Skydiving from 25 Miles Up

chisox writes "The Observer has a story about a retired French army colonel who is soon to make a free fall parachute jump from 25 miles up. In the process he will break the sound barrier, reaching a top speed of mach 1.68 before he opens his parachute 1,000 metres above the Earth. Of course, if the chute doesn't open, the hole he'll make will be about 1,000 metres deep." Well, actually his max speed will be high up and near the earth the atmosphere will have slowed him down to terminal velocity.

Comments

His Ears

[Daveman692]

Will he really experience a sonic boom? If so wouldn't that destroy his ear drums.

Re:His Ears

[Bullschmidt]

Nope. Won't be any sonic boom. He'll break the sea level speed of sound high in the atmosphere, where the speed of sound is higher. As he descends, he'll slow to terminal velocity. So there will never be a shockwave.

Physics

[drfrank]

Well, actually his max speed will be high up and near the earth the atmosphere will have slowed him down to terminal velocity.

Well, actually he'll be at terminal velocity for nearly the entire time... Terminal velocity is dependant on the density of the atmosphere. You'd think that someone that posted a link to a page which defined "terminal velopcity" would have at least read the definition...

Re:Physics

[Alsee]

actually he'll be at terminal velocity for nearly the entire time

Nope. At that altitude you are practically in a vacuum. He will accelerate for close to half the distance. You haven't hit terminal velosity untill you stop accelerating. That won't happen until his altitude gets down to around 70,000 to 90,000 feet where the atmosphere starts thickening up.

After he does hit terminal velocity, the atmosphere will thiken rapidy. The local value (for that altitude) of terminal velocity will drop rapidly. The air resistance will exceed the force of gravity and he will start slowing down, bleeding off his inertia. He will actually be ABOVE the local terminal velocity during this process - pretty much the second half of his trip.

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others trying same stunt

[what_the_heck]

Wired had an article in August 2001 about two other people attempting much the same thing.

Re:parachute necessary?

[DutchSter]

I have always wondered if there were any examples (probably from war) of people bailing over the ocean with no/unopened parachute and surviving. Terminal velocity around sea level is like 120 mph, right? That's pretty fast, but I wonder if there's some chance of surviving an impact with water at that speed.

Given that water is an incompressible liquid and you would be hitting at such a high rate of speed, you'd be better off landing in a dirt field at the same high speed. Just think about those belly-flops; they hurt from three feet up. The second you hit, the water doesn't move. It's only after the blow has rippled out that the water moves and you begin to sink.

According to the Worst-Case Scenario Survival Handbook (http://www.worstcasescenarios.com) if you plan to jump from anything high you should be prepared to at least break your legs, and clench your buttocks as you go down so as to keep water from rushing in and um, causing severe "internal" damage. Jumping from over 50 feet is ill-advised as it will almost certainaly break something other than your legs (spine) unless you hit at exactly the right angle. At 120 MPH you may not be able to adjust yourself by the time you realize that you're going to enter at a slight angle thanks to that last second cross breeze.

Interestingly though, according to the same book you can probably survive a 50 foot fall into a dumpster of boxes with few complications.

Big Airy Sponges...

[roberto0]

At 25,000 feet, the earth's atmosphere is significantly thinner than at ground level. So there's an interesting effect going on here: When the skydiver jumps from the plane, he'll accelerate until he's falling at "terminal velocity".
But as he falls, the atmosphere will be thickening around him, and the "terminal velocity" will decrease. Which is kind of cool, because he'll be slowing down as he's falling!
The atmosphere is like a big, airy sponge around the Earth...

Skydiving from 25 Miles Up

[guru312]

Well...He may get to hold the record for highest skydive but *I* hold the record for parachuting night pukes.

No one has gotten sick jumping out of an airplane at night as many times as I have.

I keep waiting for someone to try to break my record. They are all afraid to try!

See it here: http://AICommand.com/PukeDuke.htm

Guru312

Sonic "click"

[s4m7]

The sound heard on the ground as a "sonic boom" is the sudden onset and release of pressure after the buildup by the shock wave or "peak overpressure." The change in pressure caused by sonic boom is only a few pounds per square foot -- about the same pressure change we experience on an elevator as it descends two or three floors -- in a much shorter time period. It is the magnitude of this peak overpressure that describes a sonic boom.

now, all this relies on air pressure! If our skydiver hits the speed of sound up where there isn't any air to speak of, then he's not going to experience much of a boom at all now, is he?

This is not to say nothing of the fact that the boom appears to occur behind the cause, from the pilot's, or in our case the intrepid colonel's perspective. (that is, he is moving away from the sound at the speed of sound.)

NO BOOM PEOPLE, GET IT?

Better Picture

[crisco]

I like this picture better.

Re:Parachuting from space?

[Kredal]

Going down isn't the problem. If the shuttle were geosynchronous, no problem.. if you had space suit, you could make the jump no problem (well, very little problem)..

But the shuttle is also moving around the earth VERY quickly.. something like 17,000 kph (feel free to correct me), which would kill you pretty much instantly when you encountered the atmosphere, and had to slow down your sideways speed.