Main Structure of the Survey Camera for CSST: A Paradigm for Structural Design of Large-Scale Complex Space Optical Instruments

As the core observation instrument of the China Space Station Telescope (CSST), the Survey Camera (SC) features large volume, heavy weight and high complexity, which poses considerable challenges to the development of its Main Structure (MST). Focusing on the design, optimization and verification of the MST, this study aims to meet the technical requirements of lightweight, high stiffness, high strength and mechanical stability, and provide high-precision Measurement References (MRs) for components such as the Focal Plane Array (FPA). The MST is an M55J carbon fiber/cyanate ester resin composite framework and incorporates titanium alloy inserts for thread machining. The thickness of carbon fiber plies was optimized using size optimization techniques to maximize structural efficiency. The carbon fiber plies and embedded parts along the structural force transmission path were strengthened to improve structural strength. A spherically mounted retroreflector (SMR)–cube mirror composite MR system was employed, along with a contact–non-contact integrated measurement scheme, achieving a position and angle measurement uncertainty of 5.26 μm/5.53″ (3σ). Through experimental verification, the final mass of the MST was controlled at 66.8 kg, and the fundamental frequency reached 120.6 Hz. After assessment via vibration tests and thermovacuum tests, the strength, mechanical stability, and thermal stability of the structure all met the mission requirements.