Modelling and Analysis of the Decay Phase for Space Objects in LEO

This Thesis presents a low-fidelity approach to model and analyze the decay phase for space objects (space debris) originally orbiting in Low Earth Orbits (LEO). This approach is used to better characterize some of the involved uncertainties, which are propagated through the propagation of the orbit in order to characterize the re-entry time. In particular, the main source of uncertainty lies in the prediction of solar and geomagnetic indices which is performed through time series analysis techniques. The indices influence the Total Mass Density (TMD) in the Thermosphere, i.e. the layer of the Earth atmosphere from about 90 [km] of altitude to between 500 and 1000 [km]. During the decay phase, a low-fidelity 3 degree of freedom (DoF) propagator is used and the only perturbation force considered is the aerodynamic drag, which is the main one in LEO. Alongside the propagator, the Thermosphere model NRLMSISE00 is adopted in order to calculate TMD with some uncertainty depending on the indices values, which defines the re-entry time window when the propagation stops at the altitude of end orbit. A validation of the model is presented using the well-known test case of GOCE re-entry, while a demonstration of the potential of the model is given through the analysis of classes of high area to mass ratio space objects.