Seven astronauts arrived for the start of countdown to Thursday's space shuttle launch as NASA wrapped up repairs on Atlantis' fuel tank.

Damage was discovered Friday to the insulating foam on the shuttle's 15-story external tank. NASA doesn't know how or when the gouges to the foam occurred, but the damage is considered minor.

New patches of foam have been applied. It will take 16 hours for the foam to harden properly, in plenty of time for liftoff late Thursday afternoon, said NASA test director Charlie Blackwell-Thompson.

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Now that it's repaired, the foam should pose no threat to Atlantis during launch, said Blackwell-Thompson. Falling foam was disastrous in the case of Columbia in 2003, and has been a recurring problem.

Countdown clocks began ticking Monday evening. Packed safely aboard Atlantis was the European Space Agency's Columbus laboratory headed for delivery to the international space station.

Good launch weather was forecast.

"We hope it stays like this all week long," commander Stephen Frick said, standing next to his crewmates beneath a brilliantly blue sky.

French astronaut Leopold Eyharts will move into the space station for a few months and help get the Columbus science lab running.

"As I will be probably gone for a while, I would like to wish you all merry Christmas and a happy new year," Eyharts said. "See you in 2008."

This will be NASA's fourth shuttle flight of the year, all to the space station. So far, each of this year's countdowns has resulted in an on-time launch.

Ever since Discovery left a month ago, the three crew members on the space station have been working practically nonstop.

They looked pleased Monday as they wrapped up preparations for the arrival of Atlantis and the Columbus lab.

"If they launch this week, then I'll be home by Christmas," said astronaut Daniel Tani, who flew up aboard Discovery in October. He will be replaced by Eyharts and return to Earth on Atlantis.