# A Reliability Engineering Approach for Managing Risks in CubeSats
## 4 Results
### Step 2: Traceability and Identification of the Failure Modes
The TT&C can also experience _noise_ (with unexpected noise levels over the communication link, that may indicate malfunctioning of the radio-frequency equipment on-board the CubeSat), _short circuit_ (with a complete failure of the TT&C electronics), _pointing loss_ (related to the main antenna beam pointing direction, which could be misaligned from the optimal pointing), _self-lock_, _data loss_, and emphdata corruption, that are more related to failures and lock-ups on the software routines that allow the communications with ground. The ADCS can experience the same failure modes of the STR sub-system, consisting in _collapse_, _deformation or vibration_. Additionally, these active electronics can suffer from _no power_ and _no data_ modes, indicating absence of electrical power to the sensors and actuators, or absence of data transmission between the sensors and the controllers. The OBDH takes into account similar failure modes to EPS and TT&C, such as _no power_, _blackout_, _non-continuous power_, _low power_, and _short circuit_. The same descriptions provided before are applicable to the listed OBDH failure modes. In addition to these failures, other possible modes are related to the on-board software malfunctioning and failures, such as _software lock-up_, _Single Event Unit (SEU)_, _data loss_, _data corruption_, _radiation_, _buffer overflow_, _overrun_. Further more specific on-board software failures have not been considered since the level of detail achieved in the design process did not consider actual software routines coded and tested. For sake of simplicity, the main failure mode considered for the PLD sub-system is a _no power_ mode that represents the most limiting, worst case condition. Moreover, the possible failures on the optical tube extending mechanism during the spacecraft early operations are considered with the _no extension_ and _incorrect extension_ modes, indicating the complete or partial failure of the optical tube unfolding, namely. In later mission stages, the optical tube can also be strained, considered with the _deformation_ failure mode. Both the mechanical and electrical interfaces between subsystems have been taken into account in the analysis, leading to consider the following failure modes, _collapse_, _vibration_, _deformation_, (with similar effects, as the ones already discussed for STR and ADCS) and _short circuit_ (in agreement with the failure modes discussed for OBDH and EPS). _Break wirings_ is a peculiar failure mode that may affect only interfaces or even create critical effects on the interconnected subsystems. Following the system decomposition in subsystems, units and components, and the identification of the possible failures and their effects (cf. Tables 9-12), traceability is guaranteed by the generation of a code for each specific fail (as depicted in Figure 5). Few examples are provided in Table 13 (i.e., STR-1.1 representing an edge case where the STR collapse mode implies an immediate mission failure, with no need for subsequent analyses; ADC-1.1-ADC.5 represents a complete code for a failure mode of the ADC that does not propagate in other subsystems). Figure 5: Example of the code used to identify the failures.