1 /* Copyright 2002-2024 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.events;
18
19 import org.hipparchus.ode.events.Action;
20 import org.hipparchus.util.FastMath;
21 import org.hipparchus.util.MathUtils;
22 import org.orekit.frames.Frame;
23 import org.orekit.orbits.KeplerianOrbit;
24 import org.orekit.orbits.Orbit;
25 import org.orekit.orbits.OrbitType;
26 import org.orekit.orbits.PositionAngleType;
27 import org.orekit.propagation.SpacecraftState;
28 import org.orekit.propagation.events.handlers.EventHandler;
29 import org.orekit.propagation.events.handlers.StopOnIncreasing;
30
31 /** Finder for node crossing events.
32 * <p>This class finds equator crossing events (i.e. ascending
33 * or descending node crossing).</p>
34 * <p>The default implementation behavior is to {@link Action#CONTINUE continue}
35 * propagation at descending node crossing and to {@link Action#STOP stop} propagation
36 * at ascending node crossing. This can be changed by calling
37 * {@link #withHandler(EventHandler)} after construction.</p>
38 * <p>Beware that node detection will fail for almost equatorial orbits. If
39 * for example a node detector is used to trigger an {@link
40 * org.orekit.forces.maneuvers.ImpulseManeuver ImpulseManeuver} and the maneuver
41 * turn the orbit plane to equator, then the detector may completely fail just
42 * after the maneuver has been performed! This is a real case that has been
43 * encountered during validation ...</p>
44 * @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
45 * @author Luc Maisonobe
46 */
47 public class NodeDetector extends AbstractDetector<NodeDetector> {
48
49 /** Default max check interval. */
50 private static final double DEFAULT_MAX_CHECK = 1800.0;
51
52 /** Default convergence threshold. */
53 private static final double DEFAULT_THRESHOLD = 1.0e-3;
54
55 /** Frame in which the equator is defined. */
56 private final Frame frame;
57
58 /** Build a new instance.
59 * <p>The default {@link #getMaxCheckInterval() max check interval}
60 * is set to 1800s, it can be changed using {@link #withMaxCheck(double)}
61 * in the fluent API. The default {@link #getThreshold() convergence threshold}
62 * is set to 1.0e-3s, it can be changed using {@link #withThreshold(double)}
63 * in the fluent API.</p>
64 * @param frame frame in which the equator is defined (typical
65 * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
66 * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
67 * @since 10.3
68 */
69 public NodeDetector(final Frame frame) {
70 this(AdaptableInterval.of(DEFAULT_MAX_CHECK), DEFAULT_THRESHOLD, DEFAULT_MAX_ITER,
71 new StopOnIncreasing(), frame);
72 }
73
74 /** Build a new instance.
75 * <p>The orbit is used only to set an upper bound for the max check interval
76 * to a value related to nodes separation (as computed by a Keplerian model)
77 * and to set the convergence threshold according to orbit size.</p>
78 * @param orbit initial orbit
79 * @param frame frame in which the equator is defined (typical
80 * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
81 * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
82 */
83 public NodeDetector(final Orbit orbit, final Frame frame) {
84 this(1.0e-13 * orbit.getKeplerianPeriod(), orbit, frame);
85 }
86
87 /** Build a new instance.
88 * <p>The orbit is used only to set an upper bound for the max check interval
89 * to a value related to nodes separation (as computed by a Keplerian model).</p>
90 * @param threshold convergence threshold (s)
91 * @param orbit initial orbit
92 * @param frame frame in which the equator is defined (typical
93 * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
94 * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
95 */
96 public NodeDetector(final double threshold, final Orbit orbit, final Frame frame) {
97 this(AdaptableInterval.of(2 * estimateNodesTimeSeparation(orbit) / 3), threshold,
98 DEFAULT_MAX_ITER, new StopOnIncreasing(),
99 frame);
100 }
101
102 /** Protected constructor with full parameters.
103 * <p>
104 * This constructor is not public as users are expected to use the builder
105 * API with the various {@code withXxx()} methods to set up the instance
106 * in a readable manner without using a huge amount of parameters.
107 * </p>
108 * @param maxCheck maximum checking interval
109 * @param threshold convergence threshold (s)
110 * @param maxIter maximum number of iterations in the event time search
111 * @param handler event handler to call at event occurrences
112 * @param frame frame in which the equator is defined (typical
113 * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
114 * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
115 * @since 6.1
116 */
117 protected NodeDetector(final AdaptableInterval maxCheck, final double threshold,
118 final int maxIter, final EventHandler handler,
119 final Frame frame) {
120 super(maxCheck, threshold, maxIter, handler);
121 this.frame = frame;
122 }
123
124 /** {@inheritDoc} */
125 @Override
126 protected NodeDetector create(final AdaptableInterval newMaxCheck, final double newThreshold,
127 final int newMaxIter, final EventHandler newHandler) {
128 return new NodeDetector(newMaxCheck, newThreshold, newMaxIter, newHandler, frame);
129 }
130
131 /** Find time separation between nodes.
132 * <p>
133 * The estimation of time separation is based on Keplerian motion, it is only
134 * used as a rough guess for a safe setting of default max check interval for
135 * event detection.
136 * </p>
137 * @param orbit initial orbit
138 * @return minimum time separation between nodes
139 */
140 private static double estimateNodesTimeSeparation(final Orbit orbit) {
141
142 final KeplerianOrbit keplerian = (KeplerianOrbit) OrbitType.KEPLERIAN.convertType(orbit);
143
144 // mean anomaly of ascending node
145 final double ascendingM = new KeplerianOrbit(keplerian.getA(), keplerian.getE(),
146 keplerian.getI(),
147 keplerian.getPerigeeArgument(),
148 keplerian.getRightAscensionOfAscendingNode(),
149 -keplerian.getPerigeeArgument(), PositionAngleType.TRUE,
150 keplerian.getFrame(), keplerian.getDate(),
151 keplerian.getMu()).getMeanAnomaly();
152
153 // mean anomaly of descending node
154 final double descendingM = new KeplerianOrbit(keplerian.getA(), keplerian.getE(),
155 keplerian.getI(),
156 keplerian.getPerigeeArgument(),
157 keplerian.getRightAscensionOfAscendingNode(),
158 FastMath.PI - keplerian.getPerigeeArgument(), PositionAngleType.TRUE,
159 keplerian.getFrame(), keplerian.getDate(),
160 keplerian.getMu()).getMeanAnomaly();
161
162 // differences between mean anomalies
163 final double delta1 = MathUtils.normalizeAngle(ascendingM, descendingM + FastMath.PI) - descendingM;
164 final double delta2 = 2 * FastMath.PI - delta1;
165
166 // minimum time separation between the two nodes
167 return FastMath.min(delta1, delta2) / keplerian.getKeplerianMeanMotion();
168
169 }
170
171 /** Get the frame in which the equator is defined.
172 * @return the frame in which the equator is defined
173 */
174 public Frame getFrame() {
175 return frame;
176 }
177
178 /** Compute the value of the switching function.
179 * This function computes the Z position in the defined frame.
180 * @param s the current state information: date, kinematics, attitude
181 * @return value of the switching function
182 */
183 public double g(final SpacecraftState s) {
184 return s.getPosition(frame).getZ();
185 }
186
187 }