Spent upper stages are bodies consisting of components likely to survive re-entry, for example propellant tanks. Therefore, the re-entry of upper stages might be associated with high on-ground casualty risk.
Currently re-entry predictions of spent rocket bodies in GTO are highly inaccurate: the prediction uncertainty is typically above 20% of the time to re-entry. In this European Space Agency study the Astronautics Research Group, in partnership with Dinamica Srl (dinamicatech.com) and Centre National de la Recherche Scientifique (artemis.oca.eu) is facing the challenge of reducing the uncertainty of current re-entry predictions. In particular, we are implementing the Accurate Re-entry Tool (ART), which aims at computing accurate re-entry predictions by relying exclusively on public available Two Line Element set (TLE) data. TLE analysis and filtering, spacecraft parameters estimation, and combined state and parameters estimation are the main building blocks of the ART.
Figure 1 Example of performances of a TLE filter applied to perigee radius (Object 22254)
Figure 2 Accuracy of re-entry prediction computed by the ART. Predictions carried out for 92 objects in highly elliptical orbit 180 days before re-entry. The figure shows that estimating the ballistic coefficient (BC) of the spacecraft can result in more accurate predictions with respect to more complex methods based on nonlinear least squares orbit determination (OD) in which spacecraft state, BC and solar radiation pressure coefficient (SRPC) are estimated. Only for few cases for which a scarce number of TLE is available the re-entry prediction error is above 20%.
