Tri-propellant rocket engines

[Dragorans]

Tripropellant engines are theoretically the most efficient chemical rockets in existence.

Rocketdyne made an engine in the 1960s that used gaseous hydrogen, liquid fluorine and liquid lithium that resulted in incredible 542 Isp. But they are not free of problems, obviously. 

Heating lithium to become liquid is not exactly easy, and storing and injecting solid grains into a combustion chamber would be extremely problematic (if not impossible due to backfiring).

There are two types of tripropellant engines:

Sequential burning

A sequential firing rocket would be something like a half-stage, only difference is that nothing is thrown away - you change the fuel mid-flight. 

Let's call an engine by the name KS-325.

KS-325 is RP-1 and LH2 compatible engine and LOX as an oxidizer. It is possible to switch between LH2 and RP-1 mid-flight. At launch, RP-1 will be the fuel used, as its higher density only offers advantages for first stages. When RP-1 ends, it will burn hydrogen, being better for upper stages.

All this while using the exact same engine. This offers obvious advantages for an SSTO. if the KS-325 has an extendable nozzle, this would probably be one of the best engines for an SSTO with chemical engines. However, it still has disadvantages...

The rocket would have to be insanely tall to store all the Hydrogen, RP-1 and the insane amount of LOX it would need.

The only new part that would need to be added would be the engine, since hydrogen tanks are already confirmed (Nerv and  NERV-US will use them) and RP-1/LOX will obviously be added.

This is the most likely one that would be added to the game, considering there are multiple engines that already have mode switches (e.g Panther jet engine). and NERV-US operates in a very similar way,  only needed changes will the fuels, performance and model of a NERV-US

 

Simultaneous burning

Basically it's injecting a third fuel into the combustion chamber. The hydrogen-fluor-lithium engine mentioned at the beginning is this type of engine.

This type of motor can theoretically achieve very high efficiencies, but as theory is not reality, injecting room temperature solids or high temperature liquids is not exactly viable. And making an engine that injects two "normal" fuels would have no advantage compared to sequential injection engines. 

There are several other problems that will certainly not be simulated in KSP, such as how to maintain the necessary high temperature.

One suggestion of mine would be to use rubidium instead of lithium, which has a much lower melting point, only 39°C. It would be much more realistic, but I don't know if it would be highly efficient - after all, this combination has never been tested.

 

The biggest problem with adding these engine to KSP would be having to create new parts. Things that difficult development should be avoided unless it's really worth it. That's why I suggest that only the engine that burns sequentially be added, since only one new engine would need to be added, and the "programming" of this engine has already been done even in KSP1, with the RAPIER, so overall it would only need to be added a new model, and a change in resource used.

 

So that's it, I'll probably write another thread about my ideas on the science & spaceflight topic, where I can write the scientific part (my favorite) more deeply. 

so yeah, see you guys later.

Any criticism of this idea is welcome, I want to know my problems

[Vortygont]

I like especially LH2-RP1-LOX engine, I believe it will fit in game like NERV-US. About techic difficultes of creation another tri-propellant engines I have answer - technologies of future, new future materials and methods

[jimmymcgoochie]

5 hours ago, Dragorans said:

One suggestion of mine would be to use rubidium instead of lithium, which has a much lower melting point, only 39°C. 

Terrible idea, for the simple reason that rubidium has a really high atomic mass (85) compared to lithium (7) and ISP is determined by exhaust velocity, which decreases with increasing molecular mass. It's also a lot less reactive than lithium, which will readily shrug off that extra electron and hence makes for a really energetic rocket propellant when combined with fluorine which just can't wait to get hold of said extra electron. Lithium's use in batteries, fluorine's toxicity and the logistics of trying to keep both liquid in close proximity when fluorine boils at several hundred Kelvin below lithium's melting point, not to mention the hydrogen fluoride (a.k.a. hydrofluoric acid) produced as a byproduct, are just some reasons why this was A Bad Idea and, like boranes and chlorine polyfluorides, best left in the history books.

