Glonass.java
/* Copyright 2002-2018 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
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* 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,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.orekit.gnss.attitude;
import org.hipparchus.Field;
import org.hipparchus.RealFieldElement;
import org.hipparchus.util.FastMath;
import org.orekit.errors.OrekitException;
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>
* <p>
* WARNING: as of release 9.2, this feature is still considered experimental
* </p>
* @author J. Kouba original fortran routine
* @author Luc Maisonobe Java translation
* @since 9.2
*/
public class Glonass extends AbstractGNSSAttitudeProvider {
/** 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 - 14.20);
/** Yaw rates for all spacecrafts. */
private static final double YAW_RATE = FastMath.toRadians(0.250);
/** Initial yaw end at iterative search start. */
private static final double YAW_END_ZERO = FastMath.toRadians(75.0);
/** Simple constructor.
* @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 AbsoluteDate validityStart, final AbsoluteDate validityEnd,
final ExtendedPVCoordinatesProvider sun, final Frame inertialFrame) {
super(validityStart, validityEnd, sun, inertialFrame);
}
/** {@inheritDoc} */
@Override
protected TimeStampedAngularCoordinates correctedYaw(final GNSSAttitudeContext context)
throws OrekitException {
// noon beta angle limit from yaw rate
final double realBeta = context.getBeta();
final double muRate = context.getMuRate();
final double aNight = NIGHT_TURN_LIMIT;
double aNoon = FastMath.atan(muRate / YAW_RATE);
if (FastMath.abs(realBeta) < aNoon) {
double yawEnd = YAW_END_ZERO;
for (int i = 0; i < 3; ++i) {
final double delta = muRate * yawEnd / YAW_RATE;
yawEnd = 0.5 * FastMath.abs(context.computePhi(realBeta, delta) -
context.computePhi(realBeta, -delta));
}
aNoon = muRate * yawEnd / YAW_RATE;
}
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));
if (context.inTurnTimeRange(context.getDate(), 0)) {
// 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(context.getDate());
final double phiDot;
final double linearPhi;
final double phiEnd = context.getYawEnd(beta);
if (context.inSunSide()) {
// noon turn
phiDot = -FastMath.copySign(YAW_RATE, beta);
linearPhi = phiStart + phiDot * dtStart;
} else {
// midnight turn
phiDot = FastMath.copySign(YAW_RATE, beta);
linearPhi = phiStart + phiDot * dtStart;
}
if (phiEnd / linearPhi < 0 || phiEnd / linearPhi > 1) {
return context.turnCorrectedAttitude(phiEnd, 0.0);
} else {
return context.turnCorrectedAttitude(linearPhi, phiDot);
}
}
}
// in nominal yaw mode
return context.getNominalYaw();
}
/** {@inheritDoc} */
@Override
protected <T extends RealFieldElement<T>> TimeStampedFieldAngularCoordinates<T> correctedYaw(final GNSSFieldAttitudeContext<T> context)
throws OrekitException {
final Field<T> field = context.getDate().getField();
// noon beta angle limit from yaw rate
final T realBeta = context.getBeta();
final T muRate = context.getMuRate();
final T aNight = field.getZero().add(NIGHT_TURN_LIMIT);
T aNoon = FastMath.atan(muRate.divide(YAW_RATE));
if (FastMath.abs(realBeta).getReal() < aNoon.getReal()) {
T yawEnd = field.getZero().add(YAW_END_ZERO);
for (int i = 0; i < 3; ++i) {
final T delta = muRate.multiply(yawEnd).divide(YAW_RATE);
yawEnd = FastMath.abs(context.computePhi(realBeta, delta).
subtract(context.computePhi(realBeta, delta.negate()))).
multiply(0.5);
}
aNoon = muRate.multiply(yawEnd).divide(YAW_RATE);
}
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(FastMath.PI)));
if (context.inTurnTimeRange(context.getDate(), 0)) {
// 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(context.getDate());
final T phiDot;
final T linearPhi;
final T phiEnd = context.getYawEnd(beta);
if (context.inSunSide()) {
// noon turn
phiDot = field.getZero().add(-FastMath.copySign(YAW_RATE, beta.getReal()));
linearPhi = phiStart.add(phiDot.multiply(dtStart));
} else {
// midnight turn
phiDot = field.getZero().add(FastMath.copySign(YAW_RATE, beta.getReal()));
linearPhi = phiStart.add(phiDot.multiply(dtStart));
}
if (phiEnd.getReal() / linearPhi.getReal() < 0 || phiEnd.getReal() / linearPhi.getReal() > 1) {
return context.turnCorrectedAttitude(phiEnd, field.getZero());
} else {
return context.turnCorrectedAttitude(linearPhi, phiDot);
}
}
}
// in nominal yaw mode
return context.getNominalYaw();
}
}