Discussion of metallic hydrogen propulsion split from another thread.

[Snark]

More content has been removed, due to further personal remarks from folks who should know better, directly after being asked to drop it.

Please play by the rules.  Thank you.

[Soda Popinski]

What are some engine / fuel types that could substitute for a MH system?  So similar ISP with high thrust?

[Spacescifi]

40 minutes ago, Soda Popinski said:

What are some engine / fuel types that could substitute for a MH system?  So similar ISP with high thrust?

 

You won't want to hear this... but the answer is ABSOLUTELY NOTHING.... that I know of that humans actually currently have and can develop.

 

Theoretically, if we had kilogram of safely stored antimatter (we don't) and filled up some big water tanks, you could LITERALLY fly Starship X (Elon's) SSTO style wuthout boosters to orbit and land on Earth, then fly to orbit again before you ran out of water propellant.

Because AM has that much thrust when applied to liquid propellants.

Edited July 22, 2020 by Spacescifi

[Soda Popinski]

1 hour ago, Spacescifi said:

 

You won't want to hear this... but the answer is ABSOLUTELY NOTHING.... that I know of that humans actually currently have and can develop.

 

Theoretically, if we had kilogram of safely stored antimatter (we don't) and filled up some big water tanks, you could LITERALLY fly Starship X (Elon's) SSTO style wuthout boosters to orbit and land on Earth, then fly to orbit again before you ran out of water propellant.

Because AM has that much thrust when applied to liquid propellants.

I thought I heard a fusion drive, like in NASAs Discovery II white paper might fit the bill.  Re-looking at the paper, the ISP is way too high at 35,435s, and a low thrust of 18kN (NERV is 60kN).  

[Bill Phil]

37 minutes ago, Soda Popinski said:

I thought I heard a fusion drive, like in NASAs Discovery II white paper might fit the bill.  Re-looking at the paper, the ISP is way too high at 35,435s, and a low thrust of 18kN (NERV is 60kN).  

Engines like that can be “geared down” to higher thrust and lower isp. A variety of engine concepts could likely fit the various performance regimes of MH in KSP 2. Advanced nuclear thermal engines and a variety of fusion engines could do it if I recall.

But that depends on what MH’s performance in the game is.

According to Atomic Rockets MH has an isp around 1700 seconds. Impressive. But gas core fission could achieve that. And even nuclear pulse could achieve that by gearing down. The real question is how scalable the other tech is. And Project Orion is already confirmed which has a performance envelope that goes from around 2000 seconds to 10 thousand. There’s also possibilities for fusion engines that could gear down. 

But we won’t know until later.

Edited July 22, 2020 by Bill Phil

[Guest]

3 hours ago, Spacescifi said:

You won't want to hear this... but the answer is ABSOLUTELY NOTHING.... that I know of that humans actually currently have and can develop.

Wrong, actually. Liquid core fission is in similar Isp range, is a logical stepping stone to gas core, and is a technology that humans currently can develop (considering that Soviets were seriously working on gas core, well, liquid core is easier than that).

There are many different propulsion technologies. Metallic hydrogen is absolutely unnecessary in the grand scheme of things.

[K^2]

33 minutes ago, Dragon01 said:

Liquid core fission is in similar Isp range.

Do you have a citation on this? Main limiting factor on thermal rockets is temperature at the point of heat exchange. I'd be curious how one works around that with a liquid core.

Even with an open cycle gas core, there are questions of what to do about nozzle bell. At some point, it really has to be some variant of magnetic confinement, because there are no materials that can withstand contact with propellant at these temperatures. But at least, that's a solution.

[SOXBLOX]

On 7/21/2020 at 1:16 PM, K^2 said:

It's starting took bad for metastability. The tests that have been ran aren't exactly flawless, but the fact that they haven't found any signs of metallic hydrogen even at fairly high pressures, while backing off from the point where they did detect it, suggests that it's probably not all that stable even at high pressures, and that doesn't say good things about pressures in which you'd care to store it in a rocket.

