# Line-of-Sight Initial Pointing Model of Space Dynamic Optical Network and Its Verification
## 4 Experimental Results and Analysis  
In the \"one-to-two\" simultaneous laser communication demonstration test, the multi-link LOS initial pointing networking model is verified. The principle of the networking system is shown in Figure 3. The experimental system consists of three parts: the master optical terminal, the slave optical terminal 1 (airship), and the slave optical terminal 2 (ground terminal). The master optical terminal (as shown in Figure 4a) can simultaneously point to, capture, and build a chain for the airship (as shown in Figure 4b) and the ground optical terminal. The link distance between the master optical terminal and the slave optical terminal is 2 km. Testing space optical networking technology performance and indicators involves the pointing accuracy, the size of FOU, the communication rate, and the BER. Due to the conditions of the test site, the flying height of the airship is 200 m.  
Figure 4: Physical image of master optical terminal and airship: (**a**) physical image of master optical terminal; (**b**) physical image of airship. Figure 3: “One-to-two” optical networking test principle. The main technical parameters of the master and slave optical terminals are shown in Table 1.  
The master optical terminal, slave optical terminal 1, and slave optical terminal 2 are equipped with dual-antenna integrated GPS/INS navigation and positioning system to provide the necessary positional and attitude information for the LOS pointing model. The position positioning accuracy is better than 1.5 m, and the attitude accuracy is 0.1\({}^{\circ}\). The position coordinates of the three terminals in the experiment are shown in Table 2.  
In the pointing model test, three optical terminals open the LOS initial pointing unit at the same time to establish two optical links. The terminal of each link calculates the initial pointing angle in relation to the opposite end according to its own attitude angle, position, and the position of the other side terminal, and the corresponding angle of the rotation of the optical LOS points to the FOU. The size of the FOU was measured during the experiment. When the two mirrors of the main optical terminal were in the follow-up pointing state, the magnitude changes of their respective azimuth and elevation angle were recorded, and the results are shown in Figure 5. The sampling time was 60 s, and the sampling frequency was 2 Hz. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Device Parameters** & **Master Optical Terminal** & **Slave Optical Terminals** \\ \hline Beacon light emission band & 730 nm & 785 nm \\ Beacon light receiving band & 785 nm & 730 nm \\ Beacon beam divergence & 2 mrad & 1 mrad \\ Optical aperture & 186 mm & 90 mm \\ Detection field of view & 7 mrad & 7 mrad \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main technical parameters of master–slave optical terminals. Figure 5: Recorded data of azimuth and elevation changes of the mirror under the direction of follow-up: (**a**) pointing to slave optical terminal 1; (**b**) pointing to slave optical terminal 2. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Position** & **Longitude (deg)** & **Latitude (deg)** & **Altitude (m)** \\ \hline Master optical terminal & 94.73965454 & 29.72693825 & 3412.197998 \\ Slave optical terminals 1 & 94.72811127 & 29.7315197 & 3355.039063 \\ Slave optical terminals 2 & 94.74954426 & 29.71982796 & 3411.265796 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: GPS position of master and slave optical terminals. We performed statistical processing on the azimuth and elevation angles of the two mirrors to be rotated, and results recorded are shown in Figure 5. A data statistics histogram was obtained, as shown in Figure 6. Figure 6a,b show the azimuth and elevation angle data of the master optical terminal pointing to slave optical terminal 1. Figure 6c,d are the azimuth and elevation angle data of slave optical terminal 2.