MOJAVE, Calif.--Virgin Galactic founder Richard Branson and legendary aircraft designer Burt Rutan, whose SpaceShipOne took the $10 million Ansari X Prize in 2004, unveiled SpaceShipTwo Monday, a sleek commercial rocket plane that represents the ultimate thrill ride for well-heeled space tourists and amateur astronauts.

Richard Branson, left, and Burt Rutan show off SpaceShipTwo and the WhiteKnightTwo mothership. Credit: Mark Greenberg/Virgin Galactic

Seating six passengers and two pilots, SpaceShipTwo will begin test flights next year with commercial launchings carrying paying customers starting after government regulatory requirements are met. More than 300 people have already put down deposits or paid the full $200,000 cost of a ticket for future sub-orbital up-and-down flights aboard the new spacecraft.

Most of those ticket holders, along with California Gov. Arnold Schwarzenegger and New Mexico Gov. Bill Richardson, were on hand for the SpaceShipTwo unveiling Monday at Mojave airport, braving rain, high winds and frigid temperatures to witness the long-awaited rollout.

See full photo gallery of the event here.

Branson told the enthusiastic crowd that safety was Virgin Galactic's No. 1 priority and that "we will not be putting anybody into space until the test pilots have done many, many, many trips on this spaceship."

"Only when we are absolutely certain we can safely to to space will we go into space," he said. "I promise you, it will be well and truly tested before we go into space."

Schwarzenegger said attending the unveiling was "one of the coolest things I've ever done." Describing Branson as "an extraordinary visionary," he called Rutan "one of the greatest space engineers of our time."

"Space is our next great frontier," he said. "When it comes to space enterprise, California is and always has been at the forefront and leading the way."

Virgin Galactic reportedly plans to spend some $400 million to build a fleet of five or six rocket planes. Commercial flights will be launched from taxpayer-funded spaceport under construction in New Mexico. Assuming test flights go well and government requirements are met, commercial launchings could begin by 2011.

"My state is energized and raring to go," Richardson said. "We're proud to be on the ground floor of the second space age. ... I call on the Obama administration to embrace commercial space travel. We're opening up an opportunity that before now was only available to a select few, a chance to travel in space. Three hundred have already jumped at the chance, signing up to be among the first space tourists."

Turning to Schwarzenegger, Richardson said, "Governor, you should join me in going into space. But I want you to go first."

Construction of SpaceShipTwo, carried out in near-total secrecy at Rutan's Scaled Composites facility in Mojave, began in 2007. The spacecraft is a scaled-up version of the three-seat SpaceShipOne Rutan designed, with funding from Microsoft founder Paul Allen, to compete for the $10 million Ansari X Prize.

A comparison of SpaceShipOne and SpaceShipTwo. Credit: Virgin Galactic

The X Prize required competitors to complete two manned flights to an altitude of 100 kilometers, or 62 miles, the somewhat arbitrary "boundary" of space. After Rutan won the X-Prize, Branson launched Virgin Galactic and announced plans to build a fleet of larger spacecraft to carry space tourists on sub-orbital flights.

Looking to the future, Rutan said "I believe, to satisfy this market, there will need to be between 40 and 50 spaceships. Assuming we have enough spaceports and assuming we work the cost numbers appropriately we can attract that large number of people. That's what will be required" for the long-term success of commercial manned spaceflight.

Peter Diamandis, who directed the Ansari X Prize program, hailed SpaceShipTwo as an "incredible milestone" and said the industry will flourish despite the high initial cost.

"There is definitely a business model, he said in an interview. "We've got more billionaires on the planet and millionaires than ever before in the history of humanity. It's the same thing with every new technology, whether it's cellphones or airplanes, the wealthy step up first, they pay the higher ticket price and eventually it becomes available to everybody. We need to demonstrate the market and the technology will follow."

SpaceShipTwo will be carried aloft by a futuristic-looking mothercraft called WhiteKnightTwo, a four-engine jet-powered aircraft unveiled last year that features twin fuselages mounted on either side of a huge wing.

For the unveiling Monday, WhiteKnightTwo, with the rocket plane attached to the center of the wing, was rolled into view amid soaring music and floodlights.

SpaceShipTwo will be released at an altitude of 50,000 feet. A hybrid rocket motor burning solid propellant with nitrous oxide then will boost SpaceShipTwo onto a steep trajectory to an altitude of more than 62 miles.

The roomy cabin of SpaceShipTwo, about the same size as a large executive jet, features multiple portholes to give its passengers a spectacular view of Earth and space.

After about five minutes of weightlessness as the spaceplane arcs through the top of its ballistic trajectory, the rocket plane will fall back into the atmosphere, pivoting its wings upward in a "feathering" technique invented by Rutan to increase drag and ease the stress or re-entry. From there, the spacecraft will glide to a normal runway landing.

An artist's rendering showing SpaceShipTwo's wings 'feathered' for re-entry. Credit: Virgin Galactic

Rutan said the spacecraft is being built with a design philosophy that requires a much greater factor of safety than government standards for manned space flight.

"I believe it's not enough, in terms of developing something for the public, to say we'll just do the best that we can," he said. "I believe you also have to have a goal. And clearly the goal of meeting the safety of government manned spaceflight is not anywhere near acceptable, where 4 percent of the people who have left the atmosphere have died. I believe we need to set our sights more on the goal of the safety of the early airliners, and that's an extremely difficult goal.

"That's what we're shooting for, that's what has (guided) our decisions on redundancy and on quality and on training," he said. "What we will achieve now is based on how well we do in our best efforts. But at least we have a proper goal. Making sure spaceflight can attract customers and can fly safely is a much bigger job than doing a research program like we've done before."

How the budding commercial space market might react to a failure early in the program remains to be seen. But Diamandis said he is optimistic.

"If anybody can, Scaled can build a vehicle that's robust and highly reliable," he said.