Space Flight

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Re: Space Flight
« Reply #30 on: June 03, 2013, 04:18:40 AM »
When you go swimming and you are doing the breast stroke, what are you doing?
You are acting pushing the water behind you against a barrier of water that's already filled the part where your body is moving in and it propels you forward.
It's a crude way of explaining why rockets work in an atmosphere.

Try and do the breast stroke in an empty pool.
This does not explain how a rocket works. A propeller driven airplane, yes, but a rocket? No.

Rockets work by accelerating gas (which they create by burning the fuel they carry in their own on-board tanks) out of an exhaust nozzle. It doesn't need anything outside to push against, it does all it's work just by accelerating the gas in the direction the exhaust nozzle is pointing. You don't even need to burn the fuel, you could just let it escape under it's own pressure, and it would still generate thrust.
Quote from: jtelroy
...the FE'ers still found a way to deny it. Not with counter arguments. Not with proof of any kind. By simply denying it.

"Better to keep your mouth shut and be thought a fool, than to open it and remove all doubt."

Re: Space Flight
« Reply #31 on: June 03, 2013, 04:24:41 AM »
When you go swimming and you are doing the breast stroke, what are you doing?
You are acting pushing the water behind you against a barrier of water that's already filled the part where your body is moving in and it propels you forward.
It's a crude way of explaining why rockets work in an atmosphere.

Try and do the breast stroke in an empty pool.
This does not explain how a rocket works. A propeller driven airplane, yes, but a rocket? No.

Rockets work by accelerating gas (which they create by burning the fuel they carry in their own on-board tanks) out of an exhaust nozzle. It doesn't need anything outside to push against, it does all it's work just by accelerating the gas in the direction the exhaust nozzle is pointing. You don't even need to burn the fuel, you could just let it escape under it's own pressure, and it would still generate thrust.

Of course there is no need for fuel specifically, it's just used since it can create a huge amount of gas when burned.

Another simple example of a rocket would be when you release a balloon without tying its mouth. The air inside is of much greater pressure, thus it is forced out through the mouth, and pushes on the balloon as it escapes. No air from outside enters the balloon until it settles.

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Scintific Method

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Re: Space Flight
« Reply #32 on: June 03, 2013, 04:28:11 AM »
Another simple example of a rocket would be when you release a balloon without tying its mouth. The air inside is of much greater pressure, thus it is forced out through the mouth, and pushes on the balloon as it escapes. No air from outside enters the balloon until it settles.

A simple and fun demonstration of rocket physics, thanks again ican! Oh, and this will work in a vacuum too, provided the balloon is strong enough not to pop first.
Quote from: jtelroy
...the FE'ers still found a way to deny it. Not with counter arguments. Not with proof of any kind. By simply denying it.

"Better to keep your mouth shut and be thought a fool, than to open it and remove all doubt."

Re: Space Flight
« Reply #33 on: June 03, 2013, 04:35:53 AM »
Another simple example of a rocket would be when you release a balloon without tying its mouth. The air inside is of much greater pressure, thus it is forced out through the mouth, and pushes on the balloon as it escapes. No air from outside enters the balloon until it settles.

A simple and fun demonstration of rocket physics, thanks again ican! Oh, and this will work in a vacuum too, provided the balloon is strong enough not to pop first.

Yeah, it will work just the same. You fill the balloon with 1atm less pressure, and it will expand to the same size in the vacuum as it would with that 1atm extra pressure in air, it will not pop.

You can't fill a balloon with your breath in a vacuum, though :P

Re: Space Flight
« Reply #34 on: June 03, 2013, 04:43:51 AM »
Seriously, do you think this is a good analogy for your vacuum rocket.
Describe what the long pipe is doing and then you might realise.

It is a very good analogy for a rocket, vacuum or no vacuum. The long pipe is for the pump to draw water from the sea. The sea acts as the fuel tank for this "rocket", allowing the rider to not have to carry all that water with him. The pump is to make the water exiting the jet be of higher pressure, since that is what generates lift. It is exactly a rocket.

You can make a water rocket yourself, I'm sure you've heard of it too. Take a water bottle, put about 1/3 water in it, attach its end to a bike pump and position it with its mouth downward, then start pumping. At some point the pressure inside will be great enough that the bottle will separate from the pump, and from there on it's a rocket. It's the same thing that's happening in this rig too, but the pump here is much stronger and it's getting a constant stream of water from the sea, so it doesn't "run out".

