Space shuttle Atlantis rocketed off its seaside launch pad on Friday, rising atop a tower of smoke and flames as it left Earth on the final flight of the U.S. space shuttle program.

After a 30-year history that has cost nearly $200 billion and claimed the lives of 14 astronauts, the shuttles are being retired to make way for a new generation of spacecraft that President Barack Obama says will put U.S. astronauts on an asteroid and then on to Mars.

Today's launch may mark the final flight of the space shuttle but it propels us into the next era of our never-ending adventure to push the very frontiers of exploration and discovery in space, Obama said in a statement from the White House.

About 1 million sightseers witnessed the liftoff. They had lined causeways and beaches around the Kennedy Space Center in central Florida, angling for a last glimpse of the pioneering ship that has defined the U.S. space program for the past three decades as it soared through the skies.

Good luck to you and your crew on this final flight of this true American icon, shuttle launch director Mike Leinbach radioed to the crew minutes before takeoff.

Cloudy skies had threatened to delay Atlantis' launch on a planned 12-day mission to the International Space Station but conditions cleared in time for the blastoff.

However, 31 seconds before the scheduled 11:26 a.m./1526 GMT launch, computers detected a problem with the retraction of equipment used to vent gases from the fuel tank and stopped the countdown. Engineers verified the equipment's position and the shuttle lifted off three minutes later.

The shuttle is always going to be a reflection of what a great nation can do when it dares to be bold and commits to follow through, said Atlantis commander Chris Ferguson.

The shuttle's cargo of tonnes of food and equipment is intended to bridge the gap until newly hired commercial freighters are ready to begin deliveries to the station.

Atlantis and its four-member veteran crew are scheduled to arrive at the station, a recently completed orbital research outpost, on Sunday.

HIGH COSTS

NASA is ending the shuttle program primarily due to high operating costs. Its legacy includes launching and servicing the Hubble Space Telescope and dispatching dozens of planetary probes and Earth-orbiting satellites but also a troubled safety record.

In 1986, seven astronauts died aboard shuttle Challenger when a rocket booster seal failed shortly after launch. Seven more died aboard Columbia, destroyed due to heat shield failure in 2003 as it returned to Earth.

The shuttle fleet's crowning achievement was building the recently completed space station, a $100 billion project of 16 nations that orbits 230 miles above Earth.

The focus of the U.S. human spaceflight program for the next decade shifts to the space station itself, a complex the size of a five-bedroom house that has the potential for breakthrough research in medicine and technology.

NASA will rely on Russia to fly its astronauts to the station, at a cost of more than $50 million a seat, until commercial firms are ready to take over crew ferry flights.

Among the companies interested in the work is Space Exploration Technologies, or SpaceX, which already has a NASA contract to fly cargo to the station.

The company, owned by Internet entrepreneur Elon Musk, successfully tested its Dragon capsule in orbit last December and hopes to make it all the way to the station during a second test flight later this year.

The other freighter, being developed by Orbital Sciences Corp, has yet to debut.

NASA also is backing space taxi development work by Boeing Sierra Nevada Corp and Blue Origin, which is owned by Amazon founder Jeff Bezos.

The U.S. space agency also plans to use the $4 billion or so it has been spending each year to maintain and operate its three space shuttles to develop new spacecraft that can travel beyond the station's near-Earth orbit, where the shuttles cannot go.

Atlantis is scheduled to spend about a week at the space station, transferring more than 5 tonnes of food, clothing, science experiments and other gear to the station and packing up old equipment to be returned to Earth.

Upon Atlantis' return, about 3,200 space shuttle contractor employees will be laid off. Most work at the spaceport in Florida.

We're going to be going through a tough time. Change is hard, said Kennedy Space Center director Bob Cabana.

(Editing by Tom Brown and Bill Trott)

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