A Selected Operational History of the International Space Station's Early External Thermal Control System

The Early External Thermal Control System (EETCS) is the temporary system used to collect, transport, and reject waste heat from habitable volumes on the International Space Station (ISS). The EETCS collects heat from the Interface Heat Exchangers (IFHX) located on the US Laboratory module, circulates the working fluid, anhydrous ammonia, via the Pump and Flow Control Subassembly (PFCS), and rejects heat to space via two orthogonal stationary radiators. This temporary system has been active for over three years and is nearing the end of its utilization as a means of waste heat rejection for ISS pressurized modules. This paper provides a summary of the operational history of the EETCS and presents data from several interesting nominal and off-nominal events. Some of the events presented include the initial activation during the 4A mission, US Lab IFHX integration during the 5A mission, typical system performance while in various standard attitudes, system response to firmware controller operating memory errors, and system saturation due to high heat loads at high Beta angles. Finally, an outline of future operations is provided that includes transitioning from the EETCS to the permanent External Thermal Control System (ETCS) and dormant operations.