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Scintific Method

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Re: Space Flight
« Reply #35 on: June 03, 2013, 04:45:09 AM »
When you go swimming and you are doing the breast stroke, what are you doing?
You are acting pushing the water behind you against a barrier of water that's already filled the part where your body is moving in and it propels you forward.
It's a crude way of explaining why rockets work in an atmosphere.

Try and do the breast stroke in an empty pool.
This does not explain how a rocket works. A propeller driven airplane, yes, but a rocket? No.

Rockets work by accelerating gas (which they create by burning the fuel they carry in their own on-board tanks) out of an exhaust nozzle. It doesn't need anything outside to push against, it does all it's work just by accelerating the gas in the direction the exhaust nozzle is pointing. You don't even need to burn the fuel, you could just let it escape under it's own pressure, and it would still generate thrust.
So why do  rockets burn fuel on lift off then, on earth?

Releasing pressurised gas only gives you so much thrust, it's good for fine maneuvering or really small payloads, but not for big rockets. Rockets (the kind we're talking about for space travel) are big, you need more gas to move one of them, and the easiest way to generate large amounts of gas is to burn liquid (or solid) rocket fuel.
Quote from: jtelroy
...the FE'ers still found a way to deny it. Not with counter arguments. Not with proof of any kind. By simply denying it.

"Better to keep your mouth shut and be thought a fool, than to open it and remove all doubt."

Re: Space Flight
« Reply #36 on: June 03, 2013, 04:49:01 AM »
So why do  rockets burn fuel on lift off then, on earth?

They burn fuel to generate gas. This gas is what causes the propulsion due to its great pressure. Think again of that water jet: it needs to be connected to the sea to work, it needs water. It would be very inefficient for it to carry its own water around. A water rocket would have to carry its own water with it, and also create the pressure with a pump, all this takes a lot of energy and doesn't give you enough thrust to lift itself.

Well, fuel stores energy very efficiently, so burning it gives you much more gas at your disposal, so it makes it efficient to carry your fuel around. Your pump no longer has to create the exhaust pressure, it only needs to add fuel to the chamber, the burning itself is what creates pressure.

Quote
How will it work in a vacuum?

The same way it would in air, it would shoot off in one direction while shrinking as it loses its air. Just that it wouldn't come to a stop once it gains speed, since there would be no air resistance to slow it.

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Re: Space Flight
« Reply #37 on: June 03, 2013, 04:51:53 AM »
Seriously, do you think this is a good analogy for your vacuum rocket.
Describe what the long pipe is doing and then you might realise.

It is a very good analogy for a rocket, vacuum or no vacuum. The long pipe is for the pump to draw water from the sea. The sea acts as the fuel tank for this "rocket", allowing the rider to not have to carry all that water with him. The pump is to make the water exiting the jet be of higher pressure, since that is what generates lift. It is exactly a rocket.

You can make a water rocket yourself, I'm sure you've heard of it too. Take a water bottle, put about 1/3 water in it, attach its end to a bike pump and position it with its mouth downward, then start pumping. At some point the pressure inside will be great enough that the bottle will separate from the pump, and from there on it's a rocket. It's the same thing that's happening in this rig too, but the pump here is much stronger and it's getting a constant stream of water from the sea, so it doesn't "run out".
As long as the air pressure is stronger than the thing it's up against, ie, the man, then it will lift him or anything else up...but it must exhaust that pressure against something. In this case it's the air under him and the dense water.
In space, you do not have any of this, so your are rendered a dud.

You are wrong. You should learn more.
Aether is the  characteristic of action or inaction of charged  & noncharged particals.

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Re: Space Flight
« Reply #38 on: June 03, 2013, 05:12:19 AM »
Seriously, do you think this is a good analogy for your vacuum rocket.
Describe what the long pipe is doing and then you might realise.

It is a very good analogy for a rocket, vacuum or no vacuum. The long pipe is for the pump to draw water from the sea. The sea acts as the fuel tank for this "rocket", allowing the rider to not have to carry all that water with him. The pump is to make the water exiting the jet be of higher pressure, since that is what generates lift. It is exactly a rocket.

