Hacking LV-N for "Air Breathing" mode

[AeroGav]

I'm starting to think about taking my spaceplane to places like Duna and Eve, which have an atmosphere , but no oxygen.

Nuclear thermal rockets don't use combustion, but produce thrust by taking a working fluid (liquid hydrogen) , heating it in a reactor, then letting it expand through a nozzle.

This is fine for interplanetary travel, but if you're slogging through an atmosphere, why not pull it into the intakes, compress with turbines, then use that as a working fluid to heat up and expand out the nozzle?

Would like to mod the LV-N nuke so it can have Closed cycle (works like it does now) and Air Breathing modes, like the RAPIER.

In Closed Cycle mode

• Fuel consumption is like it is now.
  
• Engine mass is likely to increase by half a ton, because of the turbomachinery required to compress the intake air.
  
• Vacuum thrust will also take a small hit , because i'd like to change from a Bell to an Aerospike nozzle.
  
• However sea level thrust should be much better, because of the Aerospike.
  
• Drag should be less too.
  

In Air Breathing mode

• Liquid fuel consumption goes to zero or something very close to it.
  
• However the engine consumes large amounts of intake air.
  
• As altitude and airspeed increase, thrust will drop off. Using the Whiplash's thrust/altitude and thrust/velocity curves seems more appropriate than taking those from the RAPIER, since like the Whiplash it won't be chilling the intake air prior to compression with a cryogenic liquid fuel stream.
  

Of course, the Whiplash makes 5.8 times as much thrust at Mach 3 vs Sea level. Do we really want the LV-N chucking out that much power in air breathing mode?

I guess it depends on what limited the nuclear thermal rocket's output in normal mode. Reactor thermal output? If so, it can only ever be less powerful with something other than cryogenic hydrogen as working fluid.

OTOH , this engine was designed, first at foremost, to have the highest possible ISP, which means raising the temperature of the hydrogen to just below the melting point of the reactor materials by the time it leaves the engine.

If sufficiently large quantities of intake air are available (and have not heated up too much in the act of being compressed, which is why power will lapse with speed and alt) and we're not bothered about getting the temperature so high, the reactor might be able to increase its output without melting down.

I guess what i'm asking here is how i physically go about hacking the config files to make this happen, but I'd appreciate input on what the plausible performance levels of such an engine would be, at least within the confines of the game. Don't want something so OP it replaces RAPIER and Whiplash on Kerbin/Laythe. But something that can do most of the work getting you to orbit in lower gravity worlds, and let you cruise around in the atmosphere.

Edit - a quick google search did find this study on a airbreathing nuclear engine for Mars

http://www6.miami.edu/acfdlab/publications/AIAA-2014-3820.pdf

Edited November 6, 2015 by AeroGav

[Van Disaster]

Hmm. Rather than just hack the LV-N, there seems to be room for a more interesting propulsion system with a nuclear core & consuming devices - I'm not really sure how you'd sanely have a rocket and a thermal turbocompressor in the same pipe ( it's not a SABRE, that is using the compressor to fuel the rocket rather than as primary thrust ) given a rocket bell is not what you want stuck on a jetpipe, but there's an interesting idea for a thermal core & output devices in there. A thermal turboramjet, hmm. If you want a really hacky version of that, make a new resource and a reactor piece that provides that resource, and have the thrust devices consume that resource & reaction mass. The problem with using obvious resources like that is you can store them, but ... just don't store them.

But if you just want a LV-N that works better in atmosphere, borrow the RAPIER config and fiddle with the graphs.

Edited November 6, 2015 by Van Disaster

[Mecripp]

Or you can put this cfg in KSP/GameData/Squad/Engine/liquidEngineLV-N You can name the cfg what ever you want and play around with the thrust and curve's to what you want

