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Old 17th April 2019, 11:46 AM   #121
Armitage72
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Originally Posted by Belz... View Post
What part of "it can't go through the engine bell walls" is causing you issues?

I know this one. I remember it from an old Stundie post that compared rockets to a can of silly string. The rocket doesn't actually push the exhaust out of the nozzle, so the walls don't matter. The vacuum instantly pulls the exhaust out of the rocket and into itself, so there's no thrust.

ETA: Found it.

Originally Posted by smartcooky View Post
I submit this pearl of wisdom, from cluesforum.info

Thread: Why Rocketry Doesn't Work in the Vacuum

Poster: Vext Lynchpin

Date: June 18th, 2013, 8:00 pm

""I think the main point that the posters on this thread (who are more scientifically minded than I) have been making is that the vacuum itself exerts a force of its own that renders nil the force of the mass of gas escaping from a rocket's nozzle.

To use a simple analogy, think of a rocket and its escaping gas as an aerosol can full of silly string. When you press the button on the aerosol can, silly string is ejected at great speed. If there's enough speed, it may exert force on the aerosol can, so that the silly string is moving in one direction, and the can in the other. Newton.

But in a vacuum, the speed of the equalizing force of the vacuum is akin to someone pulling the silly string out of the aerosol can faster than it can be ejected, thus nullifying the force caused by the silly string's ejection.

Of course, the analogy isn't perfect, since pulling the silly string out would actually cause the aerosol can to move in the same direction as the pull. This wouldn't be a factor with gases being pulled into the vacuum."

Last edited by Armitage72; 17th April 2019 at 11:50 AM.
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Old 17th April 2019, 11:48 AM   #122
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Originally Posted by Belz... View Post
Well, he quotes movies as if they are wisdom and seems to have a movie understanding of science. Par for the course.

Wow, solipsism, so fast?

The problem is, you don't want it proved. You've set yourself up to be impossible to convince anyway. Part of having an open mind is realising that you can be wrong, and you've discarded that.

Density. Don't get things mixed up. Focus.
That would stop the Gish gallop, which seems to be his trade mark.
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Old 17th April 2019, 11:50 AM   #123
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It's not like you have to go to space to find a vacuum. This isn't some theoretical question we have to build a super collider the size of the moon to solve. This could be answered in any vacuum chamber here on Earth with Diet Coke and Mentos.
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Last edited by JoeMorgue; 17th April 2019 at 12:40 PM.
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Old 17th April 2019, 12:05 PM   #124
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Originally Posted by JoeMorgue View Post
It's not like you have to go to space to find a vacuum. This isn't some theoretical question we have to build a super collider the size of the moon to solve. This answered in any vacuum chamber here on Earth with Diet Coke and Mentos.
Exactly. But the video would have to be verifiably uneditable, which is tricky to prove. And if Gingervytes were actually there to witness the experiment he'd have to be in the chamber to check that it's really a vacuum. Looks like an irreducible delusion to me.
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Old 17th April 2019, 12:07 PM   #125
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Originally Posted by JoeMorgue View Post
It's not like you have to go to space to find a vacuum. This isn't some theoretical question we have to build a super collider the size of the moon to solve. This answered in any vacuum chamber here on Earth with Diet Coke and Mentos.

Any thrust would be the result of the exhaust pushing against the wall of the chamber, obviously.
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Old 17th April 2019, 12:09 PM   #126
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The "NASA" rocket equation? I thought it was the Tsiolkovsky rocket equation.

Oh, I get it.... Tsiolkovsky was "in on it", a NASA shill, 62 years before NASA was even established.
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Old 17th April 2019, 12:12 PM   #127
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Originally Posted by smartcooky View Post
The "NASA" rocket equation? I thought it was the Tsiolkovsky rocket equation.

