"We could have just done one jump, forgotten about the wind tunnel tests, the two test jumps. It might have worked, but that's not my way to do it. I'm not a daredevil," he says. "A daredevil would just put on the suit and go for it. We're not going from zero to hero."
Both of Baumgartner's test jumps have been near perfect. But he's only got to look to Kittinger to see some of the potential dangers.
During one of Kittinger's jumps, one of the gloves of his partial pressure suit didn't seal properly. He opted to go through with the jump anyways.
"At 40,000 feet, I found out my right glove was not working. Man had never gone and put his hand into a vacuum. I didn't have an awful lot to go on," Kittinger says.
His right hand swelled to twice its normal size, and after a few hours on Earth, he was back to normal.
"I knew if I told the ground, they would make me abort, and I didn't want to do that, so I didn't tell them."
During another, he spun so fast that he went unconscious, saved only by an emergency parachute.
Of course, Baumgartner has thought about the gruesome possibility that this jump could be his last. He runs through every possible scenario and imagined potential exit strategies.
"You have to come up with solutions to every problem before they come up. If you just start thinking about them when it happens, it's already too late," he says. "I have a picture [of what could happen] and the solution already in my mind. I constantly think about all these things. I inhale this project."
His engineers and safety team have briefed him on what could happen—but there's still one big unknown.
What happens to his body, and his suit, when it breaks the speed of sound?
"The consensus is that he will not have a problem going through the sound barrier," Kittinger says. "But give me a call after the jump and I'll let you know—it's an unknown. You can have all the pressure chambers and wind tunnels, but the only way you can demonstrate it is to do it."
Next month, Baumgarter, his team, and the world will know for sure.
"There's always a little bit of fear," Baumgartner says.
With any luck, sometime next month, Baumgartner will get in his nearly 3,000 pound capsule in Roswell, New Mexico and a giant, 600-foot-high polyethylene balloon will fill up with several million cubic feet of helium, taking him almost 23 miles into the air. Baumgartner will be be alone in his several-hour ascent, just the way he likes it.
"I don't want to share the glory. If there are two people sitting in that capsule, then you'd be talking to two of us right now," he says.
But he will have backup, staying loose while talking with Kittinger.
"I'm trained to run this mission all by myself—I can do everything on my own and be successful, but I don't want to. I want to have [Kittinger] there at mission control making me feel better. He's the perfect mix between serious business and having a lot of fun," he says.
"Joe's funny as hell," he says "He feels like my dad now."
Kittinger says he's finally found the man worthy of breaking his record.
"I had no idea [the record] would last 52 years," Kittinger says. "Felix is the perfect guy to do it. He's a professional athlete, he's trained, and he has a goal."
Once Baumgarter has reached 120,000 feet, he'll stand on the edge of his capsule, higher than anyone has ever been before, and he'll jump. If everything goes right, in a span of 10 minutes, he will break the speed of sound, a 52-year-old record, and drive a little more doubt into the idea that for humans, the sky is the limit.
Jason Koebler is a science and technology reporter for U.S. News & World Report. You can follow him on Twitter or reach him at email@example.com