FieldDSSTZonalContext.java

  1. /* Copyright 2002-2020 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.hipparchus.RealFieldElement;
  20. import org.hipparchus.util.FastMath;
  21. import org.orekit.forces.gravity.potential.UnnormalizedSphericalHarmonicsProvider;
  22. import org.orekit.propagation.semianalytical.dsst.utilities.FieldAuxiliaryElements;

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

  35.     // Common factors for potential computation
  36.     /** A = sqrt(μ * a). */
  37.     private final T A;
  38.     /** &Chi; = 1 / sqrt(1 - e²) = 1 / B. */
  39.     private T X;
  40.     /** &Chi;². */
  41.     private T XX;
  42.     /** &Chi;³. */
  43.     private T XXX;
  44.     /** 1 / (A * B) .*/
  45.     private T ooAB;
  46.     /** B / A .*/
  47.     private T BoA;
  48.     /** B / A(1 + B) .*/
  49.     private T BoABpo;
  50.     /** -C / (2 * A * B) .*/
  51.     private T mCo2AB;
  52.     /** -2 * a / A .*/
  53.     private T m2aoA;
  54.     /** μ / a .*/
  55.     private T muoa;
  56.     /** R / a .*/
  57.     private T roa;

  59.     /** Keplerian mean motion. */
  60.     private final T n;

  62.     // Short period terms
  63.     /** h * k. */
  64.     private T hk;
  65.     /** k² - h². */
  66.     private T k2mh2;
  67.     /** (k² - h²) / 2. */
  68.     private T k2mh2o2;
  69.     /** 1 / (n² * a²). */
  70.     private T oon2a2;
  71.     /** 1 / (n² * a) . */
  72.     private T oon2a;
  73.     /** χ³ / (n² * a). */
  74.     private T x3on2a;
  75.     /** χ / (n² * a²). */
  76.     private T xon2a2;
  77.     /** (C * χ) / ( 2 * n² * a² ). */
  78.     private T cxo2n2a2;
  79.     /** (χ²) / (n² * a² * (χ + 1 ) ). */
  80.     private T x2on2a2xp1;
  81.     /** B * B.*/
  82.     private T BB;

  84.     /**
  85.      * Simple constructor.
  86.      *
  87.      * @param auxiliaryElements auxiliary elements related to the current orbit
  88.      * @param provider provider for spherical harmonics
  89.      * @param parameters values of the force model parameters
  90.      */
  91.     FieldDSSTZonalContext(final FieldAuxiliaryElements<T> auxiliaryElements,
  92.                                  final UnnormalizedSphericalHarmonicsProvider provider,
  93.                                  final T[] parameters) {

  95.         super(auxiliaryElements);

  97.         final T mu = parameters[0];

  99.         // Keplerian mean motion
  100.         final T absA = FastMath.abs(auxiliaryElements.getSma());
  101.         n = FastMath.sqrt(mu.divide(absA)).divide(absA);

  103.         A = FastMath.sqrt(mu.multiply(auxiliaryElements.getSma()));

  105.         // &Chi; = 1 / B
  106.         X   = auxiliaryElements.getB().reciprocal();
  107.         XX  = X.multiply(X);
  108.         XXX = X.multiply(XX);

  110.         // 1 / AB
  111.         ooAB   = (A.multiply(auxiliaryElements.getB())).reciprocal();
  112.         // B / A
  113.         BoA    = auxiliaryElements.getB().divide(A);
  114.         // -C / 2AB
  115.         mCo2AB = auxiliaryElements.getC().multiply(ooAB).divide(2.).negate();
  116.         // B / A(1 + B)
  117.         BoABpo = BoA.divide(auxiliaryElements.getB().add(1.));
  118.         // -2 * a / A
  119.         m2aoA  = auxiliaryElements.getSma().divide(A).multiply(2.).negate();
  120.         // μ / a
  121.         muoa   = mu.divide(auxiliaryElements.getSma());
  122.         // R / a
  123.         roa    = auxiliaryElements.getSma().divide(provider.getAe()).reciprocal();

