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The Tech Behind SpaceX’s New Engine

443 points by _JamesA_ 8y ago

kiba 8y ago
I don't like the usage of 'impossible'. Impossible by what standard? Laws of physics forbidding it is understandable. We may likely never see the development of FTL because our understanding as we know it would see it impossible to do due to its strange implication about cause and effect.
- maneesh 8y ago
  someone didn't read the article, or notice the quotes around the word "Impossible"
  - kiba 8y ago
    There wasn't quotes around 'impossible' in the article.
    - mynameisvlad 8y ago
      Literally in the headline. And they used other words next to the unquoted impossible in the article itself like "deemed by scientists to be next to impossible". Context matters.
      - jandrese 8y ago
        The US scientists didn't think there was a metallurgy that could survive the oxygen rich environment, but the Russians did the work to find it. The part I'm confused about is how it talks about all of these 60s rockets that close the cycle but aren't as efficient because they mess up the mixture in the combustion chamber, but shouldn't the injectors be tuned for the excess fuel/oxidizer from the get go? It doesn't seem like you should be exhausting unburnt fuel/oxidizer if you have it tuned correctly.
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w8vY7ER 8y ago
As only a casual fan, this was revealing on what makes a full-flow staged combustion engine so promising. Thanks for sharing
russellbeattie 8y ago
If you live in SoCal (or even if you're just visiting), definitely take a quick trip by the SpaceX facilities in Hawthorne [1] where they have a Falcon rocket sitting outside. From a distance it looks like and industrial chimney, but as you pull up, you can see it's an actual rocket. Standing next to it gives a great sense of scale the next time you're watching a SpaceX video. 1. https://www.google.com/maps/place/SpaceX,+Rocket+Rd,+Hawthorne,+CA+90250/@33.9212982,-118.3277877,17z/data=!4m2!3m1!1s0x80c2b5dee46db32d:0x5589bf4232c10232 https://www.google.com/maps/place/SpaceX,+Rocket+Rd,+Hawthor...
- clanrebornsx 8y ago
  I work there as a Janitor, the one u see is the fake rocket basically.
  - e1ven 8y ago
    What do you mean by 'fake rocket'? A prototype built for display, not for launching?
  - FrojoS 8y ago
    Fake? Isn't it the first stage that ever landed!?
    - jlv2 8y ago
      It is -- it's B1019. I suspect that's why they are a janitor.
      - clanrebornsx 8y ago
        Sorry I've PhD in Particle Physics. Not able to find any work, so I am doing janitor work. Why do you insult Janitor's intellect?
        elif 8y ago
        If you provided supporting reasoning or evidence of any kind I believe you'd have better reception. Your unqualified assertion does not resemble the statement of a scientist, and you should not be surprised that relying on an appeal-to-authority of a janitor drew ridicule.
kumarvvr 8y ago
This is an excellent article. Just curious, how much more efficient is the full-flow engine? And, what exactly is the deal with the seals the article is talking about? Anyone have more info?
- CarVac 8y ago
  A full-flow staged combustion engine has more efficiency due to both propellants being fully vaporized before they mix, rather than a liquid-liquid mixture (as in a gas generator engine) or a liquid-gas mixture (as in a normal staged combustion engine). The seals are between the turbine side (hot gas) and compressor side (liquid fuel) of the turbopump. In a full-flow staged combustion engine, you don't have to worry about accidentally getting a little of the hot gas into the liquid propellant, because that would be mixing fuel with fuel-rich gas or oxygen with oxygen-rich gas. But in a normal staged combustion engine, you have to carefully seal off the oxygen from the fuel-rich gas (in a fuel-rich staged combustion engine) or the oxygen-rich gas from the fuel (in an oxygen-rich staged combustion engine.
  - ballooney 8y ago
    No, this is all just wrong. The efficiency is because you dont throw a load of enthalpy overboard as in a gas generator. The phase is _exremely_ second order by comparison. You’re all over this thread being wrong and confused. Source: am a rocket engine designer.
    - buboard 8y ago
      does the mass of the exhaust fuels count as well? whats the percentage of thrust being lost in a gas generator?
      - ballooney 8y ago
        It definitely counts. The effect it has on exhaust velocity is maybe 5-10%, which is a big deal when you consider that has an exponential effect on your mass fraction, i.e the percentage of total lift-off mass that is fuel vs machinery and payload.
twic 8y ago
Either approach, whether it recaptures the oxidizer or fuel rich preburner exhaust, is clearly an improvement over dumping everything overboard. But neither is an ideal solution as there’s still potentially combustible products being wasted. Are there? Here's a diagram of the RD-180, which uses an oxygen-rich preburner: https://en.wikipedia.org/wiki/RD-180#/media/File:Rd180schematic.png https://en.wikipedia.org/wiki/RD-180#/media/File:Rd180schema... Where is anything escaping other than through the combustion chamber?
- CarVac 8y ago
  There's no wasted propellant with normal staged combustion. But full flow staged combustion lets you fully vaporize both propellants before they mix, leading to more optimal burning.
  - avmich 8y ago
    More importantly, supply more power to the pumps thus allowing higher pressure in the chamber, and so higher Isp.
- ceejayoz 8y ago
