## 2 Characterisation Test Set-Up
### Angular Measurements Hardware Set-Up
The sources were placed at a variety of different positions relative to the spacecraft, with some example orientations displayed in Figure 4. This was achieved by varying the polar and azimuthal angles. The polar angle was varied by mounting the source on a movable arm that could be rotated about an axis that went through the centre of the detector. The azimuthal angle was varied by securing the spacecraft on the controllable turntable, and moving it to the required positions. The turntable was also controlled via the Python test scripts, and a separate script was written for these measurements containing the set-up commands for GMOD and the commands for the turntable to move the spacecraft to a specified range of angles. Table 3 shows the locations tested, in both polar and azimuthal angles with respect to the crystal centre and in Cartesian coordinates with respect to the centre of the spacecraft. These Cartesian coordinates are included, as they were required for the MEGAlib simulations discussed in Section 7. The final column of Table 3 shows the integration time (in seconds). During the test runs, all the scripts were run for 3.5 h; however, for locations where GMOD was most sensitive (e.g., +Y face, polar 90\({}^{\circ}\), Az 270\({}^{\circ}\)) the number of TTEs downlinked from the OBC was not representative of the number of TTEs generated by GMOD. This issue was due to the OBC being unable to manage the rate at which GMOD was producing data; this was accounted for in the data analysis. The analysis and results of these off-axis measurements are presented in Section 5. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Polar Angle (\({}^{\circ}\))** & **Azimuthal Angle (\({}^{\circ}\))** & \multicolumn{3}{c}{**Distance to Centre of Spacecraft (mm)**} & **Integration (s)** \\ \hline \multicolumn{5}{c}{X} & \multicolumn{1}{c}{Y} & \multicolumn{1}{c}{Z} \\ \hline
0 & 0 & \(-1.057\) & \(-1.450\) & 28.890 & 3112.56 \\ \hline \multirow{4}{*}{30} & 0 & \(10.193\) & \(-1.450\) & 25.876 & 8815.00 \\  & 90 & \(-1.057\) & \(9.800\) & 25.876 & 6226.38 \\  & 180 & \(-12.307\) & \(-1.450\) & 25.876 & 6137.81 \\  & 270 & \(-1.057\) & \(-12.700\) & 25.876 & 6201.48 \\ \hline \multirow{4}{*}{60} & 0 & \(18.429\) & \(-1.450\) & 17.640 & 9337.74 \\  & 60 & \(8.686\) & \(15.425\) & 17.640 & 7057.31 \\ \cline{1-1}  & 120 & \(-10.799\) & \(15.425\) & 17.640 & 6720.92 \\ \cline{1-1}  & 180 & \(-20.543\) & \(-1.450\) & 17.640 & 6895.48 \\ \cline{1-1}  & 240 & \(-10.799\) & \(-18.325\) & 17.640 & 8116.63 \\ \cline{1-1}  & 300 & \(8.686\) & \(-18.325\) & 17.640 & 8021.03 \\ \hline \end{tabular}
\end{table} 
Table 3: Positions at which the source was placed for the angular response investigation for GMOD FM. These positions are provided in polar and azimuthal angles with respect to the crystal centre and in Cartesian coordinates with respect to the centre of the spacecraft. The integration time for each measurement is provided in the final column. Figure 3: The test set-up for the measurements made to determine the angular response of GMOD. The FM was secured on a motorised turntable and the source was mounted on a moveable appendage, to vary the polar and azimuthal angles, respectively. Figure 4: **(A)** EIRSAT-1 FM on vertical integration stand mounted to the turntable for polar 0\({}^{\circ}\) measurement, i.e., the sources, circled in orange, mounted at the crystal centre in X, Y and 22.5 cm above the  
+Z face of the spacecraft. (**B**) FM on turntable with the sources, circled in orange, positioned at the polar 60\({}^{\circ}\), azimuthal 270\({}^{\circ}\) measurements. (**C**) FM on turntable with the sources, circled in orange, positioned at the polar 90\({}^{\circ}\), azimuthal 0\({}^{\circ}\) measurements. (**D**) Source positions (blue points) for all off-axis measurements. The red point marks the centre of the scintillator (40 mm in length along Y and 25 mm along X and Z). The orange point marks the centre of the spacecraft.