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I am writing a Sci-Fi story that involves space ships shooting each other, as is the custom. I'm using a lot of handwavium, e.g. reactionless drives, FTL, gravity plating, etc., but I'd like the actual combat to be closer to reality. The ships mostly shoot each other with missiles from very long ranges, but occasionally get close enough to each other to shoot each other with projectile weapons strong enough to pierce each others armor.

I'm imagining a layered armor for the space ships that consists of multiple layers of plating and non-newtonian fluids. I also want to add a fluid/material as part of the armor layers that, much like a self-sealing bike tube, seals the armor against atmosphere loss if the damaged area is small enough, using pockets covering the inner layer of the hull to make sure larger damage, e.g. from a missile hit, doesn't drain the fluid from the whole hull trying to seal a ten meter hole.

Is there a fluid or other material that hardens to vacuum and might create a seal tight enough to withstand combat maneuvers or is one conceivable?

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  • $\begingroup$ Why not also use projectile weapons at long range? It's space after all- no air resistance. $\endgroup$ – Onyz Mar 16 '18 at 13:18
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    $\begingroup$ Typical engagement range in my book is in the multiple light seconds range. By the time a projectile travels the distance to the target, it already moved for several seconds, ignoring the fact that you didn't even see it's actual position when you fired the shots, making any untargeted projectile ineffective and luck based. Even at closer ranges (10'000km) it takes weight of numbers to hit a ship with unguided weapons. A missile can travel for sixty seconds and then still home in on the target and hit it, which is why those are the primary method of combat. $\endgroup$ – Morfildur Mar 16 '18 at 13:23
  • $\begingroup$ It seems to me that it's much more likely to hit someone with a projectile weapon than a missile weapon, barring some tech in-universe that I'm unaware of. Missiles are easy to see coming, and while they're guided they have to choose between being slow or having the same likelihood of missing as a projectile. On the other hand, you can predict the movement of an enemy ship (turning around is hard, at interplanetary speeds) and fire a nearly undetectable projectile at preposterous speeds instead. $\endgroup$ – Onyz Mar 16 '18 at 13:28
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    $\begingroup$ Missiles can travel at much higher g-forces than human occupied vehicles. In my story missiles accelerate at 750g, which means that to travel thirty lightseconds, they need ~20 minutes. Their final velocity is 11000km/s, over 3% of light speed. They have their own evasive maneuvers not limited by human limits on lateral movement, which, combined with their relative velocity, makes them very hard to hit. Most of the missiles do miss or are shot down, but it takes just a few to destroy or cripple a ship. The chance to hit is still fairly low, but it's more reliable than blanketing an area. $\endgroup$ – Morfildur Mar 16 '18 at 14:15
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    $\begingroup$ Missiles don't actually hit the vessel either; they just have to get close enough to let their fragments hit the vessel. Not sure if HE missiles would work without being right on the target. More importantly, missiles guide themselves to the target while projectiles just go on a straight path. $\endgroup$ – Unassuming Guy Mar 16 '18 at 14:40
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Water

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https://medium.com/starts-with-a-bang/does-water-freeze-or-boil-in-space-7889856d7f36

Jacket your ship with water. The outer hull is not insulated and so this water will be ice. Incoming rounds will expend their energy breaking and heating the ice which is good. Heated ice might become liquid or even vapor but will rapidly lose this heat to the space-cold surrounding 100K ice and regenerate the ice jacket. You might lose some vapor or liquid to space.

A metal-less outer hull made of ice covered with plastic would be pretty cool.

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    $\begingroup$ This is a blooming fantastic answer and has the added benefit of being so outrageously simple that readers of a book wouldn't see the idea coming. Jumping on Google and discovering it's exactly as you explain would give the story fabulous credibility points. $\endgroup$ – JBH Mar 17 '18 at 0:17
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    $\begingroup$ That is an interesting solution. Water does have some disadvantages like poor compressability, and I'm not sure if it would flow far enough to cover the hole before freezing. Maybe it would take saltwater or antifreeze-like solutions to lower the freezing point to give it more time to spread before freezing. It's definitely an interesting approach that I will spend some time researching. $\endgroup$ – Morfildur Mar 17 '18 at 15:26
  • $\begingroup$ Space is really bad at cooling things - there's no convection and at 0c very little radiation. Is evaporative cooling (which stops when your material goes solid) what you have in mind? $\endgroup$ – John Dvorak Mar 17 '18 at 17:45
  • $\begingroup$ A 100-kelvin chunk of ice would lose heat extremely slowly. Most likely it would heat up instead due to the presence of nearby stars. $\endgroup$ – John Dvorak Mar 17 '18 at 17:48
  • $\begingroup$ @JohnDvorak: Yes: cooling in space must be via radiant losses and so the outer hull would maximize this (and minimize radiant warming by stars so maximally reflective). The thermal mass serves it well as regards refreezing - even if some of the ice becomes hot the thermal mass of the remainder is great, and the hot water can lose heat to the contiguous remainder via conduction and convection. Also nice re water as opposed to everything else : even if it is much liquefied with repeated impacts it would still fit in the hull because it will contract as it melts. $\endgroup$ – Willk Mar 18 '18 at 17:46
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How big of hole do you need it to seal? If it is on the micro or very small scale, maybe you could use a powder that has a high Hausner Ratio, which causes powder to flow poorly and "bridge". When exposed to a vacuum, the negative pressure would pull the powder out of the hole until it prevents itself from moving any further.

