I. Introduction
Reliability is a key issue for space applications. Satellites are expensive and out of repair in case of breakdown. They are designed to offer long life in orbit (more than 15 years for telecommunication applications) in a harsh environment (vacuum, space charging, radiation…). There are plenty of formal way to define reliability but if we consider its purpose, it is mostly the ability for a system to properly work for a given mission profile that correspond to a sequence of expected amounts of time in specific environments at given electrical conditions.