# Mechanical Structure Design and Experimental Study of Gamma-ray Monitor for Small Satellite Payload
## 3 Modeling
### Load and Boundary Conditions  
According to the DRO satellite system on-board product test conditions document, KSW-DRO-E03-2021, the product is required to withstand sinusoidal vibration, random vibration and other mechanical environments without failure or damage. The mechanical test conditions corresponding to the identification level are shown in Tables 3 and 4.  
In the ground vibration experiment at the scheme design stage, the fixed mode of the novel GRM is shown in Figure 4. According to the position of the screw hole constrained by the model in the vibration test, the six degrees of freedom of the inner surface of the four mounting holes at the bottom of the convex ear are simplified by the constraint in theoretical analysis, as shown in Figure 5.  
According to the prediction of dangerous parts and concerned areas, considering the structural characteristics, the acceleration sensors are arranged at the flange end of the crystal shell in the vibration test, as shown in Figure 6. The corresponding positions of the sensors are arranged in the vibration test, and are selected as the sampling points in the theoretical analysis.  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & \multirow{2}{*}{**Frequency Range (Hz)**} & \multicolumn{2}{c}{**Acceleration Power Spectral Density**} & \multirow{2}{*}{**Grms (g\({}^{2}\)/Hz)**} & \multirow{2}{*}{**Direction**} & \multirow{2}{*}{**Vibration Time**} \\  & & & & & \\ \hline Quasi-accreditation level & 10–150 & +6 dB/oct. & & & \\ \cline{1-1} \cline{3-5}  & 150–800 & 0.0782 g\({}^{2}\)/Hz & 10.575 & X, Y, Z & 180 \\ \cline{1-1} \cline{3-5}  & 800–2000 & \(-3\) dB/oct. & & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Random vibration test conditions.  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Component** & **Materials** & \begin{tabular}{c} **Density** \\ **(g/cm\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **Elastic Modulus** \\ **(E/MPa)** \\ \end{tabular} & \begin{tabular}{c} **Poisson’s** \\ **Ratio** \\ \end{tabular} & \begin{tabular}{c} **Tensile** \\ **Strength** \\ **(MPa)** \\ \end{tabular} \\ \hline \begin{tabular}{l} Bracket for radiant \\ cooling plate \\ \end{tabular} & ZK61M & 1.8 & 43,000 & 0.34 & 280 \\ \begin{tabular}{l} Electronic box \\ \end{tabular} & 2A12- & 2.8 & 68,000 & 0.33 & 390 \\ \begin{tabular}{l} Sodium iodide \\ crystal \\ \end{tabular} & NaI & 3.671 & 20,000 & 0.314 & / \\ \begin{tabular}{l} Be sheet \\ \end{tabular} & Be & 1.85 & 290,000 & 0.08 & 180 \\ \begin{tabular}{l} Be sheet gland \\ \end{tabular} & ZK61M & 1.8 & 43,000 & 0.34 & 280 \\ \begin{tabular}{l} Crystal box \\ \end{tabular} & ZK61M & 1.8 & 43,000 & 0.34 & 280 \\ \begin{tabular}{l} Quartz \\ \end{tabular} & K9 & 2.51 & 82,000 & 0.206 & 1050 \\ \
\begin{tabular}{l} Structural adhesive \\ \end{tabular} & GN522 & 1.03 & 1.2 & 0.48 & 2 (Shear stress) \\
\begin{tabular}{l} Heat-insulating pad \\ \end{tabular} & FR4 & 1.8 & 25,000 & 0.2 & 300 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Material parameters of each component for the novel GRM assembly.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline  & **Frequency Range (Hz)** & **Vibration Magnitude (o-p)** & **Sweep Frequency Direction** & **Loading Rate** \\ \hline
\begin{tabular}{l} Quasi-accreditation level \\ \end{tabular} & 5–15–100 & 13.8 mm & X, Y, Z & 2 oct/min \\ \hline \hline \end{tabular}
\end{table}
Table 3: Sinusoidal vibration test conditions.