However, I'm not sure what the effects of 0g have on this. I don't think it's ever been studied. I would assume thick liquids have something similar to this, but I work with powder for a living so that's my expertise.

Another thing to be aware is the cells will prevent total loss, but will also make it more vulnerable along the edge of the cells. This could be combated with a scale like layering of the cells.

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  • $\begingroup$ There's been any number of stories and films that have used a mucilage-like fluid to patch small holes from micrometeorites and the like. As you say, depending on the sizes of the breach, that's a good start. $\endgroup$ – VBartilucci Mar 16 '18 at 15:26
  • $\begingroup$ I'm not quite sure how big a projectile the size of a pistol bullet would do to the hull at relativistic speeds after it went through the plating, but I'm imagining holes around 2-10cm. For anything bigger the engineers would have to earn their pay. Scaling the armor is a nice idea, I was already trying to find a solution for the edges specifically. I'll look into the Hausner Ratio, maybe it puts me on the right track. $\endgroup$ – Morfildur Mar 16 '18 at 16:25
  • $\begingroup$ @SCMorfildur, why would you fire something so small in space is a question by itself, but let's assume a 9mm bullet (7.5g) and use this site to find the energy of the bullet at 0.9c: 2.36x10^15 joules. A 1 MT nuclear explosion releases 4.18x10^15 joules. So your 9mm bullet at 0.9c is equivalent to a one-half megaton nuke. But, like I said, why would you fire something so small? Let's send an M107 howitzer shell: 43.2Kg -> 1x10^18J ~ 239 MT. Now we're cooking with gas! $\endgroup$ – JBH Mar 17 '18 at 0:29
  • $\begingroup$ @JBH The size of the projectile that hits you it's not necessarily the size of the projectile the enemy wants to hit you with i.e. any shrapnel from missile you shoot down could still have some tiny fragments that hit you. Obviously you would like to have a massive hit to do serious damage, but this type of armor would not be likely to help in a serious breach. $\endgroup$ – Unassuming Guy Mar 19 '18 at 14:37
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It's not a fluid but self healing materials are currently being devloped around the world - https://en.m.wikipedia.org/wiki/Self-healing_material

That being said my favorite option is nanbots, at large numbers they will look like a fluid when moving and as a plus they give you an extra sci-fi feel (while still be within the hard sci-fi realm), under normal condition they resides between bulkheads but once exposed to a vacuum they have sensors that detect the air pressure drop and spring into action, covering any hole in the hull (pardon the pun) by moving to the hole and attaching to either the bulkhead or each-other until the hole is plugged.

they could also be stored in tanks with pipe leading to the outside of the hull so once activated they move on the outside hull until reaching the needed area, depending on the style you are going for seeing a tidal wave of nanobots moving on the outside of the ship to fix the damaged caused to it can be quite a scene.

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  • $\begingroup$ Nanobots are always an option, but for me they always feel too much like a cop-out. "Nanobots did it" can explain everything. It is a valid suggestion, but one I'm avoiding out of personal opinion. Thanks for the pointer to self-healing materials. It looks like an interesting topic. $\endgroup$ – Morfildur Mar 16 '18 at 16:28
  • $\begingroup$ Then how do you feel about non nano robots? think spider like things walking on the hull of the ship to the hole and spit liquid metal that hardens upon being exposed to the cold of space to close it $\endgroup$ – cypher Mar 16 '18 at 16:49
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Currently helicopters in the military have a bladder inside the bladder of the gas tank to seal bullets holes like the slim you put in tires. the bullet would pass through the first bladder the heat and contact from fuel from the bullet passing the glue seals the hole.

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