# Design and Analysis of a Novel Floating Docking Mechanism for On-Orbit Refueling
## 2 Description of the Mechanism
### Docking Process  
As mentioned in Section 1, refueling spacecraft must complete the \"approach\", \"capture\", and \"pullback\" steps before \"docking\" under the berthing docking. In this section, the sequences of the docking process are designed, as shown in Figure 8.  
The detailed descriptions of the docking process are as follows:  
1. Initial--the positions of two satellites under the docking conditions in which the probe enters the acceptance range of the drogue; the drogue is still supported by anti-overload strengthening.  
Figure 8: The process of docking: (**a**) initial, (**b**) approach, (**c**) contact and alignment I, (**d**) probe insertion and alignment II, (**e**) pin insertion and alignment III, (**f**) connector docking, (**g**) accomplishing.  
Figure 7: Configuration and design space of the elliptical-helical pipe with bias loading. The red point represents the loading point that connects the drogue and refueling pipe; the yellow point represents the center of the elliptical pipe fixed to the load-carrying plate; the pink dashed line indicates the design space for the refueling pipe, outside of which the envelope of pipe cannot extend.  
2. Approach--the system powers on, and the drogue stretches and breaks away from the anti-overload strengthening to be floated; at the same time, the probe is ready to enter into the drogue. 3. Contact and alignment I--the drogue stretches continuously to contact with the probe; the contact force adjusts deviations in the \(X\) and \(Z\) linear directions to achieve the correct alignment. 4. Probe insertion and alignment II--the probe is inserted in the hole of the drogue; the contact torque adjusts deviations in the pitch and yaw directions to achieve the correct alignment. 5. Pin insertion and alignment III--the anti-roll pins contact the grooves; the contact torque adjusts the deviation in the rolling direction to achieve the correct alignment fully. 6. Connector docking--the position and attitude of the electric connector and the fluidic connector are corrected; two connectors are ready to dock. 7. Accomplishing--the drogue is inserted continuously until the electric connector and the fluidic connector reach the designed location; the whole docking is accomplished. So far, the design of the docking mechanism is completed (except for the refueling pipe), and there are some notes need to be paid attention: 1. The drogue is not fluid-filled before accomplishing docking. 2. Two O-rings are installed in the hole of the drogue and used to prevent fluid leakage when the male fluidic connector breaks away from the female fluidic connector during separation. 3. Two docking microswitches are installed beside the two grooves, and the system powers off when the anti-roll pins trigger either of the two microswitches upon the completion of docking; a resetting microswitch is also installed on the anti-overload strengthening and the system powers off when the drogue triggers the microswitch upon the completion of resetting. 4. The trapezoidal screw locks the system by its self-locking.