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Re: [Orekit Users] Mimic TLEPropagator with Numerical?


About the free parameters you wonder about, in order to get a numerical propagator close to a given TLE propagator, you can add to the numerical propagator the force models Paul Cefola indicates earlier :

1 - a gravity field with J2, J3 and J4 coefficients (HolmesFeatherstoneAttractionModel is recommended)

2 - a drag force with a simple atmospheric model (SimpleExponentialAtmosphere or HarrisPriester are good candidates), for this you also need to set, among others, a drag coefficient CD.

Then, for the conversion, you will say that the "drag coefficient" is the free parameter, thus the conversion process will try to adapt the value of CD to fit at best the numerical propagator to the TLE propagator.

Hope this helps.


Le 31/03/2017 à 19:23, justin4leb@gmail.com a écrit :



> Try setting fp = [] here.


Yes an empty list worked.


> I'm not very familiar with the python

>interface to the library, but the convert function is expecting an

>array or a List, not a String.


Actually there are types of ways how you can pass a value for free parameters. Either to pass directly as a list of strings or a single string representing free parameter name as the method will automatically generate a list of strings based on that.

The issue kind of names the free parameter can have. When I just gave random name I got an error like this:

org.orekit.errors.OrekitException: unsupported parameter name “some_string”, supported names: central attraction coefficient


Lastly, I assume for free parameters the value should be an empty list or a list of string names or a single string saying something like -> “central attraction coefficient”. I am curious what other free parameters we can give.


Thanks to everyone who helped me out here. I managed to do the conversion.




From: Ward, Evan
Sent: Friday, March 31, 2017 08:31
To: orekit-users@orekit.org
Subject: Re: [Orekit Users] Mimic TLEPropagator with Numerical?


Justin,On Thu, 2017-03-30 at 11:43 -0400, justin4leb@gmail.com wrote:


> odeIntegratorBuilder = DormandPrince853IntegratorBuilder(0.001,

> 1000.0, 1.e-2)

> builder = NumericalPropagatorBuilder(initialOrbitA,

> odeIntegratorBuilder, PositionAngle.TRUE, 1.e-2)

> fitter = JacobianPropagatorConverter(builder, 1.e-6, 5000)

> fp = "central attraction coefficient"



Try setting fp = [] here. I'm not very familiar with the python

interface to the library, but the convert function is expecting an

array or a List, not a String.


> numpropA = fitter.convert(tleStates, False, fp)



Best Regards,