FieldAuxiliaryElements.java

  1. /* Copyright 2002-2022 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.  */
  32. public class FieldAuxiliaryElements<T extends CalculusFieldElement<T>> {

  34.     /** Orbit. */
  35.     private final FieldOrbit<T> orbit;

  37.     /** Orbit date. */
  38.     private final FieldAbsoluteDate<T> date;

  40.     /** Orbit frame. */
  41.     private final Frame frame;

  43.     /** Eccentricity. */
  44.     private final T ecc;

  46.     /** Keplerian mean motion. */
  47.     private final T n;

  49.     /** Keplerian period. */
  50.     private final T period;

  52.     /** Semi-major axis. */
  53.     private final T sma;

  55.     /** x component of eccentricity vector. */
  56.     private final T k;

  58.     /** y component of eccentricity vector. */
  59.     private final T h;

  61.     /** x component of inclination vector. */
  62.     private final T q;

  64.     /** y component of inclination vector. */
  65.     private final T p;

  67.     /** Mean longitude. */
  68.     private final T lm;

  70.     /** True longitude. */
  71.     private final T lv;

  73.     /** Eccentric longitude. */
  74.     private final T le;

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

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

  94.     /** C = 1 + p² + q². */
  95.     private final T C;

  97.     /** Equinoctial frame f vector. */
  98.     private final FieldVector3D<T> f;

  100.     /** Equinoctial frame g vector. */
  101.     private final FieldVector3D<T> g;

  103.     /** Equinoctial frame w vector. */
  104.     private final FieldVector3D<T> w;

  106.     /** Direction cosine α. */
  107.     private final T alpha;

  109.     /** Direction cosine β. */
  110.     private final T beta;

  112.     /** Direction cosine γ. */
  113.     private final T gamma;

  115.     /** Simple constructor.
  116.      * @param orbit related mean orbit for auxiliary elements
  117.      * @param retrogradeFactor retrograde factor I [Eq. 2.1.2-(2)]
  118.      */
  119.     public FieldAuxiliaryElements(final FieldOrbit<T> orbit, final int retrogradeFactor) {

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

  123.         // Orbit
  124.         this.orbit = orbit;

  126.         // Date of the orbit
  127.         date = orbit.getDate();

  129.         // Orbit definition frame
  130.         frame = orbit.getFrame();

  132.         // Eccentricity
  133.         ecc = orbit.getE();

  135.         // Keplerian mean motion
  136.         n = orbit.getKeplerianMeanMotion();

  138.         // Keplerian period
  139.         period = orbit.getKeplerianPeriod();

  141.         // Equinoctial elements [Eq. 2.1.2-(1)]
  142.         sma = orbit.getA();
  143.         k   = orbit.getEquinoctialEx();
  144.         h   = orbit.getEquinoctialEy();
  145.         q   = orbit.getHx();
  146.         p   = orbit.getHy();
  147.         lm  = MathUtils.normalizeAngle(orbit.getLM(), pi);
  148.         lv  = MathUtils.normalizeAngle(orbit.getLv(), pi);
  149.         le  = MathUtils.normalizeAngle(orbit.getLE(), pi);

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

  154.         final T k2 = k.multiply(k);
  155.         final T h2 = h.multiply(h);
  156.         final T q2 = q.multiply(q);
  157.         final T p2 = p.multiply(p);

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

  163.         // Equinoctial reference frame [Eq. 2.1.4-(1)]
  164.         final T ooC = C.reciprocal();
  165.         final T px2 = p.multiply(2.);
  166.         final T qx2 = q.multiply(2.);
  167.         final T pq2 = px2.multiply(q);
  168.         f = new FieldVector3D<>(ooC, new FieldVector3D<>(p2.negate().add(1.).add(q2), pq2, px2.multiply(I).negate()));
  169.         g = new FieldVector3D<>(ooC, new FieldVector3D<>(pq2.multiply(I), (p2.add(1.).subtract(q2)).multiply(I), qx2));
  170.         w = new FieldVector3D<>(ooC, new FieldVector3D<>(px2, qx2.negate(), (p2.add(q2).negate().add(1.)).multiply(I)));

  172.         // Direction cosines for central body [Eq. 2.1.9-(1)]
  173.         alpha = (T) f.getZ();
  174.         beta  = (T) g.getZ();
  175.         gamma = (T) w.getZ();
  176.     }

