FieldDSSTGravityContext.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.hipparchus.CalculusFieldElement;
  20. import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  21. import org.hipparchus.geometry.euclidean.threed.Vector3D;
  22. import org.hipparchus.util.FastMath;
  23. import org.orekit.forces.gravity.potential.UnnormalizedSphericalHarmonicsProvider;
  24. import org.orekit.frames.FieldStaticTransform;
  25. import org.orekit.frames.Frame;
  26. import org.orekit.propagation.semianalytical.dsst.utilities.FieldAuxiliaryElements;

  28. /**
  29.  * This class is a container for the common parameters used in {@link DSSTTesseral} and {@link DSSTZonal}.
  30.  * <p>
  31.  * It performs parameters initialization at each integration step for the Tesseral and Zonal contribution
  32.  * to the central body gravitational perturbation.
  33.  * </p>
  34.  * @author Bryan Cazabonne
  35.  * @author Maxime Journot
  36.  * @since 12.2
  37.  */
  38. public class FieldDSSTGravityContext<T extends CalculusFieldElement<T>> extends FieldForceModelContext<T> {

  40.     /** A = sqrt(μ * a). */
  41.     private final T A;

  43.     /** &Chi; = 1 / sqrt(1 - e²) = 1 / B. */
  44.     private final T chi;

  46.     /** &Chi;². */
  47.     private final T chi2;

  49.     // Common factors from equinoctial coefficients
  50.     /** 2 * a / A . */
  51.     private final T ax2oA;

  53.     /** 1 / (A * B) . */
  54.     private final T ooAB;

  56.     /** B / A . */
  57.     private final T BoA;

  59.     /** B / (A * (1 + B)) . */
  60.     private final T BoABpo;

  62.     /** C / (2 * A * B) . */
  63.     private final T Co2AB;

  65.     /** μ / a . */
  66.     private final T muoa;

  68.     /** R / a . */
  69.     private final T roa;

  71.     /** Keplerian mean motion. */
  72.     private final T n;

  74.     /** Direction cosine α. */
  75.     private final T alpha;

  77.     /** Direction cosine β. */
  78.     private final T beta;

  80.     /** Direction cosine γ. */
  81.     private final T gamma;

  83.     /** Transform from body-fixed frame to inertial frame. */
  84.     private final FieldStaticTransform<T> bodyFixedToInertialTransform;

  86.     /**
  87.      * Constructor.
  88.      *
  89.      * @param auxiliaryElements auxiliary elements related to the current orbit
  90.      * @param centralBodyFixedFrame  rotating body frame
  91.      * @param provider   provider for spherical harmonics
  92.      * @param parameters values of the force model parameters
  93.      */
  94.     FieldDSSTGravityContext(final FieldAuxiliaryElements<T> auxiliaryElements,
  95.                             final Frame centralBodyFixedFrame,
  96.                             final UnnormalizedSphericalHarmonicsProvider provider,
  97.                             final T[] parameters) {

  99.         super(auxiliaryElements);

  101.         // µ
  102.         final T mu = parameters[0];

  104.         // Semi-major axis
  105.         final T a = auxiliaryElements.getSma();

  107.         // Keplerian Mean Motion
  108.         final T absA = FastMath.abs(a);
  109.         this.n = FastMath.sqrt(mu.divide(absA)).divide(absA);

  111.         // A = sqrt(µ * |a|)
  112.         this.A = FastMath.sqrt(mu.multiply(absA));

  114.         // &Chi; = 1 / B
  115.         final T B = auxiliaryElements.getB();
  116.         this.chi = auxiliaryElements.getB().reciprocal();
  117.         this.chi2 = chi.multiply(chi);

  119.         // Common factors from equinoctial coefficients
  120.         // 2 * a / A
  121.         this.ax2oA = a.divide(A).multiply(2.);
  122.         // B / A
  123.         this.BoA = B.divide(A);;
  124.         // 1 / AB
  125.         this.ooAB = A.multiply(B).reciprocal();;
  126.         // C / 2AB
  127.         this.Co2AB =  auxiliaryElements.getC().multiply(ooAB).divide(2.);;
  128.         // B / (A * (1 + B))
  129.         this.BoABpo = BoA.divide(B.add(1.));
  130.         // &mu / a
  131.         this.muoa = mu.divide(a);
  132.         // R / a
  133.         this.roa = a.divide(provider.getAe()).reciprocal();


