Nuclear propulsion efficiency without the "nuclear" part...

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luke strawwalker

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Been doing some more research on various historical rocket prototypes and came across this and thought it was very interesting...

https://iopscience.iop.org/1742-6596/215/1/012194/pdf/1742-6596_215_1_012194.pdf

Basically it's an outline of how useful metallic hydrogen could be if we can learn to produce it industrially. Of course that's a long way off, since they're having a lot of problems even making it in the laboratory, but with the march of progress, who knows...

Basically it would allow for the construction of a moon rocket capable of delivering a 30 tonne payload (roughly the size of the Apollo moon mission) onto the lunar surface using a rocket the size of a straight up Delta IV...

It would make an SSTO shuttle possible basically the size of the existing orbiters, without the need for the ET or SRB's.

The Specific Impulse of regular molecular hydrogen burned with oxygen is about 460 seconds. Using metallic hydrogen (which is ten times denser than molecular hydrogen, meaning it's storable in MUCH smaller tanks, say 1/10 the size of an equivalent amount of molecular hydrogen) the ISP is about 1600. The reaction is basically predicated on the phase change from the metallic form of hydrogen to the molecular phase, which would release 10 times the energy of the molecular phase burning with oxygen. The temperature of the reaction is the bad part-- 6,000 K. Nothing can withstand that kind of heat, so the reaction needs a diluent injected into the chamber, either regular water (which would drop the ISP to around 460-600 seconds) or regular cryogenic molecular hydrogen (which would give a theoretical ISP of about 1200.)

I was also reading an article about using megapressures and extremely high temperatures to form "nitrogen diamonds" by getting nitrogen molecules to line up with single valent bonds into a cubic lattice structure identical to how carbon items link up into a cubic lattice structure in diamond, rather than in the flat crystalline structures of common carbon). This material would have an energy density 70 times that of the most powerful chemical explosives known, since nitrogen is naturally a molecular gas consisting of two atoms of nitrogen in a triple covalent bond...

Interesting stuff... :)
Later! OL JR :)
 
How would you use the metallic hydrogen, though? Inject oxygen into a port in a solid grain like a hybrid?

The mention of nitrogen diamonds reminded me of a hilarious post in the otherwise rather unfortunate "k875" thread about the titular motor producing not Mach diamonds, but real diamonds.
 
I (and I'm certain that others as well) would worry that anything with an ISP of 1600 would have a serious potential for... well... going BOOM in rather large and spectacular way... (as well as being very useful when it didn't).
 
Ah Yes. Metastable metallic hydrogen. Here one microsecond. Gone the next!

It would have to be one of the most expensive materials ever made. According to the paper, hydrogen has been pressurized to 400 GPa (29 kilotons per square inch) and it hasn't formed. You can not generate that pressure over a large volume, so I would assume if you could make it, you could make far less than 1 gram at a time. Then what do you do with it. You can't melt it without it going boom.

Sounds like a pipe dream enhanced by some moonshine.

Bob
 
Interesting article! The article states that metallic hydrogen may be a metastable solid, but no one knows for sure, because the stuff has never been produced in laboratory quantities. Thus, small quantities might exist under huge pressure, but as soon as the pressure is released the stuff expands out to molecular hydrogen. I think that I've heard that the center of Jupiter might be metallic hydrogen, but in that case it is constantly confined. There is always the point that you don't get something for nothing. To produce the metallic hydrogen would take a huge quantity of energy. An industrial power plant would need to be built to supply the energy. This would be expensive, but could be practical, because the power plant remains on earth and does not fly. The metallic hydrogen if it were stable would contain the stored energy.
 
A true story about dilithium crystals....

In the late '80s I was involved in a joint research project with the corporate research center of one of the big 3 aerospace companies. My sponsor and co-investigator didn't like the BS that a corporate researcher had to put up with, especially showing his lab to a corporate PR writer and photographer tasked with producing the annual corporate research magazine. These folks seemed bored with his research, but fascinated with the brilliant blue translucent silica gel crystals in a glass desiccator on his lab bench.

90338blue.jpg

The photographer started taking photos as the writer asked what was in the glass jar. My friend said they were dilithium crystals for advanced propulsion experiments. The writer was clearly fascinated by these beautiful blue crystals, quickly jotted down something in his notebook and thanked him for the lab tour.

