A Thought on Railguns, secondarily missiles and pdcs

[Ray of Meep]

So the idea goes like this: PDC's have fire rate and can shoot down missiles, but are rubbish at medium to long ranges due to the relatively low velocity and mass of the rounds. Missiles are mainstay anti-ship weaponry regardless of the ship size due to the adaptability of the payload, the ability to maneuver and make course corrections, but due to the time needed to accelerate to full velocity lest they get tracked and shot down easily, they are relegated to long ranges.

Meanwhile, railguns, capital-grade railguns specifically, fire rounds at a significant fraction of the speed of light. Such velocity brings sufficient kinetic energy to perforate multiple decks and rooms in a ship, dealing significant damage. However, the energy required to fire such a gun is also immense, requiring low rates of fire, else the mass driver overheats and damages itself. The railgun round also shares the same constraints as PDC's: the finite velocity allows for non-zero reaction time of the target to evade. This reaction time can be roughly estimated as the distance divided by the round velocity; thus, the railgun's range is limited at the top due to the time such distances give for evasion, and also limited at the bottom due to PDC dominance at close range, thanks to their high fire rate and sufficient damage output.

A railgun's range can be increased in battle through clever strategy, mind games, and prediction, theoretically to infinity, depending on the wits of the operator and the stupidity of the target. Of course, increasing the velocity also decreases reaction time, but given the first law of thermodynamics, and that KE is proportional to velocity squared, to decrease the reaction time (and increase the range) by a factor of 2, the energy input must be scaled up by a factor of four, dragging material requirements and thermal management with it as well. The improvement of the railgun's range technologically is one of diminishing returns. At some point a capital ship will not have the power generation and thermal management systems required to support a high velocity railgun, relegating such powerful weapons to stationary platforms.

 

[Uso]

"Why don't my small rail guns quickly destroy these missies?" and other things I learned from playing CoaDE, by Uso.

Smaller projectiles might not be enough to one-shot an incoming missile. Or perhaps it will damage the sensor on the tip of the missile but the missile will carry on regardless using sensor data from the other incoming missiles to continue to track its target. The follow up problem here is that this impact will knock the missile off course, specifically off course enough so that the next round is more likely to miss along with all the follow up shots from the PDC requiring it to recalculate and adjust its aim to fire another burst. This becomes an increasingly big problem when firing smaller fast moving projectiles at longer range against chonkier missiles. We also see this problem today where the classic CWIS is considered by many navies to be insufficient for missile defense, and is being replaced by missile systems and larger cannons. Firing more rounds is also less preferable to firing fewer rounds more accurately, doubly so in space when mass is a major concern.

So smaller rounds (and more of them) aren't necessarily more optimized for taking down incoming missiles.

There really isn't anything special about being a point-defense cannon. Sure, it can shoot down fast moving missiles, but every gun with modern targeting systems is going to be able to do the same thing. Even your spinal mounted railgun can be used to hit missiles at long ranges. A bigger gun that can fire heavier rounds at faster speeds is just going to be outright better than a smaller point defense cannon.


I think that rather than defending at close range, the primary reason for taking the smaller PDC weapons would be for other reasons:

• Making use of spare mass
• Covering angles your main weapon can't
• providing a shooting capability for when you don't want to use your full power
• Not being able to fit a larger weapon