Uncontrolled reentries of massive space objects

Uncontrolled reentries of objects with a mass of about 4000 kg or more, with an associated casualty expectancy of the order of 0.001, currently still represent a small fraction of the total tally of intact reentering objects with a mass greater than 500 kg. After an introduction addressing the uncontrolled reentries of massive objects during the last decade, in terms of orbital inclinations, reentry frequency, sightings, debris recovery, and relative relevance of spacecraft vs. orbital stages, the specific recent case of the Zenit second stage 2017-086D will be discussed. Finally, considering the approaching reentry of the Chinese space station Tiangong-1, an updated analysis of its trajectory evolution will be provided.