AN INDEX FOR RANKING ACTIVE DEBRIS REMOVAL TARGETS IN LEO

In order to evaluate the potential environmental criticality, regarding the evolution of orbital debris, of the objects lost or abandoned in low Earth orbit, a new normalized and dimensionless ranking index was presented, using as benchmark a nearly 1-ton object placed into an 800 km sun-synchronous orbit. It was applied to 58 objects with a mean altitude in between 600 and 1000 km and with a dry mass greater than 3000 kg. They accounted for about 11% of the mass present in low Earth orbit, operational spacecraft included. The maximum value found corresponded to the massive second stage of a Zenit launcher, abandoned close to 1000 km. Envisat ranked first among the spacecraft no longer operational, but only 22nd in the group considered, after 20 Zenit second stages and a CZ-2C rocket body. Most of the mass with a criticality index greater than 1, i.e. 90%, was concentrated at 830 +/- 40 km.