Week 13 of the Early Operations system optimization period
The team continued pre-LSST observations driven by the Feature Based Scheduler (FBS) as the primary nighttime activity. The sustained observations have provided further opportunities to examine the performance of the open-loop and closed-loop control system of the Active Optics System (AOS) as the observatory makes slews and filter changes. The team ran some of the pre-LSST observations this week with one less basis function (11 versus 12) applied during the closed-loop corrections to reduce the interplay between corrections for de-focus and spherical optical aberrations. The experiment appears to have been successful for stabilizing the focus during survey operations, and additional work is in progress to optimize the simultaneous control of de-focus and spherical aberrations. Additional dedicated engineering observations were acquired to investigate the optimal filter-specific focus offsets.
Work to enlarge the available time for survey operations continues. The team confirmed that the insulation added around utility lines to the telescope top end assembly in the past week has substantially reduced the accumulation of condensation in high humidity conditions, and accordingly, have expanded guidance on the range of acceptable dewpoint temperatures for nighttime observing. The team also demonstrated the capability to complete initial optical focus and alignment and to begin FBS-driven observations as early as -13 deg twilight, nearly reaching the design goal of -12 deg twilight for LSST.
On the night of 20 January, there were multiple interruptions to the flow of dynalene coolant to the LSST Camera, resulting in the detectors and readout electronics being powered down, and a warm-up of the Camera. Camera support scientists were closely monitoring the situation and the Camera remained safe throughout the procedure. The telescope will remain locked at horizon pointing for several days during the recovery process to restore stable coolant flow and bring the Camera back to regular operations, expected early next week.
The team is preparing for a planned engineering downtime scheduled for three weeks starting in early March. The engineering activities include maintenance of the hydrostatic oil supply system that allows the telescope to rotate in azimuth with minimal friction, and annual maintenance of the LSST Camera where a spare autochanger or shutter is swapped into the camera (autochanger this time). Additionally, a long list of post-construction punch list items will be worked on and a full refresh (system flush) of the LSSTCam cryogenic refrigeration system will occur.
During the next weeks in February leading up to the March engineering downtime, the primary objective is anticipated to be running sustained pre-LSST observations to characterize the distribution of delivered image quality and effective survey speed for candidate FBS configurations of the survey strategy to use for the start of LSST.