NASA Looks Ahead After Safe Shuttle Landing

CAPE CANAVERAL, Fla. — With a sigh of relief from NASA, the shuttle Endeavour dropped from sunny Florida skies to a safe landing Tuesday, erasing concerns for the safety of the seven astronauts and the spacecraft over a surprise gouge in the heat shield.

Now the space agency hopes it can respond with changes to the fuel tank foam insulation — which was responsible for the crevice — and keep to its schedule of shuttle launches to complete construction of the international space station.

"The flight was absolutely wonderful," astronaut and former teacher Barbara Morgan told reporters later. She acknowledged that she felt disoriented, a temporary sensation many astronauts experience as they transition from weightlessness to gravity.

"The room is still spinning a little bit," she said. "But that is OK."

The homecoming brought an upbeat end to a 13-day assembly mission that also featured Morgan’s long-awaited spaceflight debut. Morgan was the 1986 understudy for teacher-in-space Christa McAuliffe, who died in the shuttle Challenger explosion.

NASA had called an early end to the Endeavour mission in case Hurricane Dean turned toward Houston, home of NASA’s Mission Control at the Johnson Space Center.

But more than McAuliffe’s memory and the possibility of bad weather, the 3 1/2 -inch-long gash in the thermal protection under the shuttle’s right wing loomed over the mission.

Within an hour of the landing, NASA Administrator Michael Griffin and other agency officials strolled under the wing and took a close look at the gouge. Despite exposure to 2,000-degree temperatures during Endeavour’s hourlong plunge to Earth, the damage appeared essentially unchanged from the imagery taken of the gouge from space.

Later, Griffin characterized what he observed as erosion of the silica material in the shielding because of re-entry heating. The two tiles with the damage, along with a feltlike padding underneath, were to be removed for more analysis.

"We had one ugly dig, and we paid attention to it," Griffin said at a news briefing. "I personally stayed on top of it."

He praised the efforts of mission managers, who enlisted 200 engineering specialists in structures, thermodynamics and high-speed flight, to assess the threat posed by the damage with 4,000 hours of supercomputer simulation and laboratory testing.

The detective work prompted managers to forgo assigning the shuttle crew to a risky spacewalking repair.

"In our business, a lot of the discussion and decisions are really a risk-versus-risk discussion. There are no perfect answers," said Bill Gerstenmaier, NASA’s associate administrator for space operations. "When we talk about repairs, it’s not like taking your car to the dealer. There is a real risk with repairs. Our job is to look and ask what is the least risk. Is it better to leave it alone?"

Fix for foam The efforts of mission managers revealed Endeavour was struck about 58 seconds after the Aug. 8 liftoff by a baseball-size fragment of insulating foam. The origin was one of five brackets that hold a large propellant line to the outside of the shuttle’s disposable fuel tank.

"It was little underwhelming," shuttle commander Scott Kelly said of the gouge. "To see it, it looked rather small."

However, the first-time commander was mindful of the crevice as Endeavour rushed back to Earth.

"It crossed my mind for a moment, only in the sense I knew someone would ask about it. But I didn’t worry about it," he said. "Every flight we learn things, and we make corrections based on what we learn."

A modification of fuel tank brackets to stem breakaway foam will not be ready until spring, after three more scheduled missions. NASA will look for more modest changes in the interim to keep plans for missions to the space station in late October, early December and mid-February.

A short-term change under consideration would involve carving away some of the bracket foam. Another would call for applying a lubricant that would shed water.

The purpose of the foam is to prevent the super-cold temperatures of the propellants in the fuel tank from allowing moisture in the air to condense, collect on the container and freeze. Engineers believe ice grinds the foam away as a propellant line flexes in flight.

Griffin said his agency can move ahead to finish the station’s construction by 2010 — the date set by the White House for the shuttle’s retirement — without rushing. But he stressed there will be risks.

"This is very much an experiment vehicle," Griffin said. "Anyone who doesn’t believe that just doesn’t get it."

mark.carreau@chron.com