The annual research magazine was reviewed by dozens of technical folks, printed and sent to the head of corporate R&D for the final sign off before public release. The lab director knew every research project in building since he was paying for it and asked the writer who give him the story about dilithium crystals. He told the writer to remove the dilithium article as he picked up his phone and dialed my friends office number....

Bob
 
How would you use the metallic hydrogen, though? Inject oxygen into a port in a solid grain like a hybrid?

The mention of nitrogen diamonds reminded me of a hilarious post in the otherwise rather unfortunate "k875" thread about the titular motor producing not Mach diamonds, but real diamonds.

No, they said it SHOULD be a metastable crystalline material, IE, like a diamond, that when the pressure and heat is removed, remains in its cubic crystalline form instead of reverting to regular carbon black flat platelet crystalline forms... So, IOW, it could be "ground up" or formed into small granules or even possibly a liquid, or a solid suspension in a carrier liquid (regular hydrogen?)

The heat of combustion is SO high when the metallic hydrogen became regular diatomic hydrogen, releasing all that energy, that it would melt all known combustion chamber materials. SO, they recommended using REGULAR hydrogen injected into the engine as a diluent-- dilute down the reaction with regular hydrogen. They weren't really clear on how oxygen would even be used... from what I got out of it, the engine would be started on regular hydrogen and oxygen, which burns at like 5,000 degrees, and then the metallic hydrogen would be injected (whether liquid oxygen would continue to be injected or not, they didn't say). The heat from the combustion would be enough to "burn" the metallic hydrogen back into regular diatomic hydrogen, releasing all the energy captured in the crystalline metallic hydrogen structure... the regular hydrogen at that point is basically just a coolant, preventing the engine from melting down... and of course the heat it absorbs increases its energy and volume and pressure many times, causing it to blast out the back of the engine with the "burned" metallic hydrogen.

Water could also be used as a diluent, but it would reduce the ISP to around 600-800, which is still about twice the ISP of oxygen-hydrogen's theoretical limit of around 460 seconds or so. Metallic hydrogen using diatomic hydrogen (normal hydrogen) as a diluent would have an ISP of about 1600, so they say, or about 4 times that of normal hydrogen-oxygen combustion...

Of course it's all predicated on making metallic hydrogen commercially at economically viable prices... the density of it would be about the density of kerosene, so IOW very small tanks would be required... hence a vehicle the size of a shuttle that's capable of being an SSTO.

Later! OL JR :)
 
Interesting article! The article states that metallic hydrogen may be a metastable solid, but no one knows for sure, because the stuff has never been produced in laboratory quantities. Thus, small quantities might exist under huge pressure, but as soon as the pressure is released the stuff expands out to molecular hydrogen. I think that I've heard that the center of Jupiter might be metallic hydrogen, but in that case it is constantly confined. There is always the point that you don't get something for nothing. To produce the metallic hydrogen would take a huge quantity of energy. An industrial power plant would need to be built to supply the energy. This would be expensive, but could be practical, because the power plant remains on earth and does not fly. The metallic hydrogen if it were stable would contain the stored energy.

Exactly... that's the point. There's no such thing as a free launch... LOL:)

It would be enormously difficult and expensive to produce, but imagine that you have an industrial process capable of making sugar-granule size bits of metallic hydrogen, and that it is metastable. Now, you might need something the size of a refinery, with the power demands of its own power plant to operate it, running nonstop cranking out little granules of metallic hydrogen that you suspend in some carrier liquid... (maybe liquid hydrogen or something else, I dunno, they didn't go into that... but something to make it bulk pumpable and bulk injectable into a rocket engine, IOW Not a POWDER or SUGAR GRANULES). Something more like metal flake spray paint, which could be pumped and injected (despite being very abrasive, which is a physical problem to deal with).