The other engine you're describing sounds like the RD-701, a rocket engine designed for the MAKS spaceplane in the late 80s. It would burn both kerosene and hydrogen in the atmosphere for maximum thrust, then switch to just hydrogen once in space for maximum efficiency (switching off the kerosene turbopump but leaving the hydrogen one running as it had separate pumps for each fuel). The result was better efficiency than plain kerolox and better thrust than plain hydrolox, plus a denser propellant mix meaning smaller tanks were needed- useful for a spaceplane where larger tanks mean more wing and more thermal shielding are needed.

[yoarebignoob]

32 minutes ago, jimmymcgoochie said:

Terrible idea, for the simple reason that rubidium has a really high atomic mass (85) compared to lithium (7) and ISP is determined by exhaust velocity, which decreases with increasing molecular mass. It's also a lot less reactive than lithium, which will readily shrug off that extra electron and hence makes for a really energetic rocket propellant when combined with fluorine which just can't wait to get hold of said extra electron. Lithium's use in batteries, fluorine's toxicity and the logistics of trying to keep both liquid in close proximity when fluorine boils at several hundred Kelvin below lithium's melting point, not to mention the hydrogen fluoride (a.k.a. hydrofluoric acid) produced as a byproduct, are just some reasons why this was A Bad Idea and, like boranes and chlorine polyfluorides, best left in the history books.

The other engine you're describing sounds like the RD-701, a rocket engine designed for the MAKS spaceplane in the late 80s. It would burn both kerosene and hydrogen in the atmosphere for maximum thrust, then switch to just hydrogen once in space for maximum efficiency (switching off the kerosene turbopump but leaving the hydrogen one running as it had separate pumps for each fuel). The result was better efficiency than plain kerolox and better thrust than plain hydrolox, plus a denser propellant mix meaning smaller tanks were needed- useful for a spaceplane where larger tanks mean more wing and more thermal shielding are needed.

bro turned into scott manley

[Dragorans]

3 hours ago, jimmymcgoochie said:

Terrible idea, for the simple reason that rubidium has a really high atomic mass (85) compared to lithium (7) and ISP is determined by exhaust velocity, which decreases with increasing molecular mass. It's also a lot less reactive than lithium, which will readily shrug off that extra electron and hence makes for a really energetic rocket propellant when combined with fluorine which just can't wait to get hold of said extra electron. Lithium's use in batteries, fluorine's toxicity and the logistics of trying to keep both liquid in close proximity when fluorine boils at several hundred Kelvin below lithium's melting point, not to mention the hydrogen fluoride (a.k.a. hydrofluoric acid) produced as a byproduct, are just some reasons why this was A Bad Idea and, like boranes and chlorine polyfluorides, best left in the history books.

The other engine you're describing sounds like the RD-701, a rocket engine designed for the MAKS spaceplane in the late 80s. It would burn both kerosene and hydrogen in the atmosphere for maximum thrust, then switch to just hydrogen once in space for maximum efficiency (switching off the kerosene turbopump but leaving the hydrogen one running as it had separate pumps for each fuel). The result was better efficiency than plain kerolox and better thrust than plain hydrolox, plus a denser propellant mix meaning smaller tanks were needed- useful for a spaceplane where larger tanks mean more wing and more thermal shielding are needed.

 

1- I had forgotten about that fact. Rubidium is not good then.

 

2- I'm talking about in-game implementation. Kerbais can stand right next to a rocket taking off and be 100% fine . Kerbals can withstand collisions at 20 m/s and just get up and continue the mission. One problem I've noticed is that people think like human engineers, but kerbals are not humans. It would be a lot of fun to use such an engine. And I was planning to put pretty much everything you wrote about Hydrogen and Fluorine combustion and how it releases not so cool stuff. But like I said before, kerbals either die or they continue their mission as if nothing had happened. Think, why does the game let you put a kerbal in a chair for 90 years in space without any radiation protection or life support, and the kerbal doesn't show the slightest signs of health damage? Because its fun to do this. We are not talking about humans. We're talking green, clumsy alien beings who want to go to the stars, it doesn't matter if a nuclear bomb goes boom behind them, they just go.

