FieldAuxiliaryElements.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.utilities;

  19. import org.hipparchus.CalculusFieldElement;
  20. import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  21. import org.hipparchus.util.FastMath;
  22. import org.hipparchus.util.MathUtils;
  23. import org.orekit.frames.Frame;
  24. import org.orekit.orbits.FieldOrbit;
  25. import org.orekit.time.FieldAbsoluteDate;

  27. /** Container class for common parameters used by all DSST forces.
  28.  *  <p>
  29.  *  Most of them are defined in Danielson paper at § 2.1.
  30.  *  </p>
  31.  *  @author Bryan Cazabonne
  32.  * @param <T> type of the field elements
  33.  */
  34. public class FieldAuxiliaryElements<T extends CalculusFieldElement<T>> {

  36.     /** Orbit. */
  37.     private final FieldOrbit<T> orbit;

  39.     /** Orbit date. */
  40.     private final FieldAbsoluteDate<T> date;

  42.     /** Orbit frame. */
  43.     private final Frame frame;

  45.     /** Eccentricity. */
  46.     private final T ecc;

  48.     /** Keplerian mean motion. */
  49.     private final T n;

  51.     /** Keplerian period. */
  52.     private final T period;

  54.     /** Semi-major axis. */
  55.     private final T sma;

  57.     /** x component of eccentricity vector. */
  58.     private final T k;

  60.     /** y component of eccentricity vector. */
  61.     private final T h;

  63.     /** x component of inclination vector. */
  64.     private final T q;

  66.     /** y component of inclination vector. */
  67.     private final T p;

  69.     /** Mean longitude. */
  70.     private final T lm;

  72.     /** True longitude. */
  73.     private final T lv;

  75.     /** Eccentric longitude. */
  76.     private final T le;

  78.     /** Retrograde factor I.
  79.      *  <p>
  80.      *  DSST model needs equinoctial orbit as internal representation.
  81.      *  Classical equinoctial elements have discontinuities when inclination
  82.      *  is close to zero. In this representation, I = +1. <br>
  83.      *  To avoid this discontinuity, another representation exists and equinoctial
  84.      *  elements can be expressed in a different way, called "retrograde" orbit.
  85.      *  This implies I = -1. <br>
  86.      *  As Orekit doesn't implement the retrograde orbit, I is always set to +1.
  87.      *  But for the sake of consistency with the theory, the retrograde factor
  88.      *  has been kept in the formulas.
  89.      *  </p>
  90.      */
  91.     private final int    I;

  93.     /** B = sqrt(1 - h² - k²). */
  94.     private final T B;

  96.     /** C = 1 + p² + q². */
  97.     private final T C;

  99.     /** Equinoctial frame f vector. */
  100.     private final FieldVector3D<T> f;

  102.     /** Equinoctial frame g vector. */
  103.     private final FieldVector3D<T> g;

  105.     /** Equinoctial frame w vector. */
  106.     private final FieldVector3D<T> w;

  108.     /** Simple constructor.
  109.      * @param orbit related mean orbit for auxiliary elements
  110.      * @param retrogradeFactor retrograde factor I [Eq. 2.1.2-(2)]
  111.      */
  112.     public FieldAuxiliaryElements(final FieldOrbit<T> orbit, final int retrogradeFactor) {

  114.         final T pi = orbit.getDate().getField().getZero().getPi();

  116.         // Orbit
  117.         this.orbit = orbit;

  119.         // Date of the orbit
  120.         date = orbit.getDate();

  122.         // Orbit definition frame
  123.         frame = orbit.getFrame();

  125.         // Eccentricity
  126.         ecc = orbit.getE();

  128.         // Keplerian mean motion
  129.         n = orbit.getKeplerianMeanMotion();

  131.         // Keplerian period
  132.         period = orbit.getKeplerianPeriod();

  134.         // Equinoctial elements [Eq. 2.1.2-(1)]
  135.         sma = orbit.getA();
  136.         k   = orbit.getEquinoctialEx();
  137.         h   = orbit.getEquinoctialEy();
  138.         q   = orbit.getHx();
  139.         p   = orbit.getHy();
  140.         lm  = MathUtils.normalizeAngle(orbit.getLM(), pi);
  141.         lv  = MathUtils.normalizeAngle(orbit.getLv(), pi);
  142.         le  = MathUtils.normalizeAngle(orbit.getLE(), pi);

  144.         // Retrograde factor [Eq. 2.1.2-(2)]
  145.         I = retrogradeFactor;

  147.         final T k2 = k.multiply(k);
  148.         final T h2 = h.multiply(h);
  149.         final T q2 = q.multiply(q);
  150.         final T p2 = p.multiply(p);

  152.         // A, B, C parameters [Eq. 2.1.6-(1)]
  153.         B = FastMath.sqrt(k2.add(h2).negate().add(1.));
  154.         C = q2.add(p2).add(1);

