Thermite-for-demise (T4D): experiments and numerical modelling on solar array drive mechanism mock-ups containing thermite in an arc-heated wind tunnel

The ESA-TRP SPADEXO project investigated the use of thermites to provide additional enthalpy to a spacecraft re-entering towards the Earth, with the objective of limiting its casualty risk on ground. Steel mock-ups inspired by the geometry of solar array drive mechanisms were filled with thermite and placed in DLR’s L2K arc-heated hypersonic wind tunnel. In each of these samples, a set of thermocouples was installed to monitor ignition and propagation of the heat generated by the reaction. One of the thermocouples was placed in a hole machined inside the mock-up wall to monitor temperature evolution in proximity of the pyrotechnic charge, without the risk of losing the sensor due to the ignition of the thermite. The main objective of these tests was to study the dependence of the heat transferred from the internal charge to the surrounding structure from the filling level. Results showed that higher thermite filling resulted in higher transferred enthalpy. In the presence of a large thermite amount, the reaction led to the formation of a dense liquid drop close to the side wall, causing significant heat transfer towards the wall of the mock-up. Tests were rebuilt using the SCARAB re-entry software, extended with a dedicated model to represent the ignition of an internal charge. Ignition and heat transfer were adequately described by the model in most of the test configurations. Specific parameter tuning was needed for the highest filling factor tested in this work, highlighting the influence of reaction products internal dynamics on the heat transfer processes.