Week 6 of the Early Operations optimization period began with a multi-night test of extended wide-area survey observations using the Feature Based Scheduler (FBS) to evaluate the delivered image quality performance following the many updates of the past month. For this test, the team used a “constrained” version of the pre-LSST configuration with limits imposed on the rotator angle range and elevation angle range, and using only a single filter on each night. On one night, the survey observations ran continuously from evening -18 degree to morning -18 degree twilight. On multiple nights, the median estimated system contribution to delivered image quality was at the level of 0.4” while running in the constrained mode, with stable operation of the Active Optics System (AOS) closed loop over multiple hours. Further refinements to the open loop look-up tables (LUTs) for filter focus offset and elevation and physical rotator angle will be needed to achieve comparable performance for the nominal (unconstrained) LSST scheduler configuration.
Much of the remainder of the week was devoted to further tests of updated versions of the filter focus offset LUT and running FBS-driven survey observations with periodic intentionally applied perturbations to the optical state to evaluate the reliability and efficiency of the AOS closed loop convergence. Other on-sky tests included AOS closed loop stability tests as well as stray light tests aiming to reproduce known features by targeting bright sources.
Following several months of software development and in-dome dynamic testing to optimize the performance of the inertial compensation system, the telescope mount assembly (TMA) motion settings for the commanded angular velocity, acceleration, and jerk during telescope slews were increased by a factor of 2 for use during nighttime operations. The team will continue analyzing the inertial forces experienced by the primary-tertiary mirror (M1M3) and other telescope subsystems, as well as the expected improvement in the rate of acquiring visits for survey observations.