Using metalic hydrogen and red oxygen as propellants

[Spanier]

Assuming one could handle problems resulting of extreme pressures with moderate effort in structural improvements of storage options, what would presumably happen, when I fuel a spaceship with metallic hydrogen and red oxygen?

It would give us a whole new level of engine design with extreme thrust.

For all who didn't heared about these two guys:

Metallic hydrogen: Hydrogen with metallic properties

Red oxygen: An allotrope of solid oxygen (O₈)

[SargeRho]

No need for oxygen. Just let the hydrogen leak out. The pressure is enough to produce some serious thrust. Or use it in fusion engines.

[Diche Bach]

I had heard of metallic hydrogen. Sounds like it will eventually make exploration and mining of Jupiter quite lucrative. Sadly, I doubt that will occur in any of our lifetimes.

[K^2]

If metallic hydrogen requires a pressurized vessel to keep it in solid form, it's not worth the trouble. The mass of the container will offset all of the benefits of more compact storage.

On the other hand, some solid state theorists have suggested that metallic hydrogen might be metastable. Think diamond. It takes enormous pressure to convert graphite into diamond, but once you release the pressure, the diamond doesn't phase transition back to graphite unless you do something rather drastic to it. That's metastability of the phase. Well, if there is such a thing as metastable metallic hydrogen, frequently abbreviated as MSMH, then it would be the holly grail of chemical fuels. To put it into a perspective, with MSMH for fuel, you can build a personal shuttle the size of a minivan capable of reaching orbit.

The problem, of course, is making the stuff. Even if we figure out how to make enough of it, it might not be worth the investment. If, on the other hand, it naturally exists in asteroids or comets that resulted from fracturing of much larger bodies, we might be able to mine for it. This is wild speculation territory, however, as we still haven't been able to conduct any experiments to actually establish properties of metallic hydrogen.

[Diche Bach]

Is there a reason to suspect that it would NOT be metastable?

So I'm gathering that the prospect of extracting it from Jupiter is actually not very feasible based on your comments K^2, and yeah, now that I think of it: way far away, and under enormous amounts of gas. Would seem to be pretty hard to even get "close" to the surface of Jupiter's atmosphere without getting sucked into for goners, and you'd need a really long borehole to mine it from orbit, eh? Kind of a big job given where we stand right now, heh heh!

[K^2]

My understanding of condensed matter physics is nowhere near sufficient to really understand any of the details, but from what I gathered the metastability is an open debate. There is no classical reason for it to be metastable, but it's not going to be a classical system. It's all going to be hardcore quantum field theory, and we are still rather limited in how much we can do with that. Very few problems in QFT can be solved exactly and numerical solutions are very hardware-limited. So even though we know all the basic rules that individual particles are going to follow, predicting behavior of materials can be difficult, and metallic hydrogen is probably as difficult as they come. There are some models that suggest metastability. But there is no certainty on whether these models are trustworthy for the particular problem. Unfortunately, this is probably something that will have to be resolved experimentally. Fortunately, there is a lot of progress on that front.

As for mining it from Jupiter, yes, I don't think that's an option. But there is no reason why some planet that was large enough to have some metallic hydrogen at its core couldn't have been ripped apart by Jupiter some long time ago. If that state is metastable, there could still be some MSMH in the asteroid belt. If we confirm that the material can exist, we probably should look for it there. Even if we can't get enough to use it efficiently for fuel, there are many other potential uses.

[Spanier]

The idea mining metallic hydrogen from Jupiter is hilarious, you can't reach the interior of Jupiter anyways, or did someone of you recreate the submarine from "The Core", you can barely reach the "surface" of the planet itself due to ludicrous radiation levels. The only thing you could mine from a gas giant is He₃ from Saturn, but nothing else.

[Tommygun]

If it exists, would they be harder than diamonds and heavier than lead?

I can't image how hard it would be to mine and processes highly flammable diamonds into something useful.

[Fuzzy Dunlop]

Is there a reason to suspect that it would NOT be metastable?

Well K^2 gave the example of Diamond to Graphite, and while it's true that Graphite is more stable (under normal conditions) than Diamond, it's not by that much. Then energy released when Diamond is converted into Graphite is relatively tiny.

