Discovery's crew will check the shuttle's wing for damage from space junk or tiny meteorites in a first-of-its-kind procedure Friday, two days after a spacewalking astronaut accidentally let go of a spatula that now circles Earth with other orbital trash.

NASA said the spatula posed no risk to the crew, but it planned to use a 50-foot extension boom attached to the shuttle's robotic arm to look for damage from micrometeoroids, the dust-sized particles that make up the vast majority of debris circling Earth.

Sensors on the boom tip will look for near-invisible holes and cracks in the shuttle's left wing. On Saturday, astronauts will examine the right wing and nose cap.

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The military tracks about 10,000 objects in space that are larger than a softball. Only about 700 are working satellites, said William Ailor, director of the Center for Orbital and Re-entry Debris Studies at the Aerospace Corporation in Los Angeles.

The rest is space junk.

And those are just the large pieces. There are about 100,000 other fragments of orbiting trash measuring between 1 and 10 centimeters — about the size of pretzels, Ailor said.

"It's really the small things that will get you," Ailor said, adding that the shuttle program has had to replace windows that were hit by flecks of paint.

If anything but tiny debris hits the shuttle, astronauts should hear and feel it and would know to look for damage, Ailor said. But the dust-sized particles can cause unfelt damage.

If Friday's procedure works, the odds of losing the shuttle from tiny meteorites will drop from the normal 1 in 210 to maybe 1 in 282, said Steve Poulos, shuttle orbiter projects manager.

NASA worries about both man-made debris, but small meteorites pose the biggest danger, Poulos said. A chunk of rock as small as 1 mm — the thickness of a paper clip — can be fatal, he said.

NASA was a bit embarrassed when spacewalker Piers Sellers let go of a 14-inch spatula Wednesday while testing a method to apply emergency patches to a shuttle heat shield, but it will be lost in a cloud of other space junk, Ailor said.

On Thursday, NASA engineers announced they had successfully tested a system to search for cracks in the heat shield using heat-sensing infrared cameras. The infrared camera spotted a below-surface four-inch hole in a mock-up that did not show visible damage.

The camera was tested during Wednesday's spacewalk, and data came back to earth Thursday. In addition to the test, astronauts used the camera to look at a shuttle wing and "did not find a single problem," infrared program manager Mike Gazarik said.

The astronauts had few scheduled activities Thursday and spent much of their time relaxing. Crew members also had 10-minute video conferences with their families.

"We've been so busy we haven't had much time to really have a whole lot of fun," astronaut Michael Fossum said during a Fox News interview. "Of course, we played the stupid astronaut trick of throwing the M&Ms across the cockpit. But today's been the first day we've had a little bit of downtime to look out the windows a little bit and appreciate where we are."

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