Storable propellants for nuclear engine?

[FreeThinker]

Diborane will similarly to Methane, fully decompose at high temperature , the big difference is that Diborane contains  more Hydrogen molecules which will lower the average Molecular mass.  Methane  gains extra energy when decomposing, but the Carbon will soot the heat exchangers, causing them to function less efficient eventualy overheating the reactor

Edited April 5, 2016 by FreeThinker

[fredinno]

20 minutes ago, FreeThinker said:

Diborane will similarly to Methane, fully decompose at high temperature , the big difference is that Diborane contains  more Hydrogen molecules which will lower the average Molecular mass.  Methane  gains extra energy when decomposing, but the Carbon will soot the heat exchangers, causing them to function less efficient eventualy overheating the reactor

...It might work. Boron is also lighter than Carbon, so...

However, it tends to be highly reactive, so it might be dangerous while fueling. But I guess it's worth a try.

[FreeThinker]

4 minutes ago, fredinno said:

...It might work. Boron is also lighter than Carbon, so...

However, it tends to be highly reactive, so it might be dangerous while fueling. But I guess it's worth a try.

Yes the stuff is hypergolic with oxygen, so it will also be great for visits to moons and small planet like mars. The Boron is also usefull for p-B fusion.

[kunok]

27 minutes ago, FreeThinker said:

Carbon will soot

I talk from memory but I think I had read that boron is even worse in that aspect

[FreeThinker]

Just now, kunok said:

I talk from memory but I think I had read that boron is even worse in that aspect

Boron will be liquid at those temperatures, so it should not be a problem.

[kunok]

1 minute ago, FreeThinker said:

Boron will be liquid at those temperatures, so it should not be a problem.

And other boron-hydrogen compounds? I should re read Ignition or other book I have again, I think that was a problem

[kerbiloid]

9 hours ago, FreeThinker said:

Boron will be liquid at those temperatures, so it should not be a problem.

Boron itself - yes, but I had read too, that wax/glass-alike products of hydroboranes burning were found everywhere in the engines.

Btw, hydrazine → ammonia + hydrogen

Edited April 6, 2016 by kerbiloid

[FreeThinker]

9 minutes ago, kerbiloid said:

Boron itself - yes, but I had read too, that wax/glass-alike products of hydroboranes burning were found everywhere in the engines.

Btw, hydrazine → ammonia + hydrogen

I 'm sure that happens when burning yes, but we are using it in a nuclear engine. As long as the stuff doesn't create a barrier between the heat exchanger and the propellant, we are cool.

Indeed, Hydrazine should great in a NTR, with an effective Isp of 74.4% due to the extra energy released durring decompositiob.

