Compliance of the Italian satellites in low Earth orbit with the end-of-life disposal guidelines for Space Debris Mitigation and ranking of their long-term criticality for the environment

As of mid-2014, nearly 50 years since the launch of the first satellite, Italy had placed in low Earth orbit 29 objects: 27 payloads, 1 rocket body and 1 mission related object. 19 were yet in space: the IRIS rocket body and 18 payloads, 4 of which, belonging to the COSMO-SkyMed constellation, still operational and maneuverable. 16 objects had been deployed in space before the approval, in 2002, of the IADC Space Debris Mitigation Guidelines and 1 further payload had been launched before the ASI signature of the European Code of Conduct for Space Debris Mitigation, in 2005. While no object had been yet maneuvered to reduce its residual lifetime, due to the operational orbits chosen and area-to-mass ratios, 16 of them had decayed or were predicted to reenter in less than 25 years after mission completion, in agreement with current disposal recommendations. This corresponded to a compliance of 64% over 50 years, of 59% for the objects placed in orbit before the ASI signature of the European Code of Conduct, and of 75% for those launched afterwards, excluding the 4 maneuverable spacecraft still functional. Concerning the risk on the ground associated with uncontrolled reentries, just one satellite decayed in 2003 had a mass greater than 600 kg and a casualty expectancy in excess of 10^-4. For it, timely reentry predictions and alert time windows had been provided to the countries overflown. In order to evaluate the potential long-term detrimental effects on the environment of the abandoned or unmaneuverable objects, a new ranking index, also useful for active debris removal priority listing, was developed and applied. It is worth noting that all the 14 objects residing or descending below 1000 km exhibited an overall ranking index equivalent to just 8% of an average abandoned intact object in a 800 km sun-synchronous orbit.