Protect Yourself, Or Deal Some Damage

Skyrim line, smiths say it. Good title for a post about weapons and armor.

• Really got down to brass tacks about my armor. At times it felt like I was crawling over the brass tacks. But now I know pretty much exactly what my armor is made from, both human and zled. The zled armor is a boron-nitride nanotube suit under plates of a metamaterial that, though little more massive than silica, can shift its structure in nanoseconds to meet an attack with the (local) density of osmium and the melting-point of tungsten. In between there's a suit of auxetic foam, like we're currently experimenting with for blast-curtains and EOD suits. Decided zled irregular troops don't wear STF armor, they just wear the auxetic-foam/BN nanotube armor without the metamaterial plates. (One benefit the BN gives is radiation-shielding, especially vs. neutrons.)
  
  The humans' STF armor is actually nanotube-reinforced polymer textile (somewhat like Kevlar, but not Kevlar—I went with a different kind of polymer, because some of the properties I needed to know don't exist for aramids e.g. they don't melt, they sublimate/disintegrate), soaked in a polyethylene glycol gel with silica in it. As I said, PK special-forces wear only a "union suit" made of the stuff, while the heavier armor also features a cuirass and some limb-plates made of stiffer panels of the same material. The VAJRA powered armor is two-layer, the inner being ferrofluid—nano-scale magnetite powder suspended in PDMS (siloxane)—governed by sensors much like the ones in magnetorheological brakes, but much faster, single-digits of microseconds rather than milliseconds. The outer layer is boron carbide sandwiched with good old-fashioned homogeneous steel; the whole thing, minus power-plant, environment-system, and power-lifting system (i.e. just the armor itself) weighs about 18.5 kilos.
• While I was torturing myself doing this, I came across a way for the zledo to tune their lasers: one of the things you can do with optical metamaterials is tunable filters. One paper I found involved a filter tunable over a range of 3,650 nanometers, although it started at near-infrared and went into mid-infrared, whereas what I need is near-infrared to near-UV—but that's a range only 770 nanometers across, so once one has the tech to tune to UV at all, in principle tuning to near-IR is relatively simple.
• Other things I came across doing this? Nanocellulose, which is extracted from cyanobacteria or wood pulp, and is clear, stronger than Kevlar, and electrically conductive. They're thinking of using it in organic LED displays that can be rolled up, certain window applications, and it can also be used as, e.g., food thickener, because it's still just "dietary fiber". Its one weakness? Still cellulose, and not very dense, therefore it soaks up moisture—even from air—and puffs up. At the very least, serious waterproofing is required.
  
  I think the humans make windows and maybe display-screens out of aluminum oxynitride...which is also known as "transparent aluminum". You can get better performance from 4.1 centimeters of AlON than from 9.4 centimeters of bulletproof glass—the AlON will stop .50 BMG at that thickness (presumably only from a certain distance), glass won't—so it'd obviously be a popular choice for e.g. VIP vehicles.
  
  A substance that I think zledo and possibly also humans put as a coating on weapons to let them cut through practically anything, is n-tert-butoxycarbonyl-protected diphenylalanine, or BOC-protected diphenylalanine to its friends. It's apparently as strong as Kevlar and can only be scratched by diamond—and in itself it's clear (but pH dependent, apparently, so you probably don't want to make your whole weapon out of it—"got to periodically re-apply the coating" vs. "the whole blade dissolved").
• It occurs to me that, if you're going to use Raufoss-style HEIAP rounds in your coil vulcan, while only firing at the muzzle velocity of modern .50 BMG, then why not use .50 BMG and leave the coil part at home?
  
  So now the coil vulcans still shoot .50 BMG Raufoss-type HEIAP rounds, but shoot them at a muzzle velocity of 1,578.445 meters per second—giving them the same muzzle-energy as 20 millimeter, before the HEIAP is factored in, i.e. basically giving the same performance as 20 millimeter HEIAP rounds from a 13-millimeter package.
  
  Assuming it scales linearly, that muzzle-velocity means power-requirement per shot of 53,867.5675 joules, which, with silicon-air batteries, means that 1,000 shots uses a silicon-air battery massing only 1.052 kilograms.
• To calculate the total weight of a VAJRA suit, we add in the weight of the power-assist exosuit and an air-recycler. The Warrior Web weighs about 9 kilograms, so we'll say the VAJRA version—which will let you flip, though not throw, a car—is the same. The lightest scuba rebreathers I can find weigh 15 kilos; while what a VAJRA suit has is not just a rebreather but a true air-recycler, that's a good figure for the weight we're talking about.
  
