Comments by "H. de Jong" (@h.dejong2531) on "" video.

  1.  @papalegba6796  His work is reporting on how space agencies do this. There's no need for Scott to build a test stand himself.
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  2.  @papalegba6796  You're still thinking the pressure inside a rocket engine is zero?
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  3.  @papalegba6796  It does. Not my problem if you can't recognize a free body diagram when you see one.
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  4.  @papalegba6796  "rockets don't work in a vacuum" is a lie, yes.
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  5.  @papalegba6796  As you have been told before: Both free-body diagrams and work calculations demonstrate that rockets work in a vacuum. Your assumption that the pressure in the combustion chamber is zero is incorrect. Look up at night, see satellites pass overhead in the vacuum of space, and know your claims have been disproven again.
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  6.  @papalegba6796  And yet thousands of rockets have been launched to a vacuum after being tested in these vacuum test chambers.
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  7.  @Nehner  You never get tired being wrong, do you?
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  8. This is your lucky day. Fran Blanche published a video showing exactly what you want.
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  9.  @papalegba6796  imagine being on Youtube and not recognizing a video ID (last part of the video URL).
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  10.  @papalegba6796  Again, your ignorance is showing. There are 3 mechanisms for transferring heat: conduction, convection and radiation. Conduction requires contact with a second object. Convection requires an atmosphere. Radiation works fine in a vacuum. Radiation is the reason the lunar surface cools down during the lunar night.
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  11. That is incorrect. Rockets work fine in a vacuum, as is demonstrated by the satellites I can see in the sky.
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  12. Everything Scott said is verifiable reality. You are living in denial.
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  13. kAZMBAVRsCo
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  14. The command module and lunar module used reflective surfaces to reduce the amount of heat coming in from sunlight. They used insulation to avoid losing lots of heat to space (thermal radiation). These two were balanced to keep the interior of the craft at habitable temperatures with minimal need for heating or cooling. This worked well for most missions, but became a problem on Apollo 13: most of the electronics in the CM were shut down, which meant less heat was coming into the cabin than planned, and the interior got cold. The LM used sublimation cooling to reject waste heat: a closed cooling loop led to a radiator in an unpressurized compartment. Water was sprayed onto this radiator. This would freeze, then sublimate and carry away heat. The LM thermal design was good enough that they only needed a few litres of water per day. The space suits used a similar system. The heat of the LM descent engine was directed downwards as much as possible, using a heat shield. This was enough during descent. After landing, the remaining heat would warm up the surroundings of the engine. They vented the remaining propellant, which carried away that heat. The ascent engine used a similar approach, with heat shielding around the engine.
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  15.  @papalegba6796  We can test how heat transfer works in a vacuum: scientists worked this all out centuries before we could go to space, by doing heat transfer experiments in a vacuum chamber. I can see the ISS with the naked eye, and I can prove it is in space and not in our atmosphere. This disproves your claim that "nobody has been there".
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  16.  @papalegba6796  Yes, they have. We can verify this by looking up: satellites in low orbits can be visible to the naked eye. We can measure their speed and altitude from the ground. When I aim a dish antenna at a point 36,000 km above the equator, I can receive TV signals from geostationary satellites.
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  17. The effect of varying G levels is limited, and can be simulated by changing the pressure in the propellant tanks. So the moon lander engines could be tested on a test stand. An all-up flight test of the moon lander was not possible on Earth, but was done in Earth orbit.
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  18.  @papalegba6796  It is exactly in accordance with Newton's laws. It's the force diagram you have been asking for. And it is proven to work by 10,000 satellites successfully operating in orbit.
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  19. You are showing your ignorance again. 1. The metals used in rocket nozzles are far stronger in tension than in compression. So when the engine is at high altitude and the pressure inside the nozzle is higher than outside, the nozzle is in tension. It's designed to be strong enough to take the loads in this configuration. When you try to test a high-altitude engine down at sea level, the atmospheric pressure outside is higher than inside the nozzle, and the nozzle is now in compression. This is no different in principle than a coke can: when the can is full, it is strong enough to stand on. When it's empty, the can is no longer in tension and I can flatten it with my hand. 2. There are no rockets in use today where the second stage weighs 3000 tons. The Saturn V is the largest, and its third stage plus payload weighed less than 200 tons. 3. A gas that is at a higher pressure than its surroundings exerts a force on its surroundings.
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  20. Combustion does work in space. You just have to provide the oxidiser along with the fuel. Every rocket carries two tanks, one for the oxidiser and one for the fuel. These are mixed in the combustion chamber, and they combust very well indeed.
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  21. I can look at the sky and see satellites pass overhead. I can measure their speed and position, proving they are in orbit, not in our atmosphere.
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  22. The nozzle diameter depends on the ambient atmosphere. Lower pressure = you can make the nozzle larger. And you want that, because what pushes the rocket is the force exerted by the exhaust on the rocket: on the front wall of the combustion chamber, and on the nozzle. Make the nozzle larger = more of the exhaust pushes on the nozzle.
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  23. NASA is advancing the state of the art in multiple scientific disciplines every year. It has enabled us to start using space for commercial purposes, which have paid back our investment in NASA many times over.
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  24. A rocket works by pushing against its own exhaust. Action: burn some propellant, which pushes with equal force in all directions. In once direction, the rocket engine is in the way, so this force is applied to the rocket. In the other direction, nothing is in the way, so the force goes into the gas molecules from the exhaust flying away at high speed. You can try this at home: stand on a skateboard, and throw something heavy. You will move in the direction opposite to where you threw that ball.
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  25. You generally avoid running the engines in zero G: before the main engine is started, a small ullage thruster provides enough thrust to settle the propellants at the bottom of the tank so the main engine can start.
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  26. You mean the Bernoulli effect?
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  27.  @papalegba6796  A rocket engine is less efficient at sea level than at high altitude. The difference is caused by the ambient air pressure. Let that sink in: when the rocket exhaust gases have to push against the atmosphere, the rocket gets less efficient.
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  28.  @papalegba6796  w=PV applies to closed systems that change slowly (quasi-static). It's useful for piston-driven steam engines, not so much for rockets.
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  29.  @papalegba6796  A rocket in a vacuum is obviously not a closed system: the exhaust gas leaves the system.
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  30.  @papalegba6796  You mean 'real physics, except the bits I'm ignoring because they don't fit my worldview'.
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  31.  @papalegba6796  Yes, that is exactly what a closed system means.
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  32.  @TheJudyStroyer  All over YT you can find videos of satellites passing overhead. ISS, Starlink trains etc.
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