Discussion of metallic hydrogen propulsion split from another thread.

[KerikBalm]

9 hours ago, Chilkoot said:

OK, thanks.  I had a look and didn't see anything regarding the 2020 findings so far. 

There are no 2020 findings. That is a lay article from January about a research article from 2019, that had been discussed on this forum since it was available on a preprint server since june or july 2019.

9 hours ago, Chilkoot said:

Do you have any more info on why it's inaccurate?

See below

10 hours ago, Chilkoot said:

 recent metallic hydrogen developments.

You mean nearly a year and a half old, already extensively referenced on the forumss

10 hours ago, Chilkoot said:

• The Silvera/Dias results from 2017 are losing acceptance

They never had acceptence.

Misleading and inaccurate

10 hours ago, Chilkoot said:

• Their projections related to the lack of metastability are probably moot

They had no such projections in the 2017 paper. What are you talking about? Misleading and inaccurate

10 hours ago, Chilkoot said:

• A French team appears to have created testable, real, metallic hydrogen that behaves as models predict

The 2019 paper tested for metastability, and found none, as models predicted.

10 hours ago, Chilkoot said:

• The jury is still very much out on whether metastability of the solid/metallic form is possible.

Not really, the scientific literature since the 70's very much falls on the no significant metastability side, with only passing references equivalent to "but it would be great if it was metastable"

[Gargamel]

Overlapping MH threads have been merged.  

[Vanamonde]

Some content has been removed. If others disagree with you that does not mean they are being dishonest, and accusing people of intentional deceit only ends up in angry people yelling at each other unproductively. Please keep discussions polite. 

[DerkyJerkyWreaksHavoc]

Yea people come on!!! be kind and spread the kindness! at the end of the day, you guys arguing ain't gonna make KSP2 come any faster. it just slows us all!

here's a quote from elon musk: “There's a fundamental difference, if you look into the future, between a humanity that is a space-faring civilization, that's out there exploring the stars … compared with one where we are forever confined to Earth until some eventual extinction event.”

[KerikBalm]

15 hours ago, Vanamonde said:

If others disagree with you that does not mean they are being dishonest, and accusing people of intentional deceit only ends up in angry people yelling at each other unproductively.

If this is directed at my remarks of "misleading and innaccurate", I don't think I phrased it as an accusation of deceit.

Its just a factual matter of the statements. It is misleading (whether intentional or otherwise) to state something is losing acceptence if it never had it.

See this https://arxiv.org/abs/1702.04246 , https://arxiv.org/abs/1702.05125 , and https://arxiv.org/abs/1702.07192 all from Feb 2017, right after the Dias and Silvera paper.

A statement of "[Dias and Silvera's] projections related to the lack of metastability are probably moot - not proven wrong, " is  misleading (whether intentional or otherwise) when they made no such projections (see: https://science.sciencemag.org/content/355/6326/715 ), they only mention metastability once in the body of the paper, which is to cite the Brovmen paper from 1972. Its not their projection, and its not a projection of a lack of metastability. The statement made (regardless of intent) was predicated one an absolutely false premise - making the statement misleading and innaccurate. Its an objective assessment.

Following it up with a statement that 2019 observations behave as models predict (in a pro-mmh statement) is misleading if one leaves out that they observed no metstability, and that is what models predict.

Likewise, to say the jury is out when the models don't predict it, an experiment is in agreement with the models, and it was shown experimentally to not be metastable, is highly misleading. You can argue that its not 100% disproven (hard-solopsism can be used to make that argument for anything), maybe they need to test at close to 0 K, or that they need to compress it even more first... or... but the jury is not really "out", its pretty conclusive with models saying no, and experiments agreeing with the models saying no.

[MechBFP]

21 hours ago, KerikBalm said:

its pretty conclusive with models saying no, and experiments agreeing with the models saying no.

Has there been any models or studies done on predicting meta stability with various hydrogen alloys?

[mcwaffles2003]

1 hour ago, MechBFP said:

Has there been any models or studies done on predicting meta stability with various hydrogen alloys?

