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Old 10-06-2012, 12:36 AM   #1933151  /  #1
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Default Joseph Kittinger's skydive record about to be broken

http://abcnews.go.com/Technology/sky...9#.UG9781aYNRQ

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If Baumgartner succeeds he will break the record set on Aug. 16, 1960, when Air Force Col. Joe Kittinger jumped from a balloon at an altitude of 102,900 feet. He fell for almost five minutes before opening a parachute to slow his decent at 18,000 feet. He made history for the highest balloon ascent, the highest parachute jump, and the fastest speed by a human being through the atmosphere.
Video of 1960 jump is amazing if you haven't seen it before!


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Old 10-06-2012, 06:19 AM   #1933363  /  #2
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Crazy. Really the edge of space. How far up before you risk burning up on reentry?
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Old 10-06-2012, 06:35 AM   #1933369  /  #3
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"There is a reason my record has stood for 52 years," Kittinger said. "This is a calculated risk, you understand the risks that you know about but there is always unknowns. The biggest unknown we face is that nobody has transited the sound barrier without the aid of an aircraft."
Baumgartner might be the first person to break the sound barrier without an aircraft?
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Old 10-06-2012, 07:20 AM   #1933379  /  #4
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Um, ya. Might hit 690 mph

This had me loling:
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He already jumped from 90,000 feet in July. That was practice.
I mean, wow. Practice.
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Old 10-06-2012, 07:46 AM   #1933383  /  #5
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Crazy. Really the edge of space. How far up before you risk burning up on reentry?
From a balloon? Never- that happens when you are trying to lose orbital velocities.

...And I think the data actually showed Kittinger DID go supersonic.
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Old 10-06-2012, 01:47 PM   #1933451  /  #6
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Video of 1960 jump is amazing if you haven't seen it before!


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I hadn't seen the part where he surfs ashore after splashdown. Also, who was holding the camera that filmed his descent? Was it Jerome?
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Old 10-06-2012, 07:58 PM   #1933633  /  #7
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yeah, it's really only the first 1:40 that's relevant.

unfortunately the best footage available is from a music video :P
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Old 10-06-2012, 11:05 PM   #1933736  /  #8
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I actually came across this a while back. I was wondering what a typical terminal velocity was for a skydiver, and what the terminal velocity is if the skydiver does his best to minimize his aerodynamic drag. In googling, I read that this Kittinger guy held the record for highest and fastest skydive, which I then investigated. That's some crazy shit. I would never have suspected that the military had guys jumping out of balloons at like 20 miles altitude.

You gotta have some serious brass fucking balls to volunteer for that shit.
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Old 10-06-2012, 11:12 PM   #1933739  /  #9
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Crazy. Really the edge of space. How far up before you risk burning up on reentry?
From a balloon? Never- that happens when you are trying to lose orbital velocities.

...And I think the data actually showed Kittinger DID go supersonic.
Yeah, you'd have to begin your jump completely free of the atmosphere to reach sufficient velocity. It's a pretty tough calculation, because the earth's gravitational force varies with altitude, and you're covering distance as you accelerate. Plus, I don't know how fast you have to be going to burn up from the atmosphere's friction.
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Old 10-06-2012, 11:15 PM   #1933742  /  #10
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Crazy. Really the edge of space. How far up before you risk burning up on reentry?
Burning up on re-entry isn't a result of altitude, it's a consequence of the extreme speed the spacecraft undergoes. To orbit the earth a speed in excess of 17,000 MPH must be attained - the "burning up" part would never happen to something that hadn't been jettisoned to incredible speeds by rockets.
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Old 10-07-2012, 11:30 AM   #1933847  /  #11
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Crazy. Really the edge of space. How far up before you risk burning up on reentry?
From a balloon? Never- that happens when you are trying to lose orbital velocities.

...And I think the data actually showed Kittinger DID go supersonic.
Yeah, you'd have to begin your jump completely free of the atmosphere to reach sufficient velocity. It's a pretty tough calculation, because the earth's gravitational force varies with altitude, and you're covering distance as you accelerate. Plus, I don't know how fast you have to be going to burn up from the atmosphere's friction.
The SR-71 generated external surface temperatures of "well beyond 500F" flying at Mach 3.2 at 80,000'. The flight suits were made to protect the user from an estimated 450F increase in temp if there was an emergency ejection. Mach 3.2 is a bit shy of 2500 mph.

