KeplerianPropagator.java

  1. /* Copyright 2002-2024 CS GROUP
  2.  * Licensed to CS GROUP (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *   http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.orekit.propagation.analytical;

  19. import org.hipparchus.linear.RealMatrix;
  20. import org.orekit.attitudes.Attitude;
  21. import org.orekit.attitudes.AttitudeProvider;
  22. import org.orekit.attitudes.FrameAlignedProvider;
  23. import org.orekit.orbits.Orbit;
  24. import org.orekit.orbits.OrbitType;
  25. import org.orekit.orbits.PositionAngleType;
  26. import org.orekit.propagation.AbstractMatricesHarvester;
  27. import org.orekit.propagation.SpacecraftState;
  28. import org.orekit.time.AbsoluteDate;
  29. import org.orekit.utils.DoubleArrayDictionary;
  30. import org.orekit.utils.TimeSpanMap;

  32. /** Simple Keplerian orbit propagator.
  33.  * @see Orbit
  34.  * @author Guylaine Prat
  35.  */
  36. public class KeplerianPropagator extends AbstractAnalyticalPropagator {

  38.     /** All states. */
  39.     private TimeSpanMap<SpacecraftState> states;

  41.     /** Build a propagator from orbit only.
  42.      * <p>The central attraction coefficient μ is set to the same value used
  43.      * for the initial orbit definition. Mass and attitude provider are set to
  44.      * unspecified non-null arbitrary values.</p>
  45.      *
  46.      * @param initialOrbit initial orbit
  47.      * @see #KeplerianPropagator(Orbit, AttitudeProvider)
  48.      */
  49.     public KeplerianPropagator(final Orbit initialOrbit) {
  50.         this(initialOrbit, FrameAlignedProvider.of(initialOrbit.getFrame()),
  51.              initialOrbit.getMu(), DEFAULT_MASS);
  52.     }

  54.     /** Build a propagator from orbit and central attraction coefficient μ.
  55.      * <p>Mass and attitude provider are set to unspecified non-null arbitrary values.</p>
  56.      *
  57.      * @param initialOrbit initial orbit
  58.      * @param mu central attraction coefficient (m³/s²)
  59.      * @see #KeplerianPropagator(Orbit, AttitudeProvider, double)
  60.      */
  61.     public KeplerianPropagator(final Orbit initialOrbit, final double mu) {
  62.         this(initialOrbit, FrameAlignedProvider.of(initialOrbit.getFrame()),
  63.              mu, DEFAULT_MASS);
  64.     }

  66.     /** Build a propagator from orbit and attitude provider.
  67.      * <p>The central attraction coefficient μ is set to the same value
  68.      * used for the initial orbit definition. Mass is set to an unspecified
  69.      * non-null arbitrary value.</p>
  70.      * @param initialOrbit initial orbit
  71.      * @param attitudeProv  attitude provider
  72.      */
  73.     public KeplerianPropagator(final Orbit initialOrbit,
  74.                                final AttitudeProvider attitudeProv) {
  75.         this(initialOrbit, attitudeProv, initialOrbit.getMu(), DEFAULT_MASS);
  76.     }

  78.     /** Build a propagator from orbit, attitude provider and central attraction
  79.      * coefficient μ.
  80.      * <p>Mass is set to an unspecified non-null arbitrary value.</p>
  81.      * @param initialOrbit initial orbit
  82.      * @param attitudeProv attitude provider
  83.      * @param mu central attraction coefficient (m³/s²)
  84.      */
  85.     public KeplerianPropagator(final Orbit initialOrbit,
  86.                                final AttitudeProvider attitudeProv,
  87.                                final double mu) {
  88.         this(initialOrbit, attitudeProv, mu, DEFAULT_MASS);
  89.     }

  91.     /** Build propagator from orbit, attitude provider, central attraction
  92.      * coefficient μ and mass.
  93.      * @param initialOrbit initial orbit
  94.      * @param attitudeProv attitude provider
  95.      * @param mu central attraction coefficient (m³/s²)
  96.      * @param mass spacecraft mass (kg)
  97.      */
  98.     public KeplerianPropagator(final Orbit initialOrbit, final AttitudeProvider attitudeProv,
  99.                                final double mu, final double mass) {

  101.         super(attitudeProv);

  103.         // ensure the orbit use the specified mu and has no non-Keplerian derivatives
  104.         final SpacecraftState initial = fixState(initialOrbit,
  105.                                                  getAttitudeProvider().getAttitude(initialOrbit,
  106.                                                                                    initialOrbit.getDate(),
  107.                                                                                    initialOrbit.getFrame()),
  108.                                                  mass, mu, null, null);
  109.         states = new TimeSpanMap<SpacecraftState>(initial);
  110.         super.resetInitialState(initial);

