1   /* Copyright 2002-2021 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.forces.drag;
18  
19  import java.util.Collections;
20  import java.util.List;
21  
22  import org.hipparchus.CalculusFieldElement;
23  import org.hipparchus.geometry.euclidean.threed.FieldRotation;
24  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
25  import org.hipparchus.geometry.euclidean.threed.Rotation;
26  import org.hipparchus.geometry.euclidean.threed.Vector3D;
27  import org.hipparchus.util.FastMath;
28  import org.orekit.frames.Frame;
29  import org.orekit.time.AbsoluteDate;
30  import org.orekit.time.FieldAbsoluteDate;
31  import org.orekit.utils.ParameterDriver;
32  
33  /** This class models isotropic drag effects.
34   * <p>The model of this spacecraft is a simple spherical model, this
35   * means that all coefficients are constant and do not depend of
36   * the direction.</p>
37   *
38   * @see org.orekit.forces.BoxAndSolarArraySpacecraft
39   * @see org.orekit.forces.radiation.IsotropicRadiationCNES95Convention
40   * @author Luc Maisonobe
41   * @since 7.1
42   */
43  public class IsotropicDrag implements DragSensitive {
44  
45      /** Parameters scaling factor.
46       * <p>
47       * We use a power of 2 to avoid numeric noise introduction
48       * in the multiplications/divisions sequences.
49       * </p>
50       */
51      private final double SCALE = FastMath.scalb(1.0, -3);
52  
53      /** Drivers for drag coefficient parameter. */
54      private final ParameterDriver dragParametersDrivers;
55  
56      /** Cross section (m²). */
57      private final double crossSection;
58  
59      /** Constructor with drag coefficient min/max set to ±∞.
60       * @param crossSection Surface (m²)
61       * @param dragCoeff drag coefficient
62       */
63      public IsotropicDrag(final double crossSection, final double dragCoeff) {
64          this(crossSection, dragCoeff, Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);
65      }
66  
67      /** Constructor with drag coefficient min/max set by user.
68       * @param crossSection Surface (m²)
69       * @param dragCoeff drag coefficient
70       * @param dragCoeffMin Minimum value of drag coefficient
71       * @param dragCoeffMax Maximum value of drag coefficient
72       */
73      public IsotropicDrag(final double crossSection, final double dragCoeff,
74                           final double dragCoeffMin, final double dragCoeffMax) {
75          // in some corner cases (unknown spacecraft, fuel leaks, active piloting ...)
76          // the single coefficient may be arbitrary, and even negative
77          this.dragParametersDrivers = new ParameterDriver(DragSensitive.DRAG_COEFFICIENT,
78                                                           dragCoeff, SCALE,
79                                                           dragCoeffMin, dragCoeffMax);
80          this.crossSection = crossSection;
81      }
82  
83      /** {@inheritDoc} */
84      @Override
85      public List<ParameterDriver> getDragParametersDrivers() {
86          return Collections.singletonList(dragParametersDrivers);
87      }
88  
89      /** {@inheritDoc} */
90      @Override
91      public Vector3D dragAcceleration(final AbsoluteDate date, final Frame frame, final Vector3D position,
92                                       final Rotation rotation, final double mass,
93                                       final double density, final Vector3D relativeVelocity,
94                                       final double[] parameters) {
95          final double dragCoeff = parameters[0];
96          return new Vector3D(relativeVelocity.getNorm() * density * dragCoeff * crossSection / (2 * mass),
97                              relativeVelocity);
98      }
99  
100     /** {@inheritDoc} */
101     @Override
102     public <T extends CalculusFieldElement<T>> FieldVector3D<T>
103         dragAcceleration(final FieldAbsoluteDate<T> date, final Frame frame,
104                          final FieldVector3D<T> position, final FieldRotation<T> rotation,
105                          final T mass, final T density,
106                          final FieldVector3D<T> relativeVelocity,
107                          final T[] parameters) {
108         final T dragCoeff = parameters[0];
109         return new FieldVector3D<>(relativeVelocity.getNorm().multiply(density.multiply(dragCoeff).multiply(crossSection / 2)).divide(mass),
110                                    relativeVelocity);
111     }
112 }