# Tutorial for orbits from TLE data

I've been looking for a new hobby, and have been reading some about satellite tracking. I was wondering if there was a good tutorial that walks through how to use TLE data. So far I have found CelesTrack it has a lot of good material and it looks like the python code Skyfield might be a good place to start. I've started to read some about SPG4 propagation, but haven't gotten very far yet.

It seems in general there are a variety of websites for satellite orbit prediction, but some seem to be overrun by ads. Any pointers to books or good websites appreciated.

I think I would like to be able to get to the point where I could get a TLE for a particular satellite, figure out if and when it might pass over my location. Eventually, time permitting either point a telescope or radio antenna as it goes over.

So to sum up the question is there a tutorial that walks through how to go from TLE data, walks through how SPG4 can be used to propagate the orbit and then calculate the ground track? Is this the right question to be asking?

You can get much of the software you would need from the same place you get TLEs. Go to https://www.space-track.org/documentation#/sgp4 , register for a free account, and download the file Sgp4Prop_small_v8.0.zip . Inside that is the official US government implementation of Simplified General Perturbations version 4, together with wrappers in C, C++, C#, Fortran, Java, Matlab, Python, and Visual Basic, data sets you can use to run validation tests, documentation, and more. One of the nice things you get in more is the "AstroFunc" library that does lots of conversions, such as between position & velocity vectors, osculating Keplerian and equinoctial elements, azimuth & elevation, right ascension & declination, etc. It will also tell you positions for sun and moon, do IAU nutation & precession to variable expansion order, and other things you may have no idea you will need.

As for step by step how to do it, pictures of what all the different coordinate systems are and how they differ, and other useful things, you probably have to get a textbook in orbital mechanics, which is also called astrodynamics. The traditional one is Bate, Muller, and White, Fundamentals of Astrodynamics. The prettiest is probably Curtis, Orbital Mechanics for Engineering Students, and the most encyclopedic is Vallado, Fundamentals of Astrodynamics and Applications. Searching on those will lead you to a large number of other works, ranging very widely in degree of sophistication.

• Thanks for the leads! Commented Nov 24, 2020 at 14:43
• Be aware of the space-track terms of service which prohibits distributing even the results of computations done with TLEs you receive from them in addition to the TLEs themselves. It's better to get the data from Celestrak, they also have a "software" section with source code in a few languages. Commented Jun 5, 2023 at 12:47