You can make a water rocket yourself, I'm sure you've heard of it too. Take a water bottle, put about 1/3 water in it, attach its end to a bike pump and position it with its mouth downward, then start pumping. At some point the pressure inside will be great enough that the bottle will separate from the pump, and from there on it's a rocket. It's the same thing that's happening in this rig too, but the pump here is much stronger and it's getting a constant stream of water from the sea, so it doesn't "run out".
As long as the air pressure is stronger than the thing it's up against, ie, the man, then it will lift him or anything else up...but it must exhaust that pressure against something. In this case it's the air under him and the dense water.
In space, you do not have any of this, so your are rendered a dud.

You are wrong. You should learn more.
You see that long pipe attached to the man that's feeding his rocket. It's not just feeding it with water , it's feeding him with immense water pressure too.

I am correct, you should learn more and stop being took in by the lies.
Rockets do not work in space as the vacuum we are told and never have done.

If you think the exhaust of a rocket gets significant thrust by pushing on air, then you are ignorant. On your view jet propulsion should be more effective in water than air, since it is easier to push on water then air. The reality is that jet propulsion works better in air than water.
Aether is the  characteristic of action or inaction of charged  & noncharged particals.

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Re: Space Flight
« Reply #39 on: June 03, 2013, 05:24:30 AM »
I am not twisting anything. I am talking about the basics of jet propulsion. Jet propulsion does not generate thrust by pushing off of anything. Jet propulsion efficiency goes up in less viscous fluids. The facts given in my previous post illustrate this.
Aether is the  characteristic of action or inaction of charged  & noncharged particals.

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Scintific Method

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Re: Space Flight
« Reply #40 on: June 03, 2013, 05:26:52 AM »
Thrust against what?

Well, technically against the rocket itself.

To put this a way you might understand, think of what would happen if you placed an object next to a bomb when it went off. The expanding gas from the explosion would push that object away from the bomb, really fast! That's what's happening with a rocket, except with greater control of the burn: as the gas expands, it tried to expand in all directions. Thing is, there's a rocket in the way on one side, so that rocket gets pushed away. On the other side it's just a vacuum, so the gas expands freely in that direction.

It's a clumsy explanation, but I thought you might have a bit more luck getting your head around it.
Quote from: jtelroy
...the FE'ers still found a way to deny it. Not with counter arguments. Not with proof of any kind. By simply denying it.

"Better to keep your mouth shut and be thought a fool, than to open it and remove all doubt."

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Rama Set

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Re: Space Flight
« Reply #41 on: June 03, 2013, 05:31:13 AM »
I am not twisting anything. I am talking about the basics of jet propulsion. Jet propulsion does not generate thrust by pushing off of anything. Jet propulsion efficiency goes up in less viscous fluids. The facts given in my previous post illustrate this.
If a person gets thrown up on a water jet, vertically, what is keeping that person in the air?

Exactly. The jet pushes the rocket up.
Aether is the  characteristic of action or inaction of charged  & noncharged particals.

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Rama Set

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Re: Space Flight
« Reply #42 on: June 03, 2013, 05:34:59 AM »
Thrust against what?

Well, technically against the rocket itself.

To put this a way you might understand, think of what would happen if you placed an object next to a bomb when it went off. The expanding gas from the explosion would push that object away from the bomb, really fast! That's what's happening with a rocket, except with greater control of the burn: as the gas expands, it tried to expand in all directions. Thing is, there's a rocket in the way on one side, so that rocket gets pushed away. On the other side it's just a vacuum, so the gas expands freely in that direction.

It's a clumsy explanation, but I thought you might have a bit more luck getting your head around it.
Trust me I have my head wrapped around it all very well, only my stance is different from yours, so what we are going to have to do is melt each others brains until one of us accepts one explanation that cannot be refuted.

Buckle up because this isn't going to be a walk in the park by any stretch of the imagination.
A rocket is not a bomb. It burns fuel at a furious rate, that's all.

Actually a rocket is a bomb detonated in extremely controlled and precise circumstances. The challenger shuttle is an example of what happens when those circumstances become less controlled.
Aether is the  characteristic of action or inaction of charged  & noncharged particals.

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Rama Set

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Re: Space Flight
« Reply #43 on: June 03, 2013, 05:37:04 AM »
I am not twisting anything. I am talking about the basics of jet propulsion. Jet propulsion does not generate thrust by pushing off of anything. Jet propulsion efficiency goes up in less viscous fluids. The facts given in my previous post illustrate this.
If a person gets thrown up on a water jet, vertically, what is keeping that person in the air?