  Scroll one paragraph down from that quote and the RD-180's approach is mentioned. > In the 1950’s, Soviet scientists came up with something of a compromise. Instead of using a fuel-rich mixture in the preburner which produced an exhaust that couldn’t be safely recirculated into the engine, they experimented with running the preburner oxygen-rich. > Eventually the Soviets mastered the metallurgy required to build the turbine and developed several engines that operated on the oxygen-rich preburner concept. The exhaust was piped into the engine’s combustion chamber and recovered at least some of the propellants which would otherwise have been dumped overboard. The modern day Russian RD-180 engine, currently in use by the American Atlas V, is a continuation of this technology.
- deleted 8y ago
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- hoorayimhelping 8y ago
  The diagram doesn't show that the fuel used in the preburner is combusted less efficiently than the fuel used in the main combustion chamber. It comes out through the nozzle, but isn't fully combusted (it comes out as liquid, while the main fuels are gasses) and so is wasted energy. From what I understand, the fuel and oxidizer that has been through the preburners to spin the turbines is basically fungible with fuel and oxidizer that is used in the combustion chamber.
buboard 8y ago
its not impossible, considering that both the US and the russians built them (but never flown). These articles usually go overboard with the hero-worship and fail to mention that those are incremental improvements on the immense rocketry feats of the 60s.
JumpCrisscross 8y ago
“Benefits of the full-flow staged combustion cycle include turbines that run cooler and at lower pressure, due to increased mass flow, leading to a longer engine life and higher reliability.” TL; DR Full flow lowers turbine temperatures at the expense of parts complexity. Given turbopumps are the devil’s ass part of rocketry, this has been a sought-after technology. The pay-off isn’t so much efficiency as much as longevity. (This also explains why full flow hasn’t been a priority for anyone until SpaceX.) https://en.m.wikipedia.org/wiki/Staged_combustion_cycle#Full-flow_staged_combustion_cycle https://en.m.wikipedia.org/wiki/Staged_combustion_cycle#Full...
- Tuna-Fish 8y ago
  > TL; DR Full flow lowers turbine temperatures at the expense of parts complexity. Ehhh. I'd argue it also lowers part complexity, because it eliminates interpropellant seals. > The pay-off isn’t so much efficiency It improves achievable chamber pressure (assuming similar maximum pressures and temperatures at the turbines), which improves both thrust and Isp. > (This also explains why full flow hasn’t been a priority for anyone until SpaceX.) The reason it hasn't been a priority is more that no new development has been a priority since the 70's.
  - avmich 8y ago
    > ...it also lowers part complexity, because it eliminates interpropellant seals. But it adds the whole second gas generator and turbine. No, it doesn't lower part complexity as a whole :) . > It improves achievable chamber pressure Yes, I'd even argue that's the penultimate goal of full-flow scheme. 1) For a rocket engine you usually (almost always) want as high Isp (which is approximately the speed of gasses flowing from the rocket engine) as possible. 2) To get that Isp, you need as high pressure in the chamber as possible. 3) To get that high pressure, you want to supply your pumps with as much power (in Watts) as possible from the given overall fuel flow (in kilograms per second) - while not melting turbines blades (so fuel:oxidizer ratio is limited). 4) To get most power to the turbines blades at fixed (maximum) gas temperature and fixed overall fuel flow, you want to use all of that flow (classical staged combustion uses only one component, which is essentially not using the whole fuel flow) and adjust ratios fuel:oxidizer at both gas generators so that total power would be maximum. You want maximum flow both because that increases turbine efficiency and because that actually provides more power to the turbine.
tehsauce 8y ago
Rocket lab's Rutherford engine uses a closed cycle with battery powered fuel pumps. They were actually to fly an engine like this in their "electron" rocket, as early as 2017. https://en.m.wikipedia.org/wiki/Rutherford_(rocket_engine) https://en.m.wikipedia.org/wiki/Rutherford_(rocket_engine)
- wolf550e 8y ago
  This is only viable for small engines, like expander cycle is only viable for small engines. The specific energy of electric batteries cannot compare to that of kerolox or methalox. Closed cycle is not a new idea: https://en.wikipedia.org/wiki/Staged_combustion_cycle#History https://en.wikipedia.org/wiki/Staged_combustion_cycle#Histor...
  - twic 8y ago
    I still have a soft spot for expander cycles - they seem so elegant compared to staged combustion cycles, and apparently i am not the only person who thinks that: https://blogs.nasa.gov/J2X/2014/03/24/inside-the-leo-doghouse-the-art-of-expander-cycle-engines/ https://blogs.nasa.gov/J2X/2014/03/24/inside-the-leo-doghous...
    - Diederich 8y ago
      Excellent read, thank you.
    - CarVac 8y ago
      Interestingly the expander bleed cycle mentioned at the end is going to be used in the Blue Origin BE-3U, a change from the combustion tap-off of the older BE-3.
    - deleted 8y ago
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  - deleted 8y ago
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prando 8y ago
https://www.netflix.com/title/80119093 https://www.netflix.com/title/80119093 My rocket-science knowledge is abysmal, but I thoroughly enjoyed this article and the Netflix documentary that I have linked to was incredible. Anyone even remotely interested in rockets should check it out :).
- jbkkd 8y ago
  Unavailable for me in the UK, what's the name of the documentary?
  - ff_ 8y ago
    I cannot access it as well, but it should be "Cosmodrome"
  - jessriedel 8y ago
    "Cosmodrome".
  - apexalpha 8y ago
    Can't find it anywhere on the internet, not even Netflix here in my country. :(
- ridgeguy 8y ago
  Excellent, thank you. There's a parallel between Sergei Korolev and Elon Musk, I believe.
