Metalic hydrogen diamond engine?(or other form of carbon.)

[Arugela]

So, this is kind of like a skylon engine I think. As much as I can tell with how little I understand of this. I'm assuming diamond is good for the higher density. But I'm not sure what would be an ideal form of carbon. Diamond sounds more interesting though.

Basically, you store metallic hydrogen for density of hydrogen. You then store diamond potentially like a solid rocket booster or otherwise melt and drip into the engine feed(or whatever is needed.). You then collect air and liquefy it and then use the liquid nitrogen for cooling the ship hull and other parts of the ship and collect the oxygen as liquid oxygen to pump as an oxydizer.

Potentially, the idea is you melt the diamond to and mix with the metallic hydrogen in order to make literal methane or liquid methane fuel. Then use as a normal Methalox combo. Other side stuff would be used or dumped as needed. No idea how effective this would be or how much electricity would be needed. Still slowly learning things. Edit: And if there is enough nitrogen and/or stored liquid oxygen with it use one or the other as mono propellants  for maneuvering thruster at various parts of the ship if it's safe. Would that do anything interesting if they were combined in a nozzle and released somehow?

Would this allow more effective density of fuel? Would this be more effective than theoretically pure metallic hydrogen? I'm assuming you could both start with liquid oxygen and convert in flight potentially. I'm not sure how much you could get out of it yet.

Could you get up to a 20% payload mass with this?

Edited March 21 by Arugela

[Terwin]

The storage requirements for metallic hydrogen make it a non-starter for rockets.  90% of your launch mas would be fuel tank, limiting you to short, low-velocity hops.

There was a theory that metallic hydrogen had a metastable island that could make it almost shelf-storable and remove that constraint, but it did not work when tested.

 

Methane is used because it is a much more dense and easier to handle holder of hydrogen.  It would be silly to turn hydrogen into methane for rocket fuel unless you planned to store it for a while.

Diamond melts around 4500c and hydrogen evaporates at -253c, so you are not combining those in any direct way.

Metallic hydrogen converting to hydrogen gas(H2) releases much more energy than burning it does, and leaves you with pure hydrogen reaction mass, giving a theoretical isp of 1700.

Adding anything to it will only reduce that number.

[Arugela]

Oh, I thought diamond could be melted in liquid oxygen more easily.

This is also for an SSTO design and I hoped it would help cool a ship so it can survive the heat better.

Edited March 21 by Arugela

[AckSed]

If metallic hydrogen could be a thing in multi-ton lots, it wouldn't need it. MH changing phase and decomposing back to regular hydrogen would release incredible amounts of energy (216 megajoules/kg) that makes hydrolox (10 MJ/kg) and TNT (4.2 MJ/kg) seem wimpy.

Melting carbon and such to make methalox is gilding the lily, so to speak.

The decomposition is at a ferocious 6000+ deg. C, so you're stuck taking hydrogen or some other fluid anyway to cool the reaction chamber. Water might work, though the heavier exhaust products would halve the specific impulse, but increase the thrust.

[Terwin]

That is called burning and it turns the diamond into CO2.  Once the diamond is lit, it can keep burning even at very low temps, even submerged in liquid O2.

Methane is great because it is 40% 25% hydrogen by weight.  (Water is only 20% 11% hydrogen by weight)(Forgot neutrons)

Pure hydrogen is much better for the isp but ts very low density and hard to handle .

Adding anything to it just before burning can only hurt isp.

Edited March 21 by Terwin

[AckSed]

Propellant density is important with SSTO, yes, but I've seen other proposals say that it can work with normal propellants.

And I would reluctantly decline developing horizontal-takeoff SSTO spaceplanes, no matter how cool they are. Skylon's air-breathing rocket engines currently aren't getting the funding to turn them into reality.

Perhaps you heard that hydrogen doesn't have the density for SSTO. It doesn't, not until you make it very big like the ROOST proposal. Second/third stage rocket engines working in vacuum need lower pressures, and hydrolox's high specific impulse is an advantage for for orbital manoeuvring, so it's more common there.

Check this table of bulk densities for different fuels. That's the combination of LOX and a fuel in the optimal ratio. Any air-breathing rocket proposes not taking the LOX along for most of the trip to save mass.

Methalox is middle-of-the-road in performance, and was passed over for the longest time, except when talking about colonising Mars. Even now, it's the propellant of choice for Raptor because of SpaceX's Mars ambitions AND engineering talents AND the amount of money coming in from launch services and Starlink AND their tolerance of risk are pushing it to its limit.

Its ratio of 3 parts oxygen to one part methane means that the majority of propellant is dense LOX, increasing its bulk density to 8/10ths kerelox. Methane's handling is manageable and it is cheap.

[kerbiloid]

By having enough diamonds, one can buy enough liquid hydrogen tanks to have no need in its metallism.

Edited March 22 by kerbiloid

[Nuke]

diamond scarcity is mostly enforced by a small number of diamond cartels who fix the prices. diamonds are not in fact rare. granted you probably cant source enough to use as rocket fuel.

Edited March 23 by Nuke

[kerbiloid]

Afair, there is no clear vision on the diamond origins. They need a pressure of high depths, but appear on surface inside narrow volcanic pipes.
For me, these pipes look exactly like holes in a tank armor from a cumulative jet, so I prefer to think that the diamonds appear at surface, in cumulative jets of magma, pressed up by pressing a cylindric magma pipe below. A supersonic magma cumulative jet pierces the rock armor above, and the pressure of hydraulick shock should be ~3 000 kg/m3 density * 5500 km/s sound in rock * 1 000 m/s jet speed (based on 50 km altitude and air drag) /100 000 Pa atm ~= 165 kbar, while diamonds need 50 kbar.
Thus, the jet generates diamonds in the pierced rocks and throw them up, spreading around.
(Just my understanding, not official).

But what do I want to say here. There is a lot of useless deserts. Why not turn them into diamond factories by drilling and detonating a shaped set of fusionukes underground.
The ocean will provide deuterium, the solar panels and windmills - green energy to separate it, the common scheme is tested in Ivy Mike.

Also we can turn the useless Moon rocks into Golconde.