On 24 Jun 2015 at 8:45, Knapp wrote:

> My f16 analogy was weak. My point only being that all the combat
> maneuvers that I know of use turning and flares or EMC to stop or
> avoid an attack not acceleration or deceleration. Dogfighting is not
> something I think we will be seeing in space fights. Spaceships are
> easy to detect (given current know how) and hard to hide. Say you can
> move at 20g. You are being shot at by a laser. How fast can the laser
> track you VS how fast can you try and avoid this shot? If we are
> close together then you have 0 change of not getting hit. As the
> range becomes extreme so that speed of light becomes a factor then
> your acceleration VS the apparent size of the target might limit your
> contact time with the laser. This is only important if the laser is
> weak enough to need long contact times or you must be very precise to
> kill the ship.

Thing is, space combat is *inherently* different than atmospheric
combat.

When firing a laser at a target in space, the only relevant factors
are the range and the acceleration of the target.

Range gives you the lag time between the time the EM radaition
(either passively emitted or a reflection of your active radar/lidar
pulses) left the target, and when the laser pulse arrives.

At one light second range, and ignoring any delay in the sensor to
laser aiming linkage, that lag is *two* seconds.

Now, you know the velocity of the target 2 seconds before the laser
pulse will arrive. So, give decent sensor & aiming, we can treat
keeping the same velocity as a "fixed" frame of reference in which
the ship is stationary.

That reduces the targeting to how far can the target move in those
two second *from "rest" in that fixed frame of reference.

d = 0.5 * a * t^2

So at 20 g, (call it 200 m/s^2)

d = 0.5 * 200 * 2^2

d = 100 * 4

d = 400 meters

So if the ship is only 50 meters, it can have moved *8* ship lengths
in a "random" direction. In reality, the possible directions are
limited by the ability to rotate the ship (because you need to use
the main drive to give that 20 g acceleration.

So lets see how short the range has to be for the ship to move only
25 meters (which moves a "center of mass" strike to just barely
missing).

25 = 0.5 * 200 * t^2
25 = 100 * t^2
0.25 = t^2
t = sqrt(0.25)
t = 0.5

So at half a light second a ship can easily generate a clean miss.

At shorter ranges, the ship can still move enough to make a major
change in target location.

Of course, in most versions of Traveller, max accel is no more than 6
g which makes hitting easier.

With PAWs, the "flight time" is a lot slower than light speed, so the
lag time at a given range is the speed of light lag in one direction
plus the "flight time" of the particles in the other direction.

And kinetic kill weapons (rail guns, etc) it's even worse.

Missiles, at least have the possibility of correcting their course to
hit the target. But they are limited by the total delta-V they are
capable of (almost certainly a lot less than the target).

--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com