I feel like you made this video to answer my questions. Thank you very much, it's great.

I worked building RL-10's back in '89-90 when they were developing the improved thrust version that has the moveable skirt and they really ran into problems. When you increase the fuel flow needed to increase the thrust the skirt cools down which then reduces the expansion which slows the pumps. It's a really delicate balancing act on the early engines and the first attempts to increase the thrust did achieve more but they lost impulse which is no good for a second stage engine. The nozzles supplying fuel and oxygen in the 'shower head' were flowed then carefully adjusted by hand to get exactly the flow needed which was a bit tedious and often took many trips to the flow test to get it right. Happily things were worked out and the engineers at P&W were and still are the finest in the world.

I love how Elon, Tim, Tory, Destin and Scott just have a casual discussion in rocket engines on in some tweet reply chain of something unrelated.

DC-X was a 'first stage' that was lifted against Earth Gravity, using 4 RL-10's! Another cool idea is to use an expander cycle with an Aerospike nozzle. This would supposedly give some more nozzle area so the total expander cycle engine could have more thrust than with a de laval nozzle (it would 'scale' better).

This was great, please do more of these more in-depth videos on other cycles, other engines, and other space tech stuff.

I wish I understood 3% of what you're saying, but it's absolutely fascinating. Okay maybe I understand 3% but I love how much detail you get into. Thanks again, Scott.

Not going to lie, I had to back up and replay parts of this video a bunch of times - but it was really fascinating! Thanks for the introduction to Expander Cycle rocket engines!

Thank you Scott for talking about a great Engine like the RL-10, but Sorry Scott RL-10A5 used on the DCX and DCXA launched many times. I worked on the engine test program from 1991 to 1995 for P&W. You also didn't note that the RL-10A5 was very throttleable from down to 5% to 100% in less than 3 seconds, This is why it was selected for the CC program to land on the Moon. Most likely will be again just a modified Aces engine RL-10C-5. Best regards Ed.

Really looking forward to Japan’s LE-9.

I haven’t really payed attention to your subscriber count for a while and I still thought you had like 25000. Now you have 860,000!! That’s insane. Good job

Cryogenic H2 & He ... In another life I use to service vacuum pumps and systems. The most unusual pump I had to service (for the first time) was a cyro-pump using liquid helium in a "cold head" that's purpose was the condense and freeze all the residual gas left in the vacuum chamber. The liquid helium was produced by the system and there was a "temperature gauge" to indicate when the helium was cold enough to liquefy. How this was done was with SS sealed system pipe system with pressure gauge and a small bulb in the cold head and was filled H2 at 7 bar. The pressure gauge scale wasn't in pressure, rather it read the lower end of the Kelvin scale. The idea was that as the temperature dropped to cryogenic levels so did the pressure. The gauge needle would sit there doing nothing and then would slowly drop to 14K at which point the H2 would freeze in the bulb. The pressure would still drop past this point as more H2 condensed and froze. From memory the low end of the scale was 4K which is the temp of LH2. The reason for the service was they opened the connection to the gauge and let all the H2 out so it didn't work as it should. All I had to do was evacuate the system, fill with H2, evacuate again to and then fill to 7bar. The client was very surprised that it was so simple to fix and they just paid a lot of money for me to do something they could have done. Its the old story - "you're not paying me for turning the screw; rather you're paying me for knowing which screw to turn." haha

Those were some cool (or maybe hot...) new expander cycles I had not seen before. Thanks for some rocket design with my morning coffee!

Nice one Scott !!!! super informative !! extremely high KTT ratio (Knowledge To Time). loved it ...

One of the best channels on UKposts. Keep up the good work.

Thanks for expanding my knowledge on this subject!

The RL-10 is my Realism Overhaul vacuum engine of choice!

Idunno what Bob Ross was doing in that web page but now all I can think about is adding a 'happy little rocket' to the background of a painting. ..Maybe some ejecta from stage-sep .. Little sun glistening off the main body .. and a slightly broken con-trail

Thank you for explaining that. I did know that limitations in the Closed system were due to cube-square law, but it is nice to refresh memory.

