Someone else reported the same problem recently (and then wrote it up in their AAR) but I can't seem to find either post. IIRC, they pegged the cause as probably some unexpected interaction with the new missile interception code, because the separation seemed to occur at the specified distance from the point at which the first stage was predicted to intercept the target. So yeah, assuming the second stage is faster than the first, it's going to reach the target in a stern chase but not a head-on intercept.

EDIT: Took another look, turned it up here, not quite as recent as I remembered.

Its been a while now, but my new computer has finally arrived so I'm back in business. Good news is my old hard drive is still fine so I managed to recover the save for this game.

@rcj33: looks pretty solid, although personally I do prefer a fair bit more range on the bigger ships.
Somewhat inspired by your design, I'm thinking my next ship might feature energy weapons almost exclusively as the main armament, although I'll have to wait a bit for my tech to get up to scratch in that area.

In a recent NPR encounter, I attempted to engage some relatively fast ~8000 ton craft going at ~12000km/s using  my 2-stage torpedo designs. For some reason, the submunitions kept running out of endurance before reaching the targets even though I'm almost certain I left a few mkm margin between seperation distance and submunition endurance to ensure this wouldn't happen. To make things worse, the targets were steaming straight towards the missiles too, which makes their apparent lack of endurance even more inexplicable. What is going on?

Post the designs, both carrier and submunition. I'm sure we can figure it out.

So I made this monstrosity for a space opera campaign:

Atropos-class Heavy Titan (Assault)
50 size-2 launchers (1000 rds)
1 52cm spinal laser
20 35cm lasers
60 15cm lasers
20 35cm mesons
60 15cm mesons
40 gauss-5
plus 2kt hangar space

Atropos class Heavy Titan    240,000 tons     8369 Crew     78920.4 BP      TCS 4800  TH 40000  EM 36000
8333 km/s     Armour 25-344     Shields 1200-300     Sensors 1/120/0/0     Damage Control Rating 335     PPV 1317
Maint Life 4.49 Years     MSP 68914    AFR 1374%    IFR 19.1%    1YR 5529    5YR 82937    Max Repair 1264 MSP
Intended Deployment Time: 18 months    Flight Crew Berths 10   
Flag Bridge    Hangar Deck Capacity 2000 tons     Troop Capacity: 1 Battalion    Magazine 2020    Cargo Handling Multiplier 40    Tractor Beam     

2000 EP Magnetic Fusion Drive (20)    Power 2000    Fuel Use 48.57%    Signature 2000    Exp 16%
Fuel Capacity 25,000,000 Litres    Range 38.6 billion km   (53 days at full power)
Ablative Energy Sink (240)   Total Fuel Cost  3,600 Litres per hour  (86,400 per day)

Spinal CRE Pulser (1)    Range 480,000km     TS: 8333 km/s     Power 71-8     RM 7    ROF 45        71 71 71 71 71 71 71 62 55 49
Quad Small CRE Beamer (10x4)    Range 420,000km     TS: 8333 km/s     Power 24-32     RM 7    ROF 5        6 6 6 6 6 6 6 5 4 4
Quad Small CRE Beamer Turret (5x4)    Range 420,000km     TS: 16000 km/s     Power 24-32     RM 7    ROF 5        6 6 6 6 6 6 6 5 4 4
Quad Medium CRE Pulser (5x4)    Range 480,000km     TS: 8333 km/s     Power 128-32     RM 7    ROF 20        32 32 32 32 32 32 32 27 24 22
Quad Small Kaon Projector (10x4)    Range 210,000km     TS: 8333 km/s     Power 24-32     RM 21    ROF 5        1 1 1 1 1 1 1 1 1 1
Quad Small Kaon Projector Turret (5x4)    Range 210,000km     TS: 16000 km/s     Power 24-32     RM 21    ROF 5        1 1 1 1 1 1 1 1 1 1
Quad Medium Kaon Projector (5x4)    Range 480,000km     TS: 8333 km/s     Power 128-32     RM 112    ROF 20        1 1 1 1 1 1 1 1 1 1
Quad RMPA PD Turret (10x20)    Range 50,000km     TS: 32200 km/s     Power 0-0     RM 5    ROF 5        1 1 1 1 1 0 0 0 0 0
Escort Beam Fire Control (5)    Max Range: 480,000 km   TS: 16000 km/s     98 96 94 92 90 88 85 83 81 79
Spinal CRE Pulser FC (1)    Max Range: 480,000 km   TS: 10000 km/s     98 96 94 92 90 88 85 83 81 79
Secondary BFC (5)    Max Range: 480,000 km   TS: 10000 km/s     98 96 94 92 90 88 85 83 81 79
RMPA PD FC (5)    Max Range: 120,000 km   TS: 32000 km/s     92 83 75 67 58 50 42 33 25 17
Medium MC Fusor (20)     Total Power Output 2000    Armour 0    Exp 5%

