By Andrew Walker
BBC economics correspondent
A privately operated and manned spaceship, SpaceShipOne, has landed after a successful second trip to the edge of space, to claim a $10m prize.
White Knight carried the rocket plane to the launch altitude
Two successful flights within two weeks are required to win the Ansari X-Prize, offered by private donors who want to encourage commercial space travel, notably tourism.
It is a business with an uncertain future. But if space tourism really does get going, one or two features of it are fairly clear.
It will be expensive, and in the early stages consumer demand for it will therefore be fairly limited.
But with a small group of people with very high incomes willing to pay for novel experiences, space tourism is a business that might work.
'15,000 tourists by 2021'
A few people have already done it as paying passengers on the Russian spacecraft Soyuz.
The fare was as steep as the ascent - $20m for the first man who did it.
Nonetheless, a management consultancy in the US, called Futron, has estimated that the business could generate annual revenues of more than $1bn by the year 2021.
The largest area of demand, it says, is likely to be for cheaper "sub-orbital" flights - a short trip into space and back.
Sales for that type of trip could be as high as 15,000 passengers a year by 2021, the consultancy predicts.
The forecasts were based on a survey of what the company called affluent Americans.
With even a short trip likely to cost anything up to $100,000, they will need to be affluent.
They will also need to be very fit, physically and mentally. Futron warned that passengers may well have to achieve similar health and fitness standards to professional astronauts.
So if space tourism does take off, it will not be for everyone.