When these uncertainties have the potential to drive

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Unformatted text preview: as for product improvement such as greater system reliability, lower cost logistics support, and better maintenance and spares poli- NASA Systems Engineering Handbook Systems Analysis and Modeling Issues Logistics Supportability Models: Two Examples Logistics supportability models utilize the reliability and maintainability attributes a particular system design, and other logistics system variables, to quantify the demands (i.e., requirements) for scarce logistics resources during operations. The models described here were both developed for Space Station Freedom. One is a stochastic simulation in which each run is a "trial" drawn from a population of outcomes. Multiple runs must be made to develop accurate estimates of means and variances for the variables of interest. The other is a deterministic analytic model. Logistic supportability models may be of either type. These two models deal with the unique logistics environment of Freedom. SIMSYLS is a comprehensive stochastic simulation of on-orbit maintenance and logistics resupply of Freedom. It provides estimates of the demand (means and variances) for maintenance resources such as EVA and IVA, as well as for logistics upmass and downmass resources. In addition to the effects of actual and false ORU failures, the effects of various other stochastic events such as launch vehicle and ground repair delays can be quantified. SIMSYLS also produces several measures of operational availability. The model can be used in its availability mode or in its resource requirements mode. M-SPARE is an availability-based optimal spares model. It determines the mix of ORU spares at any spares budget level that maximizes station availability, defined as the probability that no ORU had more demands during a resupply cycle than it had spares to satisfy those demands. Unlike SIMSYLS, M-SPARE's availability measure deals only with the effect of spares. M-SPARE starts with a target availability (or budget) and determines the optimal inventory, a capab...
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This document was uploaded on 02/26/2014 for the course E 515 at University of Louisiana at Lafayette.

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