Abstract:

I implemented GAS modal damping for BS.
Since the noise performance at high frequency seems worse that the current OBSERVATION state, further tuning is necessary.

Detail:

I decoupled the sensors and actuators with the same manner with SR2 and SR3.
Figure 1 and 2 show the sensor and actuator matrices, respectively.
Figure 3-5 show the suspension plants at modal basis.
Figure 6-8 show the OLTF of modal damping control loops.

Figure 9 shows the spectrum comparison of IMV OSEM with LOCK_ACQUISITION state (blue), OBSERVATION state (green), and modal damping (brown).
The noise above 0.9 Hz becomes worse while the noise beow 0.9 Hz looks slightly better, so further tuning is necessary.

Due to the large earthquake, I gave up to continue the work today.

Images attached to this report

36781_1776673433_Screenshot from 2026-04-20 17-23-40.png

36781_1776673435_Screenshot from 2026-04-20 17-23-47.png

36781_1776673504_Screenshot from 2026-04-20 17-24-35.png

36781_1776673506_Screenshot from 2026-04-20 17-24-47.png

36781_1776673508_Screenshot from 2026-04-20 17-24-55.png

36781_1776673652_Screenshot from 2026-04-20 17-25-33.png

36781_1776673654_Screenshot from 2026-04-20 17-26-06.png

36781_1776673656_Screenshot from 2026-04-20 17-26-30.png

36781_1776673880_Screenshot from 2026-04-20 17-31-11.png

Comments to this report:

takafumi.ushiba - 13:12 Tuesday 21 April 2026 (36787)

Conclusion:

It is better to use GAS modal damping only for M1 and the other mode should be damped at IM stage.

Detail:

I checked the current BS GAS damping control at OBSERVATION state and found that only the 1st modal mode is damped at F0 GAS while the other mode is damped at IMV OSEM.
So, I tested the modal damping performance only with M1 controls.

Figure 1 shows the comparison of the spectra with M1 modal damping (red) and current OBSERVATION state (blue).
Owing to turning of M2 and M3 modal damping, high frequency noise reduces a lot above 1 Hz.
Since M2 and M3 mode is damped at IM stage, we can use this configuration during both lock acquisition and observation.
So, it is better to use only GAS modal damping for M1 and the other mode should be damped at IM stage.

Note:

This configuration would be better for the other Type-B suspensions, so it should be checked later.

Images attached to this comment