WK2 is said to feature several components which have been built using composite materials for the “very first time.” Its 140 ft wing spar is the longest single composite aviation component ever manufactured, according to Virgin Galactic.

“WhiteKnightTwo represents the apogee of the application of carbon composites to aerospace…,” says Burt Rutan, Founder of Scaled Composites. “… we very much hope that its efficiency will herald a wake up call to the aerospace industry and the necessity of using new materials and technologies in the future.”

The WK2 aircraft has a heavy lift, high altitude capability, and an open architecture driven design. This gives maximum versatility in the weight, mass and volume of the aircraft's payload potential. It is said to have the power, strength and manoeuvrability to provide for pre space-flight, positive G force and zero G astronaut training as well as a lift capability over 30% greater than that represented by a fully crewed SpaceShipTwo.

WK2's maximum altitude is 50 000 ft and it is powered by four Pratt and Whitney PW308A engines, said to be amongst the most powerful, economic and efficient available.

The twin fuselage and central payload area configuration allow for easy access and the design also aids operational efficiencies and turnaround times. It will be able to support up to four daily space flights.

WK2 is currently undergoing an extensive test programme, and the first flight is expected this autumn. SpaceShipTwo is expected to be rolled out in 2009 as WK2 reaches a certain stage of its test programme.

Virgin says the launch is a major milestone in the company's quest to launch the world's first private, environmentally benign, space access system for people, payload and science.

Virgin Galactic and Scaled Composites have set up a new business, The Spaceship Company (TSC), to develop similar launch applications beyond the initial requirements of Virgin Galactic.