While the metallic hydrogen fuel would be REDICULOUSLY EXPENSIVE compared to regular old hydrogen (which is produced from natural gas, and for space launches today, whatever propellants their using is down in the noise of actual launch costs...), it would allow you to build a vehicle the size of a plain-jane Delta IV, without the SRM's, capable of landing 30 tons on the moon, or a spaceplane the size of a shuttle orbiter, with internal tanks, capable of delivering itself and a shuttle-size 20 ton payload to LEO. Such a vehicle, without the necessity of mating it to a booster rocket stack, without mating it to a reusable flyback booster, and having internal tanks, were it capable of rapid turnaround and reuse (which depends a LOT on the engine design, and the overall design of the vehicle) COULD be the "DC-3 of spaceflight"... but a lot depends on the engineering.

The pumping of the propellant into the engine, and the actual engine design would be the real headache. The rocket structures would be relatively straightforward... a reusable spaceplane wouldn't be, but it's doable.

The main point *I* took away from the article is, you want SSTO?? Develop a more power-dense propellant with high density... (IOW, higher ISP). I've been reading about fluorine/hydrogen and FLOX/hydrogen rockets over on the secret projects forum... using fluorine as a propellant really increases the energy of the propellant (ISP) by a goodly amount, BUT, the handling, design, and environmental issues are daunting-- probably insurmountable. Hence the reason why FLOX propellants haven't been used outside test bench...
Heck I was reading about fluorine/hydrazine propellants... IIRC the Soviets were looking at that combination as a possible storable missile propellant at one point... (course, if the balloon has done up and we're fighting a nuclear war, how much is anybody gonna care about being poisoned by flouride compounds and fluoride salts from fluorine powered rocket engines, when they'll probably be dead from nuclear blast or fallout within a couple days??

As for "blowing up", it has to be heated to the decrystallization temperature to switch from the metallic phase to the regular diatomic phase... around 4,000 degrees IIRC...

It's interesting stuff, but at this point is very "Star-Trekky"... IOW not particularly likely in our lifetimes, anyway, if ever...

Would it be cost effective for space launch?? Depends on the industrial production costs of metallic hydrogen. SSTO, especially of a reusable vehicle, CLAIMS to be holy grail of launch vehicle design. Certainly smaller rockets are generally cheaper than bigger rockets, and if they fly more often, they gain economies of scale that lower their per-unit costs... HLV's have a big problem gaining high enough flight rates to gain any economies of scale, because they would run out of payloads... IOW, you have to have a space program with SO many expensive payloads running into many dozens of billions a year to get the flight rates up on the HLV enough to start really getting any economies of scale, and the larger the HLV, generally speaking the larger the per-unit costs (due to size and complexity) and of course, the fewer launches it takes to orbit the existing payloads, hence more expensive payloads needed to increase the flightrates to the optimum economies-of-scale numbers... (this was a point I made with the DIRECT team, who repeatedly touted their "6-8 launches per year "sweet spot" for DIRECT" versus the high costs of Ares V, which at the time under Constellation was SUPPOSEDLY going to fly two missions per year... Basically the 6-8 launches of DIRECT were the same overall programmatic cost as TWO launches of the Ares V, and they couldn't understand how NASA just ignored this... SIMPLE-- (I said), THEY ONLY HAVE TWO MISSIONS OR TWO PAYLOADS PER YEAR! The question is not "how many DIRECT launches can we buy for the price of those two Ares V launches", but "how much does TWO launches per year of DIRECT cost versus Ares V?? When you look at it from that point of view, the differences were actually MUCH smaller-- since you're not amortizing the infrastructure and manpower costs over 6-8 vehicles, but only two of EITHER type, you lose most of the cost savings via economies of scale of DIRECT over Ares V... it's still cheaper to operate, just NOT THAT MUCH CHEAPER at the lower flight rate. This is what is absolutely going to KILL the SLS... flying only ONE mission every 2-3 years, is going to make each rocket, on a per-launch cost basis, be at least in the $1.7 billion dollar range, and probably closer to $2 billion... it'll make Saturn V look positively cheap by comparison! Even shuttle would be cheaper, simply due to the higher flight rates... in fact, (as a study I summarized on "lessons learned from the shuttle", and "alternate shuttle proposals" specified) high flightrates was what was used to get the rediculously low costs of shuttle to justify it in the first place and "sell" it to Congress and Nixon... basically everybody outside NASA HQ and the Beltway KNEW there simply weren't enough payloads to justify the kind of flightrates they were proposing to make shuttle cost-effective, nor were there even MONEY to build such payloads! Plus, the actual refurbishment costs and per-flight costs of shuttle were MASSIVELY underestimated, usually by at least an order of magnitude... Figures don't lie, but liars figure!

