Austrian daredevil Felix Baumgartner will today attempt to become the first human being to break the sound barrier without any mechanical help.
The former special forces soldier is planning to make the highest skydive in history from 23 miles above the Earth's surface. On standard skydives, jumpers rarely pass 120mph due to air resistance. But 23 miles up, where the air is much thinner, Baumgartner expects to break the 768mph sound barrier. He will know that he has been successful if his body emits a sonic boom.
Failure could be fatal. Should his body go into a spin greater than 180 rotations per minute, his brain is likely to be liquidised by super-pressurised blood rushing to his head. His suit should release a corrective parachute if that happens, but no one is entirely sure it will work.
If all goes well, the 43-year-old will free-fall for five and a half minutes before opening a parachute at 5,000ft.
The jump, above Roswell, New Mexico, is the product of more than five years planning and has consumed Baumgartner. He has made two practice dives in the Roswell area, from 15 miles up in March and 18 miles in July. But this is the first time he has tried to break the current world record of 19.44 miles, set by the American pilot Joseph Kittinger in 1960.
While his jump might seem like madness, Nasa is watching his progress. Since the disintegration of the Space Shuttle Colombia in 2003, it has been looking to create a system to help astronauts survive a high-altitude crash.
The jump can only be made if wind speeds are less than two miles per hour. Baumgartner's flight will be broadcast live online, including at www.independent.co.uk.