Greeting Earthlings. If you follow the channel, you know that we recently paid a visit to Steve
Jurvetson’s amazing space collection. We got our head spinning with so many incredible artifacts,
the Apollo main couches, the MOCR console, the fuel cells,
the Soyuz panel, and so on and so forth that we covered in the previous episode.
But the collection has also quite a number of rocket engines. From the really small
to the really big. Unfortunately, I know relatively little about the rocket engines,
which is probably a good thing, or I would be tempted to start them up again.
But while we were there, this guy showed up through the door.
The space enthusiasts among you will have recognized Tim Dodd, from the popular and
oh-so-awesome Everyday Astronaut channel. Tim explains all things space with clarity and depth.
He hardly had come through the door that he got attracted to this giant thing.
A complete RL-10 engine. This amazing engine, first flown in 1963 on the Atlas rocket,
is still used today and will be flying in the SLS in the near future.
To my uneducated eye, when I see a rocket engine, I see a big bell nozzle, and lots of tubes
interconnected at random. Actually, I see a goat. Because, you see, the plumbing in a rocket engine
was clearly inspired by the interconnections of the digestive system of herbivores.
See, it’s obviously similar. Engine. Goat. Engine. Goat. Same concept, one powered by grass,
and the other by oxygen and hydrogen, which produces far bigger farts.
And of course Tim wanted figure out the digestive system of this engine.
[Tim] So both of these are hydrogen. [Steve] And these are the gimbal mounts? [Tim] Yes,
definitely. [Marc] So say again, how this flows? [Steve] Oh yes, so what
have we figured out? [Tim] Okay so from - and I'm not by any means,
I'm just... [Steve] Now you're the resident expert now, take the mantle! [Tim] No, no,
all we have to do is we've to get Scott Manley over here, he'll whip us into shape.
And as Tim rightly points out, Scott Manley has a whole episode on expander cycle engines
which includes the famous RL10, which we should have watched beforehand.
But we had not. However, you probably should.
So let’s imagine you have not watched Scott Manley’s video. How much can you figure out by
just staring at a rocket engine? So far I had obviously figured out the bell cooling tubes,
and the injector plate visible in the combustion chamber, right in the middle here.
[Steve] So we know hydrogen's going through these pipes. [Tim] We know hydrogen is - yes definitely,
because this is the hydrogen pump here. [Steve] So we're coming off here. [Tim] So yeah, at some
point. I got to figure how it first gets into here in the first place. This is what's confusing with
it being an expander. [Marc] So the hydrogen is cooling the bell? [Steve] Oh yes, key point. The
liquid hydrogen - get all this: when this is at full thrust, it's hotter than the sun
right in here, and icicles simultaneously form on the lip, at the same time. [Marc] So the
hydrogen first goes through the bell? [Tim] Yes [Marc] Through where? [Tim] I believe this is
the hydrogen inlet pipe, this is an oxygen inlet pipe. [Marc] Okay. [Tim] And then it
gets driven through there, through the... Well, because it either goes - oh god... [Marc] Yeah,
it goes it goes here. [Tim] Yeah, right. [Marc] Yep, so it goes here, it goes there...
[Tim] Oh, that's why there's two! [Steve] Why? [Tim] One's an out, one's an input, because after
it flows through the chamber it has to go through the pump back into the pump. [Steve] So wait,
maybe I was wrong on this one. Is this a separate circuit driving additional lines? [Tim] Nope,
it's the same. So it's going to only drive these tubes. Half of it, you know, splits two to one.
[Steve] So set of hydrogen comes in up here the other set comes in here? [Tim] No. [Steve's son]
So this goes into the bell up there, it comes out, and goes to the second turbo pump and then
it goes back to actually combust. [Tim] Then I don't know if it even has to go back. It
never goes back... [Steve] It goes back in the chamber. [Steve's son] It goes into combust.
At the very end of its journey, it burns. [Tim] Yes. [Steve] We know where it ends up! [Tim]
Yeah, so what i'm trying to figure out still though is... [Steve] Where's the
oxygen? [Tim] iOxygen's here. Simple: in and up to the top. [Steve] Okay. And that's it?
So just one pass through the pump? [Tim] Yup, little tiny guy.
[Steve] So is there so much more going on in the hydrogen, because of the circuitous route?
[Tim] Mostly because it's so undense, it's so sparse, that it requires substantially more,
multiple stages and a much larger pump. [Steve] More sparse in the gas phase? [Tim] Yeah,
both. [Steve] Okay, liquid too? [Tim] Yeah. So they burn like a six to one-ish ratio, liquid
hydrogen to liquid oxygen. One being hydrogen and six oxygen, which is opposite for most fuels and
or from like methalox and RP1. But so, I'm still trying to, I'm still trying to figure out though,
one of these is what has to drive. And normally,
it should be coming right. [Carl] You think it heats up, the bigger pipe would be it coming out
the bell, having been heated up and it's now more gas. And the thinner ones maybe the feed?
[Tim] That very well could be the answer. [Steve's son] This one is going this way, one's going
in the bell, comes up, it's collected out here, makes some gas. [Steve] It's also bigger,
it's expanded. I'm wondering if the side that is bigger is closer to the gas phase.
[Steve's son] And then this is the very end where it goes in. [Steve] And
notice the thickness of the pipe - the diameter rather. [Marc] Say that again? Which one goes in,
which one goes out? [Carl] Both of the pipes are about the same
size. [Tim] It might be, actually, this could be part of the throttle, believe it or not.
Like a fixed throttle orifice so you know it will never exceed a certain pressure.
Or it could be a deeper bell nozzle actually. Now that I think about it, it's more likely...
