How to set satellite mass in SGP4 orbit determination

Orekit Python Wrapper usage
1

Hi all,

I am trying for the first time the new SGP4 orbit determination feature. I could not find where to set the satellite mass.
Part of my code is the following:

matrix_decomposer = QRDecomposer(1e-11)
optimizer = GaussNewtonOptimizer(matrix_decomposer, False)
tle_prop_builder = TLEPropagatorBuilder(tle_initial, PositionAngle.MEAN, estimator_position_scale)

estimator = BatchLSEstimator(optimizer, tle_prop_builder)
estimator.setParametersConvergenceThreshold(estimator_convergence_thres)
estimator.setMaxIterations(estimator_max_iterations)
estimator.setMaxEvaluations(estimator_max_evaluations)

[...]  # Add measurements

estimated_propagator_array = estimator.estimate()

When using a numerical propagator, I was setting up the mass in the numerical propagator builder:

propagator_builder = NumericalPropagatorBuilder(orbit_initial_cartesian,
                                                integrator_builder, PositionAngle.MEAN, estimator_position_scale)
propagator_builder.setMass(mass)
propagator_builder.setAttitudeProvider(nadir_pointing)

Maybe the mass is not relevant in SGP4? Then in this case why is it required in the SGP4 propagator constructor?

Cheers
Clément

2

Mass is irrelevant in the physical model SGP4/SDP4, but required in Orekit by all propagators in order to build a SpacecraftState. It is exactly the same as attitude provider, for the same reason.

1 Like
3

Thank you Luc!