His blood could boil. His lungs could overinflate. The vessels in his brain could burst. His eyes could hemorrhage.
And, yes, he could break his neck while jumping from a mind-boggling altitude of 23 miles (37 kilometers).
But the risk of a gruesome death has never stopped "Fearless Felix" Baumgartner in all his years of skydiving and skyscraper leaping, and it's not about to now.
Next Monday over New Mexico, he will attempt the highest, fastest free fall in history and try to become the first skydiver to break the sound barrier.
"So many unknowns," Baumgartner says, "but we have solutions to survive."
The 43-year-old former military parachutist from Austria is hoping to reach 690 mph (1,110 kph), or Mach 1, after leaping from his balloon-hoisted capsule over the desert near Roswell.
He will have only a pressurized suit and helmet for protection as he tries to go supersonic 65 years after Chuck Yeager, flying an experimental rocket plane, became the first human to go faster than the speed of sound.
Doctors, engineers and others on Baumgartner's Red Bull-sponsored team have spent as much as five years studying the risks and believe they have done everything possible to bring him back alive. He has tested out his suit and capsule in two dress rehearsals, jumping from 15 miles (24 kilometers) in March and 18 miles (29 kilometers) in July.
Baumgartner will be more than three times higher than the cruising altitude of jetliners when he hops, bunny-style, out of the capsule and into a near-vacuum where there is barely any oxygen and less than 1 percent of the air pressure on Earth.
If all goes well, he will reach the speed of sound in about half a minute at an altitude of around 100,000 feet (30,480 meters). Then he will start to slow as the atmosphere gets denser, and after five minutes of free fall, he will pull his main parachute. The entire descent should last 15 to 20 minutes.
He will be rigged with cameras that will provide a live broadcast of the jump via the Internet, meaning countless viewers could end up witnessing a horrific accident.
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