SO, how does this apply?? Is it cheaper to fly a massive vehicle using common off-the-shelf technologies that has been proven to work for decades, even if the vehicle is INCREDIBLY expensive and complicated, but the propellants are dirt cheap, or is it cheaper to fly a vehicle that is very small and incredibly powerful (assuming that the tankage and plumbing and pumping and engine designs are fairly straightforward and easily duplicable) and can orbit enormous payloads very easily, yet the propellant is INCREDIBLY expensive??

In the end, it's probably a wash... Get the design, infrastructure, support, integration, and management right, and you can bring down costs of the vehicle and supporting it on the ground, preparing it for launch, and operating it. It's mainly a MANAGEMENT problem, more than engineering, although smart engineering choices MUST be made to make the paradigm work... do all that right, and you CAN cut costs of spaceflight enormously from what is now "standard", and without requiring cutting edge high technology and exotic materials... SpaceX has proven that if nothing else (now, it remains to be seen if they can do it REPEATABLY in the operational phase, and not just in the development phase!) I think that in the end, at least for the foreseeable future, this will prove to be the best way to bring the costs of space launch down, not the 'bleeding edge of technology' methods that NASA employed with shuttle in the 70's, and which this sort of thing represents... it's a fascinating proposal, and gets you SSTO, but in the end it would probably be at least as expensive as shuttle or SLS... maybe more, depending on the propellant manufacturing costs and the actual vehicle engineering and support costs...

The main lesson to learn here is, "if you want SSTO, get a better propellant"... IOW, exotic engineering/chemistry...

Later! OL JR :)
 
A true story about dilithium crystals....

In the late '80s I was involved in a joint research project with the corporate research center of one of the big 3 aerospace companies. My sponsor and co-investigator didn't like the BS that a corporate researcher had to put up with, especially showing his lab to a corporate PR writer and photographer tasked with producing the annual corporate research magazine. These folks seemed bored with his research, but fascinated with the brilliant blue translucent silica gel crystals in a glass desiccator on his lab bench.

View attachment 116046

The photographer started taking photos as the writer asked what was in the glass jar. My friend said they were dilithium crystals for advanced propulsion experiments. The writer was clearly fascinated by these beautiful blue crystals, quickly jotted down something in his notebook and thanked him for the lab tour.

The annual research magazine was reviewed by dozens of technical folks, printed and sent to the head of corporate R&D for the final sign off before public release. The lab director knew every research project in building since he was paying for it and asked the writer who give him the story about dilithium crystals. He told the writer to remove the dilithium article as he picked up his phone and dialed my friends office number....

Bob

Silly fellow... everybody knows dilithium crystals are a clearish-brownish-tan color, not blue... didn't he see that lovely necklace the Elaan of Troyius was wearing in that episode, which Kirk used to "jump start" the Enterprise's engines?? LOL:)

Later! OL JR :)
 
H4 Metallic Hydrogen aka “Quadium” was an integral part of the plot of Leonard Wibberley’s “The Mouse That Roared”.

Using Quadium; Dr Kokintz produced the “Q-Bomb" which theoretically could have destroyed the world.

As for the temperatures of the reaction; what ever happened to all those “Super Materials” that were supposed to be here by now because of “BuckyBalls”?
 
6000 C (or K, it really doesn't matter) is the temperature at the surface of the Sun. I confine high pressure 25,000 K oxygen plasmas for 2 microseconds in my space simulation chambers. You're in the gases and plasmas only region for interaction times greater than 10s of microseconds.

Bob
 
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Currently metallic hydrogen is up there with anti-matter as a source of energy for space travel. You would use up a year’s worth, perhaps more, of the entire energy output of N. America just to produce enough H4, or anti-matter, to put one payload into space.

Then there are the containment problems and if the energy releases you mention for H4 is as great as that; wouldn’t there be an enormous amount of Gamma and X-Ray radiation produced as a result? They are now discovering that lightning strikes produce both Gamma and X-Rays.

Maybe one day we’ll figure out a means by which we can “catalyze” these substances instead of using a brute force approach to their production and one or the other could become usable.
 
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