SRAM Launcher (50)    Missile Size 2    Rate of Fire 10
SRAM FC (10)     Range 4.9m km    Resolution 2
Mag-Conf SRAM (1000)  Speed: 74,200 km/s   End: 0.5m    Range: 2.2m km   WH: 10    Size: 2    TH: 247/148/74

Anti-Missile Search Sensor MR18-R1 (2)     GPS 77     Range 18.4m km    MCR 2.0m km    Resolution 1
EM Detection Sensor EM5-120 (1)     Sensitivity 120     Detect Sig Strength 1000:  120m km

ECCM-5 (1)     Compact ECCM-4 (10)         ECM 50

Strike Group
1x Flyswatter Module   Speed: 1 km/s    Size: 10
1x AECM Module   Speed: 1 km/s    Size: 10
2x SRAM Module   Speed: 1 km/s    Size: 10

Missile to hit chances are vs targets moving at 3000 km/s, 5000 km/s and 10,000 km/s

This design is classed as a Military Vessel for maintenance purposes
"Strike group" is two box launcher pods, one pod with a single missile FC for auto-killing attack craft, and a HPM pod, all 500t.

I'm using this as a "Precursor" flagship. Can the SM gift spoilers ships and have them work? I thought their AI might break so I turned 'em off and am running a couple very familiar races myself This one's not deployed yet though so tell me if I forgot something (besides the fact that I should switch to 25cm mesons to save some space. I just noticed that while typing this).

Also, I finally figured out how to make a fake fixed battery. Apparently you can set a turret's tracking speed to 0 km/s and it will use the ship's max speed instead (or your empire's best turret tracking rate, idk). This is great for me because I prefer big ships with lots of puny fixed guns, and assigning said guns to FCs while scrolling the  window every new selection gets old pretty quick.

Lighthugger?

3km-4km long "colony" ship that can travel just under the speed of light (99.999.....%).

I was thinking that what he is building is closer to a lighthugger rather then a combat carrier

pure theorycrafting , at this stage it is better to actualy go ingame and kill some stuff
1mt non overhauling military ships with fuel harvester is past my imagination
she needs 40 ! ingame years to fill tanks what is possibly on average how long many people have their games running
what is mineral cost + building time ? how long to expand shipyards and with what mineral costs ?

A year's worth of fuel harvesting gives enough to limp around a range of 1.7bkm... I suppose it really isn't all that impressive, but since I did add the infinite deployment time with the recreational facilities, it would give it something useful to do while keeping station on the fringes of known space. It's all part of the "do-everything" package.
I'm not exactly sure how long the shipyard took to get up to size, but I did mention I left it on auto-expand for a few months to a year. As for mineral costs, what else am I to do with 20 million units worth of minerals stockpiled on Earth? And there's another 500 million waiting to be exploited in Alpha Centauri...

Any ship tagged as an Orbital Habitat can be built with planetary industry, regardless if its military or commercial!

I did not know that, but those modules are absolutely huge... I think I would have to get up to 4mt or so before I could consider putting one of those on a ship.