  - ridgeguy 8y ago
    To amplify just a bit - I watched the linked video. The parallel that struck me was the description of Korolev as an amazingly multitalented person. I regard Musk as a polymath as well. It interested me that these two chose work that requires understanding of many disciplines (fluid dynamics, combustion chemistry, materials science, control systems, etc.)and were so effective as individual contributors and as leaders.
- ilogik 8y ago
taf2 8y ago
Love this article and if you read it with Curious Droids' voice it's even better: https://www.youtube.com/channel/UC726J5A0LLFRxQ0SZqr2mYQ https://www.youtube.com/channel/UC726J5A0LLFRxQ0SZqr2mYQ
mabbo 8y ago
> While the Space Shuttle has long since retired, a variation of the engine itself will go on to power the Space Launch System. It will be the most powerful rocket NASA has ever built and is slated to begin missions in 2020. 2020? I honestly doubt we'll see the SLS launch before 2024 at it's current rate.
- Hypx 8y ago
  They're nearly finished actually. The core stage is in final assembly. We'll probably see a launch in 2020 or 2021.
- Rebelgecko 8y ago
  I would bet money that SLS+Orion launches before Falcon Super Heavy+Starship. It looks like SLS is already doing integration testing for the various cores and starting to assemble the main components. I'd guess 2021 at the latest, as long as there's no multi-month government shutdowns in the meantime.
  - skunkworker 8y ago
    SLS Block I maybe, but definitely not SLS Block 2. The Starship hopper will definitely be working long before either of those two take flight.
  - btilly 8y ago
    Well, sanity check. In 2017 the SLS launch was about 2 years out, but likely to slip: https://www.nasaspaceflight.com/2017/11/sls-managers-troops-slip-2020/ https://www.nasaspaceflight.com/2017/11/sls-managers-troops-... In 2019 the SLS launch is a bit under 2 years out, but likely to slip: https://arstechnica.com/science/2019/02/nasa-still-working-toward-2020-launch-of-massive-sls-rocket/ https://arstechnica.com/science/2019/02/nasa-still-working-t... This strongly reminds me of the fact that late software projects are promised to be on time until about 6 weeks before launch, and then launch keeps getting delayed. And this is true no matter how late it eventually turns out to be. The reason why 6 weeks is the magic figure is that for a software project, that's the point where you can no longer paper over the inevitability of failure with wishful thinking. Rockets have slower schedule, but it is strongly looking like 2 years is a similar magic figure in that industry, for similar reasons. In that light, the money quote from the second article is this: However, the agency and its prime contractor for the core stage, Boeing, are on a tight timeline that has little margin for technical problems that might occur during the structural tests of the tank or the green run tests. Historically, during this integration and test process with other large rocket programs, major problems have often occurred. I am generally a believer that what happened historically shouldn't be ignored. There is therefore no way that the SLS will launch in 2020. Or 2021. In fact nobody really knows when it will launch. Furthermore the upper stage, aka Orion, is apparently in even worse shape. Right now they are going back to the drawing board to try to find a design that gets costs down. Admittedly SpaceX itself is promising the BFR in about 2 years, and also had a history of overruns. I don't think that they will launch on time. But they have a better history of getting launch vehicles up. I will therefore happily take your bet for $100, but I would like to formalize it a bit. I win if Falcon Super Heavy+Starship or whatever it gets renamed to gets successfully launched to orbit first OR if SLS+Orion gets canceled first. Vice versa you win if SLS+Orion gets successfully launched first OR if Falcon Super Heavy+Starship or whatever gets canceled first. Note that "SpaceX goes out of business" counts as canceled, even if someone else (eg Bezos) buys the remnants and then launches something based on the work. If my version is acceptable, you can contact me by email per my profile.
debt 8y ago
"For example, the turbine of the V-2 rocket was spun with steam ..." Steam technology and rocket technology have a shared history. That kind of bottleneck shape that a is quintessential shape of a rocket engine, is actually a Steam-Engine-era technology called a de Laval nozzle. I didn't know they used a tiny steam engine inside a V-2. I think it's cool that the design of such an old technology, the steam engine, lives on inside the design of such a new technology, the rocket.
- trhway 8y ago
  >I didn't know they used a tiny steam engine inside a V-2. it wasnt steam engine per.se., it was catalytic peroxide decomposition.
  - InclinedPlane 8y ago
    The Soyuz first stage uses the same system even today.
nisten 8y ago
The reason this is important is not the really the few % savings in fuel weight. Any small improvement in exhaust velocity of the engine makes a huge difference(sort of exponential) in the amount of payload it can take to orbit. In this case the 2 pre-burners also make relighting the engine in a vacuum a lot more reliable. For more on the math: https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
- avmich 8y ago
  Right, another reason to use full-flow scheme is that both components get into chamber in the gaseous form - the heated gaseous form. And fuel usually doesn't have a problem igniting in the hot oxygen flow, especially if that fuel is in gas form itself, within milliseconds.
burfog 8y ago