Edited December 11, 2022 by Dragorans

[Dragorans]

8 hours ago, Laikanaut said:

Most KSP engines are heavily inspired by real world equivalents, are there any existing or designed engines that use the tripropellant sequential burning method? It sounds interesting, and easy to integrate with KSP as being similar to the RAPIER. But I'm unsure whether they are adding more of the widely used fuel types to replace the generic "liquid fuel," which would be necessary to make this engine. Personally I think they should at least add methane/hydrogen/kerosene equivalents to add some variety to the standard fuels, and use the 3 main rocket fuels that were covered by Everyday Astronaut, but they appear to be reusing the KSP tank design which is bipropellant tanks with ratios to match the engine fuel ratios, which are all the same. Changing this would result in significant changes to a core mechanic of the lego rocket design style, but I think there are better methods, such as tanks with switchable resources. However this adds other complications that may be beyond the interest of the average player.

Overall there is a lot more to consider with adding this type of engine to the game. I know they are adding a few new fuel types like metallic hydrogen, but the current approach is that every engine with a new fuel type needs its own tanks with fuel ratios matching the engine, and this can quickly result in an overwhelming number of tanks. I'm pretty sure they said no to switchable tanks at some point, so this engine may remain in mod territory.

The different fuels have already been confirmed.

We already know very well that Liquid Hydrogen will be present in the game from the beginning, since the Nerv engine will need it. The Nerv-US engine I mentioned works because it uses hydrogen. We already know that methalox will be in the game, since the Swivel engine mentions it on its description.

About the tanks, we will have hydrogen tanks just because nuclear engines use it, and we will have nuclear engines! I dare say we will have oxygen only tanks as well, as engines like NERV-US will use them. Also we will have to separate "Hydrolox" from  "Liquid Hydrogen" like SimpleRockets 2, because that would eliminate the problem of having to balance the fuel/oxidizer ratio. Oxygen only tanks would be easy to add. Just a new engine and maybe some new tanks because size matters.

And there are examples of sequential burning engines. The Russian double-chamber RD-701 it worked in a similar way, burning all fuels on takeoff and using only hydrogen when in space. 

The RD-701 was further developed into the single-chamber RD-704. But both never flew

Edited December 11, 2022 by Dragorans

[yoarebignoob]

does liquid hydrogen+ liquid oxygen and helium count as tri-proppelant?????????

[Dragorans]

1 hour ago, yoarebignoob said:

does liquid hydrogen+ liquid oxygen and helium count as tri-proppelant?????????

No, helium doesn't even react with anything. It only serves to maintain the pressure in the tanks.

34 minutes ago, Laikanaut said:

 

 

 

Hmm, I didn't watch that video. Probably because I don't watch everyday astronaut. But it's always good to have more knowledge

[Dragorans]

20 hours ago, Laikanaut said:

Suit yourself, I linked to the time of the video which covered those engines, for the benefit of anyone interested. It includes specs and a little more info, the ISP of the second hydrogen mode was impressive.

 

It was said that the Americans thought most of these engines were impossible until they visited the Soviet Union after it collapsed, bought the engines and investigated the designs. I guess you don't know what you don't know.

 

I meant that I didn't know the video existed before you showed it to me. But I watched almost the entire video after that. Thx!

 

 

 

[AtomicTech]

On 12/10/2022 at 11:25 AM, Dragorans said:

Tripropellant engines are theoretically the most efficient chemical rockets in existence.

Rocketdyne made an engine in the 1960s that used gaseous hydrogen, liquid fluorine and liquid lithium that resulted in incredible 542 Isp. But they are not free of problems, obviously. 

