###### Abstract  
The spaceborne turntable is a piece of precision optical equipment utilized for monitoring space information and facilitating laser communication. The measurement accuracy of optical instruments is correlated to some extent with the mechanical properties of the structure. Addressing the design challenge posed by the U-frame in the spaceborne optoelectronic tracking and pointing turntable, this paper proposes a multi-constraint topology optimization method utilizing Abaqus/CAE and TOSCA. This method offers insights for U-frame design and has undergone scientific validation. Initially, the empirical design structure is established, optimization design areas are defined, and the initial model undergoes pre-processing in Abaqus/CAE. Subsequently, conceptual and mathematical models for topology optimization are developed, with the objective of minimizing structural compliance (thereby maximizing stiffness), and including constraints related to volume fraction, first-order natural frequency, and stress. Utilizing TOSCA, the U-frame topology optimization design is finalized, resulting in an optimized conceptual model. A comparative analysis of the optimized design against the empirical design structure demonstrates a significant 27.53% reduction in maximum stress, enhanced static stiffness, an increase of 11.48% in the first natural frequency, and a 4.3% reduction in mass. Moreover, the turntable that utilizes the optimized design structure not only meets reliability requirements in spacecraft structural design but also provides a stable platform for precise optical load alignment. The static and dynamic performance of the optimized U-frame has been enhanced, effectively mitigating the impact of external excitation on optical instrument measurement accuracy and meeting the lightweight design requirements for the U-frame, thus demonstrating the efficacy of the topology optimization method. This research offers valuable insights into U-frame design for spaceborne optoelectronic tracking and pointing turntables and carries significant guiding implications. space target detection. Its primary components include azimuth shafting, left and right pitch shafting, support tracking frame, locking mechanism, and carrier stage, to name a few [3] (pp. 203-217). Figure 2 displays the structural diagram of a two-dimensional satellite space turntable system. [PERSON] and [PERSON] summarized the latest progress in space optical instrument design in recent years and pointed out future research directions [4] (pp. 1983-1995). Currently, the design of the spaceborne optoelectronic tracking and pointing turntable's system structure often incorporates a \"U\"-shaped support tracking frame, attributed to its large structural stiffness, high space utilization rate, and excellent overall performance [5; 6] (pp. 879-888). Serving as the primary load-bearing component, the U-frame in the 2-D turntable simultaneously connects both the azimuth and pitch shafting. The photoelectric load is mounted on the carrier platform, interfacing with the pitch shaft system via the pitch shaft hole, and is similarly linked to the azimuth shaft system through the azimuth shaft hole. As a critical component of the spaceborne two-dimensional turntable, the U-frame not only supports the load but also facilitates the transmission of the turntable's attitude motion through its connection to the shaft system and shaft holes. Given the U-frame's considerable mass within the turntable system and the requisite stiffness for its load-bearing capacity, enhancing both its static and dynamic stiffness is crucial to the turntable's performance improvement [7] (pp. 110-115). The structural integrity of spacecraft design is significantly constrained by the launch vehicle's capacity and envelope size, making it a critical parameter. Reducing non-essential loads allows for an increased payload, thereby accommodating more detection tasks and generating greater value. Structure optimization,  
Figure 1: Schematic diagram of Space Situational Awareness.