The Simonyi Survey Telescope (formerly known as the Large Synoptic Survey Telescope) of the Rubin Observatory is an 8.4m telescope now in construction on Cerro Pachón, in Chile. This telescope has been designed to conduct a 10 years’ survey of the sky in which it will map the entire night sky every three nights. The Mirror Cell Assembly system is a 9x9m steel structure that provides positioning, support, figure correction and temperature control to the primary and tertiary mirror. It is composed of two main systems, the Support System and the Thermal Control System. The Support System provides positioning, support and figure control of the mirror as well as dynamic forces compensation. The Thermal Control System will control the bulk temperature and temperature variations throughout the mirror. The temperature variations produce thermal distortions of the mirror which produce image degrading distortion of the optical surface. Variations between the bulk temperature and the ambient degrade local seeing and can produce condensation. The mirror cell assembly was designed and build in Tucson, Arizona by the LSST engineering team, and was tested, to confirm correct integration, at the Richard F Caris Mirror Lab to confirm the optical performance of the system using the real glass mirror. After successful testing, the mirror cell assembly was disassembled, packed and shipped to the Cerro Pachón summit in Chile where it was integrated with the surrogate mirror, and installed on the telescope mount assembly (TMA) for system performance test. Once system performance test concluded, the mirror cell was transported to the maintenance level to remove the metal surrogate mirror, install the glass and coat. After coating the mirror, the mirror cell assembly will be integrated with the telescope mount assembly to conduct final testing and verification.
The Giant Magellan Telescope (GMT) primary mirror subsystem (M1S) consists of seven 8.4m diameter borosilicate primary mirrors that must be maintained at the ambient nighttime air temperature as it changes throughout the observing night to prevent seeing effects at the mirror surface. Additionally, thermal gradients internal to the mirrors must be minimized to prevent figure errors caused by distortions of the mirror due to the non-zero thermal expansion coefficient of the glass. To address these requirements, the GMT M1S team is fabricating a prototype thermal control system design that consists of a sub-critical refrigeration system utilizing high pressure (~30 to ~60 bar) CO2 (R744) refrigerant. This paper describes the design and status of the M1 Subsystem Thermal Control (M1STC).
GMTO has developed a full-scale prototype of the cell that can house an 8.4-meter borosilicate mirror. This test cell is populated with all the active support control hardware and a mass simulator that simulates the mirror weight and the moment of inertia. GMTO has implemented the control software with all the core features needed to operate the active support system. A series of tests have been carried out to verify the functions, performance, and safety of the active support control system. The tests were carried out at several different orientations of the cell to demonstrate that the active support system works with the changing zenith angle and location of the mirror on the telescope mount. This paper describes the results of important safety and dynamic response tests of the active support system.
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