Note: talking out my rear a lot here so anyone feel free to correct any or all of my statement.

As hard as it is to make hydrogen a metal in the first place, my intuition tells me that making it a metal as an alloy would be even more far fetched. If anything you would be dissociating the hydrogen and prevent the metal from actually forming in the first place (like adding salt to ice). Then if an alloy was somehow made the overlapping orbitals from the other substances would probably reduce the metastability if it ever were to exist as it would then be a system of much higher entropy. Not to mention hydrogen is really small and it's hard for me to imagine a lattice forming in an environment with MUCH larger atoms. Heck, a big problem making metallic hydrogen in the first place is avoiding the hydrogen leaking into the diamond anvils lattice and weakening it as the anvil compresses the hydrogen.

[KerikBalm]

5 hours ago, MechBFP said:

Has there been any models or studies done on predicting meta stability with various hydrogen alloys?

Studies have been done, and already discussed in this thread - back in July. All you had to do was use the search function. See what I mean about this being a pointless discussion. It only keeps going because people keep bringing up the same old points, with nothing new to add.

 

Alloys have been made already, its easier to do than to make pure mH.

Pressure required to form drops, but metastability has not been observed.

Mote importantly, molecular weight of the exhaust goes up, and performance drops.

No point in doing it even if it got you to metastability

Edited October 28, 2020 by KerikBalm

[MechBFP]

5 hours ago, KerikBalm said:

No point in doing it even if it got you to metastability

That‘s disingenuous. If launching nuclear rockets doesn’t become a thing due to public concerns then it is indeed still viable despite not being the most efficient option. 

[mcwaffles2003]

19 minutes ago, MechBFP said:

That‘s disingenuous.

He's not though.

20 minutes ago, MechBFP said:

If launching nuclear rockets doesn’t become a thing due to public concerns then it is indeed still viable despite not being the most efficient option. 

If you had to add heavy metals to the hydrogen your propellant would weigh more causing exhaust velocities to decrease, by a lot. Therefore, the Isp of your propellant would be rivaling chemical rockets making mmH pointless since the Isp is supposed to be the benefit of using one.

[MechBFP]

6 minutes ago, mcwaffles2003 said:

If you had to add heavy metals to the hydrogen your propellant would weigh more causing exhaust velocities to decrease, by a lot. Therefore, the Isp of your propellant would be rivaling chemical rockets making mmH pointless since the Isp is supposed to be the benefit of using one.

Yes, assuming only heavy metals are the only viable candidates.

[OHara]

2 minutes ago, MechBFP said:

Yes, assuming only heavy metals are the only viable candidates.

Well the lightest Lithium is the obvious candidate to alloy with Hydrogen, only 6 times as heavy as Hydrogen.

Intuitively, though, I would think that alloying would make it easier for the metallic monatomic form of hydrogen to re-arrange into H₂. 
The only physical model I've seen for metastability has these columns of equally-spaced H atoms that for reasons I don't understand were not able to shift around to let the H-atoms pair up.  Replacing a few with Li in an alloy would make the spacing uneven already.

What was your motivation in thinking of alloys?   
Speculating on what metallic-hydrogen-like material be made significantly metastable in the real world, or thinking of a good lore for KSP2 that lets us suspend disbelief in the least disturbing way, or something else ?

[KerikBalm]

47 minutes ago, MechBFP said:

Yes, assuming only heavy metals are the only viable candidates.

No, it doesn't assume that at all. I linked to examples for lithium- the third lightest element. If it doesn't work with lithium, it only gets worse as you look for other metals to alloy with.

I've been over this before

mH would have a theoretical maximum Isp of 1700s. Hydrolox can get you a theoretical maximum of  about 500s. So mH would get 1700/500= 3.4x more Isp. If you increase the MW by 3.4^2, and keep the exhaust temperature the same, then it will not outperform chemical rockets. That is an average MW of just 11.5. Now... Lithium has a MW of 6 or 7, you might say that this seems like a LiH2 alloy would work... except it won't. The temperature will be lower.

