J. Oberling, C. Gray

After this morning's NPRO shut-off, we noticed the FSS RefCav TPD was down to ~1V (the RefCav Refl spot showed that the pitch had moved significantly as well).  At the rate of decay (see attached 7 day trend), there was a good possiblity of the TPD not surviving until maintenance Tuesday (1-1-2016), so we decided, with M. Landry's permission, to go in a adjust it.  In the interest of returning to operation quickly, we only adjusted the periscope mirrors to bring the TPD back up; no investigation as to the cause of the alignment shift was done.

We began by adjusting only pitch on the top periscope mirror.  This only got us back to half way, so I decided to include the bottom periscope mirror and walk the beam.  Walking the beam down got the TPD to ~1.47.  We then did a small yaw tweak to the top periscope mirror only, which got us to ~1.51V.  We then measured the visibility of the cavity, and then turned the ISS back ON and left the PSL enclosure.  Total time in the enclosure was ~30 minutes.

• FSS RefCav TPD (ISS OFF)
  • Before adjustment: 1.08 V
  • After adjustment: 1.51 V
• RFPD DC Voltage
  • Locked: 35 mV
  • Unlocked: 220 mV
  • Visibility: 84.1%
• FSS RefCav TPD (ISS ON): 1.50 V