# ReDSHIFT: A Global Approach to Space Debris Mitigation
## 3 Additive Manufacturing  
The starting point for the design of the spacecraft is the definition of the mission requirements. The selected purpose of the spacecraft is an Earth Observation mission as detailed in Table 1. \begin{table}
\begin{tabular}{c c} \hline \hline
**Characteristic** & **Selected Value** \\ \hline Description & Earth observation multi-spectral mission with resolution 39 m (GSD) \\ Launch mass & 8 kg \\ Size & 8U as per CubeSat standard (200 \(\times\) 200 \(\times\) 200 mm) \\ Orbit type & LEO \\ Altitude & 500 km \\ Inclination & 97.4\({}^{\circ}\) \\ Power & Battery capacity 96 Wh/Power generation: 20 W (Housekeeping mode) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main features of the selected mission. Figure 9: Requirements in terms of effective area-to-mass (i.e., \(c_{R}A/m\)) for different deorbiting times with modulating solar radiation pressure strategy. The colour bar represents the required effective area-to-mass. An 8U CubeSat design has been provided by Elecnor Deimos Satellite Systems (EDSS) to act as a baseline configuration to study the potential application of additive manufacturing to small satellite primary structures. Whereas some of the sections of the spacecraft are currently being 3D printed, it is worth stressing that the first detailed design is mostly based on traditional manufacturing techniques (see Figure 10, right panel). After the first round of testing (vibrational, radiation, etc.) the design will be updated and a more advanced exploitation of the additive manufacturing techniques will be explored and applied. Preliminary analysis and tests were already done to investigate the transition from conventional machining to 3D printing of the selected 8U CubeSat satellite (e.g., Figure 11). This constitutes a baseline study for the application of additive manufacturing to small spacecraft structures. Important manufacturing issues and \"lesson learned\" arose already in the first print of an 8U CubeSat panel oriented vertically, indicating a need to redesign any vertical structure specifically for Selective Laser Melting (SLM) production. In addition, the holes quality has been proven to be poor and not acceptable. Finally, a significant deviation of the structure was observed at the corners, which does not meet the requirements for assembly. On the basis of the test print in the subject, the following recommendations for 3D printing were derived:  
Figure 11: 3D printed samples of aluminium prototypes with 200 micron core thickness. Figure 10: **Left panel**: RedSHIFT Spacecraft Mechanical Design Concept. **Right panel**: 3D printed plastic model of the test spacecraft. * The only feasible orientation to manufacturing the satellite panels designed for Computer Numerical Controlled (CNC) construction would be flat against the print plate. This implies ensuring that the panel geometry aligns with the specific 3D printer plate, which varies between machines and manufacturers. This also implies that none of the panels can be integrated together in the manufacturing stage. * 3D printing allows for great design freedom and CNC milling features should be abandoned totally. As a consequence, the actions to be taken are:
* Implement mesh structure;
* Reduce the mass to a minimum;
* Minimize the required post-manufacturing;
* Redesign the structure. * The component must be designed to minimise the amount of support structure required during the printing process. As a consequence:
* Overhang structures must be avoided;
* Sharp edges must be avoided;
* Suitable build angles must be selected. * Holes must be avoided in the printing process and must be post-manufactured to allow the required positional precision and tolerances. As a consequence:
* Holes could be included but only with the axis of the hole aligned in the print direction, not oriented parallel to the print plate;
* Small holes must be avoided. The preliminary results suggested a suitable 3D printing design optimization strategy, which will be explored in the next phase of the project.