Kind of a High End Gift Shop III

Speculative material culture. Mostly military but a lot of it has civilian applications (and implications).

• I was looking at the absorbency of EM radiation in water vapor, for zled lasers—since one of the main planets in my book is really rainy—and turns out, the optimum wavelength, with the lowest absorption, seems to be in the blue and green wavelengths (which is part, I believe, of why water looks blue-green). At least at "small arms" range, within 5 km or so. Nice thing with lasers is if you can see your enemy, you can basically shoot them, assuming your setup can focus a beam out to their range—they actually do work like Hollywood sniper rifles.
  
  Of course, using visual-wavelength lasers means eye-protection becomes important, though of course even human medicine let alone zled medicine can repair retinas. Prevention is still preferable to cure, though—and presumably needing your retinas regrown means you have to redo all your biometric logins. (Not an issue for zledo, who use the pores in their noses, of course.) I may have to add in mention of all their combat personnel (which includes their cops) putting in filter contacts every morning.
  
  Or maybe they leave them in and put in eyedrops every morning to protect their eyes? Ooh, nanobot eyedrops? That's it!
• Redoing my handgun round. Now instead of 8.16 millimeter it's exactly 8 millimeters, and instead of the propellant going 18 millimeters up the side, it goes 13.96. I based the revamped version on the 8 millimeter Kurz round used in the Sturmgewehr 44, which can get a muzzle energy of 2,197.55 Joules from a 6.998 gram bullet, using 1.847 grams of propellant—which comes to 776.1 milligrams if you replace the nitrocellulose with denatured ONC.
  
  776.1 milligrams of ONC has a volume of 392.168 cubic millimeters; the "shoulder" diameter of 8 millimeter Kurz is 11.4 millimeters. A propellant "casing" of that diameter thus has a thickness of 1.7 millimeters around an 8 millimeter bullet, and goes 13.96 millimeters up the side; its designation thus becomes "8 × 14". A normal 8 mm Kurz bullet (pointier than most handgun rounds) is 24 millimeters long, which means the overall length of this thing is 25.7 millimeters, or just over an inch.
• Since I think I did my handgun round different than I did my rifle rounds, let's double check. My rifle bullet is 7 millimeter by 31 millimeters. The propellant "casing" sticks out from it 1.6 millimeters, for a diameter of 10.2 millimeters—it was 1.85 millimeters and a diameter of 10.7 millimeters, but I'm using the "shoulder" diameter of the model cartridge (6.8 Remington SPC) now. Its 1.497 grams of denatured ONC propellant has a volume of 726.699 cubic millimeters. That, calculated the new way, goes 21.9 millimeters up the sides of the 31 millimeter bullet, resulting in an overall length of 32.6 millimeters; I guess we'll change these to "7 × 22" rifle rounds.
  
  The antimateriel round is 13 millimeters by 60 millimters and its 15.966 grams of ONC propellant has a volume of 7,750.68 cubic millimeters. Going with .50 BMG's "shoulder" diameter of 18.7 millimeters, we have a "casing" that sticks out 2.85 millimeters on each side and goes 54.4 millimeters up the side of bullet, resulting in a 62.85 millimeter-long round, which I guess would be called "13 × 54".
• Apparently power of a cartridge rises with the fourth power of propellant mass. Which is interesting, because another thing that rises with the fourth power of something else, is the efficiency of a heat-radiator, which increases with the fourth power of temperature (but only linearly with area, so you really want to make your radiator as hot as possible—hence why I make mine out of magnetically-constrained plasma).
• Some impressive people at MIT and the Lawrence Livermore National Lab are working on a metamaterial that's only as dense as aerogel, but thousands of times stronger. What this will eventually mean is you can replace a lot of the structural parts of a space vehicle or aircraft with something 17.56 times lighter than aerospace aluminum alloy (0.16 grams per cubic centimeter vs. 2.81).
  
  Now, you can't replace everything with this stuff. Armor, for example: density is at least partly non-negotiable, for that—especially for armor against energy weapons. But you can make all the other parts of a vehicle out of something that weighs only 5.7% as much, which means you might as well just have to pay for the fuel to move the armor and engines (and fuel/propellant tanks—aerogel is highly porous, so you can't really use it for that).
  
