Astronauts using a robotic arm attached a bus-sized addition to the international space station Friday, with help from a pair of spacewalkers.

The live-in compartment carried up aboard shuttle Discovery — called Harmony — weighs nearly 16 tons and increases the space station's living and working area by more than 2,500 cubic feet.

"Now the crews that are hot on our heels have a place to come," spacewalker Scott Parazynski said.

He and Douglas Wheelock got the Italian-made Harmony ready for its move out of the shuttle cargo bay.

Then Daniel Tani and Stephanie Wilson, working inside, used the station's robotic arm to slowly move Harmony toward its new home.

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Earlier Friday, the spacewalkers removed a broken antenna from the station and packed it aboard Discovery for its return to Earth, and got a giant girder ready for relocation later in the mission.

Parazynski encountered a few ammonia ice crystals that floated his way while he was disconnecting the girder's cooling lines, but his spacesuit did not seem to be contaminated.

Just in case, he followed safety procedures once he was back inside the space station, which involved taking a contamination test.

"Great day in outer space," Parazynski said as the spacewalk wrapped up.

Italian astronaut Paolo Nespoli, who joined Discovery's crew to personally deliver the pressurized chamber, coordinated the six-hour spacewalk from inside.

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Harmony's location on the station is temporary. The station crew will move it to its permanent spot once Discovery leaves in just over a week.

The chamber will also serve as the docking port for European and Japanese laboratories that will be delivered on the next three shuttle flights.

The shuttle launched from Cape Canaveral on Tuesday and linked up with the space station Thursday. It was the first time two female commanders met in space: Retired Air Force Col. Pamela Melroy is commander of Discovery, while Peggy Whitson is the station's skipper.

The 10 astronauts aboard Discovery and the space station face the most challenging construction tasks ever attempted in a single mission.

They may get a little more time to tackle their to-do list because engineers have not spotted any significant problems with the shuttle's thermal shield.

The crew set aside three hours Saturday for a focused inspection of any trouble spots, but mission management team chairman John Shannon said that examination probably won't be necessary.

NASA has made damage inspections a priority since the disintegration of the shuttle Columbia in 2003. A piece of foam broke off Columbia's external fuel tank during liftoff and gashed a wing.

Further analysis is needed before NASA can say for sure that Discovery suffered no significant launch damage.

But given all the construction work on this mission, "We are extremely lucky that we have a vehicle that is in such incredible shape," Shannon said.

The spacewalkers started their jaunt about a half hour ahead of schedule and were quickly wowed by the view of the Andes and the Amazon rain forest as they floated over South America.

"You're not going to believe this," Parazynski told Wheelock as he opened the hatch.

A veteran spacewalker, Parazynski will participate in four of the record-tying five spacewalks scheduled for this mission. This is Wheelock's first trip to space.