HOUSTON (AP) — Two spacewalking astronauts with caulking guns, putty knives and foam brushes practiced fixing deliberately damaged shuttle heat shields yesterday as NASA extended what could be its last trip to the space station for a long while.
With future shuttle flights grounded because of Discovery’s fuel-tank foam insulation loss during liftoff, mission managers decided to keep the crew at the International Space Station an extra day to help with station maintenance.
It could well be next year before the foam problem is fixed and a shuttle returns to the space station.
In a pair of tests designed in the wake of the 2003 Columbia tragedy, astronauts Soichi Noguchi and Stephen Robinson worked on custom-made samples of thermal tile and panels that were cracked and gouged before flight. They squeezed and dabbed dark goo into the crevices as they sped around the Earth.
The astronauts reported some bubbling in the two repair materials — a paintlike substance for the thermal tiles that cover most of a shuttle, and a thick paste for the reinforced carbon panels that line the wings and nose cap. The paste swelled up in the cracks like rising dough and, as the experiment wore on, was harder to get to stick because of colder-than-desired temperatures outside.
It was all valuable feedback. Engineers wanted to see how their creations fared in the weightlessness of space for possible future use in an emergency. Neither the bubbling nor swelling was surprising, said Cindy Begley, the lead spacewalk officer.
Columbia’s astronauts had no such tools or techniques at their disposal, and neither they nor flight controllers knew Columbia had a gaping hole in its left wing, left there by a 1.67-pound chunk of fuel-tank foam insulation that broke loose at launch.
A piece of foam just over half that size came off Discovery’s external fuel tank during last week’s liftoff. It missed Discovery, but was enough to ground all future shuttle flights. A smaller foam fragment may have struck the right wing, but lasers and other sensors found no evidence of damage.
The astronauts will test a third repair technique, essentially a plug, inside Discovery later this week.
Once the repaired samples are back on Earth, engineers will analyze them to see how deep and how well the filler material penetrated.
In the first of three spacewalks planned for this mission, Mr. Noguchi and Mr. Robinson also made some long-overdue space station repairs. They restored power to a gyroscope that stopped working four months ago and replaced a broken Global Positioning System antenna.
“Great job. Everything was just perfect. Extra stuff got done,” Mission Control radioed as the seven-hour spacewalk came to a close. “You guys get some rest.”
Today , NASA expects to wrap up all its analysis of Discovery’s thermal shielding and give the final safety clearance for the shuttle’s descent in another week.