ThirdBodyAttraction.java
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*
* http://www.apache.org/licenses/LICENSE-2.0
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package org.orekit.forces.gravity;
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.bodies.CelestialBodies;
import org.orekit.bodies.CelestialBody;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
/** Third body attraction force model.
*
* @author Fabien Maussion
* @author Véronique Pommier-Maurussane
*/
public class ThirdBodyAttraction extends AbstractBodyAttraction {
/** Simple constructor.
* @param body the third body to consider
* (ex: {@link CelestialBodies#getSun()} or
* {@link CelestialBodies#getMoon()})
*/
public ThirdBodyAttraction(final CelestialBody body) {
super(body);
}
/** {@inheritDoc} */
@Override
public Vector3D acceleration(final SpacecraftState s, final double[] parameters) {
final double gm = parameters[0];
// compute bodies separation vectors and squared norm
final Vector3D centralToBody = getBody().getPosition(s.getDate(), s.getFrame());
final double r2Central = centralToBody.getNormSq();
final Vector3D satToBody = centralToBody.subtract(s.getPosition());
final double r2Sat = satToBody.getNormSq();
// compute relative acceleration
return new Vector3D(gm / (r2Sat * FastMath.sqrt(r2Sat)), satToBody,
-gm / (r2Central * FastMath.sqrt(r2Central)), centralToBody);
}
/** {@inheritDoc} */
@Override
public <T extends CalculusFieldElement<T>> FieldVector3D<T> acceleration(final FieldSpacecraftState<T> s,
final T[] parameters) {
final T gm = parameters[0];
// compute bodies separation vectors and squared norm
final FieldVector3D<T> centralToBody = getBody().getPosition(s.getDate(), s.getFrame());
final T r2Central = centralToBody.getNormSq();
final FieldVector3D<T> satToBody = centralToBody.subtract(s.getPosition());
final T r2Sat = satToBody.getNormSq();
// compute relative acceleration
return new FieldVector3D<>(r2Sat.multiply(r2Sat.sqrt()).reciprocal().multiply(gm), satToBody,
r2Central.multiply(r2Central.sqrt()).reciprocal().multiply(gm).negate(), centralToBody);
}
}