Exactly. The jet pushes the rocket up.
Now what is acting on that jet of water to keep that person up?

If you are referring to something like a geyser, the geothermal energy ultimately pushes the water and the pressure comes from a combination of that energy and the area of the hole the geyser shoots through.
Aether is the  characteristic of action or inaction of charged  & noncharged particals.

Re: Space Flight
« Reply #44 on: June 03, 2013, 05:40:26 AM »
Nobody is being lied to, Scepti. You just have a wrong understanding of the concept, we're not lying to you either. These are not things we just read in a book, and they aren't things we just came up with on a whim. These are things that make sense.

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Scintific Method

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Re: Space Flight
« Reply #45 on: June 03, 2013, 05:41:43 AM »
Thrust against what?

Well, technically against the rocket itself.

To put this a way you might understand, think of what would happen if you placed an object next to a bomb when it went off. The expanding gas from the explosion would push that object away from the bomb, really fast! That's what's happening with a rocket, except with greater control of the burn: as the gas expands, it tried to expand in all directions. Thing is, there's a rocket in the way on one side, so that rocket gets pushed away. On the other side it's just a vacuum, so the gas expands freely in that direction.

It's a clumsy explanation, but I thought you might have a bit more luck getting your head around it.
Trust me I have my head wrapped around it all very well, only my stance is different from yours, so what we are going to have to do is melt each others brains until one of us accepts one explanation that cannot be refuted.

Buckle up because this isn't going to be a walk in the park by any stretch of the imagination.
A rocket is not a bomb. It burns fuel at a furious rate, that's all.

Plug the exhaust. Voila! Bomb.
Quote from: jtelroy
...the FE'ers still found a way to deny it. Not with counter arguments. Not with proof of any kind. By simply denying it.

"Better to keep your mouth shut and be thought a fool, than to open it and remove all doubt."

Re: Space Flight
« Reply #46 on: June 03, 2013, 05:43:49 AM »
I am not twisting anything. I am talking about the basics of jet propulsion. Jet propulsion does not generate thrust by pushing off of anything. Jet propulsion efficiency goes up in less viscous fluids. The facts given in my previous post illustrate this.
If a person gets thrown up on a water jet, vertically, what is keeping that person in the air?

Exactly. The jet pushes the rocket up.
Now what is acting on that jet of water to keep that person up?

The pressure of the water, created by the pumping mechanism, is keeping the person in the air. It has nothing to do with the air around the person. Honestly.

Re: Space Flight
« Reply #47 on: June 03, 2013, 06:20:14 AM »
Nobody is being lied to, Scepti. You just have a wrong understanding of the concept, we're not lying to you either. These are not things we just read in a book, and they aren't things we just came up with on a whim. These are things that make sense.
You are being lied to about how rockets work, seriously. I can tell you right now, 1000,000% that they would not work in a vacuum.

Well, I can tell you the same way that they 100% work in vacuum, and I really don't know where you're getting the opposite idea. I've tried explaining why. And I'm not being lied to, I know this myself, I can work it out without someone needing to tell me.

Re: Space Flight
« Reply #48 on: June 03, 2013, 06:38:43 AM »
Nobody is being lied to, Scepti. You just have a wrong understanding of the concept, we're not lying to you either. These are not things we just read in a book, and they aren't things we just came up with on a whim. These are things that make sense.
You are being lied to about how rockets work, seriously. I can tell you right now, 1000,000% that they would not work in a vacuum.

Well, I can tell you the same way that they 100% work in vacuum, and I really don't know where you're getting the opposite idea. I've tried explaining why. And I'm not being lied to, I know this myself, I can work it out without someone needing to tell me.
How you can possibly believe a rocket can work without an atmosphere is beyond me...but each to their own I suppose.

Well, like I said before, and tried explaining to you, I happen to know that the way a rocket's thrust works is independent of the medium it is placed in. The medium will only act to hinder the rocket's forward motion, and has no part in making the rocket work. Therefore, whether the rocket is in air, water, helium, soy sauce, honey, or a vacuum, it still works as a concept. That is what "independent" means.

Re: Space Flight
« Reply #49 on: June 03, 2013, 07:05:35 AM »
A rocket cannot work in a vacuum because it's fuel would be expended immediately upon exhaust. It would simply expand into the vacuum, creating no propulsion whatsoever.

