# Sub-orbital HALO parachuting

I guess this question boils down to “is it possible to bail out safely from the highest point of suborbital space flight”.

This is something I’ve always wondered about. We all know that spacecraft have to deal with a great deal of heat due to entering the atmosphere at a very high speed. Upon considering the situation I’m led to understand that most of this speed comes in fact from orbital speed… the energy transformed to re-entry heat is in effect a dumping of the energy added by the engines during the initial boost phase. OK so far? I’m not a rocket scientist.

So my question then becomes… let’s say you take orbital speed out of the equation. Let’s say you put a spaceman with a parachute at the “space boundary” which is arbitrarily accepted at 60 miles. No orbital speed… he just magically appears there as if Zeus had hand-placed him there. He begins to fall, a result one would expect from the influence of Earth’s gravity. Assuming his suit is adequately pressurized and supplied with breathable air, will he experience fatal re-entry heat? Will he be able to deploy his 'chute at any point without being fatally injured by the opening shock?

Just a data-point for you but this brave chap:

http://en.wikipedia.org/wiki/Joseph_Kittinger

jumped out of a helium balloon at about a third of the height you propose.

Skydiver gets ready for 25-mile jump

Kittinger jumped from 76,400 feet (14.5 miles).

“On August 16, 1960 he jumped from the Excelsior III at 102,800 feet (31,300 m).”.

Missed that, thanks. The eyeballs don’t scan to well before the coffee hits.

I’ve been playing about with the terminal velocity equations here:

http://www.grc.nasa.gov/WWW/K-12/airplane/termv.html

and the calculator (which only has an atmospheric density profile up to 100,000 ft, unfortunately). Given that I’ve no real way to estimate drag coefficient or air density at higher altitudes, and there are complications with shockwaves at supersonic speed, I’ve just plugged in various values to see what happens. And blimey the putative jumper could well reach a couple of thousand metres per second on the way down. That’s bound to have some heating effect even in rarefied atmosphere, isn’t it?

Does anyone have better data to use here?

He’ll be going a lot faster than that. Where Kittinger jumped from, the atmosphere was about 10 mb, or 1/100 the pressure at the surface. At 60 miles, you’re up in the thermosphere, where there is almost no atmosphere at all - about .001 mb. He’ll fall for 30 miles before the pressure even gets up to 1mb.

I vote for burn up on re-entry, unless he’s in some kind of drag-creating capsule with a heat shield.

Note that SpaceShip One used both a high-drag technique and a heat shield to withstand the return from non-orbital space.

Man has only jumped in a freefall from over 100,000 feet once. In 1960. For 4 1/2 minutes.