# CubeSat Imaging Payload Design for Environmental Monitoring of Greenland
## 4 Results
### Integration Development  
Once the electronic design was updated with part dimensions and footprints, the PCB and SOM dimensions were assessed to fit the enclosure's space limitations. Based on this primary requirement, TORADEX SOM was too large and needs extra thermals to decrease heat. Conversely, PICO SOMs are small and compact, which matches our PCB design and the available space. Therefore, the Payload PCB is based on a highly modified Evaluation Base Board PicoCore(tm)MX8 MP-V4I-LIN from F&S Electronics. We customize it by removing unnecessary components and adding our own for optimal functionality, and exposing interfaces with components that are verified to be compatible with the other satellite modules.  
Figure 4 shows the 3D representation of the designed PCB within the physical limitations of the enclosure.  
In parallel structural work, the payload bracket and enclosure were combined to produce a single 3D-printed part that houses the PCB and holds the cameras and lenses. A harness connects the cameras via USB to a single connector on the PCB. The enclosure design incorporates thermal chimneys, and a thermal solution is developed to manage heat dissipation for the cameras.  
The power budget for the PCB is 6 watts peak, since the Alvium cameras need 3 watts, one PICO CORE running draws 3 watts, and the IR camera needs 1 watt, and only one camera and one SOM are used at once. This power is managed throughout the orbit with aggressive use of duty cycles with the SOM in sleep mode apart from during transmission and observation. Further, the iMx8 processor chosen has multiple cores, 4 \(\times\) A53 for the Linux system, the NPU for ML acceleration and a low-power M7 micro controller. It was found that the M7 can suspend and wake the A53 cores whilst drawing 1W or less. The choice of SOM therefore provides a handy mechanism for keeping the payload operational in orbit within the budgeted nominal power budget of 1W. This solution is developed and further tested in the next stage of the project.  
Figure 5 shows the full imaging payload ready for deploying into a CubeSat.  
Figure 4: Imaging payload PCB developed with a redundant SoM.  
Figure 3: PCB electronic design: SoMs’ connection with the USB switch and cameras.  
The software used on the DISCO-2 satellite and ground segment system is distributed with each module and processor being accessible as separate nodes using the CubeSat Space Protocol (CSP), which is a simplified TCPIP-like networking protocol stack designed for CubeSats. Onboard, this is presented over CANBUS and RS422, and allows communication between all nodes. Consequently, the Camera Control software, image processing pipeline and payload scheduler on the SOM are also designed to appear as separate CSP nodes. The A53 SOM cores run a custom lightweight Yocto GNU/Linux, whilst the M7 core runs libscp on FreeRtos with software written in C and C++ drivers for the camera controller. Finally, the payload software stack features a flexible image processing pipeline that can be remotely configured for different image processing tasks including ML inference, and is capable of over-the-air updates whilst in orbit.