Converting from Metallic Hydrogen to regular would liberate a massive amount of energy, so it's slightly harder to see how it would remain stable. (Though there are lots of stable compounds that do give out a huge amount of energy when they decompose - eg TNT)

[Diche Bach]

The idea mining metallic hydrogen from Jupiter is hilarious, you can't reach the interior of Jupiter anyways, or did someone of you recreate the submarine from "The Core", you can barely reach the "surface" of the planet itself due to ludicrous radiation levels. The only thing you could mine from a gas giant is He₃ from Saturn, but nothing else.

Bummer. All this space stuff is so complicated: radiation, gravity, no air . . . sheesh

[InfinityArch]

If it exists, would they be harder than diamonds and heavier than lead?

I can't image how hard it would be to mine and processes highly flammable diamonds into something useful.

I'm not sure about the first one, but I doubt it. As for the second one, I suppose you must mean denser, and that is a resounding no. It's about twelve times denser than liquid hydrogen if my google-fu is correct, which makes it slightly less dense than water, so no, it's not denser than lead, though it is comparable in density to kerosene.

If you were to say use metastable metallic deuterium for a D-He3 fusion rocket, it also appears helium would become the "bottleneck".

Edited August 9, 2013 by InfinityArch

[Vaebn]

I didnt know about the possibility of metastable metallic hydrogen, cool!

Keep in mind that just because you make the fuel more dense doesnt mean you reduce its weight. 200tns of hydrogen will always weight 200tns no matter how much you compress it.

Also unlike what the kerbal-industrial complex would have you believe, the weight of the tank in modern rockets is often not -that- big a problem (something like 1% or so). Fuel weight as well as engines that dont explode when they try to utilize more of it are equally to more important.

[K^2]

Though there are lots of stable compounds that do give out a huge amount of energy when they decompose - eg TNT

It's not exactly the same, since TNT releases energy in chemical reaction, and here we are talking about a phase change which is a bulk property. But the general idea is similar, yes. It can release a lot of energy, but it needs activation energy first. In case of TNT that activation energy is supplied by a primer. In case of diamond you can use heat, for example. If MSMH phase exists, I would also expect it to be metastable only in certain temperature ranges. But even if it's going to be a cryo fuel, it'd be completely worth it.

Keep in mind that just because you make the fuel more dense doesnt mean you reduce its weight. 200tns of hydrogen will always weight 200tns no matter how much you compress it.

The main advantage is that the metastable phase holds a lot of additional energy. This translates to a much higher I_SP of an MSMH rocket compared to conventional LH2 rocket. Considering the fact that LH2/LOX rocket is already one of the best things we can do, having nearly twice the I_SP of that would be huge.

If you want to think of it in terms of KSP, imagine having a rocket with I_SP of LV-N and TWR of LV-T30 or better.

Edited August 9, 2013 by K^2

[Diche Bach]

So its going to form only where there is hydrogen under enormous pressure (aka Jupiter type places = really big gravity wells); it is likely to only stay in metallic form within a relatively narrow temperature range (I'm guessing colder not hotter); and it is not actually very massive per unit volume. Sounds to me like, even if it does exists, humans are not likely to ever get their hands on very much of it. Correct me if I'm wrong here, but . . . Seems like the only way any of this stuff is likely to ever get liberated from its environment of formation is in major cataclysms: supernova, galaxies crashing through one another, planets colliding (I just don't see a comet or asteroid, even a typical planet colliding with a Jupiter sort of body having much chance of splashing anything out of the big bodies gravity, eh?). The big events that might have 'seeded' some of the cosmos with this stuff long ago so that it could be dispersed to places like our solar system would seem to have involved lots of heat, which would tend to phase it back to non-metallic state (liquid if not even gas right?). And then you have the low density thing. Any amount of this stuff that ever did get blown free from its mother gas giant would tend to segregate pretty high in the centrifugal column (is that a concept or did I just make that up?), thus continuing to expose it to dispersion and 'boil-off?'

Seems like there is just about as much reason to assume it is never going to be acquirable as there is to hope that it might be and fantasize about what we could do with it.

[K^2]

Pretty much. This isn't something we should be counting on, but we might get lucky. And as I said, even small quantities can be useful. Not as fuel, but for some other applications.

