The shuttle delivered a Japan's 37-foot-long Kibo laboratory in the mission. With the addition of Japanese-made orbital research laboratory, the station has more room than a jumbo jet.

"I can hardly believe this time has come. It's been an amazing adventure," said astronaut Greg Chamitoff, who is staying behind on the station for six months. "I'm looking forward to the adventure ahead."

Chamitoff replaced station flight engineer Garrett Reisman, 40, who has been in the orbit since March and will head home to meet his wife.

"I managed not to break anything really expensive," Reisman joked as the crews gathered for a farewell ceremony.

The shuttle is scheduled to land at the Kennedy Space Center in Florida on Saturday.

Flight director Matt Abbott said the mission has gone "just phenomenally well."

Before returning home, Discovery's astronauts will pull out the laser-tipped inspection boom that they retrieved from the space station, and survey their ship's wings and nose cap.

Engineers on the ground will be looking for any damage from debris generated during the May 31 launch or from micrometeorites in orbit.