DSST6X0OrbitalState.java

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package org.orekit.propagation.conversion.averaging;

import org.orekit.forces.gravity.potential.UnnormalizedSphericalHarmonicsProvider;
import org.orekit.frames.Frame;
import org.orekit.orbits.EquinoctialOrbit;
import org.orekit.orbits.Orbit;
import org.orekit.orbits.OrbitType;
import org.orekit.orbits.PositionAngleType;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.semianalytical.dsst.DSSTPropagator;
import org.orekit.propagation.semianalytical.dsst.forces.DSSTForceModel;
import org.orekit.propagation.semianalytical.dsst.forces.DSSTZonal;
import org.orekit.time.AbsoluteDate;
import org.orekit.propagation.conversion.averaging.elements.AveragedEquinoctialWithMeanAngle;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

/**
 * Class representing an averaged orbital state as in the DSST theory using only the first 6 zonal
 * harmonics as perturbations.
 *
 * @author Romain Serra
 * @see AveragedOrbitalState
 * @see DSSTPropagator
 * @see DSSTZonal
 * @since 12.1
 */
public class DSST6X0OrbitalState extends AbstractHarmonicsBasedOrbitalState {

    /** Averaged equinoctial elements. */
    private final AveragedEquinoctialWithMeanAngle averagedElements;

    /**
     * Constructor.
     * @param date epoch
     * @param elements averaged orbital elements
     * @param frame reference frame
     * @param harmonicsProvider spherical harmonics provider
     */
    public DSST6X0OrbitalState(final AbsoluteDate date,
                               final AveragedEquinoctialWithMeanAngle elements,
                               final Frame frame,
                               final UnnormalizedSphericalHarmonicsProvider harmonicsProvider) {
        super(date, frame, harmonicsProvider);
        this.averagedElements = elements;
    }

    /**
     * Create collection of fist 6 zonal DSST forces.
     * @param provider spherical harmonics provider
     * @return six first zonal forces
     */
    public static Collection<DSSTForceModel> createForces(final UnnormalizedSphericalHarmonicsProvider provider) {
        final List<DSSTForceModel> forceModels = new ArrayList<>();
        final DSSTZonal zonal = new DSSTZonal(provider);
        forceModels.add(zonal);
        return forceModels;
    }

    /** {@inheritDoc} */
    @Override
    public OrbitType getOrbitType() {
        return OrbitType.EQUINOCTIAL;
    }

    /** {@inheritDoc} */
    @Override
    public PositionAngleType getPositionAngleType() {
        return PositionAngleType.MEAN;
    }

    /** {@inheritDoc} */
    @Override
    public AveragedEquinoctialWithMeanAngle getAveragedElements() {
        return averagedElements;
    }

    /** {@inheritDoc} */
    @Override
    public Orbit toOsculatingOrbit() {
        final EquinoctialOrbit orekitOrbit = createOrekitOrbit();
        final Collection<DSSTForceModel> forceModels = createForces(getHarmonicsProvider());
        final SpacecraftState osculatingState = DSSTPropagator.computeOsculatingState(
                new SpacecraftState(orekitOrbit), null, forceModels);
        return osculatingState.getOrbit();
    }

    /**
     * Create equinoctial orbit representation of averaged state.
     * @return equinoctial orbit
     */
    private EquinoctialOrbit createOrekitOrbit() {
        return new EquinoctialOrbit(averagedElements.getAveragedSemiMajorAxis(),
                averagedElements.getAveragedEquinoctialEx(),
                averagedElements.getAveragedEquinoctialEy(),
                averagedElements.getAveragedHx(), averagedElements.getAveragedHy(),
                averagedElements.getAveragedMeanLongitudeArgument(),
                getPositionAngleType(), getFrame(), getDate(), getMu());
    }

}