/* 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.drag;
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.Rotation;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitInternalError;
import org.orekit.errors.OrekitMessages;
import org.orekit.frames.Frame;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.ParameterObserver;
/** This class models isotropic drag effects.
* <p>The model of this spacecraft is a simple spherical model, this
* means that all coefficients are constant and do not depend of
* the direction.</p>
*
* @see org.orekit.forces.BoxAndSolarArraySpacecraft
* @see org.orekit.forces.radiation.IsotropicRadiationCNES95Convention
* @author Luc Maisonobe
* @since 7.1
*/
public class IsotropicDrag implements DragSensitive {
/** Parameters scaling factor.
* <p>
* We use a power of 2 to avoid numeric noise introduction
* in the multiplications/divisions sequences.
* </p>
*/
private final double SCALE = FastMath.scalb(1.0, -3);
/** Drivers for drag coefficient parameter. */
private final ParameterDriver[] dragParametersDrivers;
/** Cross section (m²). */
private final double crossSection;
/** Drag coefficient. */
private double dragCoeff;
/** Factory for the DerivativeStructure instances. */
private final DSFactory factory;
/** Constructor with drag coefficient min/max set to ±∞.
* @param crossSection Surface (m²)
* @param dragCoeff drag coefficient
*/
public IsotropicDrag(final double crossSection, final double dragCoeff) {
this(crossSection, dragCoeff, Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);
}
/** Constructor with drag coefficient min/max set by user.
* @param crossSection Surface (m²)
* @param dragCoeff drag coefficient
* @param dragCoeffMin Minimum value of drag coefficient
* @param dragCoeffMax Maximum value of drag coefficient
*/
public IsotropicDrag(final double crossSection, final double dragCoeff,
final double dragCoeffMin, final double dragCoeffMax) {
this.dragParametersDrivers = new ParameterDriver[1];
try {
// in some corner cases (unknown spacecraft, fuel leaks, active piloting ...)
// the single coefficient may be arbitrary, and even negative
dragParametersDrivers[0] = new ParameterDriver(DragSensitive.DRAG_COEFFICIENT,
dragCoeff, SCALE,
dragCoeffMin, dragCoeffMax);
dragParametersDrivers[0].addObserver(new ParameterObserver() {
/** {@inheritDoc} */
@Override
public void valueChanged(final double previousValue, final ParameterDriver driver) {
IsotropicDrag.this.dragCoeff = driver.getValue();
}
});
} catch (OrekitException oe) {
// this should never occur as valueChanged above never throws an exception
throw new OrekitInternalError(oe);
};
this.crossSection = crossSection;
this.dragCoeff = dragCoeff;
this.factory = new DSFactory(1, 1);
}
/** {@inheritDoc} */
@Override
public ParameterDriver[] getDragParametersDrivers() {
return dragParametersDrivers.clone();
}
/** {@inheritDoc} */
public Vector3D dragAcceleration(final AbsoluteDate date, final Frame frame, final Vector3D position,
final Rotation rotation, final double mass,
final double density, final Vector3D relativeVelocity) {
return new Vector3D(relativeVelocity.getNorm() * density * dragCoeff * crossSection / (2 * mass),
relativeVelocity);
}
/** {@inheritDoc} */
public FieldVector3D<DerivativeStructure> dragAcceleration(final AbsoluteDate date, final Frame frame, final FieldVector3D<DerivativeStructure> position,
final FieldRotation<DerivativeStructure> rotation, final DerivativeStructure mass,
final DerivativeStructure density, final FieldVector3D<DerivativeStructure> relativeVelocity) {
return new FieldVector3D<DerivativeStructure>(relativeVelocity.getNorm().multiply(density.multiply(dragCoeff * crossSection / 2)).divide(mass),
relativeVelocity);
}
/** {@inheritDoc} */
public FieldVector3D<DerivativeStructure> dragAcceleration(final AbsoluteDate date, final Frame frame, final Vector3D position,
final Rotation rotation, final double mass,
final double density, final Vector3D relativeVelocity,
final String paramName)
throws OrekitException {
if (!DRAG_COEFFICIENT.equals(paramName)) {
throw new OrekitException(OrekitMessages.UNSUPPORTED_PARAMETER_NAME, paramName, DRAG_COEFFICIENT);
}
final DerivativeStructure dragCoeffDS = factory.variable(0, dragCoeff);
return new FieldVector3D<>(dragCoeffDS.multiply(relativeVelocity.getNorm() * density * crossSection / (2 * mass)),
relativeVelocity);
}
@Override
public <T extends RealFieldElement<T>> FieldVector3D<T>
dragAcceleration(final FieldAbsoluteDate<T> date, final Frame frame,
final FieldVector3D<T> position, final FieldRotation<T> rotation,
final T mass, final T density,
final FieldVector3D<T> relativeVelocity)
throws OrekitException {
return new FieldVector3D<>(relativeVelocity.getNorm().multiply(density.multiply(dragCoeff * crossSection / 2)).divide(mass),
relativeVelocity);
}
}