# A Reliability Engineering Approach for Managing Risks in CubeSats
## 4 Results  
### Step 1: SPEC CubeSat Design and Functional Block Diagram  
In order to provide a practical application of the proposed analysis method, the SPEC (Stellar Population Evolution on CubeSats) is presented as a case study. The spacecraft was designed during the 2017 Spacecraft Design course at Sapienza University of Rome, given to the second-year students in the Space and Astronautical Engineering MSc. While the main objective of the course is to follow the preliminary design (Phase 0-Phase A [30]) of a CubeSat, the mission aim was presented to the students as input. The SPEC mission is aimed at observing M-Dwarf stars properties, by acquiring and processing the observational data according to the Daemgen method [35]. The designed 6-Units  
Figure 2: Logical scheme of inference rules for the Failure Mode, Effects, and Criticality Analysis (FMECA) index Detectability (D). \begin{table}
\begin{tabular}{c p{341.4 pt}} \hline \hline
**Score** & \multicolumn{2}{c}{**RPN: Impact of the Failure on the System**} \\ \hline
1–24 & Failure has potentially no impact on the mission. \\ \hline
25–49 & Failure may have not relevant impact on the mission; minor effects are the most likely consequences. \\ \hline
50–74 & Failure will produce effects on the mission, which may be subjected to limitations. \\ \hline
75–99 & Failure will produce major effects on the system, that probably will not be able to perform correctly, or it will drastically reduce the expected operativeness of the system. \\ \hline
100–125 & Failure is catastrophic for the mission. \\ \hline \hline \end{tabular} RPN = O*S*D.  
\end{table} 
Table 8: RPN index. (6U, approximately 20 \(\times\) 10 \(\times\) 30 cm, [36]) CubeSat is equipped with a reflecting telescope in Ritchey Chretien configuration. Part of the designed provisions on the bus components are heritage of former and current CubeSat development and operations projects managed by Sapienza University of Rome ([37; 38; 39]), whose involvement into the spacecraft development field of research usually brings to the launch of a new CubeSat every few years [33]. The CubeSat has been designed according to a set of preliminary mission requirements, generated by the observables binary systems magnitude, distance and latitude (with respect to the galactic plane). During the design phase, a risk analysis has been performed in order to prioritize the areas of concerns of the system at hand. The analysis results supported the selection of the final layout of the system in terms of choices, strategies, writing or changing of the requirements, developments of figures of merits and mitigation strategies. Following Step 1 of the proposed approach (cf. Section 3.1), the SPEC sub-systems block diagram is presented in Figure 3. The on-board software will be organized as a state machine, with different operative modes to manage the spacecraft tasks and operations. The SPEC Launch and Early Operations will be managed by specific \"Commissioning\" tasks, such as the deployment of several components or the satellite de-tumbling. The main payload operations consider a precise telescope pointing towards the observable binary system, managed by the Attitude Determination and Control Subsystem (ADCS), the Indium-Gallium-Arsenide (InGaAs) sensors data acquisition, facilitated by the native connectivity with the Low Voltage Differential Signaling ports of the On-Board Computer Field Programmable Gate Array, and gathered data down link through the uni-directional X-band communication link. Indeed, the communication system will consist of an X-band uni-directional link, to be used for the  
Figure 3: CubeSat sub-systems block diagram (dotted lines represent power lines, dashed-dotted lines represent data lines, bold dashed lines represent mechanical interfaces). UHF: Ultra-High Frequency; IMU: Inertial Measurement Unit. telescope images down-link, and of a UHF (Ultra-High Frequency) bi-directional link for telemetry and tele-commands.