BrouwerLyddaneTheory.java

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package org.orekit.propagation.conversion.osc2mean;

import org.hipparchus.CalculusFieldElement;
import org.hipparchus.Field;
import org.orekit.forces.gravity.potential.GravityFieldFactory;
import org.orekit.forces.gravity.potential.TideSystem;
import org.orekit.forces.gravity.potential.UnnormalizedSphericalHarmonicsProvider;
import org.orekit.orbits.FieldOrbit;
import org.orekit.orbits.Orbit;
import org.orekit.propagation.PropagationType;
import org.orekit.propagation.analytical.BrouwerLyddanePropagator;
import org.orekit.propagation.analytical.FieldBrouwerLyddanePropagator;
import org.orekit.time.FieldAbsoluteDate;

/**
 * Brouwer-Lyddane theory for osculating to mean orbit conversion.
 *
 * @author Pascal Parraud
 * @since 13.0
 */
public class BrouwerLyddaneTheory implements MeanTheory {

    /** Theory used for converting from osculating to mean orbit. */
    public static final String THEORY = "Brouwer-Lyddane";

    /** Provider for un-normalized spherical harmonics coefficients. */
    private final UnnormalizedSphericalHarmonicsProvider provider;

    /** Value of the M2 parameter. */
    private final double m2Value;

    /**
     * Constructor.
     * @param provider unnormalized spherical harmonics provider
     * @param m2Value  value of empirical drag coefficient in rad/s².
     *        If equal to {@link BrouwerLyddanePropagator#M2} drag is not computed
     */
    public BrouwerLyddaneTheory(final UnnormalizedSphericalHarmonicsProvider provider,
                                final double m2Value) {
        this.provider = provider;
        this.m2Value  = m2Value;
    }

    /**
     * Constructor.
     * @param referenceRadius reference radius of the Earth for the potential model (m)
     * @param mu central attraction coefficient (m³/s²)
     * @param c20 un-normalized zonal coefficient (about -1.08e-3 for Earth)
     * @param c30 un-normalized zonal coefficient (about +2.53e-6 for Earth)
     * @param c40 un-normalized zonal coefficient (about +1.62e-6 for Earth)
     * @param c50 un-normalized zonal coefficient (about +2.28e-7 for Earth)
     * @param m2Value value of empirical drag coefficient in rad/s².
     *        If equal to {@link BrouwerLyddanePropagator#M2} drag is not computed
     */
    public BrouwerLyddaneTheory(final double referenceRadius,
                                final double mu,
                                final double c20,
                                final double c30,
                                final double c40,
                                final double c50,
                                final double m2Value) {
        this(GravityFieldFactory.getUnnormalizedProvider(referenceRadius, mu,
                                                         TideSystem.UNKNOWN,
                                                         new double[][] { { 0 }, { 0 }, { c20 }, { c30 }, { c40 }, { c50 } },
                                                         new double[][] { { 0 }, { 0 }, { 0 }, { 0 }, { 0 }, { 0 } }),
             m2Value);
    }

    /** {@inheritDoc} */
    @Override
    public String getTheoryName() {
        return THEORY;
    }

    /** {@inheritDoc} */
    @Override
    public double getReferenceRadius() {
        return provider.getAe();
    };

    /** {@inheritDoc} */
    @Override
    public Orbit meanToOsculating(final Orbit mean) {
        final BrouwerLyddanePropagator propagator =
                        new BrouwerLyddanePropagator(mean, provider, PropagationType.MEAN, m2Value);
        return propagator.propagateOrbit(mean.getDate());
    }

    /** {@inheritDoc} */
    @Override
    public <T extends CalculusFieldElement<T>> FieldOrbit<T> meanToOsculating(final FieldOrbit<T> mean) {

        final FieldAbsoluteDate<T> date = mean.getDate();
        final Field<T> field = date.getField();

        final FieldBrouwerLyddanePropagator<T> propagator =
                        new FieldBrouwerLyddanePropagator<>(mean, provider, PropagationType.MEAN, m2Value);
        return propagator.propagateOrbit(date, propagator.getParameters(field, date));
    }
}