Discovery makes its final launch

The space shuttle Discovery is in space afterblasting off from Earth for the last time.

Liftoff took place at4:53p.m. ET Thursday from Kennedy Space Center in Florida. By 5:02 p.m., NASA saidtheshuttle's main engines were off and the shuttle was in space.

The shuttle's 39th takeoff, part of a mission called STS-133,attracted tens of thousands of spectators in Cape Canaveral.

Shortly before the externalfuel tank separated from the shuttle, at an altitude of around95 kilometres, debriscould beseen falling off the shuttle. Some spectators posted on Twitter their concerns the debriscould indicate damage to the shuttle's heat shielding.

Bill Gerstenmaier, NASA's associate administrator for space operations, said at a post-launch news conference the debris was likelyfoam pieces falling from the external fuel tank.

"They're not a concern to us," Gerstenmaier said. He added that the "foam losses" were not unexpected, and they didn't fall off during an "aerodynamicallysensitive" timeofthe shuttle's flight. NASA believesair gets behind the foam and then warms and expands,popping the foam off during a certain point in the flight.

The mission blog stated that the crew of Discovery will spend Friday inspecting the shuttle's thermal coverings in addition to preparing for docking at the space station.

In 2007, thermal tiles on the belly of the shuttle Endeavour were damaged by foam falling from the external fuel tank during launch. That caused some concern because damagecaused by the impact of loose foamwas blamed for the disintegration of the space shuttle Columbia as it re-entered the Earth's atmosphere in 2003. The disaster destroyed the Columbia and killed its entire crew.

However, NASA said the risk posed by the damage to Endeavour was minimal and the shuttle ultimately landed safely.

Gerstenmaier congratulated the launch crew, butnoted that theThursday is just the beginning of the 11-day mission.

"We have a huge mission in front of us all the activity in orbit is not trivial in any way, shape or form," he said,citing the mission's two spacewalks. "We need to stay focused on that, get the orbital activities done. When we get Discovery back, then we can talk about how things really went."

Discoveryistodock at the International Space Stationat 2:16 p.m.ET Saturday with:

• A crew of six astronauts, commanded by NASA veteran Steven Lindsey, a retired air force colonel.
• The Leonardo Permanent Multipurpose Module, the final module to be attached to the U.S. segment of the space station, which is full of supplies, experiments and equipment.
• A humanoid robot named Robonaut 2.

The shuttle is expected to return to the Kennedy Space Center on March 7 at 12:44 p.m. ET. After that, it will be permanently retired to a museum.

Fuelling wentsmoothly Thursday morning althoughatthe last minute, a computer glitch forced the countdown to pause five minutes before liftoff. That nearly caused NASA to miss its launch window for the day, but in the end, the problem was resolved, and the launch went ahead only three minutes later than scheduled.

The shuttle's final mission has been delayed several times.

In November, it was cancelled on launch day after cracks were discovered in the external fuel tank. NASA spent months figuring out the cause of the problem and making repairs.

Another mishap took place on Jan. 15, whenastronaut Tim Kopra was injured in a bicycle accident that left him unable to make the Discovery's flight. Hehas been replaced on the mission bySteve Bowen, who becomes the first astronaut ever to fly on consecutive missions.

Discovery's first flight was in 1984. Since then, it has flown 230 million kilometres and spent 352 days in space.

NASA has two other shuttle flights planned for 2011 before the end of its shuttle program. The shuttle Endeavour's last flight is scheduled for April and the shuttle Atlantis is expected to make one more flight in June.