Oh, I forgot to reply to a point!

I think the main problem with that idea [of using an Orbital Habitat] would be the insane-huge (military) shipyard that I would need to have in order  to build it...

Any ship tagged as an Orbital Habitat can be built with planetary industry, regardless if its military or commercial!

No shipyard required, though it does tie up your construction factories something fierce.

Anyhoo, I thought I'd post my largest military design so far. None have actually been built, mostly because I wanted to use shiny new features in newer patches.

Expansion class Command Carrier    128 200 tons     2404 Crew     13743.6 BP      TCS 2564  TH 3300  EM 0
1716 km/s    JR 2-25(C)     Armour 6-226     Shields 0-0     Sensors 80/110/0/0     Damage Control Rating 213     PPV 54
Maint Life 5.03 Years     MSP 14272    AFR 617%    IFR 8.6%    1YR 942    5YR 14128    Max Repair 315 MSP
Intended Deployment Time: 48 months    Flight Crew Berths 347   
Flag Bridge    Hangar Deck Capacity 26000 tons     Magazine 1584    Cryogenic Berths 1000    Cargo Handling Multiplier 25   

Ispartan Drive XXL     Max Ship Size 129000 tons    Distance 25k km     Squadron Size 2
Mk XIII Military Booster (11)    Power 400    Fuel Use 6.19%    Signature 300    Exp 5%
Fuel Capacity 7 000 000 Litres    Range 158.8 billion km   (1070 days at full power)

Pilum Heavy Laser Turret (6x1)    Range 320 000km     TS: 6250 km/s     Power 16-4     RM 4    ROF 20        16 16 16 16 12 10 9 8 7 6
Gauss Defense Grid (12x6)    Range 1000 km     TS: 16000 km/s     ROF 5       Base 50% To Hit
Dalian M14 Capital Targeter (2)    Max Range: 320 000 km   TS: 6000 km/s     97 94 91 88 84 81 78 75 72 69
Stellarator Fusion Reactor (4)     Total Power Output 24    Armour 0    Exp 5%

T-122 (144)  Speed: 32 000 km/s   End: 34.7m    Range: 66.7m km   WH: 9    Size: 6    TH: 117/70/35
K-125 (30)  Speed: 32 000 km/s   End: 48.2m    Range: 92.6m km   WH: 25    Size: 24    TH: 117/70/35

Dalian Torpedo Detector X1 (2)     GPS 210     Range 23.1m km    MCR 2.5m km    Resolution 1
Area Search System (1)     GPS 50400     Range 438.3m km    Resolution 160
Surveillance Telescope (1)     Sensitivity 80     Detect Sig Strength 1000:  80m km
Surveillance Grid (2)     Sensitivity 110     Detect Sig Strength 1000:  110m km

ECCM-1 (2)         ECM 10
Note: The sensors are placeholders, as the new generation sensor systems are currently under development. Effective search range is expected to double given increases in size and improvements in technology.

Expansion-class vessels represent a significant departure from previous command carrier designs as they are built from the ground up as an exploration mothership.  The 'Probe'-class variant of the standard command carriers had never been truely satisfactory, being reliant on jumpgates and constant refueling.  The Expansion class is 30% larger than the current Obsidian-class battle carrier but costs about the same to manufacture (and is 100% larger than the Probe class).  The new high-efficiency engines and most importantly the built-in jumpdrive give it drastically more flexibility and reach.  The jump drive is also capable of jumping standard heavy freighter, cryo-vessel, and troop transport designs, so an Expansion class can easily lead a convoy to establish a forward base or small colony.

