## 2 KITSUNE Satellite
### Hardware  
The 3U imaging payload is connected via a harness to the main bus system, which consists of three components: (1) camera controller board (CCB), (2) camera sensor (CAM), and (3) camera lens (Table 1). A COTS CMOS camera sensor with 31.4-megapixel (MP) resolution is controlled by Raspberry Pi Compute Module 3+ (RPi CM3+) attached to the CCB (Figure 2). The payload is enabled to capture a full resolution of 6464 \(\times\) 4852 pixels through a 300-mm custom-made RICOH lens. These three components are based on the mission objectives and requirements. Therefore, several trade-off studies have been conducted before choosing the final components to achieve a 5-m resolution. The sensor pixels and lens focal length are the two critical parameters to determine the resolution of image output and field of view. The ground spatial distance (_GSD_) can be easily calculated using Equation (1):  
\[GSD=\frac{h\times tan(FOV_{H})}{(\rho_{H}/2)}, \tag{1}\]  
where \(h\) is the altitude of the satellite, \(FOV_{H}\) is the field of view for horizontal, and \(\rho_{H}\) is the pixel number of the image sensor for horizontal.  
The payload is turned on only during mission execution from the uplink command. The activation is mainly controlled by the OBC, which provides the CAM parameters. As the payload system interfaces with each of the 2U main bus systems (Figure 3), the total energy consumed is the highest during downlink images through C-band communication, followed by camera mission execution. The detailed results are discussed thoroughly in Section 4.  
After the camera payload was selected, the thermal design was another essential task to maintain the internal temperature of KITSUNE CubeSat. It does not have an on-orbit focus adjustment function due to the difficulties of designing a system to endure the launch and space environment. The camera lenses and the associated image quality are susceptible to temperature variations. Therefore, the focal length under space conditions was calculated based on several thermal vacuum test results.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Item** & **Information** \\ \hline Sensor & \\ \hline Number of pixels & 31.4 million pixels \\ Sensor type & CMOS \\ Shutter method & Global shutter \\ Shutter speed & 30 us to 10.0 s \\ Interface & Ethernet \\ Data transmission speed & 10 Mbps \\ Power supply & +12.0 V \\ \hline Camera controller board & \\ \hline Model & Customized board with Raspberry Pi Compute Module 3+ \\ Operating system & GNU/ Linux Ubuntu distribution version 18.04 \\ CPU & ARMv8, 1.2 GHz \\ Memory & 32 GB (flash), 1 GB (RAM) \\ Image capturing speed & 0.42–8.75 frames per second (depending on image resolution) \\ Interface & Ethernet (camera), USB (programming), UART (OBC and C-band board) \\ Power supply & +5.0 V \\ \hline Optics & \\ \hline Focal length & 300 mm \\ Temperature control & Active control and multi-layer insulator \\ Heaters & Polyimide heaters \\ Heater power supply & 7.4–8.4 V (unregulated power line) \\ Temperature sensors & Radial glass thermistor (G10K3976) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Imaging payload properties.  
Figure 2: Camera Controller Board (CCB) design: (A) Raspberry Pi Compute Module 3+; (B) CCB-backplane board connector; (C) CCB-CAM sensor LAN cable hole; (D) RJ45 connector; (E) CCB-CAM sensor power cable hole; (F) temperature sensor connectors; (G) heater connectors.