Branson's final frontier.
Work on SpaceShipTwo, and its mothership White Knight Two, is nearing completion and flight tests will begin later this year. Sir Richard said this "historic occasion" could help "to answer key questions about Earth's climate and the mysteries of the universe."
A Virgin Galactic spokeswoman said more than 200 people had joined the firm's cadre of future astronauts, with 80 having been through their medical assessment and centrifuge training.
Speaking at the America Museum of Natural History in New York yesterday, Sir Richard said: "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.
"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 at a 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.
He said the two spaceships would "help change the paradigm of our relationship to space, achieving an era where space accessibility becomes a commercial and scientific norm, rather than an exception".
Sir Richard said the system could be developed into a passenger-carrying vehicle, but admitted "that may not happen for some time."
FINAL FRONTIER: Billionaire Richard Branson with a model of the mothership White Knight Two