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17th April 2019, 11:46 AM | #121 |
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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. |
17th April 2019, 11:48 AM | #122 |
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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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17th April 2019, 12:05 PM | #124 |
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17th April 2019, 12:07 PM | #125 |
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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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17th April 2019, 12:12 PM | #127 |
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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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17th April 2019, 12:14 PM | #128 |
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If you're not a scientist but you think you've destroyed the foundation of a vast scientific edifice with 10 minutes of Googling, you might want to consider the possibility that you're wrong. Its TRE45ON season... convict the F45CIST!! |
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17th April 2019, 12:18 PM | #129 |
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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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17th April 2019, 12:39 PM | #131 |
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17th April 2019, 12:45 PM | #132 |
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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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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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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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17th April 2019, 12:55 PM | #135 |
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Fair enough I was attempting to put it into terms our OP might grasp.
https://en.wikipedia.org/wiki/Tsiolk...ocket_equation |
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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17th April 2019, 01:04 PM | #137 |
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17th April 2019, 01:06 PM | #138 |
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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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17th April 2019, 01:06 PM | #139 |
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17th April 2019, 01:15 PM | #140 |
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17th April 2019, 01:19 PM | #141 |
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17th April 2019, 01:23 PM | #142 |
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17th April 2019, 01:32 PM | #143 |
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17th April 2019, 01:33 PM | #144 |
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"If NASA was willing to fake great accomplishments they'd have a second one by now." - xkcd.
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17th April 2019, 01:34 PM | #145 |
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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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17th April 2019, 01:38 PM | #147 |
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17th April 2019, 01:40 PM | #148 |
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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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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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17th April 2019, 01:42 PM | #150 | |||
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Don't believe rockets work in a vacuum?
Watch the demo
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17th April 2019, 01:46 PM | #151 |
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17th April 2019, 02:16 PM | #152 |
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17th April 2019, 02:17 PM | #153 |
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17th April 2019, 02:24 PM | #154 |
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17th April 2019, 02:25 PM | #155 |
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17th April 2019, 02:31 PM | #156 |
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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? |
17th April 2019, 02:34 PM | #157 |
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17th April 2019, 02:37 PM | #158 |
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17th April 2019, 02:55 PM | #159 |
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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:
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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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