Red Bull space jump

[DGuller]

Yeah, I always thought things burned up when re-entering the atmosphere. Like spaceships and their ablative shielding and such. Maybe that is just because they are moving much, much faster and are using the atmosphere as a brake?

In other words, a spaceship could re-enter the earth atmosphere without the need for a heat shield if it did not need to use the atmosphere to slow down?

That's my impression as well.

[jimmy olsen]

Yeah, I always thought things burned up when re-entering the atmosphere. Like spaceships and their ablative shielding and such. Maybe that is just because they are moving much, much faster and are using the atmosphere as a brake?

In other words, a spaceship could re-enter the earth atmosphere without the need for a heat shield if it did not need to use the atmosphere to slow down?

He just wasn't high up enough. If he jumped out of the ISS, then years later his dessicated corpse would burn up in the atmosphere as it came down.

[Brazen]

Lego Baumgartner. Almost as technically challenging as the real thing:
http://www.guardian.co.uk/sport/video/2012/oct/15/felix-baumgartner-skydive-lego-video

[Eddie Teach]

Lego Baumgartner. Almost as technically challenging as the real thing:
http://www.guardian.co.uk/sport/video/2012/oct/15/felix-baumgartner-skydive-lego-video

[frunk]

I wonder - assuming that you could match velocities with the planet, is there anything stopping you from free-falling from any distance in space to earth like this guy? I always sort of assumed you would burn up in the atmosphere on re-entry from the friction with the atmosphere, like a meteor - but of course meteors tend to have have a big veocity already vs. Earth.

If you get too far away the earth's gravity will no longer pull you down and you would just float in space.

It doesn't matter how far away from earth you are, you are stilled "pulled" by its gravity.  It's only a question if other forces swamp it. 

Meteors burn up in the atmosphere because they hit it at an angle.  If they hit at enough of an angle they'll bounce off.  If the meteor is coming in head on or near head on (or are big enough) like Baumgartner they don't burn up (meteorite).

[Malthus]

I wonder - assuming that you could match velocities with the planet, is there anything stopping you from free-falling from any distance in space to earth like this guy? I always sort of assumed you would burn up in the atmosphere on re-entry from the friction with the atmosphere, like a meteor - but of course meteors tend to have have a big veocity already vs. Earth.

Well, technically if you exactly matched speed with the planet, you'd just trail along behind it as it orbited the sun, and never actually "fall". But, A) I know that's not exactly what you meant--at least I don't think that's what you meant;  and B) I don't think an orbit like that's stable.

I meant assume that you could cancel out other forces so that the earth's gravity could pull you straight "down" (that is, accelerating towards the centre of the Earth, starting from rest (relative to the earth) some distance from the earth fully out of the atmosphere.

Could you free-fall to earth wearing a suit and a parachute, no heat shielding? 

[Berkut]

Malthus, isn't that exactly what he did?

I mean, I suppose you could say he was not fully out of the atmosphere, but at 128,000 feet he is surely out of the vast majority of it, and hence if he could do it from where the atmosphere is that thin, surely he could do it from where it was even thinner (if the atmosphere is the relevant variable).

I think the issue is simply one of speed. If he started from 200k feet (not possible with a balloon I imagine, but lets just say) then maybe he is going Mach 3 when he hits the think part of the atmosphere, and perhaps that is a problem?

[Malthus]

Malthus, isn't that exactly what he did?

Yup, from 37 K up. I'm asking if he could do the same from (say) 370 K up, or 3700 K up (assuming you could - I know you obviously couldn't use the balloon method). Would it make any difference at all, other than taking longer in free fall?

I assume the answer is "no" but I don't know.

Edit: I see you have added. Yes, that's the sort of issue. Normally, in some sort of atmosphere there is some limit to how fast you can go - some terminal velocity, however great. In his fall, the guy reached Mach 1.4 before being slowed by the atmosphere thickening around him - what if he fell hundreds of kilometers, rather than tens?

[Berkut]

I think the only different is that you would get going a lot faster, of course. The only thing slowing you down is air resistance, of which there is little or none about 50k ft.

Just did a quick check - the issue is angular speed. To go into orbit, you need to be going really, really fast sideways (depending on your height). So the issue is slowing down when you re-enter.

