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brandon-rhodes / python-sgp4

Python version of the SGP4 satellite position library
MIT License
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Issue with Molniya satellite #28

Closed tmamedzadeh closed 6 years ago

tmamedzadeh commented 6 years ago

I've implemented the SGP4 algorithm. It works OK for LEO satellites.

However, for Molniya 1-29 satellite there is a strange trajectory: it's not elliptic, looks like 8.

Do you have any idea?

brandon-rhodes commented 6 years ago

Could you share the diagram you've produced, as well as some sample code to produce it? I'll need to see the "8" shape to be able to guess what might be going on. Thanks!

dcajacob commented 6 years ago

Sounds like you're either looking at a ground plot, in which a Molniya's ground trace does cross over itself, like an "8" or you might be plotting rotating coordinates when you need to plot non-rotating ones.

On Sat, Jun 2, 2018 at 5:33 PM Brandon Rhodes notifications@github.com wrote:

Could you share the diagram you've produced, as well as some sample code to produce it? I'll need to see the "8" shape to be able to guess what might be going on. Thanks!

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tmamedzadeh commented 6 years ago

I'm looking at 3D and the orbit of Molniya is not elliptic.

I came up with an idea: probably that's because the resulting coordinates are in ECEF. For LEO satellite, as the period is low, the orbit was OK, but it became strange for Molniya.

Probably, I should transform to ECI?

tmamedzadeh commented 6 years ago

Yes, That it is. Thank you.