Astronauts test shield fix, inspect for shuttle damage

HOUSTON (Reuters) -- After completing a spacewalk to test a shuttle heat shield repair technique, astronauts aboard Endeavour on Friday used a sensor-studded extension boom to make sure their ship was safe for next week's re-entry.

The scan, part of the safety enhancements NASA implemented after shuttle Columbia's fatal flight in 2003, was conducted a few days earlier than usual because the next piece coming to the International Space Station is so big there is no room for an inspection boom in the shuttle's cargo bay.

Instead, Endeavour's boom will be left on the station for sister ship Discovery to use when it arrives in May with the 37-foot-long Kibo laboratory. The module, about the size of a large tour bus, is Japan's prime contribution to the $100 billion station project.

A storage room for Kibo, "hope" in Japanese, was installed during shuttle Endeavour's ongoing construction and servicing mission at the station. Crewmembers also assembled a Canadian-designed maintenance robot called Dextre.

Leaving the boom behind on the station means the final sweep of Endeavour's heat shield needed to be finished before the shuttle leaves the orbital outpost on Monday.

Typically, the final inspection, intended to detect any damage from the impact of orbital debris while the shuttle is in space, occurs after the ship departs the station.

Endeavour passed its earlier inspections, which were focused on finding heat shield damage from impact from launch debris, like the damage that precipitated Columbia's breakup and the deaths of seven astronauts.

Columbia's wing was hit and damaged by a piece of insulating foam that fell off the fuel tank during liftoff. As the ship flew through the atmosphere for landing, superheated gases blasted into the hole, tearing Columbia apart.

Earlier Friday, spacewalkers Robert Behnken and Michael Foreman tested a technique for repairing minor damage to the shuttle's heat-resistant tiles. Using a special putty and caulking gun, the astronauts filled holes and cracks in sample tiles which will be returned to Earth for analysis.

NASA wants the test results before dispatching a shuttle crew later this year to work on the Hubble Space Telescope, which is too far from the space station for astronauts to fly to for shelter should their ship be damaged during flight.

While NASA will have a second shuttle standing by on the launch pad to rescue the Hubble crew if needed, spacewalking astronauts could make repairs if the damage was minor.

However, engineers want to make sure the putty will not bubble up in microgravity, risking more serious problems. If the shuttle's surface areas are not smooth, the ship could overheat as it soars through the atmosphere prior to landing.

Endeavour, which arrived at the space station on March 12, is scheduled to land at the Kennedy Space Center in Florida on Wednesday March 26.