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Post by AdmiralObvious on Aug 9, 2018 6:53:13 GMT
Such as having an outer layer of, say RCC, some "spacing" filled with whichever fuel or oxidizer you want, and then another layer behind that? You'd need some way to suck up the fuel at the back end of the armor, but I think it would be a pretty feasible way to get some extra DeltaV. As an added bonus, provided your fuel doesn't react explosively when shot, it could also help a bit with slowing down projectiles and reducing plasma effects for the short time the gas/liquid is in the gap.
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Post by bigbombr on Aug 9, 2018 7:27:19 GMT
That would depend on the pressure that needs to be maintained. But I would worry about 'water hammers'. Using your armor as propellant tanks is fine unless it impedes it's function as armor.
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Post by orpheus on Aug 9, 2018 7:59:34 GMT
I'd be more concerned about explosive armour. By definition, almost anything that's suitable as fuel is at least somewhat combustible. But combustion in a confined space is more commonly known as explosion. There can't be that many viable rocket fuels that DON'T explode when hit by explosives, ionized outer armour, or a high-energy laser beam. The game doesn't seem to account for this (unless it does and I just haven't noticed), but IRL you can have separate fuel (combustion mass, which is burned to create heat and pressure) and propellant (reaction mass, which is the stuff ejected from the ship under pressure to actually make it move). Most or all real spacecraft to date have combined the two, using the burning fuel itself as reaction mass, but it doesn't need to be done that way (think of something like a resistojet, but using fuel combustion to generate heat instead of using electricity). Propellant doesn't need to be explosive, and actually it probably shouldn't be - water would be a good choice. So in that case, you could quite reasonably store your non-combustible propellant between hull and armour, which is functionally not much different from having external tanks that cover the entire outer surface. But the actual fuel should be somewhere more secure.
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Post by bigbombr on Aug 9, 2018 8:21:24 GMT
I'd be more concerned about explosive armour. By definition, almost anything that's suitable as fuel is at least somewhat combustible. But combustion in a confined space is more commonly known as explosion. There can't be that many viable rocket fuels that DON'T explode when hit by explosives, ionized outer armour, or a high-energy laser beam. Combustion requires an oxidizer. Without an oxidizer, there is no combustion (with the exception of monopropellants).
The game doesn't seem to account for this (unless it does and I just haven't noticed), but IRL you can have separate fuel (combustion mass, which is burned to create heat and pressure) and propellant (reaction mass, which is the stuff ejected from the ship under pressure to actually make it move). Most or all real spacecraft to date have combined the two, using the burning fuel itself as reaction mass (you're just describing combustion rockets, which is one of but not the only engine type in-game), but it doesn't need to be done that way (think of something like a resistojet (or NTR's, or MPDT's. And those are just the types in-game!), but using fuel combustion to generate heat instead of using electricity). This would lead to drastically lower exhaust velocities. Combustion rockets already have very low exhaust velocities. There would be no advantage to this.
Propellant doesn't need to be explosive, and actually it probably shouldn't be - water would be a good choice. Hydrocarbons aren't explosive if they aren't mixed with oxidizer. Water is a good propellant, just not in thermal engines (too high of an average molar mass).
So in that case, you could quite reasonably store your non-combustible propellant between hull and armour, which is functionally not much different from having external tanks that cover the entire outer surface. But the actual fuel should be somewhere more secure. What do you mean by fuel? Chemical fuel (that you burn with oxidizer) or nuclear fuel?
Try to use paragraphs. It makes your posts more readable.
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Post by jtyotjotjipaefvj on Aug 9, 2018 10:49:43 GMT
The obvious downside to this is that all your propellant is going to fly out after the first hit. I don't think it would be worth it even with segmented tanks to limit propellant loss. If you can't afford to get hit at all, why even take armor in the first place?
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Post by orpheus on Aug 9, 2018 13:08:51 GMT
Bigbombr, I wrote a long reply to your post but for some reason when I posted it, it was just an empty box. I'm short on time so I'll be a bit briefer now.
I'm aware of the need for an oxidizer in combustion. But if your ship is hit and your armour breached, there is at least the possibility of damage to the inner hull resulting in an atmosphere leak.
I know that my description specifically applied to combustion rockets. I thought that was clearly implied by the reference to real-life spacecraft, ALL of which to date have used chemical combustion rockets. I didn't mention NTRs or MPDTs because I have only a pretty vague knowledge of how they work. Part of what drew me to this game was an interest in, and desire to know more about, real-life or realistic spaceflight. This seemed like a more enjoyable way of learning than relying on textbooks alone. But there are still gaps in my knowledge, and I try not to comment on things that I don't at least roughly understand.
I also know that separating fuel and reaction mass is bad in terms of spacecraft efficiency. BUT there is a case for it, perhaps if for some reason fuel is scarce or expensive, or for a ship that isn't intended to alter its trajectory much, and which has low enough mass to reasonably be delivered to its location by another ship. In that particular instance, lower thrust might be an acceptable trade-off for NOT having to carry a huge amount of potentially explosive fuel. The case for using water as propellant is much the same. It's cheap, easy to come by, and it's hard to envisage how carrying it can be dangerous. So if you REALLY don't need a lot of mobility, it might be viable. I do realize that in normal cases it's a bad example to give, but it was just the first one that came to mind.
To your last point, both chemical and nuclear fuel shouldn't really be bolted to the outside of your ship if you can help it, at least not if you're expecting to ever get shot at. I'm aware that nuclear fuel is probably less hazardous in this context, but you still don't want it floating away when somebody shoots a hole in your armour. In extremis, one could use water or even atmosphere from the life-support system as propellant. But if you lose your fuel supply, whatever type of engine it powers, you have a lot less options.
