What is the X prize?

X prize: Inspired by Charles Lindberg's solo, non-stop transatlantic flight in 1927. Credit: © X prize

It is a $10-million jackpot that will be awarded to the first spacecraft built with private funds to carry a pilot and the weight of two passengers 100 kilometres above the earth and across the official threshold into space.

Why was it set up?

The prize was established in 1996 by space enthusiasts keen to kick-start an era of affordable, private space travel, which would resemble the commercial air industry. Until now, almost all piloted and robotic space exploration has been funded by government agencies such as NASA. X prize advocates say that the public will never be able to reach space this way, because public access is not a priority for these agencies, and because the price-tag is too steep. Instead, they believe that the private sector can come up with cheap, reliable, reusable rockets to ferry passengers skywards.

Haven't there already been space tourists?

Yes, although the experience comes at a price. The first was American businessman Dennis Tito who paid a reported $20 million to hitch a ride on a Russian rocket to the International Space Station in April 2001. The second, a year later, was a South African Internet millionaire, Mark Shuttleworth.

When will the X prize be won, and who is leading the field?

Although there are 26 teams registered for the competition, many of those involved believe that only one team, Scaled Composites, based in Mojave, California, has a real chance of winning before the end-of-year competition deadline. The team's craft, SpaceShipOne, is streaks ahead: it became the first privately financed rocket to reach space in June this year and is making an official bid for the prize in late September. See our interactive graphic learn more about this craft and some of the other competitors.

Is there a market for space tourism?

That is a matter of some debate. Those at Space Adventures, a company based in Arlington, Virginia, say they have over 100 people registered who are willing to pay $100,000 for suborbital flights, if they become available. And if the price comes down to something like $20,000, as some predict, believers say that many more adrenaline junkies would be willing to pay for the experience. But others are sceptical that there will be enough demand to support a fully fledged space tourism industry.

How high will the spacecraft go?

The contest requires that the winning spacecraft reach 100 kilometres above the Earth, an official but rather arbitrary boundary between the atmosphere and suborbital space. But a trip into suborbital space is only a joy-ride; passengers experience just a few minutes of weightlessness before gravity pulls them back to earth.

In order to spend longer in space and, for example, dock with a space hotel, a rocket would have to enter continuous orbit some 300-400 kilometres above Earth, which is where satellites and the International Space Station are sited. This would require a craft that could accelerate to speeds around eight times as fast as that of SpaceShipOne, something that would involve a vast leap in efficiency and cost. Still, some companies are already working on commercial orbital rockets.

Are there other ways to reach space?

You could become a qualified astronaut. NASA requires a science or engineering degree and research experience, plus, if you want to be a pilot, 1,000 hours' piloting time in a jet aircraft.

Could private space planes find other uses?

Some budding companies are building their business around rockets that do other work in space, such as launching satellites, with passenger flight as a possible spin-off. Roger Launius, a space history expert at the National Air and Space Museum in Washington, believes that the industry might survive if it can find a useful purpose, such as offering high-speed suborbital air travel from New York to Tokyo.