Would you use a tri-propellant rocket?

[Grand Ship Builder]

It's not a completely necessary engine, but it would certainly be useful for SSTOs and designing simple rockets (no not the game).

A tripropellant engine would have 2 proposed versions, a mix of gaseous hydrogen, liquid lithium, and liquid fluorine, which would have a rather high ISP, and one that uses kerosene at launch due to its high density and therefore thrust, smaller tanks needed, lowering the weight, and making a great engine for rocket SSTOs, and then using the more efficient but lower density liquid hydrogen, all while using the same oxidizer of liquid oxygen.

The former would be preferable for all those efficiency aficionados, and the latter would be preferable for those who just want the best of both worlds (AKA me).

This is similar to a hybrid rocket (not referring to the R.A.P.I.E.R.s) in which they generally have a solid fuel and gaseous/liquid oxidizer, though vice versa and other combinations are possible and have been used, and of course, there are mods for it.

By the way, there ARE mods that feature tripropellant rockets, which can all be found using a simple search.

However, your post indicates a liquid oxygen and hydrogen rocket which also uses intake air. This would most likely refer to a air-augmented rocket, and in a more stock sense, the R.A.P.I.E.R. which only uses intake air and liquid oxygen separately. Air-augmented rockets do not exist yet in stock Kerbal Space Program, but they do exist in mods like Mk2/Mk3 Stockalike Expansion.

Looking at your posts though, you want an engine that uses intake air, liquid hydrogen, and liquid oxygen all at the same time. That wouldn't be very practical, and I don't see much of a use in it, than say, boosted efficiency, which can all be found in R.A.P.I.E.R.s and the air-augmented rockets I mentioned earlier. Then comes the L.A.C.E.s  (Liquid Air Cycle Engine), which is probably the engine you are talking about. Those are great for rocket-powered spacecraft in a oxygenated atmosphere, since they act a bit like pre-coolers, though instead they turn the air into liquid oxygen instead of just cooling it down like the ones in the S.A.B.E.R. (the engines the R.A.P.I.E.R.s are based on) engines on the Skylon, which greatly reduces the lift-off weight. Those don't exist in Kerbal Space Program either, but once again, there are mods for it (I think).

I would like a bit of a storage tank containing intake air to help air-breathing engines last a little longer in higher altitudes, instead of using liquid oxidizer on the same altitude, to increase efficiency.

I like your thinking.

I hope this helped.

Edited May 29, 2017 by Grand Ship Builder
Adding much more information and general ideas, while simplifying.

[genericeventhandler]

You could add a resource converter to the engine, to convert IntakeAir to Oxidizer and then run a standard engine,  the code below is off the top of my head, I've not tested it because I am at work at the moment.

Spoiler

$PART[liquidEngine3]
{
	@name=AirAugmentedEngine
	@description=The Air augmented engine, is a an experimental engine that has proven useful in ssto missions.
	@title=Air Augmented Engineer
	@tags= lander orbit propuls rocket terrier vacuum air augmented
	
	MODULE
	{
		 name = ModuleResourceConverter
         ConverterName = OxidizerCompressor
         StartActionName = Start Compressor
         StopActionName = Stop Compressor

         AutoShutdown = true
		 GeneratesHeat = false
		 
		 UseSpecializationBonus = false
		 
		 INPUT_RESOURCE
		 {
			ResourceName = IntakeAir
            Ratio = 0.01
		 }
		 
		 OUTPUT_RESOURCE
		 {
			ResourceName = Oxidizer
            Ratio = 1
            DumpExcess = true
		 }
	}
}

 

GEH

[Gordon Fecyk]

On ‎1‎/‎5‎/‎2015 at 3:08 AM, Zephram Kerman said:

I stumbled onto a 1940s design called TurboRocket, which uses a bipropellant rocket as a 'gas generator' to propel a turbine.

We already have electric propeller engines with one add-on that works on Duna (Firespitter?); extending that to use LFO to drive a propeller or a turbine wouldn't be a stretch.

And I have Eve covered now.