AuxiliaryElements.java

  1. /* Copyright 2002-2018 CS Systèmes d'Information
  2.  * Licensed to CS Systèmes d'Information (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.geometry.euclidean.threed.Vector3D;
  20. import org.hipparchus.util.FastMath;
  21. import org.hipparchus.util.MathUtils;
  22. import org.orekit.frames.Frame;
  23. import org.orekit.orbits.Orbit;
  24. import org.orekit.time.AbsoluteDate;


  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 Pascal Parraud
  32.  */
  33. public class AuxiliaryElements {

  35.     /** Orbit date. */
  36.     private final AbsoluteDate date;

  38.     /** Orbit frame. */
  39.     private final Frame frame;

  41.     /** Central body attraction coefficient. */
  42.     private final double mu;

  44.     /** Eccentricity. */
  45.     private final double ecc;

  47.     /** Keplerian mean motion. */
  48.     private final double n;

  50.     /** Keplerian period. */
  51.     private final double period;

  53.     /** Semi-major axis. */
  54.     private final double sma;

  56.     /** x component of eccentricity vector. */
  57.     private final double k;

  59.     /** y component of eccentricity vector. */
  60.     private final double h;

  62.     /** x component of inclination vector. */
  63.     private final double q;

  65.     /** y component of inclination vector. */
  66.     private final double p;

  68.     /** Mean longitude. */
  69.     private final double lm;

  71.     /** True longitude. */
  72.     private final double lv;

  74.     /** Eccentric longitude. */
  75.     private final double le;

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

  92.     /** A = sqrt(μ * a). */
  93.     private final double A;

  95.     /** B = sqrt(1 - h² - k²). */
  96.     private final double B;

  98.     /** C = 1 + p² + q². */
  99.     private final double C;

  101.     /** Equinoctial frame f vector. */
  102.     private final Vector3D f;

  104.     /** Equinoctial frame g vector. */
  105.     private final Vector3D g;

  107.     /** Equinoctial frame w vector. */
  108.     private final Vector3D w;

  110.     /** Direction cosine α. */
  111.     private final double alpha;

  113.     /** Direction cosine β. */
  114.     private final double beta;

  116.     /** Direction cosine γ. */
  117.     private final double gamma;

  119.     /** Simple constructor.
  120.      * @param orbit related mean orbit for auxiliary elements
  121.      * @param retrogradeFactor retrograde factor I [Eq. 2.1.2-(2)]
  122.      */
  123.     public AuxiliaryElements(final Orbit orbit, final int retrogradeFactor) {
  124.         // Date of the orbit
  125.         date = orbit.getDate();

  127.         // Orbit definition frame
  128.         frame = orbit.getFrame();

  130.         // Central body attraction coefficient
  131.         mu = orbit.getMu();

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

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

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

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

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

  155.         final double k2 = k * k;
  156.         final double h2 = h * h;
  157.         final double q2 = q * q;
  158.         final double p2 = p * p;

  160.         // A, B, C parameters [Eq. 2.1.6-(1)]
  161.         A = FastMath.sqrt(mu * sma);
  162.         B = FastMath.sqrt(1 - k2 - h2);
  163.         C = 1 + q2 + p2;

  165.         // Equinoctial reference frame [Eq. 2.1.4-(1)]
  166.         final double ooC = 1. / C;
  167.         final double px2 = 2. * p;
  168.         final double qx2 = 2. * q;
  169.         final double pq2 = px2 * q;
  170.         f = new Vector3D(ooC, new Vector3D(1. - p2 + q2, pq2, -px2 * I));
  171.         g = new Vector3D(ooC, new Vector3D(pq2 * I, (1. + p2 - q2) * I, qx2));
  172.         w = new Vector3D(ooC, new Vector3D(px2, -qx2, (1. - p2 - q2) * I));

  174.         // Direction cosines for central body [Eq. 2.1.9-(1)]
  175.         alpha = f.getZ();
  176.         beta  = g.getZ();
  177.         gamma = w.getZ();
  178.     }

  180.     /** Get the date of the orbit.
  181.      * @return the date
  182.      */
  183.     public AbsoluteDate getDate() {
  184.         return date;
  185.     }

