Metastable He-IV-A

[palioxis1248]

So I chanced upon this idea while trawling on the web, where one of helium's two electrons is boosted into its second electron shell and given the same spin as the electron in the inner shell, leaving the helium atom in a high-energy metastable state. Bonding this metastable atom with another ordinary helium atom (don't ask me how) would in theory form a stable, combustible solid. Last I checked, it could be used as a rocket fuel with Isp of 21kps!

Being the irrelevant-detail-hunter that I am, I did a rather pointless calculation to find out what colour the helium exhaust would be. Basically I assumed exhaust velocity = rms speed of hot helium exhaust, then calculated the temperature using the ideal gas rms speed formula. I then plugged the temperature (~70000K!) into Wien's displacement law. I got a blackbody radiation wavelength of about 40nm, in the extreme ultraviolet range.

Can someone help me verify this figure? Also, if any EUV/Soft X-ray expert happens to see this, what is the TVT of air against EUV and what are the effects of EUV?

[bsalis]

All news to me and mostly beyond my chem knowledge.

How exactly does this He2 combust?

In any case I doubt it's the kind of thing that could be manufactured in bulk. Heck, even regular Helium seems to be in short supply.

[sgt_flyer]

i checked on another site, which explained a bit more : http://orbitalvector.com/Deep%20Space%20Propulsion/Metastable/Metastable%20Fuels.htm

from what he says, HE-IV-A is a solid, which can release it's stored energy simply through heating it - resulting in an theoritical ISP of 2200.

[Rakaydos]

i checked on another site, which explained a bit more : http://orbitalvector.com/Deep%20Space%20Propulsion/Metastable/Metastable%20Fuels.htm

from what he says, HE-IV-A is a solid, which can release it's stored energy simply through heating it - resulting in an theoritical ISP of 2200.

"But the problem with metastable helium is not with obtaining it, but storing it. The 2.3 hour limitation only applies to a completely isolated atom; metastable helium packed in with anything else, even other metastable helium atoms, will result in jostling and it losing its metastable state in a fraction of a second."

Ouch.

[sgt_flyer]

yes, that why they try to bond it with regular helium - which forms the HE-IV-A metastable, which should be much easier to store

[Streetwind]

Rakaydos: yes, which is exactly why there's talk about bonding it into the IV-A form which would be stable and storable unless heated.

I've been looking for more information on He IV-A, specifically reliable and trustworthy information with a real science background... but I've only really found a single unassuming research paper locked behind a paywall (without an academic login anyway). This seems to be a topic that's either being dealt with hush-hush (because JPL believes they can make it work soon and subsequently monopolize a major advantage in propulsion), or one that's so far ahead of contemporary technology that anything more than speculation is a waste of time.

A part of me wishes that it's the former, although realistically I'm forced to believe the latter

Mind you, though - as exciting as these numbers sound, if the info we currently have is to be believed, then that would mean that this fuel would be for solid rocket motors only. In other words, at best you could have a prefabricated burn sequence via grain sizing; but you'll never have liquid fuel engine advantages such as throttle control, shutdown and restarting or built-in alternators for power generation.

Edited February 5, 2014 by Streetwind

[Winter Man]

..how are they planning on bonding it? Helium's noble, so boosting the electrons to a higher state in one atom wouldn't somehow allow the other to bond, would it? I mean, unless your metastable helium is more electronegative than fluorine, then you've got a compound that will decompose more readily than the xenon fluorides. Horrible to store, no doubt.

[Ralathon]

..how are they planning on bonding it? Helium's noble, so boosting the electrons to a higher state in one atom wouldn't somehow allow the other to bond, would it? I mean, unless your metastable helium is more electronegative than fluorine, then you've got a compound that will decompose more readily than the xenon fluorides. Horrible to store, no doubt.

In simple terms, bonding occurs because atoms try to fill their electron shells. Normally helium (or any of the noble gasses) are very hard to bond because their lowest shell is completely filled. If you boost 1 electron to a higher shell you suddenly have 2 incomplete shells instead of 1 filled. So suddenly it'll bond just fine. I expect it to behave a lot like Lithium, since both have just one electron in the outermost shell.

main problem I see with this fuel is that it is essentially an SRB that ignites when you heat it, shake it, or look at it from a bad angle. Not to mention that it probably decays rather quickly, even if you manage to bond it. This limits its usability quite a bit.

[K^2]

main problem I see with this fuel is that it is essentially an SRB that ignites when you heat it, shake it, or look at it from a bad angle. Not to mention that it probably decays rather quickly, even if you manage to bond it. This limits its usability quite a bit.

There is a type of SRB which can operate with what's essentially a slow detonation wave. A fuel this unstable and this energetic would be ideal for this SRB type. Of course, this requires a polymer matrix, which will absorb a large chunk of this very impressive I_SP.

