As if reaching for a receipt at an ATM, spacewalker Stephen Robinson on Wednesday gently plucked two strips of protruding heat shielding from the bottom of the space shuttle Discovery, completing the first in-flight shuttle repair with fingertip ease.

Cameras operating from the shuttle's sensor boom and from Robinson's helmet provided spectacular views of his historic journey, as he first swooped out from Discovery's side on the end of a 55-foot crane and then curled beneath the orbiter to find and remove the two "gap fillers."

"It's coming out very easily," he said of the first one, shaped like an outsize guitar pick. Ten minutes later, using "probably even less force," he said, he removed the second one, about as big as a pair of raffle tickets.

At Mission Control, NASA handlers let out a collective sigh of relief. Officials had predicted the repair would be relatively straightforward, but "when we sent them out there to actually do it, I had a whole different level of concern," said Paul Hill, lead shuttle flight director.

The two gap fillers, which could have led to potentially hazardous hot spots on Discovery's underside during reentry, had seemed to be the last outstanding concern blocking officials from clearing the shuttle for its scheduled landing on Monday.

But Hill said teams of specialists were also considering a second unscheduled spacewalk to remove or repair a frayed and billowing piece of thermal "blanket" that has started to come loose below the port-side window where mission commander Eileen Collins will sit when she brings the shuttle home.

The blanket is not a heat hazard, as reentry temperatures on top of the shuttle never come close to the 2,300 degrees Fahrenheit that the underside must endure.

What engineers are worried about is a swatch of blanket that may tear away during reentry and cause damage. Wayne Hale, deputy shuttle program manager, said NASA wind-tunnel experts planned to run tests overnight Wednesday on impacts from 0.05-pound pieces of blanket, about the size of the afflicted area's outer layer. Final determination on another spacewalk will probably be made on Thursday, he said.

The thermal blanket, like the offending gap fillers and several large pieces of foam insulation that broke away from Discovery's external fuel tank during liftoff last week, were launch casualties that NASA tried hard to eliminate after the Columbia disaster on Feb. 1, 2003, grounded the fleet for 21/2 years.

Failure to resolve these problems, especially the shedding of foam debris, has prompted NASA to ground the fleet again while engineers figure out what went wrong and try to fix it. Officials have said that NASA must resolve the foam and gap-filler problems before the shuttle flies again.

Hill acknowledged the seriousness of the shuttle's shortcomings but noted that "everything since the first 10 minutes of the mission has gone perfectly, and most of the stuff that has gone perfectly is stuff we didn't even know how to do 21/2 years ago."

That appeared to be the case Wednesday. Without the imaging systems developed after the Columbia disaster, Mission Control would never have found the errant gap fillers and would never have undertaken a repair on the belly of the orbiter.

Even though Wednesday's spacewalk turned out to be relatively simple, Hill told reporters that Mission Control and the astronauts originally opposed it as a perhaps unnecessary task that risked damaging the shuttle's heat shielding, the orbiter's most vulnerable and, during reentry, most important component.

Robinson and fellow astronaut Soichi Noguchi left the shuttle airlock at 4:48 a.m. Eastern time to begin the third spacewalk of Discovery's eight-day sojourn at the international space station. Their agenda included a large and varied menu of tasks, with gap-filler repair shoehorned in about halfway through the schedule.

First, however, the spacewalkers wrestled a three-ton stowage platform out of the shuttle payload bay and into position, a job delayed by problems with the fasteners. Once that was finished, Mission Control deferred all the other large tasks, setting the stage for Robinson's journey.

Assisted by Noguchi outside and astronaut signal-caller Andrew Thomas inside, Robinson needed 50 minutes to prepare, shedding unnecessary tools and other paraphernalia, mounting a foot restraint on the station crane, stowing tethers and verbally running through checklists.

The key to the exercise, as NASA experts had pointed out, was never to touch the heat shielding, and to that end, all of Robinson's gear needed to be tied down, tucked away or left behind. He carried three tools, to be used only if he could not extract the gap fillers with his fingers: a pair of forceps, a modified hacksaw and a pair of astronaut scissors.

At 8:19 a.m., Robinson signaled, "Vegas, we are ready to fly."

"As always," astronaut crane operator James "Vegas" Kelly replied, "call stop three times if you see anything you don't like." And the crane lifted out of the shuttle payload bay.

The biggest uncertainty for the spacewalk was the possibility that Robinson, the first astronaut to be dangled below the shuttle, would lose communications.

"We wanted him to keep talking," spacewalk supervisor Cindy Begley said later at a Johnson Space Center news conference. "If Vegas stopped hearing him, he would stop the arm [crane]. If he stopped talking for more than a minute, Vegas would pull him out."

So Robinson talked. He soared out over the side of the shuttle in a preprogammed five-minute maneuver, then dove beneath the orbiter during a nine-minute second step, all the while expounding an informative but bizarre sotto voce tutorial.

"My plan is to do a gentle pull with the . . . fingers," he said. "If that doesn't work, I'll go to a slightly longer pull with the forceps."

The second maneuver left him stopped about seven feet in front of the first of the two gap fillers.

"I can see it very well," Robinson said. "It looks to be close to three inches on one side and 11/2 inches tall. It looks to be bent over. . . . Vegas, I'm ready to go in and get it when you are."

Inside the space station, Kelly took manual control of the crane. "Stand tall and lean forward," he said. "Once you think you can reach the gap filler, let us know so we can go brakes on."

"Steve, take it away," Thomas said.

"Body forward, two feet," Robinson said, extending his right hand toward the gap filler. The crane moved. "Good motion . . . good motion," Robinson said.

"Your hand is the closest thing to the orbiter," Kelly said.

"That's why it's out there," Robinson responded. "Good motion . . . three . . . two . . . one. Stop motion, set brakes."

The bottom of the orbiter, seen through Robinson's helmet camera, looked like snakeskin, with the scales bearing serial numbers, many of which could be clearly read. Robinson wasted no time.

In a curiously anticlimactic end to the Rube Goldberg-like choreography that preceded it, he reached out with his stubby white-fingered space glove, matter-of-factly grabbed the gap filler and pulled it out.

Ten minutes later, he had the second one. He asked Kelly to move him five feet back from the tile face so he could take pictures of his handiwork. Then he returned to the shuttle payload bay. Begley had predicted the job would last about two hours. It took 66 minutes.

"You looked good up there," Thomas said. "You trained for four years, and now you can spend the next four years signing autographs."

Astronaut Stephen Robinson holds a piece of gap filler after removing it.