NASA orders risky spacewalk to repair heat shield

By Irene Klotz

HOUSTON (Reuters) – Determined not to lose another space
shuttle and crew, NASA on Monday decided to send one of
Discovery’s astronauts on a risky spacewalk to the ship’s
fragile underside to smooth protruding fibers in the heat
shield.

The task of removing protruding material from the space
shuttle that could theoretically generate dangerous heat on
re-entry into the Earth’s atmosphere will be added to a third
previously scheduled spacewalk on Wednesday.

“This is the new NASA. If we cannot prove that it’s safe,
than we don’t want to go there,” deputy shuttle program manager
Wayne Hale told reporters at Mission Control in Houston.

The second spacewalk of the first shuttle mission since the
2003 Columbia disaster was completed on Monday, with Japanese
astronaut Soichi Noguchi and NASA’s Steve Robinson replacing a
failed gyroscope at the International Space Station.

The gyroscopes keep the orbital outpost properly positioned
in space without using the station’s limited supply of
propellant for rocket thruster burns.

Discovery does not appear to have suffered the sort of
damage to its heat shield that caused Columbia to break up over
Texas on Feb 1, 2003, as the shuttle came in to land.

But NASA engineers do not know enough about how the two
bits of material on Discovery could affect thermal and
aerodynamic forces as the vehicle plunges at 22 times the speed
of sound through the atmosphere on re-entry. They both stick
out about an inch (2.5 cm) from the smoothly tiled surface of
the ship’s belly.

‘LARGE UNCERTAINTY’

“The bottom line is there is large uncertainty because
nobody has a very good handle on aerodynamics at that altitude
and at those speeds,” Hale said.

Columbia was destroyed and its seven astronauts killed
because of heat shield damage on the ship’s wing caused by foam
falling off the fuel tank during launch.

After the accident, NASA adopted new procedures, spent $1
billion on safety upgrades and built equipment to inspect the
shuttle while it is in orbit.

But Discovery’s tank also shed large pieces of foam,
prompting NASA to postpone future flights until the tank is
repaired.

Discovery’s heat shield problem was not believed to have
been caused by a debris impact, Hale said.

More likely, the adhesive used to glue the thin
ceramic-coated material to the ship’s metal skin did not bond
properly. That may have allowed the fillers, which are tucked
between the heat shield tiles, to float out once the shuttle
reached the weightlessness of space.

While the repair plan is relatively straight-forward,
astronaut Robinson will need to take extra care not to damage
the delicate tiles that surround the protruding fillers.

“There is no situation in space that you can’t make worse,”
Hale said, quoting former astronaut and long-time NASA safety
advocate John Young. “The risk (of additional damage) is going
to be mitigated and controlled.”

In the shuttle’s 24-year history, spacewalking astronauts
have never worked on the shuttle’s belly before.

Out of direct sight from the shuttle and space station
crews and working solo from a platform on the station’s robot
arm, Robinson will first try to gently pull out the protruding
material. It that fails, he will try to cut it with a modified
hacksaw.