By Dr David Whitehouse
BBC News Online science editor
Twenty-six companies are vying for the $10m Ansari X-Prize.
There is a lot riding on the competition
A handful are serious contenders, many are less well advanced and some are just dreamers.
Analysts are looking to the US and Canada for a winner - with Burt Rutan clearly in the lead. His SpaceShipOne has flown to the top of the atmosphere and last year became the first privately built aircraft to break the sound barrier.
But even if his success seems inevitable, and it does, there are others close behind who have hardware entering the final stages of testing and evaluation. They too will enter space in the next few years.
The Canadian Da Vinci project is well advanced. It will use a balloon to carry its rocket on the first stage of its flight. From the same country is Canadian Arrow - tests with its futuristic rocket will begin this summer.
But the fact is that there are more budding astronauts out there than seats to take them into space.
You can pay for a seat on the Russian Soyuz craft that regularly fly to the International Space Station (ISS). If you have the order of $20m to spare, that is.
But places are very limited. Only multi-millionaires with lots of free time need apply.
Dreaming it up
For years, the dream of space tourism which was just a dream - a hopeful view of the future of space - did not match with the available technology or prevailing space politics.
Let's be clear. It will be a long time before taking a sub-orbital hop into space - a mission of perhaps 90 minutes duration - will be as common or as cheap as a transatlantic flight. But space advocates travel in hope.
They believe that the winning of the Ansari X-Prize will herald a new phase in the exploration of space. To many, it recalls achievements such as the famous first flight across the Atlantic by Allcock and Brown and the breaking of the sound barrier by Chuck Yeager.
The prize will be won inside five months, say organisers
The important thing, say space visionaries, is that the winning of the X-Prize will be the start of a period when the technology advances rapidly.
Whoever wins the prize will enter the history books alongside Allcock and Brown and Lindberg and Yeager. But a year or two later, the winner will be matched by two or three other companies able to put their own craft into space.
So when the X-Prize is won - almost certainly later this year - it will demonstrate that the technology needed to get into space is no longer the preserve of big-budget governmental projects, but is within the grasp of private companies with the right expertise and finances.