“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.”<p>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.)<p><a href="https://en.m.wikipedia.org/wiki/Staged_combustion_cycle#Full-flow_staged_combustion_cycle" rel="nofollow">https://en.m.wikipedia.org/wiki/Staged_combustion_cycle#Full...</a>
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:<p><a href="https://www.nextplatform.com/2015/03/27/rockets-shake-and-rattle-so-spacex-rolls-homegrown-cfd/" rel="nofollow">https://www.nextplatform.com/2015/03/27/rockets-shake-and-ra...</a><p>Here is a fantastic talk from the NVIDIA conference:<p><a href="https://www.youtube.com/watch?v=txk-VO1hzBY" rel="nofollow">https://www.youtube.com/watch?v=txk-VO1hzBY</a>
<a href="https://www.netflix.com/title/80119093" rel="nofollow">https://www.netflix.com/title/80119093</a>
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 :).
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.<p>1. <a href="https://www.google.com/maps/place/SpaceX,+Rocket+Rd,+Hawthorne,+CA+90250/@33.9212982,-118.3277877,17z/data=!4m2!3m1!1s0x80c2b5dee46db32d:0x5589bf4232c10232" rel="nofollow">https://www.google.com/maps/place/SpaceX,+Rocket+Rd,+Hawthor...</a>
> 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.<p>2020? I honestly doubt we'll see the SLS launch before 2024 at it's current rate.
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.<p>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.<p>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).<p>Full flow staged combustion is another way to solve this - put all the propellants through the gas generators and turbines.<p>I realize it's hard to write popular technical articles about medium complexity subjects and sometimes you have to take some shortcuts.<p><a href="https://en.wikipedia.org/wiki/Space_Shuttle_main_engine#/media/File:Ssme_schematic_(updated).svg" rel="nofollow">https://en.wikipedia.org/wiki/Space_Shuttle_main_engine#/med...</a>
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.<p>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.<p>[1] <a href="https://history.msfc.nasa.gov/saturn_apollo/documents/F-1_Engine.pdf" rel="nofollow">https://history.msfc.nasa.gov/saturn_apollo/documents/F-1_En...</a><p>[2] <a href="https://images.nasa.gov/details-ksc-69pc-442.html" rel="nofollow">https://images.nasa.gov/details-ksc-69pc-442.html</a>
This is an excellent article. Just curious, how much more efficient is the full-flow engine?<p>And, what exactly is the deal with the seals the article is talking about?<p>Anyone have more info?
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.
<a href="https://en.m.wikipedia.org/wiki/Rutherford_(rocket_engine)" rel="nofollow">https://en.m.wikipedia.org/wiki/Rutherford_(rocket_engine)</a>
"For example, the turbine of the V-2 rocket was spun with steam ..."<p>Steam technology and rocket technology have a shared history.<p>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.<p>I didn't know they used a tiny steam engine inside a V-2.<p>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.
Love this article and if you read it with Curious Droids' voice it's even better: <a href="https://www.youtube.com/channel/UC726J5A0LLFRxQ0SZqr2mYQ" rel="nofollow">https://www.youtube.com/channel/UC726J5A0LLFRxQ0SZqr2mYQ</a>
<i>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.</i><p>Are there? Here's a diagram of the RD-180, which uses an oxygen-rich preburner:<p><a href="https://en.wikipedia.org/wiki/RD-180#/media/File:Rd180schematic.png" rel="nofollow">https://en.wikipedia.org/wiki/RD-180#/media/File:Rd180schema...</a><p>Where is anything escaping other than through the combustion chamber?
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.<p>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.<p>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.
Nice article, but this part is a bit misleading:<p>> 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.<p>SSME performance was due to H2 vs kerosene, it was not a full flow engine.<p>Edit; also no mention of Blue Origins BE-4 which is also a full flow engine.
The reason this is important is not the really the few % savings in fuel weight.<p>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.<p>For more on the math:
<a href="https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation" rel="nofollow">https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation</a>
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.
I don't like the usage of 'impossible'. Impossible by what standard?<p>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.