TimeSpanDragForce.java
/* Copyright 2002-2020 CS GROUP
* Licensed to CS GROUP (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.
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* limitations under the License.
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package org.orekit.forces.drag;
import java.util.ArrayList;
import java.util.List;
import java.util.NavigableSet;
import java.util.stream.Stream;
import org.hipparchus.Field;
import org.hipparchus.RealFieldElement;
import org.hipparchus.analysis.differentiation.DerivativeStructure;
import org.hipparchus.analysis.differentiation.Gradient;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.ode.events.Action;
import org.hipparchus.util.MathArrays;
import org.orekit.annotation.DefaultDataContext;
import org.orekit.frames.Frame;
import org.orekit.models.earth.atmosphere.Atmosphere;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.DateDetector;
import org.orekit.propagation.events.EventDetector;
import org.orekit.propagation.events.FieldDateDetector;
import org.orekit.propagation.events.FieldEventDetector;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.time.TimeScale;
import org.orekit.time.TimeScalesFactory;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.TimeSpanMap;
import org.orekit.utils.TimeSpanMap.Span;
import org.orekit.utils.TimeSpanMap.Transition;
/** Time span atmospheric drag force model.
* <p>
* This class is closely related to {@link org.orekit.forces.drag.DragForce DragForce} class.<br>
* The difference is that it has a {@link TimeSpanMap} of {@link DragSensitive} objects as attribute
* instead of a single {@link DragSensitive} object. <br>
* The idea behind this model is to allow the user to design a drag force model that can see its physical parameters
* (drag coefficient and lift ratio) change with time, at dates chosen by the user. <br>
* </p>
* <p>
* This is a behavior that can be sought in operational orbit determination.<br>
* Indeed the solar activity has a strong influence on the local atmospheric density, and thus on the drag force effect.<br>
* Solar activity is a physical phenomenon that is difficult to model and predict. <br>
* The errors induced by this incomplete modeling can be estimated through the drag coefficients.<br>
* Being able to define and estimate drag coefficients depending on user-chosen dates in a piecewise fashion allows for
* a better modeling of solar activity uncertainties.
* </p>
* <p>
* A typical operational use case is to have a daily solar activity with three-hourly magnetic indexes provided by an
* international organization (NOAA for example).<br>
* Given this input, a user can define a piecewise drag force model with daily or three-hourly drag coefficients.<br>
* Each timed coefficient will absorb a part of the uncertainties in the solar activity and will allow for a more accurate
* orbit determination
* </p>
* <b>Usage</b>:<ul>
* <li><u>Construction</u>: constructor takes an atmospheric model and a DragSensitive model.<br>
* This last model will be your initial DragSensitive model and it will be initially valid for the whole time line.<br>
* The real validity of this first entry will be truncated as other DragSensitive models are added.
* <li><u>Time spans</u>: DragSensitive models are added using methods {@link #addDragSensitiveValidAfter(DragSensitive, AbsoluteDate)}
* or {@link #addDragSensitiveValidBefore(DragSensitive, AbsoluteDate)}.<br>
* Recommendations are the same than the ones in {@link TimeSpanMap}, meaning: <ul>
* <li>As an entry is added, it truncates the validity of the neighboring entries already present in the map;
* <li><b>The transition dates should be entered only once</b>. Repeating a transition date will lead to unexpected result and is not supported;
* <li>It is advised to order your DragSensitive models chronologically when adding them to avoid any confusion.
* </ul>
* <li><u>Naming the parameter drivers</u>: It is strongly advised to give a custom name to the {@link ParameterDriver}(s)
* of each DragSensitive model that is added to the object. This will allow you keeping track of the evolution of your models.<br>
* Different names are mandatory to differentiate the different drivers.<br>
* If you do not specify a name, a default name will be chosen. Example for the drag coefficient:<ul>
* <li>Initial DragSensitive model: the driver's default name is "{@link DragSensitive#DRAG_COEFFICIENT}";
* <li>Using {@link #addDragSensitiveValidAfter(DragSensitive, AbsoluteDate)}: the driver's default name is
* "{@link DragSensitive#DRAG_COEFFICIENT} + {@link #DATE_AFTER} + date.toString()"
* <li>Using {@link #addDragSensitiveValidBefore(DragSensitive, AbsoluteDate)}: the driver's default name is
* "{@link DragSensitive#DRAG_COEFFICIENT} + {@link #DATE_BEFORE} + date.toString()"
* </ul>
* </ul>
* <b>Example following previous recommendations</b>:<ul>
* <li>Given:
* <ul>
* <li><code>atmosphere</code>: an {@link Atmosphere atmospheric model};
* <li><code>isotropicDrag0, 1 and 2</code>: three {@link org.orekit.forces.drag.IsotropicDrag IsotropicDrag} models;
* <li><code>date</code>: an {@link AbsoluteDate}.