Heating lithium to become liquid is not exactly easy, and storing and injecting solid grains into a combustion chamber would be extremely problematic (if not impossible due to backfiring).

There are two types of tripropellant engines:

Sequential burning

A sequential firing rocket would be something like a half-stage, only difference is that nothing is thrown away - you change the fuel mid-flight. 

Let's call an engine by the name KS-325.

KS-325 is RP-1 and LH2 compatible engine and LOX as an oxidizer. It is possible to switch between LH2 and RP-1 mid-flight. At launch, RP-1 will be the fuel used, as its higher density only offers advantages for first stages. When RP-1 ends, it will burn hydrogen, being better for upper stages.

All this while using the exact same engine. This offers obvious advantages for an SSTO. if the KS-325 has an extendable nozzle, this would probably be one of the best engines for an SSTO with chemical engines. However, it still has disadvantages...

The rocket would have to be insanely tall to store all the Hydrogen, RP-1 and the insane amount of LOX it would need.

The only new part that would need to be added would be the engine, since hydrogen tanks are already confirmed (Nerv and  NERV-US will use them) and RP-1/LOX will obviously be added.

This is the most likely one that would be added to the game, considering there are multiple engines that already have mode switches (e.g Panther jet engine). and NERV-US operates in a very similar way,  only needed changes will the fuels, performance and model of a NERV-US

 

Simultaneous burning

Basically it's injecting a third fuel into the combustion chamber. The hydrogen-fluor-lithium engine mentioned at the beginning is this type of engine.

This type of motor can theoretically achieve very high efficiencies, but as theory is not reality, injecting room temperature solids or high temperature liquids is not exactly viable. And making an engine that injects two "normal" fuels would have no advantage compared to sequential injection engines. 

There are several other problems that will certainly not be simulated in KSP, such as how to maintain the necessary high temperature.

One suggestion of mine would be to use rubidium instead of lithium, which has a much lower melting point, only 39°C. It would be much more realistic, but I don't know if it would be highly efficient - after all, this combination has never been tested.

 

The biggest problem with adding these engine to KSP would be having to create new parts. Things that difficult development should be avoided unless it's really worth it. That's why I suggest that only the engine that burns sequentially be added, since only one new engine would need to be added, and the "programming" of this engine has already been done even in KSP1, with the RAPIER, so overall it would only need to be added a new model, and a change in resource used.

 

So that's it, I'll probably write another thread about my ideas on the science & spaceflight topic, where I can write the scientific part (my favorite) more deeply. 

so yeah, see you guys later.

Any criticism of this idea is welcome, I want to know my problems

 

Heck, do you want a mod patch for this?

I'd be willing to do it if you like

[Dragorans]

Im console player

14 minutes ago, AtomicTech said:

Heck, do you want a mod patch for this?

I'd be willing to do it if you like

 

[Abel Military Services]

On 12/14/2022 at 4:58 AM, AtomicTech said:

Heck, do you want a mod patch for this?

I'd be willing to do it if you like

If you want, just do it. Remember to add MOAR juice! 

My opinions: 

Maybe we can add a gas-core NTR that has a afterburner mode. It consumes Enriched Uranium(Or other fissile material, because the reactor itself will go out) Liquid Hydrogen and Oxidizer. 

Edited January 10, 2023 by Abel Military Services

[magnemoe]

Don't see it as very practical, exception might be an multi fuel nuclear thermal engine with an afterburner. 
 

[zeekzeek22]

3 hours ago, magnemoe said:

Don't see it as very practical, exception might be an multi fuel nuclear thermal engine with an afterburner. 
 

Who said anything about KSP monstrosity creations being practical?!

[magnemoe]

8 hours ago, zeekzeek22 said:

Who said anything about KSP monstrosity creations being practical?!

Sure, but then you get Orion pulse nuclear the only way to top it is antimatter.