Houston ? A key test of a daring yet wobbly spacewalking technique that could be used someday to repair space shuttle heat shields worked well Saturday and got good reviews from two astronauts from the shuttle Discovery, NASA officials said.

The repair simulation put them at the end of an oscillating, 100-foot combination of a robotic arm and an extension pole that astronaut Piers Sellers said made him feel “like a bug on the end of a fishing rod here.”

In a 7 1/2-hour spacewalk, the first of three orbital excursions planned for this mission, Sellers and Michael Fossum said they could do most of the mock tasks they were assigned with only moderate difficulty.

And that’s what NASA wanted to hear.

“It was above and beyond” what engineers expected, flight director Tony Ceccacci said after the spacewalk ended. “Hopefully, we’ll never have to use it (the boom for repairs) but we know we have the capability.”

The technique using the extension on the robotic arm was developed to make sure there is never a repeat of the Columbia disaster, which killed seven astronauts in 2003. A piece of foam from the shuttle’s external fuel tank struck Columbia’s wing during launch, creating a breach that allowed fiery gases to penetrate the shuttle during the return flight to Earth.

In this image made from NASA TV, Mike Fossum, left, and astronaut Piers Sellers work in Discovery's payload bay with the Earth in the background Saturday during a spacewalk.

Last year, emergency spacewalking repairs were needed because of heat shield damage to Discovery.

Fossum and Sellers may get a chance to use the boom for a real repair on their third spacewalk, now scheduled for Wednesday. NASA managers on Saturday were still evaluating whether a piece of fabric filler protruding from the thermal tiles on Discovery’s belly needs to be removed. If it does, Fossum and Sellers would have to go back on the boom and yank out the filler.

Orbiter project manager Steve Poulos said a decision will be made today on whether this gap filler – which is cracked, partially broken and just a couple inches at its longest point – must be removed. The early consensus is that it probably will be all right the way it is for re-entry, but engineers will pull an all-nighter to recommend what, if anything, needs to be done, he said.

Every other possible worry with the space shuttle heat shield has proven to be no big deal, deputy shuttle program manager John Shannon said. Today NASA may say Discovery is safe to land, he said, noting that Discovery’s flight has “by far” the fewest problems he has ever seen.