# In-Orbit Results and Attitude Analysis of the SNUGLITE CubeSatellite
## 3 In-Orbit Results
### Satellite Attitude  
A performance analysis of attitude estimation was conducted by comparing the two sun-pointing vectors (found using Equation (20)), and the estimated attitude with the vector from the satellite to the sun was calculated using Equation (23). Equations (26) and (27) were utilized to depict the performance of the attitude estimation. During the analysis, Equation (20) was considered as the reference sun-pointing vector. Though the pointing accuracy of the reference sun-pointing vector is somewhat low, it could be used as a rough indicator to verify the operation of the attitude estimation.  
Total 8138 full beacons that include information on attitude, temperature, and power generation during 1384 contacts were received between December 2018 and late June 2019. Four conditions needed to be met in order to extract valid epochs for the attitude estimation analysis:  
* The z-component of the GPS velocity in Earth-centered Earth-fixed (ECEF) is negative.
* The total power generation is more than 2 W.
* The power generation on the -z side is more than 100 mW.
* Reverse direction cases of sun-pointing vector by slow temperature changes are excluded.  
This type of analysis can be performed only when the satellite is exposed to the sunlight and when power is being generated. According to Figure 7, at least 2 W of power is normally generated during daylight when the battery is not fully charged. According to Figure 6, there are several full-charge cases that decrease the number of valid epochs. Another condition for the daylight is that the z-component of the velocity calculated from the GPS receiver is negative in the ECEF frame. Given that the orbit is sun-synchronous, the negative z-component of velocity indicates that the satellite is moving south during the daytime, and positive cases indicate that it is moving north during eclipse. This decreases the number of valid epochs by half. To use the sun-pointing vector for generating power levels, at least three sides of the solar panels should be exposed to the sunlight. Given that there is no solar panel on the +z side of the SNUGLITE CubeSat, the analysis can be performed only when the -z side is facing the sun. Generating power on the z-axis at more than 100 mW indicates that the -z side is exposed to the sun. In addition, the + or - directions of the x and y axes can be distinguished using the temperatures of each solar panel, as in Equation (19). When the satellite is rotating, however, there is a possibility that the indicated temperature may be that of the reverse side of the radiated panel because  
Figure 7: Power generation according to the latitude (December 2018).  
temperature changes take time to represent the right direction. These conditions also decrease the number of valid epochs.  
The valid number of epochs found by using the above filtering conditions was 587 during 158 contacts, and this was the value used to conduct the attitude analyses. Figure 8 displays the angle error between the two sun-pointing vectors, as per Equation (27), at each valid epoch.  
The mean angle error was approximately 12.6\({}^{\circ}\), and the RMS was 14.7\({}^{\circ}\). Figure 9 displays the difference between the two sun-pointing vectors using x, y, and z components for four contact cases. Figure 9b,c display the cases when the attitude estimations were calculated accurately. On the other hand, Figure 9a,d depict the cases where two sun-pointing vectors were biased. However, they displayed similar tendencies.