By Irene Klotz
CAPE CANAVERAL, Florida (Reuters) - Space shuttle Discovery blasted off for the last time on Thursday, carrying six astronauts and carting a load of supplies, spare parts and a robot for the International Space Station.
The shuttle lifted off at 4:53 p.m. EST (2153 GMT) from the Kennedy Space Center, riding a flame-tipped pillar of smoke across the Atlantic Ocean as it soared through partly cloudy skies toward space.
The launch was delayed three minutes when a range safety computer shut down before the planned 4:50 p.m. EST (2150 GMT) liftoff. The problem was resolved with seconds to spare, clearing Discovery for launch.
It was the 133rd launch in the 30-year-old shuttle program, and up to two flights remain before the United States retires its three-ship fleet later this year.
Discovery made 39 of those flights, including both return-to-flight missions following the fatal Challenger and Columbia accidents, and delivering the Hubble Space Telescope into orbit.
"For those watching, get ready to witness the power of Discovery as she lifts off one final time," shuttle commander Steve Lindsey radioed minutes before launch.
The shuttles are being retired due to high operational costs and to free up money to develop new vehicles capable of traveling beyond the space station's orbit.
Discovery is carrying a storage room, an external platform for spare parts and a prototype humanoid robot for the space station, a $100 billion project of 16 nations nearing completion after more than a decade of construction 220 miles above the Earth.
The mission had been on hold since November to fix problems with the shuttle's fuel tank.
Engineers repaired and reinforced thin metal support beams inside the tank, several of which had cracked when the ship was fueled for a launch attempt on November 5 and during a follow-up tanking test in December.
Similar modifications are planned for the fuel tanks of the two other shuttles in the fleet.
Shuttle Endeavour is set to launch April 19 with the $2 billion Alpha Magnetic Spectrometer particle detector. NASA also wants to fly the shuttle Atlantis this summer with a year's worth of supplies to tide over the space station until commercial resupply vehicles are operational.
"I think what will be most difficult will be on landing day when we know that that's the end of her mission, completely," said launch director Mike Leinbach.
NASA eventually wants to turn over station crew taxi flights, now handled by Russia at a cost of $51 million a seat, to private companies if any will offer human space flight services.
NASA had planned to follow the shuttle program with a new moon exploration initiative, but that has been canceled in favor of developing more flexible spacecraft that can reach asteroids, Mars and other destinations.
All plans, however, are on hold, pending budget allocations from Congress.
The delay launching Discovery cost the crew its lead spacewalker, Tim Kopra, who was injured in a bicycle accident in January. He was replaced by Stephen Bowen, who last flew in May.
With Bowen aboard the shuttle are commander Steven Lindsey, the former chief astronaut, pilot Eric Boe, and astronauts Alvin Drew, Michael Barratt and Nicole Stott.
The crew is scheduled to arrive at the station on Saturday for a week-long stay.