Ramjets? Scramjets?

[SpaceFace545]

1 hour ago, OOM said:

Let the construction time take decades - but you can still build

If you have SSTO of course.

 

But the question, as I understand it, was about how to fly on Dune / Mars. OK. And what is the problem of using a large wing and nuclear ramjet? In this case, you can disperse with a powerful electric motor or a small rocket stage.
I think that a modern, most compact and lightweight nuclear ramjet engine is a solution to how to fly in a CO2 atmosphere.

If without a nuclear engine, then I think that for light aircraft (400-500 kg) an ordinary, powerful electric motor is enough.

Or you can use a regular chemical rocket plane like J8M \ Me 163

You’re totally right but a nuclear engine would probably be the optimal solution as it has a limitless range 

[Incarnation of Chaos]

20 hours ago, Bej Kerman said:

What real-world rocket could get us to Alpha Centauri in a reasonable amount of time?

Project Orion could easily do it, and that was easily possible in the 50's.

But this is a false dichotomy you're setting up; because no matter what you can't "Burn" CO2. It's a product of combustion itself! You may as well be trying to make a jet engine that could burn liquid water!

Sure you could split the water into Hydrogen and Oxygen, but that would take just as much energy as you would release from their combustion and the extra dry mass from the needed equipment would result in it being too heavy to fly practically. You could also split CO2 into Carbon and Oxygen, but the same problem arises. This is chemistry we knew back in the 1800's, and hasn't seen any massive changes since. That isn't to say we couldn't ever find a different way, but seeing as KSP II is about "Near Future" technologies it isn't the place to speculate about fantastic technologies based in not even a tiny bit of real-world experience.

So you're really left with 3 options; you either bring your own Fuel and Oxidizer and have a rocketplane, use a Nuclear Thermal Jet Engine, or use Electric Propulsion. Not because we know 100% that those are the only ways to do this, but because those are the only ways we know currently and are compatible with our understanding of physics even going 100-200 years into the future.

[KerikBalm]

On 4/29/2020 at 8:38 PM, SpaceFace545 said:

Unless it’s a nuclear jet engine what is possible then it isn’t a jet. Jet engines combust fuel and oxygen to heat up and expand air. A nuclear jet engine uses the heat from a reactor to expand air.

If they're going to stick with metallic hydrogen engines, then you can simply use metallic hydrogen decompression to heat the atmosphere. Or it could be an "air agumented rocket"/"ramrocket".

It all comes down to the fact that for the same energy it takes to send 1kg of reaction mass back at 1000 m/s, you can send 100 kgs of reaction mass back at 100 m/s, for 10x the thrust.

No matter what the fuel source, you can improve effective Isp through air augmentation just by increasing mass flow.

KSP 1 could use ram rockets, KSP2 could make even better use of them when they have things like (*sigh*) metallic hydrogen that store so much energy that you'd stop caring if the air has O2 in it, just as long as there's air.

[Bingleberry]

6 hours ago, KerikBalm said:

decompression to heat the atmosphere.

Decompression always results in cooling... like why frost forms on the valve of a high pressure nozzle venting into the atmosphere... or even an expanding universe is a “cooling” universe... unless there’s something I’m missing about metallic hydrogen, it should abide by the same laws of physics that dictate heat dissipation in “regular” compressed (or liquified) gases... energy/heat must go in, to compress it, heat must be released upon expansion...  it’s a matter of entropy and energy conservation... again, unless I am missing something about metallic hydrogen?

[Lt_Duckweed]

3 hours ago, Bingleberry said:

Decompression always results in cooling... like why frost forms on the valve of a high pressure nozzle venting into the atmosphere... or even an expanding universe is a “cooling” universe... unless there’s something I’m missing about metallic hydrogen, it should abide by the same laws of physics that dictate heat dissipation in “regular” compressed (or liquified) gases... energy/heat must go in, to compress it, heat must be released upon expansion...  it’s a matter of entropy and energy conservation... again, unless I am missing something about metallic hydrogen?

