Relativity.java
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* 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
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*
* 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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*/
package org.orekit.forces.gravity;
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.forces.ForceModel;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.utils.Constants;
import org.orekit.utils.FieldPVCoordinates;
import org.orekit.utils.PVCoordinates;
import org.orekit.utils.ParameterDriver;
/**
* Post-Newtonian correction force due to general relativity. The main effect is the
* precession of perigee by a few arcseconds per year.
*
* <p> Implemented from Montenbruck and Gill equation 3.146.
*
* @author Evan Ward
* @see "Montenbruck, Oliver, and Gill, Eberhard. Satellite orbits : models, methods, and
* applications. Berlin New York: Springer, 2000."
*/
public class Relativity implements ForceModel {
/** 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);
/** Driver for gravitational parameter. */
private final ParameterDriver gmParameterDriver;
/**
* Create a force model to add post-Newtonian acceleration corrections to an Earth
* orbit.
*
* @param gm Earth's gravitational parameter.
*/
public Relativity(final double gm) {
gmParameterDriver = new ParameterDriver(NewtonianAttraction.CENTRAL_ATTRACTION_COEFFICIENT,
gm, MU_SCALE,
0.0, Double.POSITIVE_INFINITY);
}
/** {@inheritDoc} */
@Override
public boolean dependsOnPositionOnly() {
return false;
}
/** {@inheritDoc} */
@Override
public Vector3D acceleration(final SpacecraftState s, final double[] parameters) {
final double gm = parameters[0];
final PVCoordinates pv = s.getPVCoordinates();
final Vector3D p = pv.getPosition();
final Vector3D v = pv.getVelocity();
//radius
final double r2 = p.getNormSq();
final double r = FastMath.sqrt(r2);
//speed
final double s2 = v.getNormSq();
final double c2 = Constants.SPEED_OF_LIGHT * Constants.SPEED_OF_LIGHT;
//eq. 3.146
return new Vector3D(
4 * gm / r - s2,
p,
4 * p.dotProduct(v),
v)
.scalarMultiply(gm / (r2 * r * c2));
}
/** {@inheritDoc} */
@Override
public <T extends CalculusFieldElement<T>> FieldVector3D<T> acceleration(final FieldSpacecraftState<T> s,
final T[] parameters) {
final T gm = parameters[0];
final FieldPVCoordinates<T> pv = s.getPVCoordinates();
final FieldVector3D<T> p = pv.getPosition();
final FieldVector3D<T> v = pv.getVelocity();
//radius
final T r2 = p.getNormSq();
final T r = r2.sqrt();
//speed
final T s2 = v.getNormSq();
final double c2 = Constants.SPEED_OF_LIGHT * Constants.SPEED_OF_LIGHT;
//eq. 3.146
return new FieldVector3D<>(r.reciprocal().multiply(4).multiply(gm).subtract(s2),
p,
p.dotProduct(v).multiply(4),
v).scalarMultiply(r2.multiply(r).multiply(c2).reciprocal().multiply(gm));
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getParametersDrivers() {
return Collections.singletonList(gmParameterDriver);
}
}