KSP Doesn't Teach: Rocket Engine Plumbing

A huge part of rocket science is the system of tanks, piping, valves and burners which deliver the fuel from the tanks to the engine. I try to explain why different designs exist and the advantages that more complicated designs deliver.

To be clear, I'm not a rocket scientist, I only play one on the internet.

Rocket engine diagrams are largely from Wikipedia with some
Modification for narrative purposes

[LordPecka]

"It worked very well, but rocket companies didn't have any incentive to continue to work upon it" - well this single sentence sums up whole rocket science development from about 1980 to about 2005.

[johno]

The way Apollo's first stage Rocketdyne F1 engines delt with exhaust gas from the turbopump was to blow the gas down the inside walls of the exhaust nozzle (bell) to act as a cooling film. This gas was at a lower temperature than the main rocket exhaust and insulated the nozzle. During launch you can see the gas exiting is much darker in colour than further down the exhaust stream.

[MarcusHouse]

Very interesting. You could imagine the plumbing nightmare with 42 engines squashed in there together :)

[FonVegen]

"Explosive rocket happiness". How could I live without using that phrase so far?

[vadimfrolov]

Absolutely understandable for not native speakers. Thanks for your work.

[davidturpin]

The one thing I would correct is that the notion of a oxygen-rich preburn being "cooler" than a stoichiometric burn.  Oxygen rich actually is a bad double-whammy:  It runs hot and it introduces an oxidizer into a hot metallic system, leading to rapid disintegration.  This is principally why running "lean" in car engines rapidly destroys them.  The problem the Soviets found was that a fuel-rich preburn clogged the exhaust pipes and threw off the delicate flow balance into the main combustion chamber, so instead they designed turbine wheels that could survive the heat (probably the first use of Inconel turbine wheels).  The space shuttle engine got around the problem by using hydrogen fuel, which has no solid byproduct.  So they can run "rich" while still maintaining the flow balance.

[jamesdubben]

Interesting to go back and look at this after the Raptor has flown. (just not to space just yet)

[sycodeathman]

Hey Scott! At 6:33 you say the Merlin burns a bit of fuel and a lot of oxygen in the preburner, but it actually runs fuel rich, burning fuel with a tiny bit of oxygen, to generate gasses that are hot enough to drive the pumps but not extremely corrosive, as they would be with an oxygen rich cycle.

[awuma]

Excellent presentation! It really covered a lot of material. I'm very glad you ended with the cryogenic (LH2) expander cycle and its limit (about 25, 000 lb thrust), which limits the thrust of the RL-10A engine(s) of the Centaur second stage used on Atlas V. Compare this with the 210, 000 lb thrust of the Merlin 1D Vacuum. The RL-10A, of course, has higher specific impulse, so it is considerably more efficient than the Merlin, but the difference in thrust means that the Centaur may have to angle its thrust to avoid falling back into the atmosphere. This is why Centaur can have one or two RL-10A engines. In the case of the Cygnus CRS OA-6 mission, the Atlas V first stage MECO'd 5 seconds too early, which meant the single engined Centaur had to burn a minute longer, using up nearly all its fuel reserves. Cygnus dropped alarmingly low back into the atmosphere, and barely made it up. All this despite the fact that the Atlas V burns a lot longer and reaches a much higher velocity and altitude than Falcon 9 at MECO. The Indians have got around the expander cycle thrust limit by building a 50, 000 lb thrust class gas generator cycle cryogenic (LH2) engine for the second stage of their new GSLV 3 launcher (I say second stage, but actually the vehicle is launched with only two big SRBs firing, and the core first stage is ignited when the SRBs quit). The Delta IV second stage uses a single RL-10 engine, too.

One reason the Falcon 9 first stage is recoverable is that it quits at lower altitude and velocity, leaving the second stage with more work to do.

[nockieboy]

Love these videos Scott - starting to wish I'd done rocket science at uni and you were the lecturer!

[bojac]

Thanks Scott! This is my favorite series fo yours, it's unique and you do a great job taking really complicated concepts and breaking them down to something I can understand.

[Najvalsa]

Now I want to be a rocket plumber, mooning everyone with my space and time crack, and producing gasses which contain 7% of the fuel of the future.

[mcgo]

Love your record collection Scott.. Shows great minds are right about LPs! Thanks for the great and informative videos!

[RobinWootton]

A fascination-rich mixture, of clarity and technicality in equal measure.

[WhiteWeaseI]

Scott, I love these videos. For a future topic, I love to hear you go a bit more In depth of nuclear thermal rockets. Last I heard if you talk about them was way early in the interstellar quest.

[thalb]

i really like your videos. i especially like that you just explain it in one flow as opposed to too many other people who keep cutting together 3 second clips, like after 10 words they have to go and read a script.

[robertbrowne]

This is exactly what I've been looking for. I'm in the planning stage of a miniature desk rocket with a working liquid fuel engine. Now all I have to do is see how small it can be until viscosity becomes an issue.

Thank you, you steely eyed missile man!

[Noor-rksf]

As an aeronautical engineering student, your videos are not only amazing but educational and surprisingly detailed. Just wanted to say keep up the good work!

[mrboredj]

Scott, these videos are excellent. Really well constructed and written, resulting in extremely informative episodes. Please keep making these!

[JaySmith]

More of this kind of stuff! Really well-explained