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Optimal component substitution within system evolution planning considering multiple-vendor, functionally equivalent commercial products

The use of commercial-off-the-shelf components (COTS) in systems with long-term life cycles eventually affects system functionality. Such systems must undergo component substitutions to avoid component obsolescence and maintain the system operationally effective. While performing such substitutions, sustainment costs must be kept within projected budgets, and system and component evolution must seamlessly provide continued availability. However, planning system evolution while minimising costs becomes a competing resource allocation problem (even more so when multiple manufacturers offer functionally equivalent COTS that can satisfy the system requirements). This research presents a mathematical model for calculating system life cycle costs while considering different substitution alternatives, and proposes an optimisation approach and a network model to obtain an optimal substitution sequence based on a minimisation criteria of life cycle costs. It was observed that upgrading the system with available technologies often results in better affordability than keeping the same technologies for the entire system life cycle.