  178.     /** Get the date of the orbit.
  179.      * @return the date
  180.      */
  181.     public FieldAbsoluteDate<T> getDate() {
  182.         return date;
  183.     }

  185.     /** Get the definition frame of the orbit.
  186.      * @return the definition frame
  187.      */
  188.     public Frame getFrame() {
  189.         return frame;
  190.     }

  192.     /** Get the eccentricity.
  193.      * @return ecc
  194.      */
  195.     public T getEcc() {
  196.         return ecc;
  197.     }

  199.     /** Get the Keplerian mean motion.
  200.      * @return n
  201.      */
  202.     public T getMeanMotion() {
  203.         return n;
  204.     }

  206.     /** Get the Keplerian period.
  207.      * @return period
  208.      */
  209.     public T getKeplerianPeriod() {
  210.         return period;
  211.     }

  213.     /** Get the semi-major axis.
  214.      * @return the semi-major axis a
  215.      */
  216.     public T getSma() {
  217.         return sma;
  218.     }

  220.     /** Get the x component of eccentricity vector.
  221.      * <p>
  222.      * This element called k in DSST corresponds to ex
  223.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  224.      * </p>
  225.      * @return k
  226.      */
  227.     public T getK() {
  228.         return k;
  229.     }

  231.     /** Get the y component of eccentricity vector.
  232.      * <p>
  233.      * This element called h in DSST corresponds to ey
  234.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  235.      * </p>
  236.      * @return h
  237.      */
  238.     public T getH() {
  239.         return h;
  240.     }

  242.     /** Get the x component of inclination vector.
  243.      * <p>
  244.      * This element called q in DSST corresponds to hx
  245.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  246.      * </p>
  247.      * @return q
  248.      */
  249.     public T getQ() {
  250.         return q;
  251.     }

  253.     /** Get the y component of inclination vector.
  254.      * <p>
  255.      * This element called p in DSST corresponds to hy
  256.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  257.      * </p>
  258.      * @return p
  259.      */
  260.     public T getP() {
  261.         return p;
  262.     }

  264.     /** Get the mean longitude.
  265.      * @return lm
  266.      */
  267.     public T getLM() {
  268.         return lm;
  269.     }

  271.     /** Get the true longitude.
  272.      * @return lv
  273.      */
  274.     public T getLv() {
  275.         return lv;
  276.     }

  278.     /** Get the eccentric longitude.
  279.      * @return le
  280.      */
  281.     public T getLe() {
  282.         return le;
  283.     }

  285.     /** Get the retrograde factor.
  286.      * @return the retrograde factor I
  287.      */
  288.     public int getRetrogradeFactor() {
  289.         return I;
  290.     }

  292.     /** Get B = sqrt(1 - e²).
  293.      * @return B
  294.      */
  295.     public T getB() {
  296.         return B;
  297.     }

  299.     /** Get C = 1 + p² + q².
  300.      * @return C
  301.      */
  302.     public T getC() {
  303.         return C;
  304.     }

  306.     /** Get equinoctial frame vector f.
  307.      * @return f vector
  308.      */
  309.     public FieldVector3D<T> getVectorF() {
  310.         return f;
  311.     }

  313.     /** Get equinoctial frame vector g.
  314.      * @return g vector
  315.      */
  316.     public FieldVector3D<T> getVectorG() {
  317.         return g;
  318.     }

  320.     /** Get equinoctial frame vector w.
  321.      * @return w vector
  322.      */
  323.     public FieldVector3D<T> getVectorW() {
  324.         return w;
  325.     }

  327.     /** Get direction cosine α for central body.
  328.      * @return α
  329.      */
  330.     public T getAlpha() {
  331.         return alpha;
  332.     }

  334.     /** Get direction cosine β for central body.
  335.      * @return β
  336.      */
  337.     public T getBeta() {
  338.         return beta;
  339.     }

  341.     /** Get direction cosine γ for central body.
  342.      * @return γ
  343.      */
  344.     public T getGamma() {
  345.         return gamma;
  346.     }

  348.     /** Transforms the FieldAuxiliaryElements instance into an AuxiliaryElements instance.
  349.      * @return the AuxiliaryElements instance
  350.      * @since 11.3.3
  351.      */
  352.     public AuxiliaryElements toAuxiliaryElements() {
  353.         return new AuxiliaryElements(orbit.toOrbit(), getRetrogradeFactor());
  354.     }
  355. }
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