So I have now combat tested a 2 stage missile that also does not appear to work. 1st stage (the booster stage) works as intended and closes towards the target, but after the 2nd stage separates, it disappears. No event log entry or anything, just vanishes.
I'm sticking to single stage designs for a while.
Did your second stage have onboard sensors?
A missile that runs out of fuel is deleted. That means it is a mistake to put engines (or fuel) on your 'buoy' or mine (stage), as that will only shorten its life.
A missile that entirely loses sensor lock is deleted. If a later stage fails to properly inherit control from the firing ship, the missile poofs. If the 'mine' stage loses lock (or range) to the target then a warhead without sensors has also lost its lock, and poofs.
The Aurora missile system wasn't designed with mines in mind; some clever folk figured out a way to make 'mines' with it and ever since we've been dealing with the fallout.
1. All of my missile/mine stages have active sensors.
2. Fueled sensor buoys, for me, appear to have infinite life. I have yet to observe one disappear.
3. Based on my observations, my missile volley (2 stage missiles, not 3 stage mine) should never have lost sensor lock on the target. I had the target in range of several sensor platforms as well as the launch platform's MFC. At separation range, the missiles were within active sensor range of the 1st stage and they should have been within range of 2nd stage active sensors (1st and 2nd stage have same sensor radius). However I never observed any 2nd stage at all so I have no idea what happened... I was using 5 second increments with 5 second sub-pulses.