Metallic hydrogen would "decompress" the same way c4 would "decompress", by violently exploding.  Metallic hydrogen is not a gas, it would be a liquid/solid, and it is in a metastable state, meaning when it decomposes into a gas it releases a LOT of energy.

[Bingleberry]

43 minutes ago, Lt_Duckweed said:

Metallic hydrogen would "decompress" the same way c4 would "decompress", by violently exploding.  Metallic hydrogen is not a gas, it would be a liquid/solid, and it is in a metastable state, meaning when it decomposes into a gas it releases a LOT of energy.

That makes no sense... c4 doesn’t decompress, it reacts... a material transitioning into another state of matter is not “decomposition,” a semiliquid form of compressed hydrogen transitioning to hydrogen gas is not “decomposition.” What are we reacting? Like I said, expansion of a liquid, into a gaseous state, is going to cool... if you’re trying to say “react” than say “react,” decompression is very different from a chemistry standpoint

[KerikBalm]

@Bingleberry

Yes, and metallic hydrogen would also undergo a phase change which would release a lot of energy.

Metallic hydrogen does not seem to metastable, so as soon as you stop compressing it sufficiently (ie >400 GPa), it releases a lot of energy.

Also, yes, as the metallic hydrogen expands after the phase change, it will cool down... but it will still be much hotter than the air it interacts with, and hte air it interacts with will still be heated up.

Let me rephrase: then you can simply use the heat from metallic hydrogen decompression phase change and decomposition to heat the atmosphere.

As for decompress vs reacts. Its really a decomposition reaction. The phase change of metallic hydrogen to gaseous hydrogen is not like the phase change of ice to water or to water vapor. In the case of water phases, its still always H₂O. Metallic hydrogen would be a single crystral(?) structure with electrons flowing freely between hydrogen atoms, to single H atoms, transitioning to H₂ when the result cools enough. Its not the same molecule in different states as in water.

This decomposition occurs once the metallic hydrogen is not sufficiently compressed, which is why I imprecisely refered to heating from decompression.

Edited May 7, 2020 by KerikBalm

[Bingleberry]

@KerikBalm I appreciate the explanation... best I can tell is metallic hydrogen is essentially highly compressed hydrogen plasma, so it seems it really depends on the atmosphere it is discharged in. That said, I don’t know how much energy might be released upon expansion, but can we reasonably say that it would be capable of breaking a CO double bond and getting energy out? Or are we just talking about using the vent pressure to generate thrust? Because the energy output of forming an H to H bond is pretty small...

 

i also think that “decomposition” is an inapt term, since the hydrogen is essentially in a free proton state, with electrons freely flowing around the medium. You can’t really “decompose” hydrogen much further.

 

Edit: I guess with volume, the bond energy is significant... https://dash.harvard.edu/bitstream/handle/1/9569212/Silvera_Metallic.pdf

Edited May 7, 2020 by Bingleberry

[KerikBalm]

1 hour ago, Bingleberry said:

best I can tell is metallic hydrogen is essentially highly compressed hydrogen plasma,

Its a metal, not a plasma. After the phase change, it would not even be a plasma (but it would be really hot, but not hot enough to ionize monatomic hydrogen), thus the exhaust could not be contained with a magnetic nozzle. Just how "doping" it with Cesium is supposed to allow a magnetic nozzle to work (which seems to be the technobabble explanation for KSP2), I have no idea...

Quote

so it seems it really depends on the atmosphere it is discharged in. That said, I don’t know how much energy might be released upon expansion, but can we reasonably say that it would be capable of breaking a CO double bond and getting energy out? Or are we just talking about using the vent pressure to generate thrust?

A lot of energy would be released upon expansion. 216 megajoules per kilogram. So much energy that without reacting with anything, it gets an Isp of 1700s in a vacuum.

http://www.projectrho.com/public_html/rocket/enginelist.php#id--Chemical--Metastable--Metallic_Hydrogen

Vacuum Isp is directly related to "energy density" of the propellent, density in this case refering to energy released per unit mass.

