THE ART OF DEMISE
State of the Art
On average, over the past decade, a space object above 800 kg has been re-entering every week, e.g. ESA’s GOCE in 2013 and NASA’s UARS in 2011. Most of these objects do not totally demise during atmospheric re-entry. Fragments may survive and reach the ground where they pose a risk to people and things. Space agencies are currently enforcing constraints on the casualty risk for the re-entry event and different re-entry analysis tools have been developed by agencies, industries and research centres to assess this risk. At the same time, new approaches to the design of spacecraft, aimed at increasing the probability of complete demise during re-entry, offer an effective way to meet these constraints. Thus re-entry analyses approaches have to be embedded into the design process since the very beginning, to evaluate the demise probability and casualty risk of different configurations. Currently, most of the efforts are focused on structural design for demise techniques, the improvement of high fidelity and low fidelity models used to predict the aero-thermal performance and thermo-mechanical response of objects, the implementation of efficient uncertainty quantification techniques for a more correct characterisation of the risks, and better understanding and modelling of material properties. Plus, since demisability competes against the survivability of the object during its mission lifetime, design for demise can be seen as a multi-criteria design problem.
WP2 covers all activities related to the re-entry of space objects and their possible demise. It includes all multi-fidelity and multi-physics simulations, the possible design of these objects and their effect on the pollution of our planet.
Significant research efforts have been diverted towards developing a strategy to assess fragmentation using a high-fidelity structural mechanics method called peridynamics. The focus at the moment, is on developing a devisability model and no considerable progress has been made on survivability modelling.
Several validation studies have been completed to assess and benchmark peridynamics method with other structural mechanics methods like FEM for a range of fracture mechanics phenomena. A validation study of an experimental PMMA material specimen to compare with the results of peridynamics has also been performed to increase the confidence of the high-fidelity method at use. Material model calibration for aluminium alloy and steel alloy has been performed for high temperatures (close to melting). Studies on primitive shaped structures like flat plates, tensile testing specimens, cylinders and hollow box shapes have been simulated at room temperature and elevated temperatures to determine the force necessary for the fragmentation of the objects. Also, the damage model parameter calibration has been performed to model fracture at high temperatures where such experimental data is unavailable. This calibration would add the effect of structural weakening at elevated temperatures, and enables us to study a more realistic structural fragmentation during re-entry conditions. A re-entry test case study while including the above effects is in the preliminary phase of modelling.
Preliminary uncertainty estimations of a fracture mechanics parameter, integral to the structural fragmentation studies, have been performed.
No progress has been made against the development of a multi-fidelity model at the moment as the current focus is on the study of primitive shaped objects which are generally used in low-fidelity re-entry codes.
Manzi, M., Peddakotla, S. A., Stevenson, E., Vasile, M., Minisci, E., Rodriguez-Fernandez, V., Camacho, D. (2020). Intelligent Atmospheric Density Modelling for Space Operations. Stardust-R Global Virtual Workshop I, Pisa, Italy, 07-10 September 2020.