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* 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,
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package org.orekit.propagation.analytical.tle;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.MathUtils;
import org.orekit.attitudes.AttitudeProvider;
import org.orekit.errors.OrekitException;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.TimeScalesFactory;
import org.orekit.utils.Constants;
/** This class contains methods to compute propagated coordinates with the SDP4 model.
* <p>
* The user should not bother in this class since it is handled internally by the
* {@link TLEPropagator}.
* </p>
* <p>This implementation is largely inspired from the paper and source code <a
* href="http://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)
*/
abstract class SDP4 extends TLEPropagator {
// CHECKSTYLE: stop VisibilityModifierCheck
/** New perigee argument. */
protected double omgadf;
/** New mean motion. */
protected double xn;
/** Parameter for xl computation. */
protected double xll;
/** New eccentricity. */
protected double em;
/** New inclination. */
protected double xinc;
// CHECKSTYLE: resume VisibilityModifierCheck
/** Constructor for a unique initial TLE.
* @param initialTLE the TLE to propagate.
* @param attitudeProvider provider for attitude computation
* @param mass spacecraft mass (kg)
* @exception OrekitException if some specific error occurs
*/
protected SDP4(final TLE initialTLE, final AttitudeProvider attitudeProvider,
final double mass) throws OrekitException {
super(initialTLE, attitudeProvider, mass);
}
/** Initialization proper to each propagator (SGP or SDP).
* @exception OrekitException when UTC time steps can't be read
*/
protected void sxpInitialize() throws OrekitException {
luniSolarTermsComputation();
} // End of initialization
/** Propagation proper to each propagator (SGP or SDP).
* @param tSince the offset from initial epoch (minutes)
*/
protected void sxpPropagate(final double tSince) {
// Update for secular gravity and atmospheric drag
omgadf = tle.getPerigeeArgument() + omgdot * tSince;
final double xnoddf = tle.getRaan() + xnodot * tSince;
final double tSinceSq = tSince * tSince;
xnode = xnoddf + xnodcf * tSinceSq;
xn = xn0dp;
// Update for deep-space secular effects
xll = tle.getMeanAnomaly() + xmdot * tSince;
deepSecularEffects(tSince);
final double tempa = 1 - c1 * tSince;
a = FastMath.pow(TLEConstants.XKE / xn, TLEConstants.TWO_THIRD) * tempa * tempa;
em -= tle.getBStar() * c4 * tSince;
// Update for deep-space periodic effects
xll += xn0dp * t2cof * tSinceSq;
deepPeriodicEffects(tSince);
xl = xll + omgadf + xnode;
// Dundee change: Reset cosio, sinio for new xinc:
cosi0 = FastMath.cos(xinc);
sini0 = FastMath.sin(xinc);
e = em;
i = xinc;
omega = omgadf;
// end of calculus, go for PV computation
}
/** Computes SPACETRACK#3 compliant earth rotation angle.
* @param date the current date
* @return the ERA (rad)
* @exception OrekitException when UTC time steps can't be read
*/
protected static double thetaG(final AbsoluteDate date) throws OrekitException {
// Reference: The 1992 Astronomical Almanac, page B6.
final double omega_E = 1.00273790934;
final double jd = (date.durationFrom(AbsoluteDate.JULIAN_EPOCH) +
date.timeScalesOffset(TimeScalesFactory.getUTC(), TimeScalesFactory.getTT())
) / Constants.JULIAN_DAY;
// Earth rotations per sidereal day (non-constant)
final double UT = (jd + 0.5) % 1;
final double seconds_per_day = Constants.JULIAN_DAY;
final double jd_2000 = 2451545.0; /* 1.5 Jan 2000 = JD 2451545. */
final double t_cen = (jd - UT - jd_2000) / 36525.;
double GMST = 24110.54841 +
t_cen * (8640184.812866 + t_cen * (0.093104 - t_cen * 6.2E-6));
GMST = (GMST + seconds_per_day * omega_E * UT) % seconds_per_day;
if (GMST < 0.) {
GMST += seconds_per_day;
}
return MathUtils.TWO_PI * GMST / seconds_per_day;
}
/** Computes luni - solar terms from initial coordinates and epoch.
* @exception OrekitException when UTC time steps can't be read
*/
protected abstract void luniSolarTermsComputation() throws OrekitException;
/** Computes secular terms from current coordinates and epoch.
* @param t offset from initial epoch (min)
*/
protected abstract void deepSecularEffects(double t);
/** Computes periodic terms from current coordinates and epoch.
* @param t offset from initial epoch (min)
*/
protected abstract void deepPeriodicEffects(double t);
}