Re-entry predictions for uncontrolled satellites: results and challenges

Currently, approximately 70% of the re-entries of intact orbital objects are uncontrolled, corresponding to about 50% of the returning mass, i.e. about 100 metric tons per year. On average, there is one spacecraft or rocket body uncontrolled re-entry every week, with an average mass around 2000 kg. Even though a detailed demise analysis is available only occasionally, in many cases the alert casualty expectancy threshold of 1:10,000 is probably violated. Re-entry predictions are affected by various sources of inevitable uncertainty and, in spite of decades of efforts, mean relative errors of 20% often occur. This means that even predictions issued 3 hours before re-entry may be affected by an along-track uncertainty of 40,000 km (corresponding to one orbital path), possibly halved during the last hour. However, specific methods and procedures have been developed to provide understandable and unambiguous information useful for civil protection planning and applications.