Ripped glove forces early end to spacewalk; tests nearly completed
Thursday, August 16, 2007
CAPE CANAVERAL, Fla. -- After nearly a week of agonizing over a deep gouge on Endeavour's belly, NASA was close to wrapping up tests Wednesday and deciding whether to order risky repairs.
One of the astronauts who would attempt those repairs, Rick Mastracchio, had to cut his latest spacewalk short after he noticed a hole in his left glove.
The long rip in the thumb penetrated only the two outer layers of the five-layer glove, and he was never in any danger, Mission Control said. Nevertheless, he was ordered back inside early as a precaution, and his spacewalking partner quickly finished what he was doing and followed him in.
Earlier Wednesday, Mission Control informed the astronauts they may have to wait until today for a decision on possible repairs.
The unprecedented patching job, if approved, would be performed on the next spacewalk, currently scheduled for Friday but most likely to be put off until Saturday to give engineers more time to analyze the situation. That could keep Endeavour and its crew of seven, including teacher-astronaut Barbara Morgan, at the space station at least an extra day.
Preliminary results indicated no need for fixing the gouge, but mission managers were withholding judgment until the completion of heat-blasting tests on the ground.
The gouge -- the result of a debris strike at liftoff -- is in two of the thousands of black tiles that guard against the 2,000-plus temperatures of atmospheric re-entry. Part of the gouge, a narrow one-inch strip, cuts all the way through the tiles, exposing the thin felt fabric that serves as the final thermal barrier to the ship's aluminum frame.
The exposed area -- and the gouge itself -- are so small that NASA is not worried about a Columbia-type catastrophe at flight's end. Rather, the concern is that if too much heat enters the crevice, the underlying aluminum structure might be damaged enough to warrant lengthy postflight repairs. That, in turn, could lead to future launch delays and disrupt space station construction.
NASA does not want the aluminum under the gouge to get hotter than 350 degrees. As of Tuesday, computer models put the maximum exposure at 325 degrees and left mission managers "cautiously optimistic" no repairs would be needed. Engineers believe the worst of the re-entry heat should skip right over the gouge.
Endeavour's belly was smacked a minute after liftoff on Aug. 8 by a piece of debris about the size of a dishwashing sponge and weighing less than an ounce. NASA does not know if it was insulating foam or ice from the external fuel tank, or both. Whatever the material, the debris broke off a bracket on the tank, fell onto a lower tank strut, then shot up into the shuttle.
A redesign of these troublesome brackets, which support the fuel feed line on the tank, won't be ready until spring. NASA is debating whether to implement a temporary solution before the next shuttle launch in October, which could well delay that flight.
During Wednesday's spacewalk -- the third of the shuttle mission -- Mastracchio and space station resident Clay Anderson moved two rail carts and an antenna base into new positions on the orbiting outpost. They also added new antenna parts to improve voice communications and completed most of their other chores before retreating inside because of Mastracchio's ripped glove.
The spacewalk lasted 51/2 hours, an hour shorter than planned.
The next spacewalk will be trickier, if shuttle repairs are ordered. Under the latest scenario, Mastracchio and another astronaut would apply black paint to the white gouge and squirt in a caulk-like goo, while balancing themselves on the end of the shuttle's 100-foot robot arm and extension boom.
As of now, Endeavour and its crew of seven are due to leave the space station Monday and land two days later.