## Wednesday, January 5, 2011

### Some more considerations for spaceship design

Today we're doing more work on the properties of spaceships. If you'll recall, in October (good lord I need to update more often) I wrote that spaceships have the following properties:

How hard it hits
How many hits it can take
How accurately it fires
How fast it can move
How much it can carry

Again, all of these numbers depend on the other ones, so defining them will be difficult. Let's go over them.

How hard it hits

Your spaceship will be flinging around nuclear bombs. As I discussed earlier, there are other options, but none seem nearly as efficient. I'm perfectly willing to allow different kinds of weapons, but I'm not going to make some miracle sci fi death ray when A-bombs are available (No dessert until you finish your Uranium!)

So how much damage does a nuclear weapon do? Depends on how you build it. After a little bit of googling (Putting myself on FBI watchlists so you don't have to!) I find this page. If you look at the B-3 Gravity bomb, it has a yield of 9 megatons, weighing roughly 9,000 kg. Since we're talking about the future we can upgrade those stats; call it 15 MT for 5,000 kg

We'll call that the upper bound on weapon strength, starting out. Of course you'll be able to upgrade it later on. If we look at the last one on the page, we've got bombs you can dial as low as .3 KT, weighing only about 300 kg. Since those limits are largely dependent on the physics of the bomb, not the engineering problems (you have to have a certain amount of material to get a chain reaction), I don't think this is going to get much smaller. So I figure those are the same starting stats for our low end. When we outfit ships, we can feel free to use bombs of any size in those ranges.

So what does that work out into game terms? Well, I'm not yet sure. If I detonate a warhead of energy E0 at a distance R from a spherical spaceship of radius R0, how much energy does the ship absorb? Still haven't figured out the math. What's worse is that I'm having trouble figuring if it's actually a hard question or if I'm just incompetent. Or both. Depending on how I eventually work out that math, we'll have to tweak...

How many hits it can take

This is entirely dependent on the properties of the Langston field. Which I've gone over in a general sense previously. I'd like to leave the specifics of the field functions until the end, so we can shove all our fudge factor into one mass at the end. Neat.

How accurately it fires

This I've got very little idea on. I'm going to say that right up. If we take a quick stop over at the invaluable project rho, the first blue box on that page explains, in part, why we'd prefer attaching our warheads to missiles. Roughly speaking, it's very hard to predict where your opponent is going to be when your projectile hits them. Seeing as we can build targeting computers into the missiles and such, then you can have your projectile constantly accelerating towards the target. Maybe even launch it out of an electromagnetic gun so it's got a very high starting velocity...

Haven't given nearly enough thought to this so far.

How fast it can move.

This is tricky. In space, you don't have a top speed, you have a maximum acceleration. That all goes back to Newton's second law:

Force equals mass times acceleration. F=ma

To get a higher acceleration you have to increase the force (in this case you have to shovel more reaction mass out the back, or shovel it out quicker), or you have to decrease your ship's mass. Unfortunately, we're still in the realm of rocketry, which has some really complicated equations to solve. (In this case I successfully figured out that the equations are well beyond my skill level. I take what victories I can.) Fortunately for you, I can't take this through the rigorous math like I would like to, so we're going to do it all talky style.

Your mass is the sum of all the stuff you put in the ship; some for engines, some for living space, some for missles, and some for whatever else you want to bring along. Look, I understand it's a nice grand piano. And they don't let you make synthetic ivory anymore, I know. But it'll slow us down in the battle. But I digress. Again.

We're going to have to estimate masses for a lot of stuff.

How much it can carry.

This is actually almost a subset of the previous topic. Each ship will be able to carry some volume of cargo. If you make it a troop transport you should include need more mass for life support, where an ore freighter wouldn't need it.

I suppose there are a couple other parameters that constrain our ship design that I should mention, volume and cost.

There are practical limits to volume; how much air you're willing to ship up to space to fill it, how many reactor shafts you're willing to have open into the Emperor's throne room, that sort of thing. Realistically, they all are cost issues though. I'm also considering imposing an upper limit to volume based on shield physics, just so you know.

Cost as a constraint, well, that's why we're not in space right now. If I could build an atomic rocket for the cost I spend on a luxury car I'd be surfing the spaceways right now. A little more down to earth, well, all of our ships and components and a bombs and whatnot are going to cost resources. Resources which the game will allow you to produce by leveraging the massive industries of space, and so forth. Again, another really complicated can of worms.

Just some food for thought.