## 3 Proposed Methods
### Multi-Subsystems Coupling Relationship Analysis of Earth Observation Satellite  
According to the objective function of the scheduling problem, the more high-profit targets can be observed and downloaded, the higher the objective function value (i.e., total profit) that can be achieved. Factors that determine the total profit include the number of high-profit targets that can be observed, the number of targets that the observation data can download, and the available electrical energy that can be used for observation and data transmission. As stated in the previous section, the calculation methods for each subsystem's variable clearly show the relationship between the observation, data transmission, and electricity subsystems, as shown in Figure 2. Therefore, we first analyzed the mutual relationship among three subsystems including observation, data transmission, and electricity. The observation subsystem consists of the camera payload as well as the attitude control subsystem of the satellite. The data transmission subsystem consists of memory and data transmission devices, while the electricity subsystem comprises the batteries, solar wings, solar arrays, and electric parts of devices. To begin with, we analyzed the coupling relationship between the observation subsystem and the data transmission subsystem of the satellite. The satellite orbit used for this analysis was the same as the one used in Section 4, as shown in Table 2. The number of observable targets and the number of targets that the observation data can download jointly determine the total profit that can be obtained. There are two conditions that will result in a lesser total profit, which are (1) the number of observable targets is large and the data transmission time window available for the data download is short, and (2) the number of observable targets is small and the data transmission time window available for the data download is long. According to the calculation method of the data transmission time window in Appendix A, the length of the data transmission time window is determined by the attitude of the satellite when it flies over the ground station, and the angle between the position vector of the ground station and the satellite orbital plane, as shown in Figure 3. We plotted the surface of the length of the satellite's data transmission time window when the satellite maintains different roll angles and the angle between the position vector of the ground station and the orbit plane is different, as shown in Figure 4. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter Name** & **Parameter Value** \\ \hline Orbit Type & Sun-synchronous Orbit \\ Orbit Height & 650 km \\ Orbit Eccentricity & 0 \\ Orbit Inclination & 97.99\({}^{\circ}\) \\ Orbit Region of Ascending Node & 100.348\({}^{\circ}\) \\ Orbit Argument of Perigee & 0\({}^{\circ}\) \\ Attitude Maneuver Calculate Method & Trapezoidal Method \\ Max Attitude Maneuver Angular Velocity & 1\({}^{\circ}\)/s \\ Max Attitude Maneuver Angular Acceleration & 0.5\({}^{\circ}\)/s\({}^{2}\) \\ Max Maneuvering Range Half Cone Angle \(\alpha_{\max}\) & 45\({}^{\circ}\) \\ Camera’s Data Generation Rate \(R_{cam}\) & 2 Gbps \\ Data Transmission Rate \(R_{dat}\) & 1 Gbps \\ Antenna Coverage Half Cone Angle \(\alpha_{b}\) & 70\({}^{\circ}\) \\ Max Charging Electrical Power of Solar Arrays \(P_{solarwing}\) & 1.5 kW \\ Camera Electrical Power \(P_{cam}\) & 1 kW \\ Data Transmission Devices Electrical Power \(P_{datatrans}\) & 0.5 kW \\ Satellite Normal Electrical Power \(P_{normut}\) & 0.2 kW \\ Battery Electrical energy Capacity \(W_{\max}\) & 2.7 \(\times\) 10\({}^{6}\) J \\ Single Target Observation Time \(\Delta t_{o}\) & 20 s \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The satellite parameters. Figure 2: Coupling relationship diagram of satellite multi-subsystem variables.