J. Kissel

Continuing the study from last week (LHO:60766), I've gathered all the best and most recent data for all HSTSs ever built and measured under vacuum*** and compared them against the latest H1SUSFC1 (LHO:60741). 

I attach the one DOF of concern -- the (top mass) Pitch to (top mass) Pitch transfer function. 

Recall that we recently identified that H1SUSFC1 had the wrong M2 to M3 wire thickness after swapping in the optic, and the data I use here (again, LHO:60766) is from *after* the wire has been swapped out for the assembly spec'd thickness/diameter of 0.0047".

So -- let's look at the attachment. Among the 15 SUS plotted, I highlight the outliers in 
   - Magenta: H1SUSMC1 -- lowest combination of 3.21 Hz P2 mode and (nominally ~3.41 Hz ) zero, though it sits in the middle of the pack for the 3.78 Hz P3 mode.
   - Cyan: H1SUSSR2 -- middle of the pack P2 and P3 modes, but its 3.41 Hz zero is the highest aside from H1SUSFC1 at 3.5 Hz.
   - Royal Blue: L1SUSSRM -- Aside from H1SUSFC1, the highest P2 and P3 resonances at 3.26 and 3.87 Hz, respectively, but its 3.41 Hz zero is in the middle of the pack
   - Red: H1SUSFC1 -- by far the highest P2 mode and 3.41 Hz zero coming in at 3.34 Hz and 3.59 Hz, where the P2 mode is surrounded by several substantial cross-coupling peaks, and finally it has a high P3 mode roughly equal to that of H1SUSSRM.

I don't want saturate you with plots, so I won't show you other DOFs, but if you'll take my word for it, all other DOFs transfer functions show no other abnormal behavior -- FC1 does is not the outlier, and the spread for other DOFs is not this large.

Here're the actions from here:
   - Talk with the assembly team if there are any remaining issues with the assembly. It's ringing a bell that something went pearshaped with optic's prisms. And there's also the open issue of quite irregular balancing (though this was before the wire change, and may not still be in play).
   - Try a few guesses at some parameters that might only affect pitch and noodle them in the model to see if I can *quickly* reproduce the response, and if not
   - Try to resurrect Brett's fitting code he'd used to originally identify the previous "M2 to M3 wire's the wrong thickness" smoking gun from LLO aLOG 4766.
   - Take a look at the phase, and compare against the various damping loop designs out there, to see if having this high a zero and P3 mode will seriously impact the damping look design / function.


*** As I right this, I should also say that for HSTSs we never see any shift in these modes between air vs. vacuum. While they're different from SUS to SUS, each SUS stays consistent between air and vacuum.