The growing trend towards adventure holidays will literally leap out of this world and into space in the not too distant future. David Wade looks ahead

Tourism takes many forms, whether it be jumping on a plane to travel half way around the world or trundling down the motorway with a caravan hitched to the back of the car. It contributes to an annual worldwide market worth over $350 billion. The past few years has seen a particular increase in the adventure tourism market, people who are not content to lie on a beach and gently brown, but are prepared to pay for an adventure. Examples range from the mildly adventurous - trekking up Mount Kilimanjaro - to the more vigorous, climbing Everest or hiking across the polar wastes. Since 1993, adventure tourism has represented a $30 billion yearly market.

Short-lived adventures have also proved successful as holidays for adventure-seeking tourists. For instance, $2,000 can buy a 30-minute flight in a Mig 29 fighter aircraft, or for $1,000 the adventure tourist can be accelerated to 8g on the Cosmonaut Training Centre's centrifuge at Star City outside Moscow.

To many people the ultimate in adventure holidays would be a quest that was truly out of this world - the chance to fly in space. The idea of orbital and perhaps lunar hotels, met with disdain and ridicule for many years, but has recently started to generate serious interest.

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A study from the Journal of Practical Applications in Space (1995) indicated an annual market of as many as half a million space tourists to a low Earth orbiting hotel, if the price could be reduced to $20,000.

Huge strides are needed before such costs are achieved, but many people are pursuing the idea. Space tourism does not necessarily mean a two-week stay at an orbital hotel. An orbital hotel is the fourth and final step in space tourism, but we already live in the age of the second step and are quickly moving towards the third.

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Orbital tourists may be able to swim in a spherical zero-gravity swimming pool or eat as much as they like without gaining a single ounce in weight, but there would be limited cachet in telling friends they had stayed out until dawn, as sunrise would occur every 90 minutes.

The first step in space tourism has been around since the 1960s when exhibitions and museum galleries opened to show the public the technology of the dawning space age. These galleries remain one of the most popular attractions at museums such as the Science Museum, London. Even Woomera, the testing ground and launch site in the middle of the Australian outback, attracts enough visitors per year to warrant a small museum. Hardy groups of space tourists stop on their way to Ayers Rock or the opal mines of Coober Pedy.

Step two, the so-called "vomit comet" rides, are also now available for adventurers. By flying a parabolic flightpath, the occupants of a plane can experience a few seconds of weightlessness. This has been used to simulate micro-gravity conditions by space agencies for many years, but more recently adventure tourists have been allowed to pay for the experience. A number of firms in the US and Russia offer a day's training with flight experience for $2,500, sick bag included.

If an orbital hotel is step four, the one remaining step is to reduce the cost of access to space. In 1995, an international competition, the X-Prize, was established to open the space tourism market by reducing travel costs, allowing orbital hotels to become a reality in the future.

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Peter Diamandis, founder of the X-Prize, recognised that the barrier is similar to that faced by avaiation a few decades ago. The aviation industry was boosted by prizes for ever increasing flight duration, with resulting advances in aircraft technology. Prizes for crossing the English Channel and the non-stop Atlantic crossing advanced technology so rapidly that the general public could consider flying to hotter climes on holiday. To make similar gains in space tourism, Mr Diamandis has offered a $10 million prize to the first team to transport two passengers and a pilot to a 100km altitude twice within a fortnight. This is not a journey to orbit, but a quick visit to space similar to the sub-orbital hops of the early US astronauts. Passengers will qualify as astronauts by exceeding the 100km altitude threshold.

Estimates of the cost of designing and building X-Prize planes far exceed the $10 million prize money, but this has not discouraged 16 teams from registering in the hope of being first to tap the predicted lucrative market. The first attempts are scheduled for 1999.

But the market is bigger than space tourism alone. Imagine an express parcel service which guarantees delivery for a time even before you sent it, or the spin-off technology that could lead to the lower-cost deployment of satellites. The winner of this race could establish a market that will make him the next Bill Gates.

David Wade is senior lecturer in aerospace engineering, University of Kingston.

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