The TFs I took this morning show that the rubbing is back on the ETMx main chain now that we are back down to 7 Torr in pressure. The rubbing TF looks exactly like the rubbing TF we had before I opened up the gap of the EQ stops around the test mass. While we knew that the rubbing could have been possibly due to the barrel stops around the test mass OR the PUM mass above the test mass, we assumed it was specifically the stops around the test mass since those were the only ones adjusted during the Dec vent. I did not check the PUM stops (or any other stops further up the chain) yesterday. Darn it, I should have! The temp+buoyancy effect is the same on the PUM as it is on the Test mass, so the gap of the EQ stops should be bigger around the barrel there too.
So, we are re-venting today to now:
- Inspect other EQ stops, look for outliers in gap settings further up the main chain
- Open up the gap around the barrel of the PUM to the 1mm (top stops) and 1.5, (bottom stops)
We'll employ the same stripped down version of the entry/exit checklist as yesterday, namely to inspect and DI Nitrogen blow the HR face of the ETMx on the way out.
The reaction chain TFs continue to look healthy, so no problems there.
Attached here is a trend of ETMx Vertical and Pitch relative to the pressure and temp of the chamber/VEA, with some annotations of know and unknown events.
Note, the vertical seems to stall out as expected after the buoyancy sag, however the pitch trend turns over for some unknown reason at ~1:30pm PT yesterday for a yet uncorrelated reason. (Kyle paused the roughing pump for the evening at ~4pm PT, and no one claims to be doing anything with the ETMx or out at Ex. I've confirmed that the pitch offsets were not changed during any of this trend.)
During today's vent I took a few ETMx TFs at various chamber pressures. At 270 Torr, the suspension still showed rubbing. Now at 550 Torr, the suspension is free of rubbing, however the vertical trend shows that it is only ~10% into it's buoyancy "unsag". It looks like there is a wiggle at ~400 Torr which may indicate when it came fully free from the rubbing stop.