So I'm thinking one would have to get going a lot faster than that to actually burn up. Of course, if one didn't have an effective cooling system, one would cook in their own juices well before burning up.

BTW, it's not friction that causes the heat but compression.


I'm also thinking they'd have to be titanium rather than brass.
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Old 10-07-2012, 11:34 AM   #1933849  /  #12
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BTW, it's not friction that causes the heat but compression.
say wut???

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Old 10-07-2012, 11:50 AM   #1933850  /  #13
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BTW, it's not friction that causes the heat but compression.
say wut???
It's not friction that generates the heat, at least not most of it.

It's the compression of the air. If one compresses a gas, it heats up. That's how refrigerators and AC units work, they compress a gas, so it gets hot and readily bleeds off the heat energy, then decompress the gas so it cools down and can absorb heat, repeat. They run the gas through a phase change, liquid to gas, gas to liquid, because that transfers a lot more heat, but the principle is the same.

There's a lot of compression going on on the frontal surface on something traveling really fast through the atmosphere.
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Old 10-07-2012, 12:08 PM   #1933852  /  #14
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compression of a gas, though. you think that the compressed gas would then transfer its heat via conduction to the hull of the spacecraft, or something? and that is why it gets hot?

I'm thinking that the truth is probably that compression and friction both heat the spacecraft.
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Old 10-07-2012, 01:07 PM   #1933869  /  #15
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compression of a gas, though. you think that the compressed gas would then transfer its heat via conduction to the hull of the spacecraft, or something? and that is why it gets hot?

I'm thinking that the truth is probably that compression and friction both heat the spacecraft.
http://en.wikipedia.org/wiki/Space_S...tection_system

Wikipedia reference-linkReentry heating
A closer view of the tiles under the forward fuselage and the front end of the left wing. The corner of the nose-gear door can be seen at the lower left. The dark solid black tiles are new ones which have never been through a reentry yet. (At top, the white object is the open left cargo bay door.)

Reentry heating differs from the normal atmospheric heating associated with jet aircraft, and this governs TPS design and characteristics. The skin of high-speed jet aircraft can also become hot, but this is from frictional heating due to atmospheric friction, similar to warming your hands by rubbing them together. The Orbiter reenters the atmosphere as a blunt body by having a very high (40-degree) angle of attack, with its broad lower surface facing the direction of flight. Over 80% of the heating the Orbiter experiences during reentry is caused by compression of the air ahead of the hypersonic vehicle, in accordance with the basic thermodynamic relation between pressure and temperature. A hot shock wave is created in front of the vehicle, which deflects most of the heat and prevents the orbiter's surface from directly contacting the peak heat. Therefore reentry heating is largely convective heat transfer between the shock wave and the orbiter's skin through superheated plasma.[1] The key to a reusable shield against this type of heating is very low-density material, similar to how a thermos bottle inhibits convective heat transfer.[citation needed]
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Old 10-08-2012, 04:35 AM   #1934093  /  #16
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Interesting. Still, the problem of the distance one'd have to be to exceed mach 3.2 is challenging, and I suppose there's not a hard figure to provide for when one would cook, vs. "burn up."
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Old 10-08-2012, 06:15 AM   #1934111  /  #17
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I have jumped out of a perfectly good airplane ONCE.

Not a tandom jump belted to another guy, though I had an instructor next to me.

It's something you do or don't do based on your mental state at the time.

I was pretty sure I would survive, but that transition from wind rush to silence when the parachute opened and held me up was one of the high points in my life.

This guys balls are no bigger than mine, the guy in the 60's though his are as no one had done anything close.
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Old 10-08-2012, 06:16 AM   #1934112  /  #18
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Interesting. Still, the problem of the distance one'd have to be to exceed mach 3.2 is challenging, and I suppose there's not a hard figure to provide for when one would cook, vs. "burn up."
Yeah, at least for mortals like us. As you note, as one comes closer to earth, the force of gravity increases. At sealevel to 100,000' altitude, not a lot of difference as the critical measurement is from the center of the earth. Sealevel = 20,925,000' vs 21,025,000' is only about a 0.5% change. Since the force is based inversely on the square of the distance, it'd be only about a 0.25% difference.

