/* 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.radiation;
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 represents the features of a simplified spacecraft.
*
* <p>This model uses the coefficients described in the collective
* book edited by CNES in 1995: Spaceflight Dynamics (part I), in
* section 5.2.2.1.3.1 (page 296 of the English edition). The absorption
* coefficient is called α and the specular reflection coefficient is
* called τ. A comment in section 5.2.2.1.3.2 of the same book reads:
* <pre>
* Some authors prefer to express thermo-optical properties for surfaces
* using the following coefficients: Ka = α, Ks = (1-α)τ, Kd = (1-α)(1-τ)
* </pre>
* <p> Ka is the same absorption coefficient, and Ks is also called specular
* reflection coefficient, which leads to a confusion. In fact, as the Ka,
* Ks and Kd coefficients are the most frequently used ones (using the
* names Ca, Cs and Cd), when speaking about reflection coefficients, it
* is more often Cd that is considered rather than τ.
*
* <p>
* The classical set of coefficients Ca, Cs, and Cd are implemented in the
* sister class {@link IsotropicRadiationClassicalConvention}, which should
* probably be preferred to this legacy class.
* </p>
*
* @see org.orekit.forces.BoxAndSolarArraySpacecraft
* @see org.orekit.forces.drag.IsotropicDrag
* @see IsotropicRadiationClassicalConvention
* @author Luc Maisonobe
* @since 7.1
*/
public class IsotropicRadiationCNES95Convention implements RadiationSensitive {
/** 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 radiation pressure coefficient parameter. */
private final ParameterDriver[] radiationParametersDrivers;
/** Cross section (m²). */
private final double crossSection;
/** Absorption coefficient. */
private double alpha;
/** Specular reflection coefficient. */
private double tau;
/** Factory for the DerivativeStructure instances. */
private final DSFactory factory;
/** Simple constructor.
* @param crossSection Surface (m²)
* @param alpha absorption coefficient α between 0.0 an 1.0
* @param tau specular reflection coefficient τ between 0.0 an 1.0
*/
public IsotropicRadiationCNES95Convention(final double crossSection, final double alpha, final double tau) {
this.radiationParametersDrivers = new ParameterDriver[2];
try {
radiationParametersDrivers[0] = new ParameterDriver(RadiationSensitive.ABSORPTION_COEFFICIENT,
alpha, SCALE, 0.0, 1.0);
radiationParametersDrivers[0].addObserver(new ParameterObserver() {
/** {@inheritDoc} */
@Override
public void valueChanged(final double previousValue, final ParameterDriver driver) {
IsotropicRadiationCNES95Convention.this.alpha = driver.getValue();
}
});
radiationParametersDrivers[1] = new ParameterDriver(RadiationSensitive.REFLECTION_COEFFICIENT,
tau, SCALE, 0.0, 1.0);
radiationParametersDrivers[1].addObserver(new ParameterObserver() {
/** {@inheritDoc} */
@Override
public void valueChanged(final double previousValue, final ParameterDriver driver) {
/** {@inheritDoc} */
IsotropicRadiationCNES95Convention.this.tau = driver.getValue();
}
});
factory = new DSFactory(1, 1);
} catch (OrekitException oe) {
// this should never occur as valueChanged above never throws an exception
throw new OrekitInternalError(oe);
};
this.crossSection = crossSection;
this.alpha = alpha;
this.tau = tau;
}
/** {@inheritDoc} */
@Override
public ParameterDriver[] getRadiationParametersDrivers() {
return radiationParametersDrivers.clone();
}
/** {@inheritDoc} */
public Vector3D radiationPressureAcceleration(final AbsoluteDate date, final Frame frame, final Vector3D position,
final Rotation rotation, final double mass, final Vector3D flux) {
final double kP = crossSection * (1 + 4 * (1.0 - alpha) * (1.0 - tau) / 9.0);
return new Vector3D(kP / mass, flux);
}
/** {@inheritDoc} */
public FieldVector3D<DerivativeStructure> radiationPressureAcceleration(final AbsoluteDate date, final Frame frame, final FieldVector3D<DerivativeStructure> position,
final FieldRotation<DerivativeStructure> rotation, final DerivativeStructure mass,
final FieldVector3D<DerivativeStructure> flux) {
final double kP = crossSection * (1 + 4 * (1.0 - alpha) * (1.0 - tau) / 9.0);
return new FieldVector3D<DerivativeStructure>(mass.reciprocal().multiply(kP), flux);
}
/** {@inheritDoc} */
public FieldVector3D<DerivativeStructure> radiationPressureAcceleration(final AbsoluteDate date, final Frame frame, final Vector3D position,
final Rotation rotation, final double mass,
final Vector3D flux, final String paramName)
throws OrekitException {
final DerivativeStructure absorptionCoeffDS;
final DerivativeStructure specularReflectionCoeffDS;
if (ABSORPTION_COEFFICIENT.equals(paramName)) {
absorptionCoeffDS = factory.variable(0, alpha);
specularReflectionCoeffDS = factory.constant(tau);
} else if (REFLECTION_COEFFICIENT.equals(paramName)) {
absorptionCoeffDS = factory.constant(alpha);
specularReflectionCoeffDS = factory.variable(0, tau);
} else {
throw new OrekitException(OrekitMessages.UNSUPPORTED_PARAMETER_NAME, paramName,
ABSORPTION_COEFFICIENT + ", " + REFLECTION_COEFFICIENT);
}
final DerivativeStructure kP =
absorptionCoeffDS.subtract(1).multiply(specularReflectionCoeffDS.subtract(1)).multiply(4.0 / 9.0).add(1).multiply(crossSection);
return new FieldVector3D<DerivativeStructure>(kP.divide(mass), flux);
}
@Override
public <T extends RealFieldElement<T>> FieldVector3D<T>
radiationPressureAcceleration(final FieldAbsoluteDate<T> date, final Frame frame,
final FieldVector3D<T> position,
final FieldRotation<T> rotation, final T mass,
final FieldVector3D<T> flux)
throws OrekitException {
final double kP = crossSection * (1 + 4 * (1.0 - alpha) * (1.0 - tau) / 9.0);
return new FieldVector3D<T>(mass.reciprocal().multiply(kP), flux);
}
}