SingleBodyRelativeAttraction.java
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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.orekit.bodies.CelestialBodies;
import org.orekit.bodies.CelestialBody;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.utils.FieldPVCoordinates;
import org.orekit.utils.PVCoordinates;
/** Body attraction force model computed as relative acceleration towards frame center.
* @author Luc Maisonabe
* @author Julio Hernanz
*/
public class SingleBodyRelativeAttraction extends AbstractBodyAttraction {
/** Simple constructor.
* @param body the body to consider
* (ex: {@link CelestialBodies#getSun()} or
* {@link CelestialBodies#getMoon()})
*/
public SingleBodyRelativeAttraction(final CelestialBody body) {
super(body);
}
/** {@inheritDoc} */
public Vector3D acceleration(final SpacecraftState s, final double[] parameters) {
// compute bodies separation vectors and squared norm
final PVCoordinates bodyPV = getBody().getPVCoordinates(s.getDate(), s.getFrame());
final Vector3D satToBody = bodyPV.getPosition().subtract(s.getPosition());
final double r2Sat = satToBody.getNormSq();
// compute relative acceleration
final double gm = parameters[0];
final double a = gm / r2Sat;
return new Vector3D(a, satToBody.normalize()).add(bodyPV.getAcceleration());
}
/** {@inheritDoc} */
public <T extends CalculusFieldElement<T>> FieldVector3D<T> acceleration(final FieldSpacecraftState<T> s,
final T[] parameters) {
// compute bodies separation vectors and squared norm
final FieldPVCoordinates<T> bodyPV = getBody().getPVCoordinates(s.getDate(), s.getFrame());
final FieldVector3D<T> satToBody = bodyPV.getPosition().subtract(s.getPosition());
final T r2Sat = satToBody.getNormSq();
// compute relative acceleration
final T gm = parameters[0];
final T a = gm.divide(r2Sat);
return new FieldVector3D<>(a, satToBody.normalize()).add(bodyPV.getAcceleration());
}
}