1 /* Copyright 2002-2018 CS Systèmes d'Information
2 * Licensed to CS Systèmes d'Information (CS) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * CS licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.orekit.propagation.analytical.tle;
18
19 import org.hipparchus.util.FastMath;
20 import org.hipparchus.util.MathUtils;
21 import org.orekit.attitudes.AttitudeProvider;
22 import org.orekit.errors.OrekitException;
23 import org.orekit.time.AbsoluteDate;
24 import org.orekit.time.TimeScalesFactory;
25 import org.orekit.utils.Constants;
26
27 /** This class contains methods to compute propagated coordinates with the SDP4 model.
28 * <p>
29 * The user should not bother in this class since it is handled internally by the
30 * {@link TLEPropagator}.
31 * </p>
32 * <p>This implementation is largely inspired from the paper and source code <a
33 * href="http://www.celestrak.com/publications/AIAA/2006-6753/">Revisiting Spacetrack
34 * Report #3</a> and is fully compliant with its results and tests cases.</p>
35 * @author Felix R. Hoots, Ronald L. Roehrich, December 1980 (original fortran)
36 * @author David A. Vallado, Paul Crawford, Richard Hujsak, T.S. Kelso (C++ translation and improvements)
37 * @author Fabien Maussion (java translation)
38 */
39 abstract class SDP4 extends TLEPropagator {
40
41 // CHECKSTYLE: stop VisibilityModifier check
42
43 /** New perigee argument. */
44 protected double omgadf;
45
46 /** New mean motion. */
47 protected double xn;
48
49 /** Parameter for xl computation. */
50 protected double xll;
51
52 /** New eccentricity. */
53 protected double em;
54
55 /** New inclination. */
56 protected double xinc;
57
58 // CHECKSTYLE: resume VisibilityModifier check
59
60 /** Constructor for a unique initial TLE.
61 * @param initialTLE the TLE to propagate.
62 * @param attitudeProvider provider for attitude computation
63 * @param mass spacecraft mass (kg)
64 * @exception OrekitException if some specific error occurs
65 */
66 protected SDP4(final TLE initialTLE, final AttitudeProvider attitudeProvider,
67 final double mass) throws OrekitException {
68 super(initialTLE, attitudeProvider, mass);
69 }
70
71 /** Initialization proper to each propagator (SGP or SDP).
72 * @exception OrekitException when UTC time steps can't be read
73 */
74 protected void sxpInitialize() throws OrekitException {
75 luniSolarTermsComputation();
76 } // End of initialization
77
78 /** Propagation proper to each propagator (SGP or SDP).
79 * @param tSince the offset from initial epoch (minutes)
80 */
81 protected void sxpPropagate(final double tSince) {
82
83 // Update for secular gravity and atmospheric drag
84 omgadf = tle.getPerigeeArgument() + omgdot * tSince;
85 final double xnoddf = tle.getRaan() + xnodot * tSince;
86 final double tSinceSq = tSince * tSince;
87 xnode = xnoddf + xnodcf * tSinceSq;
88 xn = xn0dp;
89
90 // Update for deep-space secular effects
91 xll = tle.getMeanAnomaly() + xmdot * tSince;
92
93 deepSecularEffects(tSince);
94
95 final double tempa = 1 - c1 * tSince;
96 a = FastMath.pow(TLEConstants.XKE / xn, TLEConstants.TWO_THIRD) * tempa * tempa;
97 em -= tle.getBStar() * c4 * tSince;
98
99 // Update for deep-space periodic effects
100 xll += xn0dp * t2cof * tSinceSq;
101
102 deepPeriodicEffects(tSince);
103
104 xl = xll + omgadf + xnode;
105
106 // Dundee change: Reset cosio, sinio for new xinc:
107 cosi0 = FastMath.cos(xinc);
108 sini0 = FastMath.sin(xinc);
109 e = em;
110 i = xinc;
111 omega = omgadf;
112 // end of calculus, go for PV computation
113 }
114
115 /** Computes SPACETRACK#3 compliant earth rotation angle.
116 * @param date the current date
117 * @return the ERA (rad)
118 * @exception OrekitException when UTC time steps can't be read
119 */
120 protected static double thetaG(final AbsoluteDate date) throws OrekitException {
121
122 // Reference: The 1992 Astronomical Almanac, page B6.
123 final double omega_E = 1.00273790934;
124 final double jd = (date.durationFrom(AbsoluteDate.JULIAN_EPOCH) +
125 date.timeScalesOffset(TimeScalesFactory.getUTC(), TimeScalesFactory.getTT())
126 ) / Constants.JULIAN_DAY;
127
128 // Earth rotations per sidereal day (non-constant)
129 final double UT = (jd + 0.5) % 1;
130 final double seconds_per_day = Constants.JULIAN_DAY;
131 final double jd_2000 = 2451545.0; /* 1.5 Jan 2000 = JD 2451545. */
132 final double t_cen = (jd - UT - jd_2000) / 36525.;
133 double GMST = 24110.54841 +
134 t_cen * (8640184.812866 + t_cen * (0.093104 - t_cen * 6.2E-6));
135 GMST = (GMST + seconds_per_day * omega_E * UT) % seconds_per_day;
136 if (GMST < 0.) {
137 GMST += seconds_per_day;
138 }
139
140 return MathUtils.TWO_PI * GMST / seconds_per_day;
141
142 }
143
144 /** Computes luni - solar terms from initial coordinates and epoch.
145 * @exception OrekitException when UTC time steps can't be read
146 */
147 protected abstract void luniSolarTermsComputation() throws OrekitException;
148
149 /** Computes secular terms from current coordinates and epoch.
150 * @param t offset from initial epoch (min)
151 */
152 protected abstract void deepSecularEffects(double t);
153
154 /** Computes periodic terms from current coordinates and epoch.
155 * @param t offset from initial epoch (min)
156 */
157 protected abstract void deepPeriodicEffects(double t);
158
159 }