Liquid Droplet Radiators (LDR) and Liquid Sheet Radiators (LSR) are among the most promising technologies to realise lightweight heat exchangers for space applications. With respect to traditional solid surface radiators, favourable rejected heat flux over mass ratio (up to 1000W/kg) can be achieved provided that accurate optimisation of the global system is performed. In this work a calculation procedure to evaluate the performance of rectangular LDR is employed together with an optimisation algorithm to get the main characteristics of the LDR components as a function of the droplet sheet parameters and the working temperatures in the range 300–400 K. The influence of the intermediate heat exchanger coupling the radiator to the thermal bus system is considered in order to show the possibility to employ the LDR, in a wide range of space applications, by direct substitution of conventional solid surface radiators.