* </ul>
* <li>Name the drivers:<br>
* <code>isotropicDrag0.getDragParametersDrivers()[0].setName = "Cd0";</code><br>
* <code>isotropicDrag1.getDragParametersDrivers()[0].setName = "Cd1";</code><br>
* <code>isotropicDrag2.getDragParametersDrivers()[0].setName = "Cd2";</code><br>
* <li>Initialize the model: <br>
* <code>TimeSpanDragForce force = new TimeSpanDragForce(atmosphere, isotropicDrag0);</code>
* <li>Set the second and third model one Julian day apart each:<br>
* <code>force.addDragSensitiveValidAfter(isotropicDrag1, date.shiftedBy(Constants.JULIAN_DAY));</code><br>
* <code>force.addDragSensitiveValidAfter(isotropicDrag2, date.shiftedBy(2 * Constants.JULIAN_DAY));</code><br>
* <li>With this, your model will have the following properties:
* <ul>
* <li>t in ]-∞, date + 1 day [ / Cd = Cd0
* <li>t in [date + 1 day, date + 2days [ / Cd = Cd1
* <li>t in [date + 2 days, +∞ [ / Cd = Cd2
* </ul>
* </ul>
* <p>
* <b>Warning</b>:<br> The TimeSpanDragForce model is versatile and you could end up with non-physical modeling.<br>
* For example you could add 2 {@link org.orekit.forces.drag.IsotropicDrag IsotropicDrag} models with different areas,
* or one {@link org.orekit.forces.drag.IsotropicDrag IsotropicDrag} model and then one
* {@link org.orekit.forces.BoxAndSolarArraySpacecraft BoxAndSolarArraySpacecraft} model.<br>
* It is up to you to ensure that your models are consistent with each other, Orekit will not perform any check for that.
* </p>
* @author Maxime Journot
* @since 10.2
*/
public class TimeSpanDragForce extends AbstractDragForceModel {
/** Prefix for dates before in the parameter drivers' name. */
public static final String DATE_BEFORE = " - Before ";
/** Prefix for dates after in the parameter drivers' name. */
public static final String DATE_AFTER = " - After ";
/** Atmospheric model. */
private final Atmosphere atmosphere;
/** TimeSpanMap of DragSensitive objects. */
private final TimeSpanMap<DragSensitive> dragSensitiveTimeSpanMap;
/** Time scale used for the default names of the drag parameter drivers. */
private final TimeScale timeScale;
/** Constructor with default UTC time scale for the default names of the drag parameter drivers.
* @param atmosphere atmospheric model
* @param spacecraft Time scale used for the default names of the drag parameter drivers
*/
@DefaultDataContext
public TimeSpanDragForce(final Atmosphere atmosphere,
final DragSensitive spacecraft) {
super(atmosphere);
this.atmosphere = atmosphere;
this.dragSensitiveTimeSpanMap = new TimeSpanMap<>(spacecraft);
this.timeScale = TimeScalesFactory.getUTC();
}
/** Constructor.
* @param atmosphere atmospheric model
* @param spacecraft the initial object physical and geometric information
* @param timeScale Time scale used for the default names of the drag parameter drivers
*/
public TimeSpanDragForce(final Atmosphere atmosphere,
final DragSensitive spacecraft,
final TimeScale timeScale) {
super(atmosphere);
this.atmosphere = atmosphere;
this.dragSensitiveTimeSpanMap = new TimeSpanMap<>(spacecraft);
this.timeScale = timeScale;
}
/** Add a DragSensitive entry valid before a limit date.<br>
* Using <code>addDragSensitiveValidBefore(entry, t)</code> will make <code>entry</code>
* valid in ]-∞, t[ (note the open bracket).
