In-Space Manufacturing Production Rate and Reliability Targets for On-Demand Fabrication of ECLSS Spares

In-space manufacturing (ISM) promises to significantly reduce spares logistics mass for deep space exploration missions by enabling on-demand fabrication of ECLSS spares. The set of components whose spares could be fabricated under this new ISM-based logistics paradigm depend not only on the materials and geometries manufacturable by the ISM system, but also on the ability to complete fabrication in less than the time to effect for that component. The risk of a series of time-critical failures occurring in rapid succession presents a limiting case for the required production rate and reliability of an ISM system. To identify these requirements, a model is presented for determining the spares logistics mass savings given component properties, such as mass, mean time between failure (MTBF), and time to effect, and ISM system properties, such as production rate, MTBF, and mean time to repair. In this model, a Monte Carlo simulation is used to determine potential scenarios for component failures over a mission. Then, an on-demand manufacturing strategy is simulated to fabricate the failed components as required. This manufacturing model includes estimates for production time and handling time for the manufactured components, as well as simulated ISM system failures and repair. Only components that can be manufactured in a time not exceeding the time to effect for the component will be deemed manufacturable via ISM. The other components will need to be stored in a conventional spares cache and will not contribute to any logistics mass savings compared to the existing carry-along logistics strategy. This modeling effort reveals how adjusting ISM system production rate and reliability capabilities impact the set of manufacturable spares, and has implications for ISM system technology development targets and the confidence with which ECLSS system designs can rely on ISM spares given current and developing capabilities.