The Deployable Space Telescope (DST) project aims to reduce the stowed volume compared to other Earth observation satellites with a similar resolution. The DST demonstrator functions in the thermal infrared (TIR) domain, which imposes stringent thermal requirements on the detector. The detector must be cooled to 150 K, and the instrument box to 200 K. This thesis documents the lowering of the detector and instrument box temperatures by minimizing the heat input on the detector and the radiators. The addition of a (deployable) Earth shade door minimizes the external heat input on the radiator surfaces. The impact of the satellite's orbit on the thermal environment and the minimum and maximum worst-case scenarios were investigated, which determined that constellation flight was possible. The proposed thermal control system design is fully passive and results in stable detector and instrument box temperatures that meet the set requirements.