Here Is KSPI full nuclear propellant list

•  

Propellant	Resouese Name	Unlock Technology	Chemical	Thermal ISP multiplier	EngineThrust Multiplier	Thermal Decomposition	Full Decomposition Energy	Soot Effect	Toxic	Thermal / Electric Propellant	Average Density	ISRU
Hydrogen	LqdHydrogen	Nuclear Propulsion	H2	1	1			-0.01		Both	0.07085 kg/l	++
Diborane	Diborane	Exotic Nuclear Propulsion	B2H6	0.79	1			-0.01		Both	0.421 kg/l	--
Methane	LqdMethane	Efficient Nuclear Propulsion	CH4	0.3503 - 0.78	1 - 1.6	1000K - 3200K	19.895	0.25		Both	+	+/-
Hydrazine	Hydrazine	Exotic Nuclear Propulsion	N2H4	0.744	1.4			-0.01	yes	Both	++	-
Helium	LqdHelium	n.v.t	He	0.7	1			0		Electric	-	+
LiquidFuel	LiquidFuel	Nuclear Propulsion	?	0.744	1			0 *		Both	++	--
Ammonia	LqdAmmonia	Experimental Nuclear Propulsion	NH3	0.63	1.4			-0.01		Both	+	-
Hydogen - Fluorine *	LqdHydrogen  +       LqdFlorine	Exotic Nuclear Propulsion	H2 + F2	0.7	2.2			0		Thermal afterburner	+/-	-
Hydrolox (Hydrogen + Oxygen)	LqdHydrogen  +       LqdOxygen	Improved Nuclear Propulsion	H2 + 02	0.63	2			-0.01		Thermal afterburner	--	+/-
Methalox (Methane + Oxygen)		Efficient Nuclear Propulsion	CH4 + 02	0.25 - 0.55 ?	1 - 2	1000K - 3200K ?	19.895 ?	0.1		Thermal afterburner	+	+
LOX (Liquid Fuel + Oxidizer)		Improved Nuclear Propulsion		0.417	1			0		Thermal afterburner	++	++
Water		Exotic Nuclear Propulsion	H2O	0.3333 - 0.4714	1.2071	2000K - 4200K	2.574	-2.5		Both	++	+
Kerosine		Efficient Nuclear Propulsion		0.21888 - 0.42477	1.459	1000K - 3200K	12.305	0.4		Both	+	++
Liquid Carbondioxide		Experimental Nuclear Propulsion	CO2	0.2132 - 0.4085	1.459	3200K - 7000K	12.305	-2.5 - 0.33		Both	+/-	+/-
Liquid CarbonMonoxide		Efficient Nuclear Propulsion	CO	0.3273 - ?	?	4000K - 10000K	6.1525	0.5		Both	+/-	-
Liquid Nitrogen		Efficient Nuclear Propulsion	N2	0.3273				-0.01		Both	++	+/-

 

[fredinno]

Is there anything on Lithium as a NTR fuel?

[kunok]

On 6/4/2016 at 6:49 PM, fredinno said:

Is there anything on Lithium as a NTR fuel?

Makes sense, easily storable and light. You might need to preheat you tank a time before using your fuel, but I feel that being "easy"

[KSK]

I did a quick search for this out of curiosity. At face value, lithium looks like a good NTR fuel and since the engine will be operating in a vacuum, reactions with air and water shouldn't be too much of a problem. On the other hand, molten lithium didn't sound like the easiest material to work with. That turned out to be correct, at least according to this report - which looks like quite a reasonable source to me.

"Glasses, plastics and ceramics are all attacked by molten lithium near the melting point. Severe attack is due to formation of relatively stable but highly corrosive lithium oxide, nitride and carbide. Non- metallic impurities in the liquid metal have a profound effect on the compatibility behavior of l i t h i u m and other materials. For example, molten lithium nitride, readily formed from liquid lithium-nitrogen reactions is highly reactive. No metal or ceramic material has been found resistant to it. 

Emphasis added. Looks like it's going to be extremely difficult to build an engine that can withstand liquid lithium. I'm not saying impossible on the basis of a single document though.

Edit: I think I misread that at first. On re-reading, I'd say that no metal or ceramic has been found resistant to lithium nitride, not metallic lithium. However, from Figure 19 of that same document, many metals and alloy types appear to have limited or poor resistance to lithium. Others have good resistance but I have no idea what their thermal properties are and whether you could line a nuclear-thermal engine with them.

I stand by my original conclusion - not impossible but very difficult.

Edited April 7, 2016 by KSK

[lobe]

Why is hydrazine so good while water produces such a low impulse? I thought hydrazine was much denser than water?

[fredinno]

7 hours ago, KSK said:

I did a quick search for this out of curiosity. At face value, lithium looks like a good NTR fuel and since the engine will be operating in a vacuum, reactions with air and water shouldn't be too much of a problem. On the other hand, molten lithium didn't sound like the easiest material to work with. That turned out to be correct, at least according to this report - which looks like quite a reasonable source to me.

"Glasses, plastics and ceramics are all attacked by molten lithium near the melting point. Severe attack is due to formation of relatively stable but highly corrosive lithium oxide, nitride and carbide. Non- metallic impurities in the liquid metal have a profound effect on the compatibility behavior of l i t h i u m and other materials. For example, molten lithium nitride, readily formed from liquid lithium-nitrogen reactions is highly reactive. No metal or ceramic material has been found resistant to it. 

