Re: [Orekit Developers] From osculating parameters to mean parameters for LEO orbits

[pascal parraud <pascal.parraud@c-s.fr>]

Hi Lara,

Two points:

1- I notice the same exception in the construction of the EH propagator with your data, the point is with the value of true longitude argument (79339.41232985309),
   it induces a numerical gap that results in non converging solution. A trick is to normalize this angle [MathUtils.normalizeAngle(79339.41232985309, FastMath.PI)].
   You may open a bug report at https://www.orekit.org/forge/projects/orekit/issues

2- Using the EH propagator is not a valid option for the OsculatingToMeanConverter, as it is said in the documentation of the class, the DSST is better suited for this task.

Best regards,

Pascal

Le 15/04/2016 13:52, HUE, Lara a écrit :

Hi to all,

 

Thanks for the use of the great Orekit tool !

My question is about the computation of mean parameters from a LEO osculating orbit.

In order to get some operational parameters, I need to compute the mean parameters at each steps of the global propagation.

One way is to use the OsculatingToMeanElementsConverter with a specific propagator.

I tried with a classical EcksteinHechlerPropagator, however the following exception has been raised :

 

Exception in thread "main" org.orekit.errors.PropagationException: impossible de calculer les paramètres moyens au sens de Eckstein-Hechler après 101 itérations

        at org.orekit.propagation.analytical.EcksteinHechlerPropagator.<init>(EcksteinHechlerPropagator.java:318)

        at org.orekit.propagation.analytical.EcksteinHechlerPropagator.<init>(EcksteinHechlerPropagator.java:200)

        at main.Init.main(Init.java:91)

Caused by: org.orekit.errors.PropagationException: impossible de calculer les paramètres moyens au sens de Eckstein-Hechler après 101 itérations

        at org.orekit.propagation.analytical.EcksteinHechlerPropagator.computeMeanParameters(EcksteinHechlerPropagator.java:394)

        at org.orekit.propagation.analytical.EcksteinHechlerPropagator.resetInitialState(EcksteinHechlerPropagator.java:327)

        at org.orekit.propagation.analytical.EcksteinHechlerPropagator.<init>(EcksteinHechlerPropagator.java:311)

        ... 2 more

 

Indeed, when calling the EcksteinHechlerPropagator constructor, it takes more than 100 iterations to compute mean parameters at the initial state, and therefore the exception is raised.

Here is a specific orbit among others, retrieved from the simulation, for which the computation in mean elements is not possible :

 

AbsoluteDate t = new AbsoluteDate(2016, 07, 22, 9, 35, 42.562, TimeScalesFactory.getUTC());

Frame frame = FramesFactory.getEME2000();

Orbit orbit = new EquinoctialOrbit(7075842.806163763, 0.0012957331188810572, -4.760791390305797E-4, 0.14011350699555794, -1.1457596828634813, 79339.41232985309, PositionAngle.TRUE, frame, t, Constants.WGS84_EARTH_MU);

Double mass = 436.5;

double c20 = Constants.EIGEN5C_EARTH_C20;

double c30 = Constants.EIGEN5C_EARTH_C30;

double c40 = Constants.EIGEN5C_EARTH_C40;

double c50 = Constants.EIGEN5C_EARTH_C50;

double c60 =  Constants.EIGEN5C_EARTH_C60;

EcksteinHechlerPropagator analyticalPropagatorWrong = new EcksteinHechlerPropagator(orbit, mass, Constants.WGS84_EARTH_EQUATORIAL_RADIUS, Constants.WGS84_EARTH_MU, c20, c30, c40, c50, c60);

 

 

Is there a better way to convert osculating parameters to mean parameters?

Best,

 

Lara Hué

 

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