[1.7] [WIP] TD Advanced Propulsion Systems

[Space Nerd]

Do I need to download another mod for the LH2 tanks?

[TiktaalikDreaming]

1 hour ago, Space Nerd said:

Do I need to download another mod for the LH2 tanks?

Yes. There's probably a few, but this was designed to be a companion to my revamped Nexus mod, as the second stage engine

Use the development version on github for the best results

 

[TiktaalikDreaming]

I case anyone was wondering, I'm working on a fairing so I can add a lower stack node.  Initial dev was focused on getting a workable engine for my Nexus mod, which doesn't need a lower stack node for the second stage engine.  But for general use, these are better as vacuum engines, so I'll be adding stackability.

Teeny progress;

Edited September 23, 2019 by TiktaalikDreaming
Updated image

[TiktaalikDreaming]

Got another few minutes and added a bump/normal map.  Very early days.  And it only ended up in game this early because blender was doing daft things with it and I needed to make sure that didn't carry over to the game before continuing.  

I updated the releases to include this, as I realized I hadn't done one since adding the bottom stack node, fairing or not.

https://github.com/TiktaalikDreaming/TDAPS/releases/tag/0.4.190926

 

Edited September 25, 2019 by TiktaalikDreaming
add release link

[TiktaalikDreaming]

I've recently realized I forgot to scale this engine.  This may be slightly game breaking for any craft in flight, but shortly I will be rescaling and probably adding back some more nozzle length.  Or nozzle length on the LH2 version anyway.  The reactor core size is based off slightly optimistic (I'm assuming active neutron bombardment to decrease minimum critical volume) readings of existing studies on gaseous core reactors, and always meant to make the kerbal edition scaled down an extra kerbal factor (typically around 62-65%).  So I think this will necessitate adjusting the stack node details and so on.  It definitely means my fairing is wrong.

[MatterBeam]

@TiktaalikDreamingReally great work, especially with the radiation modeling.

From the Isp figures on the hydrogen propellant version, I work out that the temperatures here are about 30,000K.
Hydrocarbon fuels are certain to completely decompose at that temperature. Kerosene, when split into carbon and hydrogen, becomes a plasma with an average molar mass of about 4.66g/mol. This means that your exhaust velocity would drop by a factor 4.66^0.5 = 2.16

In other words, you can actually push your liquid fuel version to an Isp of 1652s!

[TiktaalikDreaming]

29 minutes ago, MatterBeam said:

@TiktaalikDreamingReally great work, especially with the radiation modeling.

From the Isp figures on the hydrogen propellant version, I work out that the temperatures here are about 30,000K.
Hydrocarbon fuels are certain to completely decompose at that temperature. Kerosene, when split into carbon and hydrogen, becomes a plasma with an average molar mass of about 4.66g/mol. This means that your exhaust velocity would drop by a factor 4.66^0.5 = 2.16

In other words, you can actually push your liquid fuel version to an Isp of 1652s!

Nice.  My estimates on the liquid fuel version are very much a case of wild guessing so far.  But a molar mass of 4.66 would certainly make it more useful for what the engine's intended for.  I was just spitballing a partial decomposition.  But yes, the temperatures are likely high enough to plasma-ify most anything.  If actually trying this, I don't know how you'd avoid weird high temperature and pressure carbon combinations and build-ups in inconvenient areas, but we have to assume some magic for KSP's liquid fuel.

A quick note that the ISP for the LH2 version in high ISP assumes cooling that LH2 flow rate can't achieve, and instead a bunch of radiators that don't exist in game yet.  The never finished pre-revamp version was going to look a bit like (I cleverly forgot a decoupler when launching this test);

 

 

[MatterBeam]

@TiktaalikDreaming

I'll do a bit of maths.

The main job of the active cooling is to absorb heat reaching the reactor chamber walls. The propellant flow does a good job of protecting it from thermal radiation, but X-rays and neutrons punch through. From gas-core NTR documents I've read, about 7% of the reactor power ends up in the walls. 

Your hydrogen-propellant engine in high Isp mode has an engine power of 3568 * 9.81 * 3500 * 1000 /2 = 61.25GW. If this is 93% of the output, then the heat reaching the reaction chamber walls is about 4.6GW. 
You mass flow is 3500 * 1000 / (3568*9.81) = 100kg/s. 

A beryllium oxide moderated gas core reactor can only handle a wall temperature of 1400K. Heating hydrogen from liquid to 1400K absorbs 20.3MJ/kg. Therefore, your hydrogen mass flow can only support 2GW of heating, which is an engine power of 26.9GW. I suggest you cut your thrust to 43.9% of its current value, or 1539kN. 

 

[TiktaalikDreaming]

8 hours ago, MatterBeam said:

@TiktaalikDreaming

I'll do a bit of maths.

The main job of the active cooling is to absorb heat reaching the reactor chamber walls. The propellant flow does a good job of protecting it from thermal radiation, but X-rays and neutrons punch through. From gas-core NTR documents I've read, about 7% of the reactor power ends up in the walls. 

Your hydrogen-propellant engine in high Isp mode has an engine power of 3568 * 9.81 * 3500 * 1000 /2 = 61.25GW. If this is 93% of the output, then the heat reaching the reaction chamber walls is about 4.6GW. 
You mass flow is 3500 * 1000 / (3568*9.81) = 100kg/s. 

