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ESA and NASA agencies agreed to run an interface compatibility test at the EADS facility between the Columbus flight module and a duplicate ground unit of a currently on-orbit US International Standard Payload Rack, the Human Research Facility (HRF) Flight Prototype Rack (FPR). The purpose of the test was to demonstrate the capability to run US payloads inside the European ISS module Columbus. One of the critical aspects to be verified to ensure suitable operations of the two systems was the combined performance of the hydraulic controls resident in the HRF and Columbus coolant loops. A hydraulic model of the HRF FPR was developed and combined with the Columbus Active Thermal Control System (ATCS) model. Several coupled thermal-hydraulic test cases were then performed, preceded by mathematical analysis, required to predict safe test conditions and to optimize the Columbus valve configurations.

The uniqueness of the International Space Station (ISS) lies on the fact that the spacecraft is built incrementally on-orbit through a series of assembly missions. During the construction phase, many systems change configuration as the modules are added to the ISS. The function of the Thermal Control System (TCS) is to maintain thermal conditions within design parameters for the ISS and user payloads. Within the TCS, the External Active Thermal Control System (EATCS) collects the heat from the Interface Heat eXchangers (IHX) and system equipment coldplates, transports the heat to the EATCS radiators and rejects the heat to space. The EATCS is comprised of two single-phase anhydrous ammonia loops. Each loop includes, among other items, several liquid -to-liquid interface heat exchangers. This paper will present the dynamic characteristics of the EATCS and the challenges to its stable dynamic control as the ISS reaches the assembly complete configuration.