Looking at the list of cycles on Wikipedia, I'm surprised that nobody seems to have used preburners to pressurize the tanks. Use a fuel-rich preburner to pressurize the fuel tank, and an oxygen-rich preburner to pressurize the oxygen tank. Mixing should be limited even if nothing special is done, due to the temperature and phase of matter and short timeframe. One could of course pay the weight penalty of a piston (need not have a perfect seal) or collapsing bag. Doing a heat exchanger (to boil and thus pressurize) is another option, but then you're back to needing a place for the exhaust. It would let you do a sort of full-flow engine without turbopumps however, which is great. All those issues with cavitation and lubrication and stress cracking just go away.
- JumpCrisscross 8y ago
  > I'm surprised that nobody seems to have used preburners to pressurize the tanks This combines the worst of both worlds. You get the weight and complexity of turbopumps. And you get the weight, explosion risk and leakiness of pressure vessels.
  - burfog 8y ago
    Skip the turbopump. That is the whole point of pressurizing. Pressurizing has weight advantages. You can use a balloon tank. The tank no longer has to have the rigidity to support itself. Rockets with typical cycles have used balloon tanks. Even modern ones like the Falcon 9 are partially that way, with just enough rigidity to be erected empty on the pad. The Falcon 9 uses helium to pressurize; that could be changed to preburner exhaust even if you did keep the moderate pressure and the turbopumps.
    - rbanffy 8y ago
      This is one of the reasons SpaceX uses supercooled fuel and oxydizer (and one of the reasons for going methalox in the first place) - the tanks self-pressurize, so they can skip the Helium system. Pumps are still good because you really don't want the tanks to pressurize at the same pressure as the combustion chamber. If you do, you'll see a rapid disassembly, but your claim on it being unscheduled will be questioned.
rbanffy 8y ago
The RD-270 got me scared. That much hydrazine flowing through anything can't be good.
- ballooney 8y ago
  Yes it can, as any chemist or rocket enginet desinger could tell you, you just dont understand the engineering.
le-mark 8y ago
Nice article, but this part is a bit misleading: > American engineers went in the opposite direction. They believed that a fuel-rich mixture in the preburner was possible and could be done with existing metal alloys, so long as hydrogen was used as the fuel instead of kerosene. This ultimately lead to the development of the Space Shuttle Main Engine, which to date remains the most efficient liquid fuel rocket engine ever flown. SSME performance was due to H2 vs kerosene, it was not a full flow engine. Edit; also no mention of Blue Origins BE-4 which is also a full flow engine.
- deleted 8y ago
  [deleted]
- Palptine 8y ago
  Not true. Be-4 is a staged combustion metholox engine.
  - itp 8y ago
    Be careful with terminology. BE-4 and Raptor are both staged combustion methalox engines. Raptor is full-flow staged combustion, while BE-4 is oxidizer-rich staged combustion.
- itp 8y ago
  The article does not claim that the SSME is full flow; as described in the quote you pulled, it's fuel-rich. BE-4 is not full flow, but oxidizer-rich (https://en.wikipedia.org/wiki/Staged_combustion_cycle#Oxidizer-rich_staged_combustion https://en.wikipedia.org/wiki/Staged_combustion_cycle#Oxidiz...).
paulsutter 8y ago
To model Raptor's hypersonic turbulent combustion SpaceX used an internally developed simulator, which uses wavelet compression to vary resolution across many orders of magnitude in both time and physical dimensions: https://www.nextplatform.com/2015/03/27/rockets-shake-and-rattle-so-spacex-rolls-homegrown-cfd/ https://www.nextplatform.com/2015/03/27/rockets-shake-and-ra... Here is a fantastic talk from the NVIDIA conference: https://www.youtube.com/watch?v=txk-VO1hzBY https://www.youtube.com/watch?v=txk-VO1hzBY
mannykannot 8y ago
The F1 engines of the Saturn V 1st. stage used a rich-mixture gas generator to drive the turbopump, but its exhaust was fed into the engine's nozzle about halfway down, through an annular manifold [1]. Up to that point, the combustion chamber and nozzle were cooled by circulating fuel through them, but beyond that point, the cooler turbopump exhaust layer protected the nozzle extension. In pictures of launches [2], you can make out the brown smoky annulus of the turbopump exhaust, for a distance about equal to the length of the nozzle extension, until it either mixes with the hot exhaust, or with ambient air and then burns, at which point the smoke particles become incandescent. [1] https://history.msfc.nasa.gov/saturn_apollo/documents/F-1_Engine.pdf https://history.msfc.nasa.gov/saturn_apollo/documents/F-1_En... [2] https://images.nasa.gov/details-ksc-69pc-442.html https://images.nasa.gov/details-ksc-69pc-442.html
Gravityloss 8y ago
The article is a bit incomplete. The space shuttle main engine already had two main turbopumps. IIRC this is because the optimal pump speed is different for pumping hydrogen and oxygen. They have very different densities. You want to avoid gearing as much as possible. And the main problem problem in the staged combustion cycle - in feeding the gas generator exhaust to the main chamber is not that it's fuel rich or oxidizer rich - it's that it's usually much lower pressure than in the main combustion chamber, because it had to go through the turbine, which causes the pressure to lower. That's why engines like NK-33 have a separate boost pump for the gas generator. RD-180 has more pump stages for the fuel entering the gas generator (all oxidizer passes through the gas generator). Full flow staged combustion is another way to solve this - put all the propellants through the gas generators and turbines. I realize it's hard to write popular technical articles about medium complexity subjects and sometimes you have to take some shortcuts. https://en.wikipedia.org/wiki/Space_Shuttle_main_engine#/media/File:Ssme_schematic_(updated).svg https://en.wikipedia.org/wiki/Space_Shuttle_main_engine#/med...