A beryllium oxide moderated gas core reactor can only handle a wall temperature of 1400K. Heating hydrogen from liquid to 1400K absorbs 20.3MJ/kg. Therefore, your hydrogen mass flow can only support 2GW of heating, which is an engine power of 26.9GW. I suggest you cut your thrust to 43.9% of its current value, or 1539kN. 

 

The active cooled version is intended to use liquid helium cooling for the reactor walls and not rely on the propellant to avoid the reactor melting.  The high ISP is due to allowing the propellant to get that hot, which limits the propellant flow rate.  You're right, the flow rate of LH2 is insufficient to cool the engine.  I think I've got it to the point where running it in active mode results in engine explosions in game.

The regeneratively cooled mode involves higher propellant flow rate to keep things from melting, so the propellant never gets as hot, but also the reactor never quite melts, and due to higher flow rate, the exhaust velocity is lower, but thrust is higher.  That *seemed* to be the set-up assumed in the sketches done up by Convair for the Nexus second stage vehicles.  I haven't actually run proper numbers for the regen cooled edition yet, and they're subject to change.  Or at least, the numbers I do have are from calculations I can't remember due to it being too long ago. 

So,

Active cooled = assume external cooling system that handles buckets of heat

Regeneratively cooled = reactor cooled with propellant

[p1t1o]

I just came across this mod via a link from project rho.

It looks super-cool, is this project still active? Would be a pity if that beautiful part went fallow.

No pressure, just an enquiry

 

[TiktaalikDreaming]

On 2/25/2020 at 2:07 AM, p1t1o said:

I just came across this mod via a link from project rho.

It looks super-cool, is this project still active? Would be a pity if that beautiful part went fallow.

No pressure, just an enquiry

 

It's active.  I'm currently focusing on a revamp of the Nexus craft mod, that spawned this.  

 

And I just realized I never put this up on spacedock.  Um, coming soon.

 

https://spacedock.info/mod/2348/TDAPS

 

Edited February 26, 2020 by TiktaalikDreaming
link

[zer0Kerbal]

8 hours ago, TiktaalikDreaming said:

And I just realized I never put this up on spacedock.  Um, coming soon.

 

https://spacedock.info/mod/2348/TDAPS

congrats on the *official* release!

[p1t1o]

Oh SWEET

There is little in this world more hardcore than a fricken gas-core nuclear engine, open-cycle. Lightbulbs are for wusses.

Push the Kzinti Lesson to maximum

[TiktaalikDreaming]

6 hours ago, zer0Kerbal said:

congrats on the *official* release!

It helps to remember to release. 

[zer0Kerbal]

14 hours ago, TiktaalikDreaming said:

It helps to remember to release. 

Oh I know - I am currently suffering from a severely plugged release pipeline myself.

[TiktaalikDreaming]

On 2/28/2020 at 12:37 PM, zer0Kerbal said:

Oh I know - I am currently suffering from a severely plugged release pipeline myself.

Too much info dude!!!

[zer0Kerbal]

1 hour ago, TiktaalikDreaming said:

Too much info dude!!!

maybe I need to attach a release drain valve

[TiktaalikDreaming]

I've had reason to use the LH2 GCR a few times recently and realized it could really do with supplementary tankage for the Tungsten and Uranium.  Started, probably be a week or so to get this done properly.  This is a combo 3.75m tank.  Needs feed lines, and more framework.  Relies too much on levitation so far.  Aiming at doing a plain tungsten and a plain uranium tank as well.

[TiktaalikDreaming]

Rotated the Tungsten cylinders, due to sanity.More framework done.

[TiktaalikDreaming]

First one in game.  

Not finished by any stretch of the imagination, but my Internet was deceased for a day, and between complaining to my ISP then my ISP's wholesaler, I had time to do a bit more work on it.  I'm basically still working on getting the bump maps right before moving on to finishing the rest of the textures.

[TiktaalikDreaming]

OK, tank thing is pretty much done now, so there's a new version on spacedock.

I also updated the blueprintish type images on the first post to reflect the current state of a whole 3 parts. 

[BigFatStupidHead]

Oh, wow. That is a real purdy engine there. NIce work!

[TiktaalikDreaming]

6 hours ago, BigFatStupidHead said:

Oh, wow. That is a real purdy engine there. NIce work!

It took a rather absurd amount of research to get it to where it is now.  I think the most recent main change was realising the LH2 pumps should be on the safe side of the shadow shield.  It's been mutating and getting more detailed for years now.

[BadModder54]

Hi! How exactly do you go about cooling the LH2 engine? I have an unholy amount of radiators, and it still explodes after a short duration firing. Thank you for your time!

[TiktaalikDreaming]

12 hours ago, BadModder54 said:

Hi! How exactly do you go about cooling the LH2 engine? I have an unholy amount of radiators, and it still explodes after a short duration firing. Thank you for your time!

In the actively cooled (high ISP) mode, I intend it to use a giant radiator I haven't made yet.  I've had some abortive attempts, but from memory of the math for this, the required radiator size is 1.3 x unholy.  Not quite in the sq km range, but well into being measured in football fields.

It is dual mode though.  The low ISP high thrust version cools using the LH2 flow (meaning it needs a much higher flow rate, resulting in lower exit temp, and lower ISP, but higher flow rate leading to greater thrust).

The radiators are basically held up because (like a clever idiot) I decided I'd try to figure out how to use the DLC robotics systems to extend parts.  Without an extending truss, the whole thing gets to be ungodly long to fit the 1.3 unholy radiators.