3 ms·

> so the expansion curve of the nozzile is made to direct exhaust directly aft with no further expansion. Exactly the opposite. The gasses will INFINITELY expa

> so the expansion curve of the nozzile is made to direct exhaust directly aft with no further expansion. Exactly the opposite. The gasses will INFINITELY expand as the atmospheric pressure on the Moon is for all intents and purposes exactly zero. > Engines are designed to extract maximum energy from the propellant, so the expansion curve of the nozzile is made to direct exhaust directly aft with no further expansion. Engines are NOT designed to extract maximum energy. Engines are designed for COMPROMISE between extracting maximum energy and other parameters like mass of the rocket. For example, the engine could extract more energy from the propellant if the bell was larger. But that would make it also heavier and would reduce the performance of the rocket as a system. Another example, part of the fuel is wasted to create screen to protect the engine from overheating. It is injected on the sides of the engine and does not burn. This waste is a planned compromise because better cooling mechanism would be much heavier and so wasting a little bit of fuel is best way to improve total performance of the rocket. > Youd' inject these into the nozzle further enough down that they go directly down and out, not to the sides. (...) You can design it so that virtually none of the material ever hits the nozzle walls No, you can't. You mister, need to learn some physics. The way engine works is by creating pressure. That pressure acts on the bell (the sides) and transfers to the rocket. The "sides" aren't there to ornament the rocket, they serve a very important purpose as they are the surfaces which direct the exhaust back and on which the pressure of the gasses act to propel the rocket. None of these two important roles can be fulfilled without the gasses actually pressing on them. The vacuum regime isn't any different. There is positive pressure within the bell and this propels the rocket forward as the gasses expand backwards. If you injected (ejected) fuel directly down and out you would get pitiful thrust the likes of your bottle of coke gets when a mint is dropped in it. There are engines that do what you describe (ion engines) but they work in a very different way.

dang 5y ago
> You mister, need to learn some physics. Please edit personal swipes out of your comments here. It's not what this site is for, and it destroys what it is for. If you wouldn't mind reviewing https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html and taking the intended spirit of the site more to heart, we'd be grateful.
- lmilcin 5y ago
  This is as a response to absolute bonkers explanation to how a rocket engine works. I tried to keep good ratio of actual factual explanation to "swipes", which I think was fully deserved. Sometimes, somebody needs to at least hint you you are telling complete and utter rubbish (ideally backed by some explanation). Now, I don't want to say everybody has to know physics or how an engine works. But if you are starting to explain to people on HN, be ready to get fact-checked. You need to learn some.
  - dang 5y ago
    You can't take that kind of potshot at people regardless of how bonkers their explanation was or you feel it was. Aggression in your reply is much more significant than inaccuracy in the other comment. This is a big deal, because everyone underestimates the negativity of their own comments by (let's say) 10x and overestimates the negativity in other people's comments by another 10x. That makes for a 100x perception gap. This causes people who aren't being careful to blast bile into the the ecosystem here—something that, long term, leads to its destruction. Therefore we all need to be careful. Maybe you don't owe people who know less physics than you better, or don't feel you do, but you owe this community better if you're participating in it. Here's what to do instead: if someone else is wrong, and you know more than they do, then patiently provide correct information. Otherwise don't post; or, alternatively, chalk it up to someone being wrong on the internet and just don't post. Punishing the other person, or strutting your stuff superciliously, does not engage curiosity, and isn't conducive to learning nor to curious conversation. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
  - burnte 5y ago
    I said nothing incorrect, you misunderstood what I was talking about, presumably due to not reading the article we're commenting on. Do you really think I'm wrong saying that fuel is burned and directed out an exhaust nozzle to impart force in the opposite direction of the flow? Am I wrong that the bell is designed to capture as much energy as possible (within constraints) by directing the flow in a single direction? Here's a 5 year old youtube video deascribing it the exact same way: https://youtu.be/l5l3CHWoHSI?t=32 https://youtu.be/l5l3CHWoHSI?t=32 I have absolutely no problem being corrected, but please don't be wrong in your correction, and don't do it with such attitude. You're agressively wrong here.
burnte 5y ago
Oooooook... So we start off with misinformation and insults. The problem here is you think I don't know what I'm talking about, and that's not a good assumption. And you're being overly pedantic in order to find flaws in what should be an ordinary conversation. 1. Yes, the gas will expand indefinitely eventually. That doesn't change anything about the way nozzle's are designed. 2. Obviously everything has cost constraints. That doesn't change the fact that within financial and material limits, you want to extract all the energy possible. A larger bell does not equal mor energy in all cases. In fact, once you have your exhaust in a non-expanding perpendicular flow, there's nothing left to extract. Alfo, fuel is run through tubing around the bell to cool it down, it's not generally wasted to be coolant, you use pumps to run it through tubes in the bell to cool the bell, heat up the fuel, and that adds pressure to the fuel as it then cycles back up and exists into the reaction chamber. 3. Yes, you 100% can design your injector to not make the material not impact the bell. I said sides to indicate where I'm talking about, no need to mock a simple word choice, I never said they were ther for ornamentation, so you're just being rude. 4. Just because exhaust has a presure doesn't mean every particle impacts the bell, or you'd have a ring of exhaust flow with nothing in the center. You can inject your material so that it flows down the center. Note, I'm talking about the ceramic material injected into the flow as described in the article, NOT THE FUEL. I think you think I'm talking about fuel this entire time, which is not correct. 6. Yes, you just explained how a rocket works in the same way I did after trying to tell me how stupid I am. 7. I was talking abut the ceramic material injected into the flow, not the engines. Nothing I described applies to ion engines. Please mke sure you understand the comment before you rup into someone.

