Would you use a tri-propellant rocket?

[Carsogen]

Note: This isn't a mod request or suggestion, merely a discussion on whether triple fuel rockets would be useful or redundant .

Edit: Altered a bit to be more specific

Would rockets that use liquid fuel, oxidiser and intake air AT THE SAME TIME be useful in KSP?

For example, a Liquid Air Cycle Engine or Air Augmented Engine.

In real life rocket lifters don't use jet engines and adding intake air would make them waayy more efficient, but in KSP I would just throw a jet engine or RAPIER on my launcher, removing the need for a triple fuel rocket.

What do you think? Do the air breathing engines and RAPIER already do the job of a rocket engine that uses intake air in atmosphere to be more efficient?

Cas.

Edited January 5, 2015 by Carsogen

[Bill Phil]

So, you mean the RAPIER right? Because tri propellant means something like LH2 - RP-1 - LOX.

[Carsogen]

So, you mean the RAPIER right? Because tri propellant means something like LH2 - RP-1 - LOX.

I think you misunderstood, I mean an engine that uses the three fuel sources AT THE SAME TIME, ie. Liquid fuel, Oxidiser and Intake Air like this http://en.wikipedia.org/wiki/Liquid_air_cycle_engine?

Sorry should have specified

Cas.

Edited January 2, 2015 by Carsogen

[Red Iron Crown]

Do you mean an air augmented rocket? One that can use any atmo regardless of whether oxygen is present? Tri-propellant usually refers to a propellant combination with three components, all carried by the rocket.

[psyper]

I think Carsogen means a bi-propellent system but it can take o2 out of the atmosphere while its available instead of using the liquid oxygen in the tanks - this has the advantage of needing less liquid oxygen to get in to orbit.

[Carsogen]

Do you mean an air augmented rocket? One that can use any atmo regardless of whether oxygen is present? Tri-propellant usually refers to a propellant combination with three components, all carried by the rocket.

Sorry I guess I'm not quite using the right terminology

what I mean is the kind of engine explained in the link in my prior comment, a rocket that uses both fuel and oxidiser but also gains oxygen to combust from the air, as opposed to the air augmented rocket which only accelerates the air but doesn't burn it.

(Sorry on my phone so can't neaten up links)

I guess they essentially do a similar job in KSP?

Cas.

- - - Updated - - -

I think Carsogen means a bi-propellent system but it can take o2 out of the atmosphere while its available instead of using the liquid oxygen in the tanks - this has the advantage of needing less liquid oxygen to get in to orbit.

Yeah basically but like the Liquid Air Cycle Engine (link in my first comment) it would use all 3 at once as opposed to the RAPIER which switches between the two.

Cas.

[Laie]

So it runs on air at low altitudes, and as the air gets thinner, it starts injecting additional O2 from the tanks? Sounds like a nice concept. Also very Sci-Fi, but that wouldn't stop me from using it if it was available.

[psyper]

Yeah basically but like the Liquid Air Cycle Engine (link in my first comment) it would use all 3 at once as opposed to the RAPIER which switches between the two.

So you're looking at an engine which will use a lot of intake air and not much liquid oxygen and as it ascends higher in to the atmosphere it'll consume more and more liquid o2 until its in space and its using liquid o2 and fuel much like a normal engine. Whereas a rapier will use no liquid o2 until its reached a threshold and switches to 100% liquid o2 straightaway with no sliding scale between the two.

[Red Iron Crown]

So sort of like a RAPIER but it changes modes gradually rather than abruptly. Interesting.

[Ravenchant]

Getting the oxidizer+air/fuel just right would probably be a bit tricky...there's a reason it was sparingly used in the past (missiles, usually). That said, they would be useful for certain SSTO configurations.

Hybrid rockets on the other hand could be more versatile, something like a throttleable, less volatile SRB and (in theory) easier to operate than a pure liquid propulsion.