It would not expand "immediately" out into the vacuum. The gas inside would be leaving the rocket a bit faster than at normal atmospheric pressure, but the difference wouldn't be dramatic. You see, what's making the gas inside the rocket "leave" is not the outside medium, it's the inner pressure of the gas inside the rocket. Or more precisely, the pressure difference between inside and outside.

Since atmospheric pressure is basically nothing compared to the pressure of the exhaust of a liquid fuel rocket, it follows that the pressure difference when used in vacuum is barely greater than the pressure difference in air. So the exhaust gas would barely have a noticeable difference inside the rocket in a vacuum environment.

The exhaust gas leaves the rocket in quite a rush in both air and vacuum (no discernible difference), but it's certainly not an instant action. And the time it takes for the exhaust to leave is the time during which it's pushing on the rocket.

Seeing that a rocket engine can burn for quite some time, depending on fuel reserves, this time can hardly be called "instantly".

Re: Space Flight
« Reply #50 on: June 03, 2013, 07:08:18 AM »
I think the problem here is that you think vacuum is a magical and extremely complicated "state" that works differently from anything else you've heard of.

Vacuum is just a "state" in which gas is at zero pressure. This doesn't make it break the laws of physics. The difference between a vacuum and normal atmospheric pressure is only 15 psi. I'm sure you can think of plenty engineering applications which involve immense pressures compared to that. So why would a 15 psi pressure difference matter for a rocket?

Re: Space Flight
« Reply #51 on: June 03, 2013, 07:33:18 AM »
There are always fissures in vacuum chambers, and air is constantly getting in, which is why there is need for constant pumping.

Yet even with these fissures, the air outside doesn't "immediately" fill the chamber, since vacuum, as I said, isn't a magic "pop and it's gone" thing. It's just a pressure difference causing air outside to go in, but not at magical breakneck speeds to fill the chamber immediately. Even if you open a larger valve, air doesn't "immediately" fill the chamber, it takes quite a few seconds usually.

So there you go, gas doesn't instantly cease to exist when in a vacuum.

Consider the pressure differences again: vacuum to atmospheric pressure is only 15 psi. A car tyre already has twice that. And then imagine the pressure of the exhaust of a rocket. 15 psi makes almost no difference for it.

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Re: Space Flight
« Reply #52 on: June 03, 2013, 07:39:46 AM »
Nobody is being lied to, Scepti. You just have a wrong understanding of the concept, we're not lying to you either. These are not things we just read in a book, and they aren't things we just came up with on a whim. These are things that make sense.
You are being lied to about how rockets work, seriously. I can tell you right now, 1000,000% that they would not work in a vacuum.

You will excuse us if we do not take your opinion on science seriously.  You are lazy in research, ignorant of theory, and extremely biased against mainstream science.  Your 1,000,000% surety is worth... nothing.
Aether is the  characteristic of action or inaction of charged  & noncharged particals.

Re: Space Flight
« Reply #53 on: June 03, 2013, 07:42:11 AM »
Http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation describes pretty well how a rocket works in vacuum.

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Re: Space Flight
« Reply #54 on: June 03, 2013, 07:45:49 AM »
Nobody is being lied to, Scepti. You just have a wrong understanding of the concept, we're not lying to you either. These are not things we just read in a book, and they aren't things we just came up with on a whim. These are things that make sense.
You are being lied to about how rockets work, seriously. I can tell you right now, 1000,000% that they would not work in a vacuum.

You will excuse us if we do not take your opinion on science seriously.  You are lazy in research, ignorant of theory, and extremely biased against mainstream science.  Your 1,000,000% surety is worth... nothing.
You take it however you feel, it's not important to me how "you" take it to be honest.

I know its not important to you, its not important to me that it is unimportant to you.  But you should also be aware that your opinion means nothing, because your responses are superficial.  If you put together substantial refutations, you would actually have some validity outside  of you and your mom's meatloaf dinner dates on Sunday.
Aether is the  characteristic of action or inaction of charged  & noncharged particals.

Re: Space Flight
« Reply #55 on: June 03, 2013, 07:49:19 AM »
http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation describes pretty well how a rocket works in vacuum.
Looking at sites like this will not enhance your prospects of ever finding the truth.

That is a law of physics whichnis proven. Why don't you take a trip to Cape Canaveral or Kourou or Baikonur... Or buy fireworks? Or build yourself your own rocket?

