## 3 Fabrication and Integration
### Electronics and Connectivity  
The CubeSat industry has adopted the PC/104 specifications [47] as a de facto standard for the electronic boards. Moreover, such specifications provide mechanical and electrical benefits towards CubeSat fabrication beyond the compatibility with different structure and electronics suppliers. Following the PC/104 specifications, all electronic boards must measure \(3.550\times 3.775\) in \({}^{2}\) (\(90\times 96\) mm\({}^{2}\)), and the electric bus must allocate four rows with 26 contacts of standard 0.1 inch spacing through-hole (THT) headers. Additionally, all necessary boards can be stacked in modules, as illustrated in Figure 9, whose maximum volume must be able to fit in a 1U CubeSat form factor. Such electronic boards can be firmly attached together with M3 standoffs, and they share the same bus connection throughout the stack, thus improving the stiffness provided by the CubeSat's structure and simplifying the internal harnessing. Figure 8: Structural frame of a 2U CubeSat (Credit: ISIS). Printed circuit boards (PCBs) are fabricated with a succession of layers of FR-4 reinforced glass fiber and copper. The standard process for PCB production can be adopted for space purposes. However, some coating materials used during PCB fabrication may not be suitable for in-orbit utilizations, due to outgassing issues. For the same reason, care should be taken for the selection of soldering mask or silkscreen products. In case of doubt, such products should be avoided for qualification or flight units. However, it is recommended that a layer of space-proof conformal coating be applied to the board after all components have been soldered, to protect electronics from environmental interaction. Some metals are susceptible to outgassing and whisker growing. Whiskers are thin metal crystals that grow under vacuum conditions and may produce short circuits between electric contacts. The list of materials to avoid includes brass, zinc and cadmium [48]. To avoid whisker growing, soft solder alloys with at least 40% of lead content are commonly used. However, silver alloys are preferred, such as 955n-5 Ag, due to its low toxicity compared to lead alloys. A fully integrated satellite can have hundreds of wires densely packed between electronic boards. The complexity of routing the harness grows exponentially with the number of wires. For this reason, it is important to simplify the mapping and minimize the number of wires. Using color-coded wires and labeling both ends of a harness may help identifying the origin of used connections. Moreover, the material of choice for wire insulation and shrinking tube should be polytetrafluoroethylene (PTFE) or polyolefin (PO), but polyvinyl chloride (PVC) should be avoided for these cases. When the umbilical interface provided by a CubeSat supplier does not cover all the required lines, the developers need to improvise additional external harnessing. This situation is not desirable, because the satellite may end up with several connectors hanging around. Ideally, if the umbilical harness cannot be handled by a single interface, all connectors should be close to each other on the same board. The miniaturization of components in a CubeSat also leads to the use of minimalistic connectors for ad hoc applications. Although these connectors can be found made of high-quality polymers, they tend to break either through the locking tabs or the wire junctions. They are especially sensitive to decoupling cycles. Developers sometimes need to use tweezers to handle the connectors; consequently, connectors can be damaged more easily. The electric power supply takes care of collecting, storing and distributing electricity to the rest of the subsystems in the satellite. A power budget analysis is necessary to study the feasibility of the mission and to size the components in the power supply chain. The power budget of the SE01's mission is summarized in Table 2. First, the power consumption required by every subsystem is gathered.