Ionizing radiations are responsible for bond scission, radical formation, and oxidative degradation of polymer matrices. This study focuses on the effects of gamma irradiation on solid propellant binders, targeting a comprehensive chemical and mechanical characterization of different formulations. Samples were produced either by conventional methods based on hydroxyl-terminated polybutadiene and standard polyaddition reaction using isocyanates, or innovative approaches involving UV-driven radical curing. The samples were irradiated for comparison and to study their evolution as a function of three absorbed doses (25, 45, 130 kGy) for preliminary characterization studies, using a 60-Co gamma source. Samples were irradiated in air at uncontrolled room temperature. The coupling of spectroscopy techniques (Fourier transform infrared—FTIR, Raman and electron paramagnetic resonance—EPR) and dynamic mechanical analysis (DMA) highlighted the key role of antioxidant agents in tailoring mechanical changes in the binder phase. The absence of antioxidants enhances radical formation, oxidation, and cross-linking. These processes lead to progressively increased rigidity and reduced flexibility as a function of the absorbed dose. Complex interactions between photocured components largely influence radical stabilization and material degradation. These findings provide valuable insights for designing novel radiation-resistant binders, enabling the development of solid propellants tailored for reliable, long-term permanence in space, and advancing the knowledge on the applicability of 3D-printed propellants.

Thermite-for-demise (T4D): thermite characteristics heuristic optimization on object- and spacecraft-oriented re-entry models Alessandro Finazzi, Filippo Ma

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.