PART
{
	name = nuclearEngine_Test
	module = Part
	author = NovaSilisko
	mesh = model.mu
	scale = 1
	rescaleFactor = 1
	node_stack_top = 0.0, 1.40383, 0.0, 0.0, 1.0, 0.0
	node_stack_bottom = 0.0, -1.731957, 0.0, 0.0, -1.0, 0.0
	mass = 3.0
	// heatConductivity = 0.06 // half default
	skinInternalConductionMult = 4.0
	emissiveConstant = 0.8 // engine nozzles are good at radiating.
	dragModelType = default
	maximum_drag = 0.2
	minimum_drag = 0.2
	angularDrag = 2
	crashTolerance = 20
	maxTemp = 2500 // = 4000
	TechRequired = aerospaceTech
	entryCost = 35000
	cost = 6000
	category = Engine
	subcategory = 0
	title = Test Engine
	manufacturer = C7 Aerospace Division and Rockomax Conglomerate
	description = Test
	attachRules = 1,0,1,1,0
	bulkheadProfiles = size1
	radiatorMax = 0.35 //Default = 0.25 but nuke engines are meant to run hot
	EFFECTS
	{
		running_closed
		{
			AUDIO
			{
				channel = Ship
				clip = sound_rocket_spurts
				volume = 0.0 0.0
				volume = 1.0 1.0
				pitch = 0.0 0.2
				pitch = 1.0 1.0
				loop = true
			}
			PREFAB_PARTICLE
			{
				prefabName = fx_smokeTrail_aeroSpike
				transformName = smokePoint
				emission = 0.0 0.0
				emission = 0.05 0.0
				emission = 0.075 0.25
				emission = 1.0 1.25
				speed = 0.0 0.25
				speed = 1.0 1.0
				localOffset = 0, 0, 1
			}
			MODEL_MULTI_PARTICLE
			{
				modelName = Squad/FX/shockExhaust_blue_small
				transformName = thrustTransform
				emission = 0.0 0.0
				emission = 0.05 0.0
				emission = 0.075 0.25
				emission = 1.0 1.25
				speed = 0.0 0.5
				speed = 1.0 1.2
			}
		}
		power_open
		{
			AUDIO
			{
				channel = Ship
				clip = sound_rocket_spurts
				volume = 0.0 0.0
				volume = 0.05 0.0
				volume = 1.0 1.0
				pitch = 0.0 0.2
				pitch = 1.0 1.0
				loop = true
			}
			MODEL_MULTI_PARTICLE
			{
				modelName = Squad/FX/shockExhaust_red_small
				transformName = thrustTransform
				emission = 0.0 0.0
				emission = 0.05 0.0
				emission = 0.075 0.25
				emission = 1.0 1.25
				speed = 0.0 0.5
				speed = 1.0 1.2
			}
		}
		running_open
		{
			AUDIO
			{
				channel = Ship
				clip = sound_jet_deep
				volume = 0.0 0.0
				volume = 0.05 0.6
				volume = 1.0 1.0
				pitch = 0.0 0.7
				pitch = 1.0 1.4
				loop = true
			}
			PREFAB_PARTICLE
			{
				prefabName = fx_smokeTrail_aeroSpike
				transformName = smokePoint
				emission = 0.0 0.0
				emission = 0.05 0.0
				emission = 0.075 0.25
				emission = 1.0 1.25
				speed = 0.0 0.25
				speed = 1.0 1.0
				localOffset = 0, 0, 1
			}
		}
		engage
		{
			AUDIO
			{
				channel = Ship
				clip = sound_vent_soft
				volume = 1.0
				pitch = 2.0
				loop = false
			}
		}
		flameout
		{
			PREFAB_PARTICLE
			{
				prefabName = fx_exhaustSparks_flameout_2
				transformName = smokePoint
				oneShot = true
			}
			AUDIO
			{
				channel = Ship
				clip = sound_explosion_low
				volume = 1.0
				pitch = 2.0
				loop = false
			}
		}
	}
	MODULE
	{
		name = MultiModeEngine
		primaryEngineID = AirBreathing
		secondaryEngineID = ClosedCycle
	}
	MODULE
	{
		name = ModuleEnginesFX
		engineID = AirBreathing
		powerEffectName = power_open
		//runningEffectName = running_open
		thrustVectorTransformName = thrustTransform
		exhaustDamage = True
		ignitionThreshold = 0.33
		minThrust = 0
		maxThrust = 105
		heatProduction = 60
		useEngineResponseTime = True
		engineAccelerationSpeed = 0.2
		engineDecelerationSpeed = 0.35
		useVelocityCurve = False		
		spoolEffectName = running_open
		engineSpoolIdle = 0.05
		engineSpoolTime = 2.0
		EngineType = Turbine
		PROPELLANT
		{
			name = LiquidFuel
			resourceFlowMode = STAGE_PRIORITY_FLOW
			ratio = 1
			DrawGauge = True
		}
		PROPELLANT
		{
			name = IntakeAir
			ignoreForIsp = True
			ratio = 6
		}
		atmosphereCurve
		{
			key = 0 3200 0 0
		}
		// Jet params
		atmChangeFlow = True
		useVelCurve = True
		useAtmCurve = True
		// no mach limit
		velCurve
		{
			key = 0 1 0 0.08333334
			key = 0.2 0.98 0.42074 0.42074
			key = 0.7 1.8 2.290406 2.290406
			key = 1.4 4.00 3.887193 3.887193
			key = 3.75 8.5 0 0
			key = 4.5 7.3 -2.831749 -2.831749
			key = 5.5 3 -5.260566 -5.260566
			key = 6 0 -0.02420209 0
		}
		atmCurve
		{
			// higher thrust at altitude than even TRJ
			key = 0 0 0 0
			key = 0.018 0.09 7.914787 7.914787
			key = 0.08 0.3 1.051923 1.051923
			key = 0.35 0.5 0.3927226 0.3927226
			key = 1 1 1.055097 0
		}
	}
	MODULE
	{
		name = ModuleEnginesFX
		engineID = ClosedCycle
		runningEffectName = running_closed
		thrustVectorTransformName = thrustTransform
		exhaustDamage = True
		ignitionThreshold = 0.1
		minThrust = 0
		maxThrust = 180
		heatProduction = 133
		fxOffset = 0, 0, 0.25
		EngineType = LiquidFuel
		PROPELLANT
		{
			name = LiquidFuel
			resourceFlowMode = STAGE_PRIORITY_FLOW
			ratio = 0.9
			DrawGauge = True
		}
		PROPELLANT
		{
			name = Oxidizer
			resourceFlowMode = STAGE_PRIORITY_FLOW
			ratio = 1.1
		}
		atmosphereCurve
		{
			key = 0 800
			key = 1 185
			key = 2 0.001
		}
	}
	MODULE
	{
		name = ModuleJettison
		jettisonName = fairingL
		bottomNodeName = bottom
		isFairing = False
		jettisonedObjectMass = 0.1
		jettisonForce = 1
		jettisonDirection = 1 0 0
	}
	MODULE
	{
		name = ModuleJettison
		jettisonName = fairingR
		bottomNodeName = bottom
		isFairing = False
		jettisonedObjectMass = 0.1
		jettisonForce = 1
		jettisonDirection = -1 0 0
	}
	MODULE
	{
		name = ModuleAnimateHeat
		ThermalAnim = overheat
	}
	MODULE
	{
		name = ModuleGimbal
		gimbalTransformName = obj_gimbal
		gimbalRange = 3
	}
	MODULE
	{
		name = ModuleTestSubject
		environments = 15
		useStaging = True
		useEvent = True
	}
	MODULE
	{
		name = ModuleAlternator
		RESOURCE
		{
			name = ElectricCharge
			rate = 5.0
		}
	}
	RESOURCE
	{
		name = ElectricCharge
		amount = 0
		maxAmount = 0
		isTweakable = false
		hideFlow = true
	}
	MODULE
	{
		name = ModuleSurfaceFX
		thrustProviderModuleIndex = 1
		fxMax = 0.5
		maxDistance = 20
		falloff = 2
		thrustTransformName = thrustTransform
	}
	MODULE
	{
		name = ModuleSurfaceFX
		thrustProviderModuleIndex = 2
		fxMax = 0.6
		maxDistance = 30
		falloff = 1.6
		thrustTransformName = thrustTransform
	}
}

EDIT- You can also change the

name = nuclearEngine_Test

to name = what ever you want. Edited November 6, 2015 by Mecripp2

[Gojira1000]

Or you can use the nuclear turbojets from Interstellar

[Mecripp]

Or they could use porkjets Atomic Age

then they don't have to have all the stuff that comes with Interstellar and there might be a hand full more they can use lol.

EDIT- Atomic Age http://forum.kerbalspaceprogram.com/threads/104855-0-90-Atomic-Age-Nuclear-Rockets

Edited November 6, 2015 by Mecripp2

[AeroGav]

OK, I can put this off no longer. Strong , sugary coffee is the order of the day as I make my first ever mod of the KSP game files. Scary stuff.

I started small. Added the half ton of extra mass. I've also added electrical output equivalent to two RTGs. The decay heat from such a reactor in shutdown state would do that at the very least - if not melt the whole spacecraft. But I digress.

And now to the first matter.

atmosphereCurve

IOW, what is the difference between ISP Vacuum and Sea Level, when in closed cycle mode (airbreathing mode is the next, and far more ambitious mod).

The stock LV-N has a ludicrous, and horrible thrust lapse.

800 Vac

185 Sea Level

It drops to just 22% of it's vacuum rating.

Then again, if we look at the Poodle, with a 350 Vaccum Rating, it also lapses to 25% ASL. Must be a seriously overexpanding bell nozzle.

It cohabits the tech tree with the Skipper lower stage engine, with a lower vacuum rating of 320, but which manages to hang on to 87.5% of that ASL.

The Rhino, with a Vac ISP of 340, does 255 ASL - 75% lapse.

The Kerbal Aerospike motor manages the same Vac rating as the Rhino but does 290 ASL, a mere 85% lapse.

Obviously great numbers but honestly this felt like cheating. Why would anyone ever pick the Rhino?

Real world aerospikes don't do quite so well.

The Space shuttle main engine does 452 Vac and 366 ASL (81% lapse).

The Aerospike motor of the ill-fated Venture Star program, had 436 and 339 (77% lapse).

