How to convert Osculating to Mean?

Thank you, I want to know how to achieve osculating to mean, how should BrouwerLyddanePropagator and computeMeanOrbit be used? What is the maximum order of the gravitational field defining parameter provider? 7*7?

Hi @newWL

Welcome to the Orekit forum!

They are several possibilities to convert osculating parameters to mean parameters. The three main ones are:

• Using the method `computeMeanOrbit` of `BrouwerLyddanePropagator`. This method will compute a mean orbit based on the zonal harmonics from J2 to J5. Here an example presenting how to use it.

• Using the method `computeMeanOrbit` of `EcksteinHechlerPropagator`. This method will compute a mean orbit based on the zonal harmonics from J2 to J6. Here an example presenting how to use it.

• Using the method `computeMeanState` of `DSSTPropagator`. This method will compute a mean orbit based on a user defined model represented by the `Collection<DSSTForceModel>`. Using DSST you can compute a mean orbit for big order and degree of Earthâ€™s potential. You can also take into account luni-solar attraction, solar radiation pressure and atmospheric drag. Here an example presenting how to do it.

I recommend you to start with the Brouwer-Lyddane or Eckstein-Hechler model. After that, you could try with the DSST which offer the possibility to have an accurate mean orbit compare to the two other ones.

Best regards,
Bryan

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Very, thank you very, I learned about the information you provided.

I noticed in STK Astrogator module, there is an option which I can select from â€śBrouwer-Lyddane Mean Longâ€ť and â€śBrouwer-Lyddane Mean Shortâ€ť, shown in the image.
My question is whether there is a way to accomplish this in Orekit.

I donâ€™t understand what they mean by â€śMean Longâ€ť or â€śMean Shortâ€ť.
In Orekit, you can initialize the Brouwer-Lyddane propagator with a mean orbit or an osculating orbit. At the end, the propagated orbit will be osculating.
Something interesting for Orekit is to have the possibility to choose between a MEAN or OSCULATING propagation for the propagated orbit, like DSST do.

Best regards,
Bryan

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What they mean by â€śshortâ€ť and â€ślongâ€ť is based on what angular variable is used for the averaging. For the â€śshortâ€ť case the angular variable is the anomaly, for the â€ślongâ€ť case the averaging is done by considering the rotation of the perigee.
There is a brief explanation here.

Best regards,
Emiliano