# Intelligent Trajectory Prediction Algorithm for Reentry Glide Target Based on Intention Inference
## 6 Simulation
### Comparison with Other Prediction Methods  
In order to demonstrate the effectiveness of the proposed method further, the proposed method was compared with prediction methods in literature [5,6] with the same condition as in case 1, and the prediction results less than 100 s are shown in Figure 20. The prediction method of literature [5] is named the VTC prediction method, and the prediction method of literature [6] is named the DBL prediction method in this paper. As can be seen from Figure 20, for the short-term trajectory prediction, the prediction errors of methods do not diverge. The accuracy of the proposed method is the highest, which is caused by the accurate prediction of the control parameter and utilization of intention information. The prediction method based on control parameter \(K_{D},\beta,K_{L}\) is more accurate than the method based on control parameters \(\xi_{v},\xi_{t},\xi_{c}\), which means that the control parameters \(K_{D},\beta,K_{L}\) better reflect the guidance mechanism of the target. The above two prediction methods for comparison rely on parameter fitting; when the extrapolation time by integration is longer than 100 s, the prediction errors of the two methods begin to diverge rapidly, and the divergence effect is shown in Figures 21 and 22. As can be seen from Figure 21a,b due to the imprecise prediction for nonlinear changes of control parameters with the pure fitting of parameters, the prediction error diverges rapidly, especially in the longitudinal direction. For the lateral direction prediction, since \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Prediction Time**} & \multirow{2}{*}{**Index**} & \multicolumn{2}{c}{**Longitudinal Error**} & \multirow{2}{*}{**Lateral Error**} & \multirow{2}{*}{**Whole Error**} \\ \hline \multirow{2}{*}{100 s} & AESD(m) & 197.53 & 1608.50 & 1647.70 \\  & MESD(m) & 424.52 & 8889.49 & 8918.06 \\ \multirow{2}{*}{200 s} & AESD(m) & 554.75 & 6503.50 & 6584.09 \\  & MESD(m) & 2081.72 & 18,374.25 & 18,416.55 \\ \multirow{2}{*}{300 s} & AESD(m) & 1296.75 & 10,505.79 & 10,662.39 \\  & MESD(m) & 3401.00 & 31,747.06 & 31,907.31 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Prediction effect within different prediction times. Figure 20: Prediction effect comparison among different methods: (**a**) represents the short-term longitudinal prediction trajectory; and (**b**) represents the short-term lateral prediction trajectory. pure parameter fitting cannot change the sign of bank angle, the direction of the target's velocity and the direction of the key point may be reversed, as shown in Figure 22a,c. From long-term trajectory prediction, as shown in Figures 21c and 22c, the proposed method obtains longitudinal prediction results within 300 s without the divergence of error. On the other hand, for the lateral prediction, because of a correct intention inference and sign variation rule of bank angle logic, the lateral long-term trajectory prediction can still maintain high precision. The specific prediction results for 100 s, 150 s and 200 s are shown in Table 2. Here, the reference method is the prediction method in the literature [18]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Methods** & **Index** & **100 s** & **150 s** & **200 s** \\ \hline Proposed & AESD(m) & 1647.70 & 5522.77 & 6584.09 \\ method & MESD(m) & 8918.06 & 17,103.62 & 18,416.55 \\ VTC prediction & AESD(m) & 23,001.35 & — & — \\ method & MESD(m) & 101,632.79 & — & — \\ DBL prediction & AESD(m) & 24,620.28 & — & — \\ method & MESD(m) & 200,958.71 & — & — \\ Reference & AESD(m) & 4231.36 & 6862.23 & 10,446.81 \\ method & MESD(m) & 17,213.44 & 26,843.11 & 52,487.36 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Prediction error between different prediction. Figure 21: Comparison of longitudinal prediction effect among different methods: (**a**) is the longitudinal prediction effect of VTC method; (**b**) is the longitudinal prediction effect of DBL method; and (**c**) is the long-term longitudinal prediction effect.