* @param dragSensitive DragSensitive entry
* @param latestValidityDate date before which the entry is valid
* (must be different from <b>all</b> dates already used for transitions)
*/
public void addDragSensitiveValidBefore(final DragSensitive dragSensitive, final AbsoluteDate latestValidityDate) {
dragSensitiveTimeSpanMap.addValidBefore(changeDragParameterDriversNames(dragSensitive,
latestValidityDate,
DATE_BEFORE),
latestValidityDate);
}
/** Add a DragSensitive entry valid after a limit date.<br>
* Using <code>addDragSensitiveValidAfter(entry, t)</code> will make <code>entry</code>
* valid in [t, +∞[ (note the closed bracket).
* @param dragSensitive DragSensitive entry
* @param earliestValidityDate date after which the entry is valid
* (must be different from <b>all</b> dates already used for transitions)
*/
public void addDragSensitiveValidAfter(final DragSensitive dragSensitive, final AbsoluteDate earliestValidityDate) {
dragSensitiveTimeSpanMap.addValidAfter(changeDragParameterDriversNames(dragSensitive,
earliestValidityDate,
DATE_AFTER),
earliestValidityDate);
}
/** Get the {@link DragSensitive} model valid at a date.
* @param date the date of validity
* @return the DragSensitive model valid at date
*/
public DragSensitive getDragSensitive(final AbsoluteDate date) {
return dragSensitiveTimeSpanMap.get(date);
}
/** Get the {@link DragSensitive} {@link Span} containing a specified date.
* @param date date belonging to the desired time span
* @return the DragSensitive time span containing the specified date
*/
public Span<DragSensitive> getDragSensitiveSpan(final AbsoluteDate date) {
return dragSensitiveTimeSpanMap.getSpan(date);
}
/** Extract a range of the {@link DragSensitive} map.
* <p>
* The object returned will be a new independent instance that will contain
* only the transitions that lie in the specified range.
* </p>
* See the {@link TimeSpanMap#extractRange TimeSpanMap.extractRange method} for more.
* @param start earliest date at which a transition is included in the range
* (may be set to {@link AbsoluteDate#PAST_INFINITY} to keep all early transitions)
* @param end latest date at which a transition is included in the r
* (may be set to {@link AbsoluteDate#FUTURE_INFINITY} to keep all late transitions)
* @return a new TimeSpanMap instance of DragSensitive with all transitions restricted to the specified range
*/
public TimeSpanMap<DragSensitive> extractDragSensitiveRange(final AbsoluteDate start, final AbsoluteDate end) {
return dragSensitiveTimeSpanMap.extractRange(start, end);
}
/** Get the {@link Transition}s of the drag sensitive time span map.
* @return the {@link Transition}s for the drag sensitive time span map
*/
public NavigableSet<Transition<DragSensitive>> getTransitions() {
return dragSensitiveTimeSpanMap.getTransitions();
}
/** {@inheritDoc} */
@Override
public Vector3D acceleration(final SpacecraftState s, final double[] parameters) {
// Local atmospheric density
final AbsoluteDate date = s.getDate();
final Frame frame = s.getFrame();
final Vector3D position = s.getPVCoordinates().getPosition();
final double rho = atmosphere.getDensity(date, position, frame);
// Spacecraft relative velocity with respect to the atmosphere
final Vector3D vAtm = atmosphere.getVelocity(date, position, frame);
final Vector3D relativeVelocity = vAtm.subtract(s.getPVCoordinates().getVelocity());
// Extract the proper parameters valid at date from the input array
final double[] extractedParameters = extractParameters(parameters, date);
// Compute and return drag acceleration
return getDragSensitive(date).dragAcceleration(date, frame, position, s.getAttitude().getRotation(),
s.getMass(), rho, relativeVelocity, extractedParameters);
}
/** {@inheritDoc} */
@SuppressWarnings("unchecked")
@Override
public <T extends RealFieldElement<T>> FieldVector3D<T> acceleration(final FieldSpacecraftState<T> s,
final T[] parameters) {
// Local atmospheric density
final FieldAbsoluteDate<T> date = s.getDate();
final Frame frame = s.getFrame();
final FieldVector3D<T> position = s.getPVCoordinates().getPosition();
// Density and its derivatives
final T rho;
// Check for faster computation dedicated to derivatives with respect to state
