August 2, 2005

NASA set for delicate shuttle heat shield repair

By Irene Klotz

HOUSTON (Reuters) - NASA on Tuesday prepared for an
unprecedented spacewalk to the belly of space shuttle Discovery
to remove dangling cloth strips from the ship's delicate heat
shield and pondered another potential problem.

U.S. space agency managers were looking into whether a
damaged insulating blanket beneath the shuttle commander's
window could break off and strike Discovery during its return
to Earth next week at the end of the first shuttle mission
since the destruction of sister ship Columbia in 2003.

NASA could add a fourth spacewalk to Discovery's mission if
more repairs are needed, said shuttle deputy program manager
Wayne Hale. A decision was expected on Thursday.

Instead of taking a planned half-day off on Tuesday, the
Discovery crew prepared for the unplanned heat shield work
slated for the third spacewalk of the mission. It was set to
begin at 4:14 a.m. EDT on Wednesday.

Stephen Robinson and Soichi Noguchi were to attach a
platform loaded with spare gear to the outside of the
International Space Station, to which Discovery is docked.
Robinson then was to strap himself onto the station's 58-foot
(18-meter) robot arm for a ride beneath the shuttle's belly.

His job is relatively simple, but he runs the risk of
damaging the shuttle's ceramic-tiled heat shield.

"No doubt about it, this is going to be a very delicate
task," Robinson said, adding that his greatest concern was
keeping his helmet from bumping the bottom of the shuttle.

"Nothing is going to happen fast," Robinson said. "It's
going to be like watching grass grow."


NASA is concerned that two pieces of protruding cloth,
which are among the thousands of "gap fillers" tucked between
the shuttle's heat-resistant tiles for cushioning during
launch, could disturb the smooth flow of air that envelopes the
ship during its initial plunge into the atmosphere.

As the air thickens, turbulence develops, heating the
shuttle to temperatures that exceed 2,500 degrees Fahrenheit
(1,371 degrees Celsius).

The protruding gap fillers, which stick up about an inch
from the surface of the shuttle's belly, could raise
temperatures dangerously high, particularly for the shuttle's
leading-edge wing panels, which failed on Columbia.

"The analysis suggests that we would be right on the edge
of the capability of the (wing panels)," said flight director
Paul Hill.

Damaged by a 1.67-pound (0.75-kg) chunk of foam insulation
that fell off the ship's fuel tank during launch, the wing
broke off during Columbia's descent through the atmosphere on
Feb. 1, 2003. All seven astronauts aboard perished.

NASA wants Robinson to pull out the protruding gap fillers,
using his gloved hand or forceps. A backup plan was to use a
small hacksaw to trim the fillers to fit flush against the
surrounding tiles.

The repair could be completed in 10 minutes or take more
than an hour.

Robinson and Noguchi already have made two spacewalks on
the mission. During Wednesday's outing, Robinson will become
the first astronaut in the 24-year shuttle program to venture
beneath one of the ships in space.

"It sounds scarier than it is," Hill said.

Discovery and the International Space Station are orbiting
220 miles above Earth. While managers are pleased with the
mission so far, Discovery will be the last shuttle to fly for a

NASA's main goal after the Columbia accident was to fix the
fuel tank so it would not shed large pieces of foam during

It failed its first test-flight during Discovery's launch
on July 26, when a chunk of foam nearly as large as the one
that downed Columbia flew off the tank. Three other areas of
the tank shed unacceptably large pieces of foam as well,
forcing NASA to ground the shuttle fleet.

In addition to the tank problem, Hale said on Tuesday the
gap filler problem also must be solved before another shuttle
flies. The program is set to be phased out in 2010 in favor of
a yet-to-be-developed spacecraft.