Demisability of critical spacecraft components during atmospheric re-entry

According to international safety guidelines, the on-ground casualty risk for a re-entering object shall not exceed 1 in 10,000. The casualty expectancy can be reduced in two ways (1) by selecting a suitable impact area and population density within, or (2) by reducing the casualty area from the surviving fragments. Due to the cost associated with a controlled targeted re-entry, the latter option has attracted a lot of attention. To achieve the requirement of reducing the casualty area, the number, size and kinetic energy of the surviving fragments have to be limited. The fragments which survive re-entry are often from recurring spacecraft components (e.g. propellant tanks, reaction wheels, solar array drive mechanisms, magnetic torquers, etc.), therefore the interest of applying designs which increase the demisability of these components is high. Understanding the demise process during re-entry helps in identifying feasible design-for-demise options. For this study, we conducted re-entry risk analysis of two critical spacecraft components, a solar array drive mechanism, and a reaction wheel using a spacecraft-oriented re-entry tool, in order to assess the break-up and demise behaviour of the components. Detailed models of the components were created using design input from the manufacturers and initial conditions for the simulations were selected within a release window (58–98 km) along a reference trajectory. We have investigated the casualty risk metrics for the components, derived the most-probable casualty area over release altitude and investigated its uncertainties. Together with the manufacturer, we identified feasible design-for-demise options for the components and evaluated their impact on the casualty risk.