Branson also announced that Virgin Galactic, his fledgling commercial space company, was expanding to include a satellite-launching service that would use a low-cost rocket system to propel payloads into orbit.
Speaking at the UK's Farnborough International Airshow, the British entrepreneur said his adult children, Holly and Sam, would accompany him on board the SpaceShipTwo on its pioneering two-hour voyage into sub-orbital space.
"It'll certainly be the most momentous moment of my life and my children's lives," Branson told CNN. "It'll be very difficult to ever cap it I think. Anyone who has ever been into space says the same thing."
Some 529 would-be astronauts, including celebrities such as Ashton Kutcher, have so far signed up for $200,000-a-seat flights which will last two hours.
Virgin executives said the figure was a milestone as it exceeds the existing number of space veterans. Six hundred are expected to fly in the first two years of service.
Launched from a carrier vessel known as WhiteKnightTwo, Virgin Galactic's space ship can carry two pilots and six passengers. SpaceShipTwo is currently undergoing testing in the Mojave Desert in California, although a replica was on display at Farnborough.
Branson acknowledged the existing price tag means that his goal of opening space travel up to ordinary people was some way off. He insisted, however, that it would drop over the next few decades as Virgin's space ambitions went further.
"The initial flights will be sub-orbital, which will give people a taste of space," he said. "From there we'll go into orbital flights and maybe one day hotels in space."
Outlining details of his new satellite service, LauncherOne, Branson said the two-stage rocket would also be carried into launching position by WhiteKnightTwo.
He said the service, capable of launching 500-pound payloads, would drastically reduce the cost of putting satellites into orbit. This, he said would open up the market to researchers, small businesses and even schools.
Several clients have already signed up for the service including Earth observation company GeoOptics and Planetary Resources, an asteroid mining company which counts Google founders Eric Schmidt and Larry Page, and movie director James Cameron as investors.
Virgin Galactic's commercial director Stephen Attenborough told CNN that the goal was to be able to offer a reliable satellite launch system for $10 million, a price tag he says undercuts existing services by up to 50%.
George Whitesides, the company's chief executive and president, said: "This will radically revolutionize the small satellite business in the way we have the space tourism business."
But Branson insisted his chief aim was to open space to researchers studying the "global crisis" of climate change.
"In America you've got a lot of skeptics about global warming, what you need is the scientific evidence that it is there one way or the other," he said.
"The majority of scientists believe we have a problem, we need to know that conclusively and we need to work towards resolving it and I think LauncherOne will make it clear one way or the other, and sadly I think it'll be the other."
On the sidelines of Wednesday's announcement, Virgin Galactic officials offered more details of what customers can expect for their money.
Whitesides said astronauts on board SpaceShipTwo would experience a little less than five minutes of weightlessness, during which time they will be free to unclip their seat harnesses and float within the cabin.
"Some people will want to focus their time looking out of the vehicle, looking down at the planet or Milky Way, whereas others may want to do spins or tricks," Whitesides told CNN.