Wednesday, May 5, 2010

The Langston Field

Been a bit since I last advanced the Terrible Secret of Space. If you'll recall, last time I was working out some necessary consequences of having spaceships that travel around the solar system. Basically, if you can get a ship up to speed, it makes a great rock to hurl at those who would oppose you. Or those who might think of opposing you. Or those who might think of looking at you funny. Or... I'd better get off this train of thought.

Specifically, at the close of my last post I didn't have a satisfactory reason for why the evil invading aliens couldn't strap a drive on just any old rock and blast capital ships out of the sky or selectively target important military installations. After duly considering the problem, I've got the solution: Cheat!

I'm stealing the Langston Field from the novel The Mote in God's Eye by Larry Niven and Jerry Pournelle. The aforementioned field drains energy from objects in motion, including such extremely high energy objects as plasma from fusion torpedoes or photons from laser cannons. Importantly though, the book also works out the restrictions. The field has to absorb that energy, which it disposes of by radiating outwards as a black body. If it can't radiate the energy faster than it takes it in, the shield heats up until it overloads, destroying the ship inside.

This has all sorts of useful applications for a boardgame. For starters, it neatly allows us to sidestep the issue of throwing rocks at capital ships; the shields will be able to survive that sort of attack. Doubly so for ground installations. It also provides a handy way to track damage done to ships; in the book the shields remained black until enough energy is absorbed that it starts changing color, from red on up the rainbow. Makes a pretty convenient way to define and measure hit points.

So what do we actually know about the shields?
1) The shields absorb energy. They reradiate it like blackbody radiation. The specific heat of the shields must be proportionally huge, they can absorb large amounts of energy.
2) They absorb momentum proportional to the cube of the incoming velocity. Which means they absorb a lot more energy from, say, an incoming particle beam than from an object moving at slow speeds.
3) They're generally spherical in shape. This probably works to our advantage otherwise, seeing as a sphere is best for radiating away excess energy.
4) Small holes can be punched through the shield. This allows useful things like laser batteries or the fusion reaction to get out.
5) Some energy gets through; there's a lot of talk in the book about how the ships get shaken about in major fleet actions, and about necessary repairs.
6) The shields dampen all motion. If you get stuck in one, it'll dampen the beating of your heart etc.
7) Absorbing energy is really useful if you want an ultra efficient sci-fi star drive. Say, the sort of thing that could stand .1g over extended periods of time. Not sure that I'm going to get into a detailed explanation of how the engines work, but it's nice to remember.
8) Shields have some thickness. They take up a volume of space. They are fields though, so they don't exclude matter from taking up the same space.
9) Until a shield overloads, it mostly radiates it's energy outward. I don't know why this is. Probably storytelling necessity. Possibly I'm screwing up my physics.
10) Not stated but implied by the logic, ground based shields will be more efficient than space based ones; they can lose energy by conduction with the ground rather than just radiation.
11) When a shield overloads the energy will The overloaded Langston field is enough to vaporize whatever steel bulkheads you've got inside it. Only about half of the energy will be going inwards (I'm assuming it's proportional to surface area), the other half will be expanding out. While it'll be a lot more diffuse, I wouldn't want to be too close to an exploding ship for fear of overloading my own shields.

After a perusal of the book, I've still got a couple questions. What happens if two shields interact?

Let's say you put one inside another. That way, if your first shield blows, you've got another ready and waiting. Trouble is, when a shield blows it'll release a lot of energy. If the amount of energy a shield can store is proportional to the volume of space it occupies then the outer shield will by necessity be able to hold more energy. Consequently, when it releases all that energy it might overload the shield on the inside in just that one action. You could design around this though; by engineering your inside shield to have at least 51% of the energy capacity of your outer shield. Even if it only buys you a couple seconds, well, a couple seconds are valuable. We could assume as a principle of the physics that you can't have one shield inside another. Only that spells doom for making the drive ultraefficient.

Or what happens if you throw one field at another? Let's say you built Langston Fields into your torpedoes to make them harder to shoot down mid flight. When you launched it at another ship, what would happen? Well, let's say the fields cancel each other. Then you'd have an effective way to toss a torpedo through a field barrier, which makes the Langston field much less useful. Ok, what if the fields simply ignore each other. Then the torpedo would crash into the other ship's field, and work like described. Unless the torpedo would have a larger field, in which case it'd appear that the ship crashed into the torpedo's field, causing massive damage to the ship without injuring the torpedo. Also not optimal.

Let's see. The shields act to absorb incoming velocities. But you can impart a velocity to a shield by moving the generator on the inside. The shields are a projection of energy, but they also block energy. So if we assume that two shields would attempt to block each other out if they collided, then the two of them would have to absorb energy equal to the collective momentum of the system. Except that would leave them both at rest, and there's no reference frame to tell us what "at rest" means in that context. I could cheat by using the board to define a reference frame, but I'd rather not. One of the things I'm trying to do with this game is to not mess up the physics unless I absolutely have to. I can think of ways to explain the interaction of two shields, but none where the math will check out when two ships collide, and therefore none that I'd be happy using.

Ok, so suppose that it works that way. Well, possibly that I'll have to use a vector based movement system to describe how pieces move about the board. Honestly though, that'd probably happen anyway. Anything else? That it'll be possible to ram ships with other ships, for whatever purpose. Why would someone do that? Well, if you just hit them with a fusion torpedo their shield heats up. But if you sent in a spaceship on automatic you might be able to change their motion, say nudging them out of orbit or into the path of an asteroid or something.

Well, that's all the physics. Well, not all. I haven't touched on the thermodynamics much at all. Before I finish though, I'm going to add a couple restrictions to Langston Field Generators. Either they're really expensive to build, or they won't cover very small areas, or both. I'm saying this to limit the unintended consequences. If you could make cheap, small field generators then you could do all sorts of things with them. Really top notch fireproofing is probably the most boring. To limit the spread of miracle gadgets that do X, Y, or Z and implies T, U, and V, I think I'm going to limit these to small star ships and up.

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