Now reacting kerosene with Oxygen gets you a maximum Isp of about 360, reacting liquid hydrogen with oxygen gets you an Isp of about 500.

Airbreathing engines beat standard rockets for 2 reasons.

1) They don't have to store the oxidizer, so the effective energy density of the propellent can basically be multiplied by: (Mass of fuel + Oxidizer)/ mass of fuel.

2) Simply using air as working mass to send more mass back at lower speed (same energy, more impulse). Turbofans are a great example of this, with their big fan sending air back with plenty of oxygen that wasn't used for combustion.

Now a standard kerosene rocket has a fuel to oxidizer mixture of like 1:2.6 IIRC. So that allows reaching about 1285 effective Isp in an atmospheric engine - most jet engines use kerosene). Most jet engines get far far far better than 1285 effective Isp - the SR-71 for example got about 2,100 effective Isp around mach 3.

So... any fuel allowing for 1285 Isp or better in a vacuum can get performance in an oxygenless atmosphere that is equal or better to a kerosene jet in an O2 atmosphere. Metallic hydrogen getting 1700s fits the bill

It wouldn't outcompete liquid hydrogen in an oxygen atmosphere, since the fuel to oxidizer ratio there is about 8:1... but metallic hydrogen would do just fine as a jet fuel even in an argon/other noble gas atmosphere, if metallic hydrogen was metastable and thus suitable for use as a fuel at all.

Edited May 7, 2020 by KerikBalm

[Bingleberry]

51 minutes ago, KerikBalm said:

2 hours ago, Bingleberry said:

 

Its a metal, not a plasma. After the phase change, it would not even be a plasma (but it would be really hot, but not hot enough to ionize monatomic hydrogen)

If it’s conductive, than the electrons are free flowing... since a hydrogen atom has one electron, if said electron flows from said hydrogen atom, it must necessarily be ionized... the ionization energy of hydrogen is about 14 eV, which is way lower than the energy involved in generating the metallic hydrogen.

 

Also, it’s metal from a conductivity standpoint, not a material-chemistry standpoint. As I’ve read, it’s not a solid, it behaves more like a liquid than a solid. The “metallic” only refers to the fact that it conducts, not because it is a ductile solid. 
 

Edit: I’m a biochemist, so my knowledge of physical chemistry ended with my last p-chem class in grad school... too much calculus! So, I am by no means an expert in this, I am just trying to rationalize why this might work

Edited May 7, 2020 by Bingleberry

[KerikBalm]

@Bingleberry

Being a metal does not mean it has to be a solid. Iron is still a metal when melted, as is mercury.

Also, whether hydrogen has 1 electron or not is not relevant to being ionized. An Ion drive doesn't strip all the electrons from Xenon, just 1. Using your logic, all metals are ionized.

You can't always think of electrons as distinct particle (good ol' wave-particle duality), its often better to think of them as clouds, and in the case of metals, the clouds go throughout the metal... as a biochemist, you should be familiar with the aromatic rings/ conjugated double, and how you can't treat the electrons as localized, but rather they must be considered delocalized over the whole conjugated system.

Lastly, the ionization energy may be lower than the energy involved in generating mH, but not all the energy involved in generating mH goes towards ionization when released.

You get about 50% ionization of hydrogen only at 10,000 K

http://www.astro.wisc.edu/~townsend/resource/teaching/astro-310-F09/hydrogen-ionization.pdf

Metallic hydrogen would only generate temperature of 6,000K when the energy from forming it is released:

http://www.projectrho.com/public_html/rocket/enginelist.php#id--Chemical--Metastable--Metallic_Hydrogen

So, no, its not significantly ionized, its not a plasma, its not confinable by magentic fields.

Edited May 8, 2020 by KerikBalm

[Bingleberry]

17 hours ago, KerikBalm said:

hydrogen has 1 electron or not is not relevant to being ionized. An Ion drive doesn't strip all the electrons from Xenon, just 1. Using your logic, all metals are ionized.