443 points by _JamesA_ 8y ago

kiba 8y ago

I don't like the usage of 'impossible'. Impossible by what standard? Laws of physics forbidding it is understandable. We may likely never see the development of FTL because our understanding as we know it would see it impossible to do due to its strange implication about cause and effect.

maneesh 8y ago
someone didn't read the article, or notice the quotes around the word "Impossible"
- kiba 8y ago
  There wasn't quotes around 'impossible' in the article.
  - mynameisvlad 8y ago
    Literally in the headline. And they used other words next to the unquoted impossible in the article itself like "deemed by scientists to be next to impossible". Context matters.
    - jandrese 8y ago
      The US scientists didn't think there was a metallurgy that could survive the oxygen rich environment, but the Russians did the work to find it. The part I'm confused about is how it talks about all of these 60s rockets that close the cycle but aren't as efficient because they mess up the mixture in the combustion chamber, but shouldn't the injectors be tuned for the excess fuel/oxidizer from the get go? It doesn't seem like you should be exhausting unburnt fuel/oxidizer if you have it tuned correctly.
  - deleted 8y ago
    [deleted]

w8vY7ER 8y ago

As only a casual fan, this was revealing on what makes a full-flow staged combustion engine so promising. Thanks for sharing

russellbeattie 8y ago

If you live in SoCal (or even if you're just visiting), definitely take a quick trip by the SpaceX facilities in Hawthorne [1] where they have a Falcon rocket sitting outside. From a distance it looks like and industrial chimney, but as you pull up, you can see it's an actual rocket. Standing next to it gives a great sense of scale the next time you're watching a SpaceX video. 1. https://www.google.com/maps/place/SpaceX,+Rocket+Rd,+Hawthorne,+CA+90250/@33.9212982,-118.3277877,17z/data=!4m2!3m1!1s0x80c2b5dee46db32d:0x5589bf4232c10232 https://www.google.com/maps/place/SpaceX,+Rocket+Rd,+Hawthor...

clanrebornsx 8y ago
I work there as a Janitor, the one u see is the fake rocket basically.
- e1ven 8y ago
  What do you mean by 'fake rocket'? A prototype built for display, not for launching?
- FrojoS 8y ago
  Fake? Isn't it the first stage that ever landed!?
  - jlv2 8y ago
    It is -- it's B1019. I suspect that's why they are a janitor.
    - clanrebornsx 8y ago
      Sorry I've PhD in Particle Physics. Not able to find any work, so I am doing janitor work. Why do you insult Janitor's intellect?
      - elif 8y ago
        If you provided supporting reasoning or evidence of any kind I believe you'd have better reception. Your unqualified assertion does not resemble the statement of a scientist, and you should not be surprised that relying on an appeal-to-authority of a janitor drew ridicule.

kumarvvr 8y ago

This is an excellent article. Just curious, how much more efficient is the full-flow engine? And, what exactly is the deal with the seals the article is talking about? Anyone have more info?

CarVac 8y ago
A full-flow staged combustion engine has more efficiency due to both propellants being fully vaporized before they mix, rather than a liquid-liquid mixture (as in a gas generator engine) or a liquid-gas mixture (as in a normal staged combustion engine). The seals are between the turbine side (hot gas) and compressor side (liquid fuel) of the turbopump. In a full-flow staged combustion engine, you don't have to worry about accidentally getting a little of the hot gas into the liquid propellant, because that would be mixing fuel with fuel-rich gas or oxygen with oxygen-rich gas. But in a normal staged combustion engine, you have to carefully seal off the oxygen from the fuel-rich gas (in a fuel-rich staged combustion engine) or the oxygen-rich gas from the fuel (in an oxygen-rich staged combustion engine.
- ballooney 8y ago
  No, this is all just wrong. The efficiency is because you dont throw a load of enthalpy overboard as in a gas generator. The phase is _exremely_ second order by comparison. You’re all over this thread being wrong and confused. Source: am a rocket engine designer.
  - buboard 8y ago
    does the mass of the exhaust fuels count as well? whats the percentage of thrust being lost in a gas generator?
    - ballooney 8y ago
      It definitely counts. The effect it has on exhaust velocity is maybe 5-10%, which is a big deal when you consider that has an exponential effect on your mass fraction, i.e the percentage of total lift-off mass that is fuel vs machinery and payload.

twic 8y ago

Either approach, whether it recaptures the oxidizer or fuel rich preburner exhaust, is clearly an improvement over dumping everything overboard. But neither is an ideal solution as there’s still potentially combustible products being wasted. Are there? Here's a diagram of the RD-180, which uses an oxygen-rich preburner: https://en.wikipedia.org/wiki/RD-180#/media/File:Rd180schematic.png https://en.wikipedia.org/wiki/RD-180#/media/File:Rd180schema... Where is anything escaping other than through the combustion chamber?