[Carsogen]

So sort of like a RAPIER but it changes modes gradually rather than abruptly. Interesting.

Yeah exactly or something that just has a set ratio and doesn't change gradually or some version of this.

Cas.

[MalfunctionM1Ke]

I remember Scott talking about this.

Skip to 12:45min

[Whirligig Girl]

The only Tripropellant there is is *shudders* Hydrogen, Lithium, and Fluorine. They produce the worst chemical ever when burnt, and to keep all the propellants there liquid, you have to have hugely complicated tank design. Not to mention the fact that liquid lithium is essentially a molten metal that will screw up all the electronics. There is an advantage, however. On paper at least, a Tripropellant rocket gets an Isp of 540 seconds.

A Tripropellant is NOT what the OP suggests. Intake-Air is not even a propellant irl, (though they are in KSP which is why jet engines are way too effective)

- - - Updated - - -

Sorry I guess I'm not quite using the right terminology

what I mean is the kind of engine explained in the link in my prior comment, a rocket that uses both fuel and oxidiser but also gains oxygen to combust from the air, as opposed to the air augmented rocket which only accelerates the air but doesn't burn it.

(Sorry on my phone so can't neaten up links)

I guess they essentially do a similar job in KSP?

Cas.

- - - Updated - - -

Yeah basically but like the Liquid Air Cycle Engine (link in my first comment) it would use all 3 at once as opposed to the RAPIER which switches between the two.

Cas.

You can edit the OP to clarify.

[Red Iron Crown]

Intake air is most certainly a propellant, both in KSP and real life.

[Ralathon]

The only Tripropellant there is is *shudders* Hydrogen, Lithium, and Fluorine. They produce the worst chemical ever when burnt, and to keep all the propellants there liquid, you have to have hugely complicated tank design. Not to mention the fact that liquid lithium is essentially a molten metal that will screw up all the electronics. There is an advantage, however. On paper at least, a Tripropellant rocket gets an Isp of 540 seconds.

Ah, the wonderful world of fluorine chemistry... An ongoing reminder that the universe hates you and everyone in it.

[Steambirds]

A rocket that burns an LFO and Monoprop. mix would be a neat addition, without having to add any new fuels. Maybe the engines for a LFOMP (Liquid Fuel Oxidiser Monopropellant) could have either a higher thrust than their LFO counterparts, or maybe could have higher ISP than LFO rockets.

[aleis]

It's a neat idea bit I don't think it's really worry adding to the game. Complications it would add to vehicle construction with out much game play added as we already have the rapier, which, though not the same concept, is very similar in function.

Also as it's not practical rocketry in RL. Problem being is the density of liquid oxygen vs atmospheric oxygen. Your air intake get you maybe 5 intake air which would have to be compressed to equal like .1 LO then you get to higher altitude and your working with much less intake.

So add that tiny addition in fuel, then subtract the massive weight of the compressors and intakes. And your nor gaining much if anything

[pincushionman]

So what you're really trying to talk about is a SABRE engine? Which, I believe, is the concept the KSP RAPIER is based on?

[cantab]

"Triproellant" can refer to several different things. "One is a rocket engine which mixes three separate streams of propellants", eg the lithium, hydrogen, fluorine combination. "Another kind of tripropellant rocket is one that uses one oxidizer but two fuels, switching between the two in mid-flight. In this way the motor can combine the high thrust of a dense fuel like kerosene early in flight with the high specific impulse of a lighter fuel like liquid hydrogen (LH2) later in flight." Neither of those are really called for in stock KSP, with its generic fuel and oxidizer. They'd be interesting in a RealFuels or similar setup though.

Then there's what the OP is referring to, an engine that makes use of both external air and onboard oxidizer. There's all sorts of ideas on this front; we have the SABRE-alike in the game already, but there are air augmented rockets that would use air and oxidizer at the same time, nuclear thermal jets (which KSPI has I believe), and more. More choice of engines like this are always welcome. In particular there's still a hole in the stock game for an engine for Eve, Duna, and Jool planes.