Granted, there are still a few things you can do to extend metastability, like dropping temperature, doping the material, adding a magnetic field... But I would hold out hope on that if we've seen any indication of metastability at least at high pressure, which we haven't. So the space of possibilities under which MSMH is a viable fuel is rapidly shrinking. Based on data we have now, I'm comfortable calling it "very unlikely".

I agree that it is looking bad for metastasis, but there is still enough wiggle room in the error for it, I think.

The only reason I'm arguing here is because some people have said the concept is totally disproven and is now "pseudo-science". It is still under debate. Only when enough data has been collected with rigorous standards can we rule out metastability.

Liquid core? Point of contact? Are you thinking closed-cycle? Let me save you some trouble, just do open-cycle, and drat the consequences!

Edited July 23, 2020 by SOXBLOX
Added stupid liquid-core idea.

[DStaal]

1 hour ago, K^2 said:

Do you have a citation on this? Main limiting factor on thermal rockets is temperature at the point of heat exchange. I'd be curious how one works around that with a liquid core.

Even with an open cycle gas core, there are questions of what to do about nozzle bell. At some point, it really has to be some variant of magnetic confinement, because there are no materials that can withstand contact with propellant at these temperatures. But at least, that's a solution.

Which really isn't a problem gameplay wise, as they were already doing magnetic confinement nozzles in the first trailer.

A better question than 'what has similar ISP and thrust' is really 'what could take a similar role in the game'.  The exact performance doesn't really matter - what you need is a set of engines that can perform the roles they had designed engines using MH to do.  Yes that requires a 'torchship' drive to take over the apparent role of late-game interplanetary and atmospheric engines, but there's a wide range of theoretically possible torchdrives which could fill the role.

[Spacescifi]

2 hours ago, Dragon01 said:

Wrong, actually. Liquid core fission is in similar Isp range, is a logical stepping stone to gas core, and is a technology that humans currently can develop (considering that Soviets were seriously working on gas core, well, liquid core is easier than that).

There are many different propulsion technologies. Metallic hydrogen is absolutely unnecessary in the grand scheme of things.

 

Maybe... but the thrust?

Seems all I ever hear is ISP with nuclear, and when anyone mentions the thrust people start frowning in dismay.

Metallic hydrogen was countef as an SSTO game changer.

The best one could do with nuclear is say sayonara to public health abd use air augmented rocketry mixed with nuclear liquid propellant project pluto style open cycle.

Because closed cycle risks melting the engine and nozzle.

And let's rememeber that magnetic nozxles are for space. And to get to orbit?

We are'nt doing that with mag nozzles.

We know why too.

[K^2]

31 minutes ago, DStaal said:

Which really isn't a problem gameplay wise

I mean, nothing is. Gameplay wise, you just have to balance it against difficulty of acquisition either by cost, manufacturing requirements, or tech tree. But that's no the topic. If we are literally discussing if particular piece of tech that's been confirmed to be part of the game should be part of the game based on it not being realistic, you can't just point to another piece of tech as an alternative and claim it's fine, because it's already in the game. That violates the premise of the discussion. If you want to argue that magnetic nozzles are far less speculative than MSMH, that's certainly an argument that can be made. But it is still an argument that has to be made. You can't just say, "It's already in the game." By that logic, so is MSMH last we've heard.

But in terms of search for alternatives to MSMH, there is no actual discussion. Nothing else stores that amount of chemical energy, so no chemical thruster can ever have the same I_SP. There are exactly three sources of energy with more of it per weight than any chemical source. Nuclear, anti-matter, or black holes. Both of the later are in league of their own with up to 100% mass defect and max theoretical I_SP of c/g, so that's a separate discussion. Which means that the only thing we have to cover the gap between conventional chemical rockets and nuclear pulse propulsion is other kinds of nuclear propulsion.

And yeah, I would very much prefer to have tech that's based on serious papers, if not prototypes, whenever possible. NERVA was a decent compromise. Things like Project Orion and Project Daedalus are a good benchmark for what should be right there on the edge of believable.

