The long-term interaction of the Italian satellites abandoned in GEO with the orbital debris environment

Four Italian satellites have been launched, so far, in geostationary orbit: SIRIO, Italsat 1, Italsat 2, and SICRAL. The latter is the only one still operational: in fact, Sirio was abandoned close to the geopotential equilibrium point at 75?E in 1985, Italsat 1 was re-orbited above the geosynchronous altitude at the beginning of 2001 and Italsat 2 was moved, in July 2002, below the synchronous height, due to an unexpected malfunction. A study was carried out in order to investigate and quantify the long-term environmental impact of the abandoned satellites on the geosynchronous region. As they were all successfully passivated, eliminating the possibility of future explosions, the only significant detrimental effect on the environment might derive from catastrophic collisions with other sizable space objects. However, the probability of such events was calculated to be extremely low, of the order of 10. 7 in one century.