes)

By Jeff Franks

HOUSTON, June 12 (Reuters) - High-tech NASA may repair a torn heat-resistant blanket on the space shuttle Atlantis in a low-tech way -- by sending an astronaut out to stitch it together, the U.S. space agency said on Tuesday.

The space-suited seamster would use stainless steel wire and a hooked needle to sew the protruding blanket into place, said deputy shuttle program manager John Shannon.

He said the universal fix-it tool -- duct tape -- was discussed, but quickly discarded.

"Duct tape doesn't work in the vacuum of space," he told reporters at Johnson Space Center.

NASA has added two days and a fourth spacewalk to the shuttle's mission to repair the small tear in the thermal blanket near the ship's tail.

The blanket peeled back during launch to expose a small triangle of underlying layers that could be damaged by heat when Atlantis returns to Earth on June 21.

Shannon said several options were being studied for the fix, but the stitch-up, using spacesuit repair materials, was the leading contender because it was the strongest repair.

"Once we put it down, we would like it to stay down," Shannon said.

Still undecided was whether the repair will be done on the third spacewalk on Friday or the fourth on Sunday.

Shuttle commander Rick Sturckow, in a television interview from space on Tuesday, said the inches-long tear did not appear to be serious but NASA's plan to fix it is "the right thing to do."

"The shuttle is an expensive piece of gear and we should do everything we can to protect it," he said.

Atlantis launched Friday from Florida and docked with the space station 220 miles (354 km) above Earth on Sunday.

Astronauts Jim Reilly and Danny Olivas performed the mission's first spacewalk on Monday when they installed a large metal truss on the station that included solar panels to generate more electricity for the orbital outpost.

On Tuesday, those panels were unfurled by remote command, stretching out 240 feet (73.15-metres) from end-to-end.

Later in the day, activities were interrupted briefly by a fire alarm on the station that turned out to be false. NASA blamed the alarm on a software problem caused by a balky navigation computer.

NASA also said sensors on the shuttle had registered what were believed to be false impacts on the wing heat shield.

The sensors suggested the wing had been struck twice, but Shannon said similar readings were registered on previous shuttle missions and no sign of impact had been found.

He said the ghost impacts were believed to be caused by "thermal settling" of the shuttle.

Space shuttle Columbia broke apart as it returned to Earth in 2003, killing its seven crewmembers, because a piece of loose insulating foam cracked its wing heat shield at launch.

On Wednesday, astronauts Patrick Forrester and Steven Swanson will make the second spacewalk of what is now scheduled to be a 13-day flight.

They will set up a rotary joint that will allow the new solar panels to track the sun and possibly help retract an old solar panel, which will be moved later to a new location on the station.

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