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Performance modeling of the Early External Active Thermal Control System for the International Space Station

The Early External Active Thermal Control System (EEATCS) is used to perform the cooling of the US Laboratory (USL) during early assembly stages of the International Space Station (ISS) to support assured early research (AER). It will provide the ability to transport the thermal load generated by the USL to space by thermal radiation via two photovoltaic radiators (PVR). The EEATCS can be described as an indirect heat rejection system composed of two ammonia loops. Each loop contains accumulators, radiators, a heat exchanger, piping and an independent pump flow control subassembly (PFCS). The PFCS contains the flow control valve (FCV), which controls the radiator bypass flow in each loop. Performance modeling of the EEATCS was accomplished to identify its capabilities under a low-Earth orbit space environment for different flight modes, orbit beta angles and vehicle torque equilibrium attitudes (TEA). The model geometry was based on finite element models developed on Master Series that were generated from CATIA Initial Graphics Exchange Specification (IGES) files. A translator program was used to convert the model to a Thermal Radiation Analyzer System (TRASYS) input deck. TRASYS was then used to determine the thermal radiation space environment. The FCV control logic was based on an algorithm developed on EASY5, and the Systems improved Numerical Differencing Analyzer and Fluid Integrator (SINDA/FLUINT) program was used to model and perform the analysis. Analytical checks were derived to help baseline the results. The analysis presented a high degree of understanding of the EEATCS capabilities.