Glonass.java
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package org.orekit.gnss.attitude;
import org.hipparchus.Field;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.analysis.CalculusFieldUnivariateFunction;
import org.hipparchus.analysis.UnivariateFunction;
import org.hipparchus.analysis.solvers.AllowedSolution;
import org.hipparchus.analysis.solvers.BracketingNthOrderBrentSolver;
import org.hipparchus.analysis.solvers.FieldBracketingNthOrderBrentSolver;
import org.hipparchus.analysis.solvers.UnivariateSolverUtils;
import org.hipparchus.util.FastMath;
import org.orekit.frames.Frame;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.ExtendedPVCoordinatesProvider;
import org.orekit.utils.TimeStampedAngularCoordinates;
import org.orekit.utils.TimeStampedFieldAngularCoordinates;
/**
* Attitude providers for Glonass 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 Glonass extends AbstractGNSSAttitudeProvider {
/** Default yaw rates for all spacecrafts in radians per seconds. */
public static final double DEFAULT_YAW_RATE = FastMath.toRadians(0.250);
/** Satellite-Sun angle limit for a midnight turn maneuver. */
private static final double NIGHT_TURN_LIMIT = FastMath.toRadians(180.0 - 14.20);
/** Initial yaw end at iterative search start. */
private static final double YAW_END_ZERO = FastMath.toRadians(75.0);
/** No margin on turn end for Glonass. */
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 Glonass(final double yawRate,
final AbsoluteDate validityStart, final AbsoluteDate validityEnd,
final ExtendedPVCoordinatesProvider 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 realBeta = context.beta(context.getDate());
final double muRate = context.getMuRate();
final double aNight = NIGHT_TURN_LIMIT;
double aNoon = FastMath.atan(muRate / yawRate);
if (FastMath.abs(realBeta) < aNoon) {
final UnivariateFunction f = yawEnd -> {
final double delta = muRate * yawEnd / yawRate;
return yawEnd - 0.5 * FastMath.abs(context.computePhi(realBeta, delta) -
context.computePhi(realBeta, -delta));
};
final double[] bracket = UnivariateSolverUtils.bracket(f, YAW_END_ZERO, 0.0, FastMath.PI);
final double yawEnd = new BracketingNthOrderBrentSolver(1.0e-14, 1.0e-8, 1.0e-15, 5).
solve(50, f, bracket[0], bracket[1], AllowedSolution.ANY_SIDE);
aNoon = muRate * yawEnd / yawRate;
}
final double cNoon = FastMath.cos(aNoon);
final double cNight = FastMath.cos(aNight);
if (context.setUpTurnRegion(cNight, cNoon)) {
context.setHalfSpan(context.inSunSide() ?
aNoon :
context.inOrbitPlaneAbsoluteAngle(aNight - FastMath.PI),
END_MARGIN);
if (context.inTurnTimeRange()) {
// we need to ensure beta sign does not change during the turn
final double beta = context.getSecuredBeta();
final double phiStart = context.getYawStart(beta);
final double dtStart = context.timeSinceTurnStart();
final double phiDot;
final double linearPhi;
final double phiEnd = context.getYawEnd(beta);
if (context.inSunSide()) {
// noon turn
phiDot = -FastMath.copySign(yawRate, beta);
linearPhi = phiStart + phiDot * dtStart;
} else {
// midnight turn
phiDot = FastMath.copySign(yawRate, beta);
linearPhi = phiStart + phiDot * dtStart;
if (phiEnd / linearPhi < 0 || phiEnd / linearPhi > 1) {
// this turn limitation is only computed for midnight turns in Kouba model
// we don't understand yet why it doesn't apply to noon turns
return context.turnCorrectedAttitude(phiEnd, 0.0);
}
}
return context.turnCorrectedAttitude(linearPhi, phiDot);
}
}
// in nominal yaw mode
return context.nominalYaw(context.getDate());
}
/** {@inheritDoc} */
@Override
protected <T extends CalculusFieldElement<T>> TimeStampedFieldAngularCoordinates<T> correctedYaw(final GNSSFieldAttitudeContext<T> context) {
final Field<T> field = context.getDate().getField();
// noon beta angle limit from yaw rate
final T realBeta = context.beta(context.getDate());
final T muRate = context.getMuRate();
final T aNight = field.getZero().newInstance(NIGHT_TURN_LIMIT);
T aNoon = FastMath.atan(muRate.divide(yawRate));
if (FastMath.abs(realBeta).getReal() < aNoon.getReal()) {
final CalculusFieldUnivariateFunction<T> f = yawEnd -> {
final T delta = muRate.multiply(yawEnd).divide(yawRate);
return yawEnd.subtract(FastMath.abs(context.computePhi(realBeta, delta).
subtract(context.computePhi(realBeta, delta.negate()))).
multiply(0.5));
};
final T[] bracket = UnivariateSolverUtils.bracket(f, field.getZero().newInstance(YAW_END_ZERO),
field.getZero(), field.getZero().getPi());
final T yawEnd = new FieldBracketingNthOrderBrentSolver<>(field.getZero().newInstance(1.0e-14),
field.getZero().newInstance(1.0e-8),
field.getZero().newInstance(1.0e-15),
5).
solve(50, f, bracket[0], bracket[1], AllowedSolution.ANY_SIDE);
aNoon = muRate.multiply(yawEnd).divide(yawRate);
}
final double cNoon = FastMath.cos(aNoon.getReal());
final double cNight = FastMath.cos(aNight.getReal());
if (context.setUpTurnRegion(cNight, cNoon)) {
context.setHalfSpan(context.inSunSide() ?
aNoon :
context.inOrbitPlaneAbsoluteAngle(aNight.subtract(aNight.getPi())),
END_MARGIN);
if (context.inTurnTimeRange()) {
// we need to ensure beta sign does not change during the turn
final T beta = context.getSecuredBeta();
final T phiStart = context.getYawStart(beta);
final T dtStart = context.timeSinceTurnStart();
final T phiDot;
final T linearPhi;
final T phiEnd = context.getYawEnd(beta);
if (context.inSunSide()) {
// noon turn
phiDot = field.getZero().newInstance(-FastMath.copySign(yawRate, beta.getReal()));
linearPhi = phiStart.add(phiDot.multiply(dtStart));
} else {
// midnight turn
phiDot = field.getZero().newInstance(FastMath.copySign(yawRate, beta.getReal()));
linearPhi = phiStart.add(phiDot.multiply(dtStart));
// this turn limitation is only computed for midnight turns in Kouba model
// we don't understand yet why it doesn't apply to noon turns
if (phiEnd.getReal() / linearPhi.getReal() < 0 || phiEnd.getReal() / linearPhi.getReal() > 1) {
return context.turnCorrectedAttitude(phiEnd, field.getZero());
}
}
return context.turnCorrectedAttitude(linearPhi, phiDot);
}
}
// in nominal yaw mode
return context.nominalYaw(context.getDate());
}
}