BrouwerLyddane and EcksteinHechler Propagators

Orekit usage
1

Hi everyone

I’m comparing the positional differences between propagators considering the numerical propagator of GMAT as the reference (baseline) and I get the following results.

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When setting the un-normalized zonal coefficients (c30, c40 and c50) of the BrouwerLyddane propagator to 0.0 I get the BL J2 plot and the same with the EcksteinHechler propagator, EH J2 plot.

I expected to have the BL J2 and the EH J2 above the SGP4/SDP4 because the last one include J2 to J4 but this is not what is happening so I’m doubting about if the EH or the BL are only including the J2 when I set the rest of the coefficients to 0.

Thanks,

Verónica

2

Eckstein-Hechler includes up to J6.

3

Thank you for the fast reply @luc .

I have defined the propagator as follows:

propagator = BrouwerLyddanePropagator(SatInitialState, Constants.EIGEN5C_EARTH_EQUATORIAL_RADIUS,
                                          Constants.EIGEN5C_EARTH_MU, Constants.EIGEN5C_EARTH_C20,
                                          0.0, 0.0, 0.0, 0.0)

So, no matter if a set the coeffcients to 0, it will include anyway the J2 to J6 perturbations?

4

If you have put 0 for the last J_n coefficients, you will get J2 only, you are right.

5

Hi!

What’s the initial error at t=0s ? Also, how did you get the TLE?

6

Mi initial error is:

4.54761228462520e-13 km

And I get the TLE as follows:

tle_propagator = TLEPropagator.selectExtrapolator(mytle)
tle_orbit_cart = tle_propagator.getInitialState().getPVCoordinates(J2000)
SatInitialState = KeplerianOrbit(tle_orbit_cart, J2000, mytle.getDate(), mu)


propagator = BrouwerLyddanePropagator(SatInitialState, Constants.EIGEN5C_EARTH_EQUATORIAL_RADIUS,
                                          Constants.EIGEN5C_EARTH_MU, Constants.EIGEN5C_EARTH_C20,
                                          0.0, 0.0, 0.0, 0.0)

Thank you

7

I was thinking about it yesterday, and maybe it is because the propagator is adding the J2^2 and this coefficient is similar, in magnitude to J4, thus, not seeing at all the differences. Is there a way to delete the second order J2?

Thank you