TMS Meeting Minutes, September 23, 2021

Attendees: Andrew, Bo Xin, Breann, Heejoo, John, Trenton, Yang (Zoom Meeting)

  • John sent out an update from the recent TMS operation
  • It appears there are some time discrepancies between TMS results and the telescope logging
  • John believes he has been able to suppress the filer changing issues that were discovered last week
  • John worries that there is possibly a similar problem with applied telescope offsets and TMS operation
    • When LBC does an offset, it always moves both sides together (moves the telescope mount, not the mirrors)
    • However, if someone is moving with MODS and LBC, there can be offsets that are not from the mount (this mode of operation is only used a few percent of the time)
  • Significant rainy period coming up, so we won't have much time for on-sky LBC use
  • John wants to ensure that the filter problem is really solved, along with the possible pointing offset problem
  • Daylight savings craziness coming up
Follow-up on 9/16 Data:
  • Need further discussion about that data set
  • It will be interesting to see what sort of individual errors there are over time, particularly in terms of pointing stability
  • Andrew notes that thermal gradients on the mirror which cause thermal coma will ALSO cause borosilicate thermal mirror tilt
  • This could be worth focusing on after we sort out the thermal focus characteristics
  • Andrew's most enjoyable night at the observatory was spent driving thermal sine waves in the mirrors
    • 1000's of nm of coma, arcminutes plus of tilt, etc.
    • However, mirror ventilation has improved since this data was taken
    • Now that we have TMS, we should look into this performance further
    • There could already be current data from regular TMS observing with LBC
Shared Risk Observing and Next Steps:
  • John recommends we do more testing with TMS to ensure that it does not have any jumps any it
  • We don't yet have the example that shows that the system works robustly over the course of 90 minutes of observing
  • Some discussion over the best way to filter jumps in data
  • There are some cases where we want to allow large movements and others where we want to blacklist measurements
  • May need to consider incorporating damper factors to stop ringing at our resolution limit or mitigate other problems upon dynamical changes
TMS Collimator Mount Review:
  • Patricio from GMTO shared illustrations of his original design
  • Some of the collimator channels are unstable upon elevation change
  • This appears to be caused by rocking of the magnetic plate on the invar plate attached to the mirror cell
  • When this was originally set up in 2017, the ball point set screws were set to the height necessary for matched pairs of each invar mirror cell location
  • Now, the alignment is quite variable, as the mount plate have become mismatched and need to be tuning
  • The mount to invar assembly is designed with the intent of first having surface contact, then using the ball set screws to constrain tilts and translation using the hole and slot, respectfully
  • With our current mismatch, we have bimodal instability of mounts, causing the collimators to rock
  • The prototype design doesn't emphasize base stability, but rather universality with the new system
Fiber Inspection Tool:
  • Leroy purchased a fiber tester tool, but we don't yet have the right connection for our fibers
  • Planning to purchase the right connector to be able to check all of the fibers
Zernike Fitting to Mirror Thermal:
  • Trenton is making progress on building up a model of mirror Zernike fitting using Andrew's Mathematica notebooks
  • Planning to use annular Zernikes, though we might be able to get away with standard Zernikes over a circular pupil since our obscuration is only ~15%
  • Could be worthwhile reaching out to Dave Ashby (who was heavily involved on the ventilation system upgrade)

-- TrentonBrendel - 23 Sep 2021
Topic revision: r1 - 24 Sep 2021, TrentonBrendel
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