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I am currently making a satellite tracker app for android. I want to test my orbit propagation algorithm and I want to make some made-up basic orbits, so I need to know how their TLE would be. I want to test:

  • A geosynchronous equatorial orbit (GEO), so Alt-azimuth would always be the same for a fixed observer.
  • Polar orbit (PO), so altitude would be the same for an observer located at one pole of the earth any at any time $t = t_0 + Period*n$, $n \in \mathbb{Z} .$

So I need to know what would be the values of Mean Motion, Argument of Pericenter, Inclination and Right Ascension of Ascending Node.

I already tried with the following data for GEO:

  • $Mean Motion=1.0$
  • $Eccentricity=0.0$
  • $Inclination=0.0$
  • $RightAscension Of Ascending Node=0.0$
  • $Argument Of Pericenter=0.0$

(In the case of PO I guess Inclination would have to be 90 degrees, leaving all the other data unchanged).

But it doesn't seem to work. I don't know if this is an error in my algorithm or if, instead, I just didn't simulate the orbit correctly. I want to find out which are the correct values for those parameters for the orbitals I want. I hope you guys can help me. Thanks in advance.

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    $\begingroup$ Objects in polar orbits don't stay at the same altitude for a polar observer. Objects in polar orbits will be seen to rise and set regardless of your location on the Planet's surface. The only type of orbit where the object maintains a constant altitude above the horizon for an observer at a chosen point on Earth is a geostationary orbit. $\endgroup$
    – notovny
    Commented Aug 3, 2022 at 1:30
  • $\begingroup$ @notovny I meant altitude will be the same at any time t' = t0+ Period*n with n being a whole number. $\endgroup$
    – fas_dev
    Commented Aug 3, 2022 at 1:54
  • $\begingroup$ The only proper way to use TLE data is to use the SPG code. You should be able to find an implementation is almost any language. If you want to write your own, it's best to test against real, known orbits first. $\endgroup$
    – Greg Miller
    Commented Aug 3, 2022 at 15:33

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You should never make your own TLEs. Even if you did manage it, the test conditions you state are incorrect, because you can't use TLEs that way. The effect of earth gravity nonuniformity, gravity of the sun and moon, atmospheric drag, and a bunch of other things are built into the format, and getting them back out again is incredibly painful. It is also unnecessary, because the easy alternative is to use the official tool from the same place you get TLEs.

What you ought to do is register for a free account on https://www.space-track.org , download the SGP4 propagator from https://www.space-track.org/documentation#/sgp4 , pick one of the dozen programming languages supported by that ZIP file, and use it to turn TLEs into other coordinates (Earth fixed or inertial position and velocity, latitude and longitude, azimuth and elevation, etc.) for you.

As for the parameters, they can be almost anything you want. If you choose the bulk download of geosynchronous objects from https://www.space-track.org/#recent , it will select everything with mean motion between 0.99 and 1.01 and eccentricity < 0.01. Inclination for most GEO sats is quite small, but there are a bunch in the 5 to 10 degree range, and a few much higher. RAAN and AOP need to be adjusted together in order to keep the satellite in its ITU-assigned slot, but RAAN is undefined if inclination is zero and AOP is undefined if eccentricity is zero, so try to avoid exact zeros.

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  • $\begingroup$ Thank you, this helped! $\endgroup$
    – fas_dev
    Commented Aug 4, 2022 at 1:45

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