ParametricAcceleration.java
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* Unless required by applicable law or agreed to in writing, software
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package org.orekit.forces.empirical;
import java.util.List;
import java.util.stream.Stream;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.Field;
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.orekit.attitudes.AttitudeProvider;
import org.orekit.forces.ForceModel;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.EventDetector;
import org.orekit.propagation.events.FieldEventDetector;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.ParameterDriver;
/** 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 10.3
* @author Luc Maisonobe
* @author Bryan Cazabonne
* @author Melina Vanel
*/
public class ParametricAcceleration implements ForceModel {
/** 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;
/** Acceleration model. */
private final AccelerationModel accelerationModel;
/** 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 accelerationModel acceleration model used to compute the contribution of the empirical acceleration
* direction
*/
public ParametricAcceleration(final Vector3D direction,
final boolean isInertial,
final AccelerationModel accelerationModel) {
this(direction, isInertial, null, accelerationModel);
}
/** Simple constructor.
* @param direction acceleration direction in overridden spacecraft frame
* 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
* @param accelerationModel acceleration model used to compute the contribution of the empirical acceleration
* direction
*/
public ParametricAcceleration(final Vector3D direction,
final AttitudeProvider attitudeOverride,
final AccelerationModel accelerationModel) {
this(direction, false, attitudeOverride, accelerationModel);
}
/** 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
* @param accelerationModel acceleration model used to compute the contribution of the empirical acceleration
* direction
*/
private ParametricAcceleration(final Vector3D direction,
final boolean isInertial,
final AttitudeProvider attitudeOverride,
final AccelerationModel accelerationModel) {
this.direction = direction;
this.isInertial = isInertial;
this.attitudeOverride = attitudeOverride;
this.accelerationModel = accelerationModel;
}
/** {@inheritDoc} */
@Override
public boolean dependsOnPositionOnly() {
return isInertial;
}
/** {@inheritDoc} */
@Override
public List<ParameterDriver> getParametersDrivers() {
return accelerationModel.getParametersDrivers();
}
/** {@inheritDoc} */
@Override
public void init(final SpacecraftState initialState, final AbsoluteDate target) {
accelerationModel.init(initialState, target);
}
/** {@inheritDoc} */
@Override
public Vector3D acceleration(final SpacecraftState state,
final double[] parameters) {
// Date
final AbsoluteDate date = state.getDate();
final Vector3D inertialDirection;
if (isInertial) {
// the acceleration direction is already defined in the inertial frame
inertialDirection = direction;
} else {
final Rotation rotation;
if (attitudeOverride == null) {
// the acceleration direction is defined in spacecraft frame as set by the propagator
rotation = state.getAttitude().getRotation();
} else {
// the acceleration direction is defined in a dedicated frame
rotation = attitudeOverride.getAttitudeRotation(state.getOrbit(), date, state.getFrame());
}
inertialDirection = rotation.applyInverseTo(direction);
}
// Call the acceleration model to compute the acceleration
return new Vector3D(accelerationModel.signedAmplitude(state, parameters), inertialDirection);
}
/** {@inheritDoc} */
@Override
public <T extends CalculusFieldElement<T>> FieldVector3D<T> acceleration(final FieldSpacecraftState<T> state,
final T[] parameters) {
// Date
final FieldAbsoluteDate<T> date = state.getDate();
final FieldVector3D<T> inertialDirection;
if (isInertial) {
// the acceleration direction is already defined in the inertial frame
inertialDirection = new FieldVector3D<>(date.getField(), direction);
} else {
final FieldRotation<T> rotation;
if (attitudeOverride == null) {
// the acceleration direction is defined in spacecraft frame as set by the propagator
rotation = state.getAttitude().getRotation();
} else {
// the acceleration direction is defined in a dedicated frame
rotation = attitudeOverride.getAttitudeRotation(state.getOrbit(), date, state.getFrame());
}
inertialDirection = rotation.applyInverseTo(direction);
}
// Call the acceleration model to compute the acceleration
return new FieldVector3D<>(accelerationModel.signedAmplitude(state, parameters), inertialDirection);
}
/** {@inheritDoc} */
@Override
public Stream<EventDetector> getEventDetectors() {
return Stream.empty();
}
/** {@inheritDoc} */
@Override
public <T extends CalculusFieldElement<T>> Stream<FieldEventDetector<T>> getFieldEventDetectors(final Field<T> field) {
return Stream.empty();
}
}