// Using finite differences instead of automatic differentiation as it seems to be much
// faster for the drag's derivatives' computation
if (isGradientStateDerivative(s)) {
rho = (T) this.getGradientDensityWrtStateUsingFiniteDifferences(date.toAbsoluteDate(), frame, (FieldVector3D<Gradient>) position);
} else if (isDSStateDerivative(s)) {
rho = (T) this.getDSDensityWrtStateUsingFiniteDifferences(date.toAbsoluteDate(), frame, (FieldVector3D<DerivativeStructure>) position);
} else {
rho = atmosphere.getDensity(date, position, frame);
}
// Spacecraft relative velocity with respect to the atmosphere
final FieldVector3D<T> vAtm = atmosphere.getVelocity(date, position, frame);
final FieldVector3D<T> relativeVelocity = vAtm.subtract(s.getPVCoordinates().getVelocity());
// Extract the proper parameters valid at date from the input array
final T[] extractedParameters = extractParameters(parameters, date);
// Compute and return drag acceleration
return getDragSensitive(date.toAbsoluteDate()).dragAcceleration(date, frame, position, s.getAttitude().getRotation(),
s.getMass(), rho, relativeVelocity, extractedParameters);
}
/**{@inheritDoc}
* <p>
* A date detector is used to cleanly stop the propagator and reset
* the state derivatives at transition dates.
* </p>
*/
@Override
public Stream<EventDetector> getEventsDetectors() {
// Get the transitions' dates from the TimeSpanMap
final AbsoluteDate[] transitionDates = getTransitionDates();
// Initialize the date detector
final DateDetector datesDetector = new DateDetector(transitionDates[0]).
withMaxCheck(60.).
withHandler((SpacecraftState state, DateDetector d, boolean increasing) -> {
return Action.RESET_DERIVATIVES;
});
// Add all transitions' dates to the date detector
for (int i = 1; i < transitionDates.length; i++) {
datesDetector.addEventDate(transitionDates[i]);
}
// Return the detector
return Stream.of(datesDetector);
}
/** {@inheritDoc}
* <p>
* A date detector is used to cleanly stop the propagator and reset
* the state derivatives at transition dates.
* </p>
*/
@Override
public <T extends RealFieldElement<T>> Stream<FieldEventDetector<T>> getFieldEventsDetectors(final Field<T> field) {
// Get the transitions' dates from the TimeSpanMap
final AbsoluteDate[] transitionDates = getTransitionDates();
// Initialize the date detector
final FieldDateDetector<T> datesDetector =
new FieldDateDetector<>(new FieldAbsoluteDate<>(field, transitionDates[0])).
withMaxCheck(field.getZero().add(60.)).
withHandler((FieldSpacecraftState<T> state, FieldDateDetector<T> d, boolean increasing) -> {
return Action.RESET_DERIVATIVES;
});
// Add all transitions' dates to the date detector
for (int i = 1; i < transitionDates.length; i++) {
datesDetector.addEventDate(new FieldAbsoluteDate<>(field, transitionDates[i]));
}
// Return the detector
return Stream.of(datesDetector);
}
/** {@inheritDoc}
* <p>
* All the parameter drivers of all DragSensitive models are returned in an array.
* Models are ordered chronologically.
* </p>
*/
@Override
public ParameterDriver[] getParametersDrivers() {
// Get all transitions from the TimeSpanMap
final List<ParameterDriver> listParameterDrivers = new ArrayList<>();
final NavigableSet<Transition<DragSensitive>> dragSensitiveTransitions = getTransitions();
// Loop on the transitions
for (Transition<DragSensitive> transition : dragSensitiveTransitions) {
// Add all the "before" parameter drivers of each transition
for (ParameterDriver driver : transition.getBefore().getDragParametersDrivers()) {
// Add the driver only if the name does not exist already
if (!findByName(listParameterDrivers, driver.getName())) {
listParameterDrivers.add(driver);
}
}
}
// Finally, add the "after" parameter drivers of the last transition
for (ParameterDriver driver : dragSensitiveTransitions.last().getAfter().getDragParametersDrivers()) {
// Adds only if the name does not exist already
if (!findByName(listParameterDrivers, driver.getName())) {
listParameterDrivers.add(driver);
}
}
// Return an array of parameter drivers with no duplicated name
return listParameterDrivers.toArray(new ParameterDriver[0]);
}
/** Extract the proper parameter drivers' values from the array in input of the
* {@link #acceleration(SpacecraftState, double[]) acceleration} method.
