CAPE CANAVERAL — Two spacewalking astronauts pulled out a caulk gun and high-tech kind of Silly Putty on Thursday night and tested a method for patching shuttle thermal tiles.
It was the fourth space walk since Endeavour arrived at the international space station last week to deliver a robot and the first section of a Japanese lab.
The long-awaited repair test was ordered up following the 2003 Columbia tragedy.
Astronaut Michael Foreman — "Mr. Goo" — squeezed the salmon-colored material from the caulk-gunlike dispenser and filled holes in deliberately damaged tile samples that were carried up aboard Endeavour. He used a small foam brush to tap down and smooth the putty, but small bubbles kept popping up.
His spacewalking partner, Robert Behnken, floated nearby, wiping excess putty from the nozzle of the caulk gun.
"You are Captain T-Rad, Mr. Goo. You're in control today," astronaut Richard Linnehan called out to Foreman. T-Rad is NASA's name for the caulk gun; it stands for tile repair ablator dispenser.
Even more of a mystery than how the caulk gun would work was how the goo would behave. Engineers were curious about whether bubbles would form and rise to the top as they do on Earth or whether any bubbles would remain inside the material and cause it to swell. This so-called rising bread-loaf effect could jeopardize a repair and endanger a crew during re-entry.
Mission Control said everyone was "absolutely captivated" by the test, which took less time than expected, and told the spacewalkers, "You're like brain surgeons up there."
Since the loss of Columbia, astronauts in orbit have tested other methods for repairing a shuttle's thermal shielding, but never this one.