1 /* Copyright 2002-2024 Luc Maisonobe
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.intervals;
18
19 import org.hipparchus.util.FastMath;
20 import org.orekit.frames.TopocentricFrame;
21 import org.orekit.frames.Transform;
22 import org.orekit.orbits.Orbit;
23 import org.orekit.propagation.events.AdaptableInterval;
24
25 /**
26 * Factory class for {@link AdaptableInterval} suitable for elevation detection on eccentric orbits.
27 * It requires {@link org.orekit.propagation.SpacecraftState} to be based on {@link Orbit} in order to work.
28 * @see AdaptableInterval
29 * @see org.orekit.propagation.events.ApsideDetector
30 * @see org.orekit.propagation.events.EventSlopeFilter
31 * @author Luc Maisonobe
32 * @since 12.1
33 */
34 public class ElevationDetectionAdaptableIntervalFactory {
35
36 /** Default elevation abovde which interval should be switched to fine interval (-5°). */
37 public static final double DEFAULT_ELEVATION_SWITCH = FastMath.toRadians(-5.0);
38
39 /**
40 * Private constructor.
41 */
42 private ElevationDetectionAdaptableIntervalFactory() {
43 // factory class
44 }
45
46 /**
47 * Method providing a candidate {@link AdaptableInterval} for arbitrary elevation detection with forward propagation.
48 * It uses a Keplerian, eccentric approximation.
49 * @param topo topocentric frame centered at ground interest point
50 * @param elevationSwitch elevation above which interval will switch to {@code fineCheckInterval}
51 * (typically {@link #DEFAULT_ELEVATION_SWITCH} which is -5°)
52 * @param fineCheckInterval check interval to use when elevation is above {@code elevationSwitch}
53 * @return adaptable interval for detection of elevation with respect to {@code topo}
54 */
55 public static AdaptableInterval getAdaptableInterval(final TopocentricFrame topo,
56 final double elevationSwitch,
57 final double fineCheckInterval) {
58 return state -> {
59 final double elevation = topo.getElevation(state.getPosition(), state.getFrame(), state.getDate());
60 if (elevation <= elevationSwitch) {
61 // we are far from visibility, estimate some large interval with huge margins
62
63 // rotation rate of the topocentric frame
64 final Transform topoToInertial = topo.getTransformTo(state.getFrame(), state.getDate());
65 final double topoAngularVelocity = topoToInertial.getAngular().getRotationRate().getNorm();
66
67 // max angular rate of spacecraft (i.e. rate at perigee)
68 final double e = state.getE();
69 final double rp = state.getA() * (1 - e);
70 final double vp = FastMath.sqrt(state.getMu() * (1 + e) / rp);
71 final double rateP = vp / rp;
72
73 // upper boundary of elevation rate
74 final double maxElevationRate = topoAngularVelocity + rateP;
75
76 return FastMath.max(fineCheckInterval, (elevationSwitch - elevation) / maxElevationRate);
77
78 } else {
79 // we are close to visibility, switch to fine check interval
80 return fineCheckInterval;
81 }
82 };
83 }
84
85 }