Astronauts strolled inside the brand new International Space Station module, named Harmony. First to enter were space station commander Peggy Whitson and Italian astronaut Paolo Nespoli. "It's a pleasure to be here in this very beautiful piece of hardware," he said. Harmony is Italian-made.

For the Discovery this is the twenty-third mission to the International Space Station. Discovery delivered its precious cargo, the U.S. Node 2 Harmony module, which expands the space station's capability for future international laboratories. Built in Italy for the United States, Harmony is a high-tech hallway and Tinker toy-like hub. It is a 23- by 14-foot passageway that will connect the U.S. segment of the station to the European and Japanese modules, to be installed later this year and early next year, respectively.

Harmony, the ISS' seventh "room", will be the first new U.S. pressurized component to be added to the station since the Quest Airlock was attached to one of Unity's six berthing ports in 2001. This means that the crew faces one of its most complicated construction missions yet.

The trickiest part is that Harmony fits where the Discovery is actually docked. This means the module will have to be assembled in space and attached after Discovery leaves the ISS. Before that, astronauts will be restricted on how long they can spend inside the new compartment because of the makeshift ventilation system currently in place.

"STS-120 is such a cool mission," said Commander Pam Melroy in a statement before the mission. "Node 2 is the expansion of the space station’s capability to bring international laboratories up. It’s the expansion of our capability to carry additional people. "It has additional life support equipment that will allow us to expand out beyond a three-person crew. It’s this big boost in the capability which is really exciting," she added.

Harmony will provide air, electricity and water for the space station, as well as additional lodging for crew members.

Mission Specialist Daniel Tani will switch places with Clayton Anderson, who will be wrapping up a four-month tour of duty as an Expedition 16 crew member. Tani will stay on the station until he returns to Earth with STS-122 later this year.