NASA managers decided Friday to change out two bolts they fear may not be secure enough in attaching an important communications antenna to space shuttle Atlantis' payload bay.

The swap-out will take place over the weekend while Atlantis is on the launch pad in preparation for an Aug. 27 liftoff. Technicians will have to build scaffolding on top of a platform six stories off the ground to reach the bolts.

The two days of work likely will wrap up Sunday but won't affect the launch schedule or the start of the countdown on Thursday, unless there is a problem, said NASA spokesman Kyle Herring.

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"The more prudent thing to do is change them out while we have the time to do it," Herring said.

Engineers suspect that two of the bolts are too short on the KU-band antenna, which transmits images and other essential data between the space shuttle and Mission Control.

Atlantis has flown with those bolts without trouble since they were first installed two decades ago.

The problem was discovered last week, after Atlantis was rolled to the launch pad, when a review of paperwork on bolts on NASA's three space shuttles was ordered because a related problem was found in Discovery.

Atlantis' crew plans to resume construction on the international space station during an 11-day mission.