Design and Development of a Thermal Switch for Spacecraft Application

Abstract

A thermal switch is used for the passive thermal management of a low earth orbit satellite where the operation time for spacecraft is less. It is used to control the temperature of electrical components within the working range temperature. It is inserted between the electrical component and an outer radiator. Presently a heat pipe is used for the same purpose but an additional heater is to be provided to prevent the temperature of component from falling below the lower limit of working temperature range as the heat pipe doesn’t have a switching facility so it will continue to transfer heat during the off condition of the component. Instead if a thermal switch is used in place of a heat pipe, the requirement of an additional heater can be removed as it has very low off state conductance. In the present work three conceptual designs of CTE (coefficient of thermal expansion) based thermal switch have been considered and the analytical calculations for the conceptual designs have been performed in order to decide the dimensions of the switch. The thermal resistive network calculations have been shown for each prototype to know the ON conductance to OFF conductance ratio which shows the effectiveness of the thermal switch. Force calculations have also been carried out to know the reaction force generated at the interface which will help in developing an idea about the thermal contact conductance of the switch. The CAD models of all prototypes have been created using NX software and their static structural analysis conducted using ANSYS software to ascertain their structural stability. The structural analysis is further validated by using analytical calculations. After satisfactory result of structural analysis and design procedure, all prototypes have been fabricated. The test setup is also designed for work related to the testing and experimentation of the thermal switch. Two prototypes (out of three) have been tested in a vacuum chamber under vacuum condition of the order 1 0 -5 mbar . The thermal performance of one of the prototype is observed to be 15.62 W/K as ON conductance and the ratio of ON conductance to OFF conductance is found to be 126. The thermal performance of the second prototype is poor in comparison to the first prototype which is 6.16 W/K as ON conductance and the ratio of ON conductance to OFF conductance is found to be 11.