# Dynamics Analysis of Space Netted Pocket System Capturing Non-Cooperative Target
## 4 Dynamic Simulation and Results
### Simulation Results and Discussion
Moreover, the positions of the center of mass of the target and the service spacecraft still stay before the contact and collision between the target and the rope net in the capturing phase. After that, due to the contact and collision, as shown in Figure 5, the positions of the center of mass of the target and the service spacecraft present slight fluctuations in the Y direction before the end of the closing, as shown in Figure 6b,d. Furthermore, in the towing phase, the positions of the center of mass in the X and Z directions are not changed obviously, which is represented by the small magnitude for the spacecraft and target. The order of magnitude for the spacecraft is \(10^{-5}\) m and the order of magnitude for the target is \(10^{-3}\) m. This is due to the contact and collision between the spacecraft and the captured target, as shown in Figure 5.  
Further, the dynamics simulation for the other two cases with different closing times of the netted pocket system are presented, respectively. For the second case, the closing time is 7.5 s. At the initial state (t = 0 s), the distance L between the ends of adjacent inflation rods is 5.78 m. Then L shortens from 5.78 m to 2.1 m. At 7.5 s, distance L decreases to the minimum value of 2.1 m, and the capturing phase ends. After the capturing phase, the service spacecraft starts to tow the target at t = 10 s. For the third case, the closing time is 5 s. At the initial state (t = 0 s), the distance L between the ends of adjacent inflation rods is 5.78 m. Then L shortens from 5.78 m to 2.1 m. At 5.0 s, distance L decreases to the minimum value of 2.1 m, and the closing phase ends. After the capturing phase, the service spacecraft starts to tows the target at t = 10 s.  
The dynamics simulation is performed and the capturing processes of both cases are presented in Figures 7 and 8, respectively. The simulation results for cases 2 and 3 are presented in Figures 9-11. Figure 9 presents the contact collision forces on the captured target. Figures 10 and 11 present the positions of the target and the service spacecraft, respectively. Comparing the three cases for different closing times of the netted pocket system, Figures 5 and 9 show that the collision force in the Y direction is larger than the collision forces in the X and Z directions. When the closing time is decreased, the collision forces in the Y direction are larger and the first collision is earlier. However, both the collision forces in the X and Z directions appear after the closing, and their amplitude is not significantly affected by the closing time. Figures 6, 10 and 11 show similar phenomena, which indicates that the target is captured successfully for different capture strategies. After the closing process is completed, the service spacecraft rows the target, which clearly shows the service spacecraft and target motion together in the Y direction in the towing phase. The positions of the center of mass of the target and the service spacecraft still stay before the contact and collide between the target and the rope net of the capturing phase of each case. Then, due to the contact and collision, as shown in Figure 9, the positions of the center of mass of the target and the service spacecraft present slight fluctuations in the Y direction just before the end of the closing for each case, as shown in Figure 10b,d as well as Figure 11b,d. However, in the towing phase, there will be smaller collision forces generated, but the positions of the center of mass in the X and Z directions are not changed obviously, which is representedby the small magnitude for the spacecraft and target. This is also due to the contact and collision between the spacecraft and the captured target, as shown in Figure 9.  
Figure 8: Simulation results of capturing process (case 3). Figure 7: Simulation results of capturing process (case 2). Figure 10: Position of the captured target: (**a,b**) for case 2; (**c,d**) for case 3. In (**a,c**), blue curve shows capturing phase and red curve shows towing phase.