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Simplified models for aerothermodynamics analysis of space craft components: "design for demise"

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Thousands of man-made objects are currently in orbit around the Earth. These range from active satellites to flecks of paint, via spent rocket stages and fragments of satellite debris. Due to the drag of the very thin high altitude atmosphere, these objects have slowly decaying orbits, and will eventually re-enter the Earth's thicker, lower atmosphere. Most will be destroyed on entry due to the aerothermal heating experienced at hypersonic velocities at altitudes between 40 and 80km. However, some objects reach the ground.
The processes involved in the re-entry of objects into the Earth's atmosphere are well known. Understanding the phenomena well enough to be able to make predictions about the survivability of particular objects is significantly more challenging. The focus of the present work is on aerothermal predictive methodologies in the context of destructive entry and the impact that simplifications have on the resultant ground casualty risk. For this purpose, an end-to-end software suite (SAM) has been developed to determine the effect of enhancing the aerothermal description of component demise and fragmentation. In particular we investigate: a reassessment of the aeroheating models used for complex and primitive geometries, including tumble averaged and attitude dependant descriptions; thermal response models which account for wall temperature effects, ablation and blowing, and provide an estimate of in-depth conduction to the surface energy balance where deemed significant; extension of ablation mechanisms beyond melting (e.g. for CFRP); rule based spacecraft fragmentation including a treatment of joints; and the significance of 6DoF trajectory propagation both for the spacecraft prior to breakup and for selected fragments. Modelling recommendations are made based on the results of these investigations. In addition, a preliminary identification of knowledge gaps and suggested future developments (e.g. supporting experimental campaigns) is provided.

Executive summary