  136.         // If (centralBodyFrame == null), then centralBodyFrame = orbit frame (see DSSTZonal constructors for more on this).
  137.         final Frame internalCentralBodyFrame = centralBodyFixedFrame == null ? auxiliaryElements.getFrame() : centralBodyFixedFrame;

  139.         // Transform from body-fixed frame (typically ITRF) to inertial frame
  140.         bodyFixedToInertialTransform = internalCentralBodyFrame.
  141.                         getStaticTransformTo(auxiliaryElements.getFrame(), auxiliaryElements.getDate());

  143.         final FieldVector3D<T> zB = bodyFixedToInertialTransform.transformVector(Vector3D.PLUS_K);

  145.         // Direction cosines for central body [Eq. 2.1.9-(1)]
  146.         alpha = FieldVector3D.dotProduct(zB, auxiliaryElements.getVectorF());
  147.         beta  = FieldVector3D.dotProduct(zB, auxiliaryElements.getVectorG());
  148.         gamma = FieldVector3D.dotProduct(zB, auxiliaryElements.getVectorW());
  149.     }

  151.     /** A = sqrt(μ * a).
  152.      * @return A
  153.      */
  154.     public T getA() {
  155.         return A;
  156.     }

  158.     /** Get &Chi; = 1 / sqrt(1 - e²) = 1 / B.
  159.      * @return chi
  160.      */
  161.     public T getChi() {
  162.         return chi;
  163.     }

  165.     /** Get &Chi;².
  166.      * @return chi2
  167.      */
  168.     public T getChi2() {
  169.         return chi2;
  170.     }

  172.     /** Getter for the ax2oA.
  173.      * @return the ax2oA
  174.      */
  175.     public T getAx2oA() {
  176.         return ax2oA;
  177.     }

  179.     /** Get ooAB = 1 / (A * B).
  180.      * @return ooAB
  181.      */
  182.     public T getOoAB() {
  183.         return ooAB;
  184.     }

  186.     /** Get B / A.
  187.      * @return BoA
  188.      */
  189.     public T getBoA() {
  190.         return BoA;
  191.     }

  193.     /** Get BoABpo = B / A(1 + B).
  194.      * @return BoABpo
  195.      */
  196.     public T getBoABpo() {
  197.         return BoABpo;
  198.     }

  200.     /** Get Co2AB = C / 2AB.
  201.      * @return Co2AB
  202.      */
  203.     public T getCo2AB() {
  204.         return Co2AB;
  205.     }

  207.     /** Get muoa = μ / a.
  208.      * @return the muoa
  209.      */
  210.     public T getMuoa() {
  211.         return muoa;
  212.     }

  214.     /** Get roa = R / a.
  215.      * @return roa
  216.      */
  217.     public T getRoa() {
  218.         return roa;
  219.     }

  221.     /** Get the Keplerian mean motion.
  222.      * <p>The Keplerian mean motion is computed directly from semi major axis
  223.      * and central acceleration constant.</p>
  224.      * @return Keplerian mean motion in radians per second
  225.      */
  226.     public T getMeanMotion() {
  227.         return n;
  228.     }

  230.     /** Get direction cosine α for central body.
  231.      * @return α
  232.      */
  233.     public T getAlpha() {
  234.         return alpha;
  235.     }

  237.     /** Get direction cosine β for central body.
  238.      * @return β
  239.      */
  240.     public T getBeta() {
  241.         return beta;
  242.     }

  244.     /** Get direction cosine γ for central body.
  245.      * @return the γ
  246.      */
  247.     public T getGamma() {
  248.         return gamma;
  249.     }

  251.     /** Getter for the bodyFixedToInertialTransform.
  252.      * @return the bodyFixedToInertialTransform
  253.      */
  254.     public FieldStaticTransform<T> getBodyFixedToInertialTransform() {
  255.         return bodyFixedToInertialTransform;
  256.     }
  257. }
Created with JaCoCo 0.8.12.202403310830