Hierarchical modeling and evaluation of phased-mission systems

This paper proposes a hierarchical and modular methodology for modeling & evaluation of phased-mission systems in which phases have constant prcdetermined duration, and where missions may evolve dynamically selecting the next phase to be performed according lo the system slate. A 2-level modeling is proposed: the higher one models the mission itself, the lower one models tllc various phases. A separate 'modeling & resolution of phases' and 'dependencies among phascs' are considered. This methodology is applied using an cxainplc of a space application. This method is conipared with previous models. The advantages of this approach are in the great flcxibility, easy applicability, and reusability of the defined models. It permits: . obtaining information on the overall behavior of thc system, . focusing on each single phase lo detect system dependability bottlenecks. The explicit niodeling of the phase changes: . is a neat and easily understandable representation of the intcrphase dependencies, . allows a straightforward modcling of the mission-profile dynamic selecbion. Cencral purpose tools available to the reliability community can sasily manage the computational complexity of the analysis.