Cometchaser ASM Mk II: (1-6, 2-10, 1-2500, 2-160)
Missile Size: 6 MSP (0.3 HS) Warhead: 6 Armour: 0 Manoeuvre Rating: 37
Speed: 33300 km/s Endurance: 30 minutes Range: 59.9m km
Cost Per Missile: 5.5083
Chance to Hit: 1k km/s 1232.1% 3k km/s 407% 5k km/s 246.4% 10k km/s 123.2%
A few points on the missiles: It is important to realize that all characteristics of an unguided missile (i.e. without sensor) scale with the size of the missile.
So if you double all stats you will have a missiles that is just as fast (except minor rounding), has exactly the same range, and the same Manoeuvre Rating (and thus the same chance to hit). It does however have twice the warhead and is twice as expensive (to build and to research). The launchers for a missile also scale with the size, so the launcher gets twice as large, or put differently, you could only have half of the launchers on a given ship ceteris paribus. Equally the space a missiles takes in the magazines is proportional to its size, so you can pack half as many of the twice as large missiles.
The important implication is that the damage that you can expect to do to an enemy without PD is independent of the size of the missiles that you choose. Both in terms of one salvo, and in terms of your entire magazine capacity: You can either launch n missiles which do x damage each, or 2*n missiles which do x/2 damage each, while both are equally likely to hit.
Of course most enemies do have PD defences, and interestingly enough PD defences allow to engage a certain
number of missiles, independently of their individual size (actually smaller missiles can be a bit harder to engage, since they are detected later by radar). So the expected raw damage you can project on an enemy massively favours a large number of small missiles, rather than a smaller number of large missiles: Suppose they can intercept m missiles every round, then you could deal raw damage of (n-m)*x, or (2n-m)*x/2=(n-m)*x+m/2. Note the later term is always larger than the former. Furthermore the reload time of a launcher scales with the size of a missile, so using the smaller missiles also allows you to launch them much more rapidly, increasing the damage dealt per second, and potentially even increasing enemy PD penetration further, as he might still deal with the first salvo, when the second shows up.
Yet there is also a reason to use larger missiles, which is due to the damage profile of missiles. When a missile hits it will leave a triangular shaped damage profile on the enemy armour, with the total penetration depth depending on the size of the warhead. For instance a 4-Warhead missile will destroy three tiles of the outermost armour layer, and one tile of the second layer when it hits. A 9-Warhead missile will destroy 5 tiles of the outermost layer, 3 tiles one layer below, and one tile on the third layer. If the respective layer does not exist its applied as internal damage. If the original missile had a warhead of 2, then the double-sized missile would have a warhead of 4. The later would be able to penetrate deeper and thus be more likely to do internal damage towards an enemy earlier. E.g. if the enemy had only 1 layer of armour then the large missile would deal internal damage from the first hit on, while at least two the smaller missiles would need to hit the same spot to do internal damage. There are twice as many, but its unlikely they hit the same location. For unguided missiles this is the only reason why you would want to use large missiles rather than smaller ones (except rounding effects).
Why did I enter into this lengthy debate? Simple, because it allows you to easily spot that something about a missile might be somewhat off when its large and does not have an optimal damage profile (spell: the warhead is not a square number). And that is the case for your missile: Size 6, Warhead 6. What damage profile would this cause? 4 tiles of the first layer of armour, 2 tile of the second. Now suppose you decreased all the allocations of the missiles by 1/3. You would get a size 4 missile with the same speed, same range, same hitchance, but warhead 4. This would have a damage profile of 3 tiles on the first layer, 1 to the second – so the penetration depth would be the same. In essence you would get a design that is harder to intercept, can be launched more rapidly, and would cause the same damage on the enemy.
Another thing is that your hitchances are very high. Your missile has a 123% chance to hit an enemy traveling at 10k km/s. 23 percentage points of that are wasted (assuming average crew grade), as of course hitchances are capped at 100%. Unless you are very certain that you will be facing very very fast enemies, this is a suboptimal design. It could be improved by diverting space from “agility” towards other categories, increasing the damage, speed or range of the design, without losing anything that is not superfluous to begin with.
Lastly, its often a good idea to arm with a mixed of obsolete and up-to-date missiles, not just because it saves resources, but also because they have different velocities. If done properly they can be launched at different times such that they arrive at the enemy at roughly the same time, saturating his PD defences.