That blog post, and the follow up NTR post, are PURE GOLD Internet manna!

5:38 when you see this after Simple RL-10 schemat

Love your videos as always! I would love to see a video about the combustion tap-off cycle. As a thought, I always wondered about a combustion tap-off cycle that uses an external starter such as an electric motor to get the turbo pump spinning before the rocket launches. I figured that starting such an engine would be extremely simple. Get the turbo pump spinning, ignite the pyros, then open the propellant valves and the engine will start and be able to run on its own. An overrunning clutch will automatically decouple it from the electric motor once the engine fully ignites, and off it goes!

I love learning from you, Scott. Your voice is like my light in the dark.

I love expander-cycle engines. It's just such an elegant concept.

It is truly amazing how something so impossibly complicated is made to seem trivial.

I love how you set up your Delta 4 and Atlas 5, while talking about their glorious upper stage and the engines that it uses.🚀👌🚀👌🚀

The best space channel on YT

6:00 Scott is surprisingly confident in our knowledge of the rankine scale.

Just w8 for the day this chanel hits long deserved 1 milion subs

And the Japanese are going with the (Open) Expander Bleed Cycle for their rocket engine LE-9, which solves the limiting thrust problem of Closed Expander Cycle, so it can give high thrust while also reducing complexity and cost albeit at a less efficiency. But the superiority(by power) yet low cost n simplicity of it is unmatched by other expander engines I believe. (I had made this comment without watching the whole video completely so I thought he missed LE9 of Japan when mentioning others earlier in the video.)

I like how the Rutherford engineer upper stage has two batteries one ejects when drained reducing the total weight to SECO down just a wee bit. Your going to need all the efficiency you can get with a 17m tall rocket.

6:18 You forgot about the RL10A-5 wich flew on the DC-X wich was used in atmospheric conditions

Thank you Scott, 99% of that just washed over me and did not stick, we really enjoyed it, and that 1% is a lot of new knowledge, you could easily win the Galactic Institute's Prize for Extreme Cleverness. It is amazing that the most tech heavy industry relies on kit and ideas that are decades old.

Now that answered my question of of tubes wrapped around the engine bell of many rocket engines. Thanks scott manley

Hey Scott Manley. If it were not for you I would never know about staged combustion closed cycle rockets! Love your channel Scott. You are the best spokesman for space exploration I have know in my 69 years. Keep it up. I have a PhD in Chemistry and learn new stuff from you daily.

IIRC the RL-10 was used on DC-X and was also planned for DC-Y. So it WAS used as a liftoff engine.

I'm amazed that after so many years that rocket design hasn't settled on a few basic designs that everyone uses. It shows that rockets are still in their infancy and have a lot of improvements yet to go.

Here from Curious Marc channel. Great explanation!

Hey Scotty! thanks for beaming me up again!!

I hope the day will come when we look upon this technology as being antiquated and quaint kind of like steam locomotives.

in my office at work i have that F1 @0:52 engine turbopump assembly cutaway hanging on my wall 36x24. great conversation starter

Great video as always. Thank you very much.

I appreciate the new Starship models behind you )

I now have a 6" Newtonian on an Equatorial with a clock drive. I'm super exited! :D

Your voice sounded great on the intro! New mic, or configuration? And do you think Kerbal 2 will be that much better? I mean the laws of physics remain the same, what could be taking them so long to establish?

I thought I was pretty sharp with propulsion with a career in business and some military aviation. Space technology...how hard can it be.? Well you just crushed me with this one. Thank You. I needed a come-uppance. 😉

The rl 10 is a workhorse of an engine logging so many flight hours awesome look into how it works

I really enjoy this channel

Can you do a vijeo on modern solid rockets? All this edumaction on liquid rockets makes me realize that they must me more complex than I've thought about...

Scott, if you ever make it out to Utah (my home state) you need to go out to ATK and experience the booster rocket tests!

There's beauty in every cycle type..

I wish he would also talk about the specific impulse or exhaust velocity of the engines as well as thrust.

Scott: ...neutral hydrogen gas... Hydrogen embrittlement: what am I, a joke to you?

