# In-Orbit Results and Attitude Analysis of the SNUGLITE CubeSatellite
## 4 Discussion  
A correlation existed between the sun-pointing error and power generation, as described in Figure 10. When there was high power generation, the accuracy of the attitude estimation was improved. Figure 8: Angle error between two sun-pointing vectors. Figure 9: Sun-pointing vector comparison: (**a**) 29 th contact on 11 December 2018; (**b**) 161 st contact on 27 December 2018; (**c**) 518 th contact on 17 February 2019; and (**d**) 657 th contact on 10 March 2019. The performances with different power generation levels are described in Table 3. When epochs whose power generation was greater than 4 W were considered, the RMS error of the estimated attitude was at its lowest, at approximately 6.1\({}^{\circ}\). Utilizing the information currently provided, it was difficult to distinguish which of the sun-pointing vectors of Equations (20) and (23) included error sources. As the power generation on each side of the satellite was considered to generate the reference vector, it was possible that the high power generation cases could make the definitive reference sun-pointing vector with less error. If this is correct, attitude performance analysis using epochs with high power generation capabilities is more reliable. Figure 11 displays the angle error of two sun-pointing vectors at epochs whose power generation was more than 4 W.  
The in-orbit real-time attitude estimation performance of the LQG-based attitude system of the SNUGLITE CubeSat was compared and analyzed with previous studies. Because of the lack of studies on the in-orbit performance of the CubeSat platform, there were no cases to present a direct comparison with the SNUGLITE CubeSat's LQG-based attitude system. For instance, the MinXSS-1 CubeSat achieved high performance attitude estimation, with an accuracy of up to 0.012\({}^{\circ}\) (3-\(\sigma\)) [5]. This was possible because of the use of a star tracker, which is very expensive and not suitable for  
Figure 11: Angle error between two sun-pointing vectors (power generation \(>\) 4 W cases). Figure 10: Correlation between sun-pointing error and power generation. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Generated Power**} & \multirow{2}{*}{**Number of Valid Epoch**} & \multicolumn{2}{c}{**Angle Difference (\(\delta\)0)**} \\ \cline{3-4}  & & **Mean (Degree)** & **RMS (Degree)** \\ \hline \(>\)2 W & 587 & 12.6 & 14.7 \\ \(>\)3 W & 287 & 7.5 & 8.5 \\ \(>\)4 W & 105 & 5.4 & 6.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Attitude estimation performance with different power generation ranges. low-cost attitude systems. The performance of a star tracker is in the arc-seconds accuracy level; however, its price is over \(\xi\)30,000 at the time of this publication [26]. The SNUGLITE CubeSat attitude sensors comprises five COTS photodiodes, one MEMS-level three-axis gyroscope, and one three-axis magnetometer, with a total price not exceeding \(\xi\)300. Therefore, the performance comparison of attitude algorithms between these two satellites was inappropriate. The attitude system of the CSTB1 CubeSat comprises 16 COTS photodiodes sensors and five two-axis magnetometers [6]. Attitude estimation was conducted based on a triad algorithm. The reference-pointing vector for attitude estimation analysis was calculated using an image from the on-board visible camera and the satellite's position. Since only one sample was considered for the preliminary attitude estimation analysis, with a pointing error was \(2.2^{\circ}\), it cannot be considered as a generalized performance. In addition, the attitude of the satellite was calculated based on the sensor data received at the ground receiving station. The ESTcube-1 CubeSat attitude estimation performance was also evaluated using the on-board camera images [9]. A total 15 images were considered for analysis, which is not sufficient for generalized performance. Its maximum pointing error was \(1.43^{\circ}\) with unscented Kalman filtering.