The Deep Space Catalog - Catalog Statstics

Jonathan C. McDowell

Aug 2020: Rev 1.0.8

Catalog Statistics

The 1023 entries in the initial release of the catalog include 908 free flying objects and 115 attached objects. There are several categories of attached object, which are given catalog entries even though they are not separate spacecraft. These include objects which failed to separate due to mission failure (example: the Apollo 13 lunar module descent stage, which remained attached to the ascent stage at Earth atmosphere entry); objects which I count as separate payloads even though not designed to separate (example: I have separate entries for the Falcon Heavy 001 second stage rocket and the Tesla car permanently affixed to its nose); solid apogee motors attached to spacecraft; and EVA spacesuits, including those that were not actually used on EVA and remained inside the spacecraft.

Of the 902 free objects, only 438 have catalog numbers in the US satellite catalog. The distribution of the current mission phases of these 902 objects is summarized in table IV, separating objects which are still in orbit from those which are now `down'. `Down' here variously means landed, crashed or destroyed in atmospheric entry. I separate objects which have never left the Earth's Hill sphere (`Deep Earth') from those which have returned to it (`Earth Return') after having been in lunar or solar orbit. The latter include lunar mission upper stages which made lunar flybys and then ended up orbiting the Earth at near-lunar distance, often never being tracked post-encounter. 63 deep-space Earth-orbiting objects are noted as `lost'. Objects in deep Earth orbit can be chaotic or nearly so and are susceptible to being perturbed into solar orbit or - even with very high initial perigees - to Earth reentry. Multiple distant lunar flybys are not uncommon and can leave the objects in quite different orbits from their initial ones. For objects last seen decades ago and not recovered with the advent of new, capable survey telescopes there is no way to know what their specific fate was. Objects in other parts of the solar system may also be lost, but at least we usually know whether they are likely still in orbit or not, and around which central body.


Distribution of free-flying deep space objects in catalog.
BodyIn OrbitDownLost
Deep Earth 41 83 18
Earth Return 9 49 49
Moon 14 145 0
Sun-Earth L1/L2 5 0 0
Sun 321 0 0
Mercury 0 1 0
Venus 7 57 0
Mars 20 64 0
Jupiter 1 4 0
Saturn 1 1 0
Titan 0 8 0
Asteroids/Comets 5 15 0