I always feel smarter after I watch one of your videos. :)

I love this kind of video’s, educational and entertaining I love you Scott, your the best space youtuber, I wish I could travel to the US to meet you

Curious Marc sent me here but I'm already an avid subscriber. Somehow I missed this video in 2019. I now understand rocket science. There should be a pin or something.

4:10 that cut out gives you a view of how intricate and technologically advanced these engines are. And apart from spacex all these are thrown away after one use. 🚀🗑😱

Scott, If the Draco engines prove too dangerous for a crewed capsule what realistic alternative engines are there to replace them? Thanks for a great channel!

A very good video... Keep teaching us.

What I would love to see would be a paraffin hybrid rocket driven by an expander cycle, since you only have to pump the oxidizer, you could get higher mass flow rates, and if you used the turbine exhaust for film cooling of the nozzle extension you could pull more energy out of it (i.e. have a lower turbine exhaust pressure). Also, since the combustion chamber wall is insulated by the fuel, you would only have to actively cool the nozzle which could allow for larger engines that are still on a closed, or partially closed cycle.

I'd like to see you do a video on the Aerojet M-1 rocket engine, especially if you can visit where the parts of the unfinished prototypes are. It had a unique solution to the efficiency loss from dumping turbopump exhaust at low pressure. Make the pumps extremely powerful so their exhaust is at high pressure then duct it to a ring of nozzles at the bottom of the skirt where they would produce a few thousand pounds of thrust instead of no thrust like other open cycle engines.

What perfect timing. I was just thinking about that...

Are there any good books on rocket engines... written for the lay person? I've read some of your other recommended books and loved them, but I'm still at a loss for understanding rocket engines (besides what I've learned from your great videos). Thanks, Scott!

Hey Scott, another great video!! Thank for sharing. Had a question... wondering if you know what kind of setup would be most efficient for a nuclear fueled rocket engine? I imagine a nuclear fueled rocket engine would be powered and or plumbed through the combustion chamber and or nozzle using a completely different style “pump” system than explained in this video to plumb the fuel out of the nozzle to generate thrust but I was wondering if you have a video on this or could explain how this would work. Thank you in advance and as always, thank you for sharing. I’ve been a fan for a while now and appreciate all of the time you take to teach and inform the public. Fly safe!

your "fly safe" at the end gave me threat vibes 0-0

tl;dr: Expander Cycles are the rocket engine equivalent of Pulling Yourself Up By Your Bootstraps

I am more than amazed when I saw the Chinese subtitles. AWESOME

hey scott can you link your rocket models somewhere? im interested, maybe you said it sometime somewhere but i cant find info on it... thanks and of course fly safe

Great video!

6:00 It's good to see the Rankine Scale used every once in a while...

Man, I feel really pumped up right now, I'm going to buy some Estes rocket motors and build a multi-motor crazy albatross rocket and see what happens! 🚀💥🔥

Would it be possible to have an open/closed hybrid expander cycle engine? That way you could run the engine in the open cycle configuration when more thrust is needed, and in closed cycle config when the thrust is not required, so that you can take advantage of the higher efficiency.

Hi Scott Manley, I wonder if/when we will see the Aerospike engine in use? Thoughts?

Hey Scott, in all this time almost no-one talks about catalyst converters in mono-propellant engines, such as the catalyst pellets depicted in the diagram of Redstone's steam turbine. Think you could an episode on that? Like, exactly is it? What is it made of? What is the chemical reaction taking place? Is it the same thing that makes the bubbles in my contact lens solution, etc. That would be cool.

I'm kinda curious if powering the turbopumps by tapping exhaust from the engine bell has ever been considered. Haha my question was answered later in the video. I wasn't expecting it to come up, it seems like a pretty different principle from the expander cycle.

Could you make an RD-170 style expander cycle, to recover proportionately more heat energy from the exhaust of a larger engine?

What a concentration of knowledge here, both by our safe flyer and commenters.

Is the RL-10 the engine that whistles at 80,000hz? And damaged a payload back around 2009?

How do they keep the boiling liquid from creating massive back pressure, or simply locking a check valve closed?