dang 5y ago

> You mister, need to learn some physics. Please edit personal swipes out of your comments here. It's not what this site is for, and it destroys what it is for. If you wouldn't mind reviewing https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html and taking the intended spirit of the site more to heart, we'd be grateful.

lmilcin 5y ago
This is as a response to absolute bonkers explanation to how a rocket engine works. I tried to keep good ratio of actual factual explanation to "swipes", which I think was fully deserved. Sometimes, somebody needs to at least hint you you are telling complete and utter rubbish (ideally backed by some explanation). Now, I don't want to say everybody has to know physics or how an engine works. But if you are starting to explain to people on HN, be ready to get fact-checked. You need to learn some.
- dang 5y ago
  You can't take that kind of potshot at people regardless of how bonkers their explanation was or you feel it was. Aggression in your reply is much more significant than inaccuracy in the other comment. This is a big deal, because everyone underestimates the negativity of their own comments by (let's say) 10x and overestimates the negativity in other people's comments by another 10x. That makes for a 100x perception gap. This causes people who aren't being careful to blast bile into the the ecosystem here—something that, long term, leads to its destruction. Therefore we all need to be careful. Maybe you don't owe people who know less physics than you better, or don't feel you do, but you owe this community better if you're participating in it. Here's what to do instead: if someone else is wrong, and you know more than they do, then patiently provide correct information. Otherwise don't post; or, alternatively, chalk it up to someone being wrong on the internet and just don't post. Punishing the other person, or strutting your stuff superciliously, does not engage curiosity, and isn't conducive to learning nor to curious conversation. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
- burnte 5y ago
  I said nothing incorrect, you misunderstood what I was talking about, presumably due to not reading the article we're commenting on. Do you really think I'm wrong saying that fuel is burned and directed out an exhaust nozzle to impart force in the opposite direction of the flow? Am I wrong that the bell is designed to capture as much energy as possible (within constraints) by directing the flow in a single direction? Here's a 5 year old youtube video deascribing it the exact same way: https://youtu.be/l5l3CHWoHSI?t=32 https://youtu.be/l5l3CHWoHSI?t=32 I have absolutely no problem being corrected, but please don't be wrong in your correction, and don't do it with such attitude. You're agressively wrong here.

burnte 5y ago

Oooooook... So we start off with misinformation and insults. The problem here is you think I don't know what I'm talking about, and that's not a good assumption. And you're being overly pedantic in order to find flaws in what should be an ordinary conversation. 1. Yes, the gas will expand indefinitely eventually. That doesn't change anything about the way nozzle's are designed. 2. Obviously everything has cost constraints. That doesn't change the fact that within financial and material limits, you want to extract all the energy possible. A larger bell does not equal mor energy in all cases. In fact, once you have your exhaust in a non-expanding perpendicular flow, there's nothing left to extract. Alfo, fuel is run through tubing around the bell to cool it down, it's not generally wasted to be coolant, you use pumps to run it through tubes in the bell to cool the bell, heat up the fuel, and that adds pressure to the fuel as it then cycles back up and exists into the reaction chamber. 3. Yes, you 100% can design your injector to not make the material not impact the bell. I said sides to indicate where I'm talking about, no need to mock a simple word choice, I never said they were ther for ornamentation, so you're just being rude. 4. Just because exhaust has a presure doesn't mean every particle impacts the bell, or you'd have a ring of exhaust flow with nothing in the center. You can inject your material so that it flows down the center. Note, I'm talking about the ceramic material injected into the flow as described in the article, NOT THE FUEL. I think you think I'm talking about fuel this entire time, which is not correct. 6. Yes, you just explained how a rocket works in the same way I did after trying to tell me how stupid I am. 7. I was talking abut the ceramic material injected into the flow, not the engines. Nothing I described applies to ion engines. Please mke sure you understand the comment before you rup into someone.