Week 11 of the Early Operations system optimization period
High dewpoint temperatures continued to delay and/or interrupt observations on parts of several nights during the week.
The team finished collecting the set of calibration data, including sets of biases, darks, and whitelight flats, for the upcoming LSST Camera sequencer CCD readout controller firmware update to adopt the natural frequency of the readout electronics. These data are currently being analyzed prior to making the new firmware the default for nighttime operation.
Most of the on-sky time during the past week was devoted to sustained pre-LSST observations with the feature based scheduler (FBS). The scheduler configuration tested this week is similar to the nominal LSST cadence with the exception of inserting Active Optics System (AOS) closed loop iterations at the position of the next scheduled visit immediately after a filter change. This approach explores a potential near-term mitigation for the observed focus drift that is still under active investigation, and is intended to improve the reliability of the delivered image quality by adding a few minutes overhead for each intra-night filter change. Work is ongoing to optimize the number of iterations and gains of the control loop to achieve the most robust and efficient re-focusing of the optics after a filter change.
In parallel, the team is analyzing data from recent weeks to prepare the refined elevation and physical rotator angle look-up table (LUT) that will incorporate both hexapod and mirror bending mode degrees of freedom.
The team collected on-sky observations to test the absolute calibration of the Rubin Observatory timing system, including the clock system and the motion of the camera shutter, that is necessary to accurately report the positions of astronomical objects such as asteroids and the timestamps of transients.
There are also ongoing efforts to optimize the timing controls and interactions between system components to reduce the wait time between completing an exposure and beginning the telescope slew, as well as reducing the settle time after the telescope slew before opening the shutter for the next exposure. These control system improvements are anticipated to reduce the total time between visits, and thus increase the overall survey speed.