System Balance for Extended Logistic Systems

An extended logistic system is a well-defined configuration of complex equipment, supporting inventory levels of components and modules, supporting maintenance facilities, supporting transportation system between local and remote inventory and maintenance sites, and procedures governing the allocation and shipment of components from remote and local sites. Examples of extended logistic systems are aircraft programs, radar systems, or networks of communication satellites. For each of these systems, the basic unit of interest (an aircraft, a radar unit, or a satellite) is a complex combination of components which are subject to failure. For each component there are supporting inventory and/or repair facilities, and specific replacement procedures for such failures. The evaluation of system performance includes system availability and the logistic costs required to obtain that level of availability. This paper extends our earlier work which developed methods for measuring system persistence times of extended logistic systems. In particular, we propose an optimization model here for examining system design and trade-off decisions. We consider a single-echelon model for a multiple-component system where components are subject to failure. For the system to be operable, a prespecified number of each component must be available. The optimization model maximizes system availability subject to a budget constraint on system cost and a time constraint on system failure time. The latter constraint is an effort to incorporate our understanding of system dynamics into the optimization by restricting the mean time between failures for the entire system. The use of the optimization model for system design and trade-off decisions is illustrated by two examples using representative data from an Air Force program. Within the optimization context, the notion of system balance is defined.