AuxiliaryElements.java

  1. /* Copyright 2002-2013 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.apache.commons.math3.geometry.euclidean.threed.Vector3D;
  20. import org.apache.commons.math3.util.FastMath;
  21. import org.apache.commons.math3.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.     /** Retrograde factor I.
  72.      *  <p>
  73.      *  DSST model needs equinoctial orbit as internal representation.
  74.      *  Classical equinoctial elements have discontinuities when inclination
  75.      *  is close to zero. In this representation, I = +1. <br>
  76.      *  To avoid this discontinuity, another representation exists and equinoctial
  77.      *  elements can be expressed in a different way, called "retrograde" orbit.
  78.      *  This implies I = -1. <br>
  79.      *  As Orekit doesn't implement the retrograde orbit, I is always set to +1.
  80.      *  But for the sake of consistency with the theory, the retrograde factor
  81.      *  has been kept in the formulas.
  82.      *  </p>
  83.      */
  84.     private final int    I;

  86.     /** A = sqrt(&mu; * a). */
  87.     private final double A;

  89.     /** B = sqrt(1 - h<sup>2</sup> - k<sup>2</sup>). */
  90.     private final double B;

  92.     /** C = 1 + p<sup>2</sup> + q<sup>2</sup>. */
  93.     private final double C;

  95.     /** Equinoctial frame f vector. */
  96.     private final Vector3D f;

  98.     /** Equinoctial frame g vector. */
  99.     private final Vector3D g;

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

  104.     /** Direction cosine &alpha;. */
  105.     private final double alpha;

  107.     /** Direction cosine &beta;. */
  108.     private final double beta;

  110.     /** Direction cosine &gamma;. */
  111.     private final double gamma;

  113.     /** Simple constructor.
  114.      * @param orbit related mean orbit for auxiliary elements
  115.      * @param retrogradeFactor retrograde factor I [Eq. 2.1.2-(2)]
  116.      */
  117.     public AuxiliaryElements(final Orbit orbit, final int retrogradeFactor) {
  118.         // Date of the orbit
  119.         date = orbit.getDate();

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

  124.         // Central body attraction coefficient
  125.         mu = orbit.getMu();

  127.         // Eccentricity
  128.         ecc = orbit.getE();

  130.         // Keplerian mean motion
  131.         n = orbit.getKeplerianMeanMotion();

  133.         // Keplerian period
  134.         period = orbit.getKeplerianPeriod();

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

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

  147.         final double k2 = k * k;
  148.         final double h2 = h * h;
  149.         final double q2 = q * q;
  150.         final double p2 = p * p;

  152.         // A, B, C parameters [Eq. 2.1.6-(1)]
  153.         A = FastMath.sqrt(mu * sma);
  154.         B = FastMath.sqrt(1 - k2 - h2);
  155.         C = 1 + q2 + p2;

  157.         // Equinoctial reference frame [Eq. 2.1.4-(1)]
  158.         final double ooC = 1. / C;
  159.         final double px2 = 2. * p;
  160.         final double qx2 = 2. * q;
  161.         final double pq2 = px2 * q;
  162.         f = new Vector3D(ooC, new Vector3D(1. - p2 + q2, pq2, -px2 * I));
  163.         g = new Vector3D(ooC, new Vector3D(pq2 * I, (1. + p2 - q2) * I, qx2));
  164.         w = new Vector3D(ooC, new Vector3D(px2, -qx2, (1. - p2 - q2) * I));

  166.         // Direction cosines for central body [Eq. 2.1.9-(1)]
  167.         alpha = f.getZ();
  168.         beta  = g.getZ();
  169.         gamma = w.getZ();
  170.     }

  172.     /** Get the date of the orbit.
  173.      * @return the date
  174.      */
  175.     public AbsoluteDate getDate() {
  176.         return date;
  177.     }

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

  186.     /** Get the central body attraction coefficient.
  187.      * @return &mu;
  188.      */
  189.     public double getMu() {
  190.         return mu;
  191.     }

  193.     /** Get the eccentricity.
  194.      * @return ecc
  195.      */
  196.     public double getEcc() {
  197.         return ecc;
  198.     }

  200.     /** Get the Keplerian mean motion.
  201.      * @return n
  202.      */
  203.     public double getMeanMotion() {
  204.         return n;
  205.     }

  207.     /** Get the Keplerian period.
  208.      * @return period
  209.      */
  210.     public double getKeplerianPeriod() {
  211.         return period;
  212.     }

  214.     /** Get the semi-major axis.
  215.      * @return the semi-major axis a
  216.      */
  217.     public double getSma() {
  218.         return sma;
  219.     }

  221.     /** Get the x component of eccentricity vector.
  222.      * <p>
  223.      * This element called k in DSST corresponds to ex
  224.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  225.      * </p>
  226.      * @return k
  227.      */
  228.     public double getK() {
  229.         return k;
  230.     }

  232.     /** Get the y component of eccentricity vector.
  233.      * <p>
  234.      * This element called h in DSST corresponds to ey
  235.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  236.      * </p>
  237.      * @return h
  238.      */
  239.     public double getH() {
  240.         return h;
  241.     }

  243.     /** Get the x component of inclination vector.
  244.      * <p>
  245.      * This element called q in DSST corresponds to hx
  246.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  247.      * </p>
  248.      * @return q
  249.      */
  250.     public double getQ() {
  251.         return q;
  252.     }

  254.     /** Get the y component of inclination vector.
  255.      * <p>
  256.      * This element called p in DSST corresponds to hy
  257.      * for the {@link org.orekit.orbits.EquinoctialOrbit}
  258.      * </p>
  259.      * @return p
  260.      */
  261.     public double getP() {
  262.         return p;
  263.     }

  265.     /** Get the mean longitude.
  266.      * @return lm
  267.      */
  268.     public double getLM() {
  269.         return lm;
  270.     }

  272.     /** Get the retrograde factor.
  273.      * @return the retrograde factor I
  274.      */
  275.     public int getRetrogradeFactor() {
  276.         return I;
  277.     }

  279.     /** Get A = sqrt(&mu; * a).
  280.      * @return A
  281.      */
  282.     public double getA() {
  283.         return A;
  284.     }

  286.     /** Get B = sqrt(1 - e<sup>2</sup>).
  287.      * @return B
  288.      */
  289.     public double getB() {
  290.         return B;
  291.     }

  293.     /** Get C = 1 + p<sup>2</sup> + q<sup>2</sup>.
  294.      * @return C
  295.      */
  296.     public double getC() {
  297.         return C;
  298.     }

  300.     /** Get equinoctial frame vector f.
  301.      * @return f vector
  302.      */
  303.     public Vector3D getVectorF() {
  304.         return f;
  305.     }

  307.     /** Get equinoctial frame vector g.
  308.      * @return g vector
  309.      */
  310.     public Vector3D getVectorG() {
  311.         return g;
  312.     }

  314.     /** Get equinoctial frame vector w.
  315.      * @return w vector
  316.      */
  317.     public Vector3D getVectorW() {
  318.         return w;
  319.     }

  321.     /** Get direction cosine &alpha; for central body.
  322.      * @return &alpha;
  323.      */
  324.     public double getAlpha() {
  325.         return alpha;
  326.     }

  328.     /** Get direction cosine &beta; for central body.
  329.      * @return &beta;
  330.      */
  331.     public double getBeta() {
  332.         return beta;
  333.     }

  335.     /** Get direction cosine &gamma; for central body.
  336.      * @return &gamma;
  337.      */
  338.     public double getGamma() {
  339.         return gamma;
  340.     }

  342. }
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