And you'd need to figure in the increasing resistance of the atmosphere.

Assuming no atmospheric resistance and about 9.5f/s2, it'd take only 395 seconds, just shy of seven minutes to accelerate to 2500 mph. That would cover about 140 miles. So my guestimate would be you'd have to start out at about 260 miles. That would give you 200 miles to accelerate in before you hit serious atmosphere, that'd get you up to about 3000 mph. Not sure that's fast enough to burn up. 560 miles will get you up to 4700 mph.

In the end, pretty sure it'll be a rather grisly death.
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Old 10-08-2012, 07:45 AM   #1934121  /  #19
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Interesting stuff, thanks all!
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Old 10-08-2012, 02:09 PM   #1934175  /  #20
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Interesting. Still, the problem of the distance one'd have to be to exceed mach 3.2 is challenging, and I suppose there's not a hard figure to provide for when one would cook, vs. "burn up."
Yeah, at least for mortals like us. As you note, as one comes closer to earth, the force of gravity increases. At sealevel to 100,000' altitude, not a lot of difference as the critical measurement is from the center of the earth. Sealevel = 20,925,000' vs 21,025,000' is only about a 0.5% change. Since the force is based inversely on the square of the distance, it'd be only about a 0.25% difference.

And you'd need to figure in the increasing resistance of the atmosphere.

Assuming no atmospheric resistance and about 9.5f/s2, it'd take only 395 seconds, just shy of seven minutes to accelerate to 2500 mph. That would cover about 140 miles. So my guestimate would be you'd have to start out at about 260 miles. That would give you 200 miles to accelerate in before you hit serious atmosphere, that'd get you up to about 3000 mph. Not sure that's fast enough to burn up. 560 miles will get you up to 4700 mph.

In the end, pretty sure it'll be a rather grisly death.
Hehe, that's awesome. How'd you make that calculation? I can calculate the time it'd take to accelerate to a given speed, but I don't know how to get the distance traveled.
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Old 10-08-2012, 02:52 PM   #1934207  /  #21
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Interesting. Still, the problem of the distance one'd have to be to exceed mach 3.2 is challenging, and I suppose there's not a hard figure to provide for when one would cook, vs. "burn up."
Yeah, at least for mortals like us. As you note, as one comes closer to earth, the force of gravity increases. At sealevel to 100,000' altitude, not a lot of difference as the critical measurement is from the center of the earth. Sealevel = 20,925,000' vs 21,025,000' is only about a 0.5% change. Since the force is based inversely on the square of the distance, it'd be only about a 0.25% difference.

And you'd need to figure in the increasing resistance of the atmosphere.

Assuming no atmospheric resistance and about 9.5f/s2, it'd take only 395 seconds, just shy of seven minutes to accelerate to 2500 mph. That would cover about 140 miles. So my guestimate would be you'd have to start out at about 260 miles. That would give you 200 miles to accelerate in before you hit serious atmosphere, that'd get you up to about 3000 mph. Not sure that's fast enough to burn up. 560 miles will get you up to 4700 mph.

In the end, pretty sure it'll be a rather grisly death.
Hehe, that's awesome. How'd you make that calculation? I can calculate the time it'd take to accelerate to a given speed, but I don't know how to get the distance traveled.
I started with a given distance, say 500 miles. the 560 less the 60 miles where I assumed the atmosphere would start to be dense enough to matter.

d = at2/2

I assumed a = 9.5 f/s. At the surface a = 9.8 or so, at 90,000', it's around 9.69. I just guessed at 9.5 as an average further out, probably a bit high.

so t = root(2d/a), root ((2x500x5280)/9.5)

