[HN Gopher] Engine cooling - why rocket engines don't melt ___________________________________________________________________ Engine cooling - why rocket engines don't melt Author : wolfram74 Score : 295 points Date : 2022-01-13 15:49 UTC (7 hours ago) (HTM) web link (everydayastronaut.com) (TXT) w3m dump (everydayastronaut.com) | Animats wrote: | Making rocket engines by metal 3D printing has become popular. A | rocket engine bell and combustion chamber has one big rigid part | with lots of channels and voids inside. That's the ideal case for | 3D printing. Much simpler than building the thing up by machining | and welding together many individual parts. | avmich wrote: | There are different problems with 3D printing than with | classical subtractive manufacturing. E.g. you need to get the | supporting powder out of long thin passages in the cooling | chamber - you don't have such problem with milling machine | approach. | m4rtink wrote: | I remember reading in an article that without 3D printing they | could simply not get the cooling channel geometry they needed | on the Super Dracos on Dragon 2. | | Without 3D printing the combustion chamber they would need to | use other cooling channel geometry, makin ghr engine heavier, | bigger and less efficient. | ortusdux wrote: | One of my favorite bits from Tim's videos was during a tour of | Firefly Aerospace's facility when they talk about engine cooling. | They discuss EDM machining small holes into the coolant channels | just before the throat, which lets a small amount of cryogenic | coolant out to cool the interior. The funny part is that you can | purposefully undersize the holes and they will melt larger until | they are big enough to adequately cool the engine. You basically | pre-season the engine with a test-fire and let it choose how much | internal cooling it needs. | | https://youtu.be/ac-V8mO0lWo?t=2203 | jamesmunns wrote: | This is just a really clearly written introduction of a lot of | rocket engine concepts. | | It was a super good read. | mountainwalker wrote: | Tim's videos are always so well done! Even if you're not a rocket | enthusiast there's tons to get out of this video. | throwaway894345 wrote: | Agreed. Tim was an old friend of mine in university, but we | lost touch over the years. He was always a good, quirky, | creative, and talented guy. He bought an old cosmonaut suit on | ebay on a lark and started doing funny/silly photo shoots with | it and then photo shoots at rocket launches and then real | educational stuff. It's been wild to see it take off (pun | intended). | bernulli wrote: | Minor nitpick: fluids are not either liquids or gases, this is | particularly true for rocket engines where many of the discussed | processes (injection, compression, regenerative coolant flow) | actually occur at super- or transcritical conditions. | | Also, I don't think you can say the faceplate is heat sink- | cooled. Remember that just behind it is the propellant manifold, | so it's rather some form of regenerative cooling. | jpm_sd wrote: | Ignorant question: are solid-fueled rockets at all interesting, | anymore? Do they have any advantages (e.g. simplicity of design) | over the fancy throttle-able liquid-fueled engines? | anarazel wrote: | Depends on the purpose. E.g. for military uses like ICBMs | they're quite important... | evo wrote: | I suspect their primary advantage remains shelf-stability at | room temperatures, which will make them stay relevant for | military applications, e.g. you don't want a cryogenics | facility in your submarine or cruise missile launch platform. | | Historically, I think they're cheaper than an equivalent | disposable liquid fueled engine but don't hold up to the fully | reusable designs of today, and from a reliability perspective | there's not a lot of room between working-as-intended and | "activate the flight termination system" at a total loss. | Terr_ wrote: | > I suspect their primary advantage remains shelf-stability | at room temperatures, which will make them stay relevant for | military applications | | I while ago I read--but barely understood--a book that went | into a lot of this: "Ignition! An Informal History of Liquid | Rocket Propellants" by John D. Clark. | | _____________________ | | IIRC there were some cases where a fuel was not militarily- | acceptable because you would need to warm/thaw the mobile | missile prior to firing in a Russian winter, or other cases | where a permanent missile-silo meant it was cost-effective to | run heating/refrigeration all the time, etc. | | > [I]n applications which do not require a low freezing | point, hydrazine itself is fused, either straight or mixed | with one of its derivatives. The fuel of the Titan II ICBM | doesn't have to have a low freezing point, since Titan II | lives in a steam-heated hole in the ground, but it does need | the highest possible performance, and hydrazine was the first | candidate for the