Ground test unit system analysis-Space Station Freedom active thermal control system

The Space station Freedom baseline active thermal control system (ATCS), a two-phase, pumped ammonia fluid loop, is discussed. It provides a 35°F and a 70°F heat sink (thermal bus) to collect the waste heat generated in the station modules and external electrical equipment and transport it to radiators for rejection to space. The 25 kW ground test unit collects heat through two cold plates, one cold rail and two heat exchangers, and rejects heat through two condensers and one subcooler to heat pipe radiator panels during thermal vacuum testing and to a separate refrigeration system during ambient testing. Pretest analyses of the unit reveal that up to 33% of the total pump flow must be diverted through the condensers and subcooler at low loads to provide sufficient subcooling under all operating conditions and that the expected subcooling loads are 0.9 to 1.7 kW