Although a powerful vessel in its own right, the Expansion's primary asset is its array of parasite warships. Standard complement is projected to be

-1 squadron of 12 Troll-class multirole Strikers (12x480tons.  12x pulse laser, 24x T-115 torpedo)
-1 Ogryn squadron, consisting of 5 Ogryn Marauders and 1 Ogryn-Magi sensor/command Marauder (6x2,000tons.  10x SR pulse laser, 10x K-125 shipkiller)
-1 Ice Hawk dropship, utilizing cryogenic technology to keep 1 Genetic Legionnaire battalion available for deployment (2,000tons)
-1 survey squadron, consisting of a TBD mix of 6 geo- and grav- survey corvettes. (6x1000 tons)

The Ogryn squadron is experimental at this point. Although generally weaker than 2 additional squadrons of strikers, the Ogryn squadron is far more capable of independent operations, up to and including missile defence and target acquisition. I anticipate being able to use them for colonial defence. They have enough maintenance capability to be left on their own for years as long as there is a colony.  By the time it becomes a problem, either a carrier should be able to reach them or a maintenance base installed. 

FAUX EDIT:

Upon a little thought, I realized the chassis is easily adaptable for utility designs. The high build cost of the command carrier version means that almost any commercial design in the same tonnage range can be built from the same tooling.  For example:

Expansion - Copy class Command Carrier    128 150 tons     2069 Crew     8870.4 BP      TCS 2563  TH 3300  EM 0
1716 km/s    JR 2-25(C)     Armour 6-226     Shields 0-0     Sensors 1/1/0/0     Damage Control Rating 213     PPV 0
MSP 9215    Max Repair 218 MSP
Intended Deployment Time: 12 months    Spare Berths 1   
Cryogenic Berths 1000    Cargo Handling Multiplier 25   
Maintenance Modules: 10 module(s) capable of supporting ships of 2000 tons

Ispartan Drive XXL     Max Ship Size 129000 tons    Distance 25k km     Squadron Size 2
Mk XIII Military Booster (11)    Power 400    Fuel Use 6.19%    Signature 300    Exp 5%
Fuel Capacity 3 000 000 Litres    Range 68.0 billion km   (458 days at full power)

Gauss Defense Grid (11x6)    Range 1000 km     TS: 16000 km/s     ROF 5       Base 50% To Hit
This design is classed as a Commercial Vessel for maintenance purposesA ready-to-go maintenance base design, capable of supporting the Ogryn-class Marauders

Unless I'm doing something wrong, 0.5% of 1mt is "only" 5000 tons. If this is invested completely in CIWS I expect to lose ~70 of 200 missiles assuming equal tech level, so around 500 points worth of damage still gets through. Good point though, I did forget to take into account pd in my previous calculations.

The issue of salvo density did get brought up before and I think the main response was sure, a highly specialised fleet of equal mass will most likely be superior to my single design. This is the price paid for being a generalist. The design decisions/features were focussed on giving the ship strategic value in the forms of long range, self-jump capability, and infinite deployment time. This consumes around 40-60% of the total mass depending on how you want to count it up. Obviously if you try to compare this to a ship optimised entirely for battle it will not hold up too well. Even so, saying it will not harm anything is going a bit far.

You are also forgetting to take into account the fighter loadout the ship carries. Seeing how salvo density is the issue, suppose I take a 100% bomber loadout. With my current bomber design of 10 launchers on a 250 ton craft I will have a fighter missile strike of 50000/250*10 = 2000 missiles. Further calculations show you need about 20% (200 000 tons) of your 1mt ship/fleet dedicated to CIWS to repel that attack. I'm not sure I've faced more than 2 NPR fleets which total at least 200 000 tons, let alone one with that amount of mass dedicated to pd.

You guys need to take it outside and fight, er I mean, go Ingame and do some skirmishes.

Perhaps I am coming off somewhat argumentative (for lack of a better word), but it is sometimes too easy to have the original intention of a message be misinterpreted over the written medium. Maybe judicious use of emoticons would resolve this, but it's just not my style. amimai, you have my apologies if I seemed way too confrontational about this (there's the word I was looking for!).

In any case, I will take a step back and acknowledge that the number of launchers is actually quite low now that I think about it some more. However, now that I've put everything together on the ship I don't quite want to remove anything to make room for more launchers. Perhaps it is worth trading off some magazine space for the launchers?