Following approximately one month of planned engineering downtime, Rubin Observatory conducted on-sky checkout of subsystems starting the night of 20 October 2025, and resumed full-system on-sky engineering tests the night of 23 October 2025.
Accomplishments during the engineering downtime included the following:
- The team installed the first three of six total panels of the Light and Wind Screen (LWS) in the dome aperture. Installing these first three panels involved the most substantial overhead work above the Simonyi telescope; the remaining three panels can be installed with daytime engineering work during the next months that is not expected to substantially impact nighttime observing. The three panels are currently not functional and kept in stowed position; commissioning of the control systems to dynamically adjust the position of the panels within the aperture during nighttime observing is planned for the next few months.
- The team replaced one of the six hexapod struts that are used for precise positioning of the secondary mirror (M2) in order to improve the reliability of the M2 hexapod subsystem. Laser tracker metrology measurements were taken to evaluate any changes after the strut replacement.
- The team repaired and reinstalled the carousel clamps and replaced slip ring connectors on the LSSTCam Filter Exchange System such that all five filter sockets are expected to be fully operational. The team also conducted maintenance of the cryogenic refrigeration system and updated Camera computing systems.
- The Observing Team used the shutdown as an opportunity to train two new Observing Specialists who joined the team recently. The team ran AuxTel most nights in the last month, which is a good starting point for training on the control system. The Observing Team also used the less intensive time to finish writing their operational procedures/guidelines/troubleshooting guides.
- AuxTel ran smoothly over the course of the downtime month. AuxTel was run when resources were available and when the summit had enough hotel rooms (which were used extensively for the engineers performing the shutdown activities). AuxTel ran for a record of 29 consecutive days, which was the longest stretch since it started running over four years ago.
- Data analyses continued throughout the downtime to support system-level verification and validation, Science Pipelines commissioning, and refinement of the active optics system (AOS) and thermal control systems.
Rubin Observatory is now entering the Early Operations System Optimization period prior to starting the 10-year LSST survey. The test plan for the next week emphasizes on-sky engineering to improve the reliability of the delivered image quality. Rubin Observatory will continue to provide regular updates on engineering work and technical progress through the start of steady-state survey-mode observing. This and future posts on the LSST Community forum will use the #early-ops-update tag.