CAPE CANAVERAL, - The six astronauts aboard the space shuttle Atlantis will conduct an unprecedented third inspection of their orbiter's heat shield before landing this week to ensure its integrity after an unidentified object appeared to shake free of the spacecraft this morning, NASA's shuttle chief said late Tuesday.
NASA space shuttle program manager Wayne Hale said Atlantis' STS-115 astronaut crew will use their orbiter's 50-foot robotic arm to scan sensitive heat shield areas Wednesday and remains on track for a planned landing at the Kennedy Space Center here Thursday at 6:21 a.m. EDT (1021 GMT).
"We still aiming for Thursday," Hale said. "We have no reason, we think, not to go take a look."
Commanded by veteran NASA spaceflyer Brent Jett, Atlantis' STS-115 crew was slated to land at the Shuttle Landing Facility here at the Kennedy Space Center (KSC) at 5:58 a.m. EDT (0958 GMT) Wednesday after an 11-day mission to resume construction of the International Space Station (ISS).
But NASA postponed the landing attempt earlier today after spotting the mystery object, which appeared to have shaken loose from the orbiter during a series of standard pre-landing flight systems and thruster checks.
"There is considerable suspicion that whatever came off the vehicle came off during the flight control systems check-out," Hale said. "We think if this piece came off...it will be easier to see. We can scan faster."
Atlantis' STS-115 astronauts have already made two detailed surveys of their orbiter's heat shield using its robotic arm and inspection boom - one just after launch and another on Monday. Both inspections turned up no signs of any damage to the spacecraft's heat shield.
Hale said the current plan is to awake Atlantis' six-astronaut crew as planned at 9:45 p.m. EDT (0145 Sept. 20 GMT) tonight and begin a five-hour survey of the orbiter's heat shield - including its underbelly - using the shuttle's Canadian-built robotic arm. Those inspections are expected to begin by about 11:45 p.m. EDT (0345 Sept. 20 GMT), he added.
Only after that inspection will shuttle engineers and mission managers decide whether to unstow Atlantis' sensor-laden inspection boom for a closer look at the orbiter's heat shield, a process that would take at least three more hours if completed on time.
"It's probably 50/50 whether we're going to bring the boom out or not," Hale said, adding that a boom inspection must end on time in order for Atlantis' crew to make their planned Thursday landing attempt for sure. "They'll make a real-time call."
Mystery objects redux
A flight controller at NASA's shuttle Mission Control room spotted the debris at about 2:45 a.m. EDT (0645 GMT) Tuesday while using one of the orbiter's payload bay cameras during routine Earth observations, shuttle officials said.
Image analysts were unable to identify what the mystery object was, and likely will not be able to, shuttle officials said, though some engineers think it could still be a small piece of plastic inadvertently left between tiles along Atlantis' underbelly.
"We don't know that for sure, but it is a likely candidate," Hale said, referring to the bit of orange plastic--known as shim stock--seen dangling from a gap between the protective heat tiles along Atlantis' belly.
But a second object photographed by Atlantis' crew is thought to be a simple plastic bag that drifted away from the orbiter.
"We do see things come off space vehicles from time to time that are really of no consequence other than we really would not like to leave litter lying around," Hale said.
Data indicating eight potential impact sites within two minutes, based on new accelerometer sensors within the leading edge of one of Atlantis' wings has been put to rest, Hale said, adding that they signals correspond to powerful movements of the shuttle's elevons.
The elevons are used to help steer the orbiter when it flies through Earth's atmosphere during reentry, and are powered by hydraulics.
Flight controllers on Earth conducted a camera survey of Atlantis' payload bay and upper orbiter surfaces while the shuttle's STS-115 crew slept, which will cut down the amount of time the astronauts spend on robotic operations on Wednesday.
"We have, through inspection of the orbiter, cleared many areas of the orbiter," Hale said of that work, adding that thermal analysis have also found no signs of any abnormal variations along the orbiter's hull. "In terms of making sure that the shuttle is safe for entry, that's our primary goal and we will know that at the end of the crew's day tomorrow."
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