Galileo.java

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package org.orekit.gnss.attitude;

import org.hipparchus.CalculusFieldElement;
import org.hipparchus.Field;
import org.hipparchus.analysis.differentiation.FieldUnivariateDerivative2;
import org.hipparchus.analysis.differentiation.UnivariateDerivative2;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.FieldSinCos;
import org.orekit.frames.Frame;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.ExtendedPositionProvider;
import org.orekit.utils.TimeStampedAngularCoordinates;
import org.orekit.utils.TimeStampedFieldAngularCoordinates;

/**
 * Attitude providers for Galileo navigation satellites.
 * <p>
 * This class is based on the May 2017 version of J. Kouba eclips.f
 * subroutine available at <a href="http://acc.igs.org/orbits">IGS Analysis
 * Center Coordinator site</a>. The eclips.f code itself is not used ; its
 * hard-coded data are used and its low level models are used, but the
 * structure of the code and the API have been completely rewritten.
 * </p>
 * @author J. Kouba original fortran routine
 * @author Luc Maisonobe Java translation
 * @since 9.2
 */
public class Galileo extends AbstractGNSSAttitudeProvider {

    /** Default yaw rates for all spacecrafts in radians per seconds. */
    public static final double DEFAULT_YAW_RATE = FastMath.toRadians(0.203);

    /** Constants for Galileo turns. */
    private static final double BETA_X = FastMath.toRadians(15.0);

    /** Limit for the noon turn. */
    private static final double COS_NOON = FastMath.cos(BETA_X);

    /** Limit for the night turn. */
    private static final double COS_NIGHT = -COS_NOON;

    /** No margin on turn end for Galileo. */
    private static final double END_MARGIN = 0.0;

    /** Yaw rate. */
    private final double yawRate;

    /** Simple constructor.
     * @param yawRate yaw rate to use in radians per seconds (typically {@link #DEFAULT_YAW_RATE})
     * @param validityStart start of validity for this provider
     * @param validityEnd end of validity for this provider
     * @param sun provider for Sun position
     * @param inertialFrame inertial frame where velocity are computed
     */
    public Galileo(final double yawRate,
                   final AbsoluteDate validityStart, final AbsoluteDate validityEnd,
                   final ExtendedPositionProvider sun, final Frame inertialFrame) {
        super(validityStart, validityEnd, sun, inertialFrame);
        this.yawRate = yawRate;
    }

    /** {@inheritDoc} */
    @Override
    protected TimeStampedAngularCoordinates correctedYaw(final GNSSAttitudeContext context) {

        // noon beta angle limit from yaw rate
        final double beta0 = FastMath.atan(context.getMuRate() / yawRate);

        if (FastMath.abs(context.betaD2().getValue()) < beta0 &&
            context.setUpTurnRegion(COS_NIGHT, COS_NOON)) {

            context.setHalfSpan(context.inSunSide() ?
                                BETA_X :
                                context.inOrbitPlaneAbsoluteAngle(BETA_X),
                                END_MARGIN);
            if (context.inTurnTimeRange()) {

                // handling both noon and midnight turns at once
                final UnivariateDerivative2              beta     = context.betaD2();
                final FieldSinCos<UnivariateDerivative2> scBeta   = FastMath.sinCos(beta);
                final UnivariateDerivative2              cosBeta  = scBeta.cos();
                final UnivariateDerivative2              sinBeta  = scBeta.sin();
                final double                             sinY     = FastMath.copySign(FastMath.sin(beta0), context.getSecuredBeta());
                final UnivariateDerivative2              sd       = FastMath.sin(context.getDeltaDS()).
                                                                    multiply(FastMath.copySign(1.0, -context.getSVBcos() * context.getDeltaDS().getPartialDerivative(1)));
                final UnivariateDerivative2              c        = sd.multiply(cosBeta);
                final UnivariateDerivative2              shy      = sinBeta.negate().subtract(sinY).
                                                                    add(sinBeta.subtract(sinY).multiply(c.abs().multiply(c.getPi().divide(FastMath.sin(BETA_X))).cos())).
                                                                    multiply(0.5);
                final UnivariateDerivative2              phi      = FastMath.atan2(shy, c);

                return context.turnCorrectedAttitude(phi);

            }

        }

        // in nominal yaw mode
        return context.nominalYaw(context.getDate());

    }

    /** {@inheritDoc} */
    @Override
    protected <T extends CalculusFieldElement<T>> TimeStampedFieldAngularCoordinates<T> correctedYaw(final GNSSFieldAttitudeContext<T> context) {

        // noon beta angle limit from yaw rate
        final double beta0 = FastMath.atan(context.getMuRate().getReal() / yawRate);

        if (FastMath.abs(context.beta(context.getDate())).getReal() < beta0 &&
            context.setUpTurnRegion(COS_NIGHT, COS_NOON)) {

            final Field<T> field = context.getDate().getField();
            final T        betaX = field.getZero().newInstance(BETA_X);
            context.setHalfSpan(context.inSunSide() ?
                                betaX :
                                context.inOrbitPlaneAbsoluteAngle(betaX),
                                END_MARGIN);
            if (context.inTurnTimeRange()) {

                // handling both noon and midnight turns at once
                final FieldUnivariateDerivative2<T>              beta    = context.betaD2();
                final FieldSinCos<FieldUnivariateDerivative2<T>> scBeta  = FastMath.sinCos(beta);
                final FieldUnivariateDerivative2<T>              cosBeta = scBeta.cos();
                final FieldUnivariateDerivative2<T>              sinBeta = scBeta.sin();
                final T                                          sinY    = FastMath.sin(field.getZero().add(beta0)).copySign(context.getSecuredBeta());
                final FieldUnivariateDerivative2<T>              sd      = FastMath.sin(context.getDeltaDS()).
                                                                           multiply(FastMath.copySign(1.0, -context.getSVBcos().getReal() * context.getDeltaDS().getPartialDerivative(1).getReal()));
                final FieldUnivariateDerivative2<T>              c       = sd.multiply(cosBeta);
                final FieldUnivariateDerivative2<T>              shy     = sinBeta.negate().subtract(sinY).
                                                                           add(sinBeta.subtract(sinY).multiply(c.abs().multiply(c.getPi().divide(FastMath.sin(BETA_X))).cos())).
                                                                           multiply(0.5);
                final FieldUnivariateDerivative2<T>              phi     = FastMath.atan2(shy, c);

                return context.turnCorrectedAttitude(phi);

            }

        }

        // in nominal yaw mode
        return context.nominalYaw(context.getDate());

    }

}