CarVac 8y ago
There's no wasted propellant with normal staged combustion. But full flow staged combustion lets you fully vaporize both propellants before they mix, leading to more optimal burning.
- avmich 8y ago
  More importantly, supply more power to the pumps thus allowing higher pressure in the chamber, and so higher Isp.
ceejayoz 8y ago
Scroll one paragraph down from that quote and the RD-180's approach is mentioned. > In the 1950’s, Soviet scientists came up with something of a compromise. Instead of using a fuel-rich mixture in the preburner which produced an exhaust that couldn’t be safely recirculated into the engine, they experimented with running the preburner oxygen-rich. > Eventually the Soviets mastered the metallurgy required to build the turbine and developed several engines that operated on the oxygen-rich preburner concept. The exhaust was piped into the engine’s combustion chamber and recovered at least some of the propellants which would otherwise have been dumped overboard. The modern day Russian RD-180 engine, currently in use by the American Atlas V, is a continuation of this technology.
deleted 8y ago
[deleted]
hoorayimhelping 8y ago
The diagram doesn't show that the fuel used in the preburner is combusted less efficiently than the fuel used in the main combustion chamber. It comes out through the nozzle, but isn't fully combusted (it comes out as liquid, while the main fuels are gasses) and so is wasted energy. From what I understand, the fuel and oxidizer that has been through the preburners to spin the turbines is basically fungible with fuel and oxidizer that is used in the combustion chamber.

buboard 8y ago

its not impossible, considering that both the US and the russians built them (but never flown). These articles usually go overboard with the hero-worship and fail to mention that those are incremental improvements on the immense rocketry feats of the 60s.

JumpCrisscross 8y ago

“Benefits of the full-flow staged combustion cycle include turbines that run cooler and at lower pressure, due to increased mass flow, leading to a longer engine life and higher reliability.” TL; DR Full flow lowers turbine temperatures at the expense of parts complexity. Given turbopumps are the devil’s ass part of rocketry, this has been a sought-after technology. The pay-off isn’t so much efficiency as much as longevity. (This also explains why full flow hasn’t been a priority for anyone until SpaceX.) https://en.m.wikipedia.org/wiki/Staged_combustion_cycle#Full-flow_staged_combustion_cycle https://en.m.wikipedia.org/wiki/Staged_combustion_cycle#Full...

Tuna-Fish 8y ago
> TL; DR Full flow lowers turbine temperatures at the expense of parts complexity. Ehhh. I'd argue it also lowers part complexity, because it eliminates interpropellant seals. > The pay-off isn’t so much efficiency It improves achievable chamber pressure (assuming similar maximum pressures and temperatures at the turbines), which improves both thrust and Isp. > (This also explains why full flow hasn’t been a priority for anyone until SpaceX.) The reason it hasn't been a priority is more that no new development has been a priority since the 70's.
- avmich 8y ago
  > ...it also lowers part complexity, because it eliminates interpropellant seals. But it adds the whole second gas generator and turbine. No, it doesn't lower part complexity as a whole :) . > It improves achievable chamber pressure Yes, I'd even argue that's the penultimate goal of full-flow scheme. 1) For a rocket engine you usually (almost always) want as high Isp (which is approximately the speed of gasses flowing from the rocket engine) as possible. 2) To get that Isp, you need as high pressure in the chamber as possible. 3) To get that high pressure, you want to supply your pumps with as much power (in Watts) as possible from the given overall fuel flow (in kilograms per second) - while not melting turbines blades (so fuel:oxidizer ratio is limited). 4) To get most power to the turbines blades at fixed (maximum) gas temperature and fixed overall fuel flow, you want to use all of that flow (classical staged combustion uses only one component, which is essentially not using the whole fuel flow) and adjust ratios fuel:oxidizer at both gas generators so that total power would be maximum. You want maximum flow both because that increases turbine efficiency and because that actually provides more power to the turbine.

tehsauce 8y ago

Rocket lab's Rutherford engine uses a closed cycle with battery powered fuel pumps. They were actually to fly an engine like this in their "electron" rocket, as early as 2017. https://en.m.wikipedia.org/wiki/Rutherford_(rocket_engine) https://en.m.wikipedia.org/wiki/Rutherford_(rocket_engine)

wolf550e 8y ago
This is only viable for small engines, like expander cycle is only viable for small engines. The specific energy of electric batteries cannot compare to that of kerolox or methalox. Closed cycle is not a new idea: https://en.wikipedia.org/wiki/Staged_combustion_cycle#History https://en.wikipedia.org/wiki/Staged_combustion_cycle#Histor...
- twic 8y ago
  I still have a soft spot for expander cycles - they seem so elegant compared to staged combustion cycles, and apparently i am not the only person who thinks that: https://blogs.nasa.gov/J2X/2014/03/24/inside-the-leo-doghouse-the-art-of-expander-cycle-engines/ https://blogs.nasa.gov/J2X/2014/03/24/inside-the-leo-doghous...
  - Diederich 8y ago
    Excellent read, thank you.
  - CarVac 8y ago
    Interestingly the expander bleed cycle mentioned at the end is going to be used in the Blue Origin BE-3U, a change from the combustion tap-off of the older BE-3.
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prando 8y ago

https://www.netflix.com/title/80119093 https://www.netflix.com/title/80119093 My rocket-science knowledge is abysmal, but I thoroughly enjoyed this article and the Netflix documentary that I have linked to was incredible. Anyone even remotely interested in rockets should check it out :).

