By Jo Twist
BBC News Online science and technology staff
The jet plane in which US adventurer Steve Fossett plans to fly non-stop around the world without refuelling will probably set off early next year.
Burt Rutan, centre, has used utralight materials for the plane
"It looks great and is performing well," said Virgin boss Richard Branson, backer of the GlobalFlyer.
Sir Richard is the reserve pilot for the flight, even though he revealed he does not have his pilot's licence.
The jet has been designed by aviation pioneer Burt Rutan, the man behind the first private spacecraft, SpaceShipOne.
His company, Scaled Composites, was also responsible for designing Voyager, a two-person aircraft that set the record for the challenge in 1986.
On that occasion Burt Rutan's 66-year-old brother, Dick, was one of the pilots, along with Jeana Yeager.
No licence to fly
Sir Richard and Mr Fossett's attempt to break the record had originally been pencilled in for April or October 2004.
"I think it will most likely fly early in the New Year," said Sir Richard.
"There are a few teething problems when you have an experimental craft, but nothing that's going to be a showstopper."
Sir Richard was Mr Fossett's partner in previous global balloon attempts, so he has a ballooning licence.
But he told BBC News Online that if were to take the pilot's seat should anything happen to Mr Fossett before the attempt, he would have to delay the mission in order to get his jet pilot's licence.
Sir Richard does not actually have a jet pilot licence
Although, he added, he was not "itching" to take the controls.
"Steve is one of the greatest adventurers on Earth today and is a very, very capable pilot," he said.
He also paid tribute to Mr Rutan, who has used advanced composite materials so that GlobalFlyer can carry more than four times its own weight in fuel on its 40,000km (25,000 mile) journey.
"Burt's achievements are just breathtaking," said Sir Richard, adding that he was a "super genius guy".
GlobalFlyer definitely had the technology to complete the record attempt, he said.
While in London last week as part of the Manx Aviation Festival, the Rutans showed off video of GlobalFlyer's test flights during a lecture at the Royal Aeronautical Society.
A couple of weeks ago, it flew an eight-hour test flight.
"It is one of the prettiest airplanes in the world," Burt Rutan said proudly.
The jet has a 34.5-metre (114ft) wingspan and is powered by a single turbofan Williams FJ44-3 ATW jet engine, which sits above the one-seater, pressurised cockpit.
Its booms will carry the fuel, making up 82% of the craft's body weight, which totals 10,000kg (22,000lbs).
"We didn't dream we could do a plane with 82% fuel," said Burt Rutan. "But the propulsion system on GlobalFlyer is considerably lighter than that on Voyager."
The ultralight carbon fibre materials used in the construction of the craft have been key to making it as efficient as possible.
Despite its massive wingspan, the craft can be wheeled out of the hangar with one hand when it is empty.
It is so light, it will need help coming down after its epic voyage, so will need some extra drag from parachutes, Mr Rutan said.
During the flight, which is expected to take 80 hours, the plane will fly in the stratosphere, reaching around 12km (38,000ft) then close to 14km (45,000ft) within hours.
It will make use of the northern hemisphere's jet stream winds, which have to be powerful enough to carry the extremely light craft.