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