KeplerianPropagator.java
/* Copyright 2002-2019 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
* limitations under the License.
*/
package org.orekit.propagation.analytical;
import java.io.NotSerializableException;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.SortedSet;
import org.orekit.attitudes.Attitude;
import org.orekit.attitudes.AttitudeProvider;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitInternalError;
import org.orekit.orbits.Orbit;
import org.orekit.orbits.OrbitType;
import org.orekit.orbits.PositionAngle;
import org.orekit.propagation.AdditionalStateProvider;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.TimeSpanMap;
/** Simple Keplerian orbit propagator.
* @see Orbit
* @author Guylaine Prat
*/
public class KeplerianPropagator extends AbstractAnalyticalPropagator implements Serializable {
/** Serializable UID. */
private static final long serialVersionUID = 20151117L;
/** Initial state. */
private SpacecraftState initialState;
/** All states. */
private transient TimeSpanMap<SpacecraftState> states;
/** Build a propagator from orbit only.
* <p>The central attraction coefficient μ is set to the same value used
* for the initial orbit definition. Mass and attitude provider are set to
* unspecified non-null arbitrary values.</p>
* @param initialOrbit initial orbit
*/
public KeplerianPropagator(final Orbit initialOrbit) {
this(initialOrbit, DEFAULT_LAW, initialOrbit.getMu(), DEFAULT_MASS);
}
/** Build a propagator from orbit and central attraction coefficient μ.
* <p>Mass and attitude provider are set to unspecified non-null arbitrary values.</p>
* @param initialOrbit initial orbit
* @param mu central attraction coefficient (m³/s²)
*/
public KeplerianPropagator(final Orbit initialOrbit, final double mu) {
this(initialOrbit, DEFAULT_LAW, mu, DEFAULT_MASS);
}
/** Build a propagator from orbit and attitude provider.
* <p>The central attraction coefficient μ is set to the same value
* used for the initial orbit definition. Mass is set to an unspecified
* non-null arbitrary value.</p>
* @param initialOrbit initial orbit
* @param attitudeProv attitude provider
*/
public KeplerianPropagator(final Orbit initialOrbit,
final AttitudeProvider attitudeProv) {
this(initialOrbit, attitudeProv, initialOrbit.getMu(), DEFAULT_MASS);
}
/** Build a propagator from orbit, attitude provider and central attraction
* coefficient μ.
* <p>Mass is set to an unspecified non-null arbitrary value.</p>
* @param initialOrbit initial orbit
* @param attitudeProv attitude provider
* @param mu central attraction coefficient (m³/s²)
*/
public KeplerianPropagator(final Orbit initialOrbit,
final AttitudeProvider attitudeProv,
final double mu) {
this(initialOrbit, attitudeProv, mu, DEFAULT_MASS);
}
/** Build propagator from orbit, attitude provider, central attraction
* coefficient μ and mass.
* @param initialOrbit initial orbit
* @param attitudeProv attitude provider
* @param mu central attraction coefficient (m³/s²)
* @param mass spacecraft mass (kg)
*/
public KeplerianPropagator(final Orbit initialOrbit, final AttitudeProvider attitudeProv,
final double mu, final double mass) {
super(attitudeProv);
// ensure the orbit use the specified mu and has no non-Keplerian derivatives
initialState = fixState(initialOrbit,
getAttitudeProvider().getAttitude(initialOrbit,
initialOrbit.getDate(),
initialOrbit.getFrame()),
mass, mu, Collections.emptyMap());
states = new TimeSpanMap<SpacecraftState>(initialState);
super.resetInitialState(initialState);
}
/** Fix state to use a specified mu and remove derivatives.
* <p>
* This ensures the propagation model (which is based on calling
* {@link Orbit#shiftedBy(double)}) is Keplerian only and uses a specified mu.
* </p>
* @param orbit orbit to fix
* @param attitude current attitude
* @param mass current mass
* @param mu gravity coefficient to use
* @param additionalStates additional states
* @return fixed orbit
*/
private SpacecraftState fixState(final Orbit orbit, final Attitude attitude, final double mass,
final double mu, final Map<String, double[]> additionalStates) {
final OrbitType type = orbit.getType();
final double[] stateVector = new double[6];
type.mapOrbitToArray(orbit, PositionAngle.TRUE, stateVector, null);
final Orbit fixedOrbit = type.mapArrayToOrbit(stateVector, null, PositionAngle.TRUE,
orbit.getDate(), mu, orbit.getFrame());
SpacecraftState fixedState = new SpacecraftState(fixedOrbit, attitude, mass);
for (final Map.Entry<String, double[]> entry : additionalStates.entrySet()) {
fixedState = fixedState.addAdditionalState(entry.getKey(), entry.getValue());
}
return fixedState;
}
/** {@inheritDoc} */
public void resetInitialState(final SpacecraftState state) {
// ensure the orbit use the specified mu and has no non-Keplerian derivatives
final double mu = initialState == null ? state.getMu() : initialState.getMu();
final SpacecraftState fixedState = fixState(state.getOrbit(),
state.getAttitude(),
state.getMass(),
mu,
state.getAdditionalStates());
initialState = fixedState;
states = new TimeSpanMap<SpacecraftState>(initialState);
super.resetInitialState(fixedState);
}
/** {@inheritDoc} */
protected void resetIntermediateState(final SpacecraftState state, final boolean forward) {
if (forward) {
states.addValidAfter(state, state.getDate());
} else {
states.addValidBefore(state, state.getDate());
}
}
/** {@inheritDoc} */
protected Orbit propagateOrbit(final AbsoluteDate date) {
// propagate orbit
Orbit orbit = states.get(date).getOrbit();
do {
// we use a loop here to compensate for very small date shifts error
// that occur with long propagation time
orbit = orbit.shiftedBy(date.durationFrom(orbit.getDate()));
} while (!date.equals(orbit.getDate()));
return orbit;
}
/** {@inheritDoc}*/
protected double getMass(final AbsoluteDate date) {
return states.get(date).getMass();
}
/** Replace the instance with a data transfer object for serialization.
