A skydiver's historic free-fall from the edge of space was put on hold Tuesday morning amid concerns about the weather, raising the possibility that it could be put off to another day.
Felix Baumgartner is aiming to jump from a higher altitude than anyone ever has -- 120,000 feet (about 23 miles), more than three times the cruising altitude of the average airliner -- with nothing but a space suit, helmet and parachute.
He also hopes to be the first person to break the sound barrier. At that altitude, the thin air provides so little resistance that after just 40 seconds, he is expected to be free-falling faster than 690 miles an hour.
The winds early Tuesday morning were moving at about 18 mph where the top of Baumgartner's balloon would be. Organizers want the winds to calm to 5 mph or lower before the jump.
There is a three-hour window in which to launch -- from 6:30 a.m. to 9:30 a.m. local time in Roswell, or 8:30 a.m. - 11:30 a.m. ET.
"I'm not nuts," Baumgartner said when CNN first interviewed him about the project in 2010. "You know, our records are meant to be broken, and I'm a very competitive person. I like the challenge."
But on a more serious note, he added, "Of course I'm afraid of dying, because I worked so hard to reach this level. You know, I'm living a good life. I think the most important thing I'm doing is to come back alive."
After years of preparations and untold costs to his primary sponsor Red Bull, the jump was scheduled for Tuesday morning at dawn. Baumgartner expects to spend two or three hours on the ascent, in a capsule hanging from a helium balloon. Then he will climb out of his capsule, jump off the step with a bunny hop and form a crouched "delta" position to maximize his speed. He plans to fall 115,000 feet in less than five minutes, before deploying a parachute for the final 5,000 feet to earth.
The attempt has serious risks. He and his team have practiced how he can avoid getting trapped in a dangerous "horizontal spin." And at temperatures that could hit 70 degrees below zero Fahrenheit or lower, and an atmosphere so thin that his blood would vaporize if he were unprotected, his life will depend on the integrity of his pressure suit. And if he loses consciousness during the five-minute plunge, he will survive only if his parachute deploys automatically.
Another unknown: the effects on the body of breaking the sound barrier. While reaching such speeds can cause stress on an aircraft, planners for this jump believe that there will be little effect on Baumgartner, because he will be at an altitude at which there is so little air that shock waves are barely transmitted.
Baumgartner is an Austrian helicopter pilot and former soldier who has BASE jumped from landmarks like the Petronas Towers in Malaysia and the Christ the Redeemer statue in Rio de Janeiro. BASE is an acronym for buildings, antennas, spans and earth, the four things from which you can jump.
He has been preparing for his latest feat for five years -- both physically and mentally.
"You have to remember all the procedures," he said in an interview during testing for the jump. "You know you're in a really hostile environment. And you cannot think about anything else. You have to be focused. Otherwise, you're gonna die."
The balloon, over 500 feet tall at launch, is light and translucent. The material is only .0008 of an inch thick, and it will change shape and size as it rises. The pressurized helmet and suit, which restrict Baumgartner's mobility and weigh 100 pounds, have been equipped with sensors and recorders to measure everything from his speed to his heart rate. Cameras on the ground and on the capsule will transmit live images of his attempt.
Baumgartner was not doing interviews on the eve of the jump, but his performance coach Andy Walshe on Sunday described him as mentally well-prepared.
"He knows that he's rehearsed it and knows what to do," he said. "We want him in the right state of mind. We ask him to reflect on what he's done, what he's been through and what he's achieving for himself personally, so he can relax and focus."
The record for such a jump is currently held by Col. Joe Kittinger, who in 1960 jumped from 102,800 feet as part of a U.S. Air Force mission. On this attempt, 52 years later, Kittinger is a consultant and mentor.
He has also been giving Baumgartner advice on what to expect. For example, he described what it feels like to fall through space when there is so little air: "There's no way you can tell how fast you're going, because there's no visual cues."
But Kittinger rejects any suggestion that he is jealous that Baumgartner is poised to beat his record.
"Oh no. I'm delighted," he told CNN recently. "He's advancing science, and he'll do a great job."