The space shuttle Endeavour has lifted off on its 11-day Earth-mapping mission. Its rockets blasted six astronauts into space from the Kennedy Space Centre, Florida at 1743GMT on Friday.

Within nine minutes and after burning nearly two million litres (420,000 gallons) of fuel, the external rockets shut down and the shuttle entered space.

The launch took place about 14 minutes after the scheduled time, as a leak check on the crew cabin had to be repeated.

"It looks like a great day to go fly," launch director Dave King told the crew shortly before liftoff. "We're ready to map the world," replied shuttle commander Kevin Kregel.

The first countdown on 31 January failed due to a combination of bad weather and technical problems. The original launch date was supposed to be in September 1999.

'Tiptop shape'

The computer unit that malfunctioned in the final minutes of the first countdown had been replaced and the extensive attention to the condition of the whole shuttle fleet in recent months meant that Endeavour was in "tiptop shape", according to shuttle programme manager Ron Dittemore.

After five hours and 20 minutes of the mission, the astronauts will begin to extend a 60-metre (197-foot) radar mast, the longest fixed structure ever to fly in space. It will be used to make the most accurate topographical map of the planet to date, with only the polar regions going unrecorded. The mapping is due to begin 14.5 hours after launch.

The mission is largely sponsored by the US National Imagery and Mapping Agency, which supplies top-secret satellite and reconnaissance images to US defence and intelligence agencies.

Never tested

Most of the best-quality maps generated by this mission will remain classified but lower resolution maps are to be made available to the public for use by scientists, civil engineers and commercial companies.

The trickiest part of the mission comes right at the start with the deployment of the mast. The steel, titanium and plastic structure has never been tested in the weightlessness of space, and Nasa admits there is some risk that the mast could bend or break.

"We know from a safety point of view, we can always protect the vehicle and the crew," said Ron Dittemore. "We would not fly if we did not think we had those risks mitigated from a safety viewpoint."