"It's been a smashing success," astronaut Piers Sellers said during an inflight interview. "All good things come to an end -- at least for a while."
Sellers and David Wolf conducted three spacewalks to install and set up a new 45-foot long truss segment to the space station's starboard, or right, side. A matching segment for the port, or left, side is scheduled to be delivered to the station next month.
Astronauts slated to fly that mission aboard shuttle Endeavour are at the Kennedy Space Center for a two-day practice launch countdown.
The Atlantis crew, which is expected to wrap up its 11-day mission with an 11:44 a.m. ET touchdown, spent Thursday putting away equipment checking their spaceship's landing systems.
"Everything checked out fine -- we had no problems at all," said flight director John Shannon. "The vehicle looks like it's in great shape to come home tomorrow."
Although the technical challenges of the Atlantis mission were formidable, the astronauts said they found it emotionally difficult to say good-bye to the space station crew after their weeklong visit ended Wednesday.
"For them, it was a little bit like having house guests," said Atlantis pilot Pamela Melroy. "They were probably really happy to see us after having been alone up there for a while."
She added: "Their commander Valery (Korzun) said to us one night as we were eating dinner together in the service module, 'Thank you, this is what we need, the human contact and all the crew together sitting and having some social time.' So we could tell that was really important for them, as well as for us."
The teary farewell between shuttle flight engineer Sandra Magnus and station science officer Peggy Whitson, who became friends during a joint assignment in Moscow, affected the rest of the astronauts, Melroy added.
"Even test pilots cry when a great thing is coming to an end," she said.