# CubeSat Imaging Payload Design for Environmental Monitoring of Greenland
## 3 Modular Design  
The ML payload is briefly described as follows. The IPU, which is the SOM, triggers image capture using the wide field and telephoto cameras. Then, it applies an ML model to recognize if each image contains relevant information to be sent to the ground station through the radio module. The SOM contains a co-processor that allows accelerated machine learning applications to analyze images. This procedure must be performed because the satellite has a limited bandwidth to download data. Furthermore, the satellite PDU has two channels available to provide power to the payload. The SOM modules that are capable of this image processing task use more power than can be provided by the PDU continuously. Thus, the SOM must be in sleep mode for the majority of an orbit to save energy, waking only during observation and transmission. These duty cycles are modeled in other work by the group. Furthermore, the CSP network onboard the satellite is based on CANBUS and has limited bandwidth, and the payload needs an extra communication network to send the images directly to the radio module. The software integration aspect tends to match the operation between the cameras and the image processing unit. Redundancy features are integrated to ensure robustness, providing fail-safe mechanisms in case of unforeseen circumstances. The system is engineered to minimize power consumption, promoting energy efficiency. Seamless communication integration facilitates data exchange between the cameras and the processing unit. However, some hardware designs were developed to reach the requirements mentioned above, which are described as follows:  
* Design 1: It is the most straightforward configuration since it uses one single SoM, and the cameras are attached to it by individual USB ports. The PDU powers on/off the system and sends messages by CAN protocol. Finally, an extra communication protocol is set to send the images directly to the RF module. However, if the SoM fails, the cameras do as well. * Design 2: This design aims for a fully redundant system where each camera and its images are processed in dependent SoM. Each SoM needs to be part of the CAN bus to exchange messages with the PDU and follow the same idea with the RF module. This hardware configuration demands a high power draw. * Design 3: To obtain redundancy and keep the power consumption low, two cameras are connected to one SoM, and the last camera to another SoM. The PDU is the communication bridge between SoMs. Nevertheless, if one SoM fails, the other cannot take over the cameras. * Design 4: The hardware configuration has two SoMs; only one is constantly running, and the other is sleeping and it can be awake only if the first SoM fails. However, it is necessary to build a USB switch to switch between SOMs, meaning there is one failure \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Requirement**} & \multicolumn{6}{c}{**Image Processing Units**} \\ \cline{2-7}  & i.MX 6 UL & i.MX 8 Xlite & i.MX 8M & Toradex & tqmA93 XCLA & PicoCore MX8 \\ \hline Repro\_1 & ✓ & ✓ & ✓ & ✓ & ✓ & ✓ \\ \hline Repro\_2 & ✓ & ✓ & ✓ & ✓ & ✓ & ✓ \\ \hline Repro\_3 & ✓ & ✓ & ✓ & ✓ & & ✓ \\ \hline Repro\_5 & ✓ & ✓ & & ✓ & ✓ & ✓ \\ \hline Repro\_8 & & ✓ & ✓ & ✓ & ✓ & ✓ \\ \hline Recam\_9 & & & & ✓ & & ✓ \\ \hline Recam\_11 & & & & ✓ & & ✓ \\ \hline \hline \end{tabular}
\end{table} 
Table 5: IPU benchmarking. Fully covered: ✓. point in this configuration. Each SoM is part of the CAN communication, sending messages to the PDU and the radio module (RF). * Design 5: It is the most robust configuration where the whole system is built from scratch without using any commercial SoM and designed as a fully customized board. However, it demands extra effort in the PCB design and software integration. These hardware configurations (Figure 2) were evaluated by faculty members in electronic design, software integration, and IoT from the Danish universities mentioned above.