The U.S. space shuttle Discovery lifts off from its seaside launch pad at Kennedy Space Station in Florida at 11:38 a.m. (1538 GMT) on Tuesday, NASA TV shows.
An area of "clear ice" near the liquid hydrogen part on the massive external tank poped up during the countdown, but after re-examining, it has been determined not to be a problem on liftoff.
The weather around the launch pad also continued to be not so cooperative. However, at the final minutes near the exact launch time, the weather turned to be "go" for launch.
Two minutes after the liftoff on a spectacular tower of smoke and flame, the twin solid rocket boosters have burned out and separated, falling back to Earth toward the Atlantic Ocean, according to NASA launch control center.
"Discovery climbs toward space, and all is going well with the flight as the shuttle's three main engines power the vehicle through Earth's atmosphere," said NASA TV commentator.
The shuttle, with seven astronauts aboard, will deliver a critical component Node 2, known as Harmony module, to the International Space Station.
During the 14-day mission designated STS-120, the shuttle crew, along with their station counterparts will take into orbit the new connecting module that will increase the space outpost's interior space.
Harmony module will provide attachment points for European and Japanese laboratory modules to be installed later this year and early next year respectively.
"STS-120 is such a cool mission," said Discovery Commander Pamela Melroy, the second woman to command a shuttle. "Node 2 is the expansion of the 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 said.
Moreover, the STS-120 mission will mark the first time females have been in command of both the space shuttle and the International Space Station at the same time, with female astronaut Peggy Whitson currently serving as the station's commander.
Built in Italy for the United States, Harmony is a high-tech hallway-like hub. Therefore, including in the Discovery crew is Italian astronaut Paolo Nespoli, the mission specialist who represents the European Space Agency.
Harmony will also 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.
The shuttle will also deliver a new crew member, Daniel Tani, to the station's Expedition 16 and bring back another one Clayton Anderson, after his five-month mission.
This mission includes the most number of spacewalks conducted while the shuttle is docked to the station. Altogether, there are five spacewalks scheduled, including one to evaluate a shuttle tile repair technique. Each spacewalk will last approximately 6.5 hours.
STS-120 is the 120th space shuttle flight, the 34th flight for shuttle Discovery and the 23rd flight to the station. If all goes well, Discovery is expected to complete its mission and return home on Nov. 6.