Europe's space laboratory, Columbus, has been unloaded from the space shuttle Atlantis and docked with the International Space Station (ISS).
The attachment of Columbus to the ISS was carried out by astronauts working outside and inside.
A spacewalk to help install the orbiting laboratory lasted nearly eight hours - longer than expected.
The outing was scheduled to take place on Sunday, but was delayed when spacewalker Hans Schlegel fell ill.
The US space agency (Nasa) has refused to elaborate on what was wrong with German astronaut Schlegel, but said it was not life-threatening.
The European Space Agency (Esa) astronaut was replaced during Monday's spacewalk by shuttle crew member Stan Love, who ventured into space with fellow American Rex Walheim.
"Welcome to spacewalking, buddy," Walheim said as Love made his way through the hatch for his first spacewalk earlier on Monday.
"It's awesome," Love replied.
Schlegel is expected to take part in the second outing of the mission on Wednesday.
Mr Schlegel was stuck inside during Monday's spacewalk
The 12.8-tonne Columbus module was plucked from its berth in the Atlantis shuttle's payload bay at 1956 GMT by the station's robotic arm. The arm was operated by astronaut Leland Melvin, a former wide receiver in the US National Football League (NFL).
During Monday's spacewalk, Walheim and Love ended up falling an hour behind. They removed protective covers from Columbus and plugged in a grappling pin for the robot arm, along with completing some other tasks.
"Man, you guys have done an amazing job," shuttle commander Stephen Frick told the weary spacewalkers at the six-hour mark.
Columbus cost about $2bn (£1bn) and has room for three researchers in fields ranging from crop breeding to the development of advanced alloys.
The lab is the first part of the ISS that Esa will control.
Before docking with the space station on Saturday, astronauts aboard Atlantis guided the shuttle in a back-flip manoeuvre that allowed crew on the space station to photograph the shuttle's protective heat-resistant tiles.
Engineers on Earth will check the images for any possible damage that may have been done to the tiles during lift-off.
This became a routine safety measure after the shuttle Columbia disintegrated on re-entering the Earth's atmosphere in 2003.
The 7m-long (24ft), 4.5m-wide, 12.8-tonne laboratory will be manoeuvred into position by the shuttle's robotic arm, and docked to the station's Harmony Node 2 connector.
Esa astronaut Leopold Eyharts will be staying on the station to commission Columbus, a process that should take a few weeks to complete.
Its installation will mean Esa becomes a full member of the orbital project.
Atlantis was launched from the Kennedy Space Center in Florida on Thursday, and is due to return to Earth now on 19 February, a day's extension to the originally planned 11-day mission.
Once the lab is in place, an intensive programme of research in weightless surroundings will begin.
The experiments will also help researchers better understand the physiological demands of long-duration spaceflight, something that will be important if humans are ever to colonise the Moon or travel to Mars.