But yeah, the problem is making it stable enough to simply be storable for any duration. A strong magnetic field can help you keep the electron spins polarized. But at cryogenic, LN2 temperatures, you'd still need something like 10T for the field to have any sort of an effect. For reference, the strongest magnet I've seen is 11T, weighs over a ton, requires liquid helium cooling, and has a bore of only about an inch in diameter.

[Winter Man]

In simple terms, bonding occurs because atoms try to fill their electron shells. Normally helium (or any of the noble gasses) are very hard to bond because their lowest shell is completely filled. If you boost 1 electron to a higher shell you suddenly have 2 incomplete shells instead of 1 filled. So suddenly it'll bond just fine. I expect it to behave a lot like Lithium, since both have just one electron in the outermost shell.

I think you're missing the point a little, he said they were trying to bond metastable with regular helium. I understand how bonds work (I have a very good knowledge of organic chemistry but not so much on the metallic side). My point was, the metastable component would have to be more electronegative than fluorine to actually get the standard helium atom to bond with it to the point of absurdity.

[Ralathon]

I think you're missing the point a little, he said they were trying to bond metastable with regular helium. I understand how bonds work (I have a very good knowledge of organic chemistry but not so much on the metallic side). My point was, the metastable component would have to be more electronegative than fluorine to actually get the standard helium atom to bond with it to the point of absurdity.

Oh, that is due to slightly more complicated reasons involving quantum effects. Basically, when you cool helium to some ridiculously cold temperature the atoms start to bond due to Van Der Whaals forces. I assume the OP refers to this bond.

Wild guess: When the 2 He atoms bond the electrons on the metastable atom are pushed away from the stable atom (Since the stable atom has both spin states locked, so Heisenberg pushes the probability function to 0 near the other atom).

This means that the probability densities of the 2 electrons on the metastable atom get comparatively closer and higher density, causing the potential barrier for decay to rise.

[Winter Man]

I would forget Van der Waals, wouldn't I. Yeah I see where they're coming from now, for some reason I was imagining a room temperature solid. Assumptions'll be the death of me.

[K^2]

Yeah, it's something that didn't occur to me right away either, but you can't have covalent bonds with this metastable Helium state. Long story short, any covalent bond would require an electron from another atom having opposite spin to get close enough to this excited He for it to be pulled right into the s1. Pretty much the same consideration would forbid any ionic bonds. Not that we would seriously consider these anyways. So Van der Waals with something really, really inert is your best bet. And something like an fcc lattice with regular He does appear like the only option.

[lajoswinkler]

Judging by the all things so far, this would be a soft slushy solid explosive presumably stable close to 0 K. The moment you heat one part of it, you initiate a propagating wave of decomposition. Yes, I do feel this would end up in a detonation. Very Kerbal.

[K^2]

Like I said, that's not necessarily bad. You can turn a detonation wave into a rocket. You just have to have a matrix that brings down the heat transfer and detonation wave speed. In principle, a det wave is a perfect way to accelerate yourself. The problem is that a conventional detonation wave reaches you with all of the momentum at once, which your structure usually can't take. If you find a way to mitigate that, then detonation gets rid of a ton of problems with conventional SRB. You don't need a nozzle or a bell. You aren't risking detonation due to a crack or other problem because, well, it's already detonating, and the shell doesn't have to hold the pressure, so it can be way lighter.

Of course, all of this in early experimental phase. But mostly, because the losses you get from the matrix often make it easier to just have a conventional SRB. Here, you have lots of excess energy, so you keep I_SP high, and it'd be entirely worth the research effort to bring it all up to operational quality.

[lajoswinkler]

I don't think any matrix would help. I doubt that this solid would exist in a much wider temperature span than let's say hydrogen, and down at those temperatures, even a small amount of heat means a lot. Even if the whole thing is possible (I doubt it), it would likely end up in an uncontrollable bang.

[fireflower]

Like I said, that's not necessarily bad. You can turn a detonation wave into a rocket. You just have to have a matrix that brings down the heat transfer and detonation wave speed. In principle, a det wave is a perfect way to accelerate yourself. The problem is that a conventional detonation wave reaches you with all of the momentum at once, which your structure usually can't take. If you find a way to mitigate that, then detonation gets rid of a ton of problems with conventional SRB. You don't need a nozzle or a bell. You aren't risking detonation due to a crack or other problem because, well, it's already detonating, and the shell doesn't have to hold the pressure, so it can be way lighter.

It makes a liquid-core nuclear-thermal rocket SSTO sound perfectly safe in comparison. Being it has almost the exact same ISP and doesn't immediately explode above 0 K I'm going with the rocket that is literally a flying nuclear reactor in perpetual meltdown.

[K^2]

It makes a liquid-core nuclear-thermal rocket SSTO sound perfectly safe in comparison. Being it has almost the exact same ISP and doesn't immediately explode above 0 K I'm going with the rocket that is literally a flying nuclear reactor in perpetual meltdown.

