Discovery has docked successfully with the International Space Station after a perfect launch two days ago from NASA's Kennedy Space Center in Florida. Commander Pamela Melroy, 46, is the second woman commander in shuttle history and was greeted on the International Space Station by another female commander, Peggy Whitson, who is in charge of the orbiting three-astronaut crew.

The docking procedure ended at 8:40 a.m. EDT, about 7 minutes later than scheduled. As now customary, the Commander and the shuttle's pilot, George Zamka, have put a spin on the Discovery so as to allow the ISS crew to photograph its entire surface, with the most focus on the shuttle’s protective heat-resistant tiles which have to be checked for damage. However, no significant damage is expected as the in-flight videos were already analyzed by NASA engineers and no major problems were detected.

The actual opening of the hatches occurred only at around 10:39 a.m. EDT, when the two female commanders could greet each other in person.

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 is to expand 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 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. The crew isn't wasting any time, as preparations were to already begin Thursday for the first of five STS-120 spacewalks, scheduled to start at 6:28 a.m. EDT Friday.

"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.

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.

Image credit: NASA TV