CAPE CANAVERAL, Fla. - NASA cleared six astronauts and their Atlantis orbiter for a Thursday landing after one last heat inspection found their spacecraft ship shape, a top shuttle official said today.

"We are cleared for entry," NASA shuttle program manager Wayne Hale told reporters after a day of inspections for Atlantis' astronaut crew. "Nothing was found to missing or damaged on the thermal protection system, the heat shield of the space shuttle Atlantis or any other part."

Atlantis is now set to land at 6:21 a.m. EDT (1021 GMT) at the Shuttle Landing Facility here at NASA's Kennedy Space Center. The shuttle could also land at 7:57 a.m. EDT (1157 GMT) if the first opportunity falls through.

"We're pretty optimistic for getting into Kennedy tomorrow or the next day," Atlantis' STS-115 mission commander Brent Jett told flight controllers today.

Jett and his crewmates are returning from a 12-day mission that delivered a massive, 17.5-ton set of trusses and two wing-like solar arrays to the International Space Station (ISS). Atlantis undocked from the station on Sept. 17 to make way for a new ISS crew, which arrived early Wednesday.

Atlantis astronauts spent the bulk of Wednesday morning using the orbiter's robotic arm and senor-equipped inspection boom to scan its heat shield and other sensitive areas after several objects were seen floating away from the spacecraft over the last two days.

"Today was a long day," Jett said, adding that he hoped flight controllers got the data they needed in Wednesday's inspections. "We understand, and everybody is trying to do the right thing. We're happy to do what it takes." 

Early Tuesday, a shuttle flight controller spied something suspected to be a bit of stray plastic drifting between Atlantis and the Earth. Later that day, Jett and his crew photographed an odd object also floating away from the spacecraft.

Then Wednesday morning, the astronauts reported three distinct objects floating away from the shuttle's payload bay.

But after one last detailed look at Atlantis' heat shield - the third such survey staged by the shuttle's crew - mission managers are confident that the objects are likely harmless bits of orbiter detritus, especially since all of the spacecraft's critical reentry systems are in pristine shape for landing.

"Whatever it was was not important," Hale said. "Sorry we're being a litter bug here."

That said, Hale added that NASA takes any type of orbital debris seriously and will redouble efforts to cut down on the potential of shedding bits of a shuttle - which does happen from time to time - in the future.

"It's a probability game, it's a big sky," Hale said of the hazard of orbital debris. "It really is a probabilistic risk that you must accept if you're going to fly anything in low Earth orbit, whether it's the space shuttle, the space station or anybody or anything else."

Atlantis' STS-115 mission marked NASA's third shuttle flight since the 2003 Columbia accident and the first dedicated to ISS construction since late 2002.

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