US President George W. Bush on Tuesday hailed the successful launch of the space shuttle Discovery and described it as a key step towards one day landing a manned mission on Mars.

"Our space program is a source of great national pride, and this flight is an essential step toward our goal of continuing to lead the world in space science, human space flight, and space exploration," Bush said in a statement.

Asked whether the president still believed in eventually sending a crew to Mars, spokesman Scott McClellan said that was the "long-term mission" and "today's launch is an important first step to put us back on track."

Bush used a January 2004 speech to unveil ambitious plans to build a base on the Moon as a jumping-off point for Mars — but has barely mentioned that initiative since.

McClellan told reporters that Bush had applauded after watching Discovery lift off from its launch pad in Cape Canaveral, Florida, on television in his private dining room off the Oval Office.

"On behalf of all Americans, I wish the crew of the Space Shuttle Discovery a safe and successful mission. Today's launch marks NASA's return to flight following the tragic loss of the Space Shuttle Columbia crew in February 2003," Bush said in his statement.

Discovery, carrying seven astronauts, reached orbit eight minutes and 40 seconds after liftoff from the Kennedy Space Center.

Two minutes after launch, Discovery's two solid fuel rocket boosters separated from the main orbiter, which also jettisoned its external fuel tank when it reached orbit, in what the US space agency called a picture-perfect start to the mission.

NASA managers heaved a sigh of relief at the successful launch that marks the first manned US space flight since the shuttle fleet was grounded after the Columbia disaster on February 1, 2003. A scheduled launch on July 13 was scrubbed because of a faulty fuel level sensor.