Great content. Thank you!

I used to learn a pretty interesting expander cycle engine design. In this engine, the pump is driven by helium in a closed system. The helium is heated by combustion chamber and then dirven the pumps of liquid hydrogen and liquid oxigen; then the helium is cooled by the tank of liquid oxigen. It was proposed by PWR and called EX-Hex cycle engine. This design could also be applied on methane-oxigen engine.

My question is how much power does a turbo pump need to pump the fuel and oxidizer in the RL 10 engine. The V2 turbo pump generated something like 600 Hp if I am not mistaken.

Came here from you're injector video and I appreciate you're response to my question. So, in an expander cycle engine does the hydrogen go thru an injector plate into the combustion chamber, and if so is it still a vapor or condensed into a liquid by that point? I was curious about the impinging flow dynamics of such a set up.

I need to watch this again.

Well these all seem a bit better then some of my concepts but I remain confident. Although my current prototype was quite promising. Due to refinements in the design and upgrading the rotational power distribution packages I have dramatically improved efficiency. This has allowed me to eliminate 3 of the 7 guinea pi........ engines. This in turn gives me better balance, allows a reduction in lettuce...... fuel and reduces the overall waste produced by the 4 remaining engines. I will continue to be inspired by my hero Ralph Kramden. I too just want to send my loved ones to the Moon.

Ah, the smile in my face when I saw 14m43s of video!

Great video. Why not have other videos focusing on the other types of engines. The gas-generator cycle and staged combustion cycle.

@12:02 we see a Closed Dual Expander Cycle (w/ split oxidizer side), and later is shown a Closed Dual Split Expander Cycle. Is there a simple explanation for why, if only one side were to be split, it would be the oxidizer side?

Dude, your shirt is awesome!

hafnium alloys are definitely worth looking into, i think a ICBM used the expanding nozzle if i remember correctly

So the dual expander cycle is kinda like the full-flow version of expander cycle engines. I do wonder, though. Do rocket engines overall gain any significant performance when it preheats its fuel and/or oxidizer as a coolant before burning it?

@szyzyg Would it not be feasible to surpass the square/cube law by using a larger count of smaller-sized combustion chambers per engine to exceed the maximum thrust achievable from an expander cycle engine?

In the final design you mention, why not dump the gas generator exhaust into the combustion chamber? Is that exhaust at a lower pressure? Or just fully combusted and not providing any benefit at that point?

_Popped up a Bob Ross video in the other tab, ready to run when Scott is done._

The expander cycle was used as a first stage on the SSTO Mcdonnell Douglas DC-X

Where did you get that Starship & Starhopper model?

Hi Scott Thanks for your excellent programs! Would you be so kind to devote one to the materials science involved in combustion chambers and rocket nozzles? I realize the materials are under extreme conditions and would be good to know about materials, properties and manufacturing procedures. Best, Roberto

Suppose we have an expander cycle engine and scale it up by a factor of two keeping the chamber pressure the same. Then the throath area becomes 4 times larger and so does chamber wall area. With the same chamber pressure the LOX/LH flow (kg/s) becomes also 4 times greater. But then we will have 4 times bigger area to warm the 4 times bigger amount of LH to turn the turbine and there does'nt seem to be any problem. So why don't we get bigger thrust by scaling? My own solution (not quite sure if its correct) is that we need to take into account the best optimazation of the engine: Burning 4 times more LOX/LH does not need 8 times bigger combustion chamber, which would be the volume after scaling everything by factor of 2. It only needs to be 4 times bigger, and in that case the chamber wall would not have 4 times bigger area, but only 4^(2/3) bigger. So not enough are to warm the LH for the turbine. The Vinci engine clearly has a longer chamber than the RL-10 to counter this effect, but increasing the camber size too much might ultimately mean a too big weight penalty. Comments please.

Hi I was wandering if there has ever been a idea to use magnetic constriction to adjust the nozzle geometry?

That T-shirt is so cool. I wish I could buy one.

Probably covered in another video but this one got me thinking about fuel/oxidizer ratios, do they target stoichiometric ratio? Or more likely a lean ratio for complete oxidization...