The White Knight Two was unveiled Monday morning at the hangar of Rutan's Scaled Composites LLC, in California. ((Virgin Galactic))

Virgin Galactic rolled out the mothership aircraft of its private space tourism business on Monday, a white four-engine plane designed to launch a passenger spaceship into low-Earth orbit.

Virgin Galactic founder Richard Branson and American aerospace designer Burt Rutan introduced the White Knight Two on Monday morning at the hangar of Rutan's Scaled Composites LLC, in California's Mojave desert.

The plane, which resembles two aircraft joined at the wing, has a 43-metre wingspan and is made mostly of lightweight carbon composite. It is designed to lift Virgin Galactic's Spaceship Two to an altitude of 15,200 metres before it blasts off into orbit. Spaceship Two is about 70 per cent complete, Virgin Galactic said.

It is the first of what is expected to be a small fleet of aircraft for Virgin Galactic. Longueuil, Que.-based Pratt & Whitney Canada, which supplies the PW308 turbofan engines for WhiteKnightTwo, said Virgin Galactic has ordered five Spaceship Two aircraft with options for at least seven White Knight Two carrier aircraft.

More than 250 well-heeled wannabe astronauts have paid $200,000 US or put down deposits for a chance to take a flight on Spaceship Two.

Physicist Stephen Hawking, former soap opera star Victoria Principal and designer Philippe Starck are among those who have signed up.

Virgin Galactic president Will Whitehorn said the first flights are expected to launch in late 2009 or early 2010.

The space trips will take off from a launch pad being built in New Mexico and last about 2½ hours. Passengers will experience about five minutes of weightlessness, Virgin Galactic said.

The unveiling comes a year after an explosion at Rutan's Scaled Composites' test site killed three technicians. The company, now owned by Northrop Grumman Corp., is appealing a California state fine of $28,870 US for workplace violations in connection with the blast, which occurred during the development of Spaceship Two's propellant system.

With files from the Associated Press