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The most popular catalog of Earth-orbiting objects is NORAD’s. The catalog provides the so-called « two-line elements » (TLE) which essentially are computed orbital parameters of a catalogued object, for a given epoch. In turn, the parameters can be used to predict the position of said object at other instants not too remote from the epoch at which the TLE were computed.

One of the most puzzling aspects of NORAD’s approach is their choice of an Earth-centered inertial (ECI) reference frame called TEME, for « True Equator, Mean Equinox ». After trying to understand what it means, and realizing how complicated/sophisticated it is, I would like to address the question of the « why ? ».

This question can be decomposed into :

  • What was NORAD’s rationale?
  • What were the alternatives for NORAD at the time ?
  • Was/is NORAD the only organization using TEME?
  • Is it justified to keep using it ?
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    $\begingroup$ I think they would have to justify the effort to stop using it and switching to something else. That has real cost on something that is not 'necessary' for NORAD to do. $\endgroup$
    – Jon Custer
    Oct 12 at 15:42
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    $\begingroup$ I have no basis to form an opinion one way or the other. I just know that changing processes is what is hard to justify - it is always easy to justify continuing to do what you are doing. $\endgroup$
    – Jon Custer
    Oct 12 at 16:35
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    $\begingroup$ It was not my intent to imply that - just that there is a current process to produce a dataset in a particular way, it works, why change it? That takes time, people, and funding... $\endgroup$
    – Jon Custer
    Oct 12 at 16:48
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    $\begingroup$ @Jon Custer, "it works" can be opinion-based. For ex., « For various reasons, there is no consensus or authoritaitive definition for the [TEME] reference frame. Consequently, the use of TEME is not recommended, ... ». extract from CCSDS Green Book 500x0g4, Nov 2019, p.22 $\endgroup$
    – Ng Ph
    Oct 12 at 17:00
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    $\begingroup$ What I believe @JonCuster is saying is "if it an't broken don't fix it." $\endgroup$ Oct 13 at 0:09

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