Yes, I am well aware of the Space-Track.org Sgp4Prop_v9. But, since they use dll_functions in all their source code it is difficult to determine the algorithm. Spacetrak Report No. 3 gives algorithm and main source code, but that’s only for finding Elements and state vectors from TLE to State Vectors in TEME Frame (Reverse calculation of Spacetrak RP No. 3 algorithm might be possible but not so easy). I want to know the algorithm used to Generate TLE from elements in TEME frame i.e. going reverse. If you have any source code (link would be great) used to generate TLE using latest version of SGP4 (Not the USSF SpOC OscVecToTLE from AstroStds lib) please let me know.
I can only suggest that you take a look at the OREKIT source code for TLE generation (in OREKIT v12.0, see package org.orekit.propagation.analytical.tle.generation).
There are 2 algorithms, fixed point and least squares, both of which use the TLEPropagator. You can draw inspiration from them if you want to use your own version of SGP4.
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Now in the version 12, this “stateToTLE” method have to use the 3rd parameter"TleGenerationAlgorithm".How do I get that? I am just a beginner and I apologize for disturbing you.
Hello @houmingyang and welcome to the Orekit forum !
No need to apologize, this is a rightful question to ask 
.
Currently we have two classes implementing the TleGenerationAlgorithm :
1 - FixedPointTleGenerationAlgorithm
2 - LeastSquaresTleGenerationAlgorithm
The one that was used by default in the previous versions of Orekit was the FixedPointTleGenerationAlgorithm which you can easily create using the following code :
TleGenerationAlgorithm algorithm = new FixedPointTleGenerationAlgorithm();
Note that you can use the other constructors if you want to customize the algorithm parameters.
Cheers,
Vincent
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Hello All,
is there a way to estimate not only the BSTAR but also the mean motion derivative ?
In TLEPropagatorBuilder, the list of propagation parameter drivers includes only BSTAR.
Thanks !
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Hi @jaapetr,
No, this parameter cannot be estimated for the simple reason that it is not used by the SGP4/SDP4 models implemented by the TLEPropagator. It only appears in the simpler SGP model, which is not implemented.
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many thanks !
Thank you very much! As a beginner in this field, this OreKit really helps the junior engineers working in the field of satellite measurement and control.
In the past, many jobs could only be done by senior engineers with many years of experience. With this Kit, we can also participate in many jobs. I especially recommend it to my elder colleagues (they are more accustomed to using their own Fortran functions and libraries). Your works are great!
Thank you very much for your reply! I have now read some of the posts in this forum and have indeed learned a lot. I found that you can answer almost all kinds of questions in a very timely manner–Regardless of whether these questions are “elementary” or not.
Dr. Mihaly Csikszentmihalyi, a doctor of psychology, once mentioned that being able to enter the “Flow” state is a very happy psychological experience.
If a person can maintain enthusiasm and engage in work that he likes, then work is actually not a burden, but a kind of happiness. I am very impressed by your professional knowledge and extraordinary enthusiasm.
I guess you must be a happy person, so I will not wish you happiness ;-P. I wish you a smooth work, a comfortable life and good health forever!
Thanks again! !
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I must say i’m at a loss for words in front of such kindness ! On behalf of all the persons contributing to Orekit, i would like to thank you because such words give us even more motivation to contribute !
As a beginner myself, i wish for both of us to continue learning about this amazing field, using Orekit of course 
!
Once again, thank you 
Cheers,
Vincent
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Hi Bryan,
What frame SpacecraftState must be in to use it in stateToTLE method?
There is no limitation on the frame since the transformation to TEME is done internally by the stateToTLE method.
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I’m doing the same thing with you, but I have two problems. First, my input is a set of Kepler elements corresponding to a certain time, but we see that you are all propagating for a period of time and storing them in the list for use, but I just want to convert this data point, I don’t understand the principle of this; The second point is that I tried to use your code, TLEPropagatorBuilder TLE parameter initialization how to initialize, hope you can answer my doubts.
Excuse me, I would like to ask what is the difference between these two methods, or what are the advantages and disadvantages, and how to choose the applicable scenarios.
Hello @gengjianben,
Regarding both methods, i think you can refer to these links for more information:
Cheers,
Vincent