However, many upper stages from launches decades ago remain in low Earth orbit and continue to pose a problem. In a presentation at the 71st International Astronautical Congress this week, Darren McKnight of Centauri presented an analysis of the 50 “statistically most concerning” debris objects in low Earth orbit.
That list was developed by combining 11 separate analyses by 19 authors, who used different approaches for ranking based on criteria such as the mass of the objects, the probability of collision and persistence of their orbits. Those analysis were combined into a single master list.
The top 20 objects in that master list are all a single class of upper stages known as SL-16, from the Zenit family of rockets. The stages are all large and are in similar orbits, raising the risk of collision, McKnight noted. The highest ranked satellite, ESA’s Envisat, which malfunctioned before it could be deorbited, is 21st on the list.
Overall, 78% of the objects on the list are rocket bodies, and 80% of the objects were launched before 2000, when countries started adopting orbital debris mitigation guidelines. “These are really lingering problems from early in the Space Age,” he said.
The development of the top-50 list can support future efforts to mitigate the risk through active debris removal. McKnight said that the risks of many of these objects are coupled to others on the list. “If you remove one, the other one may drop way down on the list,” he said. “We don’t have to take them all out. We can reduce their risk enough by taking one selectively out.”