FieldKeplerianPropagator.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;


  20. import java.util.Collections;
  21. import java.util.List;

  23. import org.hipparchus.CalculusFieldElement;
  24. import org.hipparchus.util.MathArrays;
  25. import org.orekit.attitudes.AttitudeProvider;
  26. import org.orekit.attitudes.FieldAttitude;
  27. import org.orekit.attitudes.FrameAlignedProvider;
  28. import org.orekit.orbits.FieldOrbit;
  29. import org.orekit.orbits.Orbit;
  30. import org.orekit.orbits.OrbitType;
  31. import org.orekit.orbits.PositionAngleType;
  32. import org.orekit.propagation.FieldSpacecraftState;
  33. import org.orekit.time.FieldAbsoluteDate;
  34. import org.orekit.utils.FieldArrayDictionary;
  35. import org.orekit.utils.FieldTimeSpanMap;
  36. import org.orekit.utils.ParameterDriver;

  38. /** Simple Keplerian orbit propagator.
  39.  * @see FieldOrbit
  40.  * @author Guylaine Prat
  41.  * @param <T> type of the field elements
  42.  */
  43. public class FieldKeplerianPropagator<T extends CalculusFieldElement<T>> extends FieldAbstractAnalyticalPropagator<T> {


  46.     /** All states. */
  47.     private transient FieldTimeSpanMap<FieldSpacecraftState<T>, T> states;

  49.     /** Build a propagator from orbit only.
  50.      * <p>The central attraction coefficient μ is set to the same value used
  51.      * for the initial orbit definition. Mass and attitude provider are set to
  52.      * unspecified non-null arbitrary values.</p>
  53.      *
  54.      * @param initialFieldOrbit initial orbit
  55.      * @see #FieldKeplerianPropagator(FieldOrbit, AttitudeProvider)
  56.      */
  57.     public FieldKeplerianPropagator(final FieldOrbit<T> initialFieldOrbit) {
  58.         this(initialFieldOrbit, FrameAlignedProvider.of(initialFieldOrbit.getFrame()),
  59.              initialFieldOrbit.getMu(), initialFieldOrbit.getA().getField().getZero().newInstance(DEFAULT_MASS));
  60.     }

  62.     /** Build a propagator from orbit and central attraction coefficient μ.
  63.      * <p>Mass and attitude provider are set to unspecified non-null arbitrary values.</p>
  64.      *
  65.      * @param initialFieldOrbit initial orbit
  66.      * @param mu central attraction coefficient (m³/s²)
  67.      * @see #FieldKeplerianPropagator(FieldOrbit, AttitudeProvider, CalculusFieldElement)
  68.      */
  69.     public FieldKeplerianPropagator(final FieldOrbit<T> initialFieldOrbit, final T mu) {
  70.         this(initialFieldOrbit, FrameAlignedProvider.of(initialFieldOrbit.getFrame()),
  71.              mu, initialFieldOrbit.getA().getField().getZero().newInstance(DEFAULT_MASS));
  72.     }

  74.     /** Build a propagator from orbit and attitude provider.
  75.      * <p>The central attraction coefficient μ is set to the same value
  76.      * used for the initial orbit definition. Mass is set to an unspecified
  77.      * non-null arbitrary value.</p>
  78.      * @param initialFieldOrbit initial orbit
  79.      * @param attitudeProv  attitude provider
  80.      */
  81.     public FieldKeplerianPropagator(final FieldOrbit<T> initialFieldOrbit,
  82.                                     final AttitudeProvider attitudeProv) {
  83.         this(initialFieldOrbit, attitudeProv, initialFieldOrbit.getMu(),
  84.                 initialFieldOrbit.getA().getField().getZero().newInstance(DEFAULT_MASS));
  85.     }

  87.     /** Build a propagator from orbit, attitude provider and central attraction
  88.      * coefficient μ.
  89.      * <p>Mass is set to an unspecified non-null arbitrary value.</p>
  90.      * @param initialFieldOrbit initial orbit
  91.      * @param attitudeProv attitude provider
  92.      * @param mu central attraction coefficient (m³/s²)
  93.      */
  94.     public FieldKeplerianPropagator(final FieldOrbit<T> initialFieldOrbit,
  95.                                     final AttitudeProvider attitudeProv,
  96.                                     final T mu) {
  97.         this(initialFieldOrbit, attitudeProv, mu, initialFieldOrbit.getA().getField().getZero().newInstance(DEFAULT_MASS));
  98.     }

  100.     /** Build propagator from orbit, attitude provider, central attraction
  101.      * coefficient μ and mass.
  102.      * @param initialOrbit initial orbit
  103.      * @param attitudeProv attitude provider
  104.      * @param mu central attraction coefficient (m³/s²)
  105.      * @param mass spacecraft mass (kg)
  106.      */
  107.     public FieldKeplerianPropagator(final FieldOrbit<T> initialOrbit, final AttitudeProvider attitudeProv,
  108.                                     final T mu, final T mass) {

