March 23, 2024

Aurora - 2.2+ Missile Warfare

Long-time readers will remember that 4 years ago, a new topic popped up on Naval Gazing. I started talking about Aurora, a free space-based 4X game where you design and build ships, as well as running an entire civilization. I've been a fan for a very long time, and there was recently a major update (v2.2, although this was based on 2.5) that made significant changes to missile warfare that I thought deserved analysis. We'll return to attacking ships soon.

Missile warfare, described in these three posts (read them first if you don't understand the old system and what to know what I'm talking about), used to be pretty simple, almost to the point of being solved. There was a little room for variation, but missile defense was entirely a matter of getting as many damage 1 shots out as possible, normalized for hit rate. Offensive missiles had a bit of flexibility, but even there, options were pretty much limited to tradeoffs between more damage and a lower chance of being shot down. A single hit would take out any missile, so you wanted to keep your missiles small.

So what changes did Steve make, and how do they affect ship design and operations? Well, first, beam point defense was radically changed. Instead of it dealing with each incoming salvo one at a time, allocating the next available weapon to it, the allocation is done entirely ahead of time, before a single shot is fired. This means that some shots will be wasted (CORRECTION: allocation is per-missile, not per-salvo. I misread the notes, and a lot of this math needs to be re-done.), and a few missiles are likely to leak through, where only CIWS and decoys can counter them.1 The player gets to choose which FCs are allocated first, and how many shots each FC is going to place against a given target. To discourage setting "how many shots" to the maximum, point-defense fire now incurs a failure rate, just like offensive beam fire.2 The result is that the player has to make a lot more decisions about which weapons are going to be set for PD and why. Among other things, it makes a lot less sense to use your offensive beams for defense, as they cost an arm and a leg to fix, and you have to try and balance getting enough hits to stop incoming missiles with not wasting a ton of shots on overkill. In fact, I think it might be nice to have a bit more automation here, as the biggest single variable in how many shots you want to take at each incoming missile is speed, and if you are under attack by multiple types of missiles at the same time (say, AMMs and ASMs) it can be really annoying to switch back and forth regularly.

But that still implies a setup rather like the old one, and there are a couple of other things that Steve threw in to keep life interesting. One is decoys.3 Each decoy is .5 MSP, and looks like the missile to the sensors of an incoming attack. If the ECCM rating of the system is equal to or less than the missile's ECM rating, then each attack has a 1/(1+decoy number) chance of hitting the missile. Otherwise, it will take out a decoy, making it easier for the next attack to hit. If the ECCM rating is higher, then the decoys become less effective, with the chance of hitting the missile being 1/(1+(decoy number * (1-.2(ECCM-ECM))).4 This obviously throws a great deal of uncertainty into how many shots to allocate (particularly for the first wave of a salvo), and generally makes it a lot easier for an attacker to get missiles through.

The second addition is the laser head. This is a .25 MSP system that allows standoff detonations, but at a cost in warhead strength depending on what technology has been researched. Beam defenses still get to take their shot, but only at the detonation range, which is likely to be significantly farther than the standard range that normal beam defenses are designed to work at. At best, the fire control is far less effective. More likely, this is entirely outside the range of normal beam defenses, and the defender is forced to rely on offensive beams or maybe some dedicated anti-laser head systems. The best I've come up with so far is turreted reduced-size 10 cm lasers, although depending on the detonation range you're dealing with, small high-velocity railguns might also be a viable option. Obviously, unless you're optimizing against a specific enemy that you know uses laser heads almost exclusively, it still makes sense to keep conventional short-range defenses around, too, because it's going to be hard to get a lot of shots out of longer-range PD weapons.

OK, but what about AMMs? Don't those still work reasonably similarly, decoys aside? Well, no. The other big change Steve made was deleting agility, which was used to raise the hit percentage above the standard .1*(own speed/target speed). Now, all missiles have that hit chance unless they're fitted with terminal guidance, a .25 MSP system that raises your hit percentage based on the researched tech, from a low of +25% to a high of +90%. I think this is a bad system for AMMs, because it's too big for the benefits it gives you relative to another new introduction, multiple warheads. Now, you can divide your warhead space into multiple smaller sections that attack independently, each of which adds only .1 MSP to the missile. A single additional warhead effectively doubles the effectiveness of the AMM, which is as much as the best terminal guidance can do, and with less volume. This is aided by another change, the fact that warheads below strength 1 are now useful against missiles. A fractional warhead will instantly destroy any missile that is smaller than 20 times its warhead strength, and has a chance of destroying bigger missiles, too. Obviously, picking warhead strength is another area where the player is going to have to make a decision on limited information.

But there's another system that is very useful for AMMs: Retarget Capability. This is a .5 MSP system which allows a missile that didn't hit its target the first time to go around and attack again. It's of somewhat dubious value on ASMs because the beam defenses will get another crack at it, but AMMs don't have defenses, so it effectively guarantees a hit if it has enough chances. But it's also big enough that squeezing it into a size-1 missile is probably not feasible. The other thing to keep in mind is that it won't kill the target if it runs out of fuel first, so it's probably a good idea to give it a significantly longer range than the fire control you plan to pair it with. Oh, and I checked. If a retarget-equipped AMM has multiple warheads, it will essentially check every warhead independently, and if none of them hit, then it will pass on exploding and keep attacking the next round. If even one of them hits, then it's going to disappear. Hit chances are likely to be low, so fit multiple warheads. The only real counter to this is decoys (which work against AMMs exactly like they do against beam defenses), but ECCM (a .25 MSP system) is useless unless you have an edge over the enemy's ECM, so it probably doesn't make sense to fit your AMMs with it unless you know you're facing an enemy who uses decoys and who you have an EW edge over.