job. | | _____________________ | | Another fuel-choice issue involves how badly it might self- | destruct if anything unusual happened: | | > [I]n the summer of 1960, we tried to fire a 10,000-pound | thrust Cavea B motor. [...] Well, through a combination of | this and that, the motor blew on startup. We never discovered | whether or not the [detonation] traps worked--we couldn't | find enough fragments to find out. | | > The fragments from the injector just short-circuited the | traps, smashed into the tank, and set off the 200 pounds of | propellant in that. (Each pound of propellant had more | available energy than two pounds of TNT.) I never saw such a | mess. The walls of the test cell--two feet of concrete--went | out, and the roof came in. The motor itself--a heavy, | workhorse job of solid copper-- went about 600 feet down | range. And a six-foot square of armor plate sailed into the | woods, cutting off a few trees at the root, smashing a | granite boulder, bouncing into the air and slicing off a few | treetops, and finally coming to rest some 1400 feet from | where it started. The woods looked as though a stampeding | herd of wild elephants had been through. | | > As may be imagined, this incident tended to give | monopropellants something of a bad name. Even if you could | fire them safely--and we soon saw what had gone wrong with | the ignition process--how could you use them in the field? | | > Here you have a rocket set up on the launching stand, under | battlefield conditions; and what happens if it gets hit by a | piece of shrapnel? LRPL came up with the answer to that. You | keep your monoprop in the missile in two compartments: one | full of fuel-rich propellant made up to A. = 2.2 or 2.4, and | the other containing enough acid to dilute it to X = 1.2. | Just before you fire, a can-opener arrangement inside the | missile slits open the barrier separating the two liquids, | you allow a few seconds for them to mix, and then push the | button. | j8asic wrote: | Not really. Gel propellants are a new direction. | jandrese wrote: | They are useful when you need a rocket that can take off at a | moments notice but sit idle for decades at a time. For typical | rocket launches they don't make much sense. | | I suspect the Space Shuttle SRBs were chosen because they were | a handout to ICBM manufacturers. | dylan604 wrote: | Depends on your definition of "interesting". If you mean do | people still use them for practical purposes, then yes they | are. If you mean are people still researching them for use in | exploring space, then probably not. | Robotbeat wrote: | Extremely simple (basically just one big rocket combustion | chamber with the propellant already inside, no pumps or | plumbing) and shelf storable and potentially extremely high | thrust to weight ratio. | | Useful for munitions and for one-time-use. I'd like to think | we're going to reusable rockets and not as much war, so I'd | LIKE to think they have fewer uses, but... | opwieurposiu wrote: | This thing I can not comprehend about rocket engines is how the | turbopump manages to hold together. | | A turbine blade in the SSME about the size of your thumb makes | 600 horsepower. | | https://www.enginehistory.org/Rockets/SSME/SSME6.pdf | VBprogrammer wrote: | If that interests you then this series of videos is definitely | worth watching. It details several parts of the German V2 | missile, the grand father of all modern liquid propellant | rockets. This one is about the turbopump which is one of the | most interesting parts. | | https://youtu.be/EgiMu8A3pi0 | kunai wrote: | It is pretty mind-boggling. Makes the average turbofan's | turbine assembly look like child's play, and those are also | pretty ridiculous in terms of power-to-weight ratio. | HPsquared wrote: | It's mostly because the working fluid is at very high | pressure (much denser than the air coming through an aero | engine). The turbine side works with hot gas at 100+ bar, and | the pump side is dealing with liquid. Therefore small parts | can exert a lot of force (large pressure differences) and do | a lot of work (high speeds). | | The most similar technology is a boiler feed pump (used to | feed the boilers in a steam turbine system, e.g. in a ship or | power station) - these work in a similar way, high pressure | steam is bled off from the system to drive a small turbine, | which drives a high pressure pump to feed the boiler, which | feeds the 'main' steam turbine. Similar pressure (>100 bar), | but the turbine on the rocket engine needs to handle much | higher temperatures (hot gas rather than steam). | bernulli wrote: | Also try to imagine the thermal stresses when you have | cryogenic propellants on the pump side and hot exhaust gases | (gas generator or staged combustion) on the turbine side! | jaywalk wrote: | Well, 63 blades together make 600 horsepower. But as that paper | notes, each blade is subject to 50,000 psi which is wild. | jhgb