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Post by AdmiralObvious on Aug 9, 2018 16:49:01 GMT
The obvious downside to this is that all your propellant is going to fly out after the first hit. I don't think it would be worth it even with segmented tanks to limit propellant loss. If you can't afford to get hit at all, why even take armor in the first place? I was thinking of it in more of a sense of, you have your standard fuel tanks, and then, depending on the distance you need to go, and your armor type, you could fill the extra space with additional fuel. You could also use a system in such a way that your rocket burns the "outer layer" of fuel, and then use the internal fuel tanks as your primary fuel source. If you get caught out, yeah, that's going to be really bad if someone pokes a hole in your armor, but otherwise, it seems like a good way to get some extra DV.
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Post by bigbombr on Aug 9, 2018 17:53:19 GMT
I was thinking of it in more of a sense of, you have your standard fuel tanks, and then, depending on the distance you need to go, and your armor type, you could fill the extra space with additional fuel. You could also use a system in such a way that your rocket burns the "outer layer" of fuel, and then use the internal fuel tanks as your primary fuel source. If you get caught out, yeah, that's going to be really bad if someone pokes a hole in your armor, but otherwise, it seems like a good way to get some extra DV. This makes sense. So you'd ideally use up this 'additional propellant' before encountering the enemy. It would essentially act as drop tanks you don't drop. Keeping propellant in between armor layers during combat seems like a very bad idea.
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Post by AdmiralObvious on Aug 9, 2018 18:09:07 GMT
I was thinking of it in more of a sense of, you have your standard fuel tanks, and then, depending on the distance you need to go, and your armor type, you could fill the extra space with additional fuel. You could also use a system in such a way that your rocket burns the "outer layer" of fuel, and then use the internal fuel tanks as your primary fuel source. If you get caught out, yeah, that's going to be really bad if someone pokes a hole in your armor, but otherwise, it seems like a good way to get some extra DV. This makes sense. So you'd ideally use up this 'additional propellant' before encountering the enemy. It would essentially act as drop tanks you don't drop. Keeping propellant in between armor layers during combat seems like a very bad idea. Pretty much, yeah. Why waste the resources on a disposable drop tank when the ship itself can simply hold more fuel in it's normally empty space?
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Post by AtomHeartDragon on Aug 11, 2018 7:05:34 GMT
First thing first: you need pressure vessels for your propellant, so this would take form of sticking multitude of small, balloon tanks into the spacing. They would be extremely thin-walled and have no requirement of structurally supporting themselves when emptied. The main problem I see here is plumbing - maybe some interconnected honeycomb structure would help. Depending on how critical it is to have your spacing mostly empty for your armour to function, this could work well - and you could always vent the propellant if it would interfere with armour's function.
Edit: Even if you didn't strictly *need* pressure vessels, armour's mechanical properties might suffer when cooled to cryogenic temperatures. Pressure vessels would keep contact points down to minimum.
Second, unless venting imposes too much thrust on the ship (and compartmentalization helps a lot here), penetrating armour tanks doesn't have severe implications. Yes, you do lose delta-v, but if you're using ships that are built to get hit and survive, you're either trying to establish presence somewhere or have presence there already - no matter how much delta-v you expend, you end up with ships where you wanted them and presumably within reach of assistance - any day when you're still in orbit around the same body after the battle is a good day. If you just want to hit something without establishing presence you don't send ships into combat - you send unmanned missile buses and drones, if there are any manned ships in your fleet they remain in distant fly-by trajectory doing their best to stay out of reach. Third, the main advantage of disposable tanks is that they are disposable - not only do they not require extra armour, but you can ditch the tanks themselves getting rid of unwanted mass. Intra-armour tanks are probably not going to incur much mass penalty, but this mas penalty will be there to stay.
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Post by The Astronomer on Aug 11, 2018 16:52:18 GMT
...fuel, propellant, two different things... Trust me, you do not want your nuclear fuel to get shot at.
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Post by AtomHeartDragon on Aug 11, 2018 18:52:53 GMT
...fuel, propellant, two different things... Trust me, you do not want your nuclear fuel to get shot at. Nuclear fuel *tanks* are inherently worrying.
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Post by bigbombr on Aug 11, 2018 20:59:55 GMT
...fuel, propellant, two different things... Trust me, you do not want your nuclear fuel to get shot at. Nuclear fuel *tanks* are inherently worrying. Nuclear salt water rockets for the win! This will absolutely not go wrong in catastrophic ways /s
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Post by Fgdfgfthgr on Aug 12, 2018 2:38:01 GMT
First thing first: you need pressure vessels for your propellant, so this would take form of sticking multitude of small, balloon tanks into the spacing. They would be extremely thin-walled and have no requirement of structurally supporting themselves when emptied. The main problem I see here is plumbing - maybe some interconnected honeycomb structure would help. Depending on how critical it is to have your spacing mostly empty for your armour to function, this could work well - and you could always vent the propellant if it would interfere with armour's function.
Although the game doesn't consider processing fees, I am pretty sure an armor like that is not going to be easy to build in the real world. And, you are not going to find equations about liquid armor on internet...right?
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Post by doctorsquared on Aug 12, 2018 3:38:35 GMT
While water-based NTRs, Resistojets, and MPDs lack the thrust of more energy-dense hydrocarbon-based propellants, freezing an outer layer of water (or heavy water) ice suspended between a flexible outermost layer that acts as a containment bladder (nitrile, butyl, or silicone rubbers, UHMWPE fiber, etc.) would give an ablative 'armor' layer that could be thawed by channeling the main reactor's hot coolant return loop across sections of the ship and then pumped into an internal propellant tank via a refueler. Alternatively, you could make/harvest methane hydrides and do something similar, since there would be no oxidizer the methane layer wouldn't explode.
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