Active Thermal Control System
Most of the Station's many systems produce waste heat, which needs to be transferred from the ISS to space to achieve thermal control and maintain components at acceptable temperatures. An Active Thermal Control System (ATCS) is required to achieve this heat rejection function when the combination of the ISS external environment and the generated heat loads exceeds the capabilities of the Passive Thermal Control System to maintain temperatures. An ATCS uses a mechanically pumped fluid in closed-loop circuits to perform three functions: heat collection, heat transportation, and heat rejection. Waste heat is removed in two ways, through cold plates and heat exchangers, both of which are cooled by a circulating ammonia loops on the outside of the station. The heated ammonia circulates through large radiators located on the exterior of the Space Station, releasing the heat by radiation to space that cools the ammonia as it flows through the radiators.
The ATCS consists of the Internal Active Thermal Control System (IATCS), External Active Thermal Control System (EATCS), the Photovoltaic Thermal Control System (PVTCS) and the Early External Active Thermal Control System (EEATCS). The IATCS consists of loops that circulate water through the interior of the U.S. Destiny Laboratory module to collect the excess heat from electronic and experiment equipment and distributes this heat to the Interface Heat Exchangers for transfer to the EATCS. At assembly complete, there will be nine separate ITCS water loops in the U.S. and International Partner pressurized modules.
For more information, read the Active Thermal Control System (PDF) overview.
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