wrote: | 600 horsepower _each_. The whole turbine has tens of | megawatts of mechanical power output. | jaywalk wrote: | Yep, you are correct. I misread. | TylerE wrote: | It is wild, but not as wild as you might think. | | The fuel rail in a modern diesel engine is operating at | 25-30,000 psi all the time. | HPsquared wrote: | I the power level of these engines is difficult to comprehend. | The _fuel pump_ has thousands of horsepower. Compare this to | the fuel pump on a car engine, which is a tiny little electric | thing. The combustion power must be in the gigawatt range. | | Edit: the SSME high pressure fuel pump turbine produces 63000 | hp (46 MW). There's also one for the oxygen, and a pair of low | pressure pumps as well. Crazy... | | Edit edit: the fuel pump transfers 155 lb/sec of liquid | hydrogen. If fully combusted (142 MJ/kg), that would release | 10.0 GW of heat per engine. | skykooler wrote: | This is why electric turbopumps (like those used on | RocketLab's Electron rocket) don't scale up to larger rockets | well - the power draw is just infeasible to support with | current battery technology. | Robotbeat wrote: | Not quite. Electric pumps scale just fine (that is, | linearly), but turbopumps scale better. It's hard to build | a very small turbopump but not much harder to build a | larger one, and turbopumps improve in efficiency as they | get larger. BTW, the largest electropump (4 times that of | RocketLab's Rutherford electropump engine) for a rocket | engine is the electropump for the 100kN (10 ton) thrust | rocket engine for the reusable crewed suborbital Spica | space rocket by the volunteer-run Copenhagen Suborbitals | group, which more people ought to know about: | | https://twitter.com/CopSub/status/1468280164404666373?s=20 | sephamorr wrote: | The major issue is the energy storage, not the power | plant itself. The penalty of the battery mass scales far | worse than a tank holding very energy dense rocket | propellant. | Robotbeat wrote: | Again, the energy storage scales just fine: linearly. | Rocket propellant tends to scale better than linear, but | it is not in every case better than lithium ion | batteries! For example, the R7/Soyuz rocket family is the | most-launched orbital rocket ever, and it uses a hydrogen | peroxide gas generator to drive the turbopump. That has a | concentration of 82.5% peroxide. Pure peroxide has a heat | of decomposition of 2.84MJ/kg, and turbine that is | typically 30% efficient (actually, it might be much less | than that... I think the V-2 turbine was only like 10% | efficient, maybe worse... so 30% is optimistic) gives you | a usable energy density of only 700kJ/kg, or about | 194Wh/kg. The best lithium batteries available are about | twice that, up to 400-500Wh/kg (with those in the lab | even better still), and electric motors can have 90-95% | efficiency. | | And gas generators using main propellants are better, | certainly, but less than you might think because they | have to haul all their oxidizer with them (unlike | aircraft) and are also usually run very far from | stoichiometric (maybe just 0.3 O:F ratio compared to a | stoichiometric 3.4) to keep the temperature down. So | unless you have a pretty high temperature turbine, you | might not beat peroxide by much! | | So the easiest gas generators have worse energy density | (keep in mind RocketLab does stage off batteries if | necessary...), and the next easiest, while better, aren't | MASSIVELY better without careful efficiency improvements. | The real efficiencies come when you use like an expander | cycle or a staged combustion cycle or you feed the gas | generator exhaust back into the nozzle like Merlin Vacuum | or F-1. And those are all much more complicated. A level | of complication that is not worth it for small rockets | but is for larger. | | So it's really not about electric scaling poorly | (electric scales just fine) but about the greater | complexity of better engine cycles being worth it at | larger scales. | kragen wrote: | Yeah, it's pretty amazing. Doing this in a controlled fashion | is the hard part; a largish wooden building on fire can also | dissipate 10 GW. | | A .22 LR rifle bullet might acquire 200 J in 2 ms, which | means the firing gun is producing 100 kW mechanical, plus | probably another 300 kW thermal. So another way of thinking | of this is that an engine dissipating 10 GW is equivalent to | something like 25000 handguns firing at once, without ever | stopping. | 7952 wrote: | Saturn V at take off had an equivalent power of 166GW. If | that was electricity it would be around 2x the total capacity | of all the power stations in the UK. | beerandt wrote: | And then on top of it all, throttling ability. | | People don't grasp what an unbelievably complex engineering | problem that is. It's at least an addition of difficulty at | the same magnitude as building a steady-state 63000 hp | turbine pump in the first place. | | Mechanically