Re: Space Flight
« Reply #56 on: June 03, 2013, 07:53:52 AM »
The vacuum of space will not discriminate with whatever pressure is inside a rocket, it will be ready to accept it all, in any quantity and under and pressure.

No, the pressure difference is what matters. Greater pressure gas would exert a greater force on the walls of the rocket, and leave the rocket faster.

Also, the vacuum wouldn't necessarily pull apart a closed box filled with gas, as I think you believe. If the box can take the pressure of the gas within it without breaking, then the vacuum can just go screw himself, he's not getting any of that gas in the inside.

A small example: A car tire is usually inflated to about 30 psi, which is just about double of atmospheric pressure. The pressure difference between inside the tire and outside is 15 psi. This is pressure exerted on the inner walls of the tire, pushing on them, but the tire is built to withstand this pressure.

Now, inflate the tire to 15 psi and put in in a vacuum. The pressure difference is again 15 psi, just as much as it was before. So your tire would sit in that vacuum with no worries, holding that air inside in just about the same matter. It would not explode.


Re: Space Flight
« Reply #57 on: June 03, 2013, 09:12:09 AM »
Anyway, I have no problems with this but  the release from a breach would be the same....no motion of the rocket. It would be a dud.

The release from the breach would be a jet of gas shooting out of the box/rocket, which would behave the same way as it does in air. My point with the pressure difference was basically that from the point of view of the rocket, the exhaust gas is of such high pressure that it makes no difference whether there's air or a vacuum around the rocket; since the difference in pressure is nearly the same, there's only a 15 psi difference, the atmosphere around the rocket is so thin compared to the rocket exhaust that it might as well be a vacuum. Just like for us humans, the pressure up 120,000 feet high, while not zero, might as well not exist and be called a vacuum since it's so thin.

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Re: Space Flight
« Reply #58 on: June 03, 2013, 09:48:48 AM »
Anyway, I have no problems with this but  the release from a breach would be the same....no motion of the rocket. It would be a dud.

The release from the breach would be a jet of gas shooting out of the box/rocket, which would behave the same way as it does in air. My point with the pressure difference was basically that from the point of view of the rocket, the exhaust gas is of such high pressure that it makes no difference whether there's air or a vacuum around the rocket; since the difference in pressure is nearly the same, there's only a 15 psi difference, the atmosphere around the rocket is so thin compared to the rocket exhaust that it might as well be a vacuum. Just like for us humans, the pressure up 120,000 feet high, while not zero, might as well not exist and be called a vacuum since it's so thin.
How you can believe that a rockets gases would behave the same on earth as in space is beyond me.

So you think that the law of conservation of momentum, which is a demonstrable fact, applies only on Earth's surface but not above the atmosphere?
Giess what? I am a tin foil hat conspiracy lunatic who knows nothing... See what I'm getting at here?

Re: Space Flight
« Reply #59 on: June 03, 2013, 10:07:54 AM »
Anyway, I have no problems with this but  the release from a breach would be the same....no motion of the rocket. It would be a dud.

The release from the breach would be a jet of gas shooting out of the box/rocket, which would behave the same way as it does in air. My point with the pressure difference was basically that from the point of view of the rocket, the exhaust gas is of such high pressure that it makes no difference whether there's air or a vacuum around the rocket; since the difference in pressure is nearly the same, there's only a 15 psi difference, the atmosphere around the rocket is so thin compared to the rocket exhaust that it might as well be a vacuum. Just like for us humans, the pressure up 120,000 feet high, while not zero, might as well not exist and be called a vacuum since it's so thin.
How you can believe that a rockets gases would behave the same on earth as in space is beyond me.

The answer to your question is in my post.

From the point of view of the rocket's exhaust gas, which is of extremely high pressure: atmospheric pressure of 15 psi and vacuum pressure of 0 psi are basically no different for a rocket. To post an actual comparison, nozzle pressure of a rocket's exhaust gas can reach 1000 psi. You see why a 15 psi difference is nearly irrelevant for it?

Just like for a human being, used to 15 psi, a pressure of 1 psi as a few dozen kilometers up, and a pressure of 0 psi as in vacuum, are equally deadly: it makes no difference. You would die exactly the same way if you were exposed to 1 psi as if you were exposed to a vacuum.

The same way for a rocket, used to 1000 psi, 15 psi here or there makes no big difference.