Element type returned by Brouwer Lyddane propagator

Orekit usage
1

Hi,

I am trying to implement a Brouwer Lyddane propagator, but I am confused as to whether the propagate method is returning osculating or mean elements.

Thanks,
Scott

2

Hi @skindl

Welcome to the Orekit forum! :slight_smile:

The returned elements are osculating ones.

Best regards,
Bryan

1 Like
3

Thanks!

On a similar note, does Brouwer Lyddane propagator require all the gravity coefficients to be set or can I set just J2 and the rest to 0 to only get perturbations related to J2?

4

I never tried, but I think it’s possible.

Bryan

5

I think you can yes. There are two cases:

  1. You have a value of c20 and you want that specific one to be used:
    Example with IERS2010 values:
BrouwerLyddanePropagator prop = new BrouwerLyddanePropagator(initialOrbit, Constants.IERS2010_EARTH_EQUATORIAL_RADIUS, 
                                                             Constants.IERS2010_EARTH_MU, Constants.IERS2010_EARTH_C20, 
                                                             0., 0., 0., 0.);
  1. You have a gravity field
    Load it for J2 only: UnnormalizedSphericalHarmonicsProvider provider = GravityFieldFactory.getConstantUnnormalizedProvider(2, 0);
    Use it in BL propagator
        BrouwerLyddanePropagator prop =
                        new BrouwerLyddanePropagator(initialOrbit,
                                                     provider.getAe(), provider.getMu(),
                                                     provider.onDate(initialOrbit.getDate()).getUnnormalizedCnm(2, 0),
                                                     0., 0., 0., 0.);