Sodium Potassium alloy fuel

[farmerben]

Thunderfoot performs some fascinating experiments with Sodium Potassium alloy.  He considers using it in contrails to fight global warming.

https://www.youtube.com/watch?v=bW5lqA_U7Tg

Not explored by him is the possibility of using this for space exploration.  It has several unique advantages.  It is a conductive reflective solid under nominal conditions.  But easily converts to a conductive liquid with low vapor pressure.  Meaning it could flow in space with minimal evaporation without containment tubes.  

It is possible also to make refillable solid rocket motors with NaK alloy.  

It can make mirrors.  And the smoky exhuast, NaO2 and KO2, are highly reflective compared to other types of exhaust.

It would be excellent hull shielding for both radiation and micrometeors.  There is better potential for self repair of NaK surfaces since it flows easily.  

 

I believe that NaK + 4H2O => NaO2 + KO2 + 8H 

So using pure water as an oxidizer releases lots of hydrogen, which is very good for ISP, through I don't know what the exact ISP would be.  

[Spacescifi]

28 minutes ago, farmerben said:

Thunderfoot performs some fascinating experiments with Sodium Potassium alloy.  He considers using it in contrails to fight global warming.

https://www.youtube.com/watch?v=bW5lqA_U7Tg

Not explored by him is the possibility of using this for space exploration.  It has several unique advantages.  It is a conductive reflective solid under nominal conditions.  But easily converts to a conductive liquid with low vapor pressure.  Meaning it could flow in space with minimal evaporation without containment tubes.  

It is possible also to make refillable solid rocket motors with NaK alloy.  

It can make mirrors.  And the smoky exhuast, NaO2 and KO2, are highly reflective compared to other types of exhaust.

It would be excellent hull shielding for both radiation and micrometeors.  There is better potential for self repair of NaK surfaces since it flows easily.  

 

I believe that NaK + 4H2O => NaO2 + KO2 + 8H 

So using pure water as an oxidizer releases lots of hydrogen, which is very good for ISP, through I don't know what the exact ISP would be.  

 

I warmly suggest hybrid rockers using liquid oxygen and solid propellant potassium alloy. Better thrust than pure chemical rocketry and easier to process and manufacture as well too.

 

I think wilderness refueling practically demands hybrid propellant rocketry.

 

Pure chemical requires a bunch of heavy compressors and large tanks that take up a lot of volume, which can largely be reduced with hybrid propellant rocketry.

Edited July 3, 2022 by Spacescifi

[KSK]

2 hours ago, farmerben said:

Thunderfoot performs some fascinating experiments with Sodium Potassium alloy.  He considers using it in contrails to fight global warming.

https://www.youtube.com/watch?v=bW5lqA_U7Tg

Not explored by him is the possibility of using this for space exploration.  It has several unique advantages.  It is a conductive reflective solid under nominal conditions.  But easily converts to a conductive liquid with low vapor pressure.  Meaning it could flow in space with minimal evaporation without containment tubes.  

It is possible also to make refillable solid rocket motors with NaK alloy.  

It can make mirrors.  And the smoky exhuast, NaO2 and KO2, are highly reflective compared to other types of exhaust.

It would be excellent hull shielding for both radiation and micrometeors.  There is better potential for self repair of NaK surfaces since it flows easily.  

I believe that NaK + 4H2O => NaO2 + KO2 + 8H 

So using pure water as an oxidizer releases lots of hydrogen, which is very good for ISP, through I don't know what the exact ISP would be.  

Your equation is wrong. More correct ones would be:

2Na + H₂O ---> Na₂O + H₂

or

2K + H₂0 ---> K₂O + H₂

How much potassium or sodium oxide you get will obviously depend on their ratio in the alloy.  I say 'more correct' rather than 'correct' because I have no actual idea what's going to come out the back of this rocket. Sodium oxide is hygroscopic (for example), so it'll react with any water around to make sodium hydroxide, which will then react with more sodium to make sodium oxide again.  Exactly what you get in your exhaust will probably depend heavily on how much time the NaK and water have to react. 

Either way, this is not an efficient hydrogen generator for a rocket engine given that the atomic mass of sodium is approximately 23, the atomic mass of potassium is approximately 39, and the molecular mass of water is approximately 18, so you'd need to take somewhere between 64g of reactants (for pure sodium) and 96g of reactants (for pure potassium) for every 2g of hydrogen produced.

The ISP for a NaK rocket  is going to be dreadful.  Throwing a couple of grams of hydrogen out of the nozzle isn't going to do much to improve the fact that you're also throwing out somewhere between 62g and 94g of mixed metal oxides along with it.

@Spacescifi

As for using this for wilderness refueling - forget it. Efficient wilderness refueling will depend on sourcing easily available materials which can be converted to propellant with minimal processing. NaK fails  on both counts.

For that matter, hybrid rockets in general are likely to make lousy candidates for wilderness refueling because they depend on solid fuels which are relatively complex to manufacture, and which are also precision cast into particular shapes for use. Take a look at this simplified diagram of the SpaceShipOne hybrid motor for example.

Also, hybrid rockets are chemical rockets. I have no idea where this distinction came from, unless you mean 'purely liquid fueled' when you're talking about a 'pure chemical' rocket.

[kerbiloid]

The K*Na + H₂O rocket fuel successfully works since the first fast neutron nuclear reactors had been created, using the K*Na eutectic mixture as coolant

Spoiler

, when they unmont the big curved pipes, full of solidified remains of K*Na, and start washing them by water hose, hiding from the roaring jets of flame from the pipe ends.

 

 

[sevenperforce]

4 hours ago, Spacescifi said:

I warmly suggest hybrid rockers using liquid oxygen and solid propellant potassium alloy. Better thrust than pure chemical rocketry

As @KSK already pointed out (and as I and others have now pointed out several times), hybrid rockets are chemical rockets.

4 hours ago, Spacescifi said:

I think wilderness refueling practically demands hybrid propellant rocketry.

There have been some proposals to refine aluminum powder out of lunar regolith and use it with oxygen (presumably obtained from silicon oxides in the regolith) in hybrid rockets built on the moon, but that wouldn't be "wilderness refueling" at all; that would be a large industrialized effort building expendable rockets.

If your goal is a reusable rocket that can be refueled by ISRU, I can't think of a worse way to do it than hybrids.

4 hours ago, Spacescifi said:

Pure chemical requires a bunch of heavy compressors and large tanks that take up a lot of volume, which can largely be reduced with hybrid propellant rocketry.

Compressors? What on earth are you talking about?

Hybrid rockets still require large tanks to hold the liquid propellant; you're not really improving anything. Some solid fuel types are denser than some liquid fuel types but that's true of anything.

[Piscator]

Using an alloy that's liquid or close to liquid at room temperature makes for a pretty lousy hybrid rocket, I'd assume. Probably depends on what your local room temperature is, though.

That said, I can see a use case for metal/oxygen (rich) hybrid rockets  on worlds without readily available hydrogen and low delta-V requirements like e.g. the moon.

[kerbiloid]

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

Mercury has a sodium-rich atmosphere. But requires large scoops.

Or a (solar-powered) magnetic scoop.

[sevenperforce]

7 hours ago, Piscator said:

Using an alloy that's liquid or close to liquid at room temperature makes for a pretty lousy hybrid rocket, I'd assume. Probably depends on what your local room temperature is, though.

If you did it perfectly you could use an alloy that is stored in solid form and then melts and flows into the chamber to react as a liquid at the operating temperature of the engine. No tank required.