This is actually worse than the SSME on both counts, though the SSME is not something you want to play top trumps against. It also has a nozzle design that differs from the conventional bell design so give good performance at a wide range of altitudes, since this engine is operational from sea level to vacuum too.

All things considered, I decided to steal the numbers from the Rhino.

By 10km, the stock LV-N is already not far off it's vacuum ISP, and when i get this running right you should be airbreathing that low anyway, so ISP won't hurt.

I applied a "gimp factor" based on the fact it's no longer a purely vacuum oriented nozzle. I'm assuming the Rhino could have made at least 350 if it was optimized for deep space like the Poodle, applying a similar percentage loss to the LVN's 800 gives a modded vacuum rating of 777.

Applying the Rhino's 75% thrust lapse to that 777 figure gives us a 583 sea level ISP.

PART
{
    name = ImprovedNTR
    module = Part
    author = NovaSilisko
    mesh = model.mu
    scale = 1
    rescaleFactor = 1
    node_stack_top = 0.0, 1.40383, 0.0, 0.0, 1.0, 0.0
    node_stack_bottom = 0.0, -1.731957, 0.0, 0.0, -1.0, 0.0
    fx_exhaustFlame_blue = 0.0, -1.6, 0.0, 0.0, 1.0, 0.0, running
    fx_exhaustLight_blue = 0.0, -1.6, 0.0, 0.0, 0.0, 1.0, running
    fx_smokeTrail_light = 0.0, -1.6, 0.0, 0.0, 1.0, 0.0, running
    sound_vent_medium = engage
    sound_rocket_hard = running
    sound_vent_soft = disengage
    sound_explosion_low = flameout
    TechRequired = nuclearPropulsion
    entryCost = 45000
    cost = 10000
    category = Engine
    subcategory = 0
    title = LV-N "Nerv II" Atomic Rocket Motor
    manufacturer = Jebediah Kerman's Junkyard and Spacecraft Parts Co
    description = Despite the success of the original NERV, the Gavro Aerospace corporation demanded improvements from the design team.   This first upgrade traded some vacuum thrust for much better performance down low, not to mention a built in RTG for some always-on power generation.
    attachRules = 1,0,1,0,0
    mass = 3.5 //up half a ton for the turbo machines
    // heatConductivity = 0.06 // half default
    skinInternalConductionMult = 4.0
    emissiveConstant = 0.85 // engine nozzles are good at radiating, NTRs even better
    dragModelType = default
    maximum_drag = 0.2
    minimum_drag = 0.2
    angularDrag = 2
    crashTolerance = 12
    maxTemp = 2500 // = 4000
    bulkheadProfiles = size1
    radiatorMax = 0.35 //Default = 0.25 but nuke engines are meant to run hot
    MODULE
    {
        name = ModuleEngines
        thrustVectorTransformName = thrustTransform
        exhaustDamage = True
        ignitionThreshold = 0.1
        minThrust = 0
        maxThrust = 60            // Max thrust of 60 is one third of what comparable engines do
        heatProduction = 250
        fxOffset = 0, 0, 1.6
        EngineType = Nuclear
        PROPELLANT
        {
            name = LiquidFuel
            ratio = 0.9
            DrawGauge = True
        }
        atmosphereCurve
        {
            key = 0 777              // Vacuum ISP of 800 is really good
            key = 1 583         // But at sea level, it's super lame, i'm usig rhino numbers
            key = 2 0.001        
        }
    }
    MODULE
    MODULE
    {
        name = ModuleAnimateHeat
        ThermalAnim = overheat
    }
    MODULE
    {
        name = ModuleAlternator
        RESOURCE
        {
            name = ElectricCharge
            rate = 5.0
        }
    }
    MODULE
    {
        name = ModuleGenerator
        isAlwaysActive = true
        OUTPUT_RESOURCE
        {
            name = ElectricCharge
            rate = 1.5
        }
    }
    RESOURCE
    {
        name = ElectricCharge
        amount = 0
        maxAmount = 0
        isTweakable = false
        hideFlow = true
    }
    MODULE
    {
        name = ModuleTestSubject
        environments = 8
        useStaging = False
        useEvent = True
    }
    MODULE
    {
        name = ModuleSurfaceFX
        thrustProviderModuleIndex = 0
        fxMax = 0.7
        maxDistance = 50
        falloff = 2.5
        thrustTransformName = thrustTransform
    }
}

I quickly knocked up a little flier to test this modded engine, make sure it didn't blow up or ring a dinner bell for the Kraken.

Hey Stasa, come over here. We got a job for you. Test fly this new and completely untested airframe with a new and completely untested nuclear engine on the back. And stop looking so damn nervous...

It did a pretty good "vodka burner" impersonation, trundling painfully down the KSC runway, flopping off the end, barely holding a few metres off the water, almost going into the back end of the drag curve and stalling out. But eventually, airspeed began to rise, and it began a very slow climb.

As we neared 7km, climb rate starts to improve. ISP is getting better, fuel is burning off, and drag is lessening. This airframe has horrible roll stability. In between logging thrust numbers and fighting to keep the wings level, i failed to notice for a long time that i was up against the sound barrier and encountering high drag. I eventually grabbed the pitch trim wheel and got the nose up, flying subsonic to 16km. Then i push over and accelerate through the sound barrier in a shallow dive.

Supersonic and climbing again -

Definitely supersonic

Woah....

[Mecripp]

LOL too funny

[sashan]

The stock LV-N has a ludicrous, and horrible thrust lapse.

800 Vac

185 Sea Level

It drops to just 22% of it's vacuum rating.

Of course it does, it has a very high expansion ratio that results in a very efficient nozzle, in vacuum. It's vacuum-optimized.

Real NERVA nozzles are calculated to have exhaust temp of just around 400 degrees celsius while the core can be as hot as 5000 celsius:

[AeroGav]

The next stage is to give the engine an airbreathing mode. That's going to require some careful editing of the config files, but at the end of the day is just cut n paste.

I'm agonising over what thrust curves to give it though. The "Whiplash" turboramjet makes 5.8 x normal thrust at optimum airspeed. That seems like too much.

If the working fluid is limitless you can trade ISP for thrust. Use a lower exit temperature for the fluid but pump more of it through, the reactor can operate at a higher power level without melting down. One site i found said a nuclear thermal rocket could get up to 2.7x more thrust by using water as working fluid rather than LH2. Atmospheric air won't have the specific heat capacity of water though.

http://www.niac.usra.edu/files/studies/final_report/510Maise.pdf

This site talks about a nuclear ramjet for exploring Jupiter. It mentions that a nuclear thermal rocket will have hydrogen at 50-100 atmospheres as the coolant, and that a their jovian ramjet will operate at only a few atmospheres. This airbreathing NERV is assumed to have a turbo compressor, but even the latest civil turbofans only operate at a pressure ratio of 50, and i doubt our turbo assisted nuclear thermal ramjet gets that high even with maximum ram air effect.

