Satellite re-entry prediction products for civil protection applications

In order to meet the specific requirements of civil protection authorities, since 2003 a set of tailored products has been developed and applied in Italy to define, a few days ahead of re-entry and in wide areas of interest, risk zones and corresponding alert time windows in the event of an uncontrolled satellite decay leading to undue debris impact hazard on the ground and in the overlying airspace. Based on the general properties of re-entries from nearly circular decaying orbits, on the results of detailed fragmentation analyses, when available, on standard re-entry prediction outputs, on specific simulations of endo-atmospheric debris dynamics, and on the basics of orbital motion with respect to the Earth, accurate re-entry tracks over the region(s) of interest are determined, with sufficiently conservative ground safety swaths, accounting for the sources of cross-track debris dispersion, and associated risk time windows, depending on debris flight time dispersion and residual trajectory along-track uncertainties. With the approaching re-entry and the consequent shrinking of the global uncertainty window, some of the risk zones and time windows identified in advance can be progressively discarded, leaving at most, until the end, one re-entry opportunity, but more often none, over a region the size of Italy. These products are easy to understand and are timely, accurate, unambiguous and remarkably stable, all qualities that render them particularly suitable for civil protection applications.