GPSBlockIIF.java
/* Copyright 2002-2019 CS Systèmes d'Information
* Licensed to CS Systèmes d'Information (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
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*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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package org.orekit.gnss.attitude;
import org.hipparchus.Field;
import org.hipparchus.RealFieldElement;
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 GPS block IIF 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 GPSBlockIIF extends AbstractGNSSAttitudeProvider {
/** Default yaw rates for all spacecrafts in radians per seconds. */
public static final double DEFAULT_YAW_RATE = FastMath.toRadians(0.11);
/** Default yaw bias (rad). */
public static final double DEFAULT_YAW_BIAS = FastMath.toRadians(-0.7);
/** Serializable UID. */
private static final long serialVersionUID = 20171114L;
/** Satellite-Sun angle limit for a midnight turn maneuver. */
private static final double NIGHT_TURN_LIMIT = FastMath.toRadians(180.0 - 13.25);
/** Margin on turn end. */
private final double END_MARGIN = 1800.0;
/** Yaw rate. */
private final double yawRate;
/** Yaw bias. */
private final double yawBias;
/** Simple constructor.
* @param yawRate yaw rate to use in radians per seconds (typically {@link #DEFAULT_YAW_RATE})
* @param yawBias yaw bias to use (rad) (typicall {@link #DEFAULT_YAW_BIAS})
* @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 GPSBlockIIF(final double yawRate, final double yawBias,
final AbsoluteDate validityStart, final AbsoluteDate validityEnd,
final ExtendedPVCoordinatesProvider sun, final Frame inertialFrame) {
super(validityStart, validityEnd, sun, inertialFrame);
this.yawRate = yawRate;
this.yawBias = yawBias;
}
/** {@inheritDoc} */
@Override
protected TimeStampedAngularCoordinates correctedYaw(final GNSSAttitudeContext context) {
// noon beta angle limit from yaw rate
final double aNoon = FastMath.atan(context.getMuRate() / yawRate);
final double aNight = NIGHT_TURN_LIMIT;
final double cNoon = FastMath.cos(aNoon);
final double cNight = FastMath.cos(aNight);
if (context.setUpTurnRegion(cNight, cNoon)) {
final double absBeta = FastMath.abs(context.beta(context.getDate()));
context.setHalfSpan(context.inSunSide() ?
absBeta * FastMath.sqrt(aNoon / absBeta - 1.0) :
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;
if (context.inSunSide()) {
// noon turn
if (beta > yawBias && beta < 0) {
// noon turn problem for small negative beta in block IIF
// rotation is in the wrong direction for these spacecrafts
phiDot = FastMath.copySign(yawRate, beta);
linearPhi = phiStart + phiDot * dtStart;
} else {
// regular noon turn
phiDot = -FastMath.copySign(yawRate, beta);
linearPhi = phiStart + phiDot * dtStart;
}
} else {
// midnight turn
phiDot = context.yawRate(beta);
linearPhi = phiStart + phiDot * dtStart;
}
if (context.linearModelStillActive(linearPhi, phiDot)) {
// we are still in the linear model phase
return context.turnCorrectedAttitude(linearPhi, phiDot);
}
}
}
// in nominal yaw mode
return context.nominalYaw(context.getDate());
}
/** {@inheritDoc} */
@Override
protected <T extends RealFieldElement<T>> TimeStampedFieldAngularCoordinates<T> correctedYaw(final GNSSFieldAttitudeContext<T> context) {
final Field<T> field = context.getDate().getField();
// noon beta angle limit from yaw rate
final T aNoon = FastMath.atan(context.getMuRate().divide(yawRate));
final T aNight = field.getZero().add(NIGHT_TURN_LIMIT);
final double cNoon = FastMath.cos(aNoon.getReal());
final double cNight = FastMath.cos(aNight.getReal());
if (context.setUpTurnRegion(cNight, cNoon)) {
final T absBeta = FastMath.abs(context.beta(context.getDate()));
context.setHalfSpan(context.inSunSide() ?
absBeta.multiply(FastMath.sqrt(aNoon.divide(absBeta).subtract(1.0))) :
context.inOrbitPlaneAbsoluteAngle(aNight.subtract(FastMath.PI)),
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;
if (context.inSunSide()) {
// noon turn
if (beta.getReal() > yawBias && beta.getReal() < 0) {
// noon turn problem for small negative beta in block IIF
// rotation is in the wrong direction for these spacecrafts
phiDot = field.getZero().add(FastMath.copySign(yawRate, beta.getReal()));
linearPhi = phiStart.add(phiDot.multiply(dtStart));
} else {
// regular noon turn
phiDot = field.getZero().add(-FastMath.copySign(yawRate, beta.getReal()));
linearPhi = phiStart.add(phiDot.multiply(dtStart));
}
} else {
// midnight turn
phiDot = context.yawRate(beta);
linearPhi = phiStart.add(phiDot.multiply(dtStart));
}
if (context.linearModelStillActive(linearPhi, phiDot)) {
// we are still in the linear model phase
return context.turnCorrectedAttitude(linearPhi, phiDot);
}
}
}
// in nominal yaw mode
return context.nominalYaw(context.getDate());
}
}