At present, waste heat from various cooling processes is discharged to. the environment primarily by devices using forced convection heat transfer. An alternative to this method is the use of a heat rejector, exposed to the atmosphere, which transfers heat by radiation and free convection. An experimental model was built, using flat tube-and-fin radiator panels with a model heat load applied to them. The heat transfer behavior of this device was compared to the predictions of a mathematical model which linearized the dependence of the radiative heat transfer on temperature. The tests of the device showed that it rejected significant amounts of heat at relatively low temperatures, and that the mathematical model was successful in predicting the behavior of the experimental apparatus.