After years in training and two launch countdowns, Sunita Williams [Images] on Sunday became the second woman of Indian origin after Kalpana Chawla [Images] to reach the orbit along with six other astronauts on board space shuttle Discovery that blasted off into the night sky on a 12-day repair mission to the International Space Station [Images].

Despite doubts about the take-off due to poor weather forecast and a two-hour delay before tanking operations, Discovery and its crew of seven lifted off from the Kennedy Space Center in Houston at 7:17 am IST.

It was an amazing sight as Discovery's 33rd flight steadily thundred into the darkness, lighting up the starless wintry night sky with a bright streak.

The liftoff from NASA's [Images] Kennedy Space Center was the first in darkness for a shuttle in four years. The crew members will get down to the business of completing the most challenging and complex ISS mission to date.

The mission will mark the third shuttle flight this year, the most the space agency has attempted since the fatal 2003 Columbia accident.

The launch of Discovery appeared to be an exceptionally clean space shot, NASA mission managers said.

"It all just came together perfectly," NASA launch director Mike Leinbach said in a post-launch briefing.

"Once we got into the final count, we just executed. It was like a sim-run with no problems. It was outstanding," he said. 

"What you've seen today is the successful accomplishment of the most challenging, demanding, technically state of the art difficult thing that this nation or any nation can do," NASA chief Michael Griffin said.

NASA also had to race to get launch preparations back on track after a challenging 48-hour shuttle turnaround following Thursday evening's launch scrub causing a two-hour delay in external tank refueling.

However, shuttle engineers and pad workers were able to make up for the lost time during final inspections of Discovery and the launch pad.

After reaching orbit, Discovery's crew set to work to open the payload bay doors, set up computers and equipment and check out the shuttle's robotic arm.

Heat shield inspections will begin on Sunday with a station docking scheduled for Monday at 5:05 pm.

The STS-116 crew members will dock to the International Space Station, install the new P5 truss structure and perform three spacewalks to rewire the station for electricity generated by a solar array delivered in September.

STS-116 will also swap crew members when Sunita Williams becomes a flight engineer for Expedition 14. She is expected to take a spacewalk with her colleague Curbeam to help rewire the ISS space lab and also operate the space station's robotic arm, among other tasks.

Taking Sunita's place aboard Discovery for the ride home is European Space Agency astronaut Thomas Reiter who has lived aboard the station since July.

Sunita has trained to remain aboard the space station until mid-2007, joining the outpost's current commander Mike Lopez-Alegria, and Russian cosmonaut Mikhail Tyurin. 

This is considered among the most difficult of the 19 assembly missions NASA has flown to the space station so far.

The astronauts will spend today inspecting the wings and nose of Discovery for damage to the heatshield from flying launch debris.

Though tracked by cameras and radar, Discovery's night-time departure was expected to limit detection of damage.

Columbia's disintegration was traced to undetected wing damage from falling foam fuel-tank insulation. After three daytime liftoffs in the accident's aftermath, shuttle managers were ready to resume the night launches.

Led by commander Mark Polansky, the crew is tasked with delivering a new $11 million, 11-foot-long extension for the station's growing solar power-generation system.

The current power system is adequate for the station's US laboratory. The changes will rewire the system to distribute power from the solar power module delivered by Atlantis in September and two more modules due next year and in 2008.

The added power will accommodate European and Japanese research modules and the life-support gear for more resident astronauts.

The six-hour spacewalks, which get under way in the mid-afternoon, are scheduled for Tuesday, Thursday and Saturday. The astronauts are due to return December 21.