Say you are in a capsule 100km up. To be in orbit, you have to be going something like Mach 23. So when you slow down (and hence your orbital height drops), you have to bleed an incredible amount of energy. So it is not *necessary* to burn through the atmosphere to come back down to Earth from orbit, but it isn't realistic to do otherwise. In theory, a spacecraft could simply apply acceleration to counter their angular velocity, and "come down slow", but that would require an incredible amount of thrust - probably an appreciable fraction of the amount that got them into orbit in the first place.

[Pishtaco]

Here is what a system proposed in the 60s for returning from orbit with minimal equipment looked like: http://www.astronautix.com/craft/moose.htm
From orbit, your initial speed would be closer to mach 24 than mach 3. If you were stationary relative to the earth etc. and started far enough away you could reach the same speed by the time you hit the atmosphere. But you would be in trouble, as you would be coming straight down rather than flying in at an angle, so you don't have so many options about controlling your trajectory and how fast you bleed off energy.

[DGuller]

It's an interesting question.  I guess there are two opposing forces in play.  The atmosphere slows you down, so you don't go fast enough to burn up.  But does it slow you down slowly enough but at the same time sufficiently as it's thickening?

[Razgovory]

To be out of the Earth's atmosphere he would need to be quite a bit higher.  The atmosphere slows you down quite a bit which is why we have a terminal velocity.  If you leapt out of a rocket at the point it left Earth's atmosphere, you would fall toward earth quite a bit faster then if you jumped off a very tall building or a mountain.  I don't know if it would be fast enough to burn up on retry, I mean, this is similar to what Ballistic missiles do.

[Razgovory]

Here is what a system proposed in the 60s for returning from orbit with minimal equipment looked like: http://www.astronautix.com/craft/moose.htm
From orbit, your initial speed would be closer to mach 24 than mach 3. If you were stationary relative to the earth etc. and started far enough away you could reach the same speed by the time you hit the atmosphere. But you would be in trouble, as you would be coming straight down rather than flying in at an angle, so you don't have so many options about controlling your trajectory and how fast you bleed off energy.

Well, from Malthus's statement I took his hypothetical death seeker was not coming out of orbit, so he doesn't have to worry about bleeding off the speed required to orbit the Earth.  It'd probably be like those early V2 rocket tests where they just shot one straight up to see what happened.

[Malthus]

I think the only different is that you would get going a lot faster, of course. The only thing slowing you down is air resistance, of which there is little or none about 50k ft.

Just did a quick check - the issue is angular speed. To go into orbit, you need to be going really, really fast sideways (depending on your height). So the issue is slowing down when you re-enter.

Say you are in a capsule 100km up. To be in orbit, you have to be going something like Mach 23. So when you slow down (and hence your orbital height drops), you have to bleed an incredible amount of energy. So it is not *necessary* to burn through the atmosphere to come back down to Earth from orbit, but it isn't realistic to do otherwise. In theory, a spacecraft could simply apply acceleration to counter their angular velocity, and "come down slow", but that would require an incredible amount of thrust - probably an appreciable fraction of the amount that got them into orbit in the first place.

The hypothetical presumes your test subject isn't in orbit, but at rest; so that they drop like a stone, not like a returning spacecraft. 

[mongers]

My unscientific take is that it's about the velocities of everything involve relative to earth. 

So the atmosphere is travelling at about 1000 mph relative to the centre of the earth, though ignoring effects like winds and jet-streams, is roughly keeping pace with the same place on earth.

What space craft, many satellites and the space station are doing is travelling much faster relative to the atmosphere, orbiting in say 90 minutes, 2,3 or 4 hours, so when they re-enter the atmosphere at many 1000s mph they encounter air molecules at very high impact speeds, hence all of the heating and eventual slowing down.

What our fearless Austrian guy is doing is just falling down through a gradually thickening atmosphere that naturally slows him, without ever getting near those high speeds relative to the atmosphere.

If you look at ICBMs, the early V1 only had a range of a couple of hundred miles, but still achieved significant altitudes,iirc 60-90 miles up, yet didn't need any heat shielding because they weren't producing significant speeds relative to direction of travel of the atmosphere.

Whereas modern icbms have to travel much further in 30 odd minutes and so are moving very fast relative to the air molecules when they re-enter, hence the need for shielding of the RV/warheads