GOCE reentry predictions for the Italian civil protection authorities

The uncommon nature of the GOCE reentry campaign, sharing an uncontrolled orbital decay with a finely controlled attitude along the atmospheric drag direction, made the reentry predictions for this satellite an interesting case study, especially because nobody was able to say a priori if and when the attitude control would have failed, leading to an unrestrained tumbling and a sudden variation of the orbital decay rate. As in previous cases, ISTI/CNR was in charge of reentry predictions for the Italian civil protection authorities, monitoring also the satellite decay in the frame of an international reentry campaign promoted by the Inter-Agency Space Debris Coordination Committee (IADC). Due to the peculiar nature of the GOCE reentry, the definition of reliable uncertainty windows was not easy, especially considering the critical use of this information for civil protection evaluations. However, after an initial period of test and analysis, reasonable and conservative criteria were elaborated and applied, with good and consistent results through the end of the reentry campaign. In the last three days of flight, reentries were simulated over Italy to obtain quite accurate ground tracks, debris swaths and air space crossing time windows associated with the critical passes over the national territory still included in the global uncertainty windows.