Actually, that is wrong... hydrogen has 1 proton, if the electron is freely moving in a soup, the interaction between attractive species is negligible, this is ionization. All you need is to remove 1 electron from xenon, and it’s an ion... I am not sure what you’re trying to argue here... xenon plasma is Xe1+, it’s not a bald nuclei... by definition, you are creating ionized xenon gas by removing an individual electron... once you start boiling off inner electrons you start making x-ray emitters...  also, yes, passing a charge through metal ionizes the free flowing, loosely held outer electrons, they are just quickly replacing the electrons behind them in a flow... if you keep the metal in a vacuum, pass a charge through it, and put a grounding plate on the other side of the metal, you get a cathode ray, these are electrons that are ionized off of the metal. The free flow of electrons, in a metal, is different because these electrons are outer (loosely held) electrons... these electrons are unpaired and very far from the nucleus... while the hydrogen electron is unpaired, it is as close to the nucleus as you can get.

While  metallic hydrogen might not be plasma, per se, if those electrons are not interacting with the proton in an attractive nature, that would be an ionized state... there’s just too much energy in the system. Also, when I said “not ductile,” I was referring to its state of matter... as I can tell, it THEORETICALLY forms a liquid/slush, I never said liquids couldn’t be metals, I was stating it is not a solid.

17 hours ago, KerikBalm said:

you should be familiar with the aromatic rings/ conjugated double,

I am, conductive polymers are conjugated polymers... since we have a cloud of electrons over the length of the polymer, you’d expect it to automatically be conductive, because it is like a wire... a cloud of electrons freely flowing over the length of the conjugated and catenized carbon atoms (and sometime nitrogen/sulfur/etc) looks like a linear piece of metal... but you can’t conduct unless you put a dopant in the material, allowing something to easily contribute an electron to start the flow (or a positive charged “hole”), because those pi-bond electrons are just too tightly held. Just because you have a soup of flowing electrons, like phenyl rings, it does not mean that these clouds of electrons are changing the overall charge of the particle, and would allow for metallic conduction... the whole “sea of electrons” theory of metal has been around since before I was in high school, but the “sea of electrons” is a function of the fact that these OUTER electrons are so loosely held, not because they behave as a wave and/or particle... they behave like a liquid, flowing amongst a lattice of nuclei. The outer electrons of metals have weak attraction, and can easily be ionized, just look at the photoelectric effect on most metals... you can’t get a hydrogen’s electron to “flow” without tearing it off of the nucleus first.

 

Edited May 8, 2020 by Bingleberry

[Bingleberry]

18 hours ago, KerikBalm said:

You get about 50% ionization of hydrogen only at 10,000 K

http://www.astro.wisc.edu/~townsend/resource/teaching/astro-310-F09/hydrogen-ionization.pdf

http://www.projectrho.com/public_html/rocket/enginelist.php#id--Chemical--Metastable--Metallic_Hydrogen

The first citation calculates in stellar atmospheric densities (less than one mole per cubic meter, n=10^20 /m^3), which would be orders of magnitude smaller than anything in a theoretical metallic hydrogen containment system (1 mole of hydrogen, at STP is 0.0224 m^3)... because you sure don’t need 10000 k to make room temperature hydrogen plasma... the second citation makes it sound almost as “magical” as a warp drive (from a containment and manufacturing perspective)

Edited May 8, 2020 by Bingleberry

[KerikBalm]

2 hours ago, Bingleberry said:

The first citation calculates in stellar atmospheric densities (less than one mole per cubic meter, n=10^20 /m^3), which would be orders of magnitude smaller than anything in a theoretical metallic hydrogen containment system (1 mole of hydrogen, at STP is 0.0224 m^3)... because you sure don’t need 10000 k to make room temperature hydrogen plasma... the second citation makes it sound almost as “magical” as a warp drive (from a containment and manufacturing perspective)

I haven't found anything except 10000k for ionization of hydrogen by temperature alone:

http://www.wag.caltech.edu/home/jsu/Thesis/node31.html

Sure, you can ionize it at lower temperatures. You can ionize gas at some pretty low temperatures, as in the lightening globe novelty lighting. But that ionization isn't achieved just by heating the gas.

