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> The engines are the most advanced ever made (arguably). Maybe not arguably. They embody a technology that's been considered for a long time the Holy Grail of

> The engines are the most advanced ever made (arguably). Maybe not arguably. They embody a technology that's been considered for a long time the Holy Grail of rocket science - the full-flow staged combustion cycle: https://en.wikipedia.org/wiki/Staged_combustion_cycle#Full-flow_staged_combustion_cycle https://en.wikipedia.org/wiki/Staged_combustion_cycle#Full-f...

NikolaeVarius 6y ago
As much as I love the Space Shuttle, I wish the US had not went all in on Hydrogen Oxygen. The RS-25 are amazing engines, but we could have had operational full flow staged engines 20 years ago if we had gone down that route. Though probably not the landing part.
- avmich 6y ago
  Interesting that full flow LOX-LH2 engines could be easier to get, as oxygen and hydrogen can be ignited in a wide range of ratio. With LOX-kero you might have to have a two stage gas generator, when first you ignite components with a good ratio and then add a component to the already established combustion.
  - elteto 6y ago
    > With LOX-kero Small nitpick: kerolox is much nicer sounding and what people know them as ;)
    - jsjohnst 6y ago
      If you are going to nitpick the kerolox, why not hydrolox too? ;) (I’m not one of the downvoters for the record)
      - elteto 6y ago
        Oh I just missed it :)
  - jsjohnst 6y ago
    LH2 is way less dense than RP1 though, so you’d need a significantly larger fuel tank to carry the same amount of fuel. Hydrolox (LOX-LH2) is about 30% more power than Kerolox (LOX-RP1), but is about 3.5x less density. Source: https://en.m.wikipedia.org/wiki/Liquid_rocket_propellant#Bipropellants https://en.m.wikipedia.org/wiki/Liquid_rocket_propellant#Bip... Hydrolox - Ve: 3,816 d: 0.29 Kerolox - Ve: 2,941 d: 1.03 If you were wanting to optimize for high specific impulse, it seems LOX-LH2:Be or a fluorine based fuel is the way to go purely on the numbers (not accounting for cost or stability).
- blackrock 6y ago
  NASA should’ve kept producing the Saturn V. Over time, the production costs should’ve come down. The shuttle was a rather mediocre trade off, in terms of LEO payload capacity. Although granted, the shuttle landings were pretty cool.
phendrenad2 6y ago
Thanks! Just started reading about rocket engines, I don't think most people realize how many moving parts the SpaceX engines have!
- FlyMoreRockets 6y ago
  Okay, I'll bite, How many moving parts do the SpaceX engines have? Assuming the fuel and oxidizer impellers are on a common shaft, that's one. There must be a throttle valve somewhere, so that's two. What am I missing? Are there reduction gears?
  - m4rtink 6y ago
    They use pintle injectors in the Merlins, so that does move as well (though only a short distance) and is likely what makes them so throttleable. https://en.m.wikipedia.org/wiki/Pintle_injector https://en.m.wikipedia.org/wiki/Pintle_injector
    - FlyMoreRockets 6y ago
      Not sure why I was downvoted. Are the moving pintle injectors separate from a throttle vavle? I have studied a lot of pintle injector designs and it can go either way. Reguardless, a moving pintle injector typically only has two moving parts.
marcusverus 6y ago
TL;DR: Liquid-fuel rockets work by combining a liquid fuel with oxygen. To get the fuel and oxygen into the combustion chamber in huge quantities, they use a big fancy pump. To power this big fancy pump, all liquid-fuel rockets burn fuel in a separate combustion chamber, using the hot gas to power the pump. After the gas powers the pump, it has to go somewhere. Most rockets just dump the gas (these are called 'Gas-generator cycle' engines). This is nice and easy (ha), but it also means that the gas isn't going through the main combustion chamber, so it isn't propelling the rocket. The rockets on Starship re-use the gas that drives the pumps, pushing them into the combustion chamber and burning any unused fuel/oxygen to propel the rocket.
- mschuster91 6y ago
  > The rockets on Starship re-use the gas that drives the pumps, pushing them into the combustion chamber How is that possible? From a total layman's point of view, the pressure in the combustion chamber should always be greater than whatever the pump can put out, thus leading to a pump stall... what am I missing?
  - maccam94 6y ago
    Actually the pump has to be able to put out as much if not more pressure than the pressure generated in the combustion chamber, otherwise it wouldn't be able to push a steady stream of fuel and oxidizer into the chamber. I recommend watching or reading https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/
  - lutorm 6y ago
    As the other post says, this cannot be true, otherwise how could the engine work. You'd not get any propellant into the combustion chamber.
- mabbo 6y ago
  > To power this big fancy pump, all liquid-fuel rockets burn fuel in a separate combustion chamber, using the hot gas to power the pump. There's some engineers in New Zealand who might have something to say about that... https://en.m.wikipedia.org/wiki/Electron_(rocket) https://en.m.wikipedia.org/wiki/Electron_(rocket)
DennisP 6y ago
Everyday Astronaut did a nice explanation of the Raptor and various simpler designs, and what's so great about full-flow staged combustion: https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/
mabbo 6y ago
This is the internet. I say 'arguably' because someone out there wants to argue.
- hinkley 6y ago
  And look! You found a friend!
- beamatronic 6y ago
  That is not strictly true.

