FieldSGP4.java
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package org.orekit.propagation.analytical.tle;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.FieldSinCos;
import org.orekit.annotation.DefaultDataContext;
import org.orekit.attitudes.AttitudeProvider;
import org.orekit.data.DataContext;
import org.orekit.frames.Frame;
/** This class contains methods to compute propagated coordinates with the SGP4 model.
* <p>
* The user should not bother in this class since it is handled internaly by the
* {@link TLEPropagator}.
* </p>
* <p>This implementation is largely inspired from the paper and source code <a
* href="https://www.celestrak.com/publications/AIAA/2006-6753/">Revisiting Spacetrack
* Report #3</a> and is fully compliant with its results and tests cases.</p>
* @author Felix R. Hoots, Ronald L. Roehrich, December 1980 (original fortran)
* @author David A. Vallado, Paul Crawford, Richard Hujsak, T.S. Kelso (C++ translation and improvements)
* @author Fabien Maussion (java translation)
* @author Thomas Paulet (field translation)
* @since 11.0
* @param <T> type of the field elements
*/
public class FieldSGP4<T extends CalculusFieldElement<T>> extends FieldTLEPropagator<T> {
/** If perige is less than 220 km, some calculus are avoided. */
private boolean lessThan220;
/** (1 + eta * cos(M0))³. */
private T delM0;
// CHECKSTYLE: stop JavadocVariable check
private T d2;
private T d3;
private T d4;
private T t3cof;
private T t4cof;
private T t5cof;
private T sinM0;
private T omgcof;
private T xmcof;
private T c5;
// CHECKSTYLE: resume JavadocVariable check
/** Constructor for a unique initial TLE.
*
* <p>This constructor uses the {@link DataContext#getDefault() default data context}.
*
* @param initialTLE the TLE to propagate.
* @param attitudeProvider provider for attitude computation
* @param mass spacecraft mass (kg)
* @param parameters SGP4 and SDP4 model parameters
* @see #FieldSGP4(FieldTLE, AttitudeProvider, CalculusFieldElement, Frame, CalculusFieldElement[])
*/
@DefaultDataContext
public FieldSGP4(final FieldTLE<T> initialTLE, final AttitudeProvider attitudeProvider,
final T mass, final T[] parameters) {
this(initialTLE, attitudeProvider, mass,
DataContext.getDefault().getFrames().getTEME(), parameters);
}
/** Constructor for a unique initial TLE.
* @param initialTLE the TLE to propagate.
* @param attitudeProvider provider for attitude computation
* @param mass spacecraft mass (kg)
* @param teme the TEME frame to use for propagation.
* @param parameters SGP4 and SDP4 model parameters
*/
public FieldSGP4(final FieldTLE<T> initialTLE,
final AttitudeProvider attitudeProvider,
final T mass,
final Frame teme,
final T[] parameters) {
super(initialTLE, attitudeProvider, mass, teme, parameters);
}
/** Initialization proper to each propagator (SGP or SDP).
* @param parameters model parameters
*/
protected void sxpInitialize(final T[] parameters) {
final T bStar = parameters[0];
// For perigee less than 220 kilometers, the equations are truncated to
// linear variation in sqrt a and quadratic variation in mean anomaly.
// Also, the c3 term, the delta omega term, and the delta m term are dropped.
lessThan220 = perige.getReal() < 220;
if (!lessThan220) {
final FieldSinCos<T> scM0 = FastMath.sinCos(tle.getMeanAnomaly());
final T c1sq = c1.multiply(c1);
delM0 = eta.multiply(scM0.cos()).add(1.0);
delM0 = delM0.multiply(delM0).multiply(delM0);
d2 = a0dp.multiply(tsi).multiply(c1sq).multiply(4.0);
final T temp = d2.multiply(tsi).multiply(c1).divide(3.0);
d3 = a0dp.multiply(17.0).add(s4).multiply(temp);
d4 = temp.multiply(0.5).multiply(a0dp).multiply(tsi).multiply(a0dp.multiply(221.0).add(s4.multiply(31.0))).multiply(c1);
t3cof = d2.add(c1sq.multiply(2));
t4cof = d3.multiply(3.0).add(c1.multiply(d2.multiply(12.0).add(c1sq.multiply(10)))).multiply(0.25);
t5cof = d4.multiply(3.0).add(c1.multiply(12.0).multiply(d3)).add(
d2.multiply(d2).multiply(6.0)).add(c1sq.multiply(15.0).multiply(d2.multiply(2).add(c1sq))).multiply(0.2);
sinM0 = scM0.sin();
if (tle.getE().getReal() < 1e-4) {
omgcof = c1sq.getField().getZero();
xmcof = c1sq.getField().getZero();
} else {
final T c3 = coef.multiply(tsi).multiply(xn0dp).multiply(TLEConstants.A3OVK2 * TLEConstants.NORMALIZED_EQUATORIAL_RADIUS).multiply(sini0.divide(tle.getE()));
xmcof = coef.multiply(bStar).divide(eeta).multiply(-TLEConstants.TWO_THIRD * TLEConstants.NORMALIZED_EQUATORIAL_RADIUS);
omgcof = bStar.multiply(c3).multiply(FastMath.cos(tle.getPerigeeArgument()));
}
}
c5 = coef1.multiply(2).multiply(a0dp).multiply(beta02).multiply(etasq.add(eeta).multiply(2.75).add(eeta.multiply(etasq)).add(1));
// initialized
}
/** Propagation proper to each propagator (SGP or SDP).
* @param tSince the offset from initial epoch (min)
* @param parameters model parameters
*/
protected void sxpPropagate(final T tSince, final T[] parameters) {
// Update for secular gravity and atmospheric drag.
final T bStar = parameters[0];
final T xmdf = tle.getMeanAnomaly().add(xmdot.multiply(tSince));
final T omgadf = tle.getPerigeeArgument().add(omgdot.multiply(tSince));
final T xn0ddf = tle.getRaan().add(xnodot.multiply(tSince));
omega = omgadf;
T xmp = xmdf;
final T tsq = tSince.multiply(tSince);
xnode = xn0ddf.add(xnodcf.multiply(tsq));
T tempa = c1.multiply(tSince).negate().add(1.0);
T tempe = bStar.multiply(c4).multiply(tSince);
T templ = t2cof.multiply(tsq);
if (!lessThan220) {
final T delomg = omgcof.multiply(tSince);
T delm = eta.multiply(FastMath.cos(xmdf)).add(1.0);
delm = xmcof.multiply(delm.multiply(delm).multiply(delm).subtract(delM0));
final T temp = delomg.add(delm);
xmp = xmdf.add(temp);
omega = omgadf.subtract(temp);
final T tcube = tsq.multiply(tSince);
final T tfour = tSince.multiply(tcube);
tempa = tempa.subtract(d2.multiply(tsq)).subtract(d3.multiply(tcube)).subtract(d4.multiply(tfour));
tempe = tempe.add(bStar.multiply(c5).multiply(FastMath.sin(xmp).subtract(sinM0)));
templ = templ.add(t3cof.multiply(tcube)).add(tfour.multiply(t4cof.add(tSince.multiply(t5cof))));
}
a = a0dp.multiply(tempa).multiply(tempa);
e = tle.getE().subtract(tempe);
// A highly arbitrary lower limit on e, of 1e-6:
if (e.getReal() < 1e-6) {
e = e.getField().getZero().add(1e-6);
}
xl = xmp.add(omega).add(xnode).add(xn0dp.multiply(templ));
i = tle.getI();
}
}