[Carsogen]

Hi all, sorry about the vague-ity of the original post. The kind of tri-propellant rocket I was talking about was one that burns liquid fuel, oxidiser and oxygen from the atmosphere all at once (yes they are all propellants), or that uses intake air as working mass to increase thrust and efficiency as mentioned by Red Iron Crown (but doesn't burn it).

The idea would be that the first can use only oxygen atmospheres (Kerbin/Laythe) and the second any atmosphere. I reckon that the ability to increase your efficiency in a non-burnable atmosphere would be a hugely cool thing in KSP . I'm getting off topic though because the main question was whether such an engine would be redundant in burnable atmo because we already have jets and RAPIER that we can stick on launchers etc.

Cas.

[NERVAfan]

The only Tripropellant there is is *shudders* Hydrogen, Lithium, and Fluorine. They produce the worst chemical ever when burnt, and to keep all the propellants there liquid, you have to have hugely complicated tank design. Not to mention the fact that liquid lithium is essentially a molten metal that will screw up all the electronics. There is an advantage, however. On paper at least, a Tripropellant rocket gets an Isp of 540 seconds.

Not just on paper - an actual ground test got 542 seconds Isp.

The HF in the exhaust is indeed an issue on the ground, but wouldn't matter much for use in space. The whole molten lithium/cryogenic fluorine thing is probably the deal killer.

[magnemoe]

Hi all, sorry about the vague-ity of the original post. The kind of tri-propellant rocket I was talking about was one that burns liquid fuel, oxidiser and oxygen from the atmosphere all at once (yes they are all propellants), or that uses intake air as working mass to increase thrust and efficiency as mentioned by Red Iron Crown (but doesn't burn it).

The idea would be that the first can use only oxygen atmospheres (Kerbin/Laythe) and the second any atmosphere. I reckon that the ability to increase your efficiency in a non-burnable atmosphere would be a hugely cool thing in KSP . I'm getting off topic though because the main question was whether such an engine would be redundant in burnable atmo because we already have jets and RAPIER that we can stick on launchers etc.

Cas.

Yes, I already set rapiers to closed cycle then I get low on air, typically at 35 km and 1800 m/s, this takes me too 2200 m/s with the same benefit, downside is that this reqire 3 or more engines

[Zephram Kerman]

Then there's what the OP is referring to, an engine that makes use of both external air and onboard oxidizer. There's all sorts of ideas on this front; we have the SABRE-alike in the game already, but there are air augmented rockets that would use air and oxidizer at the same time, nuclear thermal jets (which KSPI has I believe), and more. More choice of engines like this are always welcome. In particular there's still a hole in the stock game for an engine for Eve, Duna, and Jool planes.

I've been fascinated by the idea of a turbine engine for use in non-oxygen atmospheres. (I.e. Duna, Eve... Mars.) After some searching, I stumbled onto a 1940s design called TurboRocket, which uses a bipropellant rocket as a 'gas generator' to propel a turbine. There's definitely room for this thing in KSP.

[Tweeker]

I wrote a small mod to do this a while back, It's not really accurate, as the fuel ratios are off, and simulating the temperature differences of the fuels is problematic.  But if you would like to give it a shot the link is in my signature.

 

[Angeltxilon]

Tripropellant rockets are redundant (ie, like bipropellant rockets) if do use of a fuel+fuel+oxidizer mix or fuel+oxidizer+oxidizer mix.
However, these could be useful (I mean, more powerful and efficent than bipropellant rockets) if do use of the perfect reactive+reactive+reactive mix, where all the reactives has different functions and not redundant reactions.

This is the case of fluorine+hydrogen+litium tripropellant rockets. The problem is that the products of reaction are toxic and is difficult keep all the reactives because need different temperatures and can react with the container.

Edited April 9, 2016 by Angeltxilon