NikolaeVarius 6y ago

As much as I love the Space Shuttle, I wish the US had not went all in on Hydrogen Oxygen. The RS-25 are amazing engines, but we could have had operational full flow staged engines 20 years ago if we had gone down that route. Though probably not the landing part.

avmich 6y ago
Interesting that full flow LOX-LH2 engines could be easier to get, as oxygen and hydrogen can be ignited in a wide range of ratio. With LOX-kero you might have to have a two stage gas generator, when first you ignite components with a good ratio and then add a component to the already established combustion.
- elteto 6y ago
  > With LOX-kero Small nitpick: kerolox is much nicer sounding and what people know them as ;)
  - jsjohnst 6y ago
    If you are going to nitpick the kerolox, why not hydrolox too? ;) (I’m not one of the downvoters for the record)
    - elteto 6y ago
      Oh I just missed it :)
- jsjohnst 6y ago
  LH2 is way less dense than RP1 though, so you’d need a significantly larger fuel tank to carry the same amount of fuel. Hydrolox (LOX-LH2) is about 30% more power than Kerolox (LOX-RP1), but is about 3.5x less density. Source: https://en.m.wikipedia.org/wiki/Liquid_rocket_propellant#Bipropellants https://en.m.wikipedia.org/wiki/Liquid_rocket_propellant#Bip... Hydrolox - Ve: 3,816 d: 0.29 Kerolox - Ve: 2,941 d: 1.03 If you were wanting to optimize for high specific impulse, it seems LOX-LH2:Be or a fluorine based fuel is the way to go purely on the numbers (not accounting for cost or stability).
blackrock 6y ago
NASA should’ve kept producing the Saturn V. Over time, the production costs should’ve come down. The shuttle was a rather mediocre trade off, in terms of LEO payload capacity. Although granted, the shuttle landings were pretty cool.

phendrenad2 6y ago

Thanks! Just started reading about rocket engines, I don't think most people realize how many moving parts the SpaceX engines have!

FlyMoreRockets 6y ago
Okay, I'll bite, How many moving parts do the SpaceX engines have? Assuming the fuel and oxidizer impellers are on a common shaft, that's one. There must be a throttle valve somewhere, so that's two. What am I missing? Are there reduction gears?
- m4rtink 6y ago
  They use pintle injectors in the Merlins, so that does move as well (though only a short distance) and is likely what makes them so throttleable. https://en.m.wikipedia.org/wiki/Pintle_injector https://en.m.wikipedia.org/wiki/Pintle_injector
  - FlyMoreRockets 6y ago
    Not sure why I was downvoted. Are the moving pintle injectors separate from a throttle vavle? I have studied a lot of pintle injector designs and it can go either way. Reguardless, a moving pintle injector typically only has two moving parts.

marcusverus 6y ago

TL;DR: Liquid-fuel rockets work by combining a liquid fuel with oxygen. To get the fuel and oxygen into the combustion chamber in huge quantities, they use a big fancy pump. To power this big fancy pump, all liquid-fuel rockets burn fuel in a separate combustion chamber, using the hot gas to power the pump. After the gas powers the pump, it has to go somewhere. Most rockets just dump the gas (these are called 'Gas-generator cycle' engines). This is nice and easy (ha), but it also means that the gas isn't going through the main combustion chamber, so it isn't propelling the rocket. The rockets on Starship re-use the gas that drives the pumps, pushing them into the combustion chamber and burning any unused fuel/oxygen to propel the rocket.

mschuster91 6y ago
> The rockets on Starship re-use the gas that drives the pumps, pushing them into the combustion chamber How is that possible? From a total layman's point of view, the pressure in the combustion chamber should always be greater than whatever the pump can put out, thus leading to a pump stall... what am I missing?
- maccam94 6y ago
  Actually the pump has to be able to put out as much if not more pressure than the pressure generated in the combustion chamber, otherwise it wouldn't be able to push a steady stream of fuel and oxidizer into the chamber. I recommend watching or reading https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/
- lutorm 6y ago
  As the other post says, this cannot be true, otherwise how could the engine work. You'd not get any propellant into the combustion chamber.
mabbo 6y ago
> To power this big fancy pump, all liquid-fuel rockets burn fuel in a separate combustion chamber, using the hot gas to power the pump. There's some engineers in New Zealand who might have something to say about that... https://en.m.wikipedia.org/wiki/Electron_(rocket) https://en.m.wikipedia.org/wiki/Electron_(rocket)

DennisP 6y ago

Everyday Astronaut did a nice explanation of the Raptor and various simpler designs, and what's so great about full-flow staged combustion: https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/

mabbo 6y ago

This is the internet. I say 'arguably' because someone out there wants to argue.

hinkley 6y ago
And look! You found a friend!
beamatronic 6y ago
That is not strictly true.