  125.         // Short period terms

  127.         // h * k.
  128.         hk = auxiliaryElements.getH().multiply(auxiliaryElements.getK());
  129.         // k² - h².
  130.         k2mh2 = auxiliaryElements.getK().multiply(auxiliaryElements.getK()).subtract(auxiliaryElements.getH().multiply(auxiliaryElements.getH()));
  131.         // (k² - h²) / 2.
  132.         k2mh2o2 = k2mh2.divide(2.);
  133.         // 1 / (n² * a²) = 1 / (n * A)
  134.         oon2a2 = (A.multiply(n)).reciprocal();
  135.         // 1 / (n² * a) = a / (n * A)
  136.         oon2a = auxiliaryElements.getSma().multiply(oon2a2);
  137.         // χ³ / (n² * a)
  138.         x3on2a = XXX.multiply(oon2a);
  139.         // χ / (n² * a²)
  140.         xon2a2 = X.multiply(oon2a2);
  141.         // (C * χ) / ( 2 * n² * a² )
  142.         cxo2n2a2 = xon2a2.multiply(auxiliaryElements.getC()).divide(2.);
  143.         // (χ²) / (n² * a² * (χ + 1 ) )
  144.         x2on2a2xp1 = xon2a2.multiply(X).divide(X.add(1.));
  145.         // B * B
  146.         BB = auxiliaryElements.getB().multiply(auxiliaryElements.getB());

  148.     }

  150.     /** Get &Chi; = 1 / sqrt(1 - e²) = 1 / B.
  151.      * @return &Chi;
  152.      */
  153.     public T getX() {
  154.         return X;
  155.     }

  157.     /** Get &Chi;².
  158.      * @return &Chi;².
  159.      */
  160.     public T getXX() {
  161.         return XX;
  162.     }

  164.     /** Get &Chi;³.
  165.      * @return &Chi;³
  166.      */
  167.     public T getXXX() {
  168.         return XXX;
  169.     }

  171.     /** Get m2aoA = -2 * a / A.
  172.      * @return m2aoA
  173.      */
  174.     public T getM2aoA() {
  175.         return m2aoA;
  176.     }

  178.     /** Get B / A.
  179.      * @return BoA
  180.      */
  181.     public T getBoA() {
  182.         return BoA;
  183.     }

  185.     /** Get ooAB = 1 / (A * B).
  186.      * @return ooAB
  187.      */
  188.     public T getOoAB() {
  189.         return ooAB;
  190.     }

  192.     /** Get mCo2AB = -C / 2AB.
  193.      * @return mCo2AB
  194.      */
  195.     public T getMCo2AB() {
  196.         return mCo2AB;
  197.     }

  199.     /** Get BoABpo = B / A(1 + B).
  200.      * @return BoABpo
  201.      */
  202.     public T getBoABpo() {
  203.         return BoABpo;
  204.     }

  206.     /** Get μ / a .
  207.      * @return muoa
  208.      */
  209.     public T getMuoa() {
  210.         return muoa;
  211.     }

  213.     /** Get roa = R / a.
  214.      * @return roa
  215.      */
  216.     public T getRoa() {
  217.         return roa;
  218.     }

  220.     /** Get the Keplerian mean motion.
  221.      * <p>The Keplerian mean motion is computed directly from semi major axis
  222.      * and central acceleration constant.</p>
  223.      * @return Keplerian mean motion in radians per second
  224.      */
  225.     public T getMeanMotion() {
  226.         return n;
  227.     }

  229.     /** Get h * k.
  230.      * @return hk
  231.      */
  232.     public T getHK() {
  233.         return hk;
  234.     }

  236.     /** Get k² - h².
  237.      * @return k2mh2
  238.      */
  239.     public T getK2MH2() {
  240.         return k2mh2;
  241.     }

  243.     /** Get (k² - h²) / 2.
  244.      * @return k2mh2o2
  245.      */
  246.     public T getK2MH2O2() {
  247.         return k2mh2o2;
  248.     }

  250.     /** Get 1 / (n² * a²).
  251.      * @return oon2a2
  252.      */
  253.     public T getOON2A2() {
  254.         return oon2a2;
  255.     }

  257.     /** Get χ³ / (n² * a).
  258.      * @return x3on2a
  259.      */
  260.     public T getX3ON2A() {
  261.         return x3on2a;
  262.     }

  264.     /** Get χ / (n² * a²).
  265.      * @return xon2a2
  266.      */
  267.     public T getXON2A2() {
  268.         return xon2a2;
  269.     }

  271.     /** Get (C * χ) / ( 2 * n² * a² ).
  272.      * @return cxo2n2a2
  273.      */
  274.     public T getCXO2N2A2() {
  275.         return cxo2n2a2;
  276.     }

  278.     /** Get (χ²) / (n² * a² * (χ + 1 ) ).
  279.      * @return x2on2a2xp1
  280.      */
  281.     public T getX2ON2A2XP1() {
  282.         return x2on2a2xp1;
  283.     }

  285.     /** Get B * B.
  286.      * @return BB
  287.      */
  288.     public T getBB() {
  289.         return BB;
  290.     }

  292. }
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