HarmonicParametricAcceleration.java
/* Copyright 2002-2017 CS Systèmes d'Information
* Licensed to CS Systèmes d'Information (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.forces;
import org.hipparchus.RealFieldElement;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.MathUtils;
import org.orekit.attitudes.AttitudeProvider;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitInternalError;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.ParameterDriver;
/** This class implements a {@link AbstractParametricAcceleration parametric acceleration}
* with harmonic signed amplitude.
* @since 9.0
* @author Luc Maisonobe
*/
public class HarmonicParametricAcceleration extends AbstractParametricAcceleration {
/** Amplitude scaling factor.
* <p>
* 2⁻²⁰ is the order of magnitude of third body perturbing acceleration.
* </p>
* <p>
* We use a power of 2 to avoid numeric noise introduction
* in the multiplications/divisions sequences.
* </p>
*/
private static final double AMPLITUDE_SCALE = FastMath.scalb(1.0, -20);
/** Phase scaling factor.
* <p>
* 2⁻²³ is the order of magnitude of an angle corresponding to one meter along
* track for a Low Earth Orbiting satellite.
* </p>
* <p>
* We use a power of 2 to avoid numeric noise introduction
* in the multiplications/divisions sequences.
* </p>
*/
private static final double PHASE_SCALE = FastMath.scalb(1.0, -23);
/** Drivers for the parameters. */
private final ParameterDriver[] drivers;
/** Reference date for computing phase. */
private AbsoluteDate referenceDate;
/** Angular frequency ω = 2kπ/T. */
private final double omega;
/** Simple constructor.
* <p>
* The signed amplitude of the acceleration is γ sin[2kπ(t-t₀)/T + φ], where
* γ is parameter {@code 0} and represents the full amplitude, t is current
* date, t₀ is reference date, {@code T} is fundamental period, {@code k} is
* harmonic multiplier, and φ is parameter {@code 1} and represents phase at t₀.
* The value t-t₀ is in seconds.
* </p>
* <p>
* The fundamental period {@code T} is often set to the Keplerian period of the
* orbit and the harmonic multiplier {@code k} is often set to 1 or 2. The model
* has two parameters, one for the full amplitude and one for the phase at reference
* date.
* </p>
* <p>
* The two parameters for this model are the full amplitude (parameter 0) and the
* phase at reference date (parameter 1). Their reference values (used also as the
* initial values) are both set to 0. User can change them before starting the
* propagation (or orbit determination) by calling {@link #getParametersDrivers()}
* and {@link ParameterDriver#setValue(double)}.
* </p>
* @param direction acceleration direction in defining frame
* @param isInertial if true, direction is defined in the same inertial
* frame used for propagation (i.e. {@link SpacecraftState#getFrame()}),
* otherwise direction is defined in spacecraft frame (i.e. using the
* propagation {@link
* org.orekit.propagation.Propagator#setAttitudeProvider(AttitudeProvider)
* attitude law})
* @param prefix prefix to use for parameter drivers
* @param referenceDate reference date for computing phase, if null
* the reference date will be automatically set at propagation start
* @param fundamentalPeriod fundamental period (typically set to initial orbit
* {@link org.orekit.orbits.Orbit#getKeplerianPeriod() Keplerian period})
* @param harmonicMultiplier multiplier to compute harmonic period from
* fundamental period)
*/
public HarmonicParametricAcceleration(final Vector3D direction, final boolean isInertial,
final String prefix, final AbsoluteDate referenceDate,
final double fundamentalPeriod, final int harmonicMultiplier) {
this(direction, isInertial, null, prefix, referenceDate,
fundamentalPeriod, harmonicMultiplier);
}
/** Simple constructor.
* <p>
* The signed amplitude of the acceleration is γ sin[2kπ(t-t₀)/T + φ], where
* γ is parameter {@code 0} and represents the full amplitude, t is current
* date, t₀ is reference date, {@code T} is fundamental period, {@code k} is
* harmonic multiplier, and φ is parameter {@code 1} and represents phase at t₀.
* The value t-t₀ is in seconds.
* </p>
* <p>
* The fundamental period {@code T} is often set to the Keplerian period of the
* orbit and the harmonic multiplier {@code k} is often set to 1 or 2. The model
* has two parameters, one for the full amplitude and one for the phase at reference
* date.
* </p>
* <p>
* The two parameters for this model are the full amplitude (parameter 0) and the
* phase at reference date (parameter 1). Their reference values (used also as the
* initial values) are both set to 0. User can change them before starting the
* propagation (or orbit determination) by calling {@link #getParametersDrivers()}
* and {@link ParameterDriver#setValue(double)}.
