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

Liftoff took place at 4:53 p.m. ET Thursday from Kennedy Space Center in Florida. By 5:02 p.m., NASA said the shuttle's main engines were off and the shuttle was in space.

Discovery's Canadian cargo

No Canadian astronauts will be on Discovery's last flight, but several Canadian experiments will be on board:

  • Hypersole, which looks at how the skin's sensitivity changes before and after space flight. By testing the soles of astronauts' feet during Discovery's mission and two other shuttle flights, human health researcher Leah Bent, of the University of Guelph in Ontario, hopes to learn how changes in skin sensitivity are related to balance control. Among the elderly, a loss of skin sensitivity is linked to a loss of balance control and a greater incidence of falls.
  • APEX-CSA2, which involved growing white spruce seedlings for 30 days in space. The seedlings were sent up on Discovery's April 2010 flight. They are returning, harvested and frozen, on the current flight so their DNA can be analyzed by the team of Jean Beaulieu at Natural Resource Canada's Canadian Wood Fibre Centre in Quebec City.
  • VASCULAR, a study on how the structure of blood vessels changes on long space flights, similar to how they change as people age. Discovery will carry blood samples back to Earth for analysis by Richard Hughson at the University of Waterloo in Ontario and his team.

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

Shortly before the external fuel tank separated from the shuttle, at an altitude of around 95 kilometres, debris could be seen falling off the shuttle. Some spectators posted on Twitter their concerns the debris could 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 likely foam 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 "aerodynamically sensitive" time of the shuttle's flight. NASA believes air 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 damage caused by the impact of loose foam was 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, but noted that the Thursday 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."

Discovery is to dock at the International Space Station at 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 went smoothly Thursday morning although at the 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, when astronaut Tim Kopra was injured in a bicycle accident that left him unable to make the Discovery's flight. He has been replaced on the mission by Steve 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.

With files from The Associated Press