This technical overview of the Passive Thermal Control System (PTCS) for the Space Station Freedom (SSF) identifies the need for a Passive Thermal Control System, presents PTCS design concepts, highlights significant design requirements, addresses important design factors and how design goals are accomplished and summarizes development testing results as well as future development test plans.A Passive Thermal Control System is an essential component in ensuring the survivability of Space Station Freedom in the hostile space environment for a design life of 30 years. Design requirements specify a thermal environmental range of -250° F (-156.7°C) to +300° F (148.9°C), which accounts for the range of surface temperatures that can be encountered during orbit, and a maximum acceptable thermal leak from the pressurized modules. In addition, the Passive Thermal Control System is required to maintain the interior surface temperatures above 60° F (16.7°C) to prevent condensation and below 113° F (45.0°C) to protect the crew.The Passive Thermal Control System consists of multilayer insulation (MLI), coatings, thermal isolators, thermal insulation and heaters used to maintain structural temperatures in the acceptable ranges based on the local thermal environment. Thermal insulation systems in the form of multilayer insulation blankets are applied to the exterior of the pressurized element shells to thermally isolate the internal manned environment from the space environment. Thermal control anodized coatings are applied to the element meteoroid/debris (M/D) shield to locally bias the shield temperatures to acceptable ranges. Thermal insulation is placed around internal tubing and thermal control system components to prevent localized condensation. Heaters are used to provide freeze protection of fluid lines in addition to preventing condensation at different module locations.