"Space", as Captain Kirk, hero of cult television series Star Trek, once commented, "is the final frontier", but then again he was unfamiliar with Sir Richard Branson's adventurous streak and steely determination. Because in two years' time, 41 years after Neil Armstrong and Buzz Aldrin became the first men to walk on the moon, Sir Richard's newest company Virgin Galactic will take its first passengers into space.

"About 470 people have flown in space since the first rocket launched in 1961," says Will Whitehorn, president of Virgin Galactic. "We expect to carry just as many in our first year, doubling the number of people who will have travelled in space."

More than 250 people – the oldest is 88 – have already signed up for the two-and-a-half hour flight, including one who cashed in two million Air Miles, whilst over 80,000 have registered an interest in the $200,000 trip of a lifetime. It may sound expensive, but as Whitehorn points out, the first transatlantic flights on a Boeing Clipper flying boat in 1939 cost $80,000 in today's money.

Those to sign on the dotted line have been invited to a factory, located in a secure military base in the small desert town of Mojave in California, to watch their dream come to life and complete their pre-flight training.

Both Sir Richard and Whitehorn dreamed of space travel as young boys, but following a chance encounter with Aldrin in 1995 the idea of a commercial enterprise, as opposed to Kirk's Starship Enterprise, took root. Four years later, Virgin Galactic was registered as a trademark.

"About 470 people have flown in space since the first rocket launched in 1961. We will double that number within one year of operation."

"We were initially thinking of a private space project and looking for investors," recalls Whitehorn. But when the duo met Burt Rutan, a renowned American aerospace engineer to discuss possible designs for planes, their plans changed. "He showed us a space ship that he was designing and building for Paul Allen [the billionaire co-founder of Microsoft] to enter into a competition with a $10m prize," recalls Whitehorn.

The Ansari X Prize, the largest prize in history, was modelled after the $25,000 Orteig Prize, won by Charles Lindbergh in 1927 after he became the first person to fly non-stop from New York to Paris, and sought to bring about a radical breakthrough in the advancement of space travel. Rutan won the prize in October 2004 after his SpaceShipOne entered space twice within a two-week period, reaching altitudes greater than 100km – or 10 times higher than a commercial airline.

"We then bought the rights to develop the technology because we really believed this could revolutionise space travel," says Whitehorn. "Our financiers said they would back us if we could prove the public would pay deposits to fly into space." Within six months, the company had raised $10m in deposits.

Construction of SpaceShipTwo, based on the designs of its predecessor, began in 2005, and the first test flights – on which Whitehorn expects to travel – are scheduled to launch this month.

White Knight Two, a carrier plane which resembles in both look and size two Gulfstream jets joined by a single 42 metre wing, will take off from a Sir Norman Foster designed spaceport based in New Mexico. It will carry SpaceShipTwo to 50,000 feet, when the space craft, which is connected by a giant hook, will be released to continue its journey with a maximum of six passengers and two-man crew.

"Our space flights will have the same environmental impact as a single business class ticket from London to New York."

"The biggest problem of all space projects is that they launch from the ground, and 90 per cent of their weight is just the fuel needed to launch them through the atmosphere," explains Whitehorn. "And then there is the problem of re-entry. Getting through atmosphere is like trying to land in concrete."

An air launch minimises fuel use and increases safety, while the space ship's pivoted wings act like a shuttlecock to slow and control its re-entry into the atmosphere, allowing the craft to glide from 80,000 feet back to the runway.

"We have also considered the environmental impact of SpaceShipTwo," says Whitehorn. "The launch of a normal space shuttle has the same environmental impact as the population of New York City in one week. Our space flights will have the same environmental impact as a single business class ticket from London to New York. This is an incredibly advanced aircraft built of carbon composite, which is a stronger material than aluminium and much lighter. It is the most advanced piece of engineering in the world."

But what about the flight? After three days of pre-flight training, which includes pre-flight medicals, a period in a machine that simulates G-force, when the body becomes incredibly heavy, and tips on what to expect, passengers are cleared for take off.

The cabin of the space ship is similar in size to a capsule on the London Eye, giving each of the six passengers enough room to enjoy the experience of weightlessness for almost five minutes. "Every passenger has asked about weightlessness, particularly those who are disabled or in wheelchairs," says Whitehorn. "They all dream of being able to float, and there is no other experience on earth to match it."

Once disconnected from its carrier plane, SpaceShipTwo will shoot up a further 300,000 feet, 12 times higher than a normal commercial airline, and well above both NASA's and Russia's official definition of space.

For 28 seconds, the passengers will be pinned to their seats by gravity as the craft pushes through the threshold of space where the sky changes from cobalt blue to mauve, then indigo and finally to black. Travelling at 3,000 miles an hour, or twice the speed of Concorde, the passengers, wearing outfits that closely resemble airlines' sleep suits, will see the curvature of the earth and experience the silence of space until their descent, when they are strapped into seats that are virtually horizontal.

The first flight, however, has already been booked. Sir Richard will be joined by his father Ted, 92, mother Eve, 89, and children Holly and Sam on the maiden voyage, making conquering "the final frontier" a family adventure.

By Helen Dunne