ElevationDetectionAdaptableIntervalFactory.java
/* Copyright 2002-2024 Luc Maisonobe
* Licensed to CS GROUP (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
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*/
package org.orekit.propagation.events.intervals;
import org.hipparchus.util.FastMath;
import org.orekit.frames.TopocentricFrame;
import org.orekit.frames.Transform;
import org.orekit.orbits.Orbit;
import org.orekit.propagation.events.AdaptableInterval;
/**
* Factory class for {@link AdaptableInterval} suitable for elevation detection on eccentric orbits.
* It requires {@link org.orekit.propagation.SpacecraftState} to be based on {@link Orbit} in order to work.
* @see AdaptableInterval
* @see org.orekit.propagation.events.ApsideDetector
* @see org.orekit.propagation.events.EventSlopeFilter
* @author Luc Maisonobe
* @since 12.1
*/
public class ElevationDetectionAdaptableIntervalFactory {
/** Default elevation abovde which interval should be switched to fine interval (-5°). */
public static final double DEFAULT_ELEVATION_SWITCH = FastMath.toRadians(-5.0);
/**
* Private constructor.
*/
private ElevationDetectionAdaptableIntervalFactory() {
// factory class
}
/**
* Method providing a candidate {@link AdaptableInterval} for arbitrary elevation detection with forward propagation.
* It uses a Keplerian, eccentric approximation.
* @param topo topocentric frame centered at ground interest point
* @param elevationSwitch elevation above which interval will switch to {@code fineCheckInterval}
* (typically {@link #DEFAULT_ELEVATION_SWITCH} which is -5°)
* @param fineCheckInterval check interval to use when elevation is above {@code elevationSwitch}
* @return adaptable interval for detection of elevation with respect to {@code topo}
*/
public static AdaptableInterval getAdaptableInterval(final TopocentricFrame topo,
final double elevationSwitch,
final double fineCheckInterval) {
return state -> {
final double elevation = topo.getElevation(state.getPosition(), state.getFrame(), state.getDate());
if (elevation <= elevationSwitch) {
// we are far from visibility, estimate some large interval with huge margins
// rotation rate of the topocentric frame
final Transform topoToInertial = topo.getTransformTo(state.getFrame(), state.getDate());
final double topoAngularVelocity = topoToInertial.getAngular().getRotationRate().getNorm();
// max angular rate of spacecraft (i.e. rate at perigee)
final double e = state.getE();
final double rp = state.getA() * (1 - e);
final double vp = FastMath.sqrt(state.getMu() * (1 + e) / rp);
final double rateP = vp / rp;
// upper boundary of elevation rate
final double maxElevationRate = topoAngularVelocity + rateP;
return FastMath.max(fineCheckInterval, (elevationSwitch - elevation) / maxElevationRate);
} else {
// we are close to visibility, switch to fine check interval
return fineCheckInterval;
}
};
}
}