  110.         super(initialOrbit.getA().getField(), attitudeProv);

  112.         // ensure the orbit use the specified mu and has no non-Keplerian derivatives
  113.         final FieldSpacecraftState<T> initial = fixState(initialOrbit,
  114.                                                          getAttitudeProvider().getAttitude(initialOrbit,
  115.                                                                                            initialOrbit.getDate(),
  116.                                                                                            initialOrbit.getFrame()),
  117.                                                          mass, mu, null, null);
  118.         states = new FieldTimeSpanMap<>(initial, initialOrbit.getA().getField());
  119.         super.resetInitialState(initial);
  120.     }

  122.     /** Fix state to use a specified mu and remove derivatives.
  123.      * <p>
  124.      * This ensures the propagation model (which is based on calling
  125.      * {@link Orbit#shiftedBy(double)}) is Keplerian only and uses a specified mu.
  126.      * </p>
  127.      * @param orbit orbit to fix
  128.      * @param attitude current attitude
  129.      * @param mass current mass
  130.      * @param mu gravity coefficient to use
  131.      * @param additionalStates additional states (may be null)
  132.      * @param additionalStatesderivatives additional states derivatives (may be null)
  133.      * @return fixed orbit
  134.      */
  135.     private FieldSpacecraftState<T> fixState(final FieldOrbit<T> orbit, final FieldAttitude<T> attitude, final T mass, final T mu,
  136.                                              final FieldArrayDictionary<T> additionalStates,
  137.                                              final FieldArrayDictionary<T> additionalStatesderivatives) {
  138.         final OrbitType type = orbit.getType();
  139.         final T[] stateVector = MathArrays.buildArray(mass.getField(), 6);
  140.         final PositionAngleType positionAngleType = PositionAngleType.MEAN;
  141.         type.mapOrbitToArray(orbit, positionAngleType, stateVector, null);
  142.         final FieldOrbit<T> fixedOrbit = type.mapArrayToOrbit(stateVector, null, positionAngleType,
  143.                                                               orbit.getDate(), mu, orbit.getFrame());
  144.         FieldSpacecraftState<T> fixedState = new FieldSpacecraftState<>(fixedOrbit, attitude, mass);
  145.         if (additionalStates != null) {
  146.             for (final FieldArrayDictionary<T>.Entry entry : additionalStates.getData()) {
  147.                 fixedState = fixedState.addAdditionalState(entry.getKey(), entry.getValue());
  148.             }
  149.         }
  150.         if (additionalStatesderivatives != null) {
  151.             for (final FieldArrayDictionary<T>.Entry entry : additionalStatesderivatives.getData()) {
  152.                 fixedState = fixedState.addAdditionalStateDerivative(entry.getKey(), entry.getValue());
  153.             }
  154.         }
  155.         return fixedState;
  156.     }

  158.     /** {@inheritDoc} */
  159.     public void resetInitialState(final FieldSpacecraftState<T> state) {

  161.         // ensure the orbit use the specified mu and has no non-Keplerian derivatives
  162.         final FieldSpacecraftState<T> formerInitial = getInitialState();
  163.         final T mu = formerInitial == null ? state.getMu() : formerInitial.getMu();
  164.         final FieldSpacecraftState<T> fixedState = fixState(state.getOrbit(),
  165.                                                             state.getAttitude(),
  166.                                                             state.getMass(),
  167.                                                             mu,
  168.                                                             state.getAdditionalStatesValues(),
  169.                                                             state.getAdditionalStatesDerivatives());

  171.         states = new FieldTimeSpanMap<>(fixedState, state.getDate().getField());
  172.         super.resetInitialState(fixedState);

  174.     }

  176.     /** {@inheritDoc} */
  177.     protected void resetIntermediateState(final FieldSpacecraftState<T> state, final boolean forward) {
  178.         if (forward) {
  179.             states.addValidAfter(state, state.getDate());
  180.         } else {
  181.             states.addValidBefore(state, state.getDate());
  182.         }
  183.         stateChanged(state);
  184.     }

  186.     /** {@inheritDoc} */
  187.     protected FieldOrbit<T> propagateOrbit(final FieldAbsoluteDate<T> date, final T[] parameters) {
  188.         // propagate orbit
  189.         FieldOrbit<T> orbit = states.get(date).getOrbit();
  190.         do {
  191.             // we use a loop here to compensate for very small date shifts error
  192.             // that occur with long propagation time
  193.             orbit = orbit.shiftedBy(date.durationFrom(orbit.getDate()));
  194.         } while (!date.equals(orbit.getDate()));
  195.         return orbit;
  196.     }

  198.     /** {@inheritDoc}*/
  199.     protected T getMass(final FieldAbsoluteDate<T> date) {
  200.         return states.get(date).getMass();
  201.     }

  203.     /** {@inheritDoc} */
  204.     @Override
  205.     public List<ParameterDriver> getParametersDrivers() {
  206.         // Keplerian propagation model does not have parameter drivers.
  207.         return Collections.emptyList();
  208.     }

  210. }
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