In terms of safety, yeah, I think I'd go with liquid-core NTR as well. But assuming we can make both, NTR is an absolute disaster if it explodes, while He-A is just an ordinary chemical explosion. So I doubt liquid-core NTR would ever be approved unless we can make it way, way safer. He-A could still be useful for cargo even if it's high risk. At that ISP, it only needs to be better than a coin flip to be competitive.

By the way, fact that this has to be kept at just a few K, rather than LN2 temperatures as I was thinking initially, means that we can probably drop the stabilizing mag-field to just a couple of Tesla. Now that you can do with permanent magnets. They'd still be pretty heavy, but you can get a large enough bore to offset this with extra thrust.

I still can't see it being practical, seeing how expensive He has become, and how much extra expense all of this is going to be, but it might just be plausible.

[Streetwind]

By the way, fact that this has to be kept at just a few K, rather than LN2 temperatures as I was thinking initially, (...)

I would be careful with what you declare as a fact. When lajoswinkler said "around 0 K", that was purely a guesstimate on his part. Unless someone wants to put money down to unlock that research paper I mentioned or find a copy of this old booklet, we have zero information as to the properties of this solid (and even if, there's no guarantee that the paper mentions what we want to know, as it focuses on a fairly narrow topic).

This is how misinformation about a scientific topic spreads. Wild speculation should always be designated clearly as wild speculation, and any mention of the word "fact" avoided. Even as a figure of speech.

Edited February 6, 2014 by Streetwind

[lajoswinkler]

Well it's not a wild speculation if you consider other similar chemical species. We have absolutely no reason to believe this would be better than those poor noble gas compounds which are studied highly dilluted in a cryogenic matrix because they simply can't exist in other conditions.

The only wild speculation I see here is proposing an engine that uses this material in bulk quantities.

[fireflower]

In terms of safety, yeah, I think I'd go with liquid-core NTR as well. But assuming we can make both, NTR is an absolute disaster if it explodes, while He-A is just an ordinary chemical explosion. So I doubt liquid-core NTR would ever be approved unless we can make it way, way safer.

Nothing the wise and benevolent governments of the world haven't already done to various deserted regions for nuclear testing. Seriously though, that's the big question; the right answer immediately opens up the solar system. I'm looking into borrowing the designs of nuclear reactors for submarines. They're designed to shut down without leaking even in the event of catastrophic loss of the ship. I figure if you hit it with a torpedo and it doesn't leak that may just work for spacecraft safety. Though there is another question besides safety, and that is mass. Any NTR is already very heavy. Anyway, it's what's on my mind, I don't mean to take the thread on a tangent.

[palioxis1248]

Yeah, it's something that didn't occur to me right away either, but you can't have covalent bonds with this metastable Helium state. Long story short, any covalent bond would require an electron from another atom having opposite spin to get close enough to this excited He for it to be pulled right into the s1. Pretty much the same consideration would forbid any ionic bonds. Not that we would seriously consider these anyways. So Van der Waals with something really, really inert is your best bet. And something like an fcc lattice with regular He does appear like the only option.

That's strange, because from what I read He*-He would be solid at room temperatures. Hmm...... Also, as an aside, anyone willing to comment on the part about EUV?

[LLlAMnYP]

I may have missed something, but the paper in question discusses a crystal with spin-polarised He*-He* bonds, not He*-He. Something akin to metallic hydrogen.

[K^2]

I may have missed something, but the paper in question discusses a crystal with spin-polarised He*-He* bonds, not He*-He. Something akin to metallic hydrogen.

No. Nope. Better comparison would probably be Lithium, but still, no way. Look, the only way this He* atom is possible is because you have one electron removed from its ground state and placed into excited state that it can't easily drop down from. This is no longer the case in a metallic state. A valence electron in a metal does not belong to an atom. It belongs to the lattice. It no longer counts for the orbital shell. It is one of the electrons that fills the conduction band instead. And there, you also have energy levels. And you also have two electrons per energy level. And with all electrons having the same spin, every other level ends up vacant. So now imagine all the electrons in the lattice, half as many lower energy level to drop down to, and all the possible interactions. Not only is this going to take way more energy than just exciting all of the He atoms, but it's something that's going to collapse instantly.

Whatever else may be going on, He* metal is not an option.

That's strange, because from what I read He*-He would be solid at room temperatures. Hmm......

That, I'm not as certain about. Could be. But in either case, it's much easier to maintain the He* at lower temperatures, so even if it has a high melting point, we should be considering cryo options only.

Can someone help me verify this figure? Also, if any EUV/Soft X-ray expert happens to see this, what is the TVT of air against EUV and what are the effects of EUV?

Hard UV to soft X-Ray is absorbed by air extremely well. And at that energy, you can start looking at light as particles. So you are looking at mean free path as the typical absorption scale. And the effect will be ionization, which will result in Ozone production. Does that answer it?

[palioxis1248]

Hrm. So if I lit a hypothetical He* booster on the ground, I get a plume of ozone and superhot helium plasma? What's the lethal radius around the plume?