Oh, I get it.... Tsiolkovsky was "in on it", a NASA shill, 62 years before NASA was even established.
I think "NASA" means he got that equation from NASA. Tsiolkovsky's equation is different and almost (but not entirely) unrelated. Tsiolkovsky's rocket equation is about total delta-V; thrust is merely implied because without thrust, the specific impulse would always be 0.
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Old 17th April 2019, 12:14 PM   #128
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Originally Posted by dasmiller View Post
I think "NASA" means he got that equation from NASA. Tsiolkovsky's equation is different and almost (but not entirely) unrelated. Tsiolkovsky's rocket equation is about total delta-V; thrust is merely implied because without thrust, the specific impulse would always be 0.
Oh, OK

I didn't bother reading his attachment. Its sideways, and I have a sore neck this morning.
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Old 17th April 2019, 12:18 PM   #129
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Originally Posted by smartcooky View Post
I didn't bother reading his attachment. Its sideways, and I have a sore neck this morning.
tl;dr "I can substitute this for that." Refuation: No, you can't. They are dissimilar concepts.
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Old 17th April 2019, 12:35 PM   #130
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Maybe this should be moved to the Science section here, since that seem to be the place for crackpot science theories. I am not denying there is a conspiracy angle, but overall I think this should be dealt with as crackpot science.
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Old 17th April 2019, 12:39 PM   #131
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Originally Posted by dasmiller View Post
I think "NASA" means he got that equation from NASA. Tsiolkovsky's equation is different and almost (but not entirely) unrelated. Tsiolkovsky's rocket equation is about total delta-V; thrust is merely implied because without thrust, the specific impulse would always be 0.
Yes but it requires fuel mass turned into gas mass to achieve that delta v.
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Old 17th April 2019, 12:45 PM   #132
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Originally Posted by bknight View Post
Yes but it requires fuel mass turned into gas mass to achieve that delta v.
Tsiolkovsky's rocket equation doesn't assume gas at all, merely that mass is ejected to create thrust (e.g. there's reaction mass). The Rocket Equation works just fine if, instead of thrusters, you have little slingshots firing mass slugs, or you're using a water rocket
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Old 17th April 2019, 12:52 PM   #133
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We did an design exercise once to see whether you could pee with enough thrust to lift yourself off an asteroid.
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Old 17th April 2019, 12:53 PM   #134
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The thing is, NASA (and other private companies) live-stream the launches, then afterwards the whole thing is available to view on youtube.

For instance, Northrop Grumman are sending up an Antares resupply mission to the ISS, launching in about 40 minutes from now. You can watch the live stream now, here.

https://www.rocketlaunch.live/?filter=northrop-grumman

They are prepping the rocket now, and you can actually watch it all the way up from 0m above ground to space. Go and look!
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Old 17th April 2019, 12:55 PM   #135
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Originally Posted by dasmiller View Post
Tsiolkovsky's rocket equation doesn't assume gas at all, merely that mass is ejected to create thrust (e.g. there's reaction mass). The Rocket Equation works just fine if, instead of thrusters, you have little slingshots firing mass slugs, or you're using a water rocket
Fair enough I was attempting to put it into terms our OP might grasp.

https://en.wikipedia.org/wiki/Tsiolk...ocket_equation
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Old 17th April 2019, 01:04 PM   #136
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Well one good thing has come from this thread. I’ve obviously accepted that rockets work in space, but I’ve never taken the time to understand how. Now I have a much better understanding, so thanks to Jay and others.
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Old 17th April 2019, 01:04 PM   #137
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Originally Posted by JayUtah View Post
We did an design exercise once to see whether you could pee with enough thrust to lift yourself off an asteroid.
Don't leave us hanging, what was the result?
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Old 17th April 2019, 01:06 PM   #138
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Originally Posted by bknight View Post
Fair enough I was attempting to put it into terms our OP might grasp.
Ah, a worthy challenge.

And I suppose I was being a bit pedantic; offhand I don't know of any real-world space propulsion systems* that aren't arguably using gas** for reaction mass.

*Not including propulsion systems that don't have a traditional reaction mass, e.g. lightsails or clever ways to push off Earth's magnetic field.