* @return data transfer object that will be serialized
* @exception NotSerializableException if an additional state provider is not serializable
*/
private Object writeReplace() throws NotSerializableException {
try {
// managed states providers
final List<AdditionalStateProvider> serializableProviders = new ArrayList<AdditionalStateProvider>();
for (final AdditionalStateProvider provider : getAdditionalStateProviders()) {
if (provider instanceof Serializable) {
serializableProviders.add(provider);
} else {
throw new NotSerializableException(provider.getClass().getName());
}
}
// states transitions
final AbsoluteDate[] transitionDates;
final SpacecraftState[] allStates;
final SortedSet<TimeSpanMap.Transition<SpacecraftState>> transitions = states.getTransitions();
if (transitions.size() == 1 && transitions.first().getBefore() == transitions.first().getAfter()) {
// the single entry is a dummy one, without a real transition
// we ignore it completely
transitionDates = null;
allStates = null;
} else {
transitionDates = new AbsoluteDate[transitions.size()];
allStates = new SpacecraftState[transitions.size() + 1];
int i = 0;
for (final TimeSpanMap.Transition<SpacecraftState> transition : transitions) {
if (i == 0) {
// state before the first transition
allStates[i] = transition.getBefore();
}
transitionDates[i] = transition.getDate();
allStates[++i] = transition.getAfter();
}
}
return new DataTransferObject(getInitialState().getOrbit(), getAttitudeProvider(),
getInitialState().getMu(), getInitialState().getMass(),
transitionDates, allStates,
serializableProviders.toArray(new AdditionalStateProvider[serializableProviders.size()]));
} catch (OrekitException orekitException) {
// this should never happen
throw new OrekitInternalError(null);
}
}
/** Internal class used only for serialization. */
private static class DataTransferObject implements Serializable {
/** Serializable UID. */
private static final long serialVersionUID = 20151202L;
/** Initial orbit. */
private final Orbit orbit;
/** Attitude provider. */
private final AttitudeProvider attitudeProvider;
/** Central attraction coefficient (m³/s²). */
private final double mu;
/** Spacecraft mass (kg). */
private final double mass;
/** Transition dates (may be null). */
private final AbsoluteDate[] transitionDates;
/** States before and after transitions (may be null). */
private final SpacecraftState[] allStates;
/** Providers for additional states. */
private final AdditionalStateProvider[] providers;
/** Simple constructor.
* @param orbit initial orbit
* @param attitudeProvider attitude provider
* @param mu central attraction coefficient (m³/s²)
* @param mass initial spacecraft mass (kg)
* @param transitionDates transition dates (may be null)
* @param allStates states before and after transitions (may be null)
* @param providers providers for additional states
*/
DataTransferObject(final Orbit orbit,
final AttitudeProvider attitudeProvider,
final double mu, final double mass,
final AbsoluteDate[] transitionDates,
final SpacecraftState[] allStates,
final AdditionalStateProvider[] providers) {
this.orbit = orbit;
this.attitudeProvider = attitudeProvider;
this.mu = mu;
this.mass = mass;
this.transitionDates = transitionDates;
this.allStates = allStates;
this.providers = providers;
}
/** Replace the deserialized data transfer object with a {@link KeplerianPropagator}.
* @return replacement {@link KeplerianPropagator}
*/
private Object readResolve() {
try {
final KeplerianPropagator propagator =
new KeplerianPropagator(orbit, attitudeProvider, mu, mass);
for (final AdditionalStateProvider provider : providers) {
propagator.addAdditionalStateProvider(provider);
}
if (transitionDates != null) {
// override the state transitions
propagator.states = new TimeSpanMap<SpacecraftState>(allStates[0]);
for (int i = 0; i < transitionDates.length; ++i) {
propagator.states.addValidAfter(allStates[i + 1], transitionDates[i]);
}
}
return propagator;
} catch (OrekitException oe) {
throw new OrekitInternalError(oe);
}
}
}
}