So, we're using a working fluid with lower specific heat capacity than hydrogen, at a lower pressure. Does this mean our reactor has less cooling in airbreathing mode and will have to throttle back?

Well, there's one other thing you could do, change the gas path through the reactor. When closed cycle, the H2 stream goes all the way from one end of the reactor to the other, to pick up max possible temperature and get as much thrust per litre of stored H2 as possible. If unlimited intake air is available, you could feed air in at different points and not have it traverse as long, acheiving higher flow rate but lower temperature.

Lastly, we're NOT talking about a nuclear turbojet, where the turbine adds a LOT of thrust at low altitudes , but becomes a liability higher up. That means a big ass turbine and whole new nozzle, really a completely separate engine though as Van Disaster mentions in the second post, they could both share the reactor as a heat source.

What I have in mind -

Air Intake (passive compression, rises with airspeed) -> Turbo compressor (with bypass ducts at higher speeds) -> Reactor first pass (heat to 1500k max) -> Power Turbine (drives compressor) -> Reactor second pass, reheat -> Rocket chamber and nozzle.

Oh dear. I'm way over my head. It's getting late and I just want to fly something.

[AeroGav]

Alright, I've think I'm finished putting the basics in. It should work, but i won't really know till i reach another planet. Time to build a 2 nuke / 1 rapier mk2 vessel for the maiden voyage. It can refuel on Minmus, i've an IRSU spaceplane there that's already filled its boots. Flight test program, you say? Not for Kerbals. Got a brand new, untested prototype engine with a brand new, untested airframe from R&D? Time to boldly go!

On that previous flight, i think i accidentally stumbled across the most efficient airframe i've ever built. Was very definitely going to orbit on just 60kn thrust.

The airbreathing version didn't break the sound barrier, because with nothing to burn the fuel off it was too heavy to get above 10km on full tanks, subsonic. I could push the nose over, but by the time i'm through 380m/s where drag coefficient is coming back down again, i'm down to 5km altitude and the atmo drag is huge anyway.

I'm still not sure about the velocity and height curves but it's time to just fly the damn thing.

Looking at the Atomic Age mod made me realise a big flaw in my plan - IntakeAir really means intake oxygen, and existing air intakes have a checkForOxygen - if the atmosphere they are passing through has no oxy, they don't take any air in however thick it might be.

So, i've had to add another resource type to Resources.cfg (IntakeAtm), and modify the only two intakes i'm ever likely to use on a late-game ship, the pre-cooler and the shock cone, to gather IntakeAtm as well as IntakeAir. Needless to say, I set the IntakeAtm to NOT check for oxygen.

Here is the "Alpha" of my modded LVN config

PART
{
    name = ImprovedNTR
    module = Part
    author = NovaSilisko
    mesh = model.mu
    scale = 1
    rescaleFactor = 1
    node_stack_top = 0.0, 1.40383, 0.0, 0.0, 1.0, 0.0
    node_stack_bottom = 0.0, -1.731957, 0.0, 0.0, -1.0, 0.0
    //fx_exhaustFlame_blue = 0.0, -1.6, 0.0, 0.0, 1.0, 0.0, running
    //fx_exhaustLight_blue = 0.0, -1.6, 0.0, 0.0, 0.0, 1.0, running
    //fx_smokeTrail_light = 0.0, -1.6, 0.0, 0.0, 1.0, 0.0, running
    //sound_vent_medium = engage
    //sound_rocket_hard = running
    //sound_vent_soft = disengage
    //sound_explosion_low = flameout
    TechRequired = nuclearPropulsion
    entryCost = 45000
    cost = 10000
    category = Engine
    subcategory = 0
    title = LV-N "Nerv III" Atomic Rocket Motor
    manufacturer = Jebediah Kerman's Junkyard and Spacecraft Parts Co
    description = Cynics would argue that by the third installment of the LV-N series the Junkyard Parts Co were just cashing in on earlier successes.   However, for some , the airbreathing mode represents true progress. 
    attachRules = 1,0,1,0,0
    mass = 3.5 //up half a ton for the turbo machines
    // heatConductivity = 0.06 // half default
    skinInternalConductionMult = 4.0
    emissiveConstant = 0.85 
    dragModelType = default
    maximum_drag = 0.2
    minimum_drag = 0.2
    angularDrag = 2
    crashTolerance = 12
    maxTemp = 2500 
    bulkheadProfiles = size1
    radiatorMax = 0.35 
EFFECTS
    {
        power_open
        {
            AUDIO
            {
                channel = Ship
                clip = sound_jet_deep
                volume = 0.0 0.0
                volume = 0.05 0.6
                volume = 1.0 1.0
                pitch = 0.0 0.7
                pitch = 1.0 1.4
                loop = true
            }
            PREFAB_PARTICLE
            {
                prefabName = fx_smokeTrail_light
                transformName = thrustTransform
                emission = 0.0 0.0
                emission = 0.05 0.0
                emission = 0.075 0.25
                emission = 1.0 1.25
                speed = 0.0 0.5
                speed = 1.0 1.2
                localOffset = 0, 0, 1 
                localRotation = 1, 0, 0, -90 
            }
        }
        running_closed
        {
            AUDIO
            {
                channel = Ship
                clip = sound_rocket_spurts
                volume = 0.0 0.0
                volume = 1.0 1.0
                pitch = 0.0 0.2
                pitch = 1.0 1.0
                loop = true
            }
            MODEL_MULTI_PARTICLE
            {
                modelName = Squad/FX/shockExhaust_blue_small
                transformName = thrustTransform
                emission = 0.0 0.0
                emission = 0.05 0.0
                emission = 0.075 0.25
                emission = 1.0 1.25
                speed = 0.0 0.5
                speed = 1.0 1.2
            }
        }
    }    
    MODULE
    {
        name = MultiModeEngine
        primaryEngineID = AirBreathing
        secondaryEngineID = ClosedCycle
    }    
    MODULE
    {
        name = ModuleEnginesFX
        engineID = AirBreathing
        powerEffectName = power_open
        //runningEffectName = running_open
        thrustVectorTransformName = thrustTransform
        exhaustDamage = True
        ignitionThreshold = 0.33
        minThrust = 0
        maxThrust = 60
        heatProduction = 130
        useEngineResponseTime = True
        engineAccelerationSpeed = 0.2
        engineDecelerationSpeed = 0.35
        useVelocityCurve = False        
        //spoolEffectName = running_open
        engineSpoolIdle = 0.05
        engineSpoolTime = 2.0
        EngineType = Turbine
        PROPELLANT
        {
            name = IntakeAtm
            ignoreForIsp = False
            ratio = 6
        }
        atmosphereCurve
        {
            key = 0 3200 0 0
        }
        // Jet params
        atmChangeFlow = True
        useVelCurve = True
        useAtmCurve = True
        velCurve
        {
            key = 0 1 1.15 0
            key = 0.2 1.35 0 0
            key = 0.72 1.63 2.433527 2.433527
            key = 1.36 1.9 1.986082 1.986082
            key = 2.15 2.3 1.452677 1.452677
            key = 3 2.3 0.0005786046 0.0005786046
            key = 4.5 1.5 -4.279616 -4.279616
            key = 5.5 0 -0.02420209 0
        }
        atmCurve
        {
            key = 0 0 0 0
            key = 0.045 0.2 4.304647 4.304647
            key = 0.16 0.7 0.5779132 0.5779132
            key = 0.5 1.1 0.4809403 0.4809403
            key = 1 1 1.013946 0
        }
    }
    MODULE
    {
        name = ModuleEnginesFX
        engineID = ClosedCycle
        runningEffectName = running_closed
        thrustVectorTransformName = thrustTransform
        exhaustDamage = True
        ignitionThreshold = 0.1
        minThrust = 0
        maxThrust = 60            // Max thrust of 60 is one third of what comparable engines do
        heatProduction = 250
        fxOffset = 0, 0, 1.6
        EngineType = Nuclear
        PROPELLANT
        {
            name = LiquidFuel
            ratio = 0.9
            DrawGauge = True
        }
        atmosphereCurve
        {
            key = 0 777              // Vacuum ISP of 800 is really good
            key = 1 583         // But at sea level, it's super lame, i'm usig rhino numbers
            key = 2 0.001        
        }
    }
    MODULE
    {
        name = ModuleAnimateHeat
        ThermalAnim = overheat
    }
    MODULE
    {
        name = ModuleGenerator
        isAlwaysActive = true
        OUTPUT_RESOURCE
        {
            name = ElectricCharge
            rate = 5.0
        }
    }
    RESOURCE
    {
        name = ElectricCharge
        amount = 0
        maxAmount = 0
        isTweakable = false
        hideFlow = true
    }
    MODULE
    {
        name = ModuleTestSubject
        environments = 8
        useStaging = False
        useEvent = True
    }
    MODULE
    {
        name = ModuleSurfaceFX
        thrustProviderModuleIndex = 1
        fxMax = 0.5
        maxDistance = 20
        falloff = 2
        thrustTransformName = thrustTransform
    }
    MODULE
    {
        name = ModuleSurfaceFX
        thrustProviderModuleIndex = 2
        fxMax = 0.6
        maxDistance = 30
        falloff = 1.6
        thrustTransformName = thrustTransform
    }
}