If you can provide a citation for denser hydrogen being ionized by temperature alone, please provide it.... Otherwise such a metallic hydrogen engine would need some external device requiring an additional energy output to ionize the hydrogen exhaust and allow for magnetic confinement of the rouchly 6000 K exhaust.

[Bingleberry]

@KerikBalm

pressure literally ionizes hydrogen: https://arxiv.org/pdf/astro-ph/9909168.pdf

even at low temperatures: https://iopscience.iop.org/article/10.1088/0963-0252/12/4/027/pdf

https://iopscience.iop.org/article/10.1088/0370-1328/79/4/308/pdf

The transition to a hydrogen metallic state is literally called the “plasma phase transition”: https://www.pnas.org/content/pnas/107/29/12799.full.pdf

[KerikBalm]

@Bingleberry

*sigh*, this is getting really annoying. I think we need to clear up a few things/misunderstandings

On 5/8/2020 at 12:27 PM, Bingleberry said:

While  metallic hydrogen might not be plasma, per se, if...

Then what are we arguing about?

On 5/8/2020 at 12:27 PM, Bingleberry said:

when I said “not ductile,” I was referring to its state of matter... as I can tell, it THEORETICALLY forms a liquid/slush, I never said liquids couldn’t be metals, I was stating it is not a solid.

You said

On 5/7/2020 at 4:03 PM, Bingleberry said:

The “metallic” only refers to the fact that it conducts, not because it is a ductile solid. 

Considering I never said anything about it being a solid, and only stated that it was a metal, I don't know why you mentioned it being a solid. As far as I can tell you equated me mentioning it being a metal to it being solid. If that's not why you brough up solids, I have no idea why you did and it seems to come out of nowhere.

On 5/8/2020 at 12:27 PM, Bingleberry said:

I am not sure what you’re trying to argue here... xenon plasma is Xe1+, it’s not a bald nuclei... by definition, you are creating ionized xenon gas by removing an individual electron...

Ok, you agree that removing an electron regardless of how many electrons an atom has, makes it ionized, which makes your statement:

On 5/7/2020 at 4:03 PM, Bingleberry said:

since a hydrogen atom has one electron,...

confusing to me... why does it matter how many electrons it has in total, all that matters is if its missing one.

Your links are all well and good, but still no closer to the relevant question of if the relatively low pressure 6000K monatomic hydrogen exhaust (not  the stored metallic hydrogen) would be ionized/able to be controlled by magnetic fields.

 

[Bingleberry]

You said: 

On 5/7/2020 at 9:28 AM, KerikBalm said:

Its a metal, not a plasma

That’s wrong, it’s hydrogen that behaves like a metal, as such “metallic,” it is not “a metal.” Metals have very specifically described properties, like filled electron shells (why one electron in hydrogen is an important aspect), and huge valence bands, because they typically have multiple valence electrons that are far from the nucleus (hydrogen has one that is adjacent to the nucleus)... the ionization energy of hydrogen needs to be exceeded for a valence band to appear.

 

1 hour ago, KerikBalm said:

Then what are we arguing about?

I stated it is essentially highly compressed plasma, you said “no,” I gave you a paper that says one must pass the plasma phase transition to get metallic hydrogen... are you saying my peer reviewed paper is not relevant because it conflicts with your opinion?

 

1 hour ago, KerikBalm said:

Considering I never said anything about it being a solid, and only stated that it was a metal, I don't know why you mentioned it being a solid. As far as I can tell you equated me mentioning it being a metal to it being solid. If that's not why you brough up solids, I have no idea why you did and it seems to come out of nowhere.