By the way, I completely forgot to address the implied question in OP. Can we get hydrogen to reasonable densities without high pressures? In fact, yes, we can. Lithium Hydride (LiH) is an ionic solid with density 0.78g/cm³ at room temperature and normal pressure. It actually releases more energy per mole when burned with oxygen than pure hydrogen does. That compensates for lithium being slightly heavier than hydrogen. As a result, the maximum theoretical I_SP of such fuel is almost identical to that of cryogenic hydrogen.

Similar solution exists for oxygen. All things considered, the best choice is probably Dinitrogen Tetroxide (N₂O₄). It is a fluid at room temperatures, and so it is ideal for use as oxidizer in a hybrid. It is rather dense, 1.44g/cm³, and it actually adds a bit of extra energy to reaction compared to oxygen, which nearly compensates for the dead weight of nitrogen. The only downsides are low boiling point, only 21°, meaning it will boil on a hot day if not insulated or pressurized, and that it's rather toxic. Still, you can get almost the performance of LOX without having to deal with a cryogenic oxidizer, and that's often worth the extra hassles.

Of course, as somebody mentioned earlier, for a large rocket, these things aren't really a big deal. Large tanks aren't a problem if they are not significantly pressurized, and insulation is easy with large volumes. So for larger rockets it's a lot easier to simply have cryogenic hydrogen and oxygen as fuel and oxidizer. They are cheap, they are environmentally friendly, and they don't require any special containment beyond keeping them nice and chill. But for smaller rockets, especially ones that need to be stored fueled up, these are serious problems. Standard solution is to fuel the rocket with Hydrazine (N₂H₄) and Dinitrogen Tetroxide. This is what you'll find in many ICMBs and some larger AA missiles. But as I mentioned above, a Lithium Hydride hybrid is another option. As far as I know only amateur rockets with such fuel have been built, but given that broad interest in hybrids is relatively recent, I don't think that it's due to any limitations of the fuel.

[Nuke]

its totally unrelated but that kinda reminds me of this:

http://hackaday.com/2012/09/26/hybrid-rocket-engine-uses-acrylic-as-fuel/

[K^2]

Acrylics make for pretty good hybrid fuels, but the specific impulse for it is about the same as other polymer fuels, and that's a somewhat lower than I_SP of cryogenic LH2/LOX rockets.

[Nuke]

one of the videos claimed an isp of 140s and about 1.7 lbs thrust. but what they lack in power/efficiency they make up for in awesomeness. its also a good way to demonstrate how this kind of engine works. its unlikely you will have a transparent combustion chamber in a typical lox+lh2 rocket engine.

[Diche Bach]

One more question I had about the metallic hydrogen. Based on reading about Galileo and his Jupiter probe, it seems pretty clear that inside of Jupiter is quite hot. Indeed, it seems that the probe died at about 97 km because of extreme heat, and that wasn't even quite through the atmosphere.

As such, the deeper one goes into Jupiter you are going to get enormous pressure and enormous heat. Given what was said above about it staying metastable only under relatively low heat, does this mean that there is a pretty good chance the stuff doesn't actually exist at all?

[andrewas]

Metallic hydrogen is purely hypothetical, nobodies been able to produce it in the lab. There have been groups that claimed to produce it, but nothing repeatable so far. Theres a very good chance that it can't exist at all. But if it does, gas giants are probably capable of producing it, all it takes is hydrogen under enough pressure.

Temperature comes into it in terms of metastability. At 450 GPa, according to the theory, its stable. But useless, because containing that kind of pressure is very difficult, use it in a rocket and the weight of the tanks means you probably won't get off the ground. At standard pressure, its more complicated. Classical physics say its unstable and will sublimate as the pressure drops. Quantum physics, we can't solve well enough to make a real prediction but theres a chance it may be metastable at standard pressure. That means that it'll sit there, as a solid (or maybe liquid), despite being way below the pressure needed to form it, but when its disturbed enough, it'll convert back to gaseous hydrogen. It all depends on how stable it is in this form. If its just a case of keeping it below, say, 10C, then it'll be the thing that finally gets us into space in a big way, just as soon as we find a way to mass produce it. On the other hand, it might be one of those substances that blow up if you just look at it harshly, in which case its just a very expensive lab curiosity with no real uses.