March 21, 2008

Spacewalkers Test Fire Shuttle Repair Goo Gun

story was updated at 3:47 a.m. EDT.

HOUSTON - Two spacewalking astronauts test fired a high-tech caulk gun filled
with goo outside the International Space Station (ISS) Thursday to determine
whether it's a viable repair tool for dinged shuttle heat shields.

astronauts Mike Foreman and Robert Behnken squirted a pink, putty-like
substance into intentionally
damaged shuttle tiles
during their six-hour and 24-minute spacewalk to test
how the material behaves in the weightless vacuum of space.

"It goes
down really well," Foreman said as he tamped down the thick goop with a
sponge-like tool. "It really is like a loaf of bread with a lot of little
bubbles in there."

engineers developed the shuttle tile repair tool, known as the Tile Repair
Ablator Dispenser (T-RAD), in the wake of the 2003 Columbia disaster to fix
dings in the thousands of ceramic tiles that line an orbiter's underbelly.

The shuttle
Columbia disintegrated as it reentered the Earth's atmosphere, killing its
seven-astronaut crew, due to a hole in the fragile carbon-composite heat shield
panels along its left wing. NASA has developed a black heat-resistant putty for
minor panel damage, with the caulk gun and goo, small patches and a gray primer
wash reserved for dinged tiles.

this in our bag of tricks is really going to be helpful," Behnken said before
today's spacewalk.

excursion began at 6:04 p.m. EDT (2204 GMT) and marked the fourth of five
spacewalk planned for NASA's STS-123 shuttle flight aboard Endeavour. The
shuttle astronauts have delivered a new station crewmember, a Japanese module
and a massive Canadian maintenance
robot called Dextre
to the ISS during their 16-day mission.

repair test

tool, a slimmed down version of a balky backpack-mounted device, was the only
heat shield fix yet to be tested in orbit.

thrilled with what we saw today," said ISS flight director Dana Weigel after
the spacewalk, adding that T-RAD could also be used to mend torn shuttle
insulation blankets. "It behaved very similar to what we saw on the ground, so
that gives me a lot of confidence."

During the
test, Foreman squeezed the trigger of his gun-like T-RAD device, which then
mixed two different compounds into an ablative material as it squirted out into
the damaged shuttle tile samples. Some of the samples mimicked an actual
tile gouge
from Endeavour's last flight in August 2007, as well as ice
damage from post-Columbia tests on Earth.

"You are Captain
T-RAD today, Mr. Goo," Endeavour astronaut Rick Linnehan told the goo
gun-toting Foreman from inside the shuttle. "You're in control."

engineers hoped to learn how the T-RAD material behaved in space, and whether
bubbles would rise to the surface or cause the goo to swell like rising bread.

really captivated by what you're doing," astronaut Steven Robinson told the
spacewalkers from Mission Control here at NASA's Johnson Space Center. "You're
like brain surgeons up there."

Foreman and
Behnken reported seeing bubbles and some swelling, but were apparently able to
pat it down with their tools.

"I expect
that this [demonstration] will be successful and may actually teach us
something," said John Shannon, NASA's space shuttle chief, before the flight.
"Obviously, we have not had any tile damage since returning to flight that has
made us seriously consider this repair."

spacewalk marked the 108th spacewalk outside the ISS and the second career
excursion for Behnken and Foreman, both of whom are making their first

ended the orbital work with 13 hours and 17 minutes of spacewalking time, while
Foreman concluded with 13 hours and 32 minutes. Both astronauts will
participate in their mission's fifth spacewalk on Saturday.

spacewalkers also replaced a faulty circuit breaker outside the station, but
could not rewire an electrical line feeding it due to a stuck connector. They
also released a series of locks on a station module, hunted for a lost pin in a
berthing port - unsuccessfully - and removed a glove-like thermal cover from
one of the Dextre robot's hands.

"It looks
pretty good, a monstrosity," Foreman said of the robot. "Monstrous."

broadcasting Endeavour's STS-123 mission live on NASA TV. Click here for's
shuttle mission coverage and NASA TV feed.