## 5 Conclusions  
In this paper, a lateral stress detection method based on spectral split sensing using a fiber Bragg grating is proposed for the monitoring of spacecraft-small particle collision. A local lateral stress device using FBG was designed and its functionality was verified by experiments. The lateral stress sensing characteristics of the FBG were tested, its sensitivity and linearity were analyzed, and error analysis was carried out. The experiment shows that the reflectance spectrum gradually splits into two peaks with increases in lateral stress. When the lateral stress is less than 4 N, the FBG split point is not obvious in the spectrum. In the 4.0-7.0 N range, the wavelength of the left peak remains almost unchanged, while the split point and right peak gradually drift in the long-wave direction, and the distance between the two peaks is linearly related to the stress. The split point had a pressure sensitivity of 16.57 pm/N, while the right peak had a pressure sensitivity of 45.14 pm/N.  
It can be seen that the FBG could achieve lateral force detection. According to the FBG's lateral stress characteristics, combined with the axial strain measurement ability of the grating, FBGs can be further applied as part of a three-dimensional strain sensor network for shape reconstruction. Similarly, they can be combined with temperature sensors to achieve the simultaneous monitoring of spacecraft temperature and strain, so as to meet the requirements of current spacecraft structure health monitoring.  
Methodology, W.Z. and Y.Z.; conceptualization, G.C.; investigation, J.X.; resources, Y.S.; formal analysis, Y.S.; validation, K.W.; writing--original draft preparation, J.X.; writing--review and editing, W.Z.; project administration, L.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Natural Science Foundation of China, grant number 52275517, 62003346, 62105039, 61801030, Beijing Natural Science Foundation, grant number 3232018 and National 111 Project of China, grant number D17021, Teacher Rank Construction Support Plan for Universities affiliated to Beijing, grant number BPHR202203226.  
Figure 14: Residual distributions of k1, k2 and k3.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Interval Time (h)**} & \multicolumn{6}{c}{**Sensitivity (pm/N)**} \\ \cline{2-7}  & **Left Peak** & **Error** & **Split Point** & **Error** & **Right Peak** & **Error** \\  & **(k1)** & **Error** & **(k2)** & **Error** & **(k3)** & **Error** \\ \hline \multirow{2}{*}{12} & Loading & \(-\)2.85 & \(-\)0.56 & 18.00 & 2.22 & 46.57 & 3.21 \\  & Unloading & \(-\)2.71 & \(-\)0.42 & 17.57 & 1.79 & 43.43 & 0.07 \\ \hline \multirow{2}{*}{24} & Loading & \(-\)1.71 & 0.58 & 13.71 & \(-\)2.07 & 41.42 & \(-\)1.94 \\  & Unloading & \(-\)1.00 & 1.29 & 12.71 & \(-\)3.07 & 38.14 & \(-\)5.22 \\ \hline \multirow{2}{*}{48} & Loading & \(-\)1.11 & 1.18 & 16.19 & 0.41 & 46.22 & 2.86 \\  & Unloading & \(-\)4.38 & \(-\)2.09 & 16.49 & 0.71 & 44.39 & 1.03 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Sensitivity of the left peak, split point and right peak after 12 h, 24 h and 48 h.