Spacewalk slated to repair shuttle

Astronaut must trim or remove filler fabric dangling from orbiter

August 02, 2005|By Michael Cabbage and Robyn Shelton | Michael Cabbage and Robyn Shelton,ORLANDO SENTINEL

HOUSTON - Astronaut Steve Robinson will make an unprecedented spacewalk beneath the belly of shuttle Discovery tomorrow to remove two small strips of material sticking out of the ship's heat shielding.

The so-called "gap fillers" are ceramic-fiber cloths that technicians wedge between the shuttle's heat-resistant tiles during preparations for flight. Maintaining a smooth surface on the orbiter's belly is important to prevent overheating during the ship's fiery plunge home through Earth's atmosphere.

This will be the first time astronauts have taken a spacewalk to repair a shuttle.

Photographs taken by astronauts on the International Space Station during Discovery's approach last week showed two of the fillers protruding slightly after shaking loose during launch. After three days of analysis, NASA managers decided yesterday to make a fix instead of flying the shuttle home as is.

"The analysis had so much variability that we just could not preclude bad things," deputy shuttle program manager Wayne Hale said. "If we cannot prove that it's safe, then we don't want to go there. This exceeded our threshold and we needed to take action."

The task will be added to the last of three planned spacewalks, which will focus on miscellaneous assembly and maintenance jobs outside the station. The spacewalk is scheduled to start about 4:15 a.m. tomorrow.

After completing an earlier task, the station's robot arm will slowly move Robinson under Discovery. He'll be secured in a foot restraint at the arm's end and equipped with forceps, a blade similar to those in hacksaws and a pair of scissors.

Once in position, Robinson will try to remove the gap filler by simply pulling it out. If that fails, he'll use the forceps to stretch the filler taut and cut it with the blade. If he has trouble with the blade, he'll use the scissors. Then the robot arm will move him to the next gap filler, where he will repeat the job.

"It should be a simple task," said Cindy Begley, NASA's lead spacewalk officer for the mission. "It could be just as easy as grabbing it with his fingers and pulling it out. We hope that's how it's going to be."

One of the gap fillers protrudes about 1.1 inches and the other about 0.6 inches. The repair work is expected to be straightforward, leaving NASA managers more concerned about the potential for Robinson to damage the shuttle's fragile heat tiles accidentally as he works beneath the spaceship.

"The basic part of the task is to get to the work site, and that's something we've never done before - put ... [a spacewalker] underneath the vehicle," Begley said. "They are going to have to be very careful of the area not to damage anything while they're there."

Hale said a repair kit would be kept in the shuttle's airlock where it could be reached by the spacewalkers if Robinson needed to repair any accidental chips in the tile. But engineers think the chance of that happening is remote, he said.

Astronauts have unknowingly returned safely from space several times before with gap fillers protruding from the shuttle. However, new photo surveys added in the wake of the 2003 Columbia accident allowed mission managers to detect the issue for the first time before landing.

Past missions with gap filler problems showed only moderate heat tile damage. However, engineers estimated that areas behind the fillers could see increased heating by as much as 25 percent.

"The bottom line is there is large uncertainty because nobody has a very good handle on aerodynamics at those altitudes and at those speeds," Hale said.

In preparation for the job, NASA has called on some of its most experienced spacewalkers, including astronauts Joe Tanner and Jerry Ross, to help develop procedures for removing the fillers. Begley said astronauts are testing procedures in the giant NASA pool where spacewalkers practice underwater at Johnson Space Center in Houston.

While the gap-filler planning was under way on Earth, Soichi Noguchi and Robinson finished the mission's second spacewalk yesterday by replacing one of the station's washing machine-sized gyroscopes, which broke down in 2002.

The station carries four of these 600-pound devices, which maintain the outpost's proper orientation. Only two are needed to do the job and the station has been operating on just a pair since earlier this year, but NASA would prefer to have all four in working condition.

Last week, the spacewalkers restored one gyroscope by re-routing power lines to bypass a faulty circuit breaker. NASA officials say it now works properly.

"Oh, the view is priceless," Noguchi said yesterday during his spacewalk more than 200 miles above Europe. "I can see the moon."

Inside Discovery's cargo bay, the astronauts put the failed gyroscope in storage for return to Earth and retrieved its replacement. Noguchi then installed the new device, but it did not power up initially. So the astronaut reconnected the electrical cables and put it back in place.

This time, it came to life.

While they labored outside, other astronauts were busy moving supplies aboard the outpost. By yesterday afternoon, mission managers said, 15 tons of supplies and equipment that Discovery brought to orbit had been unloaded into the station. The goods were transported in a large cargo canister that will return to Earth on the shuttle.

In addition, the crews have filled the canister with science experiments, equipment and other unneeded items. Discovery also has provided the station with about 100 gallons of water, which the shuttle produces as a byproduct of generating electricity.

Today, NASA is giving Discovery's crew half a day off to rest and relax.

The Orlando Sentinel is a Tribune Publishing newspaper.

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