Solid-liquid phase-change materials (PCM) are a favoured approach to spacecraft passive thermal control for incident orbital heat fluxes or when there are wide fluctuations in onboard equipment. The PCM thermal control system consists of a container which is filled with a substance capable of undergoing a phase-change. When there is an the increase in surface temperature of spacecraft the PCM absorbs the excess heat by melting. If there is a temperature decrease, then the PCM can provide heat by solidifying. Many types of PCM systems are used in spacecrafts for different types of thermal transfer control. Characteristics and performance of phase control materials are described in this Part. Existing PCM systems are also described. The Thermal design handbook is published in 16 Parts TR 17603-31-01 Thermal design handbook Part 1: View factors TR 17603-31-02 Thermal design handbook Part 2: Holes, Grooves and Cavities TR 17603-31-03 Thermal design handbook Part 3: Spacecraft Surface Temperature TR 17603-31-04 Thermal design handbook Part 4: Conductive Heat Transfer TR 17603-31-05 Thermal design handbook Part 5: Structural Materials: Metallic and Composite TR 17603-31-06 Thermal design handbook Part 6: Thermal Control Surfaces TR 17603-31-07 Thermal design handbook Part 7: Insulations TR 17603-31-08 Thermal design handbook Part 8: Heat Pipes TR 17603-31-09 Thermal design handbook Part 9: Radiators TR 17603-31-10 Thermal design handbook Part 10: Phase Change Capacitors TR 17603-31-11 Thermal design handbook Part 11: Electrical Heating TR 17603-31-12 Thermal design handbook Part 12: Louvers TR 17603-31-13 Thermal design handbook Part 13: Fluid Loops TR 17603-31-14 Thermal design handbook Part 14: Cryogenic Cooling TR 17603-31-15 Thermal design handbook Part 15: Existing Satellites TR 17603-31-16 Thermal design handbook Part 16: Thermal Protection System