# A Reliability Engineering Approach for Managing Risks in CubeSats
## 2 Literature Review  
The diagnosis of faults is of paramount importance for determining the success of a mission. In the CubeSat domain, formal analyses become necessary, especially because CubeSat design approaches have been mostly ad hoc, with severe implications for their reliability [3]. In the reliability engineering context, the FMEA (Failure Mode and Effects Analysis), which dates back to 1950s military applications, nowadays represents a well-established method for reliability and risk analysis in a number of domains [4]. The FMEA is a method for supporting RAMS (Reliability, Availability, Maintainability, Safety) engineers at understanding the desired functional product performance through systematic and documented analyses [5]. As such, the FMEA often represents the first approach to system reliability studies, since it supports the identification of potential failure modes and the need for risk mitigation strategies. The FMEA is often extended in a FMECA, which can be considered as the combination of the traditional FMEA and a criticality analysis (CA). A CA is used normally to chart the probability of failure modes against the severity of their consequences. Therefore, the FMECA allows identifying the modes of failure within a system design, by proposing approaches to prioritize the most critical ones at earlier design stages. This approach allows to eliminate or minimize the main criticalities through simple design changes. As such, the FMECA can give an important contribution to systems well-functioning, at least if the analysis is not approached as simply a box checking exercise [6]. The general principle of the FMECA consists of analyzing the behavior of the system parts, concurrently with components failure, mainly aiming at verifying the design. In space engineering, this general principle has been pursued in the Apollo program in the mid-1960s [7] and, later on, in a wide number of satellite applications (see, e.g., [8; 9; 10; 11; 12; 13; 14; 15; 16; 17], detailed in the following paragraphs). Such space-oriented interest has been also confirmed by a NASA (National Aeronautics and Space Administration) bibliography that reviewed the published contributions about FMEA and FMECA, categorizing them in 10 major subjects (aeronautics, astronautics, chemistry and materials, engineering, geosciences, life sciences, mathematical and computer sciences, physics, social and information sciences, space sciences, and general) and 76 sub-categories, based on the NASA Scope and Subject Category Guide [8]. Traditionally, the available literature on FMECA reveals a hardware-oriented perspective. See (e.g.,) the risk analysis performed for lithium-ion battery design of a hybrid satellite in geostationary orbit developed in Korea based on the EUROSTAR 3000 platform [9], the analysis of key components of circular truss antenna, mainly detailing the criticality related to the hinge mechanism [10], or the reliability study of the power distribution module UYGAR [11]. The FMECA can be interfaced advantageously with other reliability and quality analyses by adopting a Total Quality Management (TQM) perspective, as acknowledged by the Department of Defense [12]. In this context, the FMECA has been used as a preliminary method for developing a qualitative Fault Tree Analysis (FTA) of a solar array deployment mechanism, in order to identify the most critical items for the mission [13]. It hasalso been recognized as an effective approach to generate both design and manufacturing requirements, in terms of failure mechanism caused by contaminants like particulates (dirt, sand, industrial fumes, hair, dead human cells, fibers from clothes, etc.) [14]. Acknowledging the impossibility to eliminate each single point of failure in a satellite Electrical Power Subsystem (EPS), the FMECA has been used to compare different EPS schemes suitable for power supply, i.e., the Peak Power Tracking (PPT) and the Direct Energy Transfer (DET), revealing that the DET fully regulated bus are generally preferable in terms of reliability [15].