# A Reliability Engineering Approach for Managing Risks in CubeSats
## 4 Results
### Step 4: Overall Risk Analyses  
The RPN has been obtained following the indexes (S, O, D) calculated in the Step 3 in order to enlighten the riskiest areas, guiding the team to establish guidelines or procedures, reformulating requirements, adopting strategies in order to strengthen the project features (cf. Section 3.4). Table 16 summarizes the obtained RPN, following the process described in Section 4.3 for the STR-3.B-CCC-DDDD (_vibration_ failure mode). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Failure Mode** & \multicolumn{3}{c}{**Vibration**} \\ \hline CODE & \multicolumn{3}{c}{STR-3} \\ Failure Probability & \multicolumn{3}{c}{5} \\ \hline EFFECT & Unseparated PLD & Compromised & Compromised \\  & adapter & subsystems & subsystems \\ CODE & STR-3.2 & STR-3.3 & STR-3.3 \\ Conditioned Probability & 4 & 4 & 4 \\ (subsystem) & & & \\ \hline AFFECTED ITEM & SYS & THM & PLD \\ CODE & STR-3.2 & STR-3.3-THM & STR-1.3-PLD \\ Conditioned Probability & 3 & 2 & 3 \\ (part) & & & \\ \hline Falsifiability & 2 & 2 & 2 \\ Observability & 5 & 3 & 3 \\ \hline SPECIFIC FAIL & \
\begin{tabular}{c} Unseparated PLD \\ adapter \\ \end{tabular} & Shield Damaged &
\begin{tabular}{c} Extending mechanism \\ block \\ \end{tabular} \\ CODE & STR-3.2 & STR-3.3-THM-1 & STR-3.3-PLD-6 \\ O & 4 & 4 & 4 \\ S & 5 & 5 & 5 \\ D & 5 & 4 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 15: Examples of criticality analysis for STR “Vibration” failure mode STR-3.B-CCC-DDDD. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Effect** & **Affected** & **Code** & **Specific Fail** & **RPN** \\ \hline Breakdown & SYS & STR-3.1 & Mission failure & 20 \\ \hline Unseparated PLD adapter & SYS & STR-3.2 & Mission failure & 100 \\ \hline Compromise subsystems & PLD & STR-3.3-PLD-1 & Mirrors misalignment & 80 \\ \hline  & & STR-3.3-PLD-2 & Mirrors damaged & 60 \\  & & STR-3.3-PLD-3 & Vibration noise & 64 \\  & & STR-3.3-PLD-4 & Resonance & 40 \\  & & STR-3.3-PLD-5 & Filters damaged & 100 \\  & & STR-3.3-PLD-6 & Extending mechanism block & 80 \\  & & STR-3.3-PLD-7 & Extending mechanism damage & 80 \\ \hline THM & STR-3.3-THM-1 & Shield damaged & 80 \\  & STR-3.3-THM-2 & Resonance & 40 \\ \hline EPS & STR-3.3-EPS-1 & Battery pack damaged & 36 \\  & STR-3.3-EPS-2 & Resonance & 40 \\  & STR-3.3-EPS-3 & Battery wirings disconnected & 16 \\  & STR-3.3-EPS-4 & Undeployed solar wings & 40 \\  & STR-3.3-EPS-5 & Unfolded solar panels & 40 \\  & STR-3.3-EPS-6 & Solar panels damaged & 24 \\ \hline  & STR-3.3-ADC-1 & ST Mirrors misalignment & 64 \\  & STR-3.3-ADC-2 & Vibration noise & 48 \\  & STR-3.3-ADC-3 & Resonance & 40 \\  & STR-3.3-ADC-4 & ST Mirrors damaged & 64 \\  & STR-3.3-ADC-5 & ES Mirrors misalignment & 48 \\ ADC & STR-3.3-ADC-6 & ES Mirrors damaged & 48 \\  & STR-3.3-ADC-7 & Debris on ES mirrors & 48 \\  & STR-3.3-ADC-8 & Wheels misalignment & 48 \\  & STR-3.3-ADC-9 & Wheels block & 48 \\  & STR-3.3-ADC-10 & Desaturation system malfunction & 36 \\ \hline OBD & STR-3.3-OBD-1 & OBD support damaged & 80 \\  & STR-3.3-OBD-2 & OBD components damaged & 40 \\  & STR-3.3-OBD-3 & Vibration noise & 48 \\  & STR-3.3-OBD-4 & Resonance & 40 \\ \hline  & STR-3.3-TT\&C-1 & Antenna damaged & 32 \\  & STR-3.3-TT\&C-2 & Antenna misalignment & 32 \\ TT\&C & STR-3.3-T\&C-3 & Components damaged & 32 \\  & STR-3.3-T\&C-4 & Vibration noise & 48 \\  & STR-3.3-T\&C-5 & Resonance & 40 \\ \hline Compromising interfaces & & STR-3.4 & \(\ast\) \\ \hline Break wirings (\& & & & \\ compromising subsystems) & PLD & STR-3.5-PLD & 40 \\ \hline  & THM & STR-3.5-THM & 48 \\  & EPS & STR-3.5-EPS & 40 \\  & ADC & STR-3.5-ADC & 32 \\  & OBD & STR-3.5-OBD & 40 \\  & TT\&C & STR-3.5-TT\&C & 40 \\ \hline Break wirings & & & & \\ (compromising interfaces) & & STR-3.6 & \(\ast\) \\ \hline Launcher or other PLDs & & & & \\ damages & & STR-3.7 & 20 \\ \hline Deformation & STR-3.8 & & 18 \\ \hline Collapse & STR-3.9 & & 24 \\ \hline \hline \end{tabular}
\end{table} 
Table 16: Risk Priority Number (RPN) list for STR ”Vibration” failure mode STR-3.B-CCC-DDDD.