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This is a screenshot from AstriaGraph. It mixes data sources for objects in orbit from Spacetrack/USSpacecom and JSC Vimpel.Screenshot from Astriagraph

EDIT: I've created a separate question to split out the original two questions that were embedded in this one.

Orange dots are active satellites, blue dots are in-active satellites and the purple and pink dots are rocket bodies and uncatagorised, respectively. Its hard to discern the difference between the latter two in colour.

For orientation the geostationary arc comprises the orange dots in a semi-edge-on circle stretching from about "08:30" to "02:30" as we look at the image as a clock face.

There is also a clear ellipse stretching from LEO at 03:00 to an apogee at MEO at about 09:45 and it is made up of a mixture of purple and mostly pink dots. There is another pink ellipse which is completely edge on, on the right hand side slightly above the GEO arc.

When I clicked on objects in these orbits most of them are reported as uncategorised though I did find one labeled as a rocket body part. They are all only in the Vimpel catalogue and not reported as having USSpacecom IDs.

It looks like these two arcs might be debris from a rocket body fragmentation; the separate question mentioned above asks what the causing event might be.

The question, finally: Are there really this number objects that are observed by one system, Vimpel, but not another USSpacecom? Why is this?

These objects would be close enough to Earth to be visible to radar at perigee and high enough, and thus slow enough, to be tracked optically at apogee, so LEO Labs and Exonalytic should also have an opinion.

EDIT Following PearsonArtPhoto's analysis and info (see his answer here and then trace it to the paralellel question I raised on the cause of the apparent fragmentation) I looked up the object he mentioned (USA 257, satcat 46653, COSPAR 2014-055DD) and came across this report from ODQN which suggests that the parent object is indeed a Centaur upper stage, 2014-055B:

Gabbard plot of USA 257

The fragments in the Gabbard plot to me look more spread out in altitude than those in Astriagraph, though its hard to tell. However the main thing I have learned from this, and a bit more experimenting with Astriagraph is that you can switch out populations of objects and discover that pretty much all of the uncategorised objects and a few of the inactive satellites are from the vimpel catalogue and all the rest are from USSpacecom, there may not be much overlap at all. For the moment I think my question remains as originally asked, though I am curious to understand more about the purpose of the Vimpel list.

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    $\begingroup$ This is really interesting but the title doesn't seem to match The question. $\endgroup$ – Organic Marble Dec 1 '20 at 21:35
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    $\begingroup$ Wild guess: molniya orbit? $\endgroup$ – Anton Hengst Dec 1 '20 at 22:31
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    $\begingroup$ @AntonHengst I believe the inclination of those trails are not high enough to be in Molniya orbit, which needs to be at 63.4 deg inclination. I would like to know the reason as well. Maybe the low commercial value of that orbital regime (excluding GNSS) does not justify the use of resources (i.e. tracking stations) that could be used for more frequent TLE updates at more congested regimes. That is only a guess though, because leolabs and exo should have closed this gap by now? $\endgroup$ – Manny Dec 2 '20 at 5:24
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    $\begingroup$ StuffIn.space seems to work much faster in browser, although shows less information about satellites ID and does not show the cluster of bodies with mean parameters about INC=24.7, ECC=0.51, SMA=27050, RAAN=57, AOP=237 (for example, ID 74368 or 74394). Does not have access to Vympel data? $\endgroup$ – Peter Nazarenko Dec 2 '20 at 6:24
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    $\begingroup$ @OrganicMarble Thanks, I've split it into two questions to capture the two issues. This question remains about the presence in one database but not another. $\endgroup$ – Puffin Dec 2 '20 at 10:31
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As I answered on your other question, the answer is the source of the data is rocket upper stage debris. This kind of thing is very hard to track, and it is likely that some sources are better than others at tracking the particular pieces. It may also be that Space Track just doesn't list every single tiny piece of debris they see, they have some quality requirements to what they push out.

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    $\begingroup$ Thanks. Out of curiosity what makes this kind of object hard to track? Is it the orbit or the assumption of small debris? Equally, does "hard to track" automatically mean "uncertainty in resolved orbit"? See additions to the OP. $\endgroup$ – Puffin Dec 3 '20 at 23:24
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    $\begingroup$ @Puffin Slide 18 of the presenation attached on the other question sheds some light: "Majority of discovered debris are quite faint and pretty fast simultaneously therefore larger aperture telescopes (preferably 0.5‐0.7 m and more) are required for their regular observation and detection/follow‐up of new objects associated with this event". So, at least one of the reasons you mentioned is right! $\endgroup$ – Manny Dec 4 '20 at 1:24
  • $\begingroup$ Small, far away. To properly track an object you have to have multiple tracks on it, and know that the object was the same. When there are a bunch of dim objects it can be difficult to distinguish one object from another. Smaller and further away both make the objects dimmer. $\endgroup$ – PearsonArtPhoto Dec 4 '20 at 12:44

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