DragForce.java
/* Copyright 2002-2024 CS GROUP
* Licensed to CS GROUP (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,
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* See the License for the specific language governing permissions and
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*/
package org.orekit.forces.drag;
import java.util.List;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.orekit.frames.Frame;
import org.orekit.models.earth.atmosphere.Atmosphere;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.ParameterDriver;
/** Atmospheric drag force model.
*
* The drag acceleration is computed as follows :
*
* γ = (1/2 * ρ * V² * S / Mass) * DragCoefVector
*
* With DragCoefVector = {C<sub>x</sub>, C<sub>y</sub>, C<sub>z</sub>} and S given by the user through the interface
* {@link DragSensitive}
*
* @author Édouard Delente
* @author Fabien Maussion
* @author Véronique Pommier-Maurussane
* @author Pascal Parraud
* @author Melina Vanel
*/
public class DragForce extends AbstractDragForceModel {
/** Spacecraft. */
private final DragSensitive spacecraft;
/** Constructor with default flag for finite differences.
* @param atmosphere atmospheric model
* @param spacecraft the object physical and geometrical information
*/
public DragForce(final Atmosphere atmosphere, final DragSensitive spacecraft) {
super(atmosphere);
this.spacecraft = spacecraft;
}
/** Simple constructor.
* @param atmosphere atmospheric model
* @param spacecraft the object physical and geometrical information
* @param useFiniteDifferencesOnDensityWrtPosition flag to use finite differences to compute density derivatives w.r.t.
* position (is less accurate but can be faster depending on model)
* @since 12.1
*/
public DragForce(final Atmosphere atmosphere, final DragSensitive spacecraft,
final boolean useFiniteDifferencesOnDensityWrtPosition) {
super(atmosphere, useFiniteDifferencesOnDensityWrtPosition);
this.spacecraft = spacecraft;
}
/** {@inheritDoc} */
@Override
public boolean dependsOnAttitudeRate() {
return getSpacecraft().dependsOnAttitudeRate();
}
/** {@inheritDoc} */
@Override
public Vector3D acceleration(final SpacecraftState s, final double[] parameters) {
final AbsoluteDate date = s.getDate();
final Frame frame = s.getFrame();
final Vector3D position = s.getPosition();
final double rho = getAtmosphere().getDensity(date, position, frame);
final Vector3D vAtm = getAtmosphere().getVelocity(date, position, frame);
final Vector3D relativeVelocity = vAtm.subtract(s.getPVCoordinates().getVelocity());
return spacecraft.dragAcceleration(s, rho, relativeVelocity, parameters);
}
/** {@inheritDoc} */
@Override
public <T extends CalculusFieldElement<T>> FieldVector3D<T> acceleration(final FieldSpacecraftState<T> s,
final T[] parameters) {
// Density and its derivatives
final T rho = getFieldDensity(s);
// Spacecraft relative velocity with respect to the atmosphere
final FieldAbsoluteDate<T> date = s.getDate();
final Frame frame = s.getFrame();
final FieldVector3D<T> position = s.getPosition();
final FieldVector3D<T> vAtm = getAtmosphere().getVelocity(date, position, frame);
final FieldVector3D<T> relativeVelocity = vAtm.subtract(s.getPVCoordinates().getVelocity());
// Drag acceleration along with its derivatives
return spacecraft.dragAcceleration(s, rho, relativeVelocity, parameters);
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getParametersDrivers() {
return spacecraft.getDragParametersDrivers();
}
/** Get spacecraft that are sensitive to atmospheric drag forces.
* @return drag sensitive spacecraft model
*/
public DragSensitive getSpacecraft() {
return spacecraft;
}
}