Heat pipes are widely used in the thermal control system of satellites. A coolant fluid, being pumped through a header, collects heat from the satellite components and transfer it to the radiator heat pipes. The object of this work is to obtain relationships among the heat load of radiator, the mass flow rate of coolant fluid and the main dimensions of the radiator, in order to satisfy the temperature ranges necessary for the operation of satellite components. A mathematical model was used to simulate a heat pipe radiator. Karam's data [5] has bean used to verify the validity of the program, with header length of 8 m, radiator height of 3.16 m, evaporator length of 0.15 m, number of heat pipes of 53 and satellite load of 6250 W. The output result concerning the heat transport capability of the radiator, given by the simulation program, are identical to karam's analytical results. The program was used to study the effect of some parameters like the header length, the satellite heat load and the environmental load. Changing the header length from 2 m to 10 m, it has been seen that the output coolant temperature decreases as header length increases which improves the thermal control of satellite. Changing the satellite load from 3000 W to 10000 W, it has been seen that the heat transport per pipe increases as the satellite thermal load increases. The results also showed that increasing the environmental load could stop the radiator function and consequently it should be insulated from the surrounding to work property.