/* Copyright 2002-2017 CS Systèmes d'Information
* Licensed to CS Systèmes d'Information (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
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*/
package org.orekit.propagation.semianalytical.dsst.utilities;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.MathUtils;
import org.orekit.frames.Frame;
import org.orekit.orbits.Orbit;
import org.orekit.time.AbsoluteDate;
/** Container class for common parameters used by all DSST forces.
* <p>
* Most of them are defined in Danielson paper at § 2.1.
* </p>
* @author Pascal Parraud
*/
public class AuxiliaryElements {
/** Orbit date. */
private final AbsoluteDate date;
/** Orbit frame. */
private final Frame frame;
/** Central body attraction coefficient. */
private final double mu;
/** Eccentricity. */
private final double ecc;
/** Keplerian mean motion. */
private final double n;
/** Keplerian period. */
private final double period;
/** Semi-major axis. */
private final double sma;
/** x component of eccentricity vector. */
private final double k;
/** y component of eccentricity vector. */
private final double h;
/** x component of inclination vector. */
private final double q;
/** y component of inclination vector. */
private final double p;
/** Mean longitude. */
private final double lm;
/** True longitude. */
private final double lv;
/** Eccentric longitude. */
private final double le;
/** Retrograde factor I.
* <p>
* DSST model needs equinoctial orbit as internal representation.
* Classical equinoctial elements have discontinuities when inclination
* is close to zero. In this representation, I = +1. <br>
* To avoid this discontinuity, another representation exists and equinoctial
* elements can be expressed in a different way, called "retrograde" orbit.
* This implies I = -1. <br>
* As Orekit doesn't implement the retrograde orbit, I is always set to +1.
* But for the sake of consistency with the theory, the retrograde factor
* has been kept in the formulas.
* </p>
*/
private final int I;
/** A = sqrt(μ * a). */
private final double A;
/** B = sqrt(1 - h² - k²). */
private final double B;
/** C = 1 + p² + q². */
private final double C;
/** Equinoctial frame f vector. */
private final Vector3D f;
/** Equinoctial frame g vector. */
private final Vector3D g;
/** Equinoctial frame w vector. */
private final Vector3D w;
/** Direction cosine α. */
private final double alpha;
/** Direction cosine β. */
private final double beta;
/** Direction cosine γ. */
private final double gamma;
/** Simple constructor.
* @param orbit related mean orbit for auxiliary elements
* @param retrogradeFactor retrograde factor I [Eq. 2.1.2-(2)]
*/
public AuxiliaryElements(final Orbit orbit, final int retrogradeFactor) {
// Date of the orbit
date = orbit.getDate();
// Orbit definition frame
frame = orbit.getFrame();
// Central body attraction coefficient
mu = orbit.getMu();
// Eccentricity
ecc = orbit.getE();
// Keplerian mean motion
n = orbit.getKeplerianMeanMotion();
// Keplerian period
period = orbit.getKeplerianPeriod();
// Equinoctial elements [Eq. 2.1.2-(1)]
sma = orbit.getA();
k = orbit.getEquinoctialEx();
h = orbit.getEquinoctialEy();
q = orbit.getHx();
p = orbit.getHy();
lm = MathUtils.normalizeAngle(orbit.getLM(), FastMath.PI);
lv = MathUtils.normalizeAngle(orbit.getLv(), FastMath.PI);
le = MathUtils.normalizeAngle(orbit.getLE(), FastMath.PI);
// Retrograde factor [Eq. 2.1.2-(2)]
I = retrogradeFactor;
final double k2 = k * k;
final double h2 = h * h;
final double q2 = q * q;
final double p2 = p * p;
// A, B, C parameters [Eq. 2.1.6-(1)]
A = FastMath.sqrt(mu * sma);
B = FastMath.sqrt(1 - k2 - h2);
C = 1 + q2 + p2;
// Equinoctial reference frame [Eq. 2.1.4-(1)]
final double ooC = 1. / C;
final double px2 = 2. * p;
final double qx2 = 2. * q;
final double pq2 = px2 * q;
f = new Vector3D(ooC, new Vector3D(1. - p2 + q2, pq2, -px2 * I));
g = new Vector3D(ooC, new Vector3D(pq2 * I, (1. + p2 - q2) * I, qx2));
w = new Vector3D(ooC, new Vector3D(px2, -qx2, (1. - p2 - q2) * I));
// Direction cosines for central body [Eq. 2.1.9-(1)]
alpha = f.getZ();
beta = g.getZ();
gamma = w.getZ();
}
/** Get the date of the orbit.
* @return the date
*/
public AbsoluteDate getDate() {
return date;
}
/** Get the definition frame of the orbit.
* @return the definition frame
*/
public Frame getFrame() {
return frame;
}
/** Get the central body attraction coefficient.
* @return μ
*/
public double getMu() {
return mu;
}
/** Get the eccentricity.
* @return ecc
*/
public double getEcc() {
return ecc;
}
/** Get the Keplerian mean motion.
* @return n
*/
public double getMeanMotion() {
return n;
}
/** Get the Keplerian period.
* @return period
*/
public double getKeplerianPeriod() {
return period;
}
/** Get the semi-major axis.
* @return the semi-major axis a
*/
public double getSma() {
return sma;
}
/** Get the x component of eccentricity vector.
* <p>
* This element called k in DSST corresponds to ex
* for the {@link org.orekit.orbits.EquinoctialOrbit}
* </p>
* @return k
*/
public double getK() {
return k;
}
/** Get the y component of eccentricity vector.
* <p>
* This element called h in DSST corresponds to ey
* for the {@link org.orekit.orbits.EquinoctialOrbit}
* </p>
* @return h
*/
public double getH() {
return h;
}
/** Get the x component of inclination vector.
* <p>
* This element called q in DSST corresponds to hx
* for the {@link org.orekit.orbits.EquinoctialOrbit}
* </p>
* @return q
*/
public double getQ() {
return q;
}
/** Get the y component of inclination vector.
* <p>
* This element called p in DSST corresponds to hy
* for the {@link org.orekit.orbits.EquinoctialOrbit}
* </p>
* @return p
*/
public double getP() {
return p;
}
/** Get the mean longitude.
* @return lm
*/
public double getLM() {
return lm;
}
/** Get the true longitude.
* @return lv
*/
public double getLv() {
return lv;
}
/** Get the eccentric longitude.
* @return lf
*/
public double getLf() {
return le;
}
/** Get the retrograde factor.
* @return the retrograde factor I
*/
public int getRetrogradeFactor() {
return I;
}
/** Get A = sqrt(μ * a).
* @return A
*/
public double getA() {
return A;
}
/** Get B = sqrt(1 - e²).
* @return B
*/
public double getB() {
return B;
}
/** Get C = 1 + p² + q².
* @return C
*/
public double getC() {
return C;
}
/** Get equinoctial frame vector f.
* @return f vector
*/
public Vector3D getVectorF() {
return f;
}
/** Get equinoctial frame vector g.
* @return g vector
*/
public Vector3D getVectorG() {
return g;
}
/** Get equinoctial frame vector w.
* @return w vector
*/
public Vector3D getVectorW() {
return w;
}
/** Get direction cosine α for central body.
* @return α
*/
public double getAlpha() {
return alpha;
}
/** Get direction cosine β for central body.
* @return β
*/
public double getBeta() {
return beta;
}
/** Get direction cosine γ for central body.
* @return γ
*/
public double getGamma() {
return gamma;
}
}