I'm trying to find a way to standardise the measurement of difficulty of a shot to be fired, using range, projectile speed, and the target's observed ability to accelerate.

Could I simply use something like ((range * targetAcceleration) / projectile speed) = shot difficulty, or would that get me useless results?

I think range / shot_speed is reasonably meaningful, so I guess throwing accel in the numerator would work and make some sense.

But my question is: what exactly are you trying to model here?

The difficulty of computing what point to shoot at to get the shot to intersect the target, given the target's current position and momentum.

The difficulty of knowing the target's position and momentum precisely enough to compute the above.

- due to sensor inefficiency and/or jamming

- or due to distance and the finite speed of light

The difficulty of predicting changes in the target's momentum.

Mechanical variation and/or failure in the weapon (or targeting routing hardware, whatever), such that it doesn't actually shoot at the point designated, or at the time designated.

Etc.

Accel would only seem relevant to that third one. And I guess that it would be very relevant there: given a known position, momentum, and acceleration, there's a "cone" emitting from that position of where it would be physically possible for the ship to be at time t. If you know your shot will cross the distance in 0.5s, and the "width" of the cone at t=0.5 is less than the "radius" of the target, then firing at the center of the cone would effectively ensure intersection (exactly what part of the ship you hit may vary). Once the target's possible positions no longer have an intersection, then a miss would be possible even with perfect sensors, targeting, and firing. The miss chance would probably have more to do with how much the target is trying to evade and whether there were any predictable biases of the evading helmsman, etc.

Of course, I'm assuming only one significant point of thrust on the target; if it's a fighter with a massive lateral thruster strapped to one side then its "cone" gets way more complicated.

Anyway, just trying to figure out what you're actually doing here. If it's just lasers and other light-speed weapons at short range with reliable (and undamaged) weaponry without some terri-jamming there wouldn't really be a miss chance. If it's mass drivers at 10 light-seconds with a ton of ECM then probably just call it a 10% hit chance for dumb luck

Or reconfigure the mass drivers for "meteor shower".