And if that's not enough, and there are still gaps, in my opinion, it's better to make up some sort of unobtanium that's entirely fictional and we all secretly know to be 99% unicorn farts and 1% physicist tears by volume, then to pull in a piece of speculative tech that has been if not entirely debunked, put under serious question. It's the same reason I wouldn't want to see quantum thrusters, EMDrive, or the like. These sorts of thing only confuse people trying to learn, fuel conspiracy theories, and also don't age well. Kind of like the idea of shooting people at the moon from a cannon. That's not to say that these things shouldn't show up in games - I would totally play a game based on From the Earth to the Moon - but it probably shouldn't be in KSP.

Nonetheless, that last bit is subjective. Some people will probably be ok with all manner of wildly speculative tech, and it's not objectively wrong even if I disagree with it. If these things end up in the game, I'm still going to play the game. I might avoid them in favor of alternatives. I might even go for mods to get that.

P.S. I've almost added warp drives to the list along with QTs, but honestly, the reasoning is entirely different on these. I just don't trust Intercept to implement a warp drive that has anything even remotely to do with physics. And it's not a slight against Intercept - there aren't a lot of people I'd trust with that.

[SOXBLOX]

Hmm. I will totally still use mH engines even if they are, at some point in the future, shown to be physically impossible.

 

Edited July 23, 2020 by SOXBLOX

[Guest]

6 hours ago, Spacescifi said:

Maybe... but the thrust?

Pretty good, as with any thermal rocket technology. People who think nuclear has low thrust by definition are always thinking of NERVA, which was a hydrogen upper stage engine. If you use a heavier propellant you will have better thrust. Nuclear engines do not need to have low thrust, but their TWR will be lower than that of chemical engines, because they are heavier. 

Indeed, a liquid core NTR using water as propellant would have stats broadly similar to mH engines, without the need for unobtainium. 

[KerikBalm]

13 hours ago, Soda Popinski said:

What are some engine / fuel types that could substitute for a MH system?  So similar ISP with high thrust?

Well they have shown 2 types of PSM engine in the game. One is PSM mixed with water, and the other is PSM confined by adifferent shade of PSM, whith some cesium decoration.

Stats for PSM (ie, stats for what you'd get if metallic hydrogrn were substantially metastable): 

PSM+ water: 538 Isp; PSM + lH2: 1090; PSM^2: 1700

The PSM+water engine could be replaced by a solid-corr NTR with LOx augmentation: http://www.projectrho.com/public_html/rocket/enginelist2.php#lantr

Isp: 647 -> Better than the PSM+water engine

The PSM^2 engine could be replaced by a liquid core NTR, or a closed cycle gas core (A "nuclear lightbulb":

Gas core, closed cycle: http://www.projectrho.com/public_html/rocket/enginelist2.php#basicgcr  1,100 to 3,200, relatively conservative predictions are more around 2,000.

This exceeds the PSM^s 1,700s

Liquid core ( http://www.projectrho.com/public_html/rocket/enginelist2.php#ntrliquid ): Probably around 1,630 s -> very close to the PSM^2 engine, but possibly as high as 2600.

 

9 hours ago, Dragon01 said:

Wrong, actually. Liquid core fission is in similar Isp range, is a logical stepping stone to gas core, and is a technology that humans currently can develop (considering that Soviets were seriously working on gas core, well, liquid core is easier than that).

There are many different propulsion technologies. Metallic hydrogen is absolutely unnecessary in the grand scheme of things.

8 hours ago, K^2 said:

Do you have a citation on this? Main limiting factor on thermal rockets is temperature at the point of heat exchange. I'd be curious how one works around that with a liquid core.

Even with an open cycle gas core, there are questions of what to do about nozzle bell. At some point, it really has to be some variant of magnetic confinement, because there are no materials that can withstand contact with propellant at these temperatures. But at least, that's a solution.

