# Is it possible to use zinc powder as a NTR propellant?

The ISP of a propellant is important when mass is the limiting factor; however, that is not exactly the case when launching a rocket. For the first part of the flight, the density of the propellant is also important.

Higher density → more propellant in the same tank → higher mass ratio → more $$\Delta v$$

A better metric for propellant performance for the first km/s is therefore density impulse. It is easy to notice that the extremely low density of liquid hydrogen (70.8 kg/m³) makes methane, ammonia and water outperform it as a NTR propellant in the early stages of the flight.

In the search for an even better density impulse, I tried to find high density metals with a low enough boiling point. Mercury and zinc turned out as possible candidates. For some reason, I am a bit afraid of glowing-hot, vaporized, radioactive mercury rain, so I choose instant galvanization instead. Zinc has an excellent density impulse. At an estimated 130s of ISP, the 7140kg/m³ density implies a density impulse 15 times better than hydrogen, and over twice that of water. Furthermore, as thrust is inversely proportional to exhaust velocity at the same reactor power, this is also giving the rocket a better thrust to weight ratio.

But, zinc is not a fluid, so I wonder, is it possible to have a mix of zinc powder and water or ammonia as a propellant? Is it possible to pump such a mix through the engine and prevent the reactor from clogging? Do you know of any research related to this?

Worked example of density impulse:

Sample rocket:

Dry mass: 10,000kg
Tank volume: 100m³

Sample propellants:

Hydrogen

Exhaust velocity: 9000 m/s Density: 70.8 kg/m³

$$\Delta v=9000m/s \cdot ln\left(\frac{10,000kg + 100m^3 \cdot 70.8 kg/m^3}{10,000kg}\right)$$

$$=4818 m/s$$

Water

Exhaust velocity: 4000 m/s Density: 1000 kg/m³

$$\Delta v=4000m/s \cdot ln\left(\frac{10,000kg + 100m^3 \cdot 1000 kg/m^3}{10,000kg}\right)$$

$$=9592 m/s$$

Feel free to leave out any discussion on the feasibility of using a NTRs, or potential benefits from a high density impulse from your answer.

What I really want to know is if it is possible to pump metal powder through an engine when mixed with water, ammonia or methane. If it is possible, how high concentrations of metal powder I can have, and still be able to pump it?

• Do you know any research related to this? Yes, John D. Clarke's Ignition! An Informal History of Liquid Rocket Propellants. Page 177 (chapter High Density and the Higher Foolishness) mentions mercury and page 9 uses Diethylzinc to get hypergolic engine start. Not as main fuel though. Jan 10, 2016 at 15:06
• Three possible complications: neutronics, localized cooling, radiation safety constraints on going with a hot NTR on the first stage. Jan 10, 2016 at 20:44
• You can circumvent the 'zinc is a solid' problem by having a coolant loop from the reactor to the zinc tank, melting the zinc before you use it. Jan 26, 2016 at 9:47
• What's wrong with "glowing-hot, vaporized, radioactive mercury rain"? HA... Jan 26, 2016 at 13:53
• @SF. Using a NTR is kind of like getting rid off the oxidizer... Jan 27, 2016 at 11:11