Hold on, this might be, this might be the actual expander part! Where it's taking the hot gas from
here, accelerating at supersonic [speeds], going from high pressure through a de Laval nozzle,
spinning this pump. That pump drives both the liquid oxygen and the - this
makes sense! - and the inlet comes in here. Okay, so that's your whole beauty right there!
[Carl] Yeah here's your first stage. [Tim] Is that labeled anywhere? I gotta know now,
I gotta know! [Steve] Okay, so what is this? Say one more time what the effect of this? [Tim] So
this is basically, it's a mini rocket nozzle. This is going to be the same thing as the throat
of the engine, where it's it's going to be high pressure here, they choke the flow,
which is going to get it up to supersonic speeds. And then they expand the flow again, just like
just like any thruster you see around here at all. So it's a de Laval nozzle. And so what
it's doing here, is exchanging high pressure for higher velocity. So they they do this in order to
jack up the velocity, to be able to spin the pumps, right before it spins the pumps.
I think - now again I am genuinely an amateur, but that seems plausible.
[Ken] Here's a diagram of the RL-10 engine I looked up last time I was here.
Hopefully that will help. [Tim] Okay.
[Marc] so it comes from the bell, heats up, heats up.
It's collected all the way here. So all these little tubes they make it all the way up.
[Tim] You can actually see it almost right here, this is a version of it. Right here,
you know, you can see how this manifold interfaces with these individual tubes.
[Carl] This is feeding down. [Tim] Yep. [Carl] And then they come up. [Tim] yeah. [Marc] Oh,
therefor the two to one. So it's coming in here.
So the hydrogen comes in mid-bell, through half of these little tubes, and goes downwards.
At the end of the bell, the tubes do a U turn, and come back up, all the way to the top of the bell,
then further up all the way to the top of the combustion
chamber to keep the outside of the chamber cool, as you can see here.
[Tim] Yeah we're definitely right that the bottom tube is... [Marc] The ring to which this fat pipe
is connected collects the hydrogen from the tubes. It is now heated up, and transformed into a gas at
very high pressure. This is what will drive the turbo pump. [Tim] ...is the - after it's been run
through everything. So this is what spins. [Marc] We are now looking at the inlet
(to the right) and the outlet (down and going to the left)
for the turbine that is at the bottom of the turbopump, and spins the whole thing.
[Steve's son]
The absolute final journey is going this way. [Tim] Yes. The very bottom of this big old fat
guy is what's going to go - there's going to be a vent at the end of this and that goes
into... Is there a vent somewhere? Yep, this guy. [Steve's son] Mixture ratio adjustment.
[Marc] So it goes into the combustion - the top ring is to the combustion chamber,
right? [Tim] Yes. So the top of the combustion chamber is right about here and that's going to
be your injector. [Steve's son] Which makes sense, just physically, with these tubes: the inner one
would be... [Tim] Mmm, okay, so we're definitely right, this is the final output here. [Marc] So
does all the hydrogen go through the bell? [Tim] Um, that's a good question. [Marc] Because it
looks like maybe it's only part it. [Carl] This is still super dense compared to... [Marc] But does
it get split into, one here that goes through the bell, and one that goes straight through?
Nope. All the hydrogen goes through the pump, is forced into the bell,
expands to drive the turbine of the pump, then goes into the combustion chamber.
Oh, so this is stage one, stage two. [Tim] Yep and exactly, then it's going to start staging
from there. [Marc] But then output would be here then? [Steve's son] It's also driving
the oxygen. [Marc] Oh sorry, so then the output is down there. [Steve's son] It's mechanical.
Is there like gears between these?
Which is totally makes sense. [Steve] And your oxidizer and fuel just follow those lines.
[Tim] So this is a gear box right. You're driving the oxidizer. The
oxidizer is hilariously simple. Oxidizer in and then tube going to the purge check valve,
which we should see that. [Steve's son] Purge check valve, it doesn't say purge check valve, but
mixture ratio adjustment. [Carl] This is a discharge, cool down and pressure relief
valve. [Marc] That's on the hydrogen line. [Steve] Mixture adjustment is a choke valve,
so that you can adjust the oxygen. [Tim] Yep, that would totally make sense.
[Ken] So one thing about the gearbox, is that you have to make sure the seal - because you have the
same gearbox for both the oxygen and hydrogen - you have to make sure your seals are really
good, or the oxygen and hydrogen mix. [Marc] Oh yes, that would be bad. [Ken] So sometimes
they'll have like two separate turbo pumps so then you don't have to worry about the seals.
And there you go, with the help of the Everyday Astronaut,
an everyday bunch of retro-electronicians can figure out an RL-10 rocket engine plumbing.
Kinda sorta. We could also have watched the vintage Pratt and Whitney video from
the 1960’s and gotten the explanation, that you will now follow with ease.
[Narrator] The engine itself is as simple as the diagram. To demonstrate, hydrogen enters at this
point, flows through the first stage pump, into the second stage pump, passes through
the cooling jacket manifold, down through half the tubes, to the turnaround manifold,
up the long tubes, collected at the exit manifold, through the venturi into the turbine.
There it provides the power to drive the hydrogen and oxygen pumps. Then around the large line
through the main fuel shutoff valve into the injector and then to the combustion chamber.
On the oxygen side, oxygen flows through the inlet valve through a single stage pump,
directly through the mixture ratio control valve, into the injector.
[Marc] Now, really, go see the Scott Manley video. See you in the next episode!
[Narrator] Arriving at one of the vertical test stands the RL-10
is installed and made ready for test fire.
Three, two, one, zero...
On completion of this test firing the engine will be returned to
the manufacturing area for complete disassembly, inspection, and reassembly.