  Occurs to me that another application is the frames of tanks, including the walking kind. You might well be able to have an M1 Abrams-equivalent tank with the mass and therefore mileage of a Bradley (given the armor alone on the Abrams seems to be over 20 tons).
• Let's crunch the numbers for a walking mecha. Atlas, the Boston Dynamics walking robot, masses 150 kilos and is 1.8 meters tall; scale it up to 10 meters and its mass becomes 25,720 kilos. Except that if you swap out the structural meta-aerogel for the alloy in its frame, which seems to be a titanium-aluminum one (like TC4, density of 4.43 grams per cubic centimeter), you drive the weight down to a paltry 928.94 kilos. Where before it took 634.43 kilowatts to power it, it now takes only 22.9. So basically the only major power-constraint on the mecha becomes the weight of its armor and weapons.
  
  Suppose we take the Advanced Bomb Suit used by US military EOD as the model of mecha armor, EOD suits being about the only full-body armor we make. That masses 27.2 kilograms when made (almost entirely) of Kevlar; a composite metal foam has one-third the density of typical tank armor, which is made of (among other things) steel alloy with a density of 7.8 grams per cubic centimeter, which yields a density for CMF armor of 2.6 g/cc. Kevlar's is 1.44, so an ABS made of CMF would mass 49 kilos; scaled up for a 10-meter mecha and you get 8,420.97 kilos. Moving that plus the 928.94 kilo frame—total mass 9,849.91 kilos—still only uses 242.97 kilowatts.
  
  If we give that the equivalent of two M261 rocket launchers, each holding the equivalent of 19 Hydra 70 rockets—each massing 470.38 kilos, so total mass 940.75 kilos—and a 1,282 kilo tank gun like the L7 used on western tanks, plus 40 rounds of the equivalent of M829 anti-armor shells, total weight 744 kilos, we still have a mass of only 12,816.66 kilos, requiring only 316.15 kilowatts of power.
• Of course, the tank-guns I'm using for a model aren't electromagnetically accelerated, and the ones on this weapon-system would be. A railgun is apparently only capable of about 50% efficiency in converting power to muzzle energy; given the muzzle energy of an L7 gun is 20.9529 megajoules, and 10 of those shots per minute is a net power of 3,492,150 watts, i.e. 3,492.15 kilowatts. You can do that four times when the tank carries 40 shells, which comes to 13,968.6 kilowatts—a power requirement of 27,937.2 kilowatts given 50% power-plant efficiency. That increases the total power-requirement to 28,253.35, of which almost all is the guns.
  
  Suppose that we give it the same size of power-plant as on Atlas when it has a battery, which (given it can run off a 3.7 kilowatt-hour battery for 1 hour, and the average energy-density of lithium-ion batteries of 182.5 watts per kilo), presumably masses 20.27 kilos—which comes to 3,476.33 kilos on a 10 meter version, bringing the total mass up to 16,292.99 kilos, say 16,293 for simplicity, and an energy-requirement of 401.9 kilowatts (28,339.1 with the railgun). Going with the energy-density of optimized silicon-air batteries, 14.2286 kW·hr per kilo, 3,476.33 kilos yields 49,463.31 kilowatt-hours—21,526.11 not counting the railgun. That's enough to provide 53.56 hours of operation.
• Hell, 16,293 kilos is far under the 27,400 kilo max takeoff weight of the V-22 Osprey: let's slap a pair of 440 kilo airplane engines (but not turboprops) on there, for a weight of 17,173 kilos and a powerplant requirement of 423.6 kilowatts. You'd also swap out the 2,026 kilos of tank gun and shells for 529.5 kilos of an M61 Vulcan equivalent plus feed system and ammo, but that only brings the total power requirement to move the thing by 37 kilowatts, to 386.6.
  
  Of course the Vulcan is also electromagnetic, with a muzzle energy of 54 kilojoules and a fire rate of 6,600 per minute, which comes to an energy of 5,940 kilowatts, 11,880 with 50% efficiency. Except it can't fire the full 6,600; it carries a fraction of as many (an F16 carries 511, for example). That brings the actual practical energy requirement down to 919.8 kilowatts, for a total to walk around and fight with the thing, of 1,306.4 kilowatts. That'll let this model walk around for 125.57 hours.
  
  But, this is the flying one—something along the lines of the OZ-07AMS mobile suit. And its engines would require (assuming an average improvement over internal-combustion engines of 3.5×, and the Osprey's engines having a power output of 4,596 kW) 1,310.29 kilowatts, each, and it has two, so 2,620.56 kilowatts; of course, it either flies or walks, never both. Flying and shooting requires 3,530.36 kilowatts, and the thing can fly around for 18.52 hours.