NASA ponders fix of shuttle heat shield

Houston, June 13: NASA engineers pondered how best to fix a tear in space shuttle Atlantis' heat shield while a new pair of electricity-generating solar panels were unfurled on the International Space Station.

Activities were interrupted briefly by a false fire alarm on the station and NASA said sensors on the shuttle had registered what were believed to be false impacts on the wing heat shield.

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

Deputy shuttle programme manager John Shannon said several ways were being studied to fix the blanket, which peeled back during launch to expose a small triangle of underlying layers that could be damaged by heat when Atlantis returns to Earth.

He said NASA may have a spacewalking astronaut go stitch the blanket back together with stainless steel string, if that proves to be the strongest repair.

''Once we put it down, we would like it to stay down,'' he said in a briefing at Johnson Space Center.

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

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

Shuttle astronauts Jim Reilly and Danny Olivas made the mission's first spacewalk on Monday when they installed a large metal truss that included the solar panels that were slowly unfurled by remote commands yesterday.

The 240-feet-long (73.15-metres) wings had been folded for more than six years due to delays in space station construction while NASA recovered from the Columbia accident in 2003. They will add electricity equivalent to that needed to power up to 10 houses, space station programme manager Mike Suffredini said.

Later in the day, a fire alarm sounded in the space station, prompting its crew members to start emergency procedures.

But they quickly determined there was no fire, and NASA blamed the alarm on a software problem linked to a balky navigation computer.

NASA also believes it received false readings from a sensor system that detects impacts on the shuttle's wing heat shield.

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

''We don't know exactly what is going on. We think we're getting some kind of thermal settling'' in the shuttle, he said.

A routine final heat shield inspection will be conducted near the end of the mission and would reveal a problem if there is one, Shannon said.

The sensor system was installed on shuttles after Columbia catastrophically broke apart while returning to Earth in 2003, killing the seven astronauts on board.

After the accident, NASA found that Columbia's wing heat shield had been cracked by a piece of insulating foam that fell off the fuel tank during launch.

Today, 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 that is now in the way of the new panels.

Reuters

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