NASA postpones repair decisions

NASA likely will tell the Atlantis astronauts to sew, staple or pin a piece of loose fabric heat shielding in place to cover an exposed region of the tail section of their spaceship during a spacewalk.

The space agency, which had planned to select a technique as well as the day for the repairs, postponed its decision by at least 24 hours Tuesday so engineers could conduct more tests, said John Shannon, who chairs NASA mission management team.

The assessments involve evaluating the strength of each repair technique with "pull tests." The tests re-create the damage, a 6-by-4-inch gap in the heat-resistant fabric that stretches across a maneuvering rocket mounted on the left side of the shuttle's rear section.

The gap was noticed by the shuttle crew shortly after the launch Friday on an assembly mission to the international space station. Experts believe the blanket, which may not have been installed properly, was peeled back, but not torn, by the airflow of the launching.

The shuttle Columbia's fatal breakup in 2003 was traced to an undetected hole in the thermal armoring that protects the wing from the temperature buildup that accompanies the high-speed descent through the atmosphere before landing. The breach was caused by an impact with a chunk of flyaway fuel tank insulation.

The tail section usually is exposed to lower temperatures than the wing, but Shannon said mission managers do not want to take the risk.

A 1984 shuttle mission landed safely with a similar gap in the protective material, but the temperatures were high enough to damage the housing of the rocket engine.

Even an extensive repair to Atlantis would become a setback as NASA attempts to finish the assembly of the space station before the shuttle fleet is retired in 2010.

On Monday, NASA extended the Atlantis mission by two days to June 21 to make time for a repair, which will be carried out either Friday or Sunday.

In addition to the "pull tests," shuttle engineers are scheduling wind tunnel tests that will subject the repair options to the aerodynamic forces and temperature regimes that Atlantis can expect as it returns.

Also, the space agency said small impact sensors within the left and right wings of Atlantis recorded small vibrations this week.

Mission managers believe the readings may have been in response to temperature swings rather than actual blows from a meteoroid or man-made debris.

However, the shuttle's heat shield will be examined for damage before re-entry.
Source :http://www.chron.com