This paper deals with the modelling and evaluation of mission-phased systems devoted to space applications. We propose a two level hierarchical method that allows to model such systems and to master the complexity of the analysis. Our approach considers a separate modelling and resolution of the phases, and of the dependencies among phases caused by the usage of the same system components in the different phases. Moreover, it accounts for a dynamic choice on whether some phases have to be skipped. The proposed method turns out in a great flexibility, easy applicability and reusability of the defined models. Furthermore, it permits not only to obtain information on the overall behaviour of the system, but also at the same time to focus on each single phase and hence allows to detect system dependability bottlenecks.