# A Reliability Engineering Approach for Managing Risks in CubeSats
## 4 Results
### Step 2: Traceability and Identification of the Failure Modes  
As a preliminary phase to the application of Step 2, the strategy was focused on targeting and univocally identifying each failure mode or effect, with an expressive code (as reported in Section 3.2). Tables 9-12 sketch the alpha-numeric codes used for traceability of damages. Figure 4: Spacecraft CAD model. Once formally defined the subsystems, interfaces and operations, the developed coding system supports a systematic identification and representation of the failure modes (as for Section 3.2). More specifically, the following paragraphs describe the relevant failure modes for each subsystem. The STR subsystem includes three failure modes. The _collapse_ indicates the fragmentation of structural components. When not considering the breakage of the spacecraft structure, _deformation_, indicating an unwanted plasticized strain on mechanical parts, or _vibration_, pointing out a vibrational motion of the structural parts, are taken into account for the analysis. For what concerns the passive thermal control provisions, the Mylar cover may be ripped or punctured (as for the _laceration_ failure mode), as well as being detached from the spacecraft assembly. Both these failure modes may leave uncovered parts of the spacecraft, forcing the internal components to potentially unaffordable thermal cycles, or increasing the risk of damage from external sources, such as micro-meteoroids. As last failure mode considered, the cover _degradation_ mode indicates an excessive exploitation of the insulating material, which leads to a decrease of the insulation performance. Six failure modes have been identified for the EPS. The _no power_ mode indicates a permanent absence of electrical power delivery to the components. The _blackout_ mode considers sudden power losses that have finite time duration. _Non-continuous power_ leads to temporary unavailability, while the _low power_ mode is originated by limitations on the maximum available power. Finally, the last two modes are considering major failures of the battery pack and of the relative safety equipment: the _outgassing_ mode has been identified for considering gas leakage from the battery pack, while the _explosion_ of the batteries may be caused by a failure of the provided safety provisions, leading to the catastrophic failure of the EPS and, with high likeliness, of the entire mission. As for the EPS, the TT&C subsystem considers multiple failure modes, consisting in the _no communication_ mode, indicating a permanent absence of signal from the spacecraft, in the \begin{table}
\begin{tabular}{c c} \hline \hline
**Operation** & **OPS** \\ \hline Data Acquisition & OPS1 \\ Alignment & OPS2 \\ Calibration & OPS3 \\ Deploy/Extension & OPS4 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Operations Codification. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Subsystem** & **Series** & **Subsystem** & **Series** \\ \hline System & SYS & Electrical Power & EPS \\ Payload & PLD & On-Board Data & OBD \\ Mission & MIS & Telemetry, Tracking and Command & TT\&C \\ Structures & STR & Thermal Control & THM \\ Attitude Determination and Control & ADC & Risks \& Costs & RKC \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Subsystem codification. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Subsystem Units** & **Definition** & **Subsystem** \\ \hline ST & Star Tracker & ADC \\ hw & Hardware & OBD \\ sw & Software & OBD \\ ES & Earth Sensor & ADC \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Subsystem Units Codification. \begin{table}
\begin{tabular}{c c} \hline \hline
**Operation** & **OPS** \\ \hline Data Acquisition & OPS1 \\ Alignment & OPS2 \\ Calibration & OPS3 \\ Deploy/Extension & OPS4 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: TT&C Operations Codification. communication breakdown_ mode, related to a sudden loss of contact, in the _non-continuous communication_, when experiencing more frequent discontinuities in the establishment of the communication with the satellite.