Some Leviathan Numbers

[avatar (Alistair Young)]

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@Scott <scott.kenny@gmail.com> on 2018-09-11 23:56:25 wrote

This of course begs the question of what kind of warhead the Eldrae normally stuff into their railguns.

@Alistair Young <athanasius.skytower@arkane-systems.net> on 2018-09-12 01:04:51 wrote

Coilguns, technically.

And while the big advantage of coilguns is that you can launch pretty much anything from AKVs to yeast, the most common load is plain old dumb k-rods, often plain iron because it’s cheap.

The IN certainly has a plethora of specialty warheads which it can load and fire, various of which are usually carried by mission requirements and captains’ preferences, but with the energy-on-target that a dumb slug can deliver, strapping a fancy warhead to it for regular use is just gilding the lily.

@MirrorField <mirrorfield@gmail.com> on 2018-09-19 02:26:17 wrote

I’m also assuming that with navy coilguns there is also some interesting vector control trickery involved.

Also, playing around with various internet calculators one can see that that same 10.1 Exajoules (typo in original or am I entirely incorrect? It’s been few years since my physics classes…) are sufficient to propel a 1 kilogram projectile to high-order relativistic regimen (ie. to about 0.997c, including gamma). Note that the interstellar medium would, at that velocity regimen, erode such projectile to harmlessness in just few weeks or months.

Of course, Our Gracious Host noted that the limitations are in projectile acceleration so that those near-c projectiles are currently impossible. Still, probably a hot research subject given the obvious tactical advantages.

@Ru <shearwater+eldraeverse@gmail.com> on 2018-10-01 14:58:48 wrote

that same 10.1 Exajoules... are sufficient to propel a 1 kilogram projectile to high-order relativistic regimen (ie. to about 0.997c, including gamma).

So, bit late to reply to this one, but for future reference… there are Problems associated with whacking that much energy into a small thing in a short time. I touched upon this briefly in the original leviathan thread. There are three basic problems:

Inefficiency. Some of the energy used to accelerate the slug will be lost as heat. Some of that heat will be developed in the slug. When your gun is this powerful, a teeny tiny fraction of its energy is enough to explode the slug in the gun barrel. Nothing made of matter is refractory enough.
Material limits. That’s a lot of force on a very small object. Pretty certain it exceeds its yield strength by some margin. If it doesn’t actually explode, it will certainly be splattered pretty thoroughly by the time it leaves the barrel. Nothing made of matter is tough enough.
Accelerator limits. Coilguns ain’t magic; even with space-elf supertech, there are magnetic field limits. Gotta synchronize those coils, gotta quench them ASAP. High-relativistic projectiles make this waaay more difficult, even assuming that the materials it is made out of can even cope, which they might not be able to.

TL;DR: You can’t have relativistic projectile weapons mounted on your spaceships. Quite frankly, you should feel lucky that you’ve got the .036c ones. And even then, the numbers might not have been scrutinised closely to see if they really are sufficiently plausible.

@Ru <shearwater+eldraeverse@gmail.com> on 2018-09-12 13:30:20 wrote

I had written a reply to this, but it seems to have disappeared. Sorry for the double post if it resurfaces.

Anyway, warheads seem like they’d be most useful for specialized things (at least two have been mentioned in nanofics past…) as in the general case it is hard for Big Dumb Slugs to get mission killed by point defense, and things like one-shot lasers or particle beams or plasma whatever devices would seem to be poor choices against the sorts of ship armor available (modulo comments I made in a thread some time past about the possible breakdown of thermal superconductivity in the face of ionization or lattice defects…)

@Scott <scott.kenny@gmail.com> on 2018-09-12 12:56:23 wrote

Thanks for the quick answer!

What I’d meant was, if gigatons is the upper limit, what’s the typical power level the Imperial Navy throws around?

@Ru <shearwater+eldraeverse@gmail.com> on 2018-09-12 13:25:00 wrote

it’s gonna take enough time for the shipboard powerplant to put ten exawatt-seconds in the flash accumulators that you sure aren’t going to be able to fire one of those shots every second, or anything close enough to it to avoid being a big, fat, wallowing target

As per my (possibly incorrect) calculations in the last leviathan post, the pion drive running at cruising power levels produces ~16 exawatts of gamma radiation. Obviously, lots of that will radiate in the wrong direction, and harvesting any of it without cooking yourself with excess heat is hard, but not implausible. Do the eldrae have gamma voltaics?

Cranking the engine up a bit but tapping the energy of all those extra charged pions via direct energy conversion instead of as thrust via a magnetic nozzle is also not a bad idea, and somewhat less magitechy. That’s a couple of extra exawatts right there, anyway.