HOUSTON — NASA officials 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.

At press time, Atlantis remained on track to launch toward the international space station (ISS) Aug. 27 at 4:30 p.m. EDT . 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 18-meter cargo bay.

“It would go down and the damage would not be good,” said NASA shuttle program chief Wayne Hale Aug. 16 of the potential harm a loose antenna could cause.

During the bolt swap, pad technicians removed the two aft-most bolts mating Atlantis’ almost nearly 1-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.

Hale said that between six and eight engaged bolt treads are preferred for each bolt to ensure they will hold Atlantis’ 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 Kennedy Space Center in Florida .

To replace the bolts, technicians worked from the Rotating Service Structure, which covers the orbiter’s payload bay and protects the spacecraft while at the launch pad.

Shuttle workers extended a retractable platform into the top of Atlantis’ cargo bay just between the orbiter’s airlock and forward end of its space station truss and solar array payload. From there, pad workers set up scaffolding to reach the antenna assembly , NASA officials said.

The bolt swap is one of two outlying issues engineers are working through for Atlantis’ launch. In addition to the bolt swap, engineers studied a heater thermostat glitch found in one of three auxiliary power units aboard the Discovery orbiter to make sure a similar problem does not afflict Atlantis.

The launch window for Atlantis opens on Aug. 27 and closes Sept. 7.