Phase-change thermal capacitors for ExoMars 2016 mission

Abstract

Use of heat capacitors based on Phase-Change Materials (PCM) for the effective thermal management of peak power dissipation in space systems is not a novelty. Yet, its application in real missions has been small, especially in Europe, due to mass penalty issues and relatively poor technological heritage. Three capacitor units using this technology are being manufactured and tested to be flown onboard the Entry descent & landing Demonstrator Module (EDM) of the ExoMars 2016 ESA mission, under the responsibility of Thales Alenia Space Italia (TAS-I) as prime contractor. Their use onboard ExoMars EDM is motivated by the peculiar and stringent thermal control requirements, implying thermal management of short-duration power dissipation in a highly insulated environment. ExoMars thermal capacitors are PCM-based heat exchangers using phase change waxes that transition from solid to liquid at the desired control temperature and absorb considerable heat energy in the process. In order to effectively transmit the heat into the PCM wax, which has very low conductivity of its own, the wax is contained within rugged, impact resistant, thermally conductive aluminum housings filled with an open-celled aluminum foam that acts both as a structural core material and provides a very large surface area for the wax to make contact with. These capacitors are manufactured by the US company ERG Aerospace which has also developed a proprietary technology for the aluminium foam. The development and testing of the EDM thermal capacitors is described in this paper. Their integration and operations in the frame of the overall EDM thermal design is illustrated as well.