implementing it in the inherently steady-state | design rocket of most rocket cycles. Having variable controls | able to work at those pressures. Testing structural dynamics | for a range of harmonic conditions instead of one. And do all | of that with materials that need to tolerate temperatures | going from cryogenic to white hot, without allowing thermal | expansion to affect the mechanical tolerances of parts | running at thousands of RPMs. And now you have varying flow | rates and negative pressures in the lines coming from the | external tanks, so have to design such that cryogenic liquids | (that normally would require immense positive pressure to | keep liquid) don't spontaneously boil or cavitate or cause a | shock-like wave (think water hammer turning off your bath | faucet) under changing negative pressures. | | It's really difficult even for seasoned engineers to grasp | the scale of difficulty involved. | LeifCarrotson wrote: | Appreciation of engineers for the difficulty of an | assignment like this seems bimodal. | | On the one hand, you have https://xkcd.com/793/ responses: | | > _You 're trying to predict the behavior of <complicated | system>? Just model it as a <simple object>, and then add | some secondary terms to account for <complications I just | thought of>. Easy, right? So, why does <your field> need a | whole journal, anyway?_ | | Just pressurize the tanks, and meter the flow with some | valves. Easy, right? | | They move to the other side of the distribution after a | little more thought, when they they realize it's simply | infeasible to put thousands of horsepower in a pump that | size, and declare the whole endeavor completely nonsensical | and impossible. | | Ran through this on a recent project involving an automated | sewing machine. At first, it seems ludicrous that you could | tie knots thousands of times per second. Oh wait, it's a | single motor and old cam-driven tech from the 1800s, | available off the shelf for a couple hundred dollars? | avmich wrote: | They also move to the "simple" side as well. The phrase | "the rocket science is not a rocket science" has reasons | to exist. | codeulike wrote: | _It 's really difficult even for seasoned engineers to | grasp the scale of difficulty involved._ | | Its rocket science | InitialLastName wrote: | A joke you hear unceasingly when you take tours of | engineering schools with a heavy aerospace focus. | post_break wrote: | Reminds me of fuel injectors of funny cars. Watch it go from | just idling, to full throttle. Then remember there's 8 of | them on the engine. | https://www.youtube.com/watch?v=xGTbQuhhluY | jcims wrote: | Top Fuel copypasta - | https://wediditforlove.com/techtalk21.html | dekhn wrote: | It sounded incomprehensible to me too but as I did some more | learning about the process of building rocket engines I learned | some interesting details. First, remember that people have been | making high strength metals through careful processing for | thousands of years. Second, the parts of engines are not made | as part of large-scale industrialized manufacturing. Almost all | the parts are made as few-offs, with far more energy, time, and | effort put into making sure that a single instance of something | is extremely reliable. Third, we got damn good at materials | science in the past 100 year, and metals can be absurdly | resistant to deformation under heat. | [deleted] | dokem wrote: | They also only run for a few minutes. | beerandt wrote: | SSMEs are reusable. | | Designing for thermal cycles and serviceability[0] is at | least as difficult a problem as running a hypothetical | rocket engine an equal amount of time in one longer, hotter | burn. | | (Such a design isn't needed and wouldn't be practical, but | then again multiple aspects of SSMEs being reusable turned | out not very practical either, depending on what version of | design criterea you evaluate and how the expected vs actual | usage changed over the lifetime of the program.) | | [0]In both the engineering sense, as durability of the | various loading cycles (ie lifetime turbine rotations or | number of thermal cycles before eol or failure), _and_ as | being constructed as able to undergo maintenance and | refurbishment between launches. | avmich wrote: | > SSMEs are reusable. | | Not as much as RL-10s. SSME you can disassemble - because | you should do that, as thermal stresses on turbine blades | are too dangerous, so you have to periodically replace | the parts which nearing the fault. | yetihehe wrote: | Engines in dragsters are also know to have very high power | comparing to engine size, but they also make less than 10k | rotations at full power before they fail. That is enough to | last one drag race which is several seconds. | throwaway0a5e wrote: | Don't think of it as "making horsepower", think of it as | "resisting the forces upon it". | | A gear tooth the size of your thumb pulls a semi truck up a | mountain. | Dig1t wrote: | Everyday Astronaut is such an impressive dude, I don't understand | why he doesn't just work for SpaceX at this point. He knows more | about rocket engineering and can explain it 10x better than most | aerospace new grads. | guynamedloren wrote: | Small pedantic note: this article is authored by Claire | Percival, not Tim Dodd. | | I'm not familiar with the working dynamic - Tim very well could | been involved in authoring this piece - but, credit where | credit is due. | | Edit: I partially recant this. The article includes a video by | Tim. | philipwhiuk wrote: | As I understand (as a Patreon), in general, Tim writes the | video and then one of his team write an article that covers | what the video says only with more text to substitute for the | lack of visuals. | | For Pre-Launch Previews they are written first by a team | member. | colordrops wrote: | He's probably making more money with his media that he would | working there. | paxys wrote: | Having a YouTube channel with 1M+ subscribers and videos that | get 5M+ views each is a _much_ more profitable and generally | better gig than SpaceX employee #10,000+ working 60-80 hours a | week in a high pressure culture. | philipwhiuk wrote: | There's a big difference between researching a topic to a | standard good enough for 'popular rocket science' and | 'understanding the maths well enough to work in the field'. | kragen wrote: | Has he built prototype rocket engines like Integza, Ben | Krasnow, or Tech Ingredients? They're still primarily | _divulgadores_ (there isn 't a good word for this in English) | but they have a certain amount of practical experience | getting things to work. | | OTOH at the point that you're EDM-drilling thousands of | micron-scale holes in your combustion chamber for film | cooling, you may start to need practical experience with | different things. | patrickyeon wrote: | I've never heard the term _divulgadores_ (I don't speak | Spanish, so that's no surprise), but it sounds maybe like | "science communicator" in this context? There's something a | bit more to the people you've listed in that they are also | entertainers, not straight educators, I don't know if | that's wrapped up in divulgadores as well? | mlindner wrote: | I don't actually think he's that impressive and I don't get | people's praise for him. His videos have a lot of mistakes in | them and while they're written in a way that dumbs down a topic | well for an audience who doesn't understand the subject very | well, that's his only major skill that's involved here. He's | not especially smart or ingenious, he's just a good | communicator. If he was to work somewhere it would be in a | communications department, but he probably makes more from | Youtube than such a job would provide. | | That's why he doesn't work for somewhere in the industry, | youtube makes him more. (He makes enough money to hire other | people to write for him, as we can see in the linked article.) | HectorRamos wrote: | Tim spends countless amount of time going through the | scripts, read throughs, first recordings, and so on, with | Patreons. I've been on many of these read throughs, usually | with several engineers in the aerospace industry present, and | it's meticulous how Tim makes sure any possible mistake is | identified and rectified. Even then, once you upload, there's | no editing of a video. | | The goal is to bring the subject down to a level where | everyday people can still follow. It's not meant to be a | college course, so of course there will be some dumbing down. | criley2 wrote: | SpaceX sounds pretty nasty to work for. Long hours, | machismo/sexist culture, aggressive management, and certainly | not the best pay you can find. | | He's probably happy where he is. | sgtnoodle wrote: | I worked there for a few years, on flight software. The | culture depends quite a bit on what department you're in. I | learned how to push back on schedule pressure and was able to | strike a reasonable work-life balance, and the head of my | department was very good at buffering us from management. My | departure was uncommon in that I left on good terms while I | was happy. There were other departments, though, that seemed | to operate more like a fraternity, and plenty of burnt-out | people. | geocrasher wrote: | He is definitely knowledgeable, but strikes me as too much of a | fanboy to be taken seriously. I have a hard time taking his | videos all that seriously. And it's not about his knowledge, | it's about his presentation. | texasbigdata wrote: | Take seriously? Ok let's use his last Russian rocket program | history piece....what exactly did you feel was factually | inaccurate about it? | ceejayoz wrote: | > And it's not about his knowledge, it's about his | presentation. | | They're not quibbling with the factual content. | geocrasher wrote: | I never said anything about his accuracy. | wolfram74 wrote: | Weren't you