If astronauts have to venture into the void of space to fix a deep gash on the shuttle Endeavour's belly, they will get plenty of help from a team of experts assembled to help pick and perfect the best repair technique.

NASA has put together the team of engineers, astronauts and spacewalk gurus as other specialists scrambled to determine whether the crew needed to fix the gouge to avoid extensive post-flight repairs. A decision was expected by today.

The gouge is relatively small - 9 centimeters by 5 centimeters - and the damage is benign enough for Endeavour to fly safely home. But part of it penetrates through the protective thermal tiles, leaving just a thin layer of coated felt over the space shuttle's aluminum frame to keep out the more than more than 1,000 C heat of re-entry. Fixing any resulting structural damage could be expensive and time-consuming.

To patch the gouge, spacewalking astronauts would have to perch on the end of the shuttle's 30.5-meter robotic arm and extension boom, be maneuvered under the spacecraft, apply protective black paint and then squirt in a caulk-like filler.

Mission Control told the crew late Monday that officials had ruled out a third repair technique involving a protective plate that could be screwed over the damage.

All three techniques were developed following Columbia's catastrophic re-entry, and NASA has never attempted this type of repair on an orbiting shuttle. Only the black paint has been tested in space.

Astronauts Rick Mastracchio and Dave Williams have trained extensively on the ground and could perform any necessary repairs during the mission's fourth spacewalk, which is set for Friday but may be pushed back to Saturday. NASA managers are also considering extending the mission beyond 14 days to complete the repairs, if needed.

The astronauts' last tile-repair class was just three or four weeks before launch.

"I think that regardless of what repair method is chosen over the next day or so, we could execute it if required," said John Shannon, chairman of the mission management team.

Covering the exposed white coated felt with black protective paint would keep heat from building up in the cavity, Shannon said. Squirting in the caulk-like filler from a tank attached to the astronauts' spacesuit backpack would provide extra protection. Astronauts would apply the paint first to make sure the filler stuck.

For extra heat protection, the astronauts could also squirt in the caulk-like substance from a tank attached to their spacesuit's backpack. In that case, they would apply the paint first to make sure the substance stuck.

If the repairs are ordered, astronauts on the ground will practice repairing a replica of the gouge underwater so they can create precise instructions for the spacewalkers and their crewmates.

When an astronaut from the shuttle Atlantis' June mission had to staple up a thermal blanket that had peeled back during launch, the ground crew sent him 60 pages of instructions and four videos, Shannon said.

Mastracchio and Williams have already completed two spacewalks in three days. On Monday, they removed a 600-plus-pound gyroscope from the space station's exterior that failed last October. They installed a new one in its place that was carried up aboard Endeavour. The space station has four gyroscopes to keep it steady and pointed in the right direction.

Agencies

(China Daily 08/15/2007 page7)