Well, he did it. Felix jumped out of a balloon 128,000 feet above the Earth as part of the Red Bull Stratos jump.

More on 'Fearless' Felix:

'Fearless Felix' Falls 24 Miles to Earth

Physics of the Red Bull Stratos Jump

How Claustrophobia Nearly Grounded 'Fearless Felix'

What We Can Learn from a Supersonic Skydive

What Does One Wear on a 23-Mile Skydive?

Of course, I was watching this video live. One thing interesting at the end was the altitude. It seems the plan was to jump from 120,000 feet - but the balloon got as high as 128,000 feet at one point. I think he eventually jumped somewhere between 127 and 128 thousand feet. The other interesting thing was the time of free fall. Joe Kittinger holds the record for the longest free fall at around 4 minutes and 36 seconds when he jumped from 102,000 feet. Even though Felix Baumgartner jumped from quite a bit higher, he only had a free fall time around 4 minutes and 20 seconds. Why? I guess the real question is the difference in Felix's actual jump time and his projected free fall time of 5 mins 35s.

I guess the two jumps could have different ending altitudes. However, at a terminal speed of 120 mph it would only take about 6 seconds to travel an extra 1000 feet before pulling out the parachute. This probably doesn't account for the 1 minute difference in projected time (unless Felix pulled at around 15,000 feet - which I am not exactly sure about) __Upate: __According to this press conference, he opened his chute around 8,000 feet.

My first guess was that it has to do with the starting altitude. If Felix starts from a higher position, that gives him much more time to increase his speed during the portion of the jump with very little air resistance. Let me do a quick calculation. Suppose the air resistance during the first 26,000 is super small. In that case, essentially the only force acting on Felix would be the gravitational force giving him an acceleration around 9.8 m/s2 (the gravitational field doesn't change that much at that altitude and this is just an estimation).

I don't normally like to start with this kinematic equation, but I am going to anyway. If you know the acceleration and the distance, then the following would be true:

Here, the initial velocity (v 0 ) would be 0 m/s and y - y 0 would be -26,000 feet or -7,900 meters. Solving for the final velocity, I get 393 m/s (879 mph). Why did I look at 26,000 feet change in height? After falling this distance, it would put Felix at the same starting position that Joe started at during his jump. The only difference is that Felix would already be moving super fast and Joe would be starting from rest. This means that Felix will be ahead of Joe for the rest of the fall.

Of course, this calculation is wrong. Wrong because Felix's top speed didn't get up to 879 mph (well, I am not absolutely sure since the official values haven't been released). Really, my best bet to look at the difference in altitude is to use a numerical model. Of course, I have done this before.

Let me start with some assumptions:

Air resistance with a constant drag coefficient and proportional to the square of the speed.

There is some model for the density of air as a function of altitude (based this air density model).

There was no wind and no abnormal weather that would effect the jump.

With this, I can just make two numerical models. Here is the height-time plot for a jump from 128k feet and 102k feet. With both jumps ending at 2,400 meters.

From this model, I get a 128k jump time of 4 minutes and 14 seconds. This is fairly close to the official reported value of 4 minutes and 20 seconds. The same jump from 102k gives a time of almost exactly 4 minutes. Ok - this seems to be a possible explanation. What if I change the ending height for the 102k jump to 2,000 feet instead of the reported 8,000 feet? That would increase the free fall time to 4 minutes and 30 seconds.

Just for fun, here is a plot of free fall time vs. starting height for values from 128,000 feet to 102,000 feet.

This says what most people would think. Higher starting positions have longer free fall times.

That still doesn't give the correct free fall time for Joe Kittinger's record setting free fall time. Even if he did fall to a lower altitude, I don't get the correct time. There is something else that could matter: mass. If Felix had more gear with him, or even a different shaped space suit, this could lead to different effects from air resistance. Let me just start with mass. Here is a plot of the free fall time from 102,000 feet to 3,000 feet (I think 2,000 feet was too low) as a function of jumper mass.

So, by reducing the mass of the jumper down to 70 kg I get a free fall time around 5 minutes. Of course, I kept the drag coefficient and the cross sectional area of the jumper constant.

Perhaps this could be the reason that Felix didn't break the free fall time record. It could be that Joe had a different mass (or maybe a different drag coefficient) that could lead to a different time.

__Update: __Wolfgang Rupprecht added something that I had forgotten – Joe Kittinger had a small drogue chute during his fall (here is a link with that info). This would increase his drag and decrease his speed.