  187.     /** Get the definition frame of the orbit.
  188.      * @return the definition frame
  189.      */
  190.     public Frame getFrame() {
  191.         return frame;
  192.     }

  194.     /** Get the central body attraction coefficient.
  195.      * @return μ
  196.      */
  197.     public double getMu() {
  198.         return mu;
  199.     }

  201.     /** Get the eccentricity.
  202.      * @return ecc
  203.      */
  204.     public double getEcc() {
  205.         return ecc;
  206.     }

  208.     /** Get the Keplerian mean motion.
  209.      * @return n
  210.      */
  211.     public double getMeanMotion() {
  212.         return n;
  213.     }

  215.     /** Get the Keplerian period.
  216.      * @return period
  217.      */
  218.     public double getKeplerianPeriod() {
  219.         return period;
  220.     }

  222.     /** Get the semi-major axis.
  223.      * @return the semi-major axis a
  224.      */
  225.     public double getSma() {
  226.         return sma;
  227.     }

  229.     /** Get the x component of eccentricity vector.
  230.      * <p>
  231.      * This element called k in DSST corresponds to ex
  232.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  233.      * </p>
  234.      * @return k
  235.      */
  236.     public double getK() {
  237.         return k;
  238.     }

  240.     /** Get the y component of eccentricity vector.
  241.      * <p>
  242.      * This element called h in DSST corresponds to ey
  243.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  244.      * </p>
  245.      * @return h
  246.      */
  247.     public double getH() {
  248.         return h;
  249.     }

  251.     /** Get the x component of inclination vector.
  252.      * <p>
  253.      * This element called q in DSST corresponds to hx
  254.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  255.      * </p>
  256.      * @return q
  257.      */
  258.     public double getQ() {
  259.         return q;
  260.     }

  262.     /** Get the y component of inclination vector.
  263.      * <p>
  264.      * This element called p in DSST corresponds to hy
  265.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  266.      * </p>
  267.      * @return p
  268.      */
  269.     public double getP() {
  270.         return p;
  271.     }

  273.     /** Get the mean longitude.
  274.      * @return lm
  275.      */
  276.     public double getLM() {
  277.         return lm;
  278.     }

  280.     /** Get the true longitude.
  281.      * @return lv
  282.      */
  283.     public double getLv() {
  284.         return lv;
  285.     }

  287.     /** Get the eccentric longitude.
  288.      * @return lf
  289.      */
  290.     public double getLf() {
  291.         return le;
  292.     }

  294.     /** Get the retrograde factor.
  295.      * @return the retrograde factor I
  296.      */
  297.     public int getRetrogradeFactor() {
  298.         return I;
  299.     }

  301.     /** Get A = sqrt(μ * a).
  302.      * @return A
  303.      */
  304.     public double getA() {
  305.         return A;
  306.     }

  308.     /** Get B = sqrt(1 - e²).
  309.      * @return B
  310.      */
  311.     public double getB() {
  312.         return B;
  313.     }

  315.     /** Get C = 1 + p² + q².
  316.      * @return C
  317.      */
  318.     public double getC() {
  319.         return C;
  320.     }

  322.     /** Get equinoctial frame vector f.
  323.      * @return f vector
  324.      */
  325.     public Vector3D getVectorF() {
  326.         return f;
  327.     }

  329.     /** Get equinoctial frame vector g.
  330.      * @return g vector
  331.      */
  332.     public Vector3D getVectorG() {
  333.         return g;
  334.     }

  336.     /** Get equinoctial frame vector w.
  337.      * @return w vector
  338.      */
  339.     public Vector3D getVectorW() {
  340.         return w;
  341.     }

  343.     /** Get direction cosine α for central body.
  344.      * @return α
  345.      */
  346.     public double getAlpha() {
  347.         return alpha;
  348.     }

  350.     /** Get direction cosine β for central body.
  351.      * @return β
  352.      */
  353.     public double getBeta() {
  354.         return beta;
  355.     }

  357.     /** Get direction cosine γ for central body.
  358.      * @return γ
  359.      */
  360.     public double getGamma() {
  361.         return gamma;
  362.     }

  364. }
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