SDP4.java
- /* 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
- * limitations under the License.
- */
- 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);
- }