Ordinarily, Felix Ba­umgartner wo­u­ld not need a lot of practice in the sci­ence of fal­l­i­ng.He has jumped off two of the tallest buildings in the wo­rld, as well as the st­atue of Christ in Rio de Janeiro (a 95-foot leap for which he claimed a low-altitude rec­ord for para­chuting). He has sky-dived ac­ross the English Channel. He once plunged into the black void of a 623-foot-deep cave, which he formerly considered the most difficult jump of his career.

But now Felix has something more difficult on the agenda: jumping fr­om a helium balloon in the stratosphere at least 120,000 feet above Earth. Within about half a minute, he figures, he would be going 690 miles an hour. After a free fall lasting five and a half minutes, his parachute would open and land him about 23 mi­les below the balloon. That’s the plan, th­o­ugh no one kno­ws what the shock wave will do to his body as it exceeds the speed of sound. The jump would break one of the most venerable aerospace records. For half a century, no one has surpassed (one person died trying) the altitude record set by Joe Kittinger as part of an Air Force program called Project Excelsior.

In 1960, Kittinger, then a 32-year-old Air Fo­rce pi­lot, jumped from a balloon 102,800 feet above the New Mexico desert. Today, at 81, Kittinger is a retired colonel and part of the Red Bull Stratos team working on Baumgartner’s jump.

“For 50 years,” Kittinger said, “I’ve gotten phone calls from all over the world, people wanting to bre­ak my record — one a month, sometimes two a month. But I stayed away from them because they didn’t have any idea what the challenge was. What attracted me to Red Bull was their me­tho­dological app­roach to safety and to providing scientific benefits.”

More than three dozen veterans of Nasa, the Air Force and the aerospace industry have been working for three years to plan the jump, build a balloon and pressurized capsule, and customise an astronaut’s su­­it for Baumgartner. Besides aiming at records, they’re doing physiological research and developing procedures for future astronauts to survive a loss of cabin pressure or an emergency bailout in the stratosphere.

One of the chief concerns has been to avoid the problem that almost killed Mr Kittinger during Project Excelsior. He was supposed to be stabilized during his fall by a small drogue parachute, but on one training jump in 1959 it did not op­en because the cord got ta­n­gled around his neck.