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

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.

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!

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.

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.

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

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

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

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

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

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

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

Really looking forward to Japan’s LE-9.

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.

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

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

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

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

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.

Thanks for expanding my knowledge on this subject!

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

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'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.

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.

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

I appreciate the new Starship models behind you )

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.🚀👌🚀👌🚀

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.

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

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

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

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.)

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. 🚀🗑😱

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.

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

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

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

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

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.

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

Everytime I click on new rocket related content I'm disappointed to hear SLS hasn't been shitcanned yet. Tax thieves.

The best space channel on YT

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

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! 🚀💥🔥

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...

Here from Curious Marc channel. Great explanation!

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

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. 😉

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

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

Hey Scotty! thanks for beaming me up again!!

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

There's beauty in every cycle type..

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.

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.

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

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.

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

Scott-- Very good presentation. Just 1 minor editorial comment. The LH2 fuel is never 'boiled'. The LH2 is pumped to a pressure above what is called its 'critical pressure'. Above the 'critical pressure', boiling is not possible. There is no 'discontinuous phase change', only a 'smooth' drop in density at temperatures above the 'Critical Temperature'. Rocket engine regenerative combustion NEVER operate under conditions under which the fuel can boil in the regen system. Reason--the heat transfer characteristics under boiling conditions are not stable, and quickly decay to levels that cannot support operation of the hardware. For this reason, regenerative coolant systems (at least the ones that I have experience with) all use coolant that is at supercritical pressure. Thank you very much.

consider using the expander cycle for a fuel-rich gas generator, which then drives the turbopumps to increase chamber pressure

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

00:11:30 Those units are a blast from the past.

The Rutherford engine has half of a really good idea. It uses battery powered electric motors to drive the pumps. The better idea is a hybrid expander rocket engine. Take an RL-10, add an electric motor/generator on the hydrogen turbopump shaft. Remove the gearbox and drive the LOX pump with an electric motor. You get the advantages of the electrically driven rocket: no seal between LOX and fuel requiring helium, vastly simpler startup, simpler and much faster throttle control (good for landing!), less careful balancing of the turbine power to pump demand. But you can use a much smaller battery, since the majority of the pump power comes from the turbine. Finally, you can scale to a significantly larger thrust than an expander cycle, since when you increase engine thrust, expander turbine power may not keep pace but it does increase significantly. So as the engine gets bigger the battery scales faster than the rest of the engine. Eventually that's a problem but you can get quite a bit bigger and enjoy the cost and thrust:weight advantages of a larger engine before the battery weight is a loser.

5:32 - _Powered_ the space shuttle, unless they pulled them back out of the museums while I wasn't looking.

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.

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?

Expander Bleed Cycle is just another word for, "turbo waste gate"... CHANGE MY MIND!

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

Scott, you're a computer programmer. I know that takes smarts, but how in the world did you teach yourself the complexities of all this rocket science? I'm amazed at your level of knowledge! Very impressive!

Another way is to take some of the combustion chamber gas and send it off to a hydrogen heat exchanger instead of using a separate pre-burner to augment extra heat. The now cooler flue gas can be sent to the interior of the rocket bell to recover a little more "push" that would normally be lost if it was just bled out the side.

This made me wonder how tf merlins survive all that and actually can be reused...

My head hurts. All I remember from engineering class is, the wheels on the bus, go round and round!

TIL there's a totally convention gear train in some rocket engines. Totally makes sense why they'd use it, but I never would have guessed.

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

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

A thing that would solve many of these problems is some sort of bearingless pump. Now there is no leak, so it doesn't matter what drives what. It'd be really cool if something like that existed for the pressures required...

6:05 Pretty sure this is the first time I've seen Rankine used literally anywhere outside the Wikipedia page.

I think Everyday Astronaut summarized the RL-10 best: "The RL-10 is crazy, crazy efficient. However, one thing it's not, is powerful." That's probably why I don't think it would make a good lunar lander engine, but obviously people who are a lot smarter than me have probably crunched the numbers and came to the opposite conclusion.

I wish to hit the thumbs up every time I wach this but not allowed... So here it comes right here 😁👍👍👍👍👍... Thanks for educating me 👍👍

I have an idea! We should pre-mix the oxidizer and fuel in one bigger fuel tank to reduce the complexity of the rocket designs! Less tanks, fewer moving parts, more fuel! What could possibly go wrong?

A very good video... Keep teaching us.

Great video!

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

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!

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

The more you learn about rocket science, the more complicated it gets!

Ha! Humorous to hear a different way of saying the conclusion I came to a few years back: - The essence of any engine is control and management of pressure differentials.

Great video as always. Thank you very much.

Apparently the BE7 engine is a dual expander cycle. I've no idea if it's bleed or closed (guessing bleed), but that cycle seems to have left the drawing board now.

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

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.

10:08 the Blue Origin website specifies 1420 kN thrust in vacuum, not 1100 kN. That's 160,000 lbf thrust, 50,000 more than sea-level BE-3. A huge difference. It's under engines/be-3/be-3u. To the people that want to point out that under New Glenn page, a second stage total thrust is still stated as 1100 kN, let me remind you that after the website update last autumn, the engine section was updated again, changing the 550 kN to 710 kN, and that is the latest update from the company. Feel free to check the history of the website.

I have a suggestion.. If you make the video as a documentary like A Discovery channel show instead of just narration, it will be very much good and interesting..

Two things: 1. Happy trees all day, youngsters 2. Elon said any car not a Tesla is like a horse an buggie in a few years. Maybe current rocket tech is headed that way soon? We need more rocket scientists

Looking at these articles makes switching between metric and American that much harder

2:23 feels pretty prophetic today.