The threat of exposure to near-zero atmospheric pressure levels is one of Clark’s biggest worries. If Baumgartner’s suit fails, the fluids in his body will start to boil and bubble in a process called ebullism. The resulting tissue damage could kill him if not treated immediately, so Clark is determined to have an HFV machine on the ground in case something goes wrong.
There are other concerns. At some point during his descent, Baumgartner will experience temperatures as low as –148 degrees Fahrenheit, factoring in the wind chill. For the 71,500-foot test jump, he opted not to have electric warmers installed in his gloves and boots because they decreased mobility. Afterward, he reported that his hands had been so cold he could hardly move them. “He was surprised, but we weren’t,” says Kittinger, a bit smugly. He had suspected the wind chill would make Baumgartner feel colder than he had in pressure chamber tests. “I bet he won’t do it again.”
The greatest danger to Baumgartner is a flat spin, but he hopes not to have to use the drogue chute so he can break Andreev’s record. He proved on the test jump that he can use skills he has developed over years of skydiving—slightly changing the position of his limbs to control his attitude—to prevent spinning. Stratos engineers have made Baumgartner’s suit as flexible as possible to improve his ability to make those fine adjustments.
Stratos has arranged for the Fédération Aéronautique Internationale, the world body governing aeronautics records, to be watching when Baumgartner makes his attempt from 120,000 feet. Red Bull wants to make sure the jump counts. If he’s successful, Baumgartner won’t just set the record for highest skydive. He’ll also try to set records for longest freefall and highest manned balloon flight, and may become the first person to break the sound barrier without the aid of a vehicle.
Yes, that’s possible. Because the air is so much thinner in the stratosphere, the speed known as terminal velocity—the point at which air friction cancels out gravitational acceleration—is much higher there than it is near the ground. The Stratos team reckons Felix will reach at least 690 mph, somewhere near the 105,000-foot mark. Adjusting for altitude and temperature, that should be just fast enough to break the sound barrier.
According to the Stratos team, as a shock wave builds up on his helmet, Baumgartner might feel a little vibration near his head. Then, as he reaches and surpasses the speed of sound, the sensation will move instantly to his feet and disappear until he slows and goes subsonic again, at which point he might feel another vibration. That’s if everything goes well.
What happens if things don’t go well is the only genuine mystery in this venture. Fifty-two years ago, Kittinger showed that a stratospheric jump was possible, and there should be no real surprises about the leap itself. But no one has ever crossed the sound barrier quite this way before. There’s one possibility in particular that interests Clark, something called shock-shock interaction.
When a fighter goes supersonic, separate shock waves originate from the nose of the airplane and from its other surfaces. If the shock waves intersect, they intensify enough to generate heat. A supersonic aircraft has to be designed to divert those shock waves away from one another, otherwise the heat and force of the interaction could damage or even destroy the airplane.
In theory, something similar could happen to Baumgartner when he reaches Mach 1, as shock waves bounce off of differently angled parts of his body. Clark’s thinking, though, is that because the air up there will be very thin, the shock waves will be weak. And by gradually easing across the threshold, Baumgartner will prevent any serious danger of shock-shock interaction. So for Clark, it’s more a matter of curiosity than real worry.
Clark has a personal reason for working to make Baumgartner, and future astronauts, safer. His wife, Laurel Clark, was one of the crew members lost in the 2003 Columbia accident. But unlike the space shuttle, which broke up going 13,000 mph, Baumgartner will be falling in a stable position at a comfortable Mach 1. The Stratos team suspects he might not notice when he hits the speed of sound.