1   /* Copyright 2022-2025 Romain Serra
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.control.indirect.adjoint.cost;
18  
19  
20  import org.hipparchus.geometry.euclidean.threed.Vector3D;
21  
22  /**
23   * Class for minimizing the flight duration (a.k.a. time of flight) with Cartesian coordinates.
24   * It is the integral over time of the constant one. The control is assumed to be bounded.
25   * It also assumes that no external acceleration depends on mass.
26   * If the mass flow rate factor is zero, then there is no adjoint for the mass.
27   *
28   * @author Romain Serra
29   * @see CartesianCost
30   * @since 13.0
31   */
32  public class CartesianFlightDurationCost extends AbstractCartesianCost {
33  
34      /**
35       * Maximum value of thrust force Euclidean norm.
36       */
37      private final double maximumThrustMagnitude;
38  
39      /**
40       * Constructor.
41       *
42       * @param name                   name
43       * @param massFlowRateFactor     mass flow rate factor
44       * @param maximumThrustMagnitude maximum thrust magnitude
45       */
46      public CartesianFlightDurationCost(final String name, final double massFlowRateFactor,
47                                         final double maximumThrustMagnitude) {
48          super(name, massFlowRateFactor);
49          this.maximumThrustMagnitude = maximumThrustMagnitude;
50      }
51  
52      /**
53       * Getter for maximum thrust magnitude.
54       *
55       * @return maximum thrust
56       */
57      public double getMaximumThrustMagnitude() {
58          return maximumThrustMagnitude;
59      }
60  
61      /**
62       * {@inheritDoc}
63       */
64      @Override
65      public Vector3D getThrustAccelerationVector(final double[] adjointVariables, final double mass) {
66          return new Vector3D(adjointVariables[3], adjointVariables[4], adjointVariables[5]).normalize()
67                  .scalarMultiply(maximumThrustMagnitude);
68      }
69  
70      /**
71       * {@inheritDoc}
72       */
73      @Override
74      public void updateAdjointDerivatives(final double[] adjointVariables, final double mass,
75                                           final double[] adjointDerivatives) {
76          if (getAdjointDimension() > 6) {
77              adjointDerivatives[6] += getAdjointVelocityNorm(adjointVariables) * maximumThrustMagnitude / (mass * mass);
78          }
79      }
80  
81      /**
82       * {@inheritDoc}
83       */
84      @Override
85      public double getHamiltonianContribution(final double[] adjointVariables, final double mass) {
86          return -1.;
87      }
88  }