For end v, v = at
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Old 10-08-2012, 03:01 PM   #1934215  /  #22
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As I understand it cooking or burning would likely be irrelevant, as hitting the atmosphere at that speed would generate a serious shock and if you started to tumble, it'd be over very quickly. This is a big issue for re-entry. In fact, re-entry vehicles use the hypersonic shock wave to insulate from the really, really hot gasses.
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Old 10-08-2012, 03:43 PM   #1934248  /  #23
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As I understand it cooking or burning would likely be irrelevant, as hitting the atmosphere at that speed would generate a serious shock and if you started to tumble, it'd be over very quickly. This is a big issue for re-entry. In fact, re-entry vehicles use the hypersonic shock wave to insulate from the really, really hot gasses.
Correct. I wish I had my gas dynamics book handy, I could scan the appropriate images for reference. That wikipedia article was pretty close, but some of it was oversimplified. (surprise!)

Since this (thermodynamic effects) was mostly what I took classes for in college, I remember a lot of the general concepts, and could do some of the calculations if people are really interested. I'd have to do some googling for online references, since most of my textbooks are still in storage, though.

On going suppersonic in freefall:
1. The speed of sound (Mach) actually decreases as altitude increases. (This is a particularly interesting phenomena when it comes to the U-2's flight profile.)

2. Since the air gets singificantly thinner as altitude increases, terminal velocity also increases.

These two points combined make me think that freefall from altitudes of 100k+ feet would probably at least breifly go supersonic.

Here's a chart with speed of sound vs. altitude:
http://www.aerospaceweb.org/question...re/q0112.shtml
At 100k feet, the speed of sound is 675 mph (as opposed to 760 mph at seal level), so that's still pretty damn fast. One thing most people dont know, though is that through the tropopause (~40-70k feet), the speed of sounds is pretty constant (one reason this is a nice chart), and that's where it reaches its minimum, without getting very high up. The minimum SoS that one is likely to see is in the tropopause, and that's 660 mph, according to the chart. (it's interesting to note the temperature behaviors of the atmosphere at different regions too, which is on that page).

According to this page, Kittinger reached 614 mph. That's about M = 0.93, so not quite supersonic, although that close, one might observe localized supersonic phenomena, like small standing shock waves. Probably not, though.
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Old 10-08-2012, 03:58 PM   #1934271  /  #24
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On supersonic heating:

Blunt bodies, like the space shuttle, and the old Apollo re-entry capsules, rely on getting the shock wave away from the body of the craft, becuase, as RAFH noted, the heating comes mostly from the rapid compression of the gas. Conduction, radiation, and convection all act behind the shockwave to heat the surface of the vehicle, which is what the tiles on the shuttle were for. This process is pretty well understood, but extremely complicated to model, which is why they use supercomputer clusters to do that kind of analysis. The whole point of a blunt body, though, is to use that compression effect slow down through the atmosphere.


Supersonic aircraft, on the other hand, don't want to fight the supersonic effects as much as possible, so they interact with the shockwave in a completely different way. The ideal supersonic flight surface is an infinitely thin wing (plate), and that's usually how the early aerodynamicists modelled the aircraft. If you ever get a chance to look at the leading and trailing edges of the wing of the F-104, do so. Just don't bump your head on them, they are quite sharp!

So instead of a blunt body, where the shockwave detaches, on a sharp leading edge, the shockwave is attached, and the angle of the shockwave is dependent on the mach number. That is why the inlets on supersonic aircraft are variable. (here's a good discussion of variable inlets)

I got to see one of these first hand during my undergrad studies (the U of Az has a supersonic wind tunnel.) One cool effect is that you can really clearly see the secondary shocks as they move aft along the surface as it accelerates. Eventually, they detach, which you can't quite see in this video.

So, because the shockwave eventually get very close to/attaches to a sharp body, the main aerodynamic heating comes from a combination of the shockwave (compression heating/conduction) and friction heating from the air moving over the wing.
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Old 10-08-2012, 04:44 PM   #1934312  /  #25
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Talking about variable inlets, I really like the spike solution on the SR-71.

Amazing bit of engineering. And with 1950s/early 1960s era computers to crunch the numbers.

It's also interesting they found out the plane got better mileage the faster it went (above M3) when on one of the missions the pilot was being chased by missiles and just jammed it. I've never seen any record of how fast he did get it going but he did get noticeably better mileage.
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