Impact tests and modelling for the ESA radioisotope power systems

Since 2009, ESA has been conducting R&D activities leading towards the development of a European capability in radioisotope power systems for space. The programme is focused on the use of americium-241 as an innovative alternative to the plutonium-238 currently used by the USA and Russia. Two different technologies are being developed by the University of Leicester in the UK: radioisotope thermoelectric generators and radioisotope heater units. The development of the fuel containment architectures, known as heat sources, has recently evolved from the design stage to more representative prototypic systems. Multiple containment layers ensure that the heat sources can survive accident conditions from launch failures to Earth re-entry, minimising the risk of inadvertently releasing radioactive material into the environment. Validated accident models are necessary for the design iteration process of these systems, and for the creation of a safety case for their launch. The research project here presented was a collaboration, supported by ESA , between the University of Leicester in the UK and ArianeGroup in France. The goals of this activity were to perform the first-ever impact tests for the European Am-based heat sources, and to start developing computer models to simulate the behaviour of the containment systems under different impact conditions in accident scenarios. Tested samples were then characterized both at ESA/ESTEC and at the University of Leicester, in order to understand the behaviour of the fuel containment materials under the most relevant accident conditions.