Quote:
Dauntless - I disagree that high speeds limit manuverability. Think of it this way, when you are lining up a shot, you know the position and velocity (vector) of the target. Given that, you can estimate the weapon's time to target, and thus the target's position when the weapon arrives. Let's say your rocket will take 1 minute to reach the target, and that the target's thrusters can accelerate it at a speed of 10 m/s. From a sitting position, the target will move roughly 60*10 meters. That means that your target's expected position after a minute is a sphere .6Km in radius. That's from a standstill. Now assume the target is already moving at 1,000 m/s. Again, the engines can *change* the speed 10 m/s every second. Assuming the same 1 minute for the weapon to close, the target's expected position is again a sphere .6Km in radius, but the sphere is offset from the target's current position by 1,000m/s*60s = 60,000 meters. My point being that when evading incoming fire, the only things that matter are acceleration and time to make use of that acceleration - not the target's current speed.

I agree absolutely with what I put in italics. It's not speed that truly matters, but how you use your acceleration. But in fact, it's not good to just slam on the accelerator either, since it is acceleration that causes the forces which could affect the weak parts of the hull. So really, it's acceleration + vector changes with respect to time that's important.

Plus, you have to consider all my other constraints. In my scenario, the majority of weapons will be energy-based, and hence time-to-target will be on the order of a few micro-seconds to at most a few seconds (depending on how good your scanning margin of error is to be used as a targeting system, this will determine the maximum range that combat can take place in). Given that fact, the indeterminate position of a target is greatly reduced. If a ship is moving very fast, then the only way it can rapidly change its vector (and hence it's direction) is by rotating the ship, and applying a maximum burn. This is the point I tried to make earlier in that depending on how you design the ship...these rapid turns can be hazardous to the structural integrity of the ship (one way to alleviate this problem is to mount the main thrusters on "turrets" placed near the center of mass of the shiprather than only at the rear of the vessel...this could allow for more rapid turning, but having the thruststers in such a manner would also mean that they probably wouldn't be as powerful as rear-mounted thrusters).

So to recap in a nutshell,
1)a ship moving with a high velocity can not rapidly change directions or apply too much acceleration
EDIT- It can't change direction or speed quickly (which is the definition of a vector) because if you're moving fast, you have to accelerate fast to change either your direction of movement, or your speed...and that's the problem. Not to mention rotational torque and other stress factors involved.
2) If you can't rapidly change directions or speed (change vector), your opponent can guess where you will be much better
3) If your opponent can predict where you are better, he can hit you more easily.

Therefore, slow to medium velocities will be more common because then although the toral displacement over time may be less than at high velocities, the ability to constantly change vectors creates a more unpredictable end displacement (i.e., you can sum more vectors in a period of time at slower speeds than you can if you move fast).

Also, I think kinetic weapons will be rare in ship to ship combat. Today's Aegis systems on USN vessels can blow missles out of the sky. Because of the slow time it takes for the missles to get there there's ample time for them to be shot down, or simply run out. As for high velocity railgun types, the slower speed and hence greater inaccuracy of the weapons (round time-to-target is greater, and hence target has a more unpredictable end position) will make them less desirable. Add in the fact that your ship's position will constantly be minutely affected due to the recoil (and even just a micro fraction of a degree can make a difference when you're trying to hit something on the order of tens of thousands of meters away), storage space for ammo, and the volatile nature of the ammo (just look what happened to HMS Hood) and I think kinetic weapons will be rare. One way to make missle systems better is simply to swamp your opponent with them so that he's unable to shoot them down. Drones and missles make great fiction, but I doubt they'll be that common once energy technology becomes feasible and reliable (so kinetic weapons systems might be common in the early stages of going to space).

[Edited by - Dauntless on October 13, 2004 4:31:30 PM]

Just stumbled on a page that comments on the physics problems that arises with super-sized starships, like "The Executor" in Star Wars. (17.6 km long ship)
He calculates thats the building material its made of must be able to withstand a resultant stress in excess of 1.8 TPa, when accelerating in the movie. Thats nearly 7000 times the yield stress of structural steel.

http://www.stardestroyer.net/Empire/Science/Size.html

Well I agree they can have alot of hi-tech materials.
But 7000 times is more than alot. Not even theoretical yield stresses are in the same ballpark.
Steel can take on about 20 times more stress than wood.
You need something that can take on 7000 times more than steel.
But who knows ;)

Quote:Original post by Dauntless
1)a ship moving with a high velocity can not rapidly change directions or apply too much acceleration
EDIT- It can't change direction or speed quickly (which is the definition of a vector) because if you're moving fast, you have to accelerate fast to change either your direction of movement, or your speed...and that's the problem. Not to mention rotational torque and other stress factors involved.

No, you can always change velocity rapidly, no matter what your initial velocity is. The initial velocity is only a factor if you want to change your velocity to some specific vector, which is not necessary to simply avoid a collision.

Jake's earlier example was actually a very good one. In order to hit you, an enemy must lead you by a distance determined by your current velocity and the "flight time" of the weapon. To avoid being hit, you must simply change your velocity before you get to the intercept point, such that you do not pass through that point at the time the weapon arrives there. It doesn't really matter what you change your velocity to, you just need to change it. Hell, just speeding up would do the job. The thing to realize though is that achieving that course change is exactly the same manouver at all speeds. Sure, while you are reorienting the ship to make the burn, you will cover more distance at high speeds than you will at low speed, but the enemy's lead distance will also be greater by the same amount. At any speed, you will have pretty much the same amount of time to make the manouver.

The only exception to this is if the enemy is more or less directly in front of you, in which case they don't have to figure out an intercept point, they can simply fire straight at you. In that case, a higher speed will obviously close the gap quicker, and will leave less time for manouvering. But I would expect that such head-on engagements would likely be very rare, both because of what I just mentioned, and because orbital mechanics would tend to demand less direct courses.