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The objective of the Thermal Control System Automation Project (TCSAP) is to develop an advanced Fault Detection, Isolation, and Recovery (FDIR) capability for use on the Space Station Freedom (SSF) External Active Thermal Control System (EATCS). Real-time monitoring, control, and diagnosis of the EATCS will be performed with a Knowledge-Based System (KBS). The EATCS provides heating, cooling, and control necessary to maintain elements, systems, and components within their required temperature ranges. The EATCS design has evolved from the single-phase fluid system used in Apollo and Space Shuttle to a two-phase system (ammonia liquid and vapor mixture) on SSF. Both active and passive components of the EATCS can potentially fail or become blocked. As a result, a variety of failure modes exist. When this is combined with the continuous range of normal operating conditions, EATCS management becomes very complex.