  156.         // Equinoctial reference frame [Eq. 2.1.4-(1)]
  157.         final T ooC = C.reciprocal();
  158.         final T px2 = p.multiply(2.);
  159.         final T qx2 = q.multiply(2.);
  160.         final T pq2 = px2.multiply(q);
  161.         f = new FieldVector3D<>(ooC, new FieldVector3D<>(p2.negate().add(1.).add(q2), pq2, px2.multiply(I).negate()));
  162.         g = new FieldVector3D<>(ooC, new FieldVector3D<>(pq2.multiply(I), (p2.add(1.).subtract(q2)).multiply(I), qx2));
  163.         w = new FieldVector3D<>(ooC, new FieldVector3D<>(px2, qx2.negate(), (p2.add(q2).negate().add(1.)).multiply(I)));
  164.     }

  166.     /** Get the orbit.
  167.      * @return the orbit
  168.      */
  169.     public FieldOrbit<T> getOrbit() {
  170.         return orbit;
  171.     }

  173.     /** Get the date of the orbit.
  174.      * @return the date
  175.      */
  176.     public FieldAbsoluteDate<T> getDate() {
  177.         return date;
  178.     }

  180.     /** Get the definition frame of the orbit.
  181.      * @return the definition frame
  182.      */
  183.     public Frame getFrame() {
  184.         return frame;
  185.     }

  187.     /** Get the eccentricity.
  188.      * @return ecc
  189.      */
  190.     public T getEcc() {
  191.         return ecc;
  192.     }

  194.     /** Get the Keplerian mean motion.
  195.      * @return n
  196.      */
  197.     public T getMeanMotion() {
  198.         return n;
  199.     }

  201.     /** Get the Keplerian period.
  202.      * @return period
  203.      */
  204.     public T getKeplerianPeriod() {
  205.         return period;
  206.     }

  208.     /** Get the semi-major axis.
  209.      * @return the semi-major axis a
  210.      */
  211.     public T getSma() {
  212.         return sma;
  213.     }

  215.     /** Get the x component of eccentricity vector.
  216.      * <p>
  217.      * This element called k in DSST corresponds to ex
  218.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  219.      * </p>
  220.      * @return k
  221.      */
  222.     public T getK() {
  223.         return k;
  224.     }

  226.     /** Get the y component of eccentricity vector.
  227.      * <p>
  228.      * This element called h in DSST corresponds to ey
  229.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  230.      * </p>
  231.      * @return h
  232.      */
  233.     public T getH() {
  234.         return h;
  235.     }

  237.     /** Get the x component of inclination vector.
  238.      * <p>
  239.      * This element called q in DSST corresponds to hx
  240.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  241.      * </p>
  242.      * @return q
  243.      */
  244.     public T getQ() {
  245.         return q;
  246.     }

  248.     /** Get the y component of inclination vector.
  249.      * <p>
  250.      * This element called p in DSST corresponds to hy
  251.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  252.      * </p>
  253.      * @return p
  254.      */
  255.     public T getP() {
  256.         return p;
  257.     }

  259.     /** Get the mean longitude.
  260.      * @return lm
  261.      */
  262.     public T getLM() {
  263.         return lm;
  264.     }

  266.     /** Get the true longitude.
  267.      * @return lv
  268.      */
  269.     public T getLv() {
  270.         return lv;
  271.     }

  273.     /** Get the eccentric longitude.
  274.      * @return le
  275.      */
  276.     public T getLe() {
  277.         return le;
  278.     }

  280.     /** Get the retrograde factor.
  281.      * @return the retrograde factor I
  282.      */
  283.     public int getRetrogradeFactor() {
  284.         return I;
  285.     }

  287.     /** Get B = sqrt(1 - e²).
  288.      * @return B
  289.      */
  290.     public T getB() {
  291.         return B;
  292.     }

  294.     /** Get C = 1 + p² + q².
  295.      * @return C
  296.      */
  297.     public T getC() {
  298.         return C;
  299.     }

  301.     /** Get equinoctial frame vector f.
  302.      * @return f vector
  303.      */
  304.     public FieldVector3D<T> getVectorF() {
  305.         return f;
  306.     }

  308.     /** Get equinoctial frame vector g.
  309.      * @return g vector
  310.      */
  311.     public FieldVector3D<T> getVectorG() {
  312.         return g;
  313.     }

  315.     /** Get equinoctial frame vector w.
  316.      * @return w vector
  317.      */
  318.     public FieldVector3D<T> getVectorW() {
  319.         return w;
  320.     }

  322.     /** Transforms the FieldAuxiliaryElements instance into an AuxiliaryElements instance.
  323.      * @return the AuxiliaryElements instance
  324.      * @since 11.3.3
  325.      */
  326.     public AuxiliaryElements toAuxiliaryElements() {
  327.         return new AuxiliaryElements(orbit.toOrbit(), getRetrogradeFactor());
  328.     }

  330. }
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