Optimizing reliability calculations for electronic equipment

Operational safety (SdF) encompasses reliability, maintainability, availability, and security. It is a cornerstone of highly sensitive systems engineering. In high-risk technological fields such as aeronautics, railways, defense, and space, this discipline ensures a high level of trust between users and the system. As such, it plays a decisive role in architectural decisions and technological choices, as well as in the competitiveness of manufacturers in the face of ever-increasing competition. In space, the stakes are even higher; once launched, a satellite becomes inaccessible to any direct intervention. With the exception of a few systems, such as certain modules of the International Space Station, post-launch maintenance is impossible or economically prohibitive. This constraint requires a very high level of reliability from the design stage onwards. The slightest failure can, due to cascading effects, lead to the loss of an entire system. In the space industry, the design phase is the only stage at which the essential aspects of operational safety are determined. Historically, reliability calculations have been based on standard models, such as MIL-HDBK-217 or FIDES, which assign an estimated failure rate to each component based on its type, environment, quality, and operating constraints. Unlike MIL-HDBK-217, the FIDES standard introduces mission profiles and a weighting factor linked to supply chain maturity (MRL), offering a more realistic approach to operating conditions. These values are then aggregated according to statistical rules (exponential law, combinatorial methods) to obtain an overall risk estimate. This approach has made it possible to design extremely reliable satellites, but it has several limitations: it does not take into account functional redundancies, ignores degraded operating modes, and does not integrate the actual degree of use of certain onboard electrical functions.

These methods can overestimate the risk of failure, leading to oversized systems, which in turn increases costs, weight, and complexity. But in a sector where every gram and every euro counts, this over-caution can prove counterproductive. It is precisely to address this issue that Thales Alenia Space is developing new methodologies for optimized reliability calculation, based on detailed functional analysis, targeted FMEA, and software tools such as ODYSSEUS. This approach aims to model the behavior of electronic systems more realistically, taking into account their actual use, redundancies, and functional margins. It can optimize the cost/reliability ratio without compromising safety and better meet customer requirements, particularly during the bidding phase. Demonstrating that a system is more reliable than with conventional methods, without changing the architecture, can make the difference...