# A Reliability Engineering Approach for Managing Risks in CubeSats
## 2 Literature Review
Similarly, the FMECA has been used in the design phase for exploring different failure conditions and a fault tolerant design of an active spherical phased array antenna for the transmission of satellite imagery data at high bit rates, by providing operational insights for its realization [16]. In the same phase, the FMECA has been used as a preliminary tool for exploring and comparing the reliability of different satellite architectures, i.e., CubeSat, classical satellite, and k-out of-n CubeSat swarm-like constellations [17]. Still in the CubeSat domain, a FMECA in combination with an FTA has been developed for the analysis of SwampSat, the first satellite developed at the University of Florida, to validate in flight a compact three-axis attitude control system using miniature control moment gyroscopes [18]. More formally, at the Goddard Space Flight Centre, the FMECA has been used for correlating mission parameters to risk management consequence definitions, by providing tools for their assessment and communication to decision-makers [19]. Furthermore, a FMECA-based approach prioritized items based on their criticality number, calculated by multiplying the scores assigned to severity and occurrence likelihood, under the assumption of exponentially distributed reliability [20], even with a specific interest in a typical satellite payload [21]. The prioritization of items becomes fundamental for satellite missions, even in terms of satellite management after the launch. More formally, an orbiting satellite is expected to communicate with its control center via the telemetry flow to ground, and to receive telecommands from ground. Telemetry supports the monitoring of the satellite itself and thus the identification of potential anomalies. In particular, once an anomaly has been detected through monitoring services of housekeeping data, it becomes crucial to quickly locate the origin of the anomaly, and to identify the most suitable actions for ensuring a safe continuation of the mission, under nominal conditions [22]. In this context, the Galileo project provides an example of how the FMEA can be used to develop the theoretical foundation for an automatic fault management and self-healing process, i.e., the FDIR (Fault Detection Isolation and Recovery). Similarly, an FMECA-based automatic design concept has been used for supporting the adjustment of in-formation flight, (e.g.,) to allow interferometric-based repositioning, and to reduce operational costs by limiting the radio communication link usage [23]. Therefore, an important feature of the FMECA, when performed during the design phase of a satellite, relates to the satellite capability of isolating the fault modes while the satellite is in operation [24]. This feature, often referred to as detectability, has been widely discussed in traditional industrial domains, (e.g., [25; 26; 27]), with limited systematic aspects in space domain [19]. Based on these observations, and by considering the heritage of the FMECA both in space operations and in other industrial domains, this paper proposes a semi-quantitative approach for developing a space-based FMECA to be used in the preliminary design of a CubeSat. Besides the two widely used indicators for assessing satellite's risks, i.e., severity and occurrence likelihood, the proposed approach presents hereby a third indicator, i.e., detectability. The latter aims to address the difficulty for isolating failure modes in the design phase. Furthermore, the occurrence indicator has been extended, by explicitly considering the causal chain of events. The proposed three-dimensional risk indicator supports the identification of critical failure modes, thus easing design decisions about redundancy or components' comparison. Considering its simple formulation, the method is aligned with the needs of a relatively low-cost CubeSat project, as a means to improve the obtained design in a reliability-oriented perspective.