Week 33 of the Early Operations system optimization period
The first snow of the season arrived at Cerro Pachón this week. The Simonyi Survey Telescope dome was closed due to clouds/precipitation for 4 nights this week, and that time was used to acquire calibration data with the Collimated Beam Projector (CBP) and to run a thermalization test for the primary-tertiary M1M3 mirror.
The limited on-sky time this week was devoted to pre-LSST observations.
The team continues to optimize thermal control of the M1M3 mirror to keep the bulk temperature of the glass ~1 C below the ambient temperature throughout the night while also minimizing thermal gradients that affect the mirror figure. Daytime engineering work to adjust the air flow rate through 1720 nozzles that circulate conditioned air throughout the M1M3 honeycomb cell structure has led to clear improvements for the control of radial temperature gradients in recent months. Adjustments to the air flow rate as a function of radial distance from the center of M1M3 account for radial variations in the glass thickness of M1M3. The team is also tuning the temperature set point relative to the M1M3 bulk temperature to minimize temperature gradients along the optical axis of M1M3.
The next week is expected to be primarily survey observations. The team is preparing new deployments and targeted on-sky engineering tests for the Active Optics System (AOS).
The planned filter swap to remove the y filter and install the u filter took place on 9 June such that the current filter set is ugriz.