FieldDSSTTesseralContext.java
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package org.orekit.propagation.semianalytical.dsst.forces;
import org.hipparchus.Field;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.util.FastMath;
import org.orekit.forces.gravity.potential.UnnormalizedSphericalHarmonicsProvider;
import org.orekit.frames.FieldTransform;
import org.orekit.frames.Frame;
import org.orekit.propagation.semianalytical.dsst.utilities.FieldAuxiliaryElements;
/**
* This class is a container for the common "field" parameters used in {@link DSSTTesseral}.
* <p>
* It performs parameters initialization at each integration step for the Tesseral contribution
* to the central body gravitational perturbation.
* <p>
* @author Bryan Cazabonne
* @since 10.0
*/
public class FieldDSSTTesseralContext<T extends CalculusFieldElement<T>> extends FieldForceModelContext<T> {
/** 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 static final int I = 1;
/** A = sqrt(μ * a). */
private T A;
// Common factors for potential computation
/** Χ = 1 / sqrt(1 - e²) = 1 / B. */
private T chi;
/** Χ². */
private T chi2;
/** Central body rotation angle θ. */
private T theta;
// Common factors from equinoctial coefficients
/** 2 * a / A .*/
private T ax2oA;
/** 1 / (A * B) .*/
private T ooAB;
/** B / A .*/
private T BoA;
/** B / (A * (1 + B)) .*/
private T BoABpo;
/** C / (2 * A * B) .*/
private T Co2AB;
/** μ / a .*/
private T moa;
/** R / a .*/
private T roa;
/** ecc². */
private T e2;
/** Keplerian mean motion. */
private T n;
/** Keplerian period. */
private T period;
/** Ratio of satellite period to central body rotation period. */
private T ratio;
/**
* Simple constructor.
*
* @param auxiliaryElements auxiliary elements related to the current orbit
* @param centralBodyFrame rotating body frame
* @param provider provider for spherical harmonics
* @param maxFrequencyShortPeriodics maximum value for j
* @param bodyPeriod central body rotation period (seconds)
* @param parameters values of the force model parameters
*/
FieldDSSTTesseralContext(final FieldAuxiliaryElements<T> auxiliaryElements,
final Frame centralBodyFrame,
final UnnormalizedSphericalHarmonicsProvider provider,
final int maxFrequencyShortPeriodics,
final double bodyPeriod,
final T[] parameters) {
super(auxiliaryElements);
final Field<T> field = auxiliaryElements.getDate().getField();
final T zero = field.getZero();
final T mu = parameters[0];
// Keplerian mean motion
final T absA = FastMath.abs(auxiliaryElements.getSma());
n = FastMath.sqrt(mu.divide(absA)).divide(absA);
// Keplerian period
final T a = auxiliaryElements.getSma();
period = (a.getReal() < 0) ? zero.add(Double.POSITIVE_INFINITY) : a.multiply(a.getPi().multiply(2.0)).multiply(a.divide(mu).sqrt());
A = FastMath.sqrt(mu.multiply(auxiliaryElements.getSma()));
// Eccentricity square
e2 = auxiliaryElements.getEcc().multiply(auxiliaryElements.getEcc());
// Central body rotation angle from equation 2.7.1-(3)(4).
final FieldTransform<T> t = centralBodyFrame.getTransformTo(auxiliaryElements.getFrame(), auxiliaryElements.getDate());
final FieldVector3D<T> xB = t.transformVector(FieldVector3D.getPlusI(field));
final FieldVector3D<T> yB = t.transformVector(FieldVector3D.getPlusJ(field));
theta = FastMath.atan2(auxiliaryElements.getVectorF().dotProduct(yB).negate().add((auxiliaryElements.getVectorG().dotProduct(xB)).multiply(I)),
auxiliaryElements.getVectorF().dotProduct(xB).add(auxiliaryElements.getVectorG().dotProduct(yB).multiply(I)));
// Common factors from equinoctial coefficients
// 2 * a / A
ax2oA = auxiliaryElements.getSma().divide(A).multiply(2.);
// B / A
BoA = auxiliaryElements.getB().divide(A);
// 1 / AB
ooAB = A.multiply(auxiliaryElements.getB()).reciprocal();
// C / 2AB
Co2AB = auxiliaryElements.getC().multiply(ooAB).divide(2.);
// B / (A * (1 + B))
BoABpo = BoA.divide(auxiliaryElements.getB().add(1.));
// &mu / a
moa = mu.divide(auxiliaryElements.getSma());
// R / a
roa = auxiliaryElements.getSma().divide(provider.getAe()).reciprocal();
// Χ = 1 / B
chi = auxiliaryElements.getB().reciprocal();
chi2 = chi.multiply(chi);
// Ratio of satellite to central body periods to define resonant terms
ratio = period.divide(bodyPeriod);
}
/** Get ecc².
* @return e2
*/
public T getE2() {
return e2;
}
/** Get Central body rotation angle θ.
* @return theta
*/
public T getTheta() {
return theta;
}
/** Get ax2oA = 2 * a / A .
* @return ax2oA
*/
public T getAx2oA() {
return ax2oA;
}
/** Get Χ = 1 / sqrt(1 - e²) = 1 / B.
* @return chi
*/
public T getChi() {
return chi;
}
/** Get Χ².
* @return chi2
*/
public T getChi2() {
return chi2;
}
/** Get B / A.
* @return BoA
*/
public T getBoA() {
return BoA;
}
/** Get ooAB = 1 / (A * B).
* @return ooAB
*/
public T getOoAB() {
return ooAB;
}
/** Get Co2AB = C / 2AB.
* @return Co2AB
*/
public T getCo2AB() {
return Co2AB;
}
/** Get BoABpo = B / A(1 + B).
* @return BoABpo
*/
public T getBoABpo() {
return BoABpo;
}
/** Get μ / a .
* @return moa
*/
public T getMoa() {
return moa;
}
/** Get roa = R / a.
* @return roa
*/
public T getRoa() {
return roa;
}
/** Get the Keplerian period.
* <p>The Keplerian period is computed directly from semi major axis
* and central acceleration constant.</p>
* @return Keplerian period in seconds, or positive infinity for hyperbolic orbits
*/
public T getOrbitPeriod() {
return period;
}
/** Get the Keplerian mean motion.
* <p>The Keplerian mean motion is computed directly from semi major axis
* and central acceleration constant.</p>
* @return Keplerian mean motion in radians per second
*/
public T getMeanMotion() {
return n;
}
/** Get the ratio of satellite period to central body rotation period.
* @return ratio
*/
public T getRatio() {
return ratio;
}
}