The excellent satellite tracking database www.space-track.org, which is mantained by the United States Space Command, offers to the public accurate and up-to-date orbital elements for thousands of satellites and space debris.

There are many satellites, rocket bodies and space debris (these produced by fragmentation of other satellites and rocket bodies, for example) been constantly tracked. Their origin is well known; their launch date and launch platform or their parent body in the case of orbital debris. Even spy satellites from other countries are tracked and their launch date is well known (which means that their launches are detected by some space surveillance system I'm not aware of or that they are been tracked so soon that a orbital insertion has not yet been archived and an origin can be easily established).

I've recently come across an interesting catalog of objects in this database; the so called "Well-Tracked Analyst Objects". In their FAQ they explain that

Analyst objects are on-orbit objects that are tracked by the U.S. Space Surveillance Network (SSN) with insufficient fidelity for publication in the public satellite catalog (SATCAT). The lack of fidelity may be due to infrequent tracking, cross-tagging (observation association with closely-spaced objects), or inability to associate the object with a known launch. Today there are approximately 17,000 on-orbit objects in the public SATCAT and approximately 6,000 on-orbit analyst objects for a total of 23,000.

The 18th Space Control Squadron (18 SPCS) is responsible for analyzing tracking data from the SSN to maintain the SATCAT, and creating and updating analyst objects as new satellites launch and new objects are found. The analyst range, which is denoted by a satellite number from 80,000-89,999, is used like an analytical sandbox, where Orbital Analysts (OA) can create, change, and update objects until they have sufficient data and information to transition them to the public SATCAT. Consequently, analyst numbers can be constantly reused for different objects.

So, these are a lot of objects that have been tracked poorly in the past and now we don't know if they have swapped identities with other objects or where they where launched or if they are orbital debris from undetected fragmentations (I suppose)...

That's interesting. But even more interesting is the subset of these "Analyst Objects" that are the "Well-Tracked Analyst Objects".

Well-tracked objects are generally objects that have been consistently tracked by the SSN for longer than six months that don't frequently cross-tag with other objects.

So, as far as I understand, these are not objects that have been missidentified but objects that are of unknown origin which are well-known.


  1. Are these "Well-Tracked Analyst Objects" just objects that where in the "Analyst Objects" catalog and are in the process of becoming identified specific satellites of the main catalog? Are these objects just the few satellites that slipped through the cracks of the surveillance system that detects them just after launch?
  2. What would the leading hypothesis should be for them? I see that some have close to Geostationary and HEO orbits so my guess is that they are unknown artificial satellites from other countries or fragments that were expelled from some known satellites in those orbits during some unknown fragmentation events. But there's also the possibility they are something different or am I getting the wrong feeling? For example some of these objects have crazy orbital eccentricities or move with periods that are not exact divisors of Earth's daily rotational period.
  3. Is it possible that some of these objects might be small meter-sized asteroids captured by Earth? Could they be natural satellites of Earth? I guess some meteor showers should inyect once in a while a few of these in orbit around Earth (or I'm completely messing with the orders of magnitude here?).
  4. My last question is unimportant and just for fun speculation. If an extraterrestrial intelligence is studying Earth by means of an artificial satellite around it, Would be notice? I think that the answer is yes for sure (given the tracking systems we currently have) but... Would we manage to identify it as extraterrestrial or would it simply fall into this list of unknown objects? This last question is related to whenever there where space awareness, ground-based tracking and surveillance systems capable enough by the time Earth orbit became as crowded as to start missing our own objects, or not.

1 Answer 1


This started out as a comment on 3), but this should be a rough answer by now.

  1. This means exactly what it says on the tin. They have been observed for so long that we have accurate enough data on them to not confuse them with other objects. They are not in the process of being identified as belonging to a specific launch. The cracks in the surveillance system are much larger than you think, especially in the past. It's not enough to know their position right after launch to identify them at a future date. A more or less unbroken chain of observations are required for that, which is not the case for a great number of launches.

  2. The leading hypothesis, or maybe closer to an established fact, is that these are various debris from the combined human space programs. High eccentricities are common for many types of communication and observation satellites (see for instance Molniya orbits). GEO transfers would also produce such debris in the form of spent upper stages. In any case, the general origin of these objects is no mystery, it's just that we can't ID them to what specific launch they are from. Many launches happened while observational capabilities were much smaller than today, and their predicted future position is much more sensitive to their initial state than the accuracy we have available from those launches.

  3. There's no chance of these objects being natural. An asteroid capture can happen in processes that produce (temporary) orbits at much higher altitude, and much lower relative speed. There's no known mechanism that can transport them to these sub-lunar orbits. While we generally treat these satellite orbits as "stable", they are not stable over the astronomical time scale required for them to have been there since the origin of the Earth-Moon system.

  4. It depends on what you mean by "notice". Thousands of such objects out are tracked, and we have a decent coverage of the larger ones. But unless it does some propulsive maneuver, emits a signal, or has odd spectral properties, it will just be another piece of presumed debris in the catalogue. Far from all of them have been certainly identified, and this will likely remain so.

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    $\begingroup$ Excellent answer, with one tiny nit; Toe "There's no known mechanism..." I somewhat disagree with the use of an absolute. A three-body temporarily captured orbit that includes an Earth perigee of circa 100 km but a high apogee might conceivably interact with the Earth's atmospheric drag and the Moon's perturbation to eventually settle into an orbit long-term bound to Earth. The non-conservative drag force can be thought of as propulsive thrust in reversed time. It's of course highly unlikely, but it would be hard to demonstrate that it's absolutely impossible. $\endgroup$
    – uhoh
    Sep 22, 2019 at 23:13
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    $\begingroup$ I'm sceptical to that being possible, as the initial atmospheric braking would have to be quite large to bring it low enough for the Moon to be just a perturbation. Has the mechanism you describe ever been proposed? $\endgroup$ Sep 23, 2019 at 1:00
  • 1
    $\begingroup$ Things being possible yet highly unlikely are not always proposed, but that doesn't mean they are impossible. As yet un-proposed Rube Goldberg-type machines (or in this case Rube Goldberg-type orbits) could still be possible, so I'm going to take this on as a personal space-golf challenge to see if I can come up with one! $\endgroup$
    – uhoh
    Sep 23, 2019 at 1:12

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