| PL Payload | PD Payload debris | PM Payload mission related object | PF Payload fragmentation debris | UI Unidentified |
| RB Rocket body | RD Rocket debris | RM Rocket mission related object | RF Rocket fragmentation debris |
Recent plots of the catalogued debris population include an interesting new feature “unidentified” or “grey” debris. The sudden appearance of this category of debris objects is not as a result of a fundamental change in the characteristics of the debris population, but rather the result of a change in policy.
Previously, objects were catalogued if they could be unambiguously associated with a particular launch or fragmentation event, which essentially meant that the object had an “owner” under international law.
It was then decided that it would be a better policy to include the unidentified objects that were being tracked in the publicly available catalogue, since this would allow them to be included in conjunction warning assessments, hopefully enabling active satellites to avoid them.
This policy change is welcome, but it does, however, present the space community with something of a challenge when it comes to providing year-on-year comparisons of the debris population. And this problem is only going to get worse…..
As commercial companies such as LeoLabs and national sensors such as the new Space Fence push detection thresholds down from 10 cm to perhaps 1-2 cm, many more small debris objects will be catalogued. Estimates vary significantly, (by almost a factor of two), concerning the true magnitude of the debris population in the size range 1-10 cm, but even the most conservative figures imply that the catalogue size will increase by an order of magnitude.
If these newly tracked objects are included in plots such as the one above, it will appear that the debris population is rapidly increasing, with many, many more “grey” objects appearing in the “unknown” category. In reality of course, it will simply be the case that objects which have been orbiting the Earth for many years have finally become “trackable”, (and since they have long been undetected, possibly for decades in some cases, it is almost certain that they will have no identifiable owner).
Due to its sheer size, this grey population will dominate future discussions of topics such as space insurance, the Kessler threshold, and safe orbital altitudes to use for future constellations of satellites. At present, our space legislation makes no adequate provision for this material, and it is manifestly unclear whether any “space salvage” operation to clear up this material would be “legal”. Deciding whether to include grey debris on our plots of the debris population will be the least of our concerns.
