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. More than 50 years later, Kittinger is a consultant and mentor for Baumgartner's effort.

Kittinger 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."

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."