Assessing the potential criticality of the most massive objects abandoned in LEO

As of mid-2017, there were ~7500 metric tons of mass in orbit around the Earth, of which about 95% concentrated in almost 6700 intact spacecraft and orbital stages. Among them, nearly 80% were abandoned and more than 90% could not be maneuvered. The intact objects abandoned in LEO above ~650 km, i.e. with a typical residual lifetime of more than 25 years, represent the main potential mass reservoir for the generation of new detrimental orbital debris in case of mutual collisions with the existing debris environment. A practicable strategy to assess the latent long-term environmental impact of an orbiting object is to devise a ranking scheme based on simplified and reasonable inferences. Several ranking schemes have been proposed by different authors during the last decade. Various "criticality indexes" have been devised by us (at ISTI-CNR) in the last few years, and they have been applied to evaluate the environmental impact of many families of rocket bodies and selected spacecraft. A couple of the most complete indexes formulated by us are herein applied to assess the potential criticality of the most massive objects abandoned in LEO.