As stated above, you say in no uncertain terms “[metallic hydrogen] is a metal,” I was pointing out that it is not a metal from a materials standpoint, it is a metal from a conductivity standpoint... so above, no filled electron shells, no large valence bands, etc... admittedly, my example could have used some work, but again, you state a non-metal is a metal... that is an unequivocally incorrect statement.

 

1 hour ago, KerikBalm said:

confusing to me... why does it matter how many electrons it has in total, all that matters is if its missing one.

If one is defining a “metal” the number of electrons is important... again, see above... it has metallic behavior, not a metal... is metallic iodine a metal? No, it is iodine that has been forced into a metallic-like behavior. Chemistry is, literally, a study of how electrons move, because all bonds are dictated by valence electrons... don’t ask a chemist “why does it matter how many electrons it has in total.” Because it ALWAYS matters... you’ve clearly never taken any courses in organic, inorganic, p-chem, etc, because you’d never make such an obtuse statement.

 

1 hour ago, KerikBalm said:

Your links are all well and good, but still no closer to the relevant question of if the relatively low pressure 6000K monatomic hydrogen exhaust (not  the stored metallic hydrogen) would be ionized/able to be controlled by magnetic fields.

What pressure do you think exists in the exhaust nozzle of a theoretical metallic hydrogen engine? I have a hard time thinking it is “low” by any measure, and orders of magnitude higher than the paper you presented. That said, if metallic hydrogen passes a plasma transition, what do you think it is before it transitions to atomic hydrogen?

[KerikBalm]

As they didn't see electrical conductivity when compressing it until it reached 430 GPa, with no observable hysteresis (dropping the pressure to 410 GPa resullted in a loss of metallic properties), I don't see how one can expect to have magnetic confinement of the exhaust without massive underexpansion and Isp losses that make it pointless

[SciMan]

There's nothing that says you can't make a jet engine work in an inert atmosphere. The catch is you have to bring your oxidizer with you.

Normal jet engine works like this: Air is compressed, fuel is injected and ignited, the exhaust goes thru a turbine to power the compressor, then thru a nozzle to produce thrust.

Inert atmosphere jet engine would work like this (changed steps are in bold): Atmosphere is compressed, a mixture of fuel and oxidizer is injected and ignited, the exhaust goes thru a turbine to power the compressor, then the exhaust goes thru a nozzle to produce thrust.

You could do turbofans, turboprops, turbojets, and even ram/scramjets using this method. However with ram/scramjets the thing ends up looking a lot more like an air-augmented rocket and less like any kind of jet engine. And yes, ram/scramjets would likely need turbopumps to pump the fuels into the combustion chamber.

Also, I think this topic wasn't originally about metallic hydrogen, so that discussion doesn't belong here IMO.

Edited May 17, 2020 by SciMan

[magnemoe]

On 4/29/2020 at 7:07 PM, KerBlitz Kerman said:

Ramjets would be nice, but probably similar to the j58 with a attachable axial compressor. I'd love ta have a scramjet in stock, but its not necessary like a ramjet

Yes we have the Panther, Whiplash and Rapier who is good realistic engines for high performance planes including spaceplanes, now larger versions of these makes sense. 
Nuclear jet engines is another issue, yes you could build them but as radiation don't exist in KSP they might be very OP, look at the Pluto nuclear ramjet without any radiation issues it would be an pretty perfect engine. 

[KerBlitz Kerman]

On 5/17/2020 at 2:55 PM, magnemoe said:

Yes we have the Panther, Whiplash and Rapier who is good realistic engines for high performance planes including spaceplanes, now larger versions of these makes sense. 
Nuclear jet engines is another issue, yes you could build them but as radiation don't exist in KSP they might be very OP, look at the Pluto nuclear ramjet without any radiation issues it would be an pretty perfect engine. 

Very good points, but I think that they'll (the staff) be most concerned about radiation (that is, if they add life support). This could be minimized with shadow shields. although it'd make docking an.... experience. 

 

*EDIT: By 'experience' I mean a royal pain in a spot that is very well known....

Edited May 19, 2020 by KerBlitz Kerman