T. S. Kelso tweeted the following, is this a case of lost and found? How can so many substantial objects become lost like this? The list of 23 objects "formerly known as Prince NEA" all seem pretty large to get lost!

We just got a big release of TLEs for 23 objects formerly classified as NEA—the third release this week. That removes 37 objects from the NEA list—great progress!

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2 Answers 2


When an object becomes "lost", we usually know most of the orbital information, including apogee, perigee, inclination and orbital period. Those are shown in the table.

What's not known is where in that orbit the object is currently located.

The reason for this is that the position over time is very sensitive to the initial values. As a simplified example, a 1m/s velocity error grows into a nearly 100km position error within a day.

TLEs expire, their error in position grows to about a kilometre within a couple of days (in LEO, that list has mixed orbits)

Just knowing the initial values for all these objects isn't enough to predict their position after a few weeks or months, they could potentially be anywhere in their orbit.

If the cubesats and debris listed in that table weren't observed again before their initial TLE expired, they are lost. We know they are up there, we know the shape of the orbit, but we don't known where they are. They are lost because nobody gave observing these things priority

However if they are observed again, and their TLEs re-established, it's easy to plot the orbit back in time, to confirm that they are the same objects. This is what happened here. New observations found objects that turned out to be the original lost ones.

This happens frequently with asteroids as well, we can often see in 19th and 20th century data when an asteroid was observed but subsequently lost.

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    $\begingroup$ Is there a place to submit your own observations of objects so that the people there can verify and update the TLEs? Obviously, at an amateur level. $\endgroup$ Commented Sep 12, 2019 at 13:11
  • $\begingroup$ Not as I'm aware of, but I'm not into amateur astronomy. I would imagine that the tracking capabilities of a space agency would not be significantly expanded by such observations. $\endgroup$ Commented Sep 12, 2019 at 13:18
  • $\begingroup$ okay, they are on a "lost" list because they were lost, but how? There are several rocket bodies on that list; how do you loose several rocket bodies in Earth orbit? It seems like those would be priority targets. And how did so many cubesats get lost and then found later? Those Fastrac satellites are way bigger than 1U cubes and only at about 650 km. $\endgroup$
    – uhoh
    Commented Sep 12, 2019 at 13:19
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    $\begingroup$ "Anything not saved will be lost" Unless observed, objects go to the "lost" list as the default action. If observed, they will not. They were lost because no-one gave observing these things priority. $\endgroup$ Commented Sep 12, 2019 at 13:25
  • $\begingroup$ I'd be a little surprised if these were not tracked. I wonder if in fact they were not "lost" so much as the identity assignments became unreliable. In other words, they were tracked but at some point some possible ID ambiguities arose, and an official TLE can't be issued if the identity is the least bit in question. Of course internally they use orbital data much better than TLEs, those are just for public consumption. They don't throw away historical tracing data and state vectors and just keep the TLEs. $\endgroup$
    – uhoh
    Commented Sep 12, 2019 at 13:35

Many (if not all) of the objects with "NEA" status are/were classified, or were manifested along with classified missions. Many "USA" satellites (and their rocket bodies) do not have publicly-available orbital elements.


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