**in this context, "gas" includes traditional gas (e.g. N2), plasma, and streams of ionized noble gasses.
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Old 17th April 2019, 01:06 PM   #139
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Originally Posted by cow_cat View Post
The thing is, NASA (and other private companies) live-stream the launches, then afterwards the whole thing is available to view on youtube.

For instance, Northrop Grumman are sending up an Antares resupply mission to the ISS, launching in about 40 minutes from now. You can watch the live stream now, here.

https://www.rocketlaunch.live/?filter=northrop-grumman

They are prepping the rocket now, and you can actually watch it all the way up from 0m above ground to space. Go and look!
Watched an Antares launch in the wee small hours once. The Wallops visitor center parking lot was full at 2 AM, and people were off parking on the roadside.
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Old 17th April 2019, 01:15 PM   #140
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Originally Posted by dasmiller View Post
Ah, a worthy challenge.

And I suppose I was being a bit pedantic; offhand I don't know of any real-world space propulsion systems* that aren't arguably using gas** for reaction mass.

*Not including propulsion systems that don't have a traditional reaction mass, e.g. lightsails or clever ways to push off Earth's magnetic field.

**in this context, "gas" includes traditional gas (e.g. N2), plasma, and streams of ionized noble gasses.
I'm not an aerospace engineer, but rather an inner space engineer, so some of these calculations are new to me, but I understand the math, although I'm quite sure I couldn't solve them.

I didn't take offense at your correction, BTW.
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Old 17th April 2019, 01:19 PM   #141
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Originally Posted by sts60 View Post
Watched an Antares launch in the wee small hours once. The Wallops visitor center parking lot was full at 2 AM, and people were off parking on the roadside.
Looking at te launch pad with the bay/ocean on the right, where is the parking lot?
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Old 17th April 2019, 01:23 PM   #142
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Originally Posted by Gingervytes View Post
And gas moving out of the chamber is due to pressure gradient force
Yes. Pressure. The pressure accelerates the gas out. Where is the other side of that pressure?

Hans
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Old 17th April 2019, 01:32 PM   #143
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Originally Posted by MRC_Hans View Post
Yes. Pressure. The pressure accelerates the gas out. Where is the other side of that pressure?

Hans
Is there pressure still pushing. Let us put an object on a scale and pick it up with a vacuum, why is there no opposite force on the scale?
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Old 17th April 2019, 01:33 PM   #144
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Old 17th April 2019, 01:34 PM   #145
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Originally Posted by Gingervytes View Post
Let us put an object on a scale and pick it up with a vacuum, why is there no opposite force on the scale?
Because gravity and thrust aren't the same thing.
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Old 17th April 2019, 01:37 PM   #146
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Btw. the atmospheric pressure actually plays role. It lowers efficiency of rocket engine, as the speed through the nozzle depends on difference between pressures inside the engine and outside. If there was enough outside pressure, the gasses would just stay inside, and no work would be done.
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Old 17th April 2019, 01:38 PM   #147
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Originally Posted by Dr.Sid View Post
Btw. the atmospheric pressure actually plays role. It lowers efficiency of rocket engine, as the speed through the nozzle depends on difference between pressures inside the engine and outside. If there was enough outside pressure, the gasses would just stay inside, and no work would be done.
Shill. Who's lining your pockets?

No seriously who. I want in.
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Old 17th April 2019, 01:40 PM   #148
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Originally Posted by Gingervytes View Post
Is there pressure still pushing. Let us put an object on a scale and pick it up with a vacuum, why is there no opposite force on the scale?
Why should there be? Anyway, irrelevant. Stay on topic:

The gas is accelerated out of the rocket by pressure. Pressure is a force. Where is the opposing force to the pressure?

... I'll save some iterations (and predictable diversions) by answering the question. The force acts in two directions:

1) Against the gas, which is accelerated and leaves the rocket. What happens to the gas afterwards is essentially irrelevant.

2) Opposite, against the bottom of the combustion chamber. The force of this pressure is what propels the rocket.

(actually it works in all directions, against the side walls of the chamber, but these forces cancel out.)

Hans
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Old 17th April 2019, 01:41 PM   #149
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Don't do it. Don't get drug down into nitpicking the details when the core argument is fundamentally flawed.

