I feel like there is an instability in my thought process on this. Before my tendency to try to scale and generalize this problem brings me to a full stop I will make small but quick progress.
First thing is to calculate the noise budget for a simple Michelson. The involved optics are:
all sensed with OSEMs and OpLevs only.
Things to fetch:
1. OSEM sensing noise. Where do I get the null stream (AKA butterfly mode)?
2. Oplev noise, look at the SUM channel (or this elog)
3. Actuation TF. Latest elog.
4. Coil driver noise. Going to take the HP supply curve from this elog.
5. Seismic noise + Seismic stack TF. Or maybe just take displacement noise from gwinc.
6. Laser noise. Still need to search.
7. DAC noise. Still need to search.
I'm planning on simulating the BHD readout noise in a manner very similar to the ALS noise model using Simulink. I've made a sketch of the model for the longitudinal DOFs (attached). A model for ASC will be similar but with more measurement devices (OpLevs, QPDs, WFSs).
I'm not pretending to simulate everything in this diagram on the first go, it is just a sketch of the big picture.