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Post by airc777 on Jan 19, 2019 3:23:22 GMT
How mechanically feasible is it to build an active anti laser defense instead of building passive ablative armor? Obviously, eventually a big enough laser focused on a small enough area will win, but:
Say you wrap the hull (or at least a section of it that you can keep pointed towards the laser threat) in something like a plasma window, then you fill the void between the plasma window and the hull with a gas meant to diffract the laser and diffuse heat, then you have impeller pumps cycling the gas through a radiator on the opposite side of the ship to dump the incoming heat. Or would you use an opaque gas and try to absorb all of the heat directly instead of diffusing it?
Our lasers make what, 4% of their energy as heat on target and 96% of there energy as waste heat?
I think this boils down too:
A) What depth of diffraction and diffusion medium do you need for this to be mechanically viable?
B) Could you build a system to protect a ship that used the same or less energy then the weapon system it's trying to defeat?
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Post by bigbombr on Jan 19, 2019 5:26:54 GMT
How mechanically feasible is it to build an active anti laser defense instead of building passive ablative armor? Obviously, eventually a big enough laser focused on a small enough area will win, but:
Say you wrap the hull (or at least a section of it that you can keep pointed towards the laser threat) in something like a plasma window, then you fill the void between the plasma window and the hull with a gas meant to diffract the laser and diffuse heat, then you have impeller pumps cycling the gas through a radiator on the opposite side of the ship to dump the incoming heat. Or would you use an opaque gas and try to absorb all of the heat directly instead of diffusing it?
Plasma windows require a lot of energy to run and produce plenty of waste heat of their own. They're probably unsuited for this role.
Our lasers make what, 4% of their energy as heat on target and 96% of there energy as waste heat?
Yes, but IRL combat lasers have efficiencies well over 30%, and efficiencies of 70% have been achieved in labs.
I think this boils down too:
A) What depth of diffraction and diffusion medium do you need for this to be mechanically viable? Depends on mass flow and heat capacity of the medium. Refraction and scattering are probably not practical as they'd probably require a thickness multiples of your main ship hull. Absorption might work, but then you need a high mass flow, and pulsed lasers will mess with containment.
B) Could you build a system to protect a ship that used the same or less energy then the weapon system it's trying to defeat? In atmosphere, you could use a laser to heat the air and make an incoming enemy beam less effective through atmospheric lensing.
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Post by airc777 on Jan 19, 2019 6:09:58 GMT
Plasma windows require a lot of energy to run and produce plenty of waste heat of their own. They're probably unsuited for this role. I was aware of that, I still think you could make this work economically even if it had to be a very small plasma window covering just the very front of a long and thin craft. I didn't think a solid transparent barrier would work because it would have to be perfectly transparent to all of the wavelengths of every laser system the enemy was using in order for it to withstand the attack. I didn't think actively cooling the hull directly would work either because a laser could still overwhelm a small spot on the armor.
Yes, but IRL combat lasers have efficiencies well over 30%, and efficiencies of 70% have been achieved in labs. Oh, you mean I could get away with twenty times less radiator area on my laserstars? Yeah, that would be a major problem.
In atmosphere, you could use a laser to heat the air and make an incoming enemy beam less effective through atmospheric lensing.
Cool, but that would be really limiting for our purposes here.
Would it perhaps be more mass efficient then ablative armor and/or easier to achieve the desired effect then the idea above to instead just vent an opaque gas directly in front of where ever the laser is hitting? Perhaps just storing the gas in the void between the Whipple shield and the spalling liner layers of our armors so as soon as the laser creates a hole it vents the gas through the correct area.
It would only be seconds of protection and not theoretically as long as you could power the plasma window, but you would be using all of the mass of the opaque gas to protect the ship, not just all of the mass of the solid ablative armor directly in the path of the laser.
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Post by bigbombr on Jan 19, 2019 9:19:53 GMT
Would it perhaps be more mass efficient then ablative armor and/or easier to achieve the desired effect then the idea above to instead just vent an opaque gas directly in front of where ever the laser is hitting? Perhaps just storing the gas in the void between the Whipple shield and the spalling liner layers of our armors so as soon as the laser creates a hole it vents the gas through the correct area. It would only be seconds of protection and not theoretically as long as you could power the plasma window, but you would be using all of the mass of the opaque gas to protect the ship, not just all of the mass of the solid ablative armor directly in the path of the laser.
