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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