He's trying to Jabba us.
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Old 17th April 2019, 01:42 PM   #150
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Don't believe rockets work in a vacuum?

Watch the demo

YouTube Video This video is not hosted by the ISF. The ISF can not be held responsible for the suitability or legality of this material. By clicking the link below you agree to view content from an external website.
I AGREE
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Old 17th April 2019, 01:46 PM   #151
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Originally Posted by sts60 View Post
Watched an Antares launch in the wee small hours once. The Wallops visitor center parking lot was full at 2 AM, and people were off parking on the roadside.
Very nice. I only ever saw one launch, of Shuttle STS111 from a friend's place across the river. Wallops looks like a very nice place to observe from.

But of course none of this ever happened because rockets are a lie. Or some such thing...
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Old 17th April 2019, 02:16 PM   #152
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Originally Posted by Gingervytes View Post
Too ignorant to even try understanding the argument
maybe the problem is in your argument that perhaps you can not express clearly, dasmiller has great comprehension, perhaps you should try to actually explain your self in more than sound bytes.
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Old 17th April 2019, 02:17 PM   #153
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Originally Posted by phunk View Post
Don't leave us hanging, what was the result?
Yeah, some real science is neede here.
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Old 17th April 2019, 02:24 PM   #154
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Originally Posted by bknight View Post
Looking at te launch pad with the bay/ocean on the right, where is the parking lot?
Iím not quite sure I understand your perspective, but the visitor center is north of the pad.
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Old 17th April 2019, 02:25 PM   #155
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Originally Posted by Gingervytes View Post
Is there pressure still pushing. Let us put an object on a scale and pick it up with a vacuum, why is there no opposite force on the scale?
Nope. Answer the questions and rebuttals already put to you.
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Old 17th April 2019, 02:31 PM   #156
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Originally Posted by Gingervytes View Post
Is there pressure still pushing. Let us put an object on a scale and pick it up with a vacuum, why is there no opposite force on the scale?
Gravity isn't a sort of thrust.

The thing is, you can do these experiments of thrust yourself. There are places where they can damn near make vaccuums for you, and you can find some pressurised container, make a whole in it, and see it move.

So why are you wasting time on web forums rather than testing your idea?
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Old 17th April 2019, 02:34 PM   #157
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Originally Posted by smartcooky View Post
Don't believe rockets work in a vacuum?

Watch the demo

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I AGREE
Well small engines MAYBE, but what about the big ones, ha ? You can't even fit them in vacuum this small.
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Old 17th April 2019, 02:37 PM   #158
JayUtah
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Originally Posted by Gingervytes View Post
Let us put an object on a scale and pick it up with a vacuum, why is there no opposite force on the scale?
Because gravity and momentum are two different kinds of things. None of your would-be analogies has the slightest to do with how rockets actually work. It's just a bunch of cargo-cult nonsense.
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Old 17th April 2019, 02:55 PM   #159
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Originally Posted by Belz... View Post
Gravity isn't a sort of thrust.
Nor is mechanical traction, although if you pull hard on something it will pull back. If instead of placing an object on a scale and pulling upward, you place a spring scale between an object and the hoist, the scale will register an increase in load as you begin to pull. This is inertial reaction, which combines with gravity to produce the scale reading. This is why crane operators take care not to lift speedily. The cable and tackle may well support the load's static weight, but not the additional dynamic force you might apply by starting and stopping the load abruptly.

Lifting something off a scale by drawing it upward into a vacuum immediately severs the coupling between the object and the scale. That much is obvious. However, put a giant scale underneath a rocket and measure the impingement force of its exhaust, and you will continue to get a reading as the rocket lifts off and stops weighing down the scale.

Quote:
So why are you wasting time on web forums rather than testing your idea?
Or collecting his Nobel prize in physics for having toppled Newton's laws of motion.
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Old 17th April 2019, 03:16 PM   #160
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Here, just for grins, is a seriously similar thread at Cosmoquest, where we miss Jay Utah.
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