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Discussion of metallic hydrogen propulsion split from another thread.


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1 hour ago, coyotesfrontier said:

everyone else is saying about metallic hydrogen

"Everyone else" isn't saying that. Most of us just got bored and left the discussion ages ago.

Bring on the metallic hydrogen, I say.

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13 hours ago, Deddly said:

I think the objection some have is that metastable metallic hydrogen appears to be in the realms of scifi on the level of Star Trek warp drive technology,

At least in the direction of those realms.  I read some of the papers over the last week and it seems this was always a remote speculation.

The 1935 Wigner and Huntington paper was about electronic structure of dense solid hydrogen. The first result is that, if you can push the H2 molecules close enough, the electronic bonds overlap and merge into a sea of electrons, and the nuclei space themselves equally to minimize the energy of their electrostatic repulsion. Then they say

"If  the  extremely  high compressibility  [of molecular solid hydrogen] at  ordinary  pressures ... would  hold  throughout, the molecular  form  would  be  stable  [at all pressures]. ... even  under  the  assumption  of  the  most advantageous  compressibility  at  high pressures, the  pressure  necessary for  the  transformation  is 250,000  atmos. [25 GPa],  which is  outside  the  scope of  the present  technique.
The  objection  comes  up  naturally  that  we  have calculated  the  energy  of a  body-centered  metallic lattice  only,  and  that  another  metallic  lattice may  be  much  more  stable.  We  feel  that  this objection  is justified."

They go on to speculate about whether layered structures, that violate the assumptions of the calculations they had done, could possibly give a solid monatomic (not H2) a lower pressure. They reference graphite versus diamond as part of this speculation.

So in 1935 they estimated metallic hydrogen would be stable above some pressure between 25 GPa and infinity.  Their lower bound of 25 GPa is sometimes mis-quoted as their best estimate.

The 1972 paper from Brovman, Kagan, and Kholas (English, Russian) is about crystal structures of monatomic hydrogen. They find that the electronic structure favors a long axis to the crystal structure, overcoming the tendency of positively charged nuclei to form cubic lattices where the minimum nucleus-nucleus distances are longer.  cGFYjJL.jpgThey find several structures to be significantly, ~10 eV/atom, lower-energy than body-centered cubic, including the white tin structure predicted by later papers.  However, their prediction for most-lowest-energy structure is hexagonal, like graphite, except the atoms aren't closely spaced in layers but closely spaced between layers, making 'filaments' of hydrogen atoms in a hexagonal grid.  Those filaments are weakly connected to their neighbors so free to slide along their length. This is a very strange structure for a monatomic solid; it reminds me of liquid crystals.

The Brovman paper does say (fig 11) that the atoms will spring back to position (positive frequencies phonons) if something disturbs them in any pattern, including atoms pairing up to move toward H2, and these calculations are at zero pressure.  They also confirm (p1303) that they expect solid monatomic H to be stable, at zero pressure, against uniform expansion into separate H atoms, which is not surprising.  Edwin Saltpeter (1973) references Brovman as finding a 1-eV barrier against formation of H2, but I don't see that in Brovman.   The Brovman paper itself concludes

"As  to  the  lifetime  of  the  obtained  state,  which  is metastable  with  respect  to  a  transition  to  the  molecular
phase,  this  question,  being  purely  kinetic  and  connected with  nucleus-formation,  remains  open."

and goes on to mention reasons one would expect short lifetime: light atoms and large binding energy of H2.

On 10/10/2020 at 11:16 AM, Dragon01 said:

the underlaying theory that postulates a metastable state [...] also predicted that metallic hydrogen would form at about 2.4GPa. 

I didn't find any predictions about metastable states with any quantitative pressures, so this might be one of the mis-quotes in the literature, or I might have missed something.

The later papers I've found so far make no mention of that proposed filamentary structure.  Later calculations do agree that crystals with a long axis are the most stable.  The modern predictions for crystal structure have two atoms per repeat unit (unlike the filament structure with just one) so their analogues of figure 11 from the Brovman paper shows more curves, for the additional patterns of displacement.  UV6wOoY.jpgFor densities corresponding to pressures below 250 GPa, the modern calculations show negative frequencies for the displacements that would pair hydrogen atoms.  Unlike the situation with diamond/graphite, we can easily see a way for the hydrogen atoms can shift smoothly from metal to H2.

