1 /* Copyright 2002-2022 CS GROUP
2 * Licensed to CS GROUP (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.hipparchus.util.SinCos;
22 import org.orekit.attitudes.AttitudeProvider;
23 import org.orekit.frames.Frame;
24 import org.orekit.time.AbsoluteDate;
25 import org.orekit.time.DateTimeComponents;
26 import org.orekit.utils.Constants;
27
28 /** This class contains methods to compute propagated coordinates with the SDP4 model.
29 * <p>
30 * The user should not bother in this class since it is handled internally by the
31 * {@link TLEPropagator}.
32 * </p>
33 * <p>This implementation is largely inspired from the paper and source code <a
34 * href="https://www.celestrak.com/publications/AIAA/2006-6753/">Revisiting Spacetrack
35 * Report #3</a> and is fully compliant with its results and tests cases.</p>
36 * @author Felix R. Hoots, Ronald L. Roehrich, December 1980 (original fortran)
37 * @author David A. Vallado, Paul Crawford, Richard Hujsak, T.S. Kelso (C++ translation and improvements)
38 * @author Fabien Maussion (java translation)
39 */
40 abstract class SDP4 extends TLEPropagator {
41
42 // CHECKSTYLE: stop VisibilityModifier check
43
44 /** New perigee argument. */
45 protected double omgadf;
46
47 /** New mean motion. */
48 protected double xn;
49
50 /** Parameter for xl computation. */
51 protected double xll;
52
53 /** New eccentricity. */
54 protected double em;
55
56 /** New inclination. */
57 protected double xinc;
58
59 // CHECKSTYLE: resume VisibilityModifier check
60
61 /** Constructor for a unique initial TLE.
62 * @param initialTLE the TLE to propagate.
63 * @param attitudeProvider provider for attitude computation
64 * @param mass spacecraft mass (kg)
65 * @param teme the TEME frame to use for propagation.
66 */
67 protected SDP4(final TLE initialTLE,
68 final AttitudeProvider attitudeProvider,
69 final double mass,
70 final Frame teme) {
71 super(initialTLE, attitudeProvider, mass, teme);
72 }
73
74 /** Initialization proper to each propagator (SGP or SDP).
75 */
76 protected void sxpInitialize() {
77 luniSolarTermsComputation();
78 } // End of initialization
79
80 /** Propagation proper to each propagator (SGP or SDP).
81 * @param tSince the offset from initial epoch (minutes)
82 */
83 protected void sxpPropagate(final double tSince) {
84
85 // Update for secular gravity and atmospheric drag
86 omgadf = tle.getPerigeeArgument() + omgdot * tSince;
87 final double xnoddf = tle.getRaan() + xnodot * tSince;
88 final double tSinceSq = tSince * tSince;
89 xnode = xnoddf + xnodcf * tSinceSq;
90 xn = xn0dp;
91
92 // Update for deep-space secular effects
93 xll = tle.getMeanAnomaly() + xmdot * tSince;
94
95 deepSecularEffects(tSince);
96
97 final double tempa = 1 - c1 * tSince;
98 a = FastMath.pow(TLEConstants.XKE / xn, TLEConstants.TWO_THIRD) * tempa * tempa;
99 em -= tle.getBStar() * c4 * tSince;
100
101 // Update for deep-space periodic effects
102 xll += xn0dp * t2cof * tSinceSq;
103
104 deepPeriodicEffects(tSince);
105
106 xl = xll + omgadf + xnode;
107
108 // Dundee change: Reset cosio, sinio for new xinc:
109 final SinCos scI0 = FastMath.sinCos(xinc);
110 cosi0 = scI0.cos();
111 sini0 = scI0.sin();
112 e = em;
113 i = xinc;
114 omega = omgadf;
115 // end of calculus, go for PV computation
116 }
117
118 /** Computes SPACETRACK#3 compliant earth rotation angle.
119 * @param date the current date
120 * @return the ERA (rad)
121 */
122 protected double thetaG(final AbsoluteDate date) {
123
124 // Reference: The 1992 Astronomical Almanac, page B6.
125 final double omega_E = 1.00273790934;
126 final double jd = date
127 .getComponents(utc)
128 .offsetFrom(DateTimeComponents.JULIAN_EPOCH) /
129 Constants.JULIAN_DAY;
130
131 // Earth rotations per sidereal day (non-constant)
132 final double UT = (jd + 0.5) % 1;
133 final double seconds_per_day = Constants.JULIAN_DAY;
134 final double jd_2000 = 2451545.0; /* 1.5 Jan 2000 = JD 2451545. */
135 final double t_cen = (jd - UT - jd_2000) / 36525.;
136 double GMST = 24110.54841 +
137 t_cen * (8640184.812866 + t_cen * (0.093104 - t_cen * 6.2E-6));
138 GMST = (GMST + seconds_per_day * omega_E * UT) % seconds_per_day;
139 if (GMST < 0.) {
140 GMST += seconds_per_day;
141 }
142
143 return MathUtils.TWO_PI * GMST / seconds_per_day;
144
145 }
146
147 /** Computes luni - solar terms from initial coordinates and epoch.
148 */
149 protected abstract void luniSolarTermsComputation();
150
151 /** Computes secular terms from current coordinates and epoch.
152 * @param t offset from initial epoch (min)
153 */
154 protected abstract void deepSecularEffects(double t);
155
156 /** Computes periodic terms from current coordinates and epoch.
157 * @param t offset from initial epoch (min)
158 */
159 protected abstract void deepPeriodicEffects(double t);
160
161 }