jbkkd 8y ago
Unavailable for me in the UK, what's the name of the documentary?
- ff_ 8y ago
  I cannot access it as well, but it should be "Cosmodrome"
- jessriedel 8y ago
  "Cosmodrome".
- apexalpha 8y ago
  Can't find it anywhere on the internet, not even Netflix here in my country. :(
ridgeguy 8y ago
Excellent, thank you. There's a parallel between Sergei Korolev and Elon Musk, I believe.
- ridgeguy 8y ago
  To amplify just a bit - I watched the linked video. The parallel that struck me was the description of Korolev as an amazingly multitalented person. I regard Musk as a polymath as well. It interested me that these two chose work that requires understanding of many disciplines (fluid dynamics, combustion chemistry, materials science, control systems, etc.)and were so effective as individual contributors and as leaders.
ilogik 8y ago

taf2 8y ago

Love this article and if you read it with Curious Droids' voice it's even better: https://www.youtube.com/channel/UC726J5A0LLFRxQ0SZqr2mYQ https://www.youtube.com/channel/UC726J5A0LLFRxQ0SZqr2mYQ

mabbo 8y ago

> While the Space Shuttle has long since retired, a variation of the engine itself will go on to power the Space Launch System. It will be the most powerful rocket NASA has ever built and is slated to begin missions in 2020. 2020? I honestly doubt we'll see the SLS launch before 2024 at it's current rate.

Hypx 8y ago
They're nearly finished actually. The core stage is in final assembly. We'll probably see a launch in 2020 or 2021.
Rebelgecko 8y ago
I would bet money that SLS+Orion launches before Falcon Super Heavy+Starship. It looks like SLS is already doing integration testing for the various cores and starting to assemble the main components. I'd guess 2021 at the latest, as long as there's no multi-month government shutdowns in the meantime.
- skunkworker 8y ago
  SLS Block I maybe, but definitely not SLS Block 2. The Starship hopper will definitely be working long before either of those two take flight.
- btilly 8y ago
  Well, sanity check. In 2017 the SLS launch was about 2 years out, but likely to slip: https://www.nasaspaceflight.com/2017/11/sls-managers-troops-slip-2020/ https://www.nasaspaceflight.com/2017/11/sls-managers-troops-... In 2019 the SLS launch is a bit under 2 years out, but likely to slip: https://arstechnica.com/science/2019/02/nasa-still-working-toward-2020-launch-of-massive-sls-rocket/ https://arstechnica.com/science/2019/02/nasa-still-working-t... This strongly reminds me of the fact that late software projects are promised to be on time until about 6 weeks before launch, and then launch keeps getting delayed. And this is true no matter how late it eventually turns out to be. The reason why 6 weeks is the magic figure is that for a software project, that's the point where you can no longer paper over the inevitability of failure with wishful thinking. Rockets have slower schedule, but it is strongly looking like 2 years is a similar magic figure in that industry, for similar reasons. In that light, the money quote from the second article is this: However, the agency and its prime contractor for the core stage, Boeing, are on a tight timeline that has little margin for technical problems that might occur during the structural tests of the tank or the green run tests. Historically, during this integration and test process with other large rocket programs, major problems have often occurred. I am generally a believer that what happened historically shouldn't be ignored. There is therefore no way that the SLS will launch in 2020. Or 2021. In fact nobody really knows when it will launch. Furthermore the upper stage, aka Orion, is apparently in even worse shape. Right now they are going back to the drawing board to try to find a design that gets costs down. Admittedly SpaceX itself is promising the BFR in about 2 years, and also had a history of overruns. I don't think that they will launch on time. But they have a better history of getting launch vehicles up. I will therefore happily take your bet for $100, but I would like to formalize it a bit. I win if Falcon Super Heavy+Starship or whatever it gets renamed to gets successfully launched to orbit first OR if SLS+Orion gets canceled first. Vice versa you win if SLS+Orion gets successfully launched first OR if Falcon Super Heavy+Starship or whatever gets canceled first. Note that "SpaceX goes out of business" counts as canceled, even if someone else (eg Bezos) buys the remnants and then launches something based on the work. If my version is acceptable, you can contact me by email per my profile.

debt 8y ago

"For example, the turbine of the V-2 rocket was spun with steam ..." Steam technology and rocket technology have a shared history. That kind of bottleneck shape that a is quintessential shape of a rocket engine, is actually a Steam-Engine-era technology called a de Laval nozzle. I didn't know they used a tiny steam engine inside a V-2. I think it's cool that the design of such an old technology, the steam engine, lives on inside the design of such a new technology, the rocket.

trhway 8y ago
>I didn't know they used a tiny steam engine inside a V-2. it wasnt steam engine per.se., it was catalytic peroxide decomposition.
- InclinedPlane 8y ago
  The Soyuz first stage uses the same system even today.

nisten 8y ago

The reason this is important is not the really the few % savings in fuel weight. Any small improvement in exhaust velocity of the engine makes a huge difference(sort of exponential) in the amount of payload it can take to orbit. In this case the 2 pre-burners also make relighting the engine in a vacuum a lot more reliable. For more on the math: https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

avmich 8y ago
Right, another reason to use full-flow scheme is that both components get into chamber in the gaseous form - the heated gaseous form. And fuel usually doesn't have a problem igniting in the hot oxygen flow, especially if that fuel is in gas form itself, within milliseconds.

burfog 8y ago

Looking at the list of cycles on Wikipedia, I'm surprised that nobody seems to have used preburners to pressurize the tanks. Use a fuel-rich preburner to pressurize the fuel tank, and an oxygen-rich preburner to pressurize the oxygen tank. Mixing should be limited even if nothing special is done, due to the temperature and phase of matter and short timeframe. One could of course pay the weight penalty of a piston (need not have a perfect seal) or collapsing bag. Doing a heat exchanger (to boil and thus pressurize) is another option, but then you're back to needing a place for the exhaust. It would let you do a sort of full-flow engine without turbopumps however, which is great. All those issues with cavitation and lubrication and stress cracking just go away.

