Radiation-cooled helix traveling-wave tube (TWT) is mostly used as a high-power microwave amplifier in satellite communication. The radiation shield assembly has to fit on the multistage depressed collector (MDC) to radiate waste heat into the space environment and demands efficient thermal modeling. In this work, the radiation shield assembly has been designed with a heat dissipation capacity of 100 W. Moreover, the radiation shield assembly has to withstand the mechanical vibration faced during the satellite launching. In this article, the author has proposed a detailed design and analysis of the radiation shield cooling assembly for TWT, aiming to operate both at room and extreme space temperatures. Furthermore, a 1-D analytical model has been proposed for the quick and accurate estimation of the inside temperature of the MDC electrode. The methodology adopted for the design of the radiation shield cooling assembly has been thoroughly discussed. The structure has been simulated using the ANSYS tool, and the simulation results are in close agreement with the analytical results.