NASA Orders Repair of Shuttle Heat Shielding
Tuesday, August 2, 2005
HOUSTON, Aug. 1 -- Worried about the "uncertainty" of the space shuttle Discovery flying home with two strips of heat shielding protruding from its underside, NASA officials on Monday ordered the first repair of an orbiter in flight.
NASA engineers said Stephen Robinson, 49, an engineer from Sacramento, would be lowered over the side of Discovery to either pull out or snip off two "gap fillers" sticking out between the thermal tiles cloaking the orbiter's belly.
The operation should take a little more than 90 minutes. It is simple enough to be regarded as routine, engineers said, except that it is an unplanned spacewalk and marks the first time in the shuttle's 24-year history that astronauts have been called upon to perform an in-space, onboard repair to their own vehicle.
Wayne Hale, deputy shuttle program manager, told reporters at a Johnson Space Center news conference that handlers decided on the spacewalk because they could not be sure that the protruding fabric strips would not cause dangerous hot spots in the orbiter's heat shielding during reentry.
"There is large uncertainty because nobody has a very good handle on the aerodynamics at those speeds," he said. "Nobody flies Mach 22 at 260,000 feet." A spacewalk, he added, is an "option to set our minds at rest."
Hale said astronauts and engineers on the ground developed the spacewalk plan over the past three days and practiced it "at length." He said the final package of instructions was uplinked to Discovery late Monday night.
Discovery launched last week as the much-heralded first shuttle mission since Columbia disintegrated on reentry 2 1/2 years ago, but the debut has been marred first by the loss of large pieces of foam insulation from its external fuel tank after liftoff, and now by the protruding gap fillers.
NASA grounded the shuttle fleet after the Columbia disaster and has grounded it again pending a solution to the foam problem. Hale said engineers have also formed a task force to analyze why the gap fillers come out and will change procedures for inserting them in the next two weeks.
The trouble with the hardware has contrasted sharply with the near-flawless performance of the shuttle crew, now in the middle of an eight-day sojourn at the international space station.
Robinson and fellow spacewalker Soichi Noguchi spent Monday removing a space station gyroscope that seized up for unknown reasons three years ago and replacing it with a new gyro brought from Earth.
The station uses four of these "control moment gyroscopes" to fix its position in space and had been surviving with two or three ever since the Columbia disaster. The shuttle is the only spacecraft big enough to carry items as large as the washing-machine-size gyros.
Robinson and Noguchi trained for this exacting task -- shifting 620-pound gyros 65 feet back and forth between the shuttle and the station -- for three years and carried it off with ease. They finished quickly enough to retrieve tools and rearrange equipment in the shuttle's payload bay for the Wednesday spacewalk that will include Robinson's unprecedented journey.