It is 50 years since the American Joe Kittinger made history by leaping from a balloon at 102,800ft (31km).
Many have sought to repeat the feat down the decades but all have failed.
Baumgartner, who is famous for stunts such as jumping off the Petronas Towers, aims to skydive from a balloon sent to at least 120,000 ft (37km).
It is likely that in his long freefall of more than five minutes, he will exceed the speed of sound – the first person to do so without the aid of a machine.
“No-one really knows what that will be like,” he said.
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