Emphasis added. Looks like it's going to be extremely difficult to build an engine that can withstand liquid lithium. I'm not saying impossible on the basis of a single document though.

Edit: I think I misread that at first. On re-reading, I'd say that no metal or ceramic has been found resistant to lithium nitride, not metallic lithium. However, from Figure 19 of that same document, many metals and alloy types appear to have limited or poor resistance to lithium. Others have good resistance but I have no idea what their thermal properties are and whether you could line a nuclear-thermal engine with them.

I stand by my original conclusion - not impossible but very difficult.

How about the Diborane suggestion the other guy came up with (or Boron in general- despite the insane heats it melts at, it looks fairly decent at 10 mol- I know Beryllium won't work due to high toxicity and Helium is worse than H2 due to being heavier and more cryogenic)

I have a feeling the heating requirements for Boron makes it unviable.

Or how about https://en.wikipedia.org/wiki/Lithium_hydride

It decomposes at 900C, is that too low for use in an NTR?

1 hour ago, lobe said:

Why is hydrazine so good while water produces such a low impulse? I thought hydrazine was much denser than water?

It decomposes into Ammonia, which is lighter, while water does not decompose.

Edited April 8, 2016 by fredinno

[lobe]

1 hour ago, fredinno said:

It decomposes into Ammonia

I figured as much but isn't ammonia a higher molar mass than water? 14+1+1+1=16 vs 16+1+1=18? Ok I answered my own question, hydrazine is better.

 

For the edit. Hydrazine is N₂H₄. This means when hydrazine decomposes it goes to NH₃+NH in decomposition. This means 2 extra Hydrogen needs to be available for it not to start attacking the core and draging precious uranium/plutonium/thorium/Hastelloy metals out of the tubing.

Edited April 8, 2016 by lobe
I needed to edit for math mistake. This'll be a long one.e

[KSK]

37 minutes ago, fredinno said:

How about the Diborane suggestion the other guy came up with (or Boron in general- despite the insane heats it melts at, it looks fairly decent at 10 mol- I know Beryllium won't work due to high toxicity and Helium is worse than H2 due to being heavier and more cryogenic)

I have a feeling the heating requirements for Boron makes it unviable.

Or how about https://en.wikipedia.org/wiki/Lithium_hydride

It decomposes at 900C, is that too low for use in an NTR?

It decomposes into Ammonia, which is lighter, while water does not decompose.

I'd need to go away and search for information on boron chemistry but didn't somebody already comment on this thread that it tends to coat the inside of your engine with glass? Heating shouldn't be a problem - diborane boils at -93 degrees Celsius (source) but it's also volatile, air and moisture sensitive and toxic. Toxicity isn't necessarily an issue - show me a storable rocket fuel that isnt toxic  and the other factors shouldn't be too much of an issue once you get to space. I would think the main problem with diborane is simply making enough of the stuff to fill a rocket with. 

900C does sound too low for use in an NTR, at least if you want to get any sort of ISP out of it. And once it decomposes you're back to all the lithium problems as I'm sure you already knew.

 

 

 

[fredinno]

1 hour ago, lobe said:

I figured as much but isn't ammonia a higher molar mass than water? 14+1+1+1=16 vs 16+1+1=18? Ok I answered my own question, hydrazine is better.

 

For the edit. Hydrazine is N₂H₄. This means when hydrazine decomposes it goes to NH₃+NH in decomposition. This means 2 extra Hydrogen needs to be available for it not to start attacking the core and draging precious uranium/plutonium/thorium/Hastelloy metals out of the tubing.

Well, it doesn't seems to be enough of a problem to stop mission designers from using it

1 hour ago, KSK said:

I'd need to go away and search for information on boron chemistry but didn't somebody already comment on this thread that it tends to coat the inside of your engine with glass? Heating shouldn't be a problem - diborane boils at -93 degrees Celsius (source) but it's also volatile, air and moisture sensitive and toxic. Toxicity isn't necessarily an issue - show me a storable rocket fuel that isnt toxic  and the other factors shouldn't be too much of an issue once you get to space. I would think the main problem with diborane is simply making enough of the stuff to fill a rocket with. 