Consider that uranium/plutonium has a different melting point than other materials. You could use another material with a higher melting point to contain it:

https://www.asminternational.org/web/cmdnetwork/home/-/journal_content/56/10180/25655039/NEWS since you can apparently get material that wont melt at over 4400 K

Certainly 4150K : https://en.wikipedia.org/wiki/Tantalum_hafnium_carbide

The simplest way would be to melt your fission fuel in a container of this material, and inject hydrogen into the molten mixture. The fission fuel is melted, the engine container is not.

A more advanced engine will use active cooling, and another molten fluid. Example: a Hf-Ta-C container, with molten tungsten, and molten uranium. Now, due to fissioning in the center, and cooling of the exterior, the highest temperature will be at the center, and temperature will decrease as one moves away from the center.

So now you can have the fluid at a higher temperature than your container... and you can heat the fluid to the point that it is nearly boiling. You centrifuge the whole thing to keep the fluid pressed against the walls. Of course, this is fine for a cylinder, but you need to have a nozzle at one end. So you could again rely on active cooling (as we already do with rocket engines), and if neccessary, use of a buffer gas (like injecting cold lH2 just along the edges), that cools the exhaust in contact with the nozzle, while leaving the core/center of the exhaust still very hot.

Closed cyle gas core (nuclear lightbulbs) also would rely on the use of a bufer gas vortex inside actively cooled quartz glass to keep the uranium gas from contacting the quartz glass and melting/vaporizing it. This lets the interior get much hotter than the glass wall, and rely on emission of radiation which quartz is transparent to (but so is hydrogen). That radiation escapes the glass, which has hydrogen floying past it, and a dopant is injected into the hydrogen that absorbs the UV radiation coming from the quarty "lightbulbs", and heats and expands the hydrogen. I think you'd have to design your dopant injection well so that the hydrogen directly in contact with the quartz glass is not mixed with dopant (otherwise it would heat up and melt the glass too).

These engines rely on temperature differentials, with difficult engineering problems to keep the solid parts from melting, but they certainly are possible.

7 hours ago, SOXBLOX said:

I agree that it is looking bad for metastasis, but there is still enough wiggle room in the error for it, I think.

The only reason I'm arguing here is because some people have said the concept is totally disproven and is now "pseudo-science". It is still under debate. Only when enough data has been collected with rigorous standards can we rule out metastability.

I really don't understand why I need to keep making this point over and over again. Which part is not clear?

There is precisely 0 evidence for metallic hydrogen being metastable. No theory predicts it will be, no experimental evidence using pure hydrogen, isotopes, or alloys shows any metastability. The source of the idea that it might be metastable comes from one paper, from 48 years ago, using disproven models.

At this point there is equal evidence for metastable metallic hydrogen, as there is for pixie dust and unicorn farts. Unless you can provide some evidence to argue that this is not the case, please have the intellectual honesty to admit that including metastable metallic hydrogen is the scientific equivalent of including pixie dust and unicorn fart engines, and you want to include those anyway.

Edited July 23, 2020 by KerikBalm

[kerbiloid]

So, if get some

Quote

pixie dust and unicorn farts

, this can make metallic hydrogen metastable?

 

[KSK]

8 minutes ago, kerbiloid said:

So, if get some

, this can make metallic hydrogen metastable?

 

Yes but the pixie dust has to be laced with caesium. Seems a bit harsh on the pixies to be honest.

I *think* the unicorn farts are for flowing down the sides of the magnetic nozzles to prevent them melting in case of insufficient caesium doping but I’m not a rocket scientist so I’d get a second opinion on that.

Edited July 23, 2020 by KSK

[KerikBalm]

@KSK Well, you can eliminate the need for Cesium by using Red-Mercury to make super conducting magnetic coils so that even paramagnetism is enough, and most heat that gets to the coils will be stored as chemical energy, which you can then use in a pinch to trigger fusion for a temporary boost in power.

Look, it has its own wikipedia page and everything, its not proven beyond any doubt that it doesn't exist:

https://en.wikipedia.org/wiki/Red_mercury

On another note, I have been in a discussion through PMs with someone opposed to unicorn farts, and in favor of metastable metallic hydrogen.

