NASA officials have opted to replace two bolts securing a vital antenna to the cargo bay aboard the shuttle Atlantis, though the swap should not impact the vehicle's planned Aug. 27 launch date.
"We'll be getting set up this afternoon and this evening," NASA spokesperson Tracy Young, at the agency's Kennedy Space Center (KSC) launch site, told SPACE.com. "The operation should be done by Sunday."
Atlantis remains on track to launch toward the International Space Station (ISS) at 4:30 p.m. EDT (2030 GMT) on Aug. 27. The shuttle's STS-115 astronaut crew is poised to deliver two girder-like truss segments and a new set of solar arrays to the orbital laboratory during their 11-day spaceflight.
While all four of Atlantis' Ku-band antenna bolts have performed as expected throughout the orbiter's 26-launch history, engineers chose to replace them rather than risk a failure during liftoff that could send the antenna plunging down the length of the orbiter's 60-foot (18-meter) cargo bay.
"It would go down and the damage would not be good," NASA shuttle program chief Wayne Hale Wednesday of the potential harm a loose antenna could cause.
During this weekend's bolt swap, pad technicians will remove the two aft-most bolts mating Atlantis' three-foot (almost one-meter) Ku-band antenna dish to the forward right wall of the spacecraft's cargo bay. Those two - of four total bolts - are too short, with only a few treads biting into their corresponding nuts.
Earlier this week, Hale said that between six and eight engaged bolt treads are preferred for each bolt to ensure they will hold Atlantis' 304-pound (137 kilogram) Ku-band antenna assembly fast during the eight and a half minute climb into orbit. Inspections found that only two of Atlantis' four antenna bolts were suitably secured, though a survey of all three NASA shuttles found that some were attached by as little as two-thirds of a tread, he added.
Similar too-short bolts have been replaced on the Ku-band antenna assemblies aboard the Discovery and Endeavour orbiters, both of which sit in their maintenance hangars at KSC.
Atlantis, however, sits in launch position at KSC's Pad 39B complex. To replace the bolts, technicians will work from the Rotating Service Structure (RSS), which covers the orbiter's payload bay and protects the spacecraft while at the launch pad.
Shuttle workers will extend a retractable platform into the top of Atlantis' cargo bay just between the orbiter's airlock and forward end of its ISS truss and solar array payload. From there, pad workers will set up scaffolding to reach the antenna assembly and likely carry out the actual replacement this weekend, NASA officials said.
The bolt swap is one of two outlying issues engineers are working through for Atlantis' launch. The other is a heater thermostat glitch found in one of three auxiliary power units (APUs) aboard the Discovery orbiter, which engineers are studying to make sure a similar problem does not afflict Atlantis.
NASA hopes to launch Atlantis during a window that opens on Aug. 27 and closes Sept. 7.
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