Red Bull space jump

[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.

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. 

Right. In which case I don't think there is a problem other than the need to slow down before he hits the earths surface.

[DGuller]

Right. In which case I don't think there is a problem other than the need to slow down before he hits the earths surface.

There is also a need to slow down before you hit the thick atmosphere.  My guess is that you want your speed to fall at least proportionally with the terminal velocity at the height you're traveling.  If you just zip through the thin part of the atmosphere without slowing down much, the thick part of the atmosphere will burn you up while slowing you down.

[Malthus]

Right. In which case I don't think there is a problem other than the need to slow down before he hits the earths surface.

There is also a need to slow down before you hit the thick atmosphere.  My guess is that you want your speed to fall at least proportionally with the terminal velocity at the height you're traveling.  If you just zip through the thin part of the atmosphere without slowing down much, the thick part of the atmosphere will burn you up while slowing you down.

This is indeed the issue - though I don't know the answer: whether its no problemo as long as you have space suit and parachute, or whether, without a heat shield, you will return as fried as a Scottish Mars Bar.

Problem is that pretty well nothing actually falls like this normally.

[DGuller]

We should put Mythbusters on the case.

[Malthus]

We should put Mythbusters on the case.

It's not a bad one. 

First, someone has to give them a spaceship ...

[Berkut]

Right. In which case I don't think there is a problem other than the need to slow down before he hits the earths surface.

There is also a need to slow down before you hit the thick atmosphere.  My guess is that you want your speed to fall at least proportionally with the terminal velocity at the height you're traveling.  If you just zip through the thin part of the atmosphere without slowing down much, the thick part of the atmosphere will burn you up while slowing you down.

I actually do not think that is an issue - once your speed gets high enough that you could burn up going through, you are going to be through so fast it won't matter as you impact the earth at some ridiculous speed, assuming a nearly vertical fall.

The "thick" atmosphere is pretty thin when approached at a direct angle to the earths surface. I mean, I suppose you could have some friction issues.

But look at this jump as an example = he reached way higher than terminal velocity in the initial jump, right? So he slowed down a bit once the atmosphere thickened, with no harmful effects at all - went from 700+ mph to something like 130 (if I remember TV correctly).

If he was going fast enough that friction with the air was relevant, he would be doing some speed that slowing down to avoid friction is the least of his problems - running into the surface in the next 10 seconds doing Mach 10 is a much bigger problem.

Spaceships need ablative shielding because they enter the atmosphere at an extreme angle - really just deep enough not to "skip" off as they use the atmosphere to slow them down to a safe landing speed. So they are entering the thick atmosphere at some relatively insane angular speed, and will spend quite a lot of time going nearly horizontal to the earth surface through the thick part, right?

[Berkut]

Right. In which case I don't think there is a problem other than the need to slow down before he hits the earths surface.

There is also a need to slow down before you hit the thick atmosphere.  My guess is that you want your speed to fall at least proportionally with the terminal velocity at the height you're traveling.  If you just zip through the thin part of the atmosphere without slowing down much, the thick part of the atmosphere will burn you up while slowing you down.

This is indeed the issue - though I don't know the answer: whether its no problemo as long as you have space suit and parachute, or whether, without a heat shield, you will return as fried as a Scottish Mars Bar.

I suspect that spacesuit plus parachute will work as long as your velocity on entering the atmosphere is low enough that there is sufficient time for the atmosphere to slow you down enough that the parachute will work.

In other words, at some velocity x, a perfect heat shield won't save you, because you won't slow down enough in the atmosphere to deploy your parachute. And I suspect that velocity is LOWER than the velocity where you would need a heat shield to begin with.

[Razgovory]

This thread needs Ide.

[Malthus]

This thread needs Ide.

What, are you suggesting we toss him out of a spaceship to test these theories? Nasty!

[sbr]

Why do space walking astronauts float next to the shuttle and not fall to earth?

[Berkut]

Why do space walking astronauts float next to the shuttle and not fall to earth?

Duh.

Obviously the gravity from the shuttle holds them close to it.

[Razgovory]

This thread needs Ide.

What, are you suggesting we toss him out of a spaceship to test these theories? Nasty!

Well, I'm not sure if your scenario is possible as it's difficult for an object to be "at rest" in the upper atmosphere.  I think the closest is a rocket that is shot vertically, reaches it's apogee and then fall back to earth.  This is an amateur rocket that reached space and then fell back down, http://www.ddeville.com/derek/CSXT.htm  It did not appear to burn up on the way down, though it looks a bit scuffed up.

[Razgovory]

Why do space walking astronauts float next to the shuttle and not fall to earth?

Cause they and the shuttle are both falling at the same speed, they are just falling sideways.

[frunk]

Why do space walking astronauts float next to the shuttle and not fall to earth?

The same reason the shuttle itself doesn't fall to earth, the astronaut's in orbit.  It doesn't matter if they are inside or outside the shuttle.

[dps]

This thread needs Ide.

What, are you suggesting we toss him out of a spaceship to test these theories? Nasty!

I was going to suggest Timmay.