Here is the modded ResourcesGeneric.cfg -

RESOURCE_DEFINITION
{
  name = LiquidFuel
  density = 0.005
  unitCost = 0.8
  hsp = 2010
  flowMode = STACK_PRIORITY_SEARCH
  transfer = PUMP
  isTweakable = true
}
RESOURCE_DEFINITION
{
  name = Oxidizer
  density = 0.005
  unitCost = 0.18
  hsp = 1551
  flowMode = STACK_PRIORITY_SEARCH
  transfer = PUMP
  isTweakable = true
}
RESOURCE_DEFINITION
{
  name = SolidFuel
  density = 0.0075
  unitCost = 0.6
  hsp = 920
  flowMode = NO_FLOW
  transfer = NONE
  isTweakable = true
}
RESOURCE_DEFINITION
{
  name = MonoPropellant
  density = 0.004
  unitCost = 1.2
  hsp = 3000
  flowMode = STAGE_PRIORITY_FLOW
  transfer = PUMP
  isTweakable = true
}
RESOURCE_DEFINITION
{
  name = XenonGas
  density = 0.0001  
  unitCost = 4
  hsp = 120
  flowMode = STAGE_PRIORITY_FLOW
  transfer = PUMP
  isTweakable = true
}
RESOURCE_DEFINITION
{
  name = ElectricCharge
  density = 0
  unitCost = 0
  hsp = 0
  flowMode = ALL_VESSEL
  transfer = PUMP
  isTweakable = true
}
RESOURCE_DEFINITION
{
  name = IntakeAir
  density = 0.005
  unitCost = 0
  hsp = 10
  flowMode = ALL_VESSEL
  transfer = PUMP
  isTweakable = false
}
RESOURCE_DEFINITION
{
  name = EVA Propellant
  density = 0
  unitCost = 0
  hsp = 3000
  flowMode = NO_FLOW
  transfer = PUMP
  isTweakable = false
}


RESOURCE_DEFINITION
{
  name = Ore
  density = 0.010
  unitCost = 0.02
  flowMode = ALL_VESSEL
  transfer = PUMP
  hsp = 1000
  isTweakable = true
  color = 1,0,1
}
RESOURCE_DEFINITION
{
  name = Ablator
  density = 0.001
  hsp = 400
  flowMode = NO_FLOW
  transfer = NONE
  isTweakable = True
  unitCost = 0.5
}
RESOURCE_DEFINITION
{
  name = IntakeAtm
  density = 0.005
  unitCost = 0
  hsp = 10
  flowMode = ALL_VESSEL
  transfer = PUMP
  isTweakable = false
}

Here is the modded intakeShockCone.cfg

PART
{
    name = shockConeIntake
    module = Part
    author = Porkjet
    rescaleFactor = 1
    node_stack_bottom = 0.0, -0.625, 0.0, 0.0, -1.0, 0.0
    TechRequired = hypersonicFlight
    entryCost = 21000
    cost = 3050
    category = Aero
    subcategory = 0
    title = Shock Cone Intake
    manufacturer = C7 Aerospace Division
    description = A shocking new intake from the C7 Aerospace Division that brought you much adored parts such as the Delta Wing and the Standard Nosecone!
    attachRules = 1,0,1,0,0
    mass = 0.025
    thermalMassModifier = 8
    // heatConductivity = 0.06 // half default
    heatConvectiveConstant = 0.75 // air goes into jet, not bashes on intake.
    emissiveConstant = 0.95
    dragModelType = default
    maximum_drag = 0.3
    minimum_drag = 0.3
    angularDrag = 1.2
    crashTolerance = 7
    maxTemp = 2400
    fuelCrossFeed = True
    bulkheadProfiles = size1


    MODEL
    {
        model = Squad/Parts/Aero/circularIntake/ConeIntake
    }
    DRAG_CUBE
    {
        cube = Default, 0.7486105,0.6887614,0.7221569, 0.7486105,0.6887677,0.7221569, 1.213026,0.3,1.183155, 1.213026,1,0.100694, 0.7486105,0.6903304,0.7221569, 0.7486105,0.6871722,0.7221569, 0,-0.08307549,0, 1.25,1.083849,1.25
    }


    MODULE
    {
        name = ModuleResourceIntake
        resourceName = IntakeAir
        checkForOxygen = true
        area = 0.009
        intakeSpeed = 12
        intakeTransformName = Intake
    }
    RESOURCE
    {
        name = IntakeAir
        amount = 0.9
        maxAmount = 0.9
    }
    MODULE
    {
        name = ModuleResourceIntake
        resourceName = IntakeAtm
        checkForOxygen = false
        area = 0.009
        intakeSpeed = 12
        intakeTransformName = Intake
    }
    RESOURCE
    {
        name = IntakeAtm
        amount = 0.9
        maxAmount = 0.9
    }
    MODULE
    {
        name = ModuleAnimateHeat
        ThermalAnim = IntakeConeHeat
    }
}

and engineBodyRadial.cfg (the pre-cooler)