* Parameters are filtered given an input date.
* @param parameters the input parameters array
* @param date the date
* @return the parameters given the date
*/
public double[] extractParameters(final double[] parameters, final AbsoluteDate date) {
// Get the drag parameter drivers of the date
final ParameterDriver[] dragParameterDriver = getDragSensitive(date).getDragParametersDrivers();
// Find out the indexes of the parameters in the whole array of parameters
final ParameterDriver[] allParameters = getParametersDrivers();
final double[] outParameters = new double[dragParameterDriver.length];
int index = 0;
for (int i = 0; i < allParameters.length; i++) {
final String driverName = allParameters[i].getName();
for (ParameterDriver dragDriver : dragParameterDriver) {
if (dragDriver.getName().equals(driverName)) {
outParameters[index++] = parameters[i];
}
}
}
return outParameters;
}
/** Extract the proper parameter drivers' values from the array in input of the
* {@link #acceleration(FieldSpacecraftState, RealFieldElement[]) acceleration} method.
* Parameters are filtered given an input date.
* @param parameters the input parameters array
* @param date the date
* @param <T> extends RealFieldElement
* @return the parameters given the date
*/
public <T extends RealFieldElement<T>> T[] extractParameters(final T[] parameters,
final FieldAbsoluteDate<T> date) {
// Get the drag parameter drivers of the date
final ParameterDriver[] dragPD = getDragSensitive(date.toAbsoluteDate()).getDragParametersDrivers();
// Find out the indexes of the parameters in the whole array of parameters
final ParameterDriver[] allParameters = getParametersDrivers();
final T[] outParameters = MathArrays.buildArray(date.getField(), dragPD.length);
int index = 0;
for (int i = 0; i < allParameters.length; i++) {
final String driverName = allParameters[i].getName();
for (ParameterDriver dragDriver : dragPD) {
if (dragDriver.getName().equals(driverName)) {
outParameters[index++] = parameters[i];
}
}
}
return outParameters;
}
/** Find if a parameter driver with a given name already exists in a list of parameter drivers.
* @param driversList the list of parameter drivers
* @param name the parameter driver's name to filter with
* @return true if the name was found, false otherwise
*/
private boolean findByName(final List<ParameterDriver> driversList, final String name) {
for (final ParameterDriver d : driversList) {
if (d.getName().equals(name)) {
return true;
}
}
return false;
}
/** Get the dates of the transitions for the drag sensitive models {@link TimeSpanMap}.
* @return dates of the transitions for the drag sensitive models {@link TimeSpanMap}
*/
private AbsoluteDate[] getTransitionDates() {
// Get all transitions
final List<AbsoluteDate> listDates = new ArrayList<>();
final NavigableSet<Transition<DragSensitive>> dragSensitiveTransitions = getTransitions();
// Extract all the transitions' dates
for (Transition<DragSensitive> transition : dragSensitiveTransitions) {
listDates.add(transition.getDate());
}
// Return the array of transition dates
return listDates.toArray(new AbsoluteDate[0]);
}
/** Change the parameter drivers names of a {@link DragSensitive} model, if needed.
* <p>
* This is done to avoid that several parameter drivers have the same name.<br>
* It is done only if the user hasn't modify the DragSensitive parameter drivers default names.
* </p>
* @param dragSensitive the DragSensitive model
* @param date the date used in the parameter driver's name
* @param datePrefix the date prefix used in the parameter driver's name
* @return the DragSensitive with its drivers' names changed
*/
private DragSensitive changeDragParameterDriversNames(final DragSensitive dragSensitive,
final AbsoluteDate date,
final String datePrefix) {
// Loop on the parameter drivers of the DragSensitive model
for (ParameterDriver driver: dragSensitive.getDragParametersDrivers()) {
final String driverName = driver.getName();
// If the name is the default name for DragSensitive parameter drivers
// Modify the name to add the prefix and the date
if (driverName.equals(DragSensitive.DRAG_COEFFICIENT) || driverName.equals(DragSensitive.LIFT_RATIO)) {
driver.setName(driverName + datePrefix + date.toString(timeScale));
}
}
return dragSensitive;
}
}