Lithium is already in the metallic state. Even using the lighter isotope of lithium: Metallic LiH₂ would be 3/4 lithium by mass. To a first estimate, your alloy is only going to store a bit more than 1/4th the energy per unit mass compared to mH. 1/4th the energy results in 1/2 the Isp... then you add in an exhaust with an average MW of... what, 3? You get 0.5 /sqrt(3) = about 0.29x the initial Isp. Which gives you 490s.. worse than chemical.

Ok, what about LiH₄? Sure, that will do better... but you remember how LiH_x isn't metastable anyway, and going to higher values of x is only going to make it worse? Yea, you've got to move on.... and go heavier... and oops, its already not working with the lightest metal, its only going to get worse as you get higher. But sure... you can just have more hydrogens per atom of heavier element... but then you start to require a loooottttt of hydrogens, making you wonder how you expect a single atom of the other stuff to stabilize all that...

[mcwaffles2003]

9 minutes ago, KerikBalm said:

Lithium is already in the metallic state. Even using the lighter isotope of lithium: Metallic LiH₂ would be 3/4 lithium by mass. To a first estimate, your alloy is only going to store a bit more than 1/4th the energy per unit mass compared to mH. 1/4th the energy results in 1/2 the Isp... then you add in an exhaust with an average MW of... what, 3? You get 0.5 /sqrt(3) = about 0.29x the initial Isp. Which gives you 490s.. worse than chemical.

And this doesn't even include the energy lost from the lithium taking the place of metallic hydrogen bonds thus lowering the total stored energy available per mole of propellant

[KerikBalm]

So I looked more into it, They've also made superconducting (metallic) LiPH_3/4/6/7 ,  and H₂S. Those are some high MWs. Its really not getting any better as you look to heavier elements than lithium.

https://www.nature.com/articles/s41524-019-0244-6 (don't go gaga over the mention of metastable: not it says "at high pressure", and in the context, its speaking of rearrangements from LiPH₃ toLiPH₄ or stuff like that).

https://www.nature.com/articles/nature14964 metallic superconducting H₂S at high pressure.

They are looking into metallic combinations of Hydrogen with other elements, not as metastable rocket fuel, but as superconductors. Not a single one remains metallic when pressure is released. I can't find any predictions that they will.

[SOXBLOX]

13 hours ago, KerikBalm said:

See what I mean about this being a pointless discussion.

You aren't being forced to post here, right? If you are, we can help.

6 hours ago, OHara said:

...good lore for KSP2 that lets us suspend disbelief in the least disturbing way...

Its called "Suspension of Disbelief", and is a necessary component for all fiction.

And even if KSP was perfectly, exactly scientifically accurate (it isn't and can't be) then it would still be fiction. Why? The rockets you are "building" don't exist. They're fiction.

As for lore, just say that the Kerbal universe is just slightly different from our own, and mmH works there.

[MechBFP]

On 10/28/2020 at 8:50 AM, KerikBalm said:

But sure... you can just have more hydrogens per atom of heavier element... but then you start to require a loooottttt of hydrogens, making you wonder how you expect a single atom of the other stuff to stabilize all that...

That’s the part I am curious about. It certainly doesn’t sound plausible as I think the number of chemical bonds possible is going to be extremely small relative to the other elements weight and without the chemical bonds it’s obviously not going to be stable by just adding more unbonded hydrogen to the mix. 

Edited October 29, 2020 by MechBFP

[mcwaffles2003]

10 hours ago, SOXBLOX said:

Its called "Suspension of Disbelief", and is a necessary component for all fiction.

And even if KSP was perfectly, exactly scientifically accurate (it isn't and can't be) then it would still be fiction. Why? The rockets you are "building" don't exist. They're fiction.

This is a fair point, I just hope there are many variations of nuclear engines as well and mmH isn't taking place of a more fascinating alternative since "kerbals dont suffer from radiation" is an equally plausible basis. I am just hoping the game takes on a more involved approach as you progress in a similar method to KSPIE (the system of designing the power train with different reactors/fuels/nozzles/energy supplies/propellant's) and adding mmH doesn't just give workarounds to keep things simple in this regard.

