Commander Michael Bloomfield leads the 13th shuttle mission to the ISS

But high winds have been approaching the limit deemed safe for a launch and two fighter jets were scrambled to intercept a small passenger plane that entered a no-fly zone around the centre.

The latest mission to the International Space Station (ISS) has been delayed by four days.

Fuelling was halted on Thursday due to a leak in fuel lines that sent clouds of hydrogen billowing into the air.

Engineers worked through the weekend to fix a cracked pipe on the pad.

Seven astronauts arrived amid heightened security and secrecy on Monday as thick clouds gathered, also threatening the mission.

They included Jerry Ross, whose planned seventh take-off will set a record.

'Innocent intrusion'

As the sun rose, the National Aeronautics and Space Administration began pumping fuel into Atlantis' external tank.

Less than three hours later, the tank was filled without last week's problems but a plane sparked security fears when it flew close to the launch pad.

An army spokesman at the Kennedy Space Center said the pilot of the small plane had been co-operative after he entered the 55km (30-mile) diameter no-fly zone.

"We believe that this is an innocent intrusion," he said.

The small Cessna plane was intercepted at 1155 local time (1555 GMT) and accompanied to an airport near the town of Titusville, north of the space centre. Authorities have opened an investigation, officials said.

'Secret'

The US space agency kept the new launch time of 2039 GMT secret until Sunday.

It is implementing a new safety policy intended to protect the shuttle and its seven astronauts from terrorist attack.

When it does launch, the orbiter's crew will fit the first part of the backbone of the station and carry out scientific experiments.

Atlantis will be powered on the flight by a new set of shuttle engines, built without welds in the turbo-pumps to improve safety and reliability.

The crew of seven will spend 12 days in space, working with the three members of the ISS crew to extend the orbiting platform.

Plant experiments

The main component they are carrying into orbit is a 12-tonne girder called Truss S0, which will form the first section of the backbone of the station.

They are also carrying a cart that will run along rails on the backbone and allow the station's robotic arm to move across the platform.

The shuttle will also carry several scientific experiments, including one to grow wheat and mustard family plants in space.

This is part of a long-term programme to develop potential life support technologies for long space missions.