Thread: Understanding the SGP4 algorithm

1. Understanding the SGP4 algorithm

Hi,
I am working on the SGP4 orbit determination algorithm, so that I can write a program for it in C.
I came across the Spacetrack Report #3 which gives the FORTRAN code listing for SGP4 algorithm.
Now, this report has listed a set of calculations to be carried out (in the same sequence as given in the report), to find the satellite's position and velocity at any given time. What I could do is, write a C code that carries out these calculations in the given sequence without bothering to understand the physics behind the calculations. As a programmer, I could well treat those calculations as a black box.The problem with this is, I won't be in a position to rectify the errors that might come up in the code.

So, I wish to do the following things before getting down to the coding:
1.Comprehend the math given in Spacetrack Report #3.
2.Understand Orbital mechanics that lead to those calculations.

Also, I would like to understand how exactly the SGP4 algorithm works. What I wish to know is this- which part of the algorithm is responsible for what. The report does not explain all this. All it does is, give a set of calculations and a FORTRAN code that implements them.
I wish to understand why the algorithm is the way it is.

Can anyone please help me achieve these goals?
Thank you in anticipation.

Regards,
Sanjeev.

2. Re: Understanding the SGP4 algorithm

Hi Sanjeev,
I too am working on using SGP4 on an Arduino and have it all going except for the Azimuth values, they go a bit strange at extreme elevations.

If you want to know all about the algorithm I suggest you by the book fundamentals of astrodynamics and applications by david vallado, it explains everything, after all he was one of the original authors.

Good luck.

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