This is Week 4 of the Early Operations optimization period. A general update on the technical activities and demonstrated performance during Early Operations was presented at the LSST Discovery Alliance Member Representative meeting on 20 November.
During the week, the team deployed and tested several updates for the Active Optics System (AOS), including
- improved selection of out-of-focus “donut images” of the telescope pupil on the corner wavefront sensors to use for wavefront estimation using a pre-generated catalog of suitable target stars;
- improved modeling of the spatial variation of intrinsic aberrations across the focal plane including the as-built optics and micro-scale variations in the relative sensor heights;
- continued refinement of the filter-specific focus offsets to apply during filter changes;
- and updates to region of interest (ROI) selection for the specialized guider sensors on the corner rafts to enable routine guider measurements to evaluate contributions to the delivered image quality on timescales faster than the 30-second visits.
In addition to dedicated tests to support the updates above, on-sky testing included further long sequences at fixed telescope orientation to evaluate the stability of the open loop and closed loop AOS control systems under a range of conditions.
The team continued the campaign of stray light testing, in this instance, using Saturn as a bright source to test reflections off surfaces within LSSTCam.
As part of evaluating performance during wide-area surveys driven by the Feature Based Scheduler (FBS), the team exercised the capability to interrupt standard pre-LSST observations with Target of Opportunity (ToO) observations. The multi-epoch ToO observations largely replaced the pre-LSST survey, such that the total time allocated for FBS-driven observations continued to be 1-2 hours per night, on average, during the week.