Shuttle astronauts set for second spacewalk

By Jeff Franks

HOUSTON (Reuters) – Two shuttle astronauts were set to
replace a failed gyroscope on the International Space Station
on Monday in the second of three planned spacewalks as NASA
pondered whether to add a fourth to repair loose material on
Discovery’s heat shield.

Steve Robinson and Japan’s Soichi Noguchi were to work
outside Discovery and the space station, linked together 220
miles above Earth, for 6 1/2 hours to remove the bad gyroscope
and replace it with a new one brought by the shuttle.

Gyroscopes keep the 200-ton space station correctly
positioned. It has four of them but only two were working
before Discovery’s arrival.

Robinson and Noguchi repaired the other malfunctioning
gyroscope in their first spacewalk on Saturday.

The $95 billion station can maintain position with just two
working gyroscopes but if only one is functioning, the station
crew would have to fire rocket thrusters, which burn precious
fuel, to keep it steady.

Discovery is making the first shuttle flight since the
Columbia disaster on Feb. 1, 2003, and is the first shuttle to
link up with the space station since November 2002.

The spacewalking astronauts were scheduled to venture out
once more on Wednesday to install a storage platform outside
the station.

NASA said on Sunday they might be asked to perform an
unprecedented repair to the shuttle’s heat shield during that
spacewalk or it may add a fourth spacewalk on Friday for the
task.

Video inspections of Discovery after it launched last week
found that two strips of material known as “gap fillers”
between heat-resistant tiles on the shuttle’s belly are
protruding about an inch.

NASA managers fear the protrusions could change
aerodynamics and increase heat on the shuttle by as much as 25
percent when it re-enters Earth’s atmosphere for landing
scheduled on Aug. 8.

Heat shield damage was responsible for the loss of shuttle
Columbia and its seven astronauts on Feb. 1, 2003.

The gap filler problem has cropped up on previous missions
and the shuttles landed without problems but deputy shuttle
program manager Wayne Hale said NASA engineers were assessing
the risk of trying it again versus performing a repair that
would involve trimming or removing the loose material.

“I think the jury is out at this point on whether we’ll do
anything,” Hale said.

But, he said, “The Columbia accident made us realize that
we had been playing Russian roulette with the shuttle crews.”

The Columbia disaster was caused by a piece of foam
insulation that broke off the ship’s fuel tank during launch
and smashed into the ship’s wing.

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.

Videos showed pieces of tank foam flying off during
Discovery’s launch, which prompted NASA to ground the shuttle
fleet until the problem is solved.

The shuttle suffered minor damage to its heat shield, but
the protruding material is not believed to have been caused by
foam impacts.