  112.     }

  114.     /** Fix state to use a specified mu and remove derivatives.
  115.      * <p>
  116.      * This ensures the propagation model (which is based on calling
  117.      * {@link Orbit#shiftedBy(double)}) is Keplerian only and uses a specified mu.
  118.      * </p>
  119.      * @param orbit orbit to fix
  120.      * @param attitude current attitude
  121.      * @param mass current mass
  122.      * @param mu gravity coefficient to use
  123.      * @param additionalStates additional states (may be null)
  124.      * @param additionalStatesDerivatives additional states derivatives (may be null)
  125.      * @return fixed orbit
  126.      */
  127.     private SpacecraftState fixState(final Orbit orbit, final Attitude attitude, final double mass, final double mu,
  128.                                      final DoubleArrayDictionary additionalStates,
  129.                                      final DoubleArrayDictionary additionalStatesDerivatives) {
  130.         final OrbitType type = orbit.getType();
  131.         final double[] stateVector = new double[6];
  132.         final PositionAngleType positionAngleType = PositionAngleType.MEAN;
  133.         type.mapOrbitToArray(orbit, positionAngleType, stateVector, null);
  134.         final Orbit fixedOrbit = type.mapArrayToOrbit(stateVector, null, positionAngleType,
  135.                                                       orbit.getDate(), mu, orbit.getFrame());
  136.         SpacecraftState fixedState = new SpacecraftState(fixedOrbit, attitude, mass);
  137.         if (additionalStates != null) {
  138.             for (final DoubleArrayDictionary.Entry entry : additionalStates.getData()) {
  139.                 fixedState = fixedState.addAdditionalState(entry.getKey(), entry.getValue());
  140.             }
  141.         }
  142.         if (additionalStatesDerivatives != null) {
  143.             for (final DoubleArrayDictionary.Entry entry : additionalStatesDerivatives.getData()) {
  144.                 fixedState = fixedState.addAdditionalStateDerivative(entry.getKey(), entry.getValue());
  145.             }
  146.         }
  147.         return fixedState;
  148.     }

  150.     /** {@inheritDoc} */
  151.     public void resetInitialState(final SpacecraftState state) {

  153.         // ensure the orbit use the specified mu and has no non-Keplerian derivatives
  154.         final SpacecraftState formerInitial = getInitialState();
  155.         final double mu = formerInitial == null ? state.getMu() : formerInitial.getMu();
  156.         final SpacecraftState fixedState = fixState(state.getOrbit(),
  157.                                                     state.getAttitude(),
  158.                                                     state.getMass(),
  159.                                                     mu,
  160.                                                     state.getAdditionalStatesValues(),
  161.                                                     state.getAdditionalStatesDerivatives());

  163.         states = new TimeSpanMap<SpacecraftState>(fixedState);
  164.         super.resetInitialState(fixedState);

  166.     }

  168.     /** {@inheritDoc} */
  169.     protected void resetIntermediateState(final SpacecraftState state, final boolean forward) {
  170.         if (forward) {
  171.             states.addValidAfter(state, state.getDate(), false);
  172.         } else {
  173.             states.addValidBefore(state, state.getDate(), false);
  174.         }
  175.         stateChanged(state);
  176.     }

  178.     /** {@inheritDoc} */
  179.     protected Orbit propagateOrbit(final AbsoluteDate date) {

  181.         // propagate orbit
  182.         Orbit orbit = states.get(date).getOrbit();
  183.         do {
  184.             // we use a loop here to compensate for very small date shifts error
  185.             // that occur with long propagation time
  186.             orbit = orbit.shiftedBy(date.durationFrom(orbit.getDate()));
  187.         } while (!date.equals(orbit.getDate()));

  189.         return orbit;

  191.     }

  193.     /** {@inheritDoc}*/
  194.     protected double getMass(final AbsoluteDate date) {
  195.         return states.get(date).getMass();
  196.     }

  198.     /** {@inheritDoc} */
  199.     @Override
  200.     protected AbstractMatricesHarvester createHarvester(final String stmName, final RealMatrix initialStm,
  201.                                                         final DoubleArrayDictionary initialJacobianColumns) {
  202.         // Create the harvester
  203.         final KeplerianHarvester harvester = new KeplerianHarvester(this, stmName, initialStm, initialJacobianColumns);
  204.         // Update the list of additional state provider
  205.         addAdditionalStateProvider(harvester);
  206.         // Return the configured harvester
  207.         return harvester;
  208.     }

  210. }
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