This might work, and the expansion of gas has a cooling effect (p*V=N*R*T). I personally am more fond of solid armor (especially carbon allotropes) because they allow for non-ablative defense below a certain intensity threshold (against continuous lasers, pulsed lasers will reach ablation intensities easier). As the armor gets hit by a laser beam, it will heat up, but as its temperature increases it starts radiating more and more heat away (the same way as a radiator), and as radiated power scales with the 4th power of temperature (in Kelvin), materials with a high melting point can withstand decently high intensities without any ablation at all. For any type of laser armor, heat capacity is also very important, as this dictates how much energy is required to heat up a given mass of armor by one Kelvin. A higher heat capacity means the laser needs to expend more energy to heat up the armor. Next up, heat of fusion and heat of vaporization are also important, as they dictate the amount of energy per mass needed for a fase change. The higher these values, the more of a cooling effect the melting and vaporizing of armor will have on the underlying armor, providing some protection. Against pulsed lasers, you also need mechanical strength to resist cratering. Keeping pressurized gas inside your armor might impart a lot of mechanical stress on your armor, especially as the armor and the gas start to heat up. I'm not sure if a gaseous heatsing as ablative laser armor would be worthwhile, but I'd love to test it out. Keep in mind that what I just discussed is more in detail than what the game accounts for. The game accounts for heat capacity and melting point, it doesn't account for heat of fusion, heat of vaporization, heat radiation by the armor, mechanical stress on the armor by the rapid heating, ... The game also has material-specific maximum ablation rates, meaning aramid fiber and polyethylene make in game the best anti-laser armor while IRL graphite and amorphous carbon would be much better. When the ablation cap was removed by someone for testing by editing the game files, amorphous carbon turned out to be the best anti-laser armor. For more information on laser ablation and armoring against lasers (and a lot of other hard scifi stuff), I recommend the ToughSF discord (https://discord.gg/ZQrE4Z9).
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Post by airc777 on Jan 19, 2019 19:12:18 GMT
What about deploying an opaque ionic liquid to sit on the surface of the craft and then actively cooling the liquid? Ionic liquids can handle a strong vacuum for a long time without boiling. Could you get away without containing the liquid at all if you only needed it to provide a few minutes protection? Could it be possible to find a liquid that would take longer to boil off due to vapor pressure then it would for amorphous carbon to fail due to the laser and then actively cool it?
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Post by bigbombr on Jan 19, 2019 19:19:45 GMT
What about deploying an opaque ionic liquid to sit on the surface of the craft and then actively cooling the liquid? Ionic liquids can handle a strong vacuum for a long time without boiling. Could you get away without containing the liquid at all if you only needed it to provide a few minutes protection? Could it be possible to find a liquid that would take longer to boil off due to vapor pressure then it would for amorphous carbon to fail due to the laser and then actively cool it? Depends on the vapor pressure of the fluid. It might work, but I get the impression that more conventional armor gives a better protection at a lower mass for longer periods of time. I'm not sure though, as I haven't looked into the particulars. Though fluids would be able too tolerate much smaller increases in temperature.
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Post by doctorsquared on Jan 20, 2019 3:03:33 GMT
You could build layers of polymer blended with or thin films of metal hydroxides like aluminum trihydride or magnesium hydroxide that undergo an endothermic reaction that yields water vapor that cools the surface and sinks heat when undergoing combustion. When a polymer is blended with a metal hydride and a synergist compound like zinc borate or antimony trioxide you can have a compound that will still heat up and undergo thermal decomposition but the rate of heating will be reduced and any volatiles yielded will undergo Fridel-Crafts Alkylation to form a less dense char layer on the surface that will increase the thickness that needs to be burned through. This is mostly used here on Earth as a non-halogenated flame retardant for plastics.
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Post by bigbombr on Jan 20, 2019 7:01:01 GMT
You could build layers of polymer blended with or thin films of metal hydroxides like aluminum trihydride or magnesium hydroxide that undergo an endothermic reaction that yields water vapor that cools the surface and sinks heat when undergoing combustion. When a polymer is blended with a metal hydride and a synergist compound like zinc borate or antimony trioxide you can have a compound that will still heat up and undergo thermal decomposition but the rate of heating will be reduced and any volatiles yielded will undergo Fridel-Crafts Alkylation to form a less dense char layer on the surface that will increase the thickness that needs to be burned through. This is mostly used here on Earth as a non-halogenated flame retardant for plastics. Does it work in a variety of pressures though? But it does seem interesting. This is the first time I've heard of this type of anti-laser armor.
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Post by doctorsquared on Jan 20, 2019 19:28:27 GMT
You could build layers of polymer blended with or thin films of metal hydroxides like aluminum trihydride or magnesium hydroxide that undergo an endothermic reaction that yields water vapor that cools the surface and sinks heat when undergoing combustion. When a polymer is blended with a metal hydride and a synergist compound like zinc borate or antimony trioxide you can have a compound that will still heat up and undergo thermal decomposition but the rate of heating will be reduced and any volatiles yielded will undergo Fridel-Crafts Alkylation to form a less dense char layer on the surface that will increase the thickness that needs to be burned through. This is mostly used here on Earth as a non-halogenated flame retardant for plastics. Does it work in a variety of pressures though? But it does seem interesting. This is the first time I've heard of this type of anti-laser armor. That would be something that would have to be tested out, and I've really only encountered this used in plastics for wire and cable jacketing in the aerospace and telecom field. I'm mostly hypothesizing that if ~1mm of it can survive exposure to a 500W flame for thirty seconds without burning clean through (per Underwriters Laboratories spec at room temperature under one atmosphere of pressure) it might have applications as an ablative coating.
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