material is plutonium dioxide. A single RHU weighs just 42 grams and can fit in a cylindrical enclosure 26 mm in diameter and 32 mm long. Each unit also generates 1 W of heat at encapsulation, however the heat generation rate decreases with time. A total of 117 RHUs were used on the Cassini mission. Radiators Excess waste heat created on the spacecraft is rejected to space by the use of radiators. Radiators come in several different forms, such as spacecraft structural panels, flat-plate radiators mounted to the side of the spacecraft, and panels deployed after the spacecraft is on orbit. Whatever the configuration, all radiators reject heat by infrared (IR) radiation from their surfaces. The radiating power depends on the surface's emittance and temperature. The radiator must reject both the spacecraft waste heat and any radiant-heat loads from the environment. Most radiators are therefore given surface finishes with high IR emittance to maximize heat rejection and low solar absorptance to limit heat from the Sun. Most spacecraft radiators reject between 100 and 350 W of internally generated electronics waste heat per square meter. Radiators' weight typically varies from almost nothing, if an existing structural panel is used as a radiator, to around 12 kg/m2 for a heavy deployable radiator and its support structure. The radiators of the International Space Station are clearly visible as arrays of white square panels attached to the main truss. Heat pipes Heat pipes use a closed two-phase liquid-flow cycle with an evaporator and a condenser to transport relatively large quantities of heat from one location to another without electrical power. Aerospace-grade specific heat pipes such as Constant Conductance Heat Pipes (CCHPs) or Axial Groove heat pipes are aluminum extrusions with ammonia used as the working fluid. Typical Applications Include: Payload thermal management Heat transport,Isothermalization, Radiator panel thermal enhancement Future of thermal control systems Composite materials Heat rejection through advanced passive radiators Spray cooling devices (e.g. liquid droplet radiator) Lightweight thermal insulation Variable-emittance technologies Diamond films Advanced thermal control coatings Microsheets Advanced spray on thin films Silvered quartz mirrors Advanced metallized polymer-based films 3D printed evaporators for Loop Heat Pipes Space Copper-water Heat Pipes for chip-level cooling Events A major event in the field of space thermal control is the International Conference on Environmental Systems, organized every year by AIAA. Another is the European Space Thermal Analysis Workshop Sun shield In spacecraft design, a Sun