1   /* Copyright 2002-2025 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.empirical;
18  
19  import org.hipparchus.CalculusFieldElement;
20  import org.orekit.propagation.FieldSpacecraftState;
21  import org.orekit.propagation.SpacecraftState;
22  import org.orekit.time.AbsoluteDate;
23  import org.orekit.utils.ParameterDriversProvider;
24  
25  /** Acceleration model used by empirical force.
26   * @author Bryan Cazabonne
27   * @since 10.3
28   */
29  public interface AccelerationModel extends ParameterDriversProvider {
30  
31      /** Initialize the acceleration model at the start of the propagation.
32       * <p>
33       * The default implementation of this method does nothing
34       * </p>
35       * @param initialState spacecraft state at the start of propagation.
36       * @param target       date of propagation. Not equal to {@code initialState.getDate()}.
37       */
38      default void init(SpacecraftState initialState, AbsoluteDate target) {
39          // Nothing by default
40      }
41  
42      /** Compute the signed amplitude of the acceleration.
43       * <p>
44       * The acceleration is the direction multiplied by the signed amplitude. So if
45       * signed amplitude is negative, the acceleratin is towards the opposite of the
46       * direction specified at construction.
47       * </p>
48       * @param state current state information: date, kinematics, attitude
49       * @param parameters values of the force model parameters
50       * @return norm of the acceleration
51       */
52      double signedAmplitude(SpacecraftState state, double[] parameters);
53  
54      /** Compute the signed amplitude of the acceleration.
55       * <p>
56       * The acceleration is the direction multiplied by the signed amplitude. So if
57       * signed amplitude is negative, the acceleratin is towards the opposite of the
58       * direction specified at construction.
59       * </p>
60       * @param state current state information: date, kinematics, attitude
61       * @param parameters values of the force model parameters
62       * @param <T> type of the elements
63       * @return norm of the acceleration
64       */
65      <T extends CalculusFieldElement<T>> T signedAmplitude(FieldSpacecraftState<T> state, T[] parameters);
66  }