Depends what you want to do. If you're planning to take a ride on Sir Richard Branson's proposed Virgin Galactic service, the plans are that you'll need a week, as opposed to the years it takes to train as an astronaut.
What that training will involve is unclear at present but David Ashford, director of Bristol Spaceplanes, reckons that a week is overkill.
"You could do it in a day," he says. "All you're doing is sitting in a seat and you're strapped in - you've got no control over anything. What Virgin Galactic are talking about is a very brief whip up to space and back, being out of the atmosphere for maybe a few minutes."
The training you need will mainly get you used to the g-forces experienced during the trip.
"When you come back in from space, you pull out of a [steep] dive," says Ashford. "You're talking about four or five g for 10-20 seconds. That's quite a lot. You probably have to go in a centrifuge [in training] to check out you're OK."
Prospective passengers will also need a medical exam, but Ashford says this will probably be straightforward. In any case, a lot of the training will be just a precaution.
"Because this is a new industry, the authorities will start off being cautious and only take fit people and give them a lot more training than they need," says Ashford. "We'll find out by trial and error what training, what medical tests are needed."
Ashford says that if the Virgin plan is successful, it could trigger the far more tantalising idea of developing commercial spacecraft that can go into orbit, and potentially send people into space to stay in hotels there. In this case, passengers would need lots more training. They would be wearing pressure suits (so they'd need to know how to operate those) and would need to be happy with weightlessness by training in aeroplanes on parabolic flights - the so-called "vomit comets".
Ashford says: "In 15 years' time there will be a million people a year going to space hotels."
