# Design and Analysis of a Novel Floating Docking Mechanism for On-Orbit Refueling
## 5 Conclusions  
This paper proposes a novel floating docking mechanism for on-orbit refueling during berthing, and the design details are described exhaustively. A probe-drogue configuration is adopted for the proposed mechanism to achieve passive alignment and self-resetting for five DOFs. Two double-winding servo motors are equipped with a redundancy design to increase docking reliability. The proposed mechanism is light, compact, and simple, aiming to achieve a lower driving force. Considering the characteristics of berthing docking, mechanical analysis of the docking process, and the compactness required for on-orbit mechanisms, an elliptical-helical pipe with bias loading is proposed to decrease the requirement of the driving force. The formula for axial stiffness is derived using the energy-based method, and strength checking is derived using the third strength theory. To verify the validity of the proposed model and method, three types of simulations and experiments were performed: static analysis of the mechanical properties of the refueling pipe, kinematic analysis of the tolerance range of the docking mechanism, and dynamic analysis of the driving force of the docking mechanism. For the static analysis, the relative error of the axial stiffness and maximum stress of the theoretical resolution and simulation are less than 1.2% and 0.6%, respectively, and the relative error of the axial stiffness of the theoretical and experimental result is less than 4.4%, which verifies the accuracy of the formula of axial stiffness. For the kinematic analysis, the results of the simulations and experiments verify the correctness of the estimated tolerance range with values of \(\pm 4\) mm on two linear misalignments and \(\pm 2.5^{\circ}\) on three angular misalignments and the self-resetting ability, which meet R1 and R2 in Section 2. For the dynamic analysis, all trends and values of the contact force under four typical working conditions obtained by the simulations coincide with the experiments, which verifies the validity of the dynamic simulation model. Then, the dynamic simulation model obtains the driving forces of the docking mechanism with four types of pipes (circular-helical or elliptical-helical pipe with center loading or bias loading). Both the envelope and the maximum driving force of the mechanism with the elliptical-helical pipe are superior to those of the circular-helical pipe, which is suitable for the proposed docking mechanism, meeting R3 in Section 2. Conceptualization, Z.S., S.L. and X.S. ; Methodology, Z.S. and H.Z. ; Software, Z.S. and H.L. ; Validation, Z.S. and H.L. ; Formal analysis, Z.S., S.L. and X.S. ; Investigation, Z.S. ;  
Figure 24: Results of driving forces by simulation: (\(X-2\) mm, \(Z-2\) mm, Roll \(-1^{\circ}\), Yaw \(-1^{\circ}\), Pitch \(-1^{\circ}\)). The maximal driving forces (listed from pipe 1 to pipe 4) are 49.17 N, \(-60.48\) N, \(-74.23\) N, and \(-81.78\) N. (The definitions of the points B, C and D can be found in Figure 22.)  
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