Design, assembly and validation of the Filter Exchange System of LSSTCam

The Filter Exchange System (FES) of the Legacy Survey of Space and Time camera (LSSTCam) for the Vera C. Rubin Observatory has been integrated into the camera assembly before shipping to Chile. It holds five 75-cm filters weighing 25.5 to 38 kg. The main requirement for the FES is to perform each exchange in under 90s, with 100-mu m positioning in the focal plane, while operating within the envelope of the camera body. The FES is split into three motorized subsystems: the Carousel stores the filters and rotates the selected filter to the standby position, the Autochanger moves the filter between the standby position and the focal plane, and the Loader can be mounted on the camera body to swap filters in and out during daytime, allowing the use of the full 6-filter set of LSSTCam. The locking mechanisms are also motorized, and their designs and qualifications account for seisms up to magnitude 7. Additional design constraints come from the temperature range at the Observatory and the cleanliness requirements for the filters and lenses. Programmable Logic Controllers enforce the safety equations of the system, and the control of the FES has been integrated into the overall Camera Control System software. After assembly of a full-scale prototype, the FES has been assembled and tested in France on a test-stand simulating telescope attitude, then integrated into the camera body at SLAC National Accelerator Laboratory. It meets its required performances, including an average exchange time of 83s.