[SOXBLOX]

5 hours ago, mcwaffles2003 said:

I just hope there are many variations of nuclear engines

Me too, to be sure! They can fill the same performance regime, but I bet they'll be bulkier, and, of course, they'll need shielding. I think...

Maybe mmH will be the fuel of choice for surface-to-orbit, and nuclear will be better for orbit-to-orbit? And is mmH going to be transferable through regular docking ports, or even at all? If it weren't, it would nerf it significantly. Maybe @Nate Simpson can say?

[DerkyJerkyWreaksHavoc]

Just now, SOXBLOX said:

Me too, to be sure! They can fill the same performance regime, but I bet they'll be bulkier, and, of course, they'll need shielding. I think...

Maybe mmH will be the fuel of choice for surface-to-orbit, and nuclear will be better for orbit-to-orbit? And is mmH going to be transferable through regular docking ports, or even at all? If it weren't, it would nerf it significantly. Maybe @Nate Simpson can say?

I wonder what will be the first thing people will do in KSP2? I have an idea... i'll make a discussion thread out of it!

 

[Nate Simpson]

On 10/29/2020 at 8:28 AM, SOXBLOX said:

 

Maybe mmH will be the fuel of choice for surface-to-orbit, and nuclear will be better for orbit-to-orbit? And is mmH going to be transferable through regular docking ports, or even at all?  @Nate Simpson

On your first point, that is correct. Especially given that you'll encounter some very deep gravity wells  in other star systems. On your second point: yep, transferable through regular docking ports. 

[Guest]

53 minutes ago, Nate Simpson said:

On your first point, that is correct. Especially given that you'll encounter some very deep gravity wells  in other star systems. On your second point: yep, transferable through regular docking ports. 

So then we will need to rely on the Metallic Hydrogen to get off pretty big vacuum planets/moons? Is there alternative propulsions to getting from surface to orbit? Maybe regular propulsion (or to those speculation peeps out there Antimatter.)

[Incarnation of Chaos]

1 hour ago, The Doodling Astronaut said:

So then we will need to rely on the Metallic Hydrogen to get off pretty big vacuum planets/moons? Is there alternative propulsions to getting from surface to orbit? Maybe regular propulsion (or to those speculation peeps out there Antimatter.)

Lower mass or push the TWR into insane ranges, might also be able to use something like Orion and have it land well downrange of a colony and use rovers/other rockets to shuttle crew to the main colony.

KSP2 is going to have clustering plates by default, so brute-force will always be an option when all else fails.

[KerikBalm]

4 hours ago, Nate Simpson said:

On your first point, that is correct. Especially given that you'll encounter some very deep gravity wells  in other star systems. On your second point: yep, transferable through regular docking ports. 

Dissappointing that you continue not to address the science behind mmH and admit that you made factually incorrect statements.

Also dissappointing that there are no mentions of competing propulsion like Lantr or air augmented rockets. After all, a deep gravity well means it should have an atmosphere (tylo being quite unrealistic).

A water cooled mmH rocket would be outcompeted by a chemical air augmented rockets

[Incarnation of Chaos]

55 minutes ago, KerikBalm said:

Dissappointing that you continue not to address the science behind mmH and admit that you made factually incorrect statements.

Also dissappointing that there are no mentions of competing propulsion like Lantr or air augmented rockets. After all, a deep gravity well means it should have an atmosphere (tylo being quite unrealistic).

A water cooled mmH rocket would be outcompeted by a chemical air augmented rockets

Unless it got blown off, think the cores remaining from hot jupiters or super-earths around red dwarfs that couldn't generate enough of a magnetic field to hang on to it during their flaring. It's not absolutely impossible to have a planet without atmosphere, and high gravity. Unlike metastable metallic hydrogen

But yeah, air augmented rockets are the birds. I had a couple of janky heavy lifters that used "Flashfire" or something similar as their booster segments (They were MK3 parts in style, from a mod ofc), and the sheer amount of payload they could haul for the fuel efficiencies they had was basically unbeatable until i got to either far heavier payloads (>Kt) or nuclear Aerospikes.