Isaac Silvera has done a lot of serious work in high-pressure physics, and has also speculated on the uses of metastable metallic hydrogen.  That speculation follows qualifiers[*] like "If atomic hydrogen is metastable and if ..." but unfortunately the speculation is in the same papers as his popular descriptions of serious work.  I don't see anyone else working in high pressure physics who even speculates on metastable monatomic hydrogen. Speculation is within the scope of Atomic Rockets, and they file it under "unobtanium".

[* Edit: Looking at the 2017 article by Silvera in Science, I read in the first paragraph "other predictions suggest solid metallic hydrogen (SMH) is metastable at room temperature when the pressure is released [Brovman 1972]. The combination of these expected properties makes SMH important for solving energy problems and can potentially revolutionize rocketry as a powerful propellant."  That isn't very well labelled as speculation. After reading Brovman, though, I find the leap to proposing this as rocket  to be wildly speculative.  If the KSP2 team was fooled by this, I can't blame them.]

11 hours ago, mcwaffles2003 said:

I believe the problem, gameplay wise, is the lack of a nonradioactive exhaust/high thrust/ medium or high Isp/ near habitats solution and the devs want a rocket that fills that position.

Maybe so. Nothing other than the speculated metastable metallic hydrogen fills the gap between chemical explosives (nitroglycerin, e.g.) and nuclear fuels.

It reminds me of the situation with overpowered reaction wheels in KSP1.  They make initial game-play a bit easier but are very unrealistic in terms of any performance measures with numbers. Acknowledging that the reaction wheels are unrealistic is a good thing to do, for players who also want know about real gyroscopes.

Edited by OHara
re-read the Science article
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29 minutes ago, OHara said:

Nothing other than the speculated metastable metallic hydrogen fills the gap between chemical explosives (nitroglycerin, e.g.) and nuclear fuels.

This phrase will start the next round...

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13 minutes ago, SpaceFace545 said:

can we please get these metallic hydrogen threads closed, it's going to be in the game no matter if you want it or not.

It's a discussion, but yes I agree it's not producing any value to the forums

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1 hour ago, SpaceFace545 said:

can we please get these metallic hydrogen threads closed, it's going to be in the game no matter if you want it or not.

There is no reason the discussion should not be allowed, and there is only one thread. 

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1 hour ago, SpaceFace545 said:

can we please get these metallic hydrogen threads closed, it's going to be in the game no matter if you want it or not.

It's one thread and it already has to do the job for 2 or 3 different arguments, closing this down would make the OT about metallic hyrdogen in every other thread completely justfied.

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# Pro mmH Contra mmH
1    
...    

I suggest to make a small table with arguments of both parties, and let everyone just write numbers of the theses supported by him, to make the posts much shorter and more readable.
(Anyway there is an infinite loop of them).

Or make two polls with these theses and let everyone mark what he prefers.

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11 minutes ago, kerbiloid said:

Or make two polls with these theses and let everyone mark what he prefers.

 

Maybe @Dragon01 can edit the message to make a poll where people can see who is on pro-MH and on con-MH

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Personally, I preferred it when this was a discussion of the feasibility vs infeasibility of the tech rather than an attempt at dividing us into two camps.

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3 minutes ago, Deddly said:

Personally, I preferred it when this was a discussion of the feasibility vs infeasibility of the tech rather than an attempt at dividing us into two camps.

The good ol' days :P

My summary of my view of MH feasibility would be this:

I don't think humanity right now could find ways to make MH propulsion, but I believe that humans if they want to find how will find how. It's always been that way. Humanity will find a way one way or another.

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Ok, then I'm for realistic nuke engines which effectively replace the metallic hydrogen, and see no reason to worry about the radiation when the launchpad for any of them should be placed far from the base, because it's pure hydrogen under high pressure.

But if the devs want the mmH as a cheating option, it can exist additionally to be ignored by nerds and used by those who don't care.

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35 minutes ago, The Doodling Astronaut said:

The good ol' days :P

My summary of my view of MH feasibility would be this:

I don't think humanity right now could find ways to make MH propulsion, but I believe that humans if they want to find how will find how. It's always been that way. Humanity will find a way one way or another.

