FieldAuxiliaryElements.java
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package org.orekit.propagation.semianalytical.dsst.utilities;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.MathUtils;
import org.orekit.frames.Frame;
import org.orekit.orbits.FieldOrbit;
import org.orekit.time.FieldAbsoluteDate;
/** Container class for common parameters used by all DSST forces.
* <p>
* Most of them are defined in Danielson paper at § 2.1.
* </p>
*/
public class FieldAuxiliaryElements<T extends CalculusFieldElement<T>> {
/** Orbit date. */
private final FieldAbsoluteDate<T> date;
/** Orbit frame. */
private final Frame frame;
/** Eccentricity. */
private final T ecc;
/** Keplerian mean motion. */
private final T n;
/** Keplerian period. */
private final T period;
/** Semi-major axis. */
private final T sma;
/** x component of eccentricity vector. */
private final T k;
/** y component of eccentricity vector. */
private final T h;
/** x component of inclination vector. */
private final T q;
/** y component of inclination vector. */
private final T p;
/** Mean longitude. */
private final T lm;
/** True longitude. */
private final T lv;
/** Eccentric longitude. */
private final T 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;
/** B = sqrt(1 - h² - k²). */
private final T B;
/** C = 1 + p² + q². */
private final T C;
/** Equinoctial frame f vector. */
private final FieldVector3D<T> f;
/** Equinoctial frame g vector. */
private final FieldVector3D<T> g;
/** Equinoctial frame w vector. */
private final FieldVector3D<T> w;
/** Direction cosine α. */
private final T alpha;
/** Direction cosine β. */
private final T beta;
/** Direction cosine γ. */
private final T gamma;
/** Simple constructor.
* @param orbit related mean orbit for auxiliary elements
* @param retrogradeFactor retrograde factor I [Eq. 2.1.2-(2)]
*/
public FieldAuxiliaryElements(final FieldOrbit<T> orbit, final int retrogradeFactor) {
final T pi = orbit.getDate().getField().getZero().getPi();
// Date of the orbit
date = orbit.getDate();
// Orbit definition frame
frame = orbit.getFrame();
// 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(), pi);
lv = MathUtils.normalizeAngle(orbit.getLv(), pi);
le = MathUtils.normalizeAngle(orbit.getLE(), pi);
// Retrograde factor [Eq. 2.1.2-(2)]
I = retrogradeFactor;
final T k2 = k.multiply(k);
final T h2 = h.multiply(h);
final T q2 = q.multiply(q);
final T p2 = p.multiply(p);
// A, B, C parameters [Eq. 2.1.6-(1)]
B = FastMath.sqrt(k2.add(h2).negate().add(1.));
C = q2.add(p2).add(1);
// Equinoctial reference frame [Eq. 2.1.4-(1)]
final T ooC = C.reciprocal();
final T px2 = p.multiply(2.);
final T qx2 = q.multiply(2.);
final T pq2 = px2.multiply(q);
f = new FieldVector3D<>(ooC, new FieldVector3D<>(p2.negate().add(1.).add(q2), pq2, px2.multiply(I).negate()));
g = new FieldVector3D<>(ooC, new FieldVector3D<>(pq2.multiply(I), (p2.add(1.).subtract(q2)).multiply(I), qx2));
w = new FieldVector3D<>(ooC, new FieldVector3D<>(px2, qx2.negate(), (p2.add(q2).negate().add(1.)).multiply(I)));
// Direction cosines for central body [Eq. 2.1.9-(1)]
alpha = (T) f.getZ();
beta = (T) g.getZ();
gamma = (T) w.getZ();
}
/** Get the date of the orbit.
* @return the date
*/
public FieldAbsoluteDate<T> getDate() {
return date;
}
/** Get the definition frame of the orbit.
* @return the definition frame
*/
public Frame getFrame() {
return frame;
}
/** Get the eccentricity.
* @return ecc
*/
public T getEcc() {
return ecc;
}
/** Get the Keplerian mean motion.
* @return n
*/
public T getMeanMotion() {
return n;
}
/** Get the Keplerian period.
* @return period
*/
public T getKeplerianPeriod() {
return period;
}
/** Get the semi-major axis.
* @return the semi-major axis a
*/
public T 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 T 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 T 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 T 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 T getP() {
return p;
}
/** Get the mean longitude.
* @return lm
*/
public T getLM() {
return lm;
}
/** Get the true longitude.
* @return lv
*/
public T getLv() {
return lv;
}
/** Get the eccentric longitude.
* @return le
*/
public T getLe() {
return le;
}
/** Get the retrograde factor.
* @return the retrograde factor I
*/
public int getRetrogradeFactor() {
return I;
}
/** Get B = sqrt(1 - e²).
* @return B
*/
public T getB() {
return B;
}
/** Get C = 1 + p² + q².
* @return C
*/
public T getC() {
return C;
}
/** Get equinoctial frame vector f.
* @return f vector
*/
public FieldVector3D<T> getVectorF() {
return f;
}
/** Get equinoctial frame vector g.
* @return g vector
*/
public FieldVector3D<T> getVectorG() {
return g;
}
/** Get equinoctial frame vector w.
* @return w vector
*/
public FieldVector3D<T> getVectorW() {
return w;
}
/** Get direction cosine α for central body.
* @return α
*/
public T getAlpha() {
return alpha;
}
/** Get direction cosine β for central body.
* @return β
*/
public T getBeta() {
return beta;
}
/** Get direction cosine γ for central body.
* @return γ
*/
public T getGamma() {
return gamma;
}
}