any PD weapon can cover this missile threat
16km/s missile without salvo density in magneto era means no hits unless there is real swarm of such FACs ( with a such swarm better to do bigger design for economy reason )
also boxes means salvo density and guarantee something can leak through defence
Even in the best case, most PD ships will have 1 FC/pd turret, or 1 FC/AMM launcher. When the missiles get close, you'd need 90 FCs to attempt intercepting all of them withing the 30 or so seconds that they'll be approaching.
Remember, this is 91 separate salvos of 1 missile. As opposed to 1 salvo of 91 missiles. 1 FC with a gauss cannon can only shoot down 1 salvo of 1 missile per 5 sec increment. The same FC and GC can take down several of the missiles in a 91 missile salvo in that same increment. I don't knwo of too many ship designs that roll around with more than 10 FCs, and even those are rather specialized, or unnecessarily large.
boxes are like 15k rp from standard launchers, if not more.
so that's like this with magneto plasma, versus ion tech with boxes
Boxes might take a bit of initial research cost to unlock the boxes themsevles, but once are researched, are done themselves, as opposed to regular launchers that need reload upgrades that can get over 100krp. Guess this is actually a rather odd way of trying ot accomplish the same role of ship with cheaper launchers RP wise.
Details! 
Of course we could slap some armour on... or take some precautions to avoid being shot at.
Slow missiles have a lot of flexibility. If I don't blow 40% of missile weight on a 2-damage warhead, I can easily get 150-200m range with some space left over for more agility. Even if we lose 10% effective range to our peculiar attack run, that should be a safe distance for FACs. Of course, this would require a more powerful missiles fire control and probably cost us a magazine.
Only major problem I have with the design itself is the missile, which its tohit chance seems a little low for your tech level
Thanks for the encouragement. While your suggestion would shorten the attack run, multiple launchers would sacrifice some of the salvo dispersion that was a main reason for this approach.
I only chose 1000t FACs for a high ratio of magazines to launchers/FC, which in turn requires a long attack run and limits a secondary role as AMM escorts... if that trade-off is not desired, I'd simply use smaller ships (possibly fighters).
Multiple launchers can be made to have the same salvo dispersion via having equal numbers of launchers and FCs, Might end up sacrificing some magazine space to do this, but this is why they'd carry their reloads on a supporting collier.
Which leads me to what I'm personally going to try myself, a variant of this based around a fighter. (will post below, for your consideration) alogn with a fighter sized collier to make the attack run with. Nice thing about it. It's pretty safe during its attack run because not much will pick it up and start firing on it.
You might be able to get around the slow missile speed by using two-stage missiles: the first is a slowish stage that allows the FAC to keep pace, and the second is a zippy little missile that separates from the first stage after the FAC's magazine has been emptied, but before the salvos get engaged by the enemy AMMs. The combined stage will probably be larger than your current missiles, but they may get more warheads onto the target in the end.
Probably worth considering. Size 2 missile with a trawling size 1 stage, and a size 1 missile, set them all to separate around 30mkm (outside of most all AMM systems at this low tech
Aside from minor deviation due to target movement while on the attack run, all the missiles should separate at the same range, and about the same time (give or take an increment) and start blasting their way towards the target at say 40kkm/s. Also could have longer overall range with this tactic.
Concept fighter variation for MY testing, pls note, this is an ion tech craft, not magneto plasma. And its engines are limited to a 2x modifier due to my current tech level.
Also I haven't designed the particular missile yet as I will have a couple of weapons to arm the craft with. Both a 14400 speed missile, and another 17820 speed missile (because reasons)
numbers might be a little off from the one I'd actually use in practice because this is beign thrown together on my laptop in a "testing" save, which has a higher level armor tech than a regular ion equipped player would, so range and fittings of "non mission tonnage" may vary.
But the concept its there. For the same tonnage and a slight bit more BP, you can get 32 missiles out from similar range, but but much more safely due to the difficulty in targeting fighters at long ranges. This without eating up a FAC Naval yard that might be putting out another design (since most players generally don't do too much with fighters)
ZJSF-0A Mirage class Fighter-bomber 500 tons 10 Crew 165 BP TCS 10 TH 72 EM 0
14400 km/s Armour 1-5 Shields 0-0 Sensors 1/1/0/0 Damage Control Rating 0 PPV 1
Maint Life 4.29 Years MSP 21 AFR 20% IFR 0.3% 1YR 2 5YR 28 Max Repair 45 MSP
Intended Deployment Time: 0.3 months Spare Berths 4
Magazine 16
24 EP Ion Drive (6) Power 24 Fuel Use 392.02% Signature 12 Exp 20%
Fuel Capacity 5,000 Litres Range 0.5 billion km (8 hours at full power)
Size 1 Missile Launcher (1) Missile Size 1 Rate of Fire 10
Missile Fire Control FC78-R80 (1) Range 78.9m km Resolution 80
This design is classed as a Fighter for production, combat and maintenance purposesAs far as massing them, the design I'm planning on doing below, I might make either 3+1collier, or 6+2 colliers, shove them in a CV and give em a test run.... they work, good, they've earned their place in the carrier, they don't oh well, not too much money or RP invested (at the small magazine size, theres no benefit of producing a single size 3 magazine for the collier, just use 3 size 1s, and any size 1 magazine costs 50 RP to research with 1HTK)
But for a 4 ship squadron of concept fighters, that will be 96 missiles in space for 2000t of cheap disposable fighter, that doesn't rely on me retooling any navy yards. Stripping out the collier and just building a regular squad all fighters will put out about 64 in a run before having to RTB
Mind you a standard size 1 armed box fighter at the same tech, can only pack ~13 size 1 boxes into the same space as the magazine and launcher... but requires a hangar reload... so you be the judge.
Perhaps it might be an interesting way in a multifaction campaign to create doctrines for 2 different empires that are using fighters.
