1   /* Copyright 2002-2025 CS GROUP
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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
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9    *   http://www.apache.org/licenses/LICENSE-2.0
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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
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16   */
17  package org.orekit.propagation.semianalytical.dsst;
18  
19  import org.hipparchus.analysis.differentiation.Gradient;
20  import org.orekit.attitudes.AttitudeProvider;
21  import org.orekit.attitudes.FieldAttitude;
22  import org.orekit.orbits.FieldEquinoctialOrbit;
23  import org.orekit.orbits.FieldOrbit;
24  import org.orekit.orbits.Orbit;
25  import org.orekit.orbits.PositionAngleType;
26  import org.orekit.propagation.FieldSpacecraftState;
27  import org.orekit.propagation.SpacecraftState;
28  import org.orekit.propagation.integration.AbstractGradientConverter;
29  import org.orekit.time.AbsoluteDate;
30  import org.orekit.time.FieldAbsoluteDate;
31  
32  /** Converter for states and parameters arrays.
33   * @author Luc Maisonobe
34   * @author Bryan Cazabonne
35   * @since 10.2
36   */
37  class DSSTGradientConverter extends AbstractGradientConverter {
38  
39      /** Fixed dimension of the state. */
40      private static final int FREE_STATE_PARAMETERS = 6;
41  
42      /** Simple constructor.
43       * @param state regular state
44       * @param provider provider to use if attitude needs to be recomputed
45       */
46      DSSTGradientConverter(final SpacecraftState state, final AttitudeProvider provider) {
47  
48          super(FREE_STATE_PARAMETERS);
49  
50          // equinoctial parameters always has derivatives
51          final Orbit orbit = state.getOrbit();
52          final Gradient sma  = Gradient.variable(FREE_STATE_PARAMETERS, 0, orbit.getA());
53          final Gradient ex   = Gradient.variable(FREE_STATE_PARAMETERS, 1, orbit.getEquinoctialEx());
54          final Gradient ey   = Gradient.variable(FREE_STATE_PARAMETERS, 2, orbit.getEquinoctialEy());
55          final Gradient hx   = Gradient.variable(FREE_STATE_PARAMETERS, 3, orbit.getHx());
56          final Gradient hy   = Gradient.variable(FREE_STATE_PARAMETERS, 4, orbit.getHy());
57          final Gradient l    = Gradient.variable(FREE_STATE_PARAMETERS, 5, orbit.getLM());
58  
59          final Gradient gMu = Gradient.constant(FREE_STATE_PARAMETERS, orbit.getMu());
60  
61          // date
62          final AbsoluteDate date = state.getDate();
63          final FieldAbsoluteDate<Gradient> dateField = new FieldAbsoluteDate<>(sma.getField(), date);
64  
65          // mass never has derivatives
66          final Gradient gM = Gradient.constant(FREE_STATE_PARAMETERS, state.getMass());
67  
68          final FieldOrbit<Gradient> gOrbit =
69                          new FieldEquinoctialOrbit<>(sma, ex, ey, hx, hy, l,
70                                                      PositionAngleType.MEAN,
71                                                      state.getFrame(),
72                                                      dateField,
73                                                      gMu);
74  
75          final FieldAttitude<Gradient> gAttitude;
76          // compute attitude partial derivatives
77          gAttitude = provider.getAttitude(gOrbit, gOrbit.getDate(), gOrbit.getFrame());
78  
79          // initialize the list with the state having 0 force model parameters
80          initStates(new FieldSpacecraftState<>(gOrbit, gAttitude).withMass(gM));
81  
82      }
83  
84  }