1 /* Copyright 2002-2019 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.time.AbsoluteDate;
23 import org.orekit.time.TimeScalesFactory;
24 import org.orekit.utils.Constants;
25
26 /** This class contains methods to compute propagated coordinates with the SDP4 model.
27 * <p>
28 * The user should not bother in this class since it is handled internally by the
29 * {@link TLEPropagator}.
30 * </p>
31 * <p>This implementation is largely inspired from the paper and source code <a
32 * href="http://www.celestrak.com/publications/AIAA/2006-6753/">Revisiting Spacetrack
33 * Report #3</a> and is fully compliant with its results and tests cases.</p>
34 * @author Felix R. Hoots, Ronald L. Roehrich, December 1980 (original fortran)
35 * @author David A. Vallado, Paul Crawford, Richard Hujsak, T.S. Kelso (C++ translation and improvements)
36 * @author Fabien Maussion (java translation)
37 */
38 abstract class SDP4 extends TLEPropagator {
39
40 // CHECKSTYLE: stop VisibilityModifier check
41
42 /** New perigee argument. */
43 protected double omgadf;
44
45 /** New mean motion. */
46 protected double xn;
47
48 /** Parameter for xl computation. */
49 protected double xll;
50
51 /** New eccentricity. */
52 protected double em;
53
54 /** New inclination. */
55 protected double xinc;
56
57 // CHECKSTYLE: resume VisibilityModifier check
58
59 /** Constructor for a unique initial TLE.
60 * @param initialTLE the TLE to propagate.
61 * @param attitudeProvider provider for attitude computation
62 * @param mass spacecraft mass (kg)
63 */
64 protected SDP4(final TLE initialTLE, final AttitudeProvider attitudeProvider,
65 final double mass) {
66 super(initialTLE, attitudeProvider, mass);
67 }
68
69 /** Initialization proper to each propagator (SGP or SDP).
70 */
71 protected void sxpInitialize() {
72 luniSolarTermsComputation();
73 } // End of initialization
74
75 /** Propagation proper to each propagator (SGP or SDP).
76 * @param tSince the offset from initial epoch (minutes)
77 */
78 protected void sxpPropagate(final double tSince) {
79
80 // Update for secular gravity and atmospheric drag
81 omgadf = tle.getPerigeeArgument() + omgdot * tSince;
82 final double xnoddf = tle.getRaan() + xnodot * tSince;
83 final double tSinceSq = tSince * tSince;
84 xnode = xnoddf + xnodcf * tSinceSq;
85 xn = xn0dp;
86
87 // Update for deep-space secular effects
88 xll = tle.getMeanAnomaly() + xmdot * tSince;
89
90 deepSecularEffects(tSince);
91
92 final double tempa = 1 - c1 * tSince;
93 a = FastMath.pow(TLEConstants.XKE / xn, TLEConstants.TWO_THIRD) * tempa * tempa;
94 em -= tle.getBStar() * c4 * tSince;
95
96 // Update for deep-space periodic effects
97 xll += xn0dp * t2cof * tSinceSq;
98
99 deepPeriodicEffects(tSince);
100
101 xl = xll + omgadf + xnode;
102
103 // Dundee change: Reset cosio, sinio for new xinc:
104 cosi0 = FastMath.cos(xinc);
105 sini0 = FastMath.sin(xinc);
106 e = em;
107 i = xinc;
108 omega = omgadf;
109 // end of calculus, go for PV computation
110 }
111
112 /** Computes SPACETRACK#3 compliant earth rotation angle.
113 * @param date the current date
114 * @return the ERA (rad)
115 */
116 protected static double thetaG(final AbsoluteDate date) {
117
118 // Reference: The 1992 Astronomical Almanac, page B6.
119 final double omega_E = 1.00273790934;
120 final double jd = (date.durationFrom(AbsoluteDate.JULIAN_EPOCH) +
121 date.timeScalesOffset(TimeScalesFactory.getUTC(), TimeScalesFactory.getTT())
122 ) / Constants.JULIAN_DAY;
123
124 // Earth rotations per sidereal day (non-constant)
125 final double UT = (jd + 0.5) % 1;
126 final double seconds_per_day = Constants.JULIAN_DAY;
127 final double jd_2000 = 2451545.0; /* 1.5 Jan 2000 = JD 2451545. */
128 final double t_cen = (jd - UT - jd_2000) / 36525.;
129 double GMST = 24110.54841 +
130 t_cen * (8640184.812866 + t_cen * (0.093104 - t_cen * 6.2E-6));
131 GMST = (GMST + seconds_per_day * omega_E * UT) % seconds_per_day;
132 if (GMST < 0.) {
133 GMST += seconds_per_day;
134 }
135
136 return MathUtils.TWO_PI * GMST / seconds_per_day;
137
138 }
139
140 /** Computes luni - solar terms from initial coordinates and epoch.
141 */
142 protected abstract void luniSolarTermsComputation();
143
144 /** Computes secular terms from current coordinates and epoch.
145 * @param t offset from initial epoch (min)
146 */
147 protected abstract void deepSecularEffects(double t);
148
149 /** Computes periodic terms from current coordinates and epoch.
150 * @param t offset from initial epoch (min)
151 */
152 protected abstract void deepPeriodicEffects(double t);
153
154 }