Shuttle Atlantis Set for Thursday Countdown

A banner cheers the space shuttle on as it reached Launch Pad 39B at NASA's Kennedy Space Center on Aug. 2, 2006. CREDIT: NASA/T. Gray.

CAPE CANAVERAL - NASA is poised to pick up the countdown to launch of shuttle Atlantis this week after swapping out two suspect bolts securing a key communications antenna inside the ship's cargo bay.

The work, which was finished Sunday at Kennedy Space Center's launch pad 39B, put NASA in position to start a three-day countdown Thursday. Liftoff of Atlantis and six astronauts remains scheduled for about 4:30 p.m. Sunday.

"Everything is looking good," said KSC spokeswoman Tracy Young.

Working atop a platform and scaffolding near the top of the shuttle's six-story payload bay, technicians replaced two of the four bolts holding the antenna in place with longer bolts.

The engineers had feared that the two original bolts were not adequately engaged and that the 304-pound antenna -- located at the forward end of the payload bay -- might break free during launch.

In that case, the antenna could have plunged the entire length of the 60-foot-long cargo bay, causing critical damage to the shuttle and its $372 million payload.

NASA managers ordered the replacement work Friday. The shuttle's clamshell-like cargo bay doors were opened that night, and technicians spent the better part of Saturday setting up equipment for the job.

A work platform was extended into the bay near the top of a towering room that provides access to shuttle cargoes on five levels.

Scaffolding then was built up on the platform, and the gangplank was fixed atop it so that a technician wearing safety harnesses could reach the bolts.

The actual replacement work began late Saturday and was completed Sunday.

The Atlantis astronauts are scheduled to arrive at KSC Thursday for final launch preparations. They plan to deliver a new central truss segment to the International Space Station.

Published under license from FLORIDA TODAY. Copyright ? 2006 FLORIDA TODAY. No portion of this material may be reproduced in any way without the written consent of FLORIDA TODAY.

• VIDEO: STS-115: First Tasks
• Complete Space Shuttle Mission Coverage
• NASA's STS-115: Shuttle Atlantis to Jump Start ISS Construction
• The Great Space Quiz: Space Shuttle Countdown