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. The IEA contains a thermal control system, called PV TCS, which is used to cool batteries and other electronic boxes on the IEA. The EEATCS is designed to use the same hardware (pumps, flow control valves, and radiators) used for the PV TCS to eliminate need for new hardware and to maintain commonality of design between the two systems. The long spacer of ITS P6 is used to mount EEATCS hardware. During later stages, the hardware used for EEATCS is used for PV TCS, as needed.The paper describes the design requirements for the EEATCS, how the current design meets the requirements, and the controls strategy used to maintain interface requirements during normal and abnormal operating conditions. The paper also describes the performance of the EEATCS over a range of operating conditions, and the start-up of the EEATCS.