900C does sound too low for use in an NTR, at least if you want to get any sort of ISP out of it. And once it decomposes you're back to all the lithium problems as I'm sure you already knew.

 

 

 

https://en.wikipedia.org/wiki/Beryllium_hydride

https://en.wikipedia.org/wiki/Beryllium

Beryllium Hydride is another decent idea. It needs to be transported in a granulated powder, as it decomposes at its melting point of 250C, however, the hydrogen and Beryllium is very light, and storable. Pure Beryllium is toxic, but it doesn't seem to be toxic in its hydrogen compound.

Unfortunately, Beryllium only boils at 2469C, meaning you might have to deal with droplets of Beryllium on the walls of the nozzle. No idea if this is enough of a problem, or if Beryllium will be hot enough to boil regardless in an NTR.

Edited April 8, 2016 by fredinno

[lobe]

I mean, to be honest, I would like people that are honest in trying to replicate a hydrazine mission to Mars to message me. I mean, as fredinno knows, for a mission with a hypergolic mixture over 12 thousand tons of fuel are needed, and I would like that to be a little lower.

[fredinno]

7 minutes ago, lobe said:

I mean, to be honest, I would like people that are honest in trying to replicate a hydrazine mission to Mars to message me. I mean, as fredinno knows, for a mission with a hypergolic mixture over 12 thousand tons of fuel are needed, and I would like that to be a little lower.

Unless you use NTR hydrazine

[lobe]

19 minutes ago, fredinno said:

Unless you use NTR hydrazine

which is what I mean.

[shynung]

Why hasn't anyone proposed using water as propellant? Not exactly great I_sp, sure, but it cuts down a lot on spacecraft logistics. No need for funky storage systems, temperature requirements identical to the hab module, can be cracked into hydrogen and oxygen for LSS, fuel for chemical propulsion systems, and Anthraquinone'd into hydrogen peroxide for RCS. If ISRU is available, it's quite common in the Solar system inside icy asteroids.

Edited April 8, 2016 by shynung

[fredinno]

6 hours ago, shynung said:

Why hasn't anyone proposed using water as propellant? Not exactly great I_sp, sure, but it cuts down a lot on spacecraft logistics. No need for funky storage systems, temperature requirements identical to the hab module, can be cracked into hydrogen and oxygen for LSS, fuel for chemical propulsion systems, and Anthraquinone'd into hydrogen peroxide for RCS. If ISRU is available, it's quite common in the Solar system inside icy asteroids.

People have talked about it, a lot. It's low ISP means it sucks unless you have ISRU. http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150016188.pdf

[kunok]

7 hours ago, shynung said:

and Anthraquinone'd into hydrogen peroxide for RCS

Why not directly use steam? A little oven is simpler than that, even with an little pressure tank for the steam. It's not like you usually have unexpected manoeuvres.

[kerbiloid]

Hydrazine is RCS.

[todofwar]

This is one of those things that still doesn't make sense to me. I understand the velocity of a gas goes up as you decrease its mass, but the rocket equation also depends on mass of fuel exhausted. If you can speed up Argon to match H2 it should give you more umph. I guess if there was a way to do that someone would have done it, but for some reason something in the back of my mind keeps saying that's not right.

Another thing, someone was asking about why different gases don't exactly track with mass, and I'm willing to bet it has more to do with deviations from the ideal gas law than it does with decomposition. Water and ammonia are "sticky" while helium or methane will bounce off each other more, and of course methane is bigger in size and stores more energy in vibrations so you need to get it hotter to have the same amount of kinetic energy in its translational modes.

[YumonStudios]

7 hours ago, todofwar said:

 

This is one of those things that still doesn't make sense to me. I understand the velocity of a gas goes up as you decrease its mass, but the rocket equation also depends on mass of fuel exhausted. If you can speed up Argon to match H2 it should give you more umph. I guess if there was a way to do that someone would have done it, but for some reason something in the back of my mind keeps saying that's not right.

 

You can do that. It's called an Ion drive.

Also, @KSK anything on those alternate NTR propellants?