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This paper describes a new approach to spacecraft thermal control based on a passive thin-film smart radiator device (SRD) that employs a variable heat-transfer/emitter structure. The SRD employs an integrated thin-film structure based on V1-x-yMxNyOn that can be applied to existing Al thermal radiators. The SRD operates passively in response to changes in the temperature of the space structure. The V1-x-yMxNyOn exhibits a metal/insulator transition with temperature, varying from an IR transmissive insulating state at lower temperatures, to a semiconducting state at higher temperatures. Dopants, M and N, are employed to tailor the thermo-optic characteristics and the transition temperature of the passive SRD. The transition temperature can be preset over a wide range from below -30°C to above 68°C using suitable dopants. A proprietary SRD structure has been developed that facilitates emissivities below 0.2 to dark space at lower temperatures to reduce heater requirements.