NASA gave space shuttle Atlantis the all-clear to come home Thursday after a stem-to-stern inspection prompted by a mysterious flurry of orbital litter found no damage to the ship.

NASA could not say for certain what the five floating pieces of junk were — perhaps a plastic filler strip, maybe a garbage bag. But shuttle program manager Wayne Hale said there was no reason to worry, because nothing of any importance was missing from the spacecraft.

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"We are cleared for entry. Nothing was found to be missing or damaged on the thermal protection system, the heat shield of the space shuttle Atlantis or in fact any other part of the space shuttle Atlantis," Hale said after two inspections lasting a total of 7 1/2 hours. "So we feel we're very confident that we're in good shape for a landing opportunity."

Even the weather forecast was good for a 6:21 a.m. EDT landing attempt at the Kennedy Space Center in Florida.

Atlantis' 11-day mission was extended an extra day Tuesday after NASA spotted two mysterious objects in orbit and became worried that something vital broke off the shuttle or damaged the ship's heat shield or other systems when it came loose.

So Atlantis' six astronauts spent Wednesday using the shuttle's robot arm and a 50-foot extension boom to give the shuttle the twice-over. During the inspections, astronauts spotted three additional mystery objects that probably escaped from the shuttle harmlessly, Hale said.

For Atlantis, the crucial cosmic math is this: a 17 1/2-ton addition connected to the international space station; three spacewalks; five mysterious pieces of space junk; two last-minute inspections; one extra day in space and "zero defects on the heat shield," Hale said. "That is really the bottom line."

Damage to Columbia's heat shield led to its 2003 disintegration during its return to Earth, so NASA is now more cautious about any damage to the shuttle's tiles or leading edges.

"We've seen a new standard in NASA vigilance," Hale said.

John Logsdon, a member of the independent board that investigated the Columbia accident, praised NASA for being "prudent" in taking the extra day to make sure everything was safe.

While Atlantis' crew of six slept, engineers on the ground operated cameras on the robot arm to check out the cargo bay and flight control systems. Then, when the astronauts woke up, they used the shuttle's arm for a 4 1/2-hour inspection and then the arm-and-boom for a two-hour examination of harder-to-see places.

"It was a long day, especially for Fergie and Dan," Atlantis commander Brent Jett radioed Mission Control, referring to pilot Chris Ferguson and astronaut Dan Burbank, who operated the robotic arm. "But you do what you need to do. ... We understand everybody's doing the right thing, so we're happy to do what it takes."

The astronauts were so tired they went to sleep early.

Atlantis' complex mission — resuming construction on the international space station after a nearly four-year delay — sputtered to get off the ground with four technical and weather delays. But the mission itself was nearly flawless.

Hale said that the mysterious objects all probably came from the shuttle, and that his best guest is that one piece was probably an orange plastic filler placed in between the tiles that protect the shuttle from the blasting heat of re-entry. He said another object appeared to a garbage bag.

The other pieces were described by Jett as two rings and a piece of foil.

Hale said they were nothing to worry about: "Sorry, we're being a litterbug here."