The world's largest carbon fibre aeroplane will be unveiled in the Mojave desert tomorrow. Its purpose will be to airlift Virgin Galactic's SpaceShipTwo, the first commercial space rocket, to 50,000 feet before it blasts off into sub-orbit. The spaceship is still being built but is expected to be ready for testing later this year.

The plane, WhiteKnightTwo, was designed by Burt Rutan for Virgin Galactic as part of its space programme, but it is expected to have other functions including use for a Nasa science programme and the launch of smaller low-Earth orbit satellites. Rutan's company, Scaled Composites, based 80 miles from Los Angeles, built the plane.

Californian Governor Arnold Schwarzenegger, actress Victoria Principal and Virgin Galactic's founding astronauts will be among the guests when Sir Richard Branson, head of the Virgin Group, and Rutan, roll out the finished plane onto the Mojave airstrip for the first time.

Will Whitehorn, the Scottish-born president of Virgin Galactic, said tomorrow's event would be a significant milestone for the aviation industry. "We see WhiteKnightTwo as the future of commercial aviation. While Virgin Galactic has captured the headlines for its plans to take people into space, we've also been using cutting edge innovation in composite technology to reduce the environmental impact of flying," he told the Sunday Herald.

WhiteKnightTwo looks like a catamaran with its twin-hulls and, when completed, SpaceShipTwo will be tucked underneath it for take off. Then at 50,000ft, the spacecraft will be air launched, its rocket motors fired and within eight seconds it will become supersonic, reaching speeds of Mach 4. It will then travel out 110km, to a region officially classified as space, before gliding back to Earth and landing like a conventional aeroplane.

More than 200 people have already paid $200,000 each for the two-hour trips. The cost is expected to drop dramatically once the initial flights have proven reliable and safe, thus reducing insurance costs.

Rutan is a record-breaking designer, with prototypes featured at the Smithsonian Institute in Washington. He is famous for having won the Ansari X Prize in 2004 with his design of a mothership and spacecraft for Microsoft co-founder Paul Allen. The X Prize's WhiteKnightOne and SpaceShipOne are the prototypes for Virgin Galactic's larger passenger-carrying planes.

The four-engined WhiteKnightTwo, which is the width of a B29 bomber, is being hailed as the future for commercial aircraft with its carbon composition. The world's leading airframe makers, including Boeing and Airbus, have increased the percentage of composites in their new generation of planes such as the Airbus A380 and the Boeing 787 Dreamliner, but Rutan has been the pioneer in carbon technologies.

He designed the all-carbon composite Voyager aircraft that took nine days to fly around the world non-stop without refuelling in December 1986. And he designed its successor, Virgin Atlantic GlobalFlyer, which broke the Voyager record on Steve Fossett's solo venture in 2005. Tomorrow, Governor Schwarzenegger will announce the name of the first of the two WhiteKnightTwo prototypes - Spirit of Steve Fossett - in memory of the aviator who went missing in the Nevada desert last year.

Many of the lessons learned from Rutan's previous composite planes have been incorporated into the design of WhiteKnightTwo, which is capable of carrying a payload of 12 tonnes to 50,000 feet. The plane is powered by four Pratt & Whitney PW308A engines, which are among the most powerful, economic and efficient aircraft engines available.

Carbon composites are lighter and stronger, and allow planes to use significantly less fuel. The composite material is woven fibres of glass graphite and aramid (the generic name for Kevlar, known for its use in bulletproof jackets), which is bonded with epoxy resins. It is then heated in an autoclave making the structure immensely strong and lighter than the pressed aluminium and titanium used in the current generation of commercial planes.

WhiteKnightTwo is the largest all-composite plane ever built and Virgin Galactic says the wingspan, at 140ft, is the largest single composite carbon fibre item ever made. By comparison, the new Boeing 787 is 60% composite.

The plane will have other uses besides launching tourist space ships. Virgin Galactic is now in discussions with Nasa about its use in a high altitude atmospheric measurement programme for global warming.

"What Burt Rutan and his team at Scaled Composites have achieved since winning the X Prize is truly outstanding," said Whitehorn. "Our all-composite planes will use 50% less fuel than a normal plane. Our test programme begins soon and our ambition of taking people into space is now a step nearer."

Whitehorn said a site in Scotland, such as Lossiemouth in Moray, was still under consideration for future space flights. An Aberdeen University graduate, he said there was a possibility Virgin Galactic flights might take off from the northeast of Scotland for a few weeks during the summer, weather permitting, and that Scotland's space tourists would fly through the Northern Lights - known as the Aurora Borealis. To date, Virgin Galactic's SpaceShipTwo, which will carry six passengers and two crew members, is 75% complete.

Kenny Kemp is the author of Destination Space: How Space Tourism Is Making Science Fiction A Reality