Comments on: THE CRUCIBLE OF EMPIRE — Snippet 38

By: Johnny

Johnny — Sun, 13 Dec 2009 02:13:12 +0000

You’re right that railguns only need conductive projectiles, and kind of right about how railguns compare to chemical propellants. There’s no speed of sound limitation on chemical projectiles; my .270 has a muzzle velocity of 2960 ft/s, which is about three times the speed of sound. However, railguns are superior in that they don’t have a real limit on velocity; the projectile will accelerate more with a longer rail and a stronger current. Chemical propellants are limited due to the rate of expansion of gas. However, a huge problem with rain guns is that the rails degrade over time from the projectiles. If the ship doesn’t want to keep replacing rails, chemical is the way to go. However, a 64 mJ railgun like is in development now would cause massive damage to a ship. I imagine the big chemical guns were guns they could build in a year. There’s no point in building a railgun that shoots a projectile with more energy than a 16 inch shell if it takes 5 years to develop and the Ekhat show up in 3.

By: Cypherpunks

Cypherpunks — Sat, 12 Dec 2009 06:00:32 +0000

No, railguns do NOT require a megnetic projectile; they require a CONDUCTIVE projectile, or a conductive base. Most tests copper or aluminum slugs, although some use metal foil to start an arc behind a plastic block.

Railguns are inferior to good chemical propellants in all ways except one: they have no speed-of-sound limitation.

Although I can understand Eric not wanting to bog down the narrative with technical details (this story is about the cultures, not the technologies, and I appreciate that), I wish I understood Ekhat/Jao propulsion technology better. I assume it’s reactionless, or we’d remember the Kzinti lesson…

By: Johnny

Johnny — Fri, 11 Dec 2009 00:27:54 +0000

The entire Lexington might have heat sinks for railguns, true, but the railguns aren’t evenly spaced out through the ship; they’re all in weapons spines, that are easily detatched and so probably not as connected into heat transfer pipes like the rest of the ship. Not only that, but shooting a 500mm depleted uranium round that masses in the neighborhood of 50-100 tons would require a huge amount of power. Maybe it was easier to just have enough power come to the spines for lighting and computers and use chemical propellants that were “good enough.” They still had lasers for long-range engagements, and the spines to provide more armor.

By: Grant

Grant — Thu, 10 Dec 2009 18:54:49 +0000

Sorry, “near relativistic” was off the cuff and a poor choice of terms. But we are talking velocities that are multiples of what any chemically propelled round are going to acheive. And the plasma in the photosphere, while not terribly dense, is hot as hell. A projectile having to tear through it at many thousand m/s is taking a serious beating. Adding additional stresses to the equation when you already have a working solution just seems ill advised even without the heat-sinking problems for the ship the other posters have raised.

@Masterson: Railguns use electromagnetic acceleration. You need a magnetic projectile for it to work properly. And before the humans gave them the idea of using kinetic weapons the Jao and Ekhat were incapable of fighting battles in the photosphere precisely because their weapons tech (including their missiles) was useless inside it. That’s mentioned in ‘Course’…. whatever shield tech the Jao use for their ships isn’t adaptable to missiles. At least not as things stand now. IThe system is no doubt mass intensive.

By: robert

robert — Thu, 10 Dec 2009 18:38:45 +0000

Based on past works, neither author has exhibited a lot of concern with future tech, unlike David Weber, who may even overdo it at times. Their oeuvre is more about human-human and human-nonhuman interaction and behavior under unusual conditions. So whatever they do in the way of weapons and space transport (modified submarines indeed! What fun.) does not really matter in the context of the story being told. It is what it is or not. But that does not mean that the reader can’t have some fun with the stuff that is there.

And I see the sequel to Boundary is due in June, speaking of unusual conditions. Will there be snippets? Actually a lot of stuff is due in that timeframe so snippet-world should be rich.

By: Mr. Masterson

Mr. Masterson — Thu, 10 Dec 2009 14:34:12 +0000

Pretty impressive conversation. I like how everyone kept on target yet also thinking outside the box. I have to agree I was little through back when I read chemical propellant for the rail-guns. The firing of a missile at such distances seems like it would be easy for any EK antimissile defense to tackle. Unless their some sort of stealth mode. And using a rail-gun to fire such a massive round at near-relativistic velocities you won’t be able to control it like some torpedo/ missiles. They’ll fly straight and true. It’ll only work if your close or you have software that compensate for movement and distance. I wonder does it mater if your using DU rounds at near-relativistic velocities. I mean doesn’t the round become the forth stage of matter a that point. Another point about rail-guns I was lead to believe was that a rail-gun could fire any material down it’s coil as long as the round is shaped right and sure metal probably works better, but the point is a rail-gun is like beef up particle accelerator right? Also you guys must be right about the heat on the ship because of the photosphere it must be a JAO tech. with a few Human tweaks. They probably have that same tech. for the missiles too. But what do I know?

By: saul

saul — Thu, 10 Dec 2009 06:06:12 +0000

You convert it to electricity, or you use a laser as a heat pump.

Just a note, we have no idea what warheads they will decide to use. They are probably working on the assumption the EK have not received reports of the last battle or had time to adapt either way. As such, DU rounds might not be the sort that is desired.
They might even go for shaped rounds designed to penatrate a dense liquid/gas. ie like the anti-torpedo rounds shaped to pass through water at high speed.

By: Just me

Just me — Thu, 10 Dec 2009 06:06:04 +0000

You sink heat into your heat sinks, obviously. You don’t radiate it into space in a photosphere, and it has to go somewhere, so you need to have heat sinks. They hold the heat until the ship is in a situation where it can actually start radiating heat into space again. Unless you prefer the heat to just build up generally throughout the ship until it starts frying delicate and necessary electronic components. And crew members.

By: Mike

Mike — Thu, 10 Dec 2009 04:16:47 +0000

Where do you sink heat to, inside a photosphere? That makes no sense.

By: Just me

Just me — Thu, 10 Dec 2009 03:40:40 +0000

A vessel the size of the lexington, intended to operate within the photosphere of a sun, will almost certainly have heat pumps and heat sinks adequate to deal with any number of railguns - especially since you can hardly pretend the chemical propellants are heat-neutral. I’m more inclined to believe that it’s a matter of chemical propellants being proven technology, with limited time to innovate before finalizing the design, and possibly that railguns would just be overkill for the ranges and velocities expected in framepoint combat.