They continually declined to offer any argument as to why mmH is on better footing than unicorn farts... and then started to ask me to help make the argument for them. When I said no, and that they made the claim, the burden was on them to back it up, they said: "I'm doing you a favour, the least you can do is help."

I kid you not...

Edited July 23, 2020 by KerikBalm

[kerbiloid]

"Unicornium" sounds like some artifical heavy element. So, maybe its emanation includes some special phase of hydrogen.

Also, as there were "Transfermium wars", maybe we could use Transfermium to transfer, instead of the hydrogen.

[Soda Popinski]

3 hours ago, kerbiloid said:

"Unicornium" sounds like some artifical heavy element. So, maybe its emanation includes some special phase of hydrogen.

Also, as there were "Transfermium wars", maybe we could use Transfermium to transfer, instead of the hydrogen.

Well, we do have precedent for unusually dense materials in the game.  Whatever the hell Kerbin is made of has got to be pretty dense to get Earth-like surface gravity with a planet with 1/9500 the volume of Earth.

[K^2]

9 hours ago, KerikBalm said:

Ah, so it's also open cycle, got it. I thought LC was supposed to be closed cycle, making it very similar to SC. Yeah, with an open cycle, you don't have a heat exchanger, so there are ways to inject cooler layers between the really hot stuff and containment, giving you ability to push I_SP by at least a factor of "a few" compared to chemical. There are still limits, of course, but you ought to be able to get well above 1,000s with the right propellant mix and well designed reaction chamber and nozzle.

[KerikBalm]

29 minutes ago, K^2 said:

Ah, so it's also open cycle, got it. I thought LC was supposed to be closed cycle, making it very similar to SC. Yeah, with an open cycle, you don't have a heat exchanger, so there are ways to inject cooler layers between the really hot stuff and containment, giving you ability to push I_SP by at least a factor of "a few" compared to chemical. There are still limits, of course, but you ought to be able to get well above 1,000s with the right propellant mix and well designed reaction chamber and nozzle.

Well open cycle is generally only bad if it results in fission products in the exhaust.

You should be able to minimize that with the centrifugation, but yea, I don't know if it can have "clean" exhaust.

There's the closed cycle gas core as an alternative as well

[KSK]

6 hours ago, kerbiloid said:

"Unicornium" sounds like some artifical heavy element. So, maybe its emanation includes some special phase of hydrogen.

Also, as there were "Transfermium wars", maybe we could use Transfermium to transfer, instead of the hydrogen.

Transfermiums - robots hydrogen in disguise!

[Spacescifi]

4 hours ago, Soda Popinski said:

Well, we do have precedent for unusually dense materials in the game.  Whatever the hell Kerbin is made of has got to be pretty dense to get Earth-like surface gravity with a planet with 1/9500 the volume of Earth.

 

Hahaha...

Nice.

[K^2]

1 hour ago, KerikBalm said:

You should be able to minimize that with the centrifugation, but yea, I don't know if it can have "clean" exhaust.

The answer is most definitely not, but you can probably make it clean enough to use in interplanetary without worrying that you might create belts of contamination with repeated use. AKA, good enough.

[Codraroll]

Forgive me for waltzing into this thread as a layperson like a cow into a china store, but if we're discussing this strictly in a KSP2 perspective, wouldn't it be possible to assume some technology to stabilize hydrogen in a metallic form? The game has RTGs burning forever, magic reaction wheels, parts that never deteriorate and stuff like that (even large metal claws that can grip soft foam fuel tanks without leaving marks), so a Kerbal Stabilization Procedure (TM) to create metallic hydrogen wouldn't be too far outside the question for me. 

While the real world seems to be sadly lacking in ways for metallic hydrogen to exist, there appears to be a pretty unison understanding of how it would behave if it did. Provided the right disclaimers were presented, I think its ground isn't so flimsy it warrants exclusion from a video game.

Edited July 23, 2020 by Codraroll