Fluid loops are used to control the temperature of sensitive components in spacecraft systems in order to ensure that they can function correctly. While there are several methods for thermal control (such as passive thermal insulations, thermoelectric devices, phase change materials, heat pipes and short-term discharge systems), fluid loops have a specific application area. This Part 13 provides a detailed description of fluid loop systems for use in spacecraft. 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