That's great except the universe does have laws... Dry ice in the desert sun will always sublimate, water in a vacuum will always boil, and it seems metallic Hydrogen upon releasing pressure will always disassociate. Science isn't magic, we can't just will the universe to behave in a new way. If it happens  to be that nothing can go faster then light nothing we do will get us faster than light.

Edited by mcwaffles2003
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47 minutes ago, mcwaffles2003 said:

That's great except the universe does have laws... Dry ice in the desert sun will always sublimate, water in a vacuum will always boil, and it seems metallic Hydrogen upon releasing pressure will always disassociate. Science isn't magic, we can't just will the universe to behave in a new way. If it happens  to be that nothing can go faster then light nothing we do will get us faster than light.

thing is Metallic Hydrogen hasn't been disproven yet. So it's still in the air.

If metallic hydrogen exist in Jupiter's core in large amounts, what's preventing us from doing so?

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1 hour ago, The Doodling Astronaut said:

thing is Metallic Hydrogen hasn't been disproven yet. So it's still in the air.

If metallic hydrogen exist in Jupiter's core in large amounts, what's preventing us from doing so?

....

Again, nobody is disputing metallic hydrogen exists. The dispute is that a metastable state of metallic hydrogen exists. 

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11 hours ago, The Doodling Astronaut said:

If metallic hydrogen exist in Jupiter's core in large amounts, what's preventing us from doing so?

As @Incarnation of Chaos says above, the problem is metastability. We are pretty sure we can and have actually made a small amount of metallic hydrogen, and it appears to display great properties like superconductivity, but as soon as the pressure is released, the material appears to turn back to regular hydrogen. The pressure needed to keep it in its metallic state is so incredibly high that no currently conceivable container could hold it.

There is a small possibility that the studies demonstrating this are wrong, and it is possible that there could be some very advanced future technology that could contain such high pressures, but that might be in the realms of EM drive and warp drive FTL travel. In other words, closer to scifi at this moment in time. 

This is a shame for real life applications, but it is (evidently) highly debatable whether it should affect the use of metallic hydrogen as a rocket propellant in KSP2. Nate apparently got what he wanted - we have all learned about some interesting science :)

Edited by Deddly
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Also(as said before, the debate is just going in circles) if it is not metastable, and you just use a super strong container... It is literally just a compressed gas rocket.

There would be no need to restrict to hydrogen either. You could do a metallic helium rocket too, metallic nitrogen, etc.

But the strength to mass ratios for such a tank to work would also allow suuupppeerrr light tanks for standard hydrolox rockeys, and said hydrolix rockets would then outperform the compressed gad rocket.

It simply makes no sense if it is not metastable, and that is an inherent property if the material, science can't change that, and currently science strongly suggests that it posseses no such property.

It. Won't. Work.

Period

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Only specific unknown quantum effects can save the mmH rocket.
When the mH exists in mmH state as the only statistically possible.

But this condition means that we can manage the quantum effects so effectively, that just have no need in mmH rocket.

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13 hours ago, The Doodling Astronaut said:

thing is Metallic Hydrogen hasn't been disproven yet. So it's still in the air.

If metallic hydrogen exist in Jupiter's core in large amounts, what's preventing us from doing so?

We have made metallic hydrogen, metallic hydrogen exists, but it's metastability has been shown to be missing in the region predicted. If metastability were to exist, it would have existed there. 

Since metastability was not in the predicted region we no longer have a reason to assume hydrogen has metastability. That is the story. You can believe it exists or that we'll find out, but now it is no longer a question of technology but of physical property. Just like no technology will ever make room temperature solid helium or -100 C steam

2 hours ago, kerbiloid said:

Only specific unknown quantum effects can save the mmH rocket.
When the mH exists in mmH state as the only statistically possible.

But this condition means that we can manage the quantum effects so effectively, that just have no need in mmH rocket.

And any system to manage such a feat would eliminate its usefulness as it would either weight a ton or require insane amounts of energy and at that point it wouldn't even be metastable but instead atoms forcefully held in place.. You might as well make an insane pressure vessel and hold the hydrogen at 250 GPa

Edited by mcwaffles2003
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