JumpCrisscross 8y ago
> I'm surprised that nobody seems to have used preburners to pressurize the tanks This combines the worst of both worlds. You get the weight and complexity of turbopumps. And you get the weight, explosion risk and leakiness of pressure vessels.
- burfog 8y ago
  Skip the turbopump. That is the whole point of pressurizing. Pressurizing has weight advantages. You can use a balloon tank. The tank no longer has to have the rigidity to support itself. Rockets with typical cycles have used balloon tanks. Even modern ones like the Falcon 9 are partially that way, with just enough rigidity to be erected empty on the pad. The Falcon 9 uses helium to pressurize; that could be changed to preburner exhaust even if you did keep the moderate pressure and the turbopumps.
  - rbanffy 8y ago
    This is one of the reasons SpaceX uses supercooled fuel and oxydizer (and one of the reasons for going methalox in the first place) - the tanks self-pressurize, so they can skip the Helium system. Pumps are still good because you really don't want the tanks to pressurize at the same pressure as the combustion chamber. If you do, you'll see a rapid disassembly, but your claim on it being unscheduled will be questioned.

rbanffy 8y ago

The RD-270 got me scared. That much hydrazine flowing through anything can't be good.

ballooney 8y ago
Yes it can, as any chemist or rocket enginet desinger could tell you, you just dont understand the engineering.

le-mark 8y ago

Nice article, but this part is a bit misleading: > American engineers went in the opposite direction. They believed that a fuel-rich mixture in the preburner was possible and could be done with existing metal alloys, so long as hydrogen was used as the fuel instead of kerosene. This ultimately lead to the development of the Space Shuttle Main Engine, which to date remains the most efficient liquid fuel rocket engine ever flown. SSME performance was due to H2 vs kerosene, it was not a full flow engine. Edit; also no mention of Blue Origins BE-4 which is also a full flow engine.

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Palptine 8y ago
Not true. Be-4 is a staged combustion metholox engine.
- itp 8y ago
  Be careful with terminology. BE-4 and Raptor are both staged combustion methalox engines. Raptor is full-flow staged combustion, while BE-4 is oxidizer-rich staged combustion.
itp 8y ago
The article does not claim that the SSME is full flow; as described in the quote you pulled, it's fuel-rich. BE-4 is not full flow, but oxidizer-rich (https://en.wikipedia.org/wiki/Staged_combustion_cycle#Oxidizer-rich_staged_combustion https://en.wikipedia.org/wiki/Staged_combustion_cycle#Oxidiz...).

paulsutter 8y ago

To model Raptor's hypersonic turbulent combustion SpaceX used an internally developed simulator, which uses wavelet compression to vary resolution across many orders of magnitude in both time and physical dimensions: https://www.nextplatform.com/2015/03/27/rockets-shake-and-rattle-so-spacex-rolls-homegrown-cfd/ https://www.nextplatform.com/2015/03/27/rockets-shake-and-ra... Here is a fantastic talk from the NVIDIA conference: https://www.youtube.com/watch?v=txk-VO1hzBY https://www.youtube.com/watch?v=txk-VO1hzBY

mannykannot 8y ago

The F1 engines of the Saturn V 1st. stage used a rich-mixture gas generator to drive the turbopump, but its exhaust was fed into the engine's nozzle about halfway down, through an annular manifold [1]. Up to that point, the combustion chamber and nozzle were cooled by circulating fuel through them, but beyond that point, the cooler turbopump exhaust layer protected the nozzle extension. In pictures of launches [2], you can make out the brown smoky annulus of the turbopump exhaust, for a distance about equal to the length of the nozzle extension, until it either mixes with the hot exhaust, or with ambient air and then burns, at which point the smoke particles become incandescent. [1] https://history.msfc.nasa.gov/saturn_apollo/documents/F-1_Engine.pdf https://history.msfc.nasa.gov/saturn_apollo/documents/F-1_En... [2] https://images.nasa.gov/details-ksc-69pc-442.html https://images.nasa.gov/details-ksc-69pc-442.html

Gravityloss 8y ago

The article is a bit incomplete. The space shuttle main engine already had two main turbopumps. IIRC this is because the optimal pump speed is different for pumping hydrogen and oxygen. They have very different densities. You want to avoid gearing as much as possible. And the main problem problem in the staged combustion cycle - in feeding the gas generator exhaust to the main chamber is not that it's fuel rich or oxidizer rich - it's that it's usually much lower pressure than in the main combustion chamber, because it had to go through the turbine, which causes the pressure to lower. That's why engines like NK-33 have a separate boost pump for the gas generator. RD-180 has more pump stages for the fuel entering the gas generator (all oxidizer passes through the gas generator). Full flow staged combustion is another way to solve this - put all the propellants through the gas generators and turbines. I realize it's hard to write popular technical articles about medium complexity subjects and sometimes you have to take some shortcuts. https://en.wikipedia.org/wiki/Space_Shuttle_main_engine#/media/File:Ssme_schematic_(updated).svg https://en.wikipedia.org/wiki/Space_Shuttle_main_engine#/med...