Wednesday, January 2, 2008

Lead or Pure?

In en earlier post I promised to post more screenshots of a larger ship battle. I haven't done that yet because playing in that battle brought up some issues that I have been fixing. Mostly just little stuff when you click through each of your ships and giving them orders and then go back and click on one of the ships you already gave orders to, there is no indication that it has orders. So this made it very hard to know if you had already given a ship orders or not. So I made the "new" orders visible when you click on a ship.

Also, it became clear that I need a better guidance system for very fast travelling projectiles. Rail Guns (or Mass Drivers) fire a projectile very very fast. On the order of tens of kilometers per second. While current hypothetical weapon designs for mass drivers would involve a simple slug as the projectile, I think that any star ship worthy weapon is going to have some kind of guidance. After all, 10 km/s is fast, but if your target is 100km away (or even 10 km away), they aren't going to be there by the time the projectile arrives.

Up to now, all projectiles in Fleet Combat Online have been using "pure pursuit". That is, they constantly look at their target and steer toward it. This is the same guidance model as first generation air to air missiles like the AIM-9P Sidewinder. This form of guidance (and its primitive IR sensor) meant that you could only fire that missile in "rear aspect" -- meaning from behind. If the target was moving across the missiles field of view, then the pure pursuit model always puts the missile a little bit behind the target because you are steering directly at it, but it is moving sideways.

I have found the same kind of behavior with the mass drivers in the game. At first I thought "fine, that is a disadvantage to an otherwise very powerful weapon". But upon playing it makes it very hard to hit anything with them. And at least in the "early" eras of star ship combat, a vessel armed with a mass driver is not likely to have much in the way of other weapons because of the power required (and heat generated) by that big rail gun.

Slower rocket powered missiles don't really have that problem as they aren't as likely to whizz by the target before they can alter their course enough to hit it. As they get closer to the target, their course becomes more parallel to the target and they sort of fall in line behind it before catching up and hitting it.

So I need to change the guidance model for the mass driver projectiles to have a "lead pursuit" model. That is where you look at the targets speed and direction and try to predict where the target will be by the time you get there. You can see this different logic if you ever see video of the later AIM-9M missile being fired. The target is directly in front of the plane but moving to the right. When the missile is fired, it immediately takes a hard right turn making you wonder where it is going, but it is just "leading" the target.

Here is an article about the differences at one of my long time favorite sites Sim HQ.

So that's what I am working on now. Hopefully it won't make those mass drivers too deadly -- oh the joys of play balancing...

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