Mathematical probabilities are tough to calculate – particularly because they had developed enough redundancy in their systems (both human and technological) that any incident would have to have been a chain of events.
However, here are a few of the risks:
- Supersonic speed. Someone with more of a background with physics can confirm this, but it’s conceivable that the colliding forces caused by a body breaking the sound barrier could be very dramatic. In the stratosphere, these forces are a lot less – but there was still the possibility of an issue. At lower altitudes, the air can collide with the force of an explosion.One worry I heard – “What would happen if one of his organs reached the speed of sound before another one?” Interesting to think about (and obviously, given that he reached Mach 1.24, this point is moot – at least for the altitude he was at).
- Exposure. It’s freakin’ cold up there! Were Felix to in any way be exposed to the atmosphere, not only the extreme temperatures from the air, but also wind-chill could cause him to freeze. But that’s okay, because the next one would probably kill him (or at least knock him out) first.
- External Pressure. If his pressure suit were to lose pressurization, Felix’s body could be subjected to some awful stuff. Above 63,000 feet (known as the Armstrong Line), due to the ambient air pressure, water boils at 98.6 degrees F (37 degrees C) – the temperature of the human body. If one’s body is exposed to the ambient outside pressure, one’s bodily liquids (particularly saliva, tears, and the liquids wetting the alvioli in the lungs) can boil. The blood won’t boil due to the elastic pressure of the blood vessels, but the damage will have likely already been done. http://www.geoffreylandis.com/va… (It’s notable that partial exposure can work out alright. Joe Kittinger’s hand was partially exposed during his freefall from 102,800 feet and reportedly swelled to twice its normal size. Upon landing, it was unusable. Within three hours of landing, it was back to normal.)
- Balloon stress issues. The balloon is 0.0008 inches thick (roughly as thick as a plastic dry cleaner bag) and can be subject to numerous issues. Conceivably, it could be nicked on the ground. It could be stressed by the extreme temperature variances passing through the tropopause. Any damage from the ground or the ascent will only get worse with altitude as conditions become more extreme … until possible catastrophic failure of the balloon occurs. http://www.redbullstratos.com/te…
- Wind gusts during the ascent. Weather is fickle. The balloon is thin, and almost brittle, in the cold. At worst, they could damage the balloon; at best, they could blow Felix off-course. Given the tracking technology, these issues probably wouldn’t be fatal … but could cause complications.
- UV radiation. UV radiation at 120,000 feet is more than 100,000 times as strong as it is on the ground. Felix should have only a short exposure, so this is unlikely to be a major problem.
- Gear issues. Oxygen supply, difficulty with the capsule mechanisms, radio failure, or issues with other gear all could happen. Not sure if it was caused by the failure of a heating unit (report remains to be seen), but it was reported that Felix’s visor fogged up during the actual freefall. He lost visibility of the ground, his altimeter, and other instruments. He ultimately wound up deploying slightly higher than planned, presumably (I’m 100% speculating, here) when his limited vision allowed him to estimate that he was getting closer to the ground (either from the view of the earth or a partial view of his altimeter). Had he not, his automatic activation device would have likely deployed for him … but that’s a chance we as skydivers don’t like to take. (Equipment fails. I’d rather not stake my life on a small electronic piece of equipment that’s just been almost to space and back.)
- Instability. As skydivers, we learn to use the resistance of the air to stabilize ourselves and fly our bodies. In the thin air, there’s less to push off of. Thus, if Felix was to begin spinning, it could become difficult to regain control due to not having the aerodynamic forces to counteract the spin. This ‘flat spin’ could result in loss of consciousness, as well as damage to Felix’s eyes, brain, and cardiovascular system. To guard against this possibility, the team has developed a drogue parachute to automatically deploy and stabilize Felix should he become unstable for more than a specified period of time. http://www.redbullstratos.com/te…
- Problems with the drogue deployment. In the event Felix needs to use the drogue, his unstable position could lead to an entanglement. Which is a nuisance standing on the ground … but can be fatal traveling at 600+mph. If he became entangled with the drogue, Felix would need to clear it (which will be difficult if he’s unconscious) – otherwise, he could wind up deploying his parachute into a tangled mess (which would in turn foul up the deployment of his reserve parachute).
- Premature deployment of his main or reserve parachute. Again, depending on body position, this could become an issue of being ‘gift wrapped’ by ~270 square feet of fabric and lines while traveling at a high rate of speed. At higher altitudes, a parachute could conceivably disintegrate at the speeds he’s traveling, leaving remnants behind to foul the deployment of the reserve parachute. At lower altitudes, a premature deployment could lead to bodily injury – the severity of which would again depend on body position (ask any skydiver – unexpected rapid deceleration can hurt. I’ve seen stars a few times myself).
Again, sorry I can’t break down the mathematical probabilities … but from what I know, all of the above are some of the considerations when making a jump like this. A lot of them (the drogue deployment, or premature deployment of a parachute) can be problems during certain types of skydives from normal altitude – but on a jump like this, their significance increases.
Of all of them, I’d personally think that instability, drogue entanglement, and premature deployment of the main or reserve parachute presented the biggest risk. The rest were monitored and could be fixed or aborted prior to him stepping off the platform.
Once you’re out in the thin air, however, there’s a lot more that is out of your control … and there’s no “do-over” switch.