/* Copyright 2002-2017 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.forces.gravity;
import java.util.stream.Stream;
import org.hipparchus.Field;
import org.hipparchus.RealFieldElement;
import org.hipparchus.analysis.differentiation.DSFactory;
import org.hipparchus.analysis.differentiation.DerivativeStructure;
import org.hipparchus.geometry.euclidean.threed.FieldRotation;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.orekit.bodies.CelestialBody;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitInternalError;
import org.orekit.forces.AbstractForceModel;
import org.orekit.frames.Frame;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.EventDetector;
import org.orekit.propagation.events.FieldEventDetector;
import org.orekit.propagation.numerical.FieldTimeDerivativesEquations;
import org.orekit.propagation.numerical.TimeDerivativesEquations;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.ParameterObserver;
/** Third body attraction force model.
*
* @author Fabien Maussion
* @author Véronique Pommier-Maurussane
*/
public class ThirdBodyAttraction extends AbstractForceModel {
/** Suffix for parameter name for attraction coefficient enabling jacobian processing. */
public static final String ATTRACTION_COEFFICIENT_SUFFIX = " attraction coefficient";
/** Central attraction scaling factor.
* <p>
* We use a power of 2 to avoid numeric noise introduction
* in the multiplications/divisions sequences.
* </p>
*/
private static final double MU_SCALE = FastMath.scalb(1.0, 32);
/** Drivers for force model parameters. */
private final ParameterDriver[] parametersDrivers;
/** The body to consider. */
private final CelestialBody body;
/** Local value for body attraction coefficient. */
private double gm;
/** Factory for the DerivativeStructure instances. */
private final DSFactory factory;
/** Simple constructor.
* @param body the third body to consider
* (ex: {@link org.orekit.bodies.CelestialBodyFactory#getSun()} or
* {@link org.orekit.bodies.CelestialBodyFactory#getMoon()})
*/
public ThirdBodyAttraction(final CelestialBody body) {
this.parametersDrivers = new ParameterDriver[1];
try {
parametersDrivers[0] = new ParameterDriver(body.getName() + ATTRACTION_COEFFICIENT_SUFFIX,
body.getGM(), MU_SCALE,
0.0, Double.POSITIVE_INFINITY);
parametersDrivers[0].addObserver(new ParameterObserver() {
/** {@inheritDoc} */
public void valueChanged(final double previousValue, final ParameterDriver driver) {
ThirdBodyAttraction.this.gm = driver.getValue();
}
});
} catch (OrekitException oe) {
// this should never occur as valueChanged above never throws an exception
throw new OrekitInternalError(oe);
};
this.body = body;
this.gm = body.getGM();
this.factory = new DSFactory(1, 1);
}
/** {@inheritDoc} */
public void addContribution(final SpacecraftState s, final TimeDerivativesEquations adder)
throws OrekitException {
// compute bodies separation vectors and squared norm
final Vector3D centralToBody = body.getPVCoordinates(s.getDate(), s.getFrame()).getPosition();
final double r2Central = centralToBody.getNormSq();
final Vector3D satToBody = centralToBody.subtract(s.getPVCoordinates().getPosition());
final double r2Sat = satToBody.getNormSq();
// compute relative acceleration
final Vector3D gamma =
new Vector3D(gm / (r2Sat * FastMath.sqrt(r2Sat)), satToBody,
-gm / (r2Central * FastMath.sqrt(r2Central)), centralToBody);
// add contribution to the ODE second member
adder.addXYZAcceleration(gamma.getX(), gamma.getY(), gamma.getZ());
}
/** {@inheritDoc} */
public FieldVector3D<DerivativeStructure> accelerationDerivatives(final AbsoluteDate date, final Frame frame,
final FieldVector3D<DerivativeStructure> position,
final FieldVector3D<DerivativeStructure> velocity,
final FieldRotation<DerivativeStructure> rotation,
final DerivativeStructure mass)
throws OrekitException {
// compute bodies separation vectors and squared norm
final Vector3D centralToBody = body.getPVCoordinates(date, frame).getPosition();
final double r2Central = centralToBody.getNormSq();
final FieldVector3D<DerivativeStructure> satToBody = position.subtract(centralToBody).negate();
final DerivativeStructure r2Sat = satToBody.getNormSq();
// compute relative acceleration
final FieldVector3D<DerivativeStructure> satAcc =
new FieldVector3D<DerivativeStructure>(r2Sat.sqrt().multiply(r2Sat).reciprocal().multiply(gm), satToBody);
final Vector3D centralAcc =
new Vector3D(gm / (r2Central * FastMath.sqrt(r2Central)), centralToBody);
return satAcc.subtract(centralAcc);
}
/** {@inheritDoc} */
public FieldVector3D<DerivativeStructure> accelerationDerivatives(final SpacecraftState s, final String paramName)
throws OrekitException {
complainIfNotSupported(paramName);
// compute bodies separation vectors and squared norm
final Vector3D centralToBody = body.getPVCoordinates(s.getDate(), s.getFrame()).getPosition();
final double r2Central = centralToBody.getNormSq();
final Vector3D satToBody = centralToBody.subtract(s.getPVCoordinates().getPosition());
final double r2Sat = satToBody.getNormSq();
final DerivativeStructure gmds = factory.variable(0, gm);
// compute relative acceleration
return new FieldVector3D<DerivativeStructure>(gmds.divide(r2Sat * FastMath.sqrt(r2Sat)), satToBody,
gmds.divide(-r2Central * FastMath.sqrt(r2Central)), centralToBody);
}
/** {@inheritDoc} */
public Stream<EventDetector> getEventsDetectors() {
return Stream.empty();
}
@Override
/** {@inheritDoc} */
public <T extends RealFieldElement<T>> Stream<FieldEventDetector<T>> getFieldEventsDetectors(final Field<T> field) {
return Stream.empty();
}
/** {@inheritDoc} */
public ParameterDriver[] getParametersDrivers() {
return parametersDrivers.clone();
}
/**{@inheritDoc} */
public <T extends RealFieldElement<T>> void
addContribution(final FieldSpacecraftState<T> s,
final FieldTimeDerivativesEquations<T> adder)
throws OrekitException {
final T zero = s.getA().getField().getZero();
// compute bodies separation vectors and squared norm
final FieldVector3D<T> centralToBody = new FieldVector3D<T>(zero.add(body.getPVCoordinates(s.getDate().toAbsoluteDate(), s.getFrame()).getPosition().getX()),
zero.add(body.getPVCoordinates(s.getDate().toAbsoluteDate(), s.getFrame()).getPosition().getY()),
zero.add(body.getPVCoordinates(s.getDate().toAbsoluteDate(), s.getFrame()).getPosition().getZ())
);
final T r2Central = centralToBody.getNormSq();
final FieldVector3D<T> satToBody = centralToBody.subtract(s.getPVCoordinates().getPosition());
final T r2Sat = satToBody.getNormSq();
// compute relative acceleration
final FieldVector3D<T> gamma =
new FieldVector3D<T>(r2Sat.multiply(r2Sat.sqrt()).reciprocal().multiply(gm), satToBody,
r2Central.multiply(r2Central.sqrt()).reciprocal().multiply(-gm), centralToBody);
adder.addXYZAcceleration(gamma.getX(), gamma.getY(), gamma.getZ());
}
}