Week 32 of the Early Operations system optimization period
Rubin Observatory continued with mostly pre-LSST observations this week. The Simonyi Survey Telescope was off sky for ~1.5 nights due to clouds and 1 night due to unscheduled engineering downtime. A total of ~2700 pre-LSST visits were acquired. During the pre-LSST observations, the estimated instrument contribution to the PSF FWHM was generally stable at the level 0.4 – 0.45 arcseconds and the per-night median delivered PSF FWHM varied from 0.8 – 1.0 arcseconds.
The team continues the thermal control test for the primary-tertiary mirror (M1M3) that reduces the maximum rate of change for the thermal set point in order to minimize thermally induced distortions of the optical figure.
The team tested an update for the Active Optics System (AOS) wavefront estimation pipeline that more accurately models the variable optical throughput of light passing through the LSST Camera filters as a function of the angle of incidence of the incoming beam. This effect modifies the radial intensity pattern from the inner to outer edges of (intentionally) out-of-focus images of the telescope pupil used for wavefront measurement, with the largest expected impact for the u and y filters.
The team also validated the capability to synchronize telescope pointing corrections together with optical focus and alignment corrections within the standard slew-and-expose sequence, thereby improving the pointing accuracy and reducing image quality contributions related to telescope tracking drift. The pointing corrections use the optical model to pre-emptively compensate for offsets induced by adjusting the rigid body degrees of the freedom (tip, tilt, translation) of optical elements controlled by the AOS.
The next week is expected to be mostly pre-LSST observations.
The currently installed filter set is grizy, with the next swap to remove y and install u planned for 9 June.