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Thread: Armor vs nukes

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    Armor vs nukes

    What would be good protection for a crewed spacecraft against a nearby sudden pulse of EM radiation, but still light enough not to totally screw up your mass ratio? Asking for hard-SF story.
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    It depends a little on the size of the spacecraft. The usual thing that is suggested it the storage of the craft's water supply (and sewage recycling), but you really would want about 2 meters of that to block the EM Gammas and charged particles from a nearby nuclear explosion. It wouldn't be low mass, but by also being useful, it can be justified.
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    Suppose a very large deep space vessel, like aircraft-carrier territory, and a burst close enough to heat the hull significantly.

    ADDED: I should say close enough to induce thermal shock in most materials.
    Last edited by Noclevername; 2020-Sep-05 at 04:49 PM.
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    Does it travel at a detectable fraction of c? I suspect that an aircraft carrier sized manned spaceship would need some thick and complex armor just to stop damage from relativistic meteoroids.
    The EM radiation will pretty much all be stopped by two meters of solid or liquid matter. Neutral muons will go through a lot more, but the explosion wouldn't generate a lot of those. It would be the case that armor very close to the explosion might evaporate quickly exposing areas behind it to more radiation than planned for. I don't have a handy formula to determine how much radiation such shielding could thermalize before turning into gas or plasma and blowing off into space.
    If you were to select a material, and a distance and an amount of energy released promptly by the explosion, it might be simple to calculate.
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    Quote Originally Posted by antoniseb View Post
    Does it travel at a detectable fraction of c? I suspect that an aircraft carrier sized manned spaceship would need some thick and complex armor just to stop damage from relativistic meteoroids.
    Nope. Slow and steady.

    The EM radiation will pretty much all be stopped by two meters of solid or liquid matter. Neutral muons will go through a lot more, but the explosion wouldn't generate a lot of those. It would be the case that armor very close to the explosion might evaporate quickly exposing areas behind it to more radiation than planned for. I don't have a handy formula to determine how much radiation such shielding could thermalize before turning into gas or plasma and blowing off into space.
    Should there be an ablative coating? I know for some designs of Nuclear Pulse Orion, a layer of oil would be sprayed onto the pusher plate to protect from the blast.

    If you were to select a material, and a distance and an amount of energy released promptly by the explosion, it might be simple to calculate.
    Let's go with 30 KT at 1000 meters. I don't know what would work best for outer materials, maybe maraging steel?
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    Quote Originally Posted by Noclevername View Post
    Let's go with 30 KT at 1000 meters. I don't know what would work best for outer materials, maybe maraging steel?
    So, the explosion would be 1.2 x10^21 ergs, and at 1000 meters the sphere has an area of 1.2x10^11 square cm, so that would be ten billion ergs per square centimeter of the surface of the ship. That would be a lot to dissipate. You might need 10 or more meters of ablative shielding... (hand-waving guess, not something I've actually calculated).
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    So, I need to back off on the energy and distance. Let's try 20 KT at 2000 meters.
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    OK, 20kT and 2000 meters reduces it by a factor of six, so only 1.4 billion ergs per square cm.
    Followup, I had been giving the total ergs for the explosion, but charts say that only 15% of the explosion's energy is in the form of ionizing radiation. About 50% is in the form of "blast energy" which in space would be the material of the bomb accelerated away from the bomb. The remaining 35% is given as "thermal energy", but in space I imagine that the thermalization of energy must be from gammas and x-rays being stopped by surrounding material and being heated up, so maybe that 15% for ionizing radiation is too low. It is worth noting that this means that for your 20kT at 2000 meters, that ship's armor will have to endure 700 million ergs per square centimeter of fairly high energy particles hitting it in a fraction of a second, after it gets hit with the (perhaps) 700 ergs per square cm of gamma rays and x-rays. Atomic Archive
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    Thanks!
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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