The mothership which will launch the first space tourists into the atmosphere was unveiled by Sir Richard Branson in California today.

WhiteKnightTwo (WK2), the carrier aircraft which will be used to launch SpaceShipTwo into orbit, 'will allow thousands of people to realise their dreams' and 'act as a catalyst to transform human access to space', Sir Richard said.

Speaking at the launch ceremony in the spaceship's hangar at the Mojave Air and Spaceport in California, the British billionaire, who will be among the first space tourists with his family, said the venture would help the world 'wake up' to the fragility of the planet and the importance of protecting Earth.

Space is 'the final frontier that is so essential to the future of civilisation on this planet', Sir Richard said.

Mothership: Richard Branson celebrates with his mother, Eve, who the craft has been named after.

'The first generation of space tourists, many of whom are with us today, will be paving the way as they marvel at the beauty of our planet and experience the freedom of weightlessness and the blackness of space,' he said.

'The rollout of WhiteKnightTwo takes the Virgin Galactic vision to the next level and continues to provide tangible evidence that this most ambitious of projects is not only for real but is making tremendous progress towards our goal of safe commercial operation.'

Sir Richard said that the first tourists could be launched into space in around 18 months' time, but there is no official launch date yet - SpaceShipTwo needs to be completed before a series of test flights and safety tests are carried out.

More than 250 customers have paid 200,000 dollars (£100,000), or put down a deposit, for the chance to be one of Virgin Galactic's first space tourists.

The 140ft WK2, which was renamed Eve in honour of Sir Richard's mother who performed the opening ceremony attended by astronaut Buzz Aldrin, is the largest all-carbon composite aircraft and is capable of reaching 50,000ft.

'If our new system could carry only people into space, that would be enough for me, because of the transforming effect it will have on the thousands who will travel with us,' Sir Richard said.

'It is quite clear from every astronaut that I've ever spoken to that seeing the planet from out there, surrounded by the incredibly thin protective layer of atmosphere, helps one to wake up to the fragility of the small portion of the planet's mass that we inhabit, and to the importance of protecting the Earth.'

But he said the spaceships would also be able to launch small payloads and satellites into orbit at a relatively low cost.

'This system offers tremendous potential to researchers who will be able to fly experiments much more often than before, helping to answer key questions about Earth's climate and the mysteries of the universe,' he said.