The exact number of artificial objects in outer space will never be known. Many factors rule the game:
- How objects are numbered, for instance a complex Apollo rover may be counted as one object or split into its detachable elements: antennas, cameras, batteries, seats, console, hand tools carrier, fenders, etc. (see the Apollo 15’s rover in the picture below, credit: NASA);
- The number of debris resulting from impacts, collisions and spent stage breakups, provided those events will ever be known;
- The number of objects that emerge from deployments and separation of spacecraft (explosive bolts, lens caps, dust covers, clamp bands, fairings, shrouds, etc.);
- Untold or unknown events such as classified missions and experiments, private belongings secretly left on the moon by the Apollo astronauts, family items hidden into space hardware by mission staff and technicians, or Apollo hardware unofficially returned to Earth as souvenirs by the astronauts.
Additionally, it is almost impossible to pinpoint most of the orbiting objects, not only because inert items and defunct probes are untrackable, but also because their trajectories are perturbed by the unpredictable orbital mechanics, rendering trajectories calculations useless in the long-term. Thus, some objects are listed on one table but should probably lie on another one.
However, access to Space Agencies records and databases to fetch detailed information about actual flight hardware, exact deployment sequences and other critical information would greatly help establishing more accurate listings.