aware? learning is #SeriousBusiness, no fun | allowed. | geocrasher wrote: | It's not about _fun_ it 's about getting past the "ZOMG | SPACEX!!!!!" stage. | [deleted] | Bellend wrote: | I know you are getting a lot of snarky comments, but | honestly I know what you are saying. I can't watch his | channel for whatever that gushiness thing is. | geocrasher wrote: | I appreciate that. Thanks. | m_mueller wrote: | Worth checking it out again, he toned it down a lot | recently IMO. Still prefer Scott Manley, but only | astronaut gets the level of access like that. I mean Elon | showed him basically everything in front of a camera. | geocrasher wrote: | There's definitely reason to watch his channel, and that | particular two part series was one I consumed in whole. | Loved it. HUGE takeaways from it. | lilyball wrote: | > _too much of a fanboy to be taken seriously_ | | I would be really interested to know why "caring too much" is | a disqualification. | Dig1t wrote: | I guess some people's exuberance can turn people off, but | honestly its great in my opinion. Why should someone's joyful | exuberance for something make his educational content not | worth watching? The guy is obviously just very passionate | about spaceflight and people who are pushing the boundaries | of science/technology. I think 99% percent of the people I | talk to approach this kind of stuff with mundane indifference | and cynicism, so I think seeing someone genuinely passionate | and excited by it is a breath of fresh air. | geocrasher wrote: | I sincerely appreciate his passion. It just goes over the | top _for my personality_ and keeps me from really getting | into it. | sebzim4500 wrote: | Classic SpaceX fanboys, always making 90 minute documentaries | about the history of every Russian rocket engine. | geocrasher wrote: | If you can pick your video to base your assessment of my | comment on, then so can I: | | https://www.youtube.com/watch?v=7STa-tiQajQ | | And by the way, I never mentioned SpaceX | thamer wrote: | I've seen this kind of comment before about his presentation, | and I don't really understand it. It's true that he's a | fanboy and that's especially visible in his video | interviews/visits with Elon Musk, but the style of those | videos is markedly different from the more educational ones | which are often trying to cover a topic with a lot of detail | while remaining relatively accessible. | | I watched the video version of the article linked here this | morning, and don't recall any part that was fawning over | anyone or anything in particular. | | What is it about his presentation that puts you off? | geocrasher wrote: | I don't know what the right word is for it. I used "fanboy" | but maybe there's some other better word. Somebody else | above used "gushiness" I think and that sounds about right. | | It's like having a friend who won't shut up about a new | sushi place they found. Yes, the sushi is amazing. Yes, the | staff is nice. Yes, the atmosphere is great. And I could | enjoy it more if my friend would stop making a big deal | about every little thing about it. | | Edit: Just skipped through the video this thread is about | and that vibe just won't go away. I don't feel like I'm | being informed, I feel like I'm being _sold_. The | information itself is very, very good! | | For what it's worth, the Professor of Rock on YT has the | same vibe for me. | mlindner wrote: | I completely agree, but the fanboy aspect isn't really my | main sticking point, it's his tone that feels like he's | teaching elementary schoolers something. | dvtrn wrote: | Isn't that the point of the channel? Making astronomy | accessible to "Everyday" people? | piyh wrote: | He's teaching literal rocket science to the masses. | GuB-42 wrote: | I find he toned down the fanboy aspect a bit. A few years | ago, he could have been part of SpaceX marketing department. | | He still loves SpaceX, and to be fair, who doesn't. You may | not like Elon Musk, his fanboys, the outrageous claims, and | the way the company is run, but most of the exciting news in | rocketry for the last decade are about SpaceX. But for the | last few years, it is clear that he makes some efforts to be | impartial and focus on the technical aspects. | | And you should watch the videos he made with Elon Musk when | he visited SpaceX. I expected little more than an ad for | SpaceX, and it turned out surprisingly technical and hype- | free. | geocrasher wrote: | I did watch both those videos, and they were excellent! | Well, Elon's parts were excellent. I still found the | questions to be more on the fanboi side than the | engineering side, and that's okay. It's his brand, he can | do what he likes. | | I prefer Scott Manley's approach to things, and so I watch | him instead. And when he says that EverydayAstronaut has a | great video, I go watch it :) ___________________________________________________________________ (page generated 2022-01-13 23:00 UTC)