DSSTZonalContext.java

  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.propagation.semianalytical.dsst.forces;

  19. import org.orekit.forces.gravity.potential.UnnormalizedSphericalHarmonicsProvider;
  20. import org.orekit.frames.Frame;
  21. import org.orekit.propagation.semianalytical.dsst.utilities.AuxiliaryElements;

  23. /**
  24.  * This class is a container for the common parameters used in {@link DSSTZonal}.
  25.  * <p>
  26.  * It performs parameters initialization at each integration step for the Zonal contribution
  27.  * to the central body gravitational perturbation.
  28.  * </p>
  29.  * @author Bryan Cazabonne
  30.  * @since 10.0
  31.  */
  32. public class DSSTZonalContext extends DSSTGravityContext {

  34.     /** &Chi;³ = 1 / B³. */
  35.     private final double chi3;

  37.     // Short period terms
  38.     /** h * k. */
  39.     private double hk;
  40.     /** k² - h². */
  41.     private double k2mh2;
  42.     /** (k² - h²) / 2. */
  43.     private double k2mh2o2;
  44.     /** 1 / (n² * a²). */
  45.     private double oon2a2;
  46.     /** 1 / (n² * a) . */
  47.     private double oon2a;
  48.     /** χ³ / (n² * a). */
  49.     private double x3on2a;
  50.     /** χ / (n² * a²). */
  51.     private double xon2a2;
  52.     /** (C * χ) / ( 2 * n² * a² ). */
  53.     private double cxo2n2a2;
  54.     /** (χ²) / (n² * a² * (χ + 1 ) ). */
  55.     private double x2on2a2xp1;
  56.     /** B * B. */
  57.     private double BB;

  59.     /**
  60.      * Constructor with central body frame potentially different than orbit frame.
  61.      *
  62.      * @param auxiliaryElements auxiliary elements related to the current orbit
  63.      * @param bodyFixedFrame    rotating body frame
  64.      * @param provider          provider for spherical harmonics
  65.      * @param parameters        values of the force model parameters
  66.      * @since 12.2
  67.      */
  68.     DSSTZonalContext(final AuxiliaryElements auxiliaryElements,
  69.                      final Frame bodyFixedFrame,
  70.                      final UnnormalizedSphericalHarmonicsProvider provider,
  71.                      final double[] parameters) {

  73.         super(auxiliaryElements, bodyFixedFrame, provider, parameters);

  75.         // Chi3
  76.         final double chi = getChi();
  77.         this.chi3 = chi * getChi2();

  79.         // Short period terms
  80.         // -----

  82.         // h * k.
  83.         hk = auxiliaryElements.getH() * auxiliaryElements.getK();
  84.         // k² - h².
  85.         k2mh2 = auxiliaryElements.getK() * auxiliaryElements.getK() - auxiliaryElements.getH() * auxiliaryElements.getH();
  86.         // (k² - h²) / 2.
  87.         k2mh2o2 = k2mh2 / 2.;
  88.         // 1 / (n² * a²) = 1 / (n * A)
  89.         oon2a2 = 1 / (getA() * getMeanMotion());
  90.         // 1 / (n² * a) = a / (n * A)
  91.         oon2a = auxiliaryElements.getSma() * oon2a2;
  92.         // χ³ / (n² * a)
  93.         x3on2a = chi3 * oon2a;
  94.         // χ / (n² * a²)
  95.         xon2a2 = getChi() * oon2a2;
  96.         // (C * χ) / ( 2 * n² * a² )
  97.         cxo2n2a2 = xon2a2 * auxiliaryElements.getC() / 2;
  98.         // (χ²) / (n² * a² * (χ + 1 ) )
  99.         x2on2a2xp1 = xon2a2 * chi / (chi + 1);
  100.         // B * B
  101.         BB = auxiliaryElements.getB() * auxiliaryElements.getB();
  102.     }

  104.     /** Getter for the &Chi;³.
  105.      * @return the &Chi;³
  106.      */
  107.     public double getChi3() {
  108.         return chi3;
  109.     }

  111.     /** Get h * k.
  112.      * @return hk
  113.      */
  114.     public double getHK() {
  115.         return hk;
  116.     }

  118.     /** Get k² - h².
  119.      * @return k2mh2
  120.      */
  121.     public double getK2MH2() {
  122.         return k2mh2;
  123.     }

  125.     /** Get (k² - h²) / 2.
  126.      * @return k2mh2o2
  127.      */
  128.     public double getK2MH2O2() {
  129.         return k2mh2o2;
  130.     }

  132.     /** Get 1 / (n² * a²).
  133.      * @return oon2a2
  134.      */
  135.     public double getOON2A2() {
  136.         return oon2a2;
  137.     }

  139.     /** Get χ³ / (n² * a).
  140.      * @return x3on2a
  141.      */
  142.     public double getX3ON2A() {
  143.         return x3on2a;
  144.     }

  146.     /** Get χ / (n² * a²).
  147.      * @return xon2a2
  148.      */
  149.     public double getXON2A2() {
  150.         return xon2a2;
  151.     }

  153.     /** Get (C * χ) / ( 2 * n² * a² ).
  154.      * @return cxo2n2a2
  155.      */
  156.     public double getCXO2N2A2() {
  157.         return cxo2n2a2;
  158.     }

  160.     /** Get (χ²) / (n² * a² * (χ + 1 ) ).
  161.      * @return x2on2a2xp1
  162.      */
  163.     public double getX2ON2A2XP1() {
  164.         return x2on2a2xp1;
  165.     }

  167.     /** Get B * B.
  168.      * @return BB
  169.      */
  170.     public double getBB() {
  171.         return BB;
  172.     }

  174. }
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