IsotropicDrag.java
/* Copyright 2002-2024 CS GROUP
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* 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
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* Unless required by applicable law or agreed to in writing, software
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package org.orekit.forces.drag;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.utils.ParameterDriver;
/** 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 List<ParameterDriver> dragParametersDrivers;
/** Cross section (m²). */
private final double crossSection;
/** 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) {
// in some corner cases (unknown spacecraft, fuel leaks, active piloting ...)
// the single coefficient may be arbitrary, and even negative
// the DRAG_COEFFICIENT parameter should be sufficient, but GLOBAL_DRAG_FACTOR
// was added as of 12.0 for consistency with BoxAndSolarArraySpacecraft
// that only has a global multiplicatof factor, hence allowing this name
// to be used for both models
this.dragParametersDrivers = new ArrayList<>(2);
dragParametersDrivers.add(new ParameterDriver(DragSensitive.GLOBAL_DRAG_FACTOR,
1.0, SCALE,
0.0, Double.POSITIVE_INFINITY));
dragParametersDrivers.add(new ParameterDriver(DragSensitive.DRAG_COEFFICIENT,
dragCoeff, SCALE,
dragCoeffMin, dragCoeffMax));
this.crossSection = crossSection;
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getDragParametersDrivers() {
return Collections.unmodifiableList(dragParametersDrivers);
}
/** {@inheritDoc} */
@Override
public Vector3D dragAcceleration(final SpacecraftState state,
final double density, final Vector3D relativeVelocity,
final double[] parameters) {
final double dragCoeff = parameters[0] * parameters[1];
return new Vector3D(relativeVelocity.getNorm() * density * dragCoeff * crossSection / (2 * state.getMass()),
relativeVelocity);
}
/** {@inheritDoc} */
@Override
public <T extends CalculusFieldElement<T>> FieldVector3D<T>
dragAcceleration(final FieldSpacecraftState<T> state, final T density,
final FieldVector3D<T> relativeVelocity,
final T[] parameters) {
final T dragCoeff = parameters[0].multiply(parameters[1]);
return new FieldVector3D<>(relativeVelocity.getNorm().
multiply(density.multiply(dragCoeff).multiply(crossSection / 2)).
divide(state.getMass()),
relativeVelocity);
}
}