But what are the implications if you want to use missiles yourself? In a lot of ways, they're the inverse of what I've discussed on the defensive side. Decoys are very powerful, and you should make use of them unless the enemy has a huge edge in electronic warfare (and in that case, you're probably dead anyway).5 ECCM is almost mandatory, as there's a new missile jammer which multiplies the chance of a missile hitting by (1-.2*(ECM-ECCM)),6 which rapidly cuts into your hits. Terminal guidance can be quite useful if your accuracy is lower than you'd like and you have a big missile, while retargeting is probably not worth it because you go through PD fire again. I can't see much use for multiple warheads. Unlike with an AMM, doubling your chance of a hit and halving the strength of a warhead isn't usually a good trade for ASMs.

And then there's laser heads, which as discussed above are great for bypassing beam defenses, but particularly early on, you're losing a ton of damage. (That said, you're getting the high-penetration laser damage pattern instead of the low-penetration missile one, so it might not be quite as bad as it sounds.) The big question is what to set the detonation range for during missile design. Besides the technology that sets what fraction of normal warhead damage goes into the laser head, there's another one that sets the focus range. If the warhead goes off within the focus range, then the laser head deals full damage. If it's further out, damage is multiplied by (focus range/distance), with a cap of twice the racial beam fire control tech range. Obviously there's no reason to ever set it closer than focus range (detonation range doesn't make any difference on hit chance), but it might occasionally be useful to set it off further out if necessary to avoid a particular defense system. Oh, and laser heads and multiple warheads are incompatible.

On the whole, I'm very excited for the new missile system. Steve said that his goal was to make big missiles more useful relative to the previous tactic of spamming lots of small ones, and on the whole, I think he's done a great job of it. Decoys in particular are a significant boon to bigger missiles, enough to make them competitive with smaller missiles, although if you're wanting to go for maximum defense penetration, then smaller missiles are still the way to go.

1 Or you can try and use shields to absorb the leakers, which I've found works quite well.

2 MATH FOOTNOTE: Because of how probabilities work, you will want to aim for slight overkill. For instance, against a 6-missile salvo with hit probability of .34, shooting 3v1 has a 58% chance of getting a leaker, while 4v1 drops this to 24% and 5v1 down to 7%. Smaller salvoes increase the odds of leakers slightly, as do lower hit probabilities when the product of (Ph*shot number) is held constant. The opposite is generally true, although with small salvoes, low shots can start to overwhelm a high Ph in terms of leaker odds. If you want to investigate this more yourself, the keyword you want is "binominal distribution", or you can use the Monte Carlo spreadsheet attached below.

3 It's worth noting that there are now also decoys for ships. Basically, if enough missiles leak through beam fire, your ship can launch a decoy, which will have a certain size, and absorb incoming missiles in proportion to the ratio between its size and the size of the ship. I've only used them a tiny bit, and have not come away particularly impressed with their utility.

4 I think this equation could use some tweaking. There is no difference between, say, shooting at an ECM 5 missile with an ECCM 5 fire control, and shooting at an ECM 10 missile with no ECCM whatsoever. I get why it doesn't work like the normal system where an equal-level ECCM completely counters ECM, but it might be nice to have full effectiveness at, say, 2 levels of ECM overmatch instead of at the same level. If nothing else, this setup greatly reduces the incentive to use ECCM on AMMs.

5 MATH FOOTNOTE: Because decoys go away if the actual missile is killed, the average number of hits required to kill a missile is equal to 1+.5*decoys, assuming that you shoot single shots at it until it dies, then stop. (If this doesn't make sense, think of it as there being a 50/50 chance that a new decoy will be targeted before the missile or after it.) This is not a perfect assumption for anything other than 1v1 single-warhead AMMs (multi-warhead AMMs all attack the same missile, so there's a tiny bit of slop there, but it should be pretty close to accurate in that case, too), and it gets rather weird with beams, where allocation is on a per-salvo basis. A Monte Carlo simulation (essentially rolling dice a bunch of times and counting the outcomes) suggests that beam defenses facing a salvo with 6 2-decoy missiles would have at least one leaker about 40% of the time if they fired the 2 hits per missile (assuming 100% hit rate for simplicity) that this math suggests. If they fire 2.5 hits per missile, then this drops to something under 5%. Smaller salvoes seem to have slightly fewer leakers at 2 hits and more at 2.5 hits, while large salvoes show the opposite pattern. There's a more sophisticated version available here that can accommodate up to 12 missiles per salvo and takes both hit probability and decoys into account. Yellow boxes are inputs, blue are outputs. It runs 1,000 different salvoes and sums the results. Note that "leakers" is the percentage of salvoes that have leakers, not the percentage of leakers.

6 There are similar systems for beam FC and active sensors, and this is a significant improvement over the old system where you could often completely block the enemy with a much smaller edge, although as usual, I rather wish it wasn't quite so even.


  1. March 24, 2024Alexander said...

    Have you seen Nebulous: Fleet command? I've not played it, but it has a strong ship (and missile) design element. The gameplay is focused on tactical command during a battle rather than building an interstellar empire, so you won't be able to chase down commerce raiders with overwhelmingly superior battle cruisers, or have to help a survey vessel escape from the precursor automated defence platforms it has disturbed. Still, a tighter focus on the combat does mean you get to see your designs being given a thorough test in battle.

  2. March 24, 2024bean said...

    I have seen it, and played a little bit. It didn't grab me the same way, but I also haven't had the time to get over the learning curve.

  3. April 03, 2024Bernd said...

    Thanks for the update: I haven't had any time to check out 2.0 yet. Iceranger is going to have a lot of run completely rewriting his missile optimizer if he hasn't already!

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