PART
{
    name = radialEngineBody
    module = Part
    author = C. Jenkins, Porkjet
    rescaleFactor = 1
    node_stack_top = 0.0, 0.9375, 0.0, 0.0, 1.0, 0.0
    node_stack_bottom = 0.0, -0.9375, 0.0, 0.0, -1.0, 0.0
    node_attach = 0.0, 0.0, 0.625, 0.0, 0.0, -1.0, 1
    TechRequired = hypersonicFlight
    entryCost = 6200
    cost = 1650
    category = Aero
    subcategory = 0
    title = Engine Pre-cooler
    manufacturer = C7 Aerospace Division
    description = Improves jet performance by pre-compressing and rapidly cooling the intake air.
    attachRules = 1,1,1,1,0
    mass = 0.15
    dragModelType = default
    thermalMassModifier = 1
    emissiveConstant = 0.95
    maximum_drag = 0.2
    minimum_drag = 0.3
    angularDrag = 1
    crashTolerance = 20
    maxTemp = 2000 // = 2900
    fuelCrossFeed = True
    bulkheadProfiles = size1, srf
    MODEL
    {
        model = Squad/Parts/Aero/engineNacelle/Nacelle2
    }
    MODULE
    {
        name = ModuleResourceIntake
        resourceName = IntakeAir
        checkForOxygen = true
        area = 0.005
        intakeSpeed = 10
        intakeTransformName = Intake
    }
    MODULE
    {
        name = ModuleResourceIntake
        resourceName = IntakeAtm
        checkForOxygen = false
        area = 0.005
        intakeSpeed = 10
        intakeTransformName = Intake
    }
    RESOURCE
    {
        name = IntakeAtm
        amount = 0.5
        maxAmount = 0.5
    }
    RESOURCE
    {
        name = IntakeAir
        amount = 0.5
        maxAmount = 0.5
    }
    RESOURCE
    {
        name = LiquidFuel
        amount = 40
        maxAmount = 40
    }
    MODULE
    {
        name = ModuleAnimateHeat
        ThermalAnim = Nacelle2Heat
    }
}

Thanks for everyone's contributions, and particular the creators of the atomic age mod. Would never have figured this out on my own.

[AeroGav]

Decided to run one flight test on the new airframe after all, since there is nothing worse than flying to another planet, re-entering then discovering your plane is uncontrollable empty. So, I emptied all the tanks, filled the cockpit with A listers and took it for a brief spin. It appears there's little agreement between the crew as to whether it's a sound design or not.

It's surprisingly nimble and has a very low stall speed, perhaps below 30 m/s , but it's hard to say because this is the first creation of mine that really does STALL as opposed to running out of pitch authority and starting to sag. The nose stays level while airspeed and lift drop to almost nothing and AoA shoots to 70 deg quicker than you can blink. Need to slam the stick forward to recover.

20T/30T - there's not much difference in dry/wet mass, for a spacecraft.

Payload is a science junior, mystery goo and collection of instruments. I'm including a crew cabin for RP reasons - maybe just maybe there's enough room for a space toilet, shower, bunk bed, microwave and xbox. Well, if the crew were romantically involved at any rate.

It also has 3 Vernier engines thrusting straight down from the belly,a small tailwheel and two big ass reaction wheels, to make the horizontal landing on Minmus safer. We'll see...

[AeroGav]

Update. hmm more test flights in order. The airbreathing nukes got it up to 14km, a brief burst from the rapier in airbreathing mode with stick backpressure released gets us supersonic at the expense of 2km. However , the nuke airbreathers won't go much above 650 m/s and 17km. I start up the rapier, but their thrust continues to fall off severely - like 14kn by 20km. So, onto closed cycle they go. We reach orbit, but barely enough delta V to intercept Mun, let alone Minmus.

I'll tweak the numbers again, so they don't loose thrust quite so fast at altitude.

		velCurve
		{
			key = 0 1.05 0 0
			key = 0.2 1.15 0 0
			key = 0.72 1.4 2.433527 2.433527
			key = 1.36 1.9 1.986082 1.986082
			key = 2.15 2.2 1.452677 1.452677
			key = 3 2.5 0.0005786046 0.0005786046
			key = 4.5 1.5 -4.279616 -4.279616
			key = 5.5 0 -0.02420209 0
		}
		atmCurve
		{
			key = 0 0 0 0
			key = 0.045 0.32 4.304647 4.304647	//30km on kerbin, like 70k ft on earth
			key = 0.16 1.4 0.5779132 0.5779132	//a bit over 10km on kerbin, 43,000 ft on  earth
			key = 0.5 1.2 0.4809403 0.4809403        //about 18,000 ft on earth, about 15,000 ft on kerbin
			key = 1 1 1.013946 0      //sea level
		}

But my spaceplane needs more than 1700 liquid fuel. The precooler intakes and cargo bays are major attachment nodes for the rest of the structure. Touch those, i may as well start over. But I reckon i can add a couple mark 1 liquid fuel fuselage sections ahead of the precoolers, and not have it look to awful. I had more oxidizer than was really necessary, so i may remove the small ft-100 rocket fuel tank from forward cargo bay (was locked, the idea being to guarantee enough for vernier retro burn on minmus). Put an orbital survey scanner in it's place, and just be vigilant to terminate the rocket burn with a little bit to spare....

[John FX]

Interesting read. My personal preference would be an engine that works like the whiplash and can cruise around 20km and 700m/s using no fuel which could then be switched to closed cycle for the rest of the ascent.

This may be the engine I need for a Duna flying drone.

[Van Disaster]

Nuclear turbojets have actually run but the reactor was seperate ( the engines were basically J-58s ), and I couldn't find any rocket designs that didn't have the reactor as an integral part - so nowhere to really start for a modular system.

Presumably you could use a variable profile bell on something that small, given it's less thrust than a lot of afterburning jet engines which have quite complicated & variable nozzles. Would be cool to know how efficient various atmospheres are as reaction mass - I think I've seen a table somewhere of individual elements but not one for a composite.

[AeroGav]

I'm struggling to work out the velocity and altitude curves still. Engines still feel overpowered below 15km and underpowered above. The original plan was they'd be little more than conventional NERV engines that help to lift part of their own weight on kerbin, without using any fuel while in atmosphere. In lower gravity environments they might shine.

Now back to the curves, first principles (as far as i understand, please chime in)

1. Thrust should fall off linearly with air pressure except

2. It will get a boost that peaks at the bottom of the Stratosphere, from lowered air temps - 40%?

3. Thrust should rise linearly with speed

Flying a normal ascent profile, getting faster as the air gets thinner, thrust should stay fairly constant until the limits are reached. The ram air compression from increasing speed compensates for the decreasing air pressure to an extent, but the problem is, the more you compress air the more it heats up, eventually thermal limits are being reached and then the only thing you can do is allow air pressures and volume into the combustion chamber to fall. Also this compression isn't free - ram air compression causes drag, having the turbomachinery do the work means more energy has to be extracted from the exhaust gas to drive it. Also at some point it exceeds max RPM and flies apart, but that's not something Kerbals worry about.

