AbstractParametricAcceleration.java
/* Copyright 2002-2018 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
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*/
package org.orekit.forces;
import java.util.stream.Stream;
import org.hipparchus.Field;
import org.hipparchus.RealFieldElement;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.orekit.attitudes.Attitude;
import org.orekit.attitudes.AttitudeProvider;
import org.orekit.attitudes.FieldAttitude;
import org.orekit.errors.OrekitException;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.EventDetector;
import org.orekit.propagation.events.FieldEventDetector;
/** This class implements a parametric acceleration.
* <p>Parametric accelerations are intended to model lesser-known
* forces, estimating a few defining parameters from a parametric
* function using orbit determination. Typical parametric functions
* are polynomial (often limited to a constant term) and harmonic
* (often with either orbital period or half orbital period).</p>
* <p>An important operational example is the infamous GPS Y-bias,
* which is thought to be related to a radiator thermal radiation.
* Other examples could be to model leaks that produce roughly constant
* trust in some spacecraft-related direction.</p>
* <p>The acceleration direction is considered constant in either:
* </p>
* <ul>
* <li>inertial frame</li>
* <li>spacecraft frame</li>
* <li>a dedicated attitude frame overriding spacecraft attitude
* (this could for example be used to model solar arrays orientation
* if the force is related to solar arrays)</li>
* </ul>
* <p>
* If the direction of the acceleration is unknown, then three instances
* of this class should be used, one along the X axis, one along the Y
* axis and one along the Z axis and their parameters estimated as usual.
* </p>
* @since 9.0
* @author Luc Maisonobe
*/
public abstract class AbstractParametricAcceleration extends AbstractForceModel {
/** Direction of the acceleration in defining frame. */
private final Vector3D direction;
/** Flag for inertial acceleration direction. */
private final boolean isInertial;
/** The attitude to override, if set. */
private final AttitudeProvider attitudeOverride;
/** Simple constructor.
* @param direction acceleration direction in overridden spacecraft frame
* @param isInertial if true, direction is defined in the same inertial
* frame used for propagation (i.e. {@link SpacecraftState#getFrame()}),
* otherwise direction is defined in spacecraft frame (i.e. using the
* propagation {@link
* org.orekit.propagation.Propagator#setAttitudeProvider(AttitudeProvider)
* attitude law})
* @param attitudeOverride provider for attitude used to compute acceleration
* direction
*/
protected AbstractParametricAcceleration(final Vector3D direction, final boolean isInertial,
final AttitudeProvider attitudeOverride) {
this.direction = direction;
this.isInertial = isInertial;
this.attitudeOverride = attitudeOverride;
}
/** Check if direction is inertial.
* @return true if direction is inertial
*/
protected boolean isInertial() {
return isInertial;
}
/** Compute the signed amplitude of the acceleration.
* <p>
* The acceleration is the direction multiplied by the signed amplitude. So if
* signed amplitude is negative, the acceleratin is towards the opposite of the
* direction specified at construction.
* </p>
* @param state current state information: date, kinematics, attitude
* @param parameters values of the force model parameters
* @return norm of the acceleration
*/
protected abstract double signedAmplitude(SpacecraftState state, double[] parameters);
/** Compute the signed amplitude of the acceleration.
* <p>
* The acceleration is the direction multiplied by the signed amplitude. So if
* signed amplitude is negative, the acceleratin is towards the opposite of the
* direction specified at construction.
* </p>
* @param state current state information: date, kinematics, attitude
* @param parameters values of the force model parameters
* @param <T> type of the elements
* @return norm of the acceleration
*/
protected abstract <T extends RealFieldElement<T>> T signedAmplitude(FieldSpacecraftState<T> state, T[] parameters);
/** {@inheritDoc} */
@Override
public Vector3D acceleration(final SpacecraftState state, final double[] parameters)
throws OrekitException {
final Vector3D inertialDirection;
if (isInertial) {
// the acceleration direction is already defined in the inertial frame
inertialDirection = direction;
} else {
final Attitude attitude;
if (attitudeOverride == null) {
// the acceleration direction is defined in spacecraft frame as set by the propagator
attitude = state.getAttitude();
} else {
// the acceleration direction is defined in a dedicated frame
attitude = attitudeOverride.getAttitude(state.getOrbit(), state.getDate(), state.getFrame());
}
inertialDirection = attitude.getRotation().applyInverseTo(direction);
}
return new Vector3D(signedAmplitude(state, parameters), inertialDirection);
}
/** {@inheritDoc} */
@Override
public <T extends RealFieldElement<T>> FieldVector3D<T> acceleration(final FieldSpacecraftState<T> state,
final T[] parameters)
throws OrekitException {
final FieldVector3D<T> inertialDirection;
if (isInertial) {
// the acceleration direction is already defined in the inertial frame
inertialDirection = new FieldVector3D<>(state.getDate().getField(), direction);
} else {
final FieldAttitude<T> attitude;
if (attitudeOverride == null) {
// the acceleration direction is defined in spacecraft frame as set by the propagator
attitude = state.getAttitude();
} else {
// the acceleration direction is defined in a dedicated frame
attitude = attitudeOverride.getAttitude(state.getOrbit(), state.getDate(), state.getFrame());
}
inertialDirection = attitude.getRotation().applyInverseTo(direction);
}
return new FieldVector3D<>(signedAmplitude(state, parameters), inertialDirection);
}
/** {@inheritDoc} */
@Override
public Stream<EventDetector> getEventsDetectors() {
return Stream.empty();
}
/** {@inheritDoc} */
@Override
public <T extends RealFieldElement<T>> Stream<FieldEventDetector<T>> getFieldEventsDetectors(final Field<T> field) {
return Stream.empty();
}
}