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The early external active thermal control system (EEATCS) is used to perform the cooling of the United States Laboratory (USL) during early assembly stages of the International Space Station (ISS) to support assured early research. The EEATCS provides 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 flow 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. Test performance of the EEATCS was accomplished at Kennedy Space Center (KSC) to identify its capabilities and characteristics under several designed test conditions. These test conditions challenge the EEATCS to respond to adverse environment and operational conditions.

The early external active thermal control system (EEATCS) is designed to cool the U.S. Laboratory (USL), during early assembly stages of the International Space Station (ISS), to support assured early research (AER). The ISS is assembled on orbit over a period of about 5 years and over 40 stages. During later stages, about half way through the assembly, the USL is cooled by the external active thermal control system (EATCS), but that system is not available during early stages. To assure research, during early stages, the USL is cooled by the EEATCS; at a later stage, the USL cooling is switched to EATCS. During early stages, electric power is provided by the integrated truss segment (ITS) P6, which consists of photovoltaic (PV) arrays to convert sunlight into direct current power, an integrated equipment assembly (IEA) to support hardware required to store and condition electric power, and a long spacer to provide spacing between outboard power modules.

A description is presented on how to perform fundamental analyses for accumulators used to maintain pressure control in closed-loop fluid systems. This includes how to charge the loop to meet pump net positive suction pressure (NPSP), accommodate leakage and ground fill uncertainties, and maximize operating and nonoperating pressures. Additionally, the no-fault propagation requirement must be satisfied such that a failure of one accumulator will not fail another. A SINDA/FLUINT model of the early external active thermal control system (EEATCS) was developed. The EEATCS is used to perform the cooling of the United States (U.S.) Laboratory (USL) during early assembly stages of the International Space Station (ISS) to support assured early research. The EEATCS provides the ability to transport the thermal load generated by the USL to space by thermal radiation via two deployable radiators.