The Solar Upper Transition Region Imager (SUTRI) is an extreme ultraviolet solar imaging telescope that focuses on dynamically observing the solar transition region within a narrow band at 46.5nm. This paper describes the optical parameters, optomechanical structural design, finite element simulation, and on-ground environmental testing. To satisfy the narrow band requirement, the telescope employs multilayers coated on Ritchey-Chrétien optics and filters mounted at the front aperture and ahead of the focal plane. The primary and secondary mirrors are glued to invar frames that provide peripheral support. The telescope contains three mechanisms, which are a focus mechanism, a filter wheel, and a front door. In addition, this paper carried out finite element simulation of modal analysis, optical performance and structural strength. These simulations verified that the opto-mechanical system design is feasible. Finally, the telescope successfully underwent a series of on-ground environmental testing and was subsequently launched carried by SATech-01 satellite in July 2022.
Aluminum alloy mirror by additive manufacturing (AM) has attracted much attention in recent years because of its excellent strength, machinability, and high design freedom. This paper describes the machining process of lightweight mirror based on AM AlSi10Mg body. The mirror is processed to the accuracy of 45.6 nm in RMS, and the surface roughness reaches 0.585 nm in Rq. Initially, the mirror substrate is processed using selective laser melting (SLM) with AlSi10Mg powders. Then the backside surfaces and optical front surface of the mirror substrate are processed by CNC turning and single-point diamond turning (SPDT). After the Nickel-Phosphorus (NiP) coating is electroplated, ultra-precision machining is used to process the optical surface finally, in which, SPDT and magnetorheological finishing (MRF) is used to ensure the surface accuracy. Then subsequent polishing eliminated low frequency stripes and MRF marks, significantly reducing the roughness. In addition, the thorough release of internal stress is an important factor to ensure the stability of the surface accuracy. The experiment results prove that the process chain can satisfy the ultra-precision fabrication of infrared optical surface and the roughness has the potential to be applied in ultraviolet optical system.
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