  That, of course, brings the total mass of the suit to 42.5 kilos, the weight of a twelve-and-a-half-year-old. The exosuit, of course, cancels that out, and the weight also makes it a lot easier to, e.g., stand up to the recoil of your "muzzle energy (therefore recoil) of a 20-millimeter" coil-vulcan. It also makes it slightly harder for a zled to just fling you like a rag-doll, though not enough harder that it actually prevents it ("All right, we'll goad this guy into tossing us like unwanted toys. After eight or nine of us, he'll be too tired to keep fighting!")
• This article on coilguns and railguns says, about using them for anti-missile CIWSs, quote:

  If incoming round interception can be accomplished with good reliability, it will make armored vehicles as obsolete as knights on horseback.

  Can you count the errors in that sentence? I see at least two. One is, "good reliability" is not the same thing as "100% reliability". We've had missile-interceptor CIWSs on ships for decades, we still armor them.
  
  The second is, knights in armor weren't rendered obsolete because of something that shot down bullets; they were rendered obsolete because bullets became good enough that wearing enough armor to stop them became prohibitively heavy. Taking the risk of not having armor rather than have to slog around 50 pounds of steel, was the option they went with; there was no alternative to armor (except "run for cover more quickly than armor permits") that did it.
  
  Besides, what if your enemy decides that, indeed, anti-tank missiles aren't worth the effort, because of your electromagnetic CIWS...and then he shoots your vehicle with a laser, or with an EM gun much like the one your CIWS uses (e.g., a 30 mm coil version of the A-10's GAU-8 Avenger, which is also used on the Goalkeeper CIWS)? Boom (literally)—bet you wish you'd had some armor on that slag-heap that used to be a vehicle.
• I realize, of course, that recoil force ("felt recoil", anyway) is a fraction of actual muzzle-energy, but, on a spaceship at least, it isn't all that different. Recoil on a planet goes down into the ground through the shooter's body, or through the mounting of a mounted gun, but recoil on a spaceship has nowhere to go. (The same is also true of airplanes; certain large autocannons—the Gsh-6-30 on the MiG-27, notably—need special mountings, and still cause unpleasant noise and vibrations, the latter of which can even damage fuel tanks, avionics, and landing lights.)
  
  Another factor is that rail- and coilguns are quite likely to have more recoil forces than firearms, since their "ejecta" consist of a bullet and a negligible mass of plasma, whereas a firearm is ejecting all the gases produced by burning its propellant, along with the bullet. You can put vents on the top or sides of a firearm's muzzle to let some of the ejecta escape at a different angle; that's not possible on an electromagnetic gun. (Maybe some kind of counterweight piston like in the AEK-971, self-contained—maybe connected directly to the bullet's motion down the barrel—rather than using propellant gases?)
• Recall, please, that the reasonable distance for space-combat is one light-second, which is just a bit under 300,000 kilometers. How to design a space missile? Let's start by giving it a dry mass equal to the launch-mass of the biggest air-to-air missile ever, the Soviet K-100 series, since those 750 kilograms are going to be necessary to hold our 600-kilo magnetic-confinement fusion rocket. Then give it a mass-ratio equal to that of the AMRAAM (19:11, given its I_sp of 254 seconds and cruise speed of Mach 4—I don't think that's a national-security issue).
  
  That mass-ratio, coupled with MC fusion's 8,000,000 meters per second exhaust velocity, results in a delta-v of approximately 1.5% (1.4678%) the speed of light. That can cross a light-second in 68.13 seconds, or 4,400.37 kilometers in one second flat. A direct hit of an entirely-empty missile, at that speed, hits with the force of a 1.74 megaton nuke; since the most space available for the warhead is 136 kilos (if it scales like the KS-172), the actual explosive (not counting the kinetic kill—you don't make space-missiles dependent on direct hits), and the maximum achievable in a nuke is 6 megatons per megagram, the explosive yield of such a missile is 816 kilotons, around the yield of Soviet RT-2PM Topol ICBMs.