# Research on the Dynamics of the Space Tubular Expandable Structure Driving Deployment Unit
## 5 Conclusions  
To align with future space exploration strategies, research has focused on addressing issues related to expansion precision, stiffness, and distance in space telescope collapsible structures when utilizing traditional driving and pre-tensioning devices for axial expansion. In response to the limitations of conventional driving and pre-tensioning devices, the concept of a variable-diameter inner-drive device has been proposed. However, achieving the desired working motion state and design rationality of this variable-diameter inner-drive device necessitates a shift from a conventional flexible beam structure to a thin-walled flexible beam structure. Consequently, there is a need to explore space-based methods for describing the node displacements of the driving and expanding unit with a thin-walled flexible beam structure, aiming to enhance the structure's deformability and improve its motion stability. This study is based on the theoretical framework of the Space Absolute Nodal Coordinate Formulation (ANCF). Its objective is to analyze the positional states and displacement variations of flexible beam structures, thin-walled flexible beam structures, and parallel structures with triangular configurations at different nodes. To achieve this, the positional states are transformed into the global coordinate system, obtaining the three-dimensional displacement field and angular rotation variations. The approach involves using global shape functions and unit absolute nodal coordinate vectors to construct the element absolute nodal coordinate vector. Additionally, the element shape function matrix is established by combining the unit shape functions and interpolation polynomials, which is then inserted into the face position vector of the thin-walled flexible beam structure. By taking the derivative with respect to time, the study calculates the element kinetic and strain energies, leading to the derivation of dynamic equations for the thin-walled flexible beam structure. Furthermore, specialized node descriptions are applied for the triangular configurations and parallel structures, and fitting analyses are conducted for the displacement field and attitude of the thin-walled flexible beam structure under both free-end and overall states. During the validation work, a prototype model of the driving and unfolding unit structure was established. The model incorporated the theoretical node displacement description using the Space absolute nodal coordinate formulation (ANCF) for the thin-walled flexible beam structure. Coupled analyses were conducted to explore the displacement variation cloud maps of the structure at different time intervals in the space environment. The experimental results demonstrated a remarkable consistency between the positional changes at different time intervals and the fitted curves based on the theoretical Space ANCF, with an error range between 0.32% and 0.41%. The correctness of the theoretical Space ANCF in studying the flexible multibody dynamics of the thin-walled flexible beam structure was successfully verified through the design and fabrication of a 1:1 scale experimental prototype. Additionally, the effectiveness of the coupled analysis approach in analyzing the positional responses of the thin-walled flexible beam structure at various time intervals was thoroughly confirmed. Due to constraints in knowledge and time, this study is considered preliminary compared to the complexity of space exploration structures. As a part of future work, it is essential to investigate the impact of the unit structure itself on elastic friction contact during the inter-level transition phase of the driving deployment unit within the tubular deployable structure of the space telescope. By understanding the friction factors at different times and their relation to the external force applied to the driving deployment unit, the overall stiffness and motion accuracy can be further enhanced. Conceptualization, W.H. and H.Y. ; Methodology, W.H. ; Software, Y.G. ; Validation, W.H., H.Y. and Y.G.