* </p>
* @param direction acceleration direction in overridden spacecraft frame
* @param attitudeOverride provider for attitude used to compute acceleration
* direction
* @param prefix prefix to use for parameter drivers
* @param referenceDate reference date for computing phase, if null
* the reference date will be automatically set at propagation start
* @param fundamentalPeriod fundamental period (typically set to initial orbit
* {@link org.orekit.orbits.Orbit#getKeplerianPeriod() Keplerian period})
* @param harmonicMultiplier multiplier to compute harmonic period from
* fundamental period)
*/
public HarmonicParametricAcceleration(final Vector3D direction, final AttitudeProvider attitudeOverride,
final String prefix, final AbsoluteDate referenceDate,
final double fundamentalPeriod, final int harmonicMultiplier) {
this(direction, false, attitudeOverride, prefix, referenceDate,
fundamentalPeriod, harmonicMultiplier);
}
/** Simple constructor.
* @param direction acceleration direction in overridden spacecraft frame
* @param isInertial if true, direction is defined in the same inertial
* frame used for propagation (i.e. {@link SpacecraftState#getFrame()}),
* otherwise direction is defined in spacecraft frame (i.e. using the
* propagation {@link
* org.orekit.propagation.Propagator#setAttitudeProvider(AttitudeProvider)
* attitude law})
* @param attitudeOverride provider for attitude used to compute acceleration
* direction
* @param prefix prefix to use for parameter drivers
* @param referenceDate reference date for computing polynomials, if null
* the reference date will be automatically set at propagation start
* @param fundamentalPeriod fundamental period (typically set to initial orbit
* {@link org.orekit.orbits.Orbit#getKeplerianPeriod() Keplerian period})
* @param harmonicMultiplier multiplier to compute harmonic period from
* fundamental period)
*/
private HarmonicParametricAcceleration(final Vector3D direction, final boolean isInertial,
final AttitudeProvider attitudeOverride,
final String prefix, final AbsoluteDate referenceDate,
final double fundamentalPeriod, final int harmonicMultiplier) {
super(direction, isInertial, attitudeOverride);
this.referenceDate = referenceDate;
this.omega = harmonicMultiplier * MathUtils.TWO_PI / fundamentalPeriod;
try {
drivers = new ParameterDriver[] {
new ParameterDriver(prefix + " γ",
0.0, AMPLITUDE_SCALE, Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY),
new ParameterDriver(prefix + " φ",
0.0, PHASE_SCALE, -MathUtils.TWO_PI, MathUtils.TWO_PI),
};
} catch (OrekitException oe) {
// this should never happen as scales are hard-coded
throw new OrekitInternalError(oe);
}
}
/** {@inheritDoc} */
@Override
public boolean dependsOnPositionOnly() {
return isInertial();
}
/** {@inheritDoc} */
@Override
public void init(final SpacecraftState initialState, final AbsoluteDate target)
throws OrekitException {
if (referenceDate == null) {
referenceDate = initialState.getDate();
}
}
/** {@inheritDoc}.
* The signed amplitude of the acceleration is γ sin[2kπ(t-t₀)/T + φ], where
* γ is parameter {@code 0} and represents the full amplitude, t is current
* date, t₀ is reference date, {@code T} is fundamental period, {@code k} is
* harmonic multiplier, and φ is parameter {@code 1} and represents phase at t₀.
* The value t-t₀ is in seconds.
*/
@Override
protected double signedAmplitude(final SpacecraftState state, final double[] parameters) {
final double dt = state.getDate().durationFrom(referenceDate);
return parameters[0] * FastMath.sin(dt * omega + parameters[1]);
}
/** {@inheritDoc}
* The signed amplitude of the acceleration is γ sin[2kπ(t-t₀)/T + φ], where
* γ is parameter {@code 0} and represents the full amplitude, t is current
* date, t₀ is reference date, {@code T} is fundamental period, {@code k} is
* harmonic multiplier, and φ is parameter {@code 1} and represents phase at t₀.
* The value t-t₀ is in seconds.
*/
@Override
protected <T extends RealFieldElement<T>> T signedAmplitude(final FieldSpacecraftState<T> state, final T[] parameters) {
final T dt = state.getDate().durationFrom(referenceDate);
return parameters[0].multiply(dt.multiply(omega).add(parameters[1]).sin());
}
/** {@inheritDoc} */
@Override
public ParameterDriver[] getParametersDrivers() {
return drivers.clone();
}
}