A limiting feature in spacecraft such as communication satellites is becoming the amount of surface (5,6) available for dissipating waste heat from the electrical equipment in the satellite. The invention provides a deployable radiator (11) which carries a number of capillary pumped loops consisting of an evaporator, an outward limb and a return limb. The panel (11) is rolled up to coil the elements prior to launch, and unrolled when in orbit. The outward and return lengths of tube act as condenser for the capillary pumped loop, transport the heat over the radiating panel (11) and also provide the spring force for the panel to unroll.