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Good performance of the Columbus water loop active control system has been demonstrated by several analyses, ground test and is further confirmed by the current flight data. Even so, a comprehensive description of the control within the classical theory is needed, in order to complete the system description, posing also the basis for similar applications to come. Thermal and hydraulic control loops are considered as two separate systems and linear control methods are applied. Loop stability and performance is discussed by computing stability regions of the PI control coefficients at different loop configurations and results compared with available test, flight and simulation data.

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.