Heck, there game's modelling of choke, rpm and critical temperatures is oversimplified to say the least... you're never going to create a realistically modelled engine.

Meanwhile, my new "batwing" ship finally made it to Minmus, managed to land without busting any critical parts off on the third attempt, and got her tanks brimmed by my other space plane/IRSU vessel, "the goose". While docked, i transferred the three tourists to the goose (their ticket only goes this far, sorry), and will leave them to annoy Bill Kerman for the next three years while Arjorie, Jeb and Bob go gallivanting to the red planet. This will be my first manned mission in any save.

Actually, looking at this link,

http://wiki.kerbalspaceprogram.com/images/7/73/KerbinDeltaVMap.png

I realised the setup i have now is total overkill. Nuke engines plus 2550 liquid fuel and we're already up at Minmus orbit. I could go literally anywhere on a fraction of the fuel load. But lets stick to the plan eh, and see how it flies in Duna, besides i have a contract to complete..

[Van Disaster]

I've lost track of what you're modelling now - are you still doing a multi-propellant NTR, or is it now some odd turbine/rocket hybrid? I'm going to assume it's the former still. If you want realistic jets you need AJE, but I'm having the same problems trying to set up a decent SABRE-type engine with AJE as you're getting with this ( and my engine actually uses a turbocompressor ) - they're not jet engines and probably shouldn't try and be, what we really need are more sophisticated intakes. But yes in essence the limiting factor is still the exhaust temperature which is still dependent on reaction mass density at some point, which is a function of speed & altitude and intake size.

Would a thermal rocket care about reaction mass temperature? if you can keep the incoming mass dense enough I don't see how it'd matter. There will be a structural hard limit to the amount of mass you can move through the thing & heat, so it should behave like a normal rocket until your intake drops below that critical mass and then presumably if you don't throttle down it'll start overheating as well as losing thrust. I would imagine a real installation would have a compressor somewhere, but not sure if you have to bother modelling that.

[cantab]

Looks like some good work. A few things I'd think about:

Solid-core NTRs actually have an exhaust that's rather cooler than chemical rockets, but making the exhaust pure hydrogen more than makes up for that allowing the high Isp. The limiting factor is that the reactor core needs to avoid meltdown.

That same limit will apply to a nuclear ramjet. The performance will I think be similar to a normal ramjet once you take into account the reactor core temperature.

I'm not sure how quickly you could control the reactor to vary its power. It could have a rather sluggish response. I think it would also need a reserve cooling system to prevent meltdowns - in an extreme case, imagine the reactor is running at high power with a high airflow and suddenly the intakes become blocked. Of course if it's a jet/rocket hybrid, said reserve cooling is to let the hydrogen flow through it.

[Van Disaster]

Couldn't you just leave the reactor running & vary the thrust by changing the bell shape/using vents? would seem *far* easier than attempting to throttle a reactor and you'd be able to keep up the mass flow to stop it burning. This isn't a very big engine ( and as you said quite cool ), a variable nozzle shouldn't be *too* heavy. However to get some decent performance out of just throwing any fuel into it I suspect the engine itself should be pretty big & heavy... having a cool & dense supply of reaction mass might help but then you have the mass of the cooler & compressor.

[John FX]

What`s to stop someone adding a second stage where an oxidiser is added to the hydrogen exhaust meaning it could then combust to increase the exhaust velocity?

Would that result in an increased Isp?

EDIT : Or if in an atmosphere with oxygen, using that.

Edited November 9, 2015 by John FX

[cantab]

What`s to stop someone adding a second stage where an oxidiser is added to the hydrogen exhaust meaning it could then combust to increase the exhaust velocity?

Would that result in an increased Isp?

EDIT : Or if in an atmosphere with oxygen, using that.

In either scenario that would increase thrust but reduce specific impulse.

[Van Disaster]

Well, then you've got a rocket and you don't need to lug several tons of reactor around

There's a lot of possible systems for propulsion in atmospheres with no oxygen - in a methane atmosphere you could just tank oxidizer & use the atmosphere for the other reactant ( a terrestrial engine in reverse ). On planets with inert atmosphere you can tank oxidizer and some fuel & use atmosphere as inert mass in piston engines ( this has been done in submarines using the exhaust as the inert gas ), which is massively more economical than using a rocket. If you managed to make a suitable mixer that'd also work for turbines I guess. That would probably even work on Duna, although you'd want a *giant* turbocharger for a piston engine. You could use your reactor along with a heat exchanger to power a closed cycle heat engine if you can insert the extra plumbing somehow - that'd be quite fun, a nuclear powered spaceplane with propellors of some sort... ( although at that point we're back to nuclear turbojets again ).

Edited November 9, 2015 by Van Disaster

[AeroGav]

I've lost track of what you're modelling now - are you still doing a multi-propellant NTR, or is it now some odd turbine/rocket hybrid? I'm going to assume it's the former still. If you want realistic jets you need AJE, but I'm having the same problems trying to set up a decent SABRE-type engine with AJE as you're getting with this ( and my engine actually uses a turbocompressor ) - they're not jet engines and probably shouldn't try and be, what we really need are more sophisticated intakes. But yes in essence the limiting factor is still the exhaust temperature which is still dependent on reaction mass density at some point, which is a function of speed & altitude and intake size.

Would a thermal rocket care about reaction mass temperature? if you can keep the incoming mass dense enough I don't see how it'd matter. There will be a structural hard limit to the amount of mass you can move through the thing & heat, so it should behave like a normal rocket until your intake drops below that critical mass and then presumably if you don't throttle down it'll start overheating as well as losing thrust. I would imagine a real installation would have a compressor somewhere, but not sure if you have to bother modelling that.

not sure if i mentioned this before, but I'm trying to model a nuclear SABRE without the heat exchanger incoming air chiller bit.

As i understand it, a SABRE is

1. ram air intake, velocity of vehicle compressing incoming air

2. heat exchanger, using the hydrogen fuel stream to chill the incoming air

3. turbine compressor of incoming air

4. hydrogen fuel will have been set boiling by the intake air (which was be hot from the compression it already endured going through the ram intake), so expands through a turbine, driving the compressor

5. compressed intake air fed into rocket chamber where it meets with the hydrogen and does the usual rocket thing.

My "engine" was intended to be

1. Ram air intake

2. Compressor for intake air

3. First pass through reactor, heating it up to a max of 1600k , in order to

4. drive the turbine stage, which powers the compressor

5. Second reheat pass through the reactor, taking it up to max working temp of reactor if needed (higher than limits of turbine by some way)

6. expand through rocket nozzle.

Since the air charge passes through turbomachinery with a maximum rpm at which it can remain intact, there is going to be less mass flow though the reactor at 20km than at sea level, therefore given the same max reactor temp, lower potential output. Ram air effect will compensate to an extent, but this means the air charge is already compressed with respect to its starting pressure before it even reaches the compressor stage. Even though the outside air temp at 60,000 feet is -40C, by the time you've boosted it back to 1 atm with ram effect, it will be quite a bit hotter by the time it hits the compressor stage than 1 atm air at sea level with no ram effect at ambient temperature.

