NASA's Space Station Freedom Program encompasses unmanned polar-orbiting platforms (POPs) in low-earth orbit (LEO) designed to support a variety of scientific and earth-observation missions. The platforms are modular in design, permitting in-orbit maintenance and replacement of limited-life subsystem and payload components. Such in-orbit servicing can extend the platform's useful life to 15 years or more, far exceeding that of a typical LEO spacecraft. The long life and modular design has forced a new approach to thermal control subsystem (TCS) design. The platform's TCS must be readily adaptable to, and compatible with, the physical reconfiguration and resultant heat load changes. NASA has, in fact, identified thermal management as a critical factor in the overall platform design.A dual approach was used for the current polar platform TCS design. Platform thermal control is maintained using a distributed network of heat pipe panels, while payload thermal control is maintained via a centralized system of two-phase capillary pumped loops. This paper describes this baseline platform thermal design and the analytical tools used to validate the design concepts.