Will have to take a look at this AJE mod, sounds interesting. With stock game mechanics ALL airbreathing engines gain thrust with airspeed and loose it with altitude. That's not how real jets work - if you put a GE90 on a rocket sled at sea level and blast it to mach 5, it will not produce 5x it's static thrust, nor remain in one piece. But due to the way you're likely to gain airspeed and altitude at same time these curves will largely cancel each other out.

Am also intrigued to try a mod with separate reactor making a resource - reactor heat and separate consumers -

nuclear turbojet - consumes heat and intake atm, makes thrust up to mach 3

nuclear ramjet - as nuclear turbo jet, no thrust below mach 1 but produces thrust up to mach 5

turbo generator - consumes heat and intake atm , to make electricity

nuclear thermal rocket - consumes heat and liquid fuel to make thrust

You could tailor your setup towards a particular mission. ATM I'm struggling to think of curves that work corectly in Kerbin, Eve and Duna.

Due to work commitments i'm going to have to leave this be till Friday. :-(

[Van Disaster]

Well, the modular approach really is easy: just have to add a new resource produced by your reactor ( in vast quantities I suggest so it can't realistically be stored ) and just use it as fuel for the propulsive devices. I did something similar to make a crude vectoring jet once, just made the jet produce bleedAir & no thrust & hacked some tiny rocket nozzles to use bleedAir as fuel. Given your resource is doing practically the same thing as burning fuel would be ( bar the pollution ) setting the propulsive bits up probably shouldn't be different.

SABRE's projected thrust curve is rather odd and I don't yet know why ( lack of study ). There is a bypass in the SABRE intake design which suggests a hard limit ( well obviously the ideal limit is set by how much H2 you can get in the rocket motor ), your motor on the other hand would seem to benefit from being a partial ramjet. Mixing bypass air would also help keep the exhaust temperature in limits, I guess. However you've basically detailed a complicated nuclear turbojet which people have already done, I didn't see any mention of vacuum mode? I guess you could add a turbopump to the same shaft as the atm compressor & double up the pipework.

I keep having an idea about taking that modular thing a bit further & having mechanical generators + consumers, so you could just have a turbine part that converted heat + resource into something ( work? ), and a generator/propellor/gearbox + set of wheels that used it - making the assumption there is a power turbine in the system. Sticking a nozzle on the end & converting work to thrust would give you a jet engine ( and conveniently get all the mass in the right place, too ).

Edited November 9, 2015 by Van Disaster

[AeroGav]

Update - I finally completed the Duna mission with this aircraft. The engines provided enough thrust to reach 1200m/s and 12km before "flaming out" which is a sub-orbital trajectory , a minor additional kick in "closed cycle" mode puts you in a proper orbit, with plenty of fuel left for the home journey.

[URL=http://s1144.photobucket.com/user/narostel/media/LVN%20Mod%201%20test/2015-11-13_00029_zpshkgkyztg.jpg.html][IMG]http://i1144.photobucket.com/albums/o492/narostel/LVN%20Mod%201%20test/2015-11-13_00029_zpshkgkyztg.jpg[/IMG][/URL]

Landing speeds on Duna are pretty scary. Burning the three Vernier motors on the belly helps arrest the rate of descent without pitching up to the point of risking a tailstrike, or increasing airspeed even further.

[URL=http://s1144.photobucket.com/user/narostel/media/LVN%20Mod%201%20test/2015-11-13_00038_zpsg7e3c3kx.jpg.html][IMG]http://i1144.photobucket.com/albums/o492/narostel/LVN%20Mod%201%20test/2015-11-13_00038_zpsg7e3c3kx.jpg[/IMG][/URL]

Success ! After about 20 crash landings, I finally put down in one piece. Duna does not seem to have any flat terrain. I flew around quite a while looking for it. Time to get the science.

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If he can't figure out how to get out of there, he's going home coach class.

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Obligatory selfie #1

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For the Eve mission, I became aware that aerodynamics had changed in the newest patch. If SSTO was possible at all, it was also going to be very marginal, so i started stripping stuff off the airplane.

1. The Vernier motors went, as did one of the reaction wheels, and the small tail bumper undercarriage leg. I was hoping to reach minmus with extra fuel thanks to all the changes, so would be able to land vertically. If not, the refuelling tender could always fly up and meet it, though neither is nimble or suited for docking maneuvers.

2. Because of the single reaction wheel, i can get all the science stuff in one small cargo bay.

3. The crew cabin went. I'm flying the mining ship to Eve orbit with this aircraft, so it can refuel just before deorbit. The Kerbals can use the crew cabin on this vessel to chill out.

4. The nose intake and type 2-1 adapter went, replaced by a mark 2 cockpit which apparently creates less drag, since there is less need for intakes. The downside is, it's the first thing to explode in the case of re-entry heating, and the first part to hit the ground in any mishap, without the crumple zone we used to have. The lethality of my "whoops" moments has increased dramatically, but i'm save scumming anyway because i CBA to refly the whole mission, nor can my space program budget afford to keep replacing very expensive aircraft like this.

5. Extra mk2 liquid fuel tanks went in in place of the above..

6. And the rapier gets replaced by another modded LV-N. It now has 3 LV-N motors as sole propulsion.


Unfortunately, it appears atmospheric re-entry on Eve is very hard since 1.05. This aircraft re-entered Kerbin from Duna orbit and re-entered Kerbin from Minmus orbit OK, but Eve is another matter. Speeds are high, and the atmosphere thickens very suddenly between 80 and 75km. I kept blowing up at 75km. Eventually I cheated and turned off heating. Turns out that despite being heavy with fuel, by 70km this airplane can stop it's descent with only 10 deg alpha.

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Posing with the new , sleeker Batwing. Couldn't afford the drag penalty of a set of ladders , so we did the next best thing..

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Departure from Eve...

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Unfortunately, this is as far as I was able to get.

It appears the sound barrier is at a lower speed on Eve, and my engines make max thrust at about 800m/s. Any faster and they lose power.

They also produce twice their closed cycle rating lower in the atmosphere at around mach 1.6, but by 36km, even at their optimal 800m/s, they are down to 60kN thrust.

Unfortunately this isn't enough for me to climb any higher with. Even if i did, thrust would fall off. At this point, I can switch to closed cycle, but the more attentive among you will know that that is the Vacuum thrust rating of the LV-N. So it won't actually help. Well eventually, my plane will get lighter from burning off liquid fuel, which will maybe get us up some more, but I think it's fair to say we're a long way from SSTO.

What more can I do?

Well, could switch to a mk1 fuselage throughout, get rid of the shock cones from the nacelles and add a couple degrees incidence to the wings. Also worthy of note, in that pic I'm at about 5 deg